NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Process Design and Economics 

for the Production of Algal 

Biomass:

Algal Biomass Production in Open Pond 

Systems and Processing Through 

Dewatering for Downstream Conversion

Ryan Davis, Jennifer Markham, 

Christopher Kinchin, Nicholas Grundl, and 

Eric C.D. Tan

National Renewable Energy Laboratory

David Humbird

DWH Process Consulting

Technical Report

NREL/TP-5100-64772

February 2016
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Process Design and Economics 

for the Production of Algal 

Biomass:

Algal Biomass Production in Open 

Pond Systems and Processing Through 

Dewatering for Downstream Conversion

Ryan Davis, Jennifer Markham, 

Christopher Kinchin, Nicholas Grundl, and 

Eric C.D. Tan

National Renewable Energy Laboratory

David Humbird

DWH Process Consulting

Prepared under Task No. BB14.1110

Technical Report

NREL/TP-5100-64772

February 2016
NOTICE

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iii

Acknowledgements

We gratefully acknowledge inputs and assistance from the following individuals who furnished 

the National Renewable Energy Laboratory (NREL) with detailed design and cost estimates for 

the pond system configurations considered in the present analysis:

Bill Crump – Leidos Engineering

David Hazlebeck – Global Algae Innovations

Ian Woertz, Tryg Lundquist, John Benemann – MicroBio Engineering

John Lukas, Danielle Sexton – Harris Group
iv

Executive Summary

The U.S. Department of Energy (DOE) promotes the production of a range of liquid fuels and 

fuel blendstocks from biomass feedstocks by funding fundamental and applied research that 

advances the state of technology in biomass production, conversion, and sustainability. As part 

of its involvement in this program, the National Renewable Energy Laboratory (NREL) 

investigates the conceptual production economics of these fuels. This includes fuel pathways 

from lignocellulosic (terrestrial) biomass, as well as from algal (aquatic) biomass systems. 

Over the past decade, NREL conducted a campaign to quantify the economic implications 

associated with observed and aspirational performance for the conversion of corn stover to 

ethanol through techno-economic modeling. This effort served two important purposes: (1) to 

establish a benchmark representing the initial “state of technology” at the time and (2) to set 

goals for near-term R&D and cost targets, as well as to track progress toward achieving these 

targets by periodically updating the models based on the latest research improvements. 

Beginning in 2013, DOE began transitioning from a singular focus on ethanol to a broad slate of 

products and conversion pathways targeting hydrocarbon fuels, including a number of pathways 

from terrestrial biomass (woody/herbaceous feedstocks) and from algal biomass. To date, two 

reports have been published under the DOE platforms considering the economic potential for 

conversion of algal biomass to fuels, both based on an assumed feedstock cost for upstream 

biomass production and processing which was outside the scope of the analyses, but which also 

contributed to fuel production costs substantially more than conversion costs [1,2]. 

This report describes in detail a set of aspirational design and process targets to better understand 

the realistic economic potential for the production of algal biomass for subsequent conversion to 

biofuels and/or coproducts, based on the use of open pond cultivation systems and a series of 

dewatering operations to concentrate the biomass up to 20 wt% solids (ash-free dry weight 

[AFDW] basis). The overarching process design utilizes purified CO2 sourced from power plant 

flue gas (the CO2 purification step is outside scope boundary limits) and commodity fertilizer 

nutrients to support the cultivation of algal biomass to a mid-level lipid content of 27 wt%. This 

is followed by harvesting the biomass from the ponds and processing it through three dewatering 

steps in series consisting of gravity settling, hollow fiber membranes, and centrifugation, to 

concentrate the biomass from 0.5 g/L (0.05 wt% AFDW) at harvest up to 200 g/L (20 wt%) in 

the product stream. The production ponds also are coupled with an inoculum propagation system 

consisting of closed photobioreactors, covered ponds, and open fully-lined ponds of increasingly 

larger culture volumes. Ancillary areas required to support the facility operations—CO2 storage 

and distribution, water circulation pipelines, and product storage tanks—also are included in the 

design. A key attribute of this analysis is the consideration of eight separate open pond systems 

furnished by four separate consultants and experts in the field across three discrete pond sizes, 

incorporated into the integrated process model to elucidate implications on biomass production 

costs associated with pond sizing and resultant economy of scale impacts. Detailed material and 

energy balances and capital and operating costs for the process models also are documented.

This case study techno-economic model provides a production cost for the thickened algal 

biomass product that can be used to gauge the technology potential and to quantify critical cost 

drivers. The analysis presented here also includes consideration of life-cycle implications by 

tracking environmental sustainability metrics for the modeled production facility, including 

greenhouse gas emissions, fossil energy demand, and consumptive water use. 

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.
v

Following similar methods for design report modeling as conducted over recent years, NREL, 

supported by four expert contributors who furnished pond design and cost estimates (see 

Acknowledgements section), performed a feasibility-level analysis for a plausible commercial 

algal biomass production facility to understand “what it really takes” to reach a range of algal 

biomass costs. The modeled facility consists of 5,000 acres (approximately 2,020 hectares) of 

production pond cultivation area with a total facility footprint of 7,600 acres (3,075 hectares) and 

achieves an annual biomass product yield of 38 U.S. ton/cultivation acre/year attributed to a 

cultivation productivity target of 25 g/m2

/day as an annual average across varying seasonal rates. 

Based on “nth-plant” design assumptions, project costs, and financing, coupled with targets 

projected to be demonstrated by the year 2022, the minimum biomass selling price (MBSP) is 

seen to distinctly follow a trend inversely proportional with individual pond size, varying from 

$576–$649/ton AFDW (average $612/ton in 2011 dollars) of dewatered biomass for “small” 2-

acre pond designs, $452–$545/ton (average $491/ton) for “medium” 10-acre pond designs, and 

$392–$419/ton (average $406/ton) for “large” hypothetical 50-acre designs, although the latter 

scenario was primarily only considered to further quantify economy of scale trends over a larger 

range of pond sizes. This result suggests that although algal cultivation ponds larger than 

approximately 2–3 acres in size do not currently exist commercially today, moving toward larger 

pond sizes on the order of 10 acres is critical in enabling economically viable algal biomass 

production as required for subsequent conversion to commodity fuel products.

The analysis also reiterates that economics are influenced strongly by achievable cultivation 

productivity, with particularly dramatic penalties on MBSP if productivity was lower than the 

targeted 25 g/m2

/day annual average. However, this tradeoff must be balanced carefully against 

associated nutrient requirements, given known linkages between high-nutrient (particularly 

nitrogen) feeding strategies and increased biomass productivity, where a sensitivity analysis 

found that if nutrient inputs and resultant biomass composition were to be adjusted from the 

nutrient-limited mid-lipid biomass baseline to nutrient-replete low-lipid (high-protein) biomass, 

the resulting nutrient costs increase to such a level that it would require more than a 40% 

improvement in productivity to ultimately lower the MBSP. Recycling nutrients fixed in the 

biomass back to the production ponds is critical for both controlling costs and minimizing the 

greenhouse gas footprint of an algal process; however, to ensure applicability of this effort’s 

outputs to any downstream conversion processing pathway, no credit is assumed for such 

recycles (instead, any such credit may be applied on the downstream conversion process to 

reduce final fuel/product costs). If recycle credits were accounted for here instead, the cost 

impacts attributed to compositional variations may be less pronounced. Additionally, the work 

also reiterates that it is critical to avoid the use of fully lined ponds, but instead to situate the 

pond facilities in locations with high native clay content of the soil such that plastic liners are 

only required to cover small targeted areas of the ponds for erosion control (in the base case

scenarios, liners only covered 2-25% of total pond area depending on specific pond design). If 

instead ponds were fully lined across the full 5,000 acres of cultivation area, MBSP costs would 

increase more than $125/ton on average for the 10-acre pond design scenarios relative to the 

costs indicated above. Finally, the report also includes a high-level discussion on cost tradeoffs 

and logistical issues between sourcing CO2 via carbon capture from power plant flue gas versus 

direct utilization of bulk flue gas, with concentrated CO2 costs adding significantly to MBSP; 

however, flue gas is challenged by substantial logistical and practicality constraints for a facility 

of this size.
vi

Figure ES-1. Economic summary sheet for the “base case” based on average 

costs of the four 10-acre pond designs. (Note: all per-ton cost and yield metrics are based on ash-free 

dry weight biomass.)
vii

Table of Contents

1 Introduction........................................................................................................................................... 1

1.1 Background and Motivation .........................................................................................................................1

1.2 Techno-Economic Analysis Approach.........................................................................................................4

1.3 About nth-Plant Assumptions........................................................................................................................6

2 Design Basis and Conventions........................................................................................................... 7

2.1 Process Overview.........................................................................................................................................7

2.2 Facility Size and Layout...............................................................................................................................9

2.3 Biomass Composition.................................................................................................................................12

2.4 Modeling Basis Parameters........................................................................................................................15

3 “Top-Down” Analysis of Cultivation Cost Demands ...................................................................... 16

4 “Bottom-Up” Integrated Model: Process Design and Capital Cost Estimation Details .............. 18

4.1 Area 100: Biomass Production...................................................................................................................18

4.1.1 Overview......................................................................................................................................18

4.1.2 Design Basis.................................................................................................................................20

4.1.3 Cost Estimation ............................................................................................................................32

4.2 Area 200: Inoculum System .......................................................................................................................36

4.2.1 Overview......................................................................................................................................36

4.2.2 Design Basis.................................................................................................................................36

4.2.3 Cost Estimation ............................................................................................................................38

4.3 Area 300: CO2 Delivery .............................................................................................................................39

4.3.1 Overview......................................................................................................................................39

4.3.2 Design Basis.................................................................................................................................39

4.3.3 Cost Estimation ............................................................................................................................40

4.4 Area 400: Makeup Water Delivery + On-Site Circulation to/from Dewatering.........................................41

4.4.1 Overview......................................................................................................................................41

4.4.2 Design Basis.................................................................................................................................41

4.4.3 Cost Estimation ............................................................................................................................42

4.5 Area 500: Dewatering.................................................................................................................................43

4.5.1 Overview......................................................................................................................................43

4.5.2 Design Basis.................................................................................................................................44

4.5.3 Cost Estimation ............................................................................................................................49

4.6 Area 600: Storage.......................................................................................................................................51

4.6.1 Overview......................................................................................................................................51

4.6.2 Design Basis.................................................................................................................................51

4.6.3 Cost Basis.....................................................................................................................................51

5 Process Economics ........................................................................................................................... 52

5.1 About Cost-Year Indices............................................................................................................................53

5.2 Total Capital Investment (TCI) ..................................................................................................................54

5.3 Variable Operating Costs ...........................................................................................................................59

5.4 Fixed Operating Costs................................................................................................................................60

5.5 Discounted Cash Flow Analysis and the Minimum Selling Price of Biomass...........................................62

6 Analysis and Discussion ................................................................................................................... 68

6.1 Cost Sensitivity Analysis............................................................................................................................68

6.2 Sustainability Metrics for Base Model .......................................................................................................82

7 Concluding Remarks.......................................................................................................................... 86

7.1 Summary ....................................................................................................................................................86

7.2 Future Work ...............................................................................................................................................89

References................................................................................................................................................. 91

Appendix A. Individual Equipment Cost Summary ............................................................................... 99

Appendix B. Additional Design and Cost Details for Leidos Pond Scenarios ................................. 102

Appendix C. Discounted Cash Flow Rate of Return Worksheet........................................................ 103

Appendix D. Process Flow Diagrams ................................................................................................... 105

Appendix E. TEA Summary Worksheets for Individual Pond Scenarios .......................................... 112
viii

Acronyms

ACCE Aspen capital cost estimator

AFDW ash-free dry weight

ALU algal lipid upgrading

ANL Argonne National Laboratory

ASU Arizona State University

BETO Bioenergy Technologies 

Office

BGY billion gallons per year

BLS Bureau of Labor Statistics

CAPEX capital expenditures

CCS carbon capture and storage 

technology

DAF dissolved air flotation

DAP diammonium phosphate

DB declining balance

DCFROR discounted cash flow rate of 

return

DOE U.S. Department of Energy

DW dry weight

EOR enhanced oil recovery

FAME fatty acid methyl ester

FCI fixed capital investment

GAI Global Algae Innovations

GGE gallon gasoline equivalent

GHG greenhouse gas

ha hectare

HCSD high-carbohydrate (midharvest) Scenedesmus

HLSD high-lipid (late harvest) 

Scenedesmus

HPSD high-protein (early harvest) 

Scenedesmus

HDPE high-density polyethylene

HRT hydraulic retention time

HTL hydrothermal 

liquefaction

INWG inches of water gauge

IRR internal rate of return

ISBL inside battery limits (of the 

plant)

LCA life-cycle assessment

LCI life-cycle inventory 

MACRS IRS Modified Accelerated 

Cost Recovery System

MBSP minimum biomass selling 

price

MEA monoethanolamine

MFSP minimum fuel selling price

MM million (e.g., MMBTU or 

$__MM)

MYPP DOE-BETO’s Multi-Year 

Program Plan

NH3 ammonia

NPV net present value

NREL National Renewable Energy 

Laboratory

OPEX operating expenditures

OSBL outside battery limits

PBR photo bioreactor

PFD process flow diagram

PNNL Pacific Northwest National 

Laboratory

PVC polyvinyl chloride

R&D research and development

RA resource assessment

TCI total capital investment

TDC total direct cost

TEA techno-economic analysis

TIC total installed cost
1

1 Introduction

1.1 Background and Motivation

The U.S. Department of Energy (DOE) Bioenergy Technologies Office (BETO) promotes the 

production of liquid fuels and coproducts from lignocellulosic and algal feedstocks by 

sponsoring programs in fundamental and applied research that aim to advance the state of 

technology, spanning the supply chain from biomass production through processing and 

conversion to fuels. Within the algae platform, these programs include laboratory research to 

improve biological characteristics (e.g., algal cultivation productivity, biomass composition, and 

strain robustness) through screening and synthetic biology; engineering studies of potential 

systems for growth, dewatering, and conversion technologies; improvement of laboratory 

analytical capabilities to accurately characterize feed and product materials; and support for 

biomass production test-bed and processing demonstration facilities. This research is conducted 

by national laboratories, universities, and private industry, both individually and through multiorganization consortia partnerships.

To support the DOE program, the National Renewable Energy Laboratory (NREL) investigates 

the process design and economics of numerous biofuel processing pathways to develop a plant

gate price projection based on process and plant design assumptions consistent with applicable 

best practices in engineering, construction, and operation. This plant gate price is referred to as 

the “minimum fuel selling price” or MFSP, when focused on the conversion stage within the 

supply chain from biomass-to-fuel products. The MFSP can be used by DOE to assess the costcompetitiveness and market penetration potential of a given biofuel technology in comparison 

with petroleum-derived fuels and established biofuel pathways such as starch- or sugar-based 

ethanol, vegetable oil-based biodiesel, etc. The projected MFSP for any given biofuel pathway is 

typically strongly dependent on the cost of producing and processing the biomass feedstock up to 

the point of delivery to the conversion biorefinery [1,3,4], which is particularly true in the case of 

algal biofuels whose targeted production costs attributed to biomass production and preprocessing may reach 70% or more of overall MFSP [1,2]. As such, it is critical to also establish 

sound projections for biomass feedstock costs to present a clear picture for overall economic 

viability in a “farm-to-wheel” supply chain.

In addition to establishing absolute plant-gate prices for biomass or resultant biofuels, technoeconomic analysis (TEA) modeling also helps to direct research activities by examining 

sensitivities of these prices to process alternatives and research advances. Proposed research and 

its anticipated results can be translated into a new selling price that can be compared to 

established benchmark cases. Such comparison helps to quantify the economic impact of core 

research targets and to track progress toward meeting competitive cost goals. It also allows DOE 

to make more informed decisions about research proposals that claim to reduce costs. 

In 2014, NREL and Pacific Northwest National Laboratory (PNNL) published design report 

documents projecting MFSP targets anticipated to be achievable by year 2022 for the conversion 

of algal biomass to fuels via algal lipid extraction and upgrading (ALU) and hydrothermal 

liquefaction (HTL), respectively [1,2]. Both reports documented a set of targets for yields and 

processing conditions that would support a modeled MFSP of roughly $4–4.5/GGE for the 

respective conversion technology pathways, dependent on an assumed biomass feedstock cost of 

$430/ton ash-free dry weight (AFDW) following upstream dewatering to 20 wt% solids, based in 
2

turn off of BETO target projections for algal biomass production costs by 2022 [5]. Both 

conversion pathways also indicated strong economic sensitivities to the biomass cost, with an

opportunity to reduce MFSP by nearly $1/GGE at a cost of $300/ton algal biomass or a similar 

cost penalty increasing MFSP by slightly less than $1/GGE at a cost of $550/ton. Such strong 

economic sensitivity to the cost of algal biomass as attributed to “front-end” operations 

(cultivation and dewatering) is well-documented elsewhere [1,6-9]. 

Significant progress has been made in recent years to reduce uncertainties on processing steps, 

yields, and resultant costs for converting algal biomass to fuels enabled by experimental data 

published from real-world (outdoor), commercially relevant processing conditions [2,10,11]. 

However, substantial uncertainties and lack of public agreement still remain with respect to 

demonstrated or achievable performance from front-end cultivation and dewatering operations, 

and resulting yields and system costs. Indeed, projected economics from public literature range 

from $270–$2,450/ton algal biomass or $2–$110/gal algal biofuels, with a range in algal biomass 

production yield spanning between 11 and 89 ton per acre per year (7–60 g/m2/day annual 

average at 330 days/year on-stream factor) [7,8,10,12-22]. Figure 1 provides an overview of 

some of the published estimates for cultivation and processing costs of biomass and algal oil, and 

shows significant variation across system yields and costs (after adjusting all original cost 

estimates to 2011 dollars). The figure is broken down into publications focused on projecting 

toward future targets based on optimistic productivities or undemonstrated technology, labeled as 

“future,” versus existing, deployable systems and current productivity performance claims, 

labeled as “current,” with all cases focused only on open pond cultivation methods. Even when 

isolated to today’s current baseline performance alone, estimates range for biomass 

productivities between 7 and 35 g/m2

/day, biomass costs between $280 and $2,450/ton, and biocrude costs between $2 and $112/gal. Future projections range for productivities between 15 and 

60 g/m2/day, biomass costs between $280 and $860/ton, and bio-crude costs between $2 and 

$25/gal. A large contributor to such disparity in cost estimates frequently lies in several key 

assumptions including cultivation productivity or cultivation system design details, and it has 

been shown that harmonizing for such key metrics may be seen to considerably reduce cost 

variability [14], which is a primary point we will demonstrate in this report as well.
3 

Figure 1. Literature scan demonstrating variability in estimated cost of algal biomass and bio-oil, 

differentiating between “current performance” versus “future projections” [7,8,10,12-22] 

The first in-depth analysis undertaken by NREL and partners in estimating costs for algae 

production and processing was done under BETO’s 2012 “Harmonization Initiative,” which 

brought together modeling partners from NREL, Argonne National Laboratory (ANL), and 

PNNL to harmonize their conceptual models around TEA, life-cycle assessment (LCA), and 

resource assessment (RA), respectively, such that the results from each model would carry the 

same implications being based on consistent inputs and assumptions. This effort included a 

workshop to serve as a vetting process for the respective collaborators to present the details of 

their models to a group of expert stakeholders in industry, academia, and other national 

laboratories, to begin validating or improving key modeling assumptions. This ultimately 

resulted in the publication of a harmonization report (referred to as such hereafter) documenting 

model details and the resulting near-term cost, sustainability, and resource implications for 

production of 5 billion gallons per year (BGY) of renewable diesel at the national scale spread 

across a large consortium of individual unit farms [23]. While this represented an important step 

forward in better understanding plausible processing details and costs, including cultivation and 

harvesting steps, the study was limited by (1) being based on a single set of design and cost 

inputs, largely pulling from available public literature, which at the time remained scarce, and (2) 

focusing on what economics would look like “today” (in 2012) based on benchmark estimates 

for current productivity performance (~13 g/m2

/day) and dewatering technologies (leveraging 

from industrial practices for wastewater processing), but largely avoiding projections for future 

performance and cost targets.

The focus of this report is to document a number of modeling pathway scenarios to project 

plausible costs for algal biomass production and pre-processing (harvesting/dewatering 

nominally to 20 wt% solids) as targets to be achieved by 2022. This objective is approached in 

two ways: first, by presenting a “top-down” analysis for what a production system “needs to 

cost” coupled with what the annual algal biomass productivity “needs to be” in order to achieve 

a given cost target for minimum biomass selling price on a dollar-per-ton basis (see Section 3 of 

this report). This is presented first as an objective way to address what level the system must 

0 25 50 75 100

-500

0

500

1000

1500

2000

2500

3000

-20

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 Productivity (g/m2/day)

Algal Oil Cost ($/Gallon)

Biomass Cost ($/U.S. Ton)

Annual production assuming 330 day/year operation (U.S. Ton/acre/yr)

Algal Oil Current

Algal Oil Future

Biomass Current

Biomass Future
4

perform at if it is to profitably produce dewatered algal biomass at a stipulated cost, given the 

uncertainties and challenges discussed previously around reaching consensus for either of these 

metrics, particularly for projecting what these metrics may be by 2022. Second, we perform a 

“bottom-up” analysis to consider a number of discrete design configurations and associated cost 

estimates for cultivation systems integrated with downstream harvesting/dewatering as well as 

upstream delivery of CO2, makeup water, and nutrients, to determine biomass selling price 

estimates for each scenario attributed to a hypothetical commercial “farm” facility made up of 

5,000 acres (2,023 ha) of cultivation area dedicated to biomass production. To support this effort 

we have solicited assistance and inputs from a number of engineering subcontractors, 

consultants, and industry experts to incorporate these individual design configurations into the 

integrated model and to ensure consistent application of resultant cost estimates. The scope of 

this analysis focuses on open pond cultivation scenarios, and does not include photobioreactor 

(PBR) cultivation aside from its use in an inoculum system to inoculate open ponds. This 

decision was made to focus on pond systems, for which the most details on credible design and 

costing estimates are available publicly, to highlight an important conclusion: that in fact open 

pond costs are more consistent than current public understanding may infer, which is a critical 

point to establish in order to move forward in projecting future algal biomass production costs. 

PBR cultivation is currently envisioned to be the subject of a follow-on analysis in 2016.

Similar to caveats noted in prior NREL design reports, we stress that this design report serves to 

describe a limited number of feasible production and processing scenarios and to transparently 

document the assumptions and details that went into their designs, based either on publicly 

available information or information otherwise furnished to NREL with the intent to be 

incorporated into this public analysis. This report is not meant to provide an exhaustive survey of 

all process alternatives or cost-sensitivity analyses. Furthermore, it is important to reiterate that 

algal biomass production and processing as a technology platform is in a more nascent stage of 

development and understanding than other, more-established processes based on terrestrial 

biomass, and continue to suffer from a dearth of available public data on production and 

processing performance at sufficient scale. While the key inputs assumed in this analysis are 

leveraged from vendors, engineering companies, and other experts in the field, or otherwise 

supported by operational performance data at demonstration scale (e.g., for dewatering 

operations selected as the “base case”), further experimental work and scale-up is required to 

reduce model uncertainties. Moving forward, as the science and technology progresses, the 

process models and economic tools developed for this report may be updated in a similar fashion 

as prior NREL design report iterations have evolved.

1.2 Techno-Economic Analysis Approach

Figure 2 describes the engineering approach used for modeling the production and harvesting 

process for algal biomass up to the point of delivery to downstream conversion operations 

(outside the scope of this analysis), including process design, process modeling, and economic 

analysis. This approach was largely followed for this study as well, albeit under a condensed 

timeline and with additional extrapolations around areas with more limited supporting 

experimental data to date (e.g., large-scale operational data for dewatering specific to algal 

biomass material). As such, this report is less prescriptive in some sections than previous reports 

due to the early stages of development for algal biomass production, particularly regarding scaleup logistics to a large commercial facility as envisioned here.
5

Figure 2. NREL’s approach to process design and economic analysis

Starting from the general process flow diagram (PFD) shown in Figure 3 and the more detailed 

PFDs contained in Appendix D, a process simulation was developed using Aspen Plus software 

[24]. This process model computes material and energy balances for each unit operation in this 

conceptual integrated process. While it is recognized that the use of Aspen Plus is not as critical 

for this particular process schematic compared to biorefinery conversion processes, which 

require thermodynamic rigor in modeling separations, vapor-liquid equilibria, heat integration, 

and conversion reactions, Aspen modeling is still useful in tracking recycle streams, CO2 

injection, and biomass elemental balances. The material and energy balance data from the Aspen 

simulation are next used to assist in determining the number and size of capital equipment items. 

As process conditions and flows change, baseline equipment costs are automatically adjusted in 

an Excel spreadsheet using a scaling factor (described in Section 5.2). In the case of pond 

systems, these baseline cost estimates were derived from detailed designs developed by others 

either in published literature (e.g., Lundquist et al. [17] via MicroBio Engineering [25]) or 

furnished to NREL by engineering subcontractors (e.g., Harris Group and Leidos) and experts in 

the field (e.g., Global Algae Innovations). In the case of dewatering and piping equipment, cost 

estimates were provided from vendor quotes typically based on AACE Class 4 estimates [26],

consultation with industry experts, and internal estimates generated using Aspen Capital Cost 

Estimator (ACCE) [24]. Final equipment costs for this report are tabulated in Appendix A.
6

Once equipment costs are determined, direct and indirect overhead cost factors (e.g., installation 

costs and project contingency) are applied to determine a total capital investment (TCI). The 

TCI, along with the plant operating expenses (also developed using flow rates from the Aspen 

model), are used in a discounted cash flow rate of return (DCFROR) analysis to determine a 

plant gate price for dewatered algal biomass feedstock, which in reality may be viewed as a 

“transfer price” to be delivered to downstream conversion operations co-located nearby. This 

plant gate price is termed here the “minimum biomass selling price” (MBSP, in $/ton) required 

to obtain a net present value (NPV) of zero for a 10% internal rate of return (IRR) after taxes.

The product of the analysis described above is a techno-economic model that reasonably 

estimates a product price for a pre-commercial process. The resultant MBSP is unique for the set 

of process conditions simulated, and it should be emphasized that a certain amount of uncertainty 

always exists around these chosen conditions, as well as around the assumptions made for capital 

and raw material costs. Without a detailed understanding of the basis behind it, the absolute 

computed MBSP carries a risk of being taken out of context. While the MBSP can be used to 

assess the economic viability of a given set of inputs and conditions, it is best suited for 

comparing design or processing configurations against one another or for performing sensitivity 

analyses that indicate where economic or process performance improvements are needed.

1.3 About nth-Plant Assumptions

The techno-economic analysis reported here uses what are known as “nth-plant” economics. The 

key assumption implied by nth-plant economics is that our analysis does not describe a pioneer 

plant; instead, it assumes several facilities using the same technology have already been built and 

are operating. In other words, it reflects a mature future in which a successful industry of n plants 

has been established. Because the techno-economic model is primarily a tool for studying new 

process technologies or integration schemes to comment on their comparative economic impact, 

nth-plant analysis avoids artificial inflation of project costs associated with risk financing

(implying higher than 10% IRR requirements), longer start-ups, equipment overdesign, and other 

costs associated with first-of-a-kind or pioneer plants, lest these overshadow the real economic

impact of research advances in algal biomass cultivation or process integration. At the very least, 

these nth-plant economics should help to provide justification and support for early technology 

adopters and pioneer plants.

The nth-plant assumptions in the present analysis apply primarily to the factored cost model used 

to determine the total capital investment from the purchased equipment cost and to the choices 

made in plant financing. The nth-plant assumption also applies to some operating parameters, 

such as process uptime of 90%. This factor was selected to maintain consistency with a similar 

90% uptime assumed in the above-referenced algal biofuel conversion models (HTL and ALU,

respectively [1,2]), and is particularly noteworthy for the present modeling scope focused on 

algal cultivation under an nth-plant scenario, which implicitly assumes the use of a robust strain 

resistant to crashes. This is in contrast to today’s performance which lags this target given more 

frequent culture crashes observed under BETO’s test-bed consortia sites, particularly for 

freshwater strains [27,28].
7 

2 Design Basis and Conventions

2.1 Process Overview

The process described here considers open pond systems for algal biomass production (multiple 

pond sizes, designs, and developer/contractor costs are evaluated as discussed in Section 4.1) 

coupled with upstream inoculum production operations and downstream harvesting and 

dewatering steps to increase the biomass solids content for processing through subsequent 

conversion operations (outside the scope of this report). The design also includes equipment for 

CO2 delivery, delivery of fresh makeup water and on-site circulation, and product storage. The 

process is divided into six areas (see Figure 3). 

Area 100: Production Ponds. This is the primary section of the process, accounting for 

the majority of system costs and facility footprint. The scope of the present analysis 

limits the focus for the production system to the use of open pond cultivation (PBR 

systems will be considered in a later analysis), but considers detailed pond designs 

attributed to four separate sources (including consultants, developers, and industry 

experts) across three individual pond sizes (2-, 10-, and 50-acre ponds) to more firmly 

draw conclusions about pond costs and scale requirements. The base case scenarios 

assume the use of unlined ponds, except in specific areas of the pond where a plastic liner 

is required for erosion control. Areas 100 and 200 follow a continuous mode of operation. 

Area 200: Inoculum System. In this area, biomass inoculum is produced in a scale-up 

system to continuously inoculate a fraction of the production ponds when upsets or 

culture crashes occur. The inoculum system consists of closed PBRs, covered ponds, and 

open/lined ponds of increasingly larger volumes, sized to allow for an inoculum 

concentration of 0.1 g/L AFDW in the production ponds. 

Area 300: CO2 Delivery. This section accounts for delivery, on-site storage, and injection 

of CO2 to the inoculum and production processes. The analysis base case assumes the use 

of concentrated/pressurized CO2 (sourced from power plant flue gas), but considers lowpressure bulk flue gas transport and delivery as an alternative. As the scope of the present 

design excludes “back-end” conversion and upgrading operations, no recycle of CO2 is 

accounted for and all requirements for the process are met using fresh CO2 from off site. 

Area 400: Makeup Water Delivery + On-Site Circulation to/from Dewatering. Makeup 

water to the facility is provided by pipeline transport from a nearby local water resource 

in keeping with prior modeling work. Within the facility limits, water/culture circulation 

to and from dewatering operations is handled by a series of pipeline and aqueduct 

channels, leveraging the natural land slope to circulate partially dewatered culture to 

central dewatering over a “terraced” facility layout.

Area 500: Dewatering. The biomass is harvested from the ponds at 0.5 g/L AFDW

density, and concentrated across three dewatering steps consisting of gravity settling, 

membranes, and centrifugation to a final concentration of 200 g/L (20 wt%) AFDW. 

Clarified water from each step is recycled to the production ponds, less a small fraction 

removed as blowdown to mitigate buildup of salts and other inorganics.

Area 600: Storage. This area provides bulk storage for the dewatered algal biomass 

product, as well as makeup water, fire suppression water, and nutrient inputs.
8 

A100

BIOMASS PRODUCTION

A200

INOCULUM SYSTEM

A400

MAKEUP WATER DELIVERY + ONSITE CIRCULATION TO/FROM 

DEWATERING

A300

CO2 DELIVERY

A500

DEWATERING 

ALGAE BIOMASS 

CONVERSION TO 

BIOFUELS (not modeled 

here)

A600

STORAGE

JULY 2015 PFD-001

OVERALL PROCESS:

ALGAL PRODUCTION PROCESS

ALGAE 

(0.05 wt% solids)

AMMONIA

DIAMMONIUM 

PHOSPHATE

INOCULUM ALGAE 

(0.05 wt% solids)

ALGAE PRODUCT

(20 wt% solids)

ALGAE PRODUCT 

(20 wt% solids)

DIAMMONIUM 

PHOSPHATE

WATER

RECYCLE WATER

AMMONIA

CO2

CO2

CO2 (From outside of 

facility) MAKEUP WATER

RECYCLE WATER

Figure 3. Simplified flow diagram of the overall process. (Key streams only; see Appendix D for more detailed diagram and PFDs.)
9 

2.2 Facility Size and Layout

The facility in the present design is sized for a total production pond cultivation area of 5,000 

wetted acres (2,023 ha) excluding the inoculum system, which in the base case discussed in 

Section 4 enables the production of 0.19 MM U.S. dry tons per year of algal biomass based on 

the productivity and seasonality assumptions employed here (Section 4.1.2); as a general note, 

this biomass yield and all other biomass cost, yield, and concentration values discussed in this 

report are based on an ash-free dry weight (AFDW) basis unless otherwise noted. The 5,000-acre 

size is smaller than prior modeling efforts that assumed very large commercial systems (up to 

10,000 acres of ponds [23]), recognizing that extremely large sizes such as 10,000 acres may 

present too many logistical challenges and siting constraints to be practical. However, it is still 

critical to maintain at least a 5,000-acre overall area of production ponds in the facility (whether 

a “facility” is defined as a single contiguous farm as modeled here, or as a grouping of smaller 

farms located in very close proximity to each other), given strong economy of scale sensitivities

for downstream processing, conversion, and upgrading operations. Namely, reducing the facility 

size from 5,000 to 1,000 acres of production ponds would increase biomass selling price by 

roughly $100/ton relative to the base case described below (see Section 6.1), while further 

reducing the size to 500 acres would add another $100/ton. Extending the analysis to include 

downstream conversion to fuels via either the HTL or ALU pathways mentioned above (while 

beyond the focus of this work), the combination of higher biomass prices and lower throughputs 

would translate to substantial increases in fuel selling prices by roughly $2-3/GGE for a 1,000-

acre farm basis, or by $5-6/GGE for a 500-acre farm basis [29]. Such a cost premium could 

impose significant challenges in achieving economic viability for algal biofuels. 

While a 5,000 acre algae farm is much larger than current demonstration-scale facilities operated 

by private entities in the US (focused on algal fuel production), this is a similar premise to the 

establishment of terrestrial lignocellulosic ethanol biorefinery scales considered under BETO 

modeling analyses, typically 2,000 dry metric tons/day, which had been established based on 

tradeoffs between feedstock harvest/logistical constraints and economy of scale ramifications for 

the biorefinery [30]. Beyond economy of scale sensitivities noted above, additional factors also 

support a 5,000-acre farm basis. First, there are lower limits on operability for certain 

downstream conversion/upgrading equipment items, such as conversion reactors, extraction 

equipment, and upgrading (hydroprocessing) units, which may not be practical for outputs from 

smaller 500-1,000 acre algae farms (which would approach more of a “depot” concept in terms 

of annual biomass production). Moreover, while terrestrial crop farms vary dramatically in size, 

as of 2012 there were roughly 24,000 large commercial “mega-farms” of 5,000 acres or more in 

the US, which combined account for roughly one-third of all farmed cropland [31] thus, 

precedent for farms of this size is well-established in traditional agriculture. Within the 

commercial algae industry for food products, a 7,000-acre algae farm is in operation today in 

Australia [32]. Finally, a survey of industry peer reviewers of this report confirmed that there are 

no logistical reasons that would prevent a 5,000-acre algae facility of this nature from being 

viable from a practicality or operational standpoint (subject to location siting constraints). Thus, 

moving forward it will be important to consider this topic, e.g., through resource assessment 

models, to better understand implications on land availability for such farms on a national scale.

The design assumes dewatered algal biomass product is sold “at the gate” and does not take into 

account transportation costs to an off-site location; at 20 wt% solids (80% water content), it is 
10 

not envisioned that the biomass would be transported off site, but rather would be sent directly to 

downstream operations for biomass conversion to fuels or products located on site or very 

nearby. Thus, the minimum biomass selling price presented here represents a “transfer price” to 

the downstream conversion portion of the facility. While it is not as straightforward to draw a 

system boundary in this way as it is for terrestrial biomass that has distinctly independent supply 

chain stages for biomass production and biorefinery conversion, a fully integrated algal 

production and conversion facility would naturally divide itself along these boundaries fairly 

easily anyway, as very little heating or cooling demands are incurred on the “front-end” 

operations considered here that would require integration with the “back-end” conversion 

process, nor are there substantial amounts of recycle streams between the two stages. Any 

recycle streams which may be provided from downstream conversion/upgrading operations 

(including CO2, water, or nutrient streams) are excluded from consideration in this analysis, but 

may instead be taken credit for on the “back-end” conversion models, e.g., by reducing estimated 

fuel costs or greenhouse gas profiles. Additionally, the overall land footprint and associated land 

cost assumed here includes allowances for integration with the downstream conversion facility. 

The overall site layout assumes that ponds are grouped into unit “modules” of 100 wetted acres 

each. The actual module land footprint is larger than 100 acres to include allowances for pond 

access and piping, as well as in-ground settling ponds, which serve as first-stage dewatering prior 

to further dewatering that occurs in a central location serving all modules. The full facility 

contains 5,000 wetted acres of biomass production ponds grouped into 50 individual modules 

connected via a network of pipelines and roadways. The modules form a uniform grid of seven

columns by eight rows. The eighth row comprises a single biomass production module as well as 

the dewatering facility, algae inoculum system, and support buildings, with the remaining 

acreage allocated for a hypothetical downstream algal conversion plant. The site is assumed to be 

situated on land with a continuous 1% slope (consistent with grading and civil costs estimated by 

the various sources for pond design discussed in Section 4.1.2); this slope is graded to be level 

within the individual modules where ponds and supporting equipment are located, but left 

ungraded everywhere else, thus forming a “terraced” layout that assists in harvesting and 

circulation logistics following pond cultivation and primary dewatering. The “terraced” concept 

has also recently been considered elsewhere in literature as a plausible design for large 

commercial-scale facilities [10,33]. However, although this allows for low-cost harvesting and 

circulation of culture to central dewatering, it considerably increases pipeline and pumping costs 

for returning water back uphill to the top of such a large facility, and thus may not necessarily 

offer substantial net cost savings compared to a more level facility layout. An alternative 

configuration based on a net level facility grade is evaluated as a sensitivity scenario in Section 

6.1, which considers pipeline circulation and pumping both to and from the production ponds 

and dewatering (which may also approximate a facility with more distributed high and low areas 

instead of a continuous 1% slope). Figure 4 shows the layout of the modules within the overall 

facility footprint along with the primary pipelines and channels required for on-site circulation 

and transport of media. 

The specific pond design within each module affects both the overall dimensions of the facility 

as well as the piping length requirements. An overview of the three general pond designs 

considered and their effect on facility footprint, as well as total lengths for overall site circulation 

piping, is shown below in Table 1. Pumps and pipelines internal to the 100-acre modules 

(including circulation between ponds and primary dewatering, as well as clarified water return 
11 

from primary dewatering back to ponds) are discussed later in Section 4.1. The module 

dimensions (A & B) include spacing between ponds for access, piping, and electrical. Facility 

dimensions (C & D) include surrounding roads and fences in addition to the primary settler 

footprint, which is constant across all pond design choices. The physical configuration for some 

pond designs may have room for further optimization to slightly alter the overall module 

dimensions and reduce pipe distances (this is the case for the Global Algae Innovations pond 

designs which may allow for more compact pond spacing than that assumed here), but for 

simplicity a single basis for pond layout and spacing was utilized for each discrete pond size; 

variants for slightly more or less space-efficient layouts would impact overall biomass selling 

prices by less than 2%. Based on the given piping diameters and lengths shown in Table 1, 

circulation pumps to send material back “uphill” (e.g., clarified water from second and third 

stage dewatering and inoculum for pond re-starts) were modeled in Aspen Plus to estimate 

pumping power required to overcome head and frictional losses for uphill circulation. Because 

these pumps and pipelines normally only carry clarified effluent from central dewatering back up 

the facility grade, the pumping power is not significant (4%–9% of total facility power in the 

peak summer months), given that this amount of circulation only represents roughly onetwentieth of the amount of water circulated internally within the 100-acre modules from primary 

dewatering. If instead all dewatering operations occurred centrally, i.e., at the bottom of the 

grade, the amount of clarified water recycle would be 22 times higher, which would dramatically 

increase recirculation pumping power. 

Table 1. Effect of Individual Pond Sizing on Facility/Module Dimensions and Pipeline Length

Pond size 2 acres 10 acres 50 acres

Facility and module dimensions (see Figure 4 for “A-D” labels)

Module width (“A”, ft) 5,570 4,588 2,700

Module length (“B”, ft) 950 1,070 2,412

Facility width (“C”, ft) 39,915 33,041 19,825

Facility length (“D”, ft) 8,500 9,460 20,196

Facility size (Acre) 7,789 7,176 9,192

Distribution pipeline requirements (ft)

34" ID 6,745 5,883 5,337

26" ID 11,390 9,426 5,650

20" ID 12,055 9,991 6,215

16" ID 8,400 9,360 20,096

14" ID 8,400 9,360 20,096

12" ID 8,400 9,360 20,096

For each pond scenario, underground distribution pipelines for water and CO2 are laid out to 

minimize required piping and vary based on the module dimensions. Running along the bottom 

edge of the facility is the primary water recirculation pipeline, which decreases in diameter as 

water is split off for module columns. The four vertical pipelines connecting successive terraces 

are identical and decrease in diameter every two terraces as water is again split off for individual 

modules. Changes in diameter are noted in Figure 4 and are consistent across all pond sizes. 

Connecting piping from the vertical distribution pipeline manifolds to the individual modules, 

along with clarified water recycle piping from primary settler dewatering (within the individual 

modules), is included in the pond cost estimates (Section 4.1) rather than overall facility 
12 

circulation piping (Section 4.4), but is depicted for clarity in the overall facility diagram in 

Figure 4 as well. 

Following harvesting from ponds at a concentration of 0.5 g/L and preliminary dewatering to 10 

g/L (AFDW) via primary gravity settling within the 100-acre modules, the partially concentrated 

harvest stream is routed via aqueduct channels from the modules to central dewatering at the 

bottom of the facility grade, following the distribution pipeline network. The channels proceed 

from high to low elevation along the 1% terraced sloping of the site footprint. Roads allow 

access to all modules. The support buildings include a laboratory, office spaces, warehouses, and 

nutrient storage, which are situated between the dewatering facility and inoculum ponds at the 

bottom edge of the facility. Placement of sensitive culture areas (PBR and lined ponds in the 

inoculum system) in close proximity to the laboratory allows for ease of monitoring and control. 

100 Wetted Acre 

Module

A

C

E-39 E-40

E-41 E-42 E-43

E-54 E-52 E-48

E-55 E-47 E-50

E-59 E-58

E-61 E-63

Algal biomass conversion operations footprint (not modeled here)

100'

50' 50'

440' B

D

Warehouse, Lab, 

Nutrient Storage

Dewatering 

Facility

75'

Ø34"

Inoculum Ponds

Ø26"

Ø20"

Ø16"

Ø14"

Ø12"

Ø

Distribution 

Pipeline

Production 

Parcel

Channel Settler Road Inner 

Diameter

CO2 

Distribution

Clarified 

Water Return

Pond Size A (ft) B (ft) C (ft) D (ft) Facility (acre)

Facility and Module Dimensions

2 acre 5,570 950 39,915 8,500 7,789

10 acre 4,588 1,070 33,041 9,460 7,176

50 acre 2,700 2,412 19,825 20,196 9,192

Figure 4. Schematic diagram for overall facility layout, depicting location of 100-acre modules and 

connections to overall circulation networks including allowances for dewatering, inoculum, and 

downstream conversion operations. (Dimensions not to scale.)

2.3 Biomass Composition

For purposes of tracking nutrient and CO2 requirements as well as harvested biomass 

composition, the base case assumes the use of Scenedesmus acutus (LRB-AP 0401), a freshwater 

algal strain that has been well-characterized at NREL based on harvested biomass provided by 

Arizona State University (ASU). To generate the biomass at ASU, batch harvests were taken in 

early-, mid-, and late-cultivation stages, corresponding to low-, mid-, and high-nitrogen 
13 

starvation states and also to high-protein (“HP”), high-carbohydrate (“HC”), and high-lipid 

(“HL”) content biomass, respectively; associated cultivation batch times typically ranged from 

3–5 days following nutrient depletion for mid-harvest biomass and 6-9 days for late-harvest 

biomass, while early-harvest biomass was obtained prior to nutrient depletion [1,34]. Table 2 

provides the biomass compositional details for these cases, consistent with the above-referenced 

ALU design report and originally published by Laurens et al. [11]. For the base case, the midharvest Scenedesmus scenario titled “HCSD” in Table 2 was selected for use in the model given 

a reasonable 27% lipid content, which is a critical parameter to consider alongside corresponding 

biomass productivity (set at an annual target of 25 g/m2/day as discussed in Section 4.1) in light 

of known tradeoffs between achievable growth rate and lipid content [35,36]. While the earlyharvest/high-protein scenario would most easily allow for achieving high biomass productivity 

targets, the low lipid and carbon content of the biomass would be expected to translate to poor 

yields and/or product quality during downstream conversion through either the ALU or HTL 

conversion pathways [1,2,37]. Alternatively, the late-harvest/high-lipid case would allow for 

highest fuel yields during downstream conversion, but at 41% lipid content would place 

additional burdens on achievable cultivation biomass productivity. Sensitivities to these tradeoffs 

are explored in Section 6.1. As the experimental basis for biomass grown to the specific 

harvesting points described above was originally done in batch cultures at ASU, it is assumed 

that the same compositions may be seen for a continuous growth/harvesting regime as is 

modeled here, enabled by optimized production schemes, nutrient feeding strategies, and 

resultant growth rates. 

In addition to the compositional details for Scenedesmus over the given range of harvesting 

regimes, Table 2 provides similar information for Chlorella vulgaris (LRB-AZ 1201) (also a 

freshwater strain) and Nannochloropsis granulata (a saline strain), also provided by ASU over a 

similar range of harvesting time points; the latter two strains are investigated as sensitivity 

scenarios in Section 6.1. For all three species, there is a clear measured shift in composition of 

the biomass across the early, mid, and late stages of cultivation, which is typical for nutrient 

limited biomass, with corresponding protein, lipid, and carbohydrate values consistent with 

earlier reports for these species [38-40]. In both freshwater cases, the ash content is seen to 

reduce from 6%–7% to <3% between the early and late harvest points, while measured protein 

content drops dramatically from 34% to 9% for Scenedesmus or from 40% to 13% for Chlorella

(elemental nitrogen content closely tracks a similar trend with protein). Similar trends are also 

seen for Nannochloropsis, but with a higher ash content as typical for a saline strain. Further 

details related to the assumptions used to close component mass balances for modeling purposes 

(bottom portion of the table), as well as explanation of component categories in Table 2, are

provided in the 2014 ALU design report [1]. One item that bears repeating is the definition of 

“lipid content” as shown in Table 2, which is based on fatty acid lipids as FAME (fatty acid 

methyl esters) produced by transesterification of the biomass lipids following NREL published 

methods [41]. Thus, this does not include other hydrocarbon-based lipid species such as straight 

and branched-chain hydrocarbons, sterols, and isoprenoid-based compounds. 
14 

Table 2. Elemental and Component Compositions for Early-Harvest (HPSD), Mid-Harvest (HCSD), and Late-Harvest (HLSD) Algal 

Biomass for Three Strains. (Top portion = raw analytical data, bottom portion = adjusted values to achieve 100% mass closure for modeling) 

[11,34]

Measured: Scenedesmus sp. Chlorella sp. Nannochloropsis sp. 

Wt% composition (dry basis) Early 

(HPSD)

Mid

(HCSD)

Late 

(HLSD)

Early 

(HPCZ)

Mid

(HCCZ)

Late 

(HLCZ)

Early 

(HPNC)

Mid

(HCNC)

Late 

(HLNC)

C 49.3 52.9 56.3 48.7 49.8 54.7 46.6 48.2 61.6

H 7.1 8.0 8.5 6.9 7.5 8.3 7.0 7.3 9.6

N 8.3 1.8 1.6 8.8 2.7 2.2 6.6 4.5 2.0

O 28.7 34.8 31.2 28.0 36.5 31.5 29.0 30.0 22.9

S 0.0 0.2 0.2 0.6 0.4 0.4 0.6 0.5 0.3

P 0.97 0.22 0.20 1.08 0.15 0.11 ND ND ND

Total a 94.4 97.9 98.0 94.0 97.0 97.2 89.8 90.0 96.3

Ash 6.7 2.3 2.1 6.1 3.0 2.8 14.2 13.6 5.1

Fermentable carbohydrates 24.3 46.3 37.9 5.8 36.7 23.6 6.0 8.8 8.9

Other carbohydrates b 3.4 1.6 1.3 5.9 5.0 3.5 2.9 2.4 2.0

Protein 34.5 12.8 8.9 40.8 13.4 12.9 32.7 23.1 9.4

Lipids (fuel-relevant lipids as FAME) 6.6 26.5 40.9 13 22.1 40.5 12.3 25.6 57.3

Non-fuel polar lipid impurities ND c ND ND ND ND ND ND ND ND

Cell mass ND ND ND ND ND ND ND ND ND

Total 75.5 89.5 91.1 71.6 80.2 83.3 68.1 73.5 82.7

Adjusted to close mass balances: Scenedesmus sp. Chlorella sp. Nannochloropsis sp. 

Wt% composition (dry basis) Early 

(HPSD)

Mid

(HCSD)

Late 

(HLSD)

Early 

(HPCZ)

Mid

(HCCZ)

Late 

(HLCZ)

Early 

(HPNC)

Mid

(HCNC)

Late 

(HLNC)

C 52.2 54.0 57.4 51.8 51.3 56.3 51.4 53.2 63.8

H 7.5 8.2 8.7 7.3 7.7 8.5 7.7 8.1 9.9

N 8.8 1.8 1.6 9.3 2.8 2.2 7.3 5.0 2.0

O 30.4 35.5 31.8 29.8 37.7 32.4 32.0 32.6 23.7

S 0.0 0.2 0.2 0.6 0.4 0.4 0.7 0.5 0.3

P 1.03 0.22 0.20 1.15 0.15 0.11 0.88 d 0.60 d 0.24 d

Total a 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Ash 6.7 2.4 2.1 6.1 3.0 2.8 14.2 13.6 5.1

Fermentable carbohydrates 26.2 47.8 38.2 6.8 39.2 25.2 8.2 11.0 9.8

Other carbohydrates b 12.8 5.0 3.9 20.7 16.0 11.2 11.9 9.0 6.6

Protein 43.2 13.2 9.0 47.8 14.3 13.8 44.6 28.9 10.4

Lipids (fuel-relevant lipids as FAME) 8.3 27.4 41.2 15.2 23.6 43.3 16.8 32.0 63.2

Non-fuel polar lipid impurities 0.8 2.7 2.1 1.5 2.4 2.2 1.7 3.2 3.2

Cell mass 1.9 1.6 3.5 1.8 1.6 1.6 2.7 2.3 1.7

Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 a Measured element balance on dry weight basis; adjusted to AFDW basis for model (bottom portion of table). b Non-fermentable carbohydrates. c ND = not determined. d Elemental P content estimated for modeling based on assumed P:N weight ratio of 0.12:1 per separate analytical data for Nannochloropsis oceanica [42].
15 

Beyond the basis of reasonable/mid-level lipid content justifying the strain/harvest selection, the 

choice of Scenedesmus itself as the base case strain also supports the intent to be agnostic to the 

downstream conversion method, i.e., ALU or HTL, while making use of a representative strain 

with commercial relevance (recognizing that there is not yet a “commercial” industry for algal 

biomass beyond Spirulina for the food market). As noted above, this particular strain has been 

well-characterized for both elemental and component analysis to a high degree of mass closure 

[11], thus reducing uncertainties regarding both nutrient/CO2 input demands as well as harvested 

biomass C/N/P content and thereby potential fuel yields during downstream conversion. Such 

amount of detail for high mass closure is difficult to attain for most strains available in literature, 

particularly for presenting both the elemental composition (required for the HTL modeling basis 

[2]) and associated component composition (required for the ALU modeling basis [1]). Making 

use of the mid-harvest Scenedesmus information across both compositional data sets allows for 

equally usable inputs to be consistently evaluated through either conversion pathway. 

Additionally, Scenedesmus may be reasonably viewed as a representative strain with 

commercially relevant potential for fuel or coproduct opportunities, as it is closely related to 

Desmodesmus, a strain produced both at Cellana in partnership with the Cornell Consortium as 

well as at Sapphire, with favorable published results [43,33]. Sensitivities attributed to the use of 

a number of alternative strains (primarily impacting nutrient and CO2 inputs, with one saline 

scenario also considered) also are presented in Section 6.1. 

2.4 Modeling Basis Parameters

Similar to other recently published design reports under DOE-BETO efforts [2,23,44], a number 

of key modeling assumptions are fixed constant to allow for comparable modeling outputs. 

These parameters include:

1. Design and construction time: 36 months 

2. Facility start-up time: 0.5 year (6 months) 

3. Cost-year dollar basis: 2011 dollars (all cost results presented here will be in 2011 

dollars) 

4. Facility on-stream time: 90% (330 days/year or 7,920 hours/year). Note, this is intended 

to represent an nth-plant facility and may be a higher factor than what is achievable today, 

particularly when considering the algal cultivation step, which is dependent on strain 

robustness to withstand culture crashes (discussed above in Section 1.3). This on-stream 

factor assumes year-round operation with approximately one month per year allocated to 

facility shut-down, whether due to planned maintenance, pond upsets (such as culture 

crashes or freezes), or other downtime factors. 
16 

3 “Top-Down” Analysis of Cultivation Cost Demands

Before considering specific pond system designs and costs as well as cultivation productivity 

projections, it is useful to begin with an analysis conducted from the “top down” to objectively 

present what both of these metrics must be in order to achieve a desired biomass selling price. To 

do this, the design and cost basis assumptions for all other operations aside from cultivation were 

first set consistently with the details documented in Sections 4.2–4.6, including the inoculum 

system, dewatering operations, delivery of CO2 and makeup water, on-site circulation of harvest 

and recycle water streams, and storage. Additionally, the same seasonal assumptions for pond 

evaporation rates as well as fractional variability in cultivation productivity were employed as 

discussed in Section 4.1.2 (i.e., productivity ratio between summer and spring, fall, or winter 

were set at factors of 1.2, 1.4, and 3.0, respectively). Based on these assumptions, Figure 5 

presents a scan of pond costs in dollars-per-acre for all pertinent pond elements (including civil 

work, paddlewheel or other circulation device, concrete, lining or other leakage control methods, 

piping between individual ponds and central headers, and electrical) versus cultivation biomass 

productivity (g/m2/day, annual average) both as independent variables, with the contour lines 

representing the resulting MBSP attributed to inputting these two variables into the overall 

model framework. The bottom bound for the selected contour lines corresponds to an optimistic 

goal of $300/ton, followed by $430/ton, which represents the current BETO 2022 target as 

published in recent Multi-Year Program Plan (MYPP) documents, while the top bound is closer 

to today’s current estimated baseline costs of roughly $1,000/ton or higher [45,46]. 

As shown in Figure 5, the economics for biomass production depend strongly on both achievable 

productivity and the capital expenses for the cultivation system when the latter costs are high 

enough to represent the primary cost driver behind MBSP (i.e., the $1,000/ton contour line 

shows a much steeper slope across the span of productivity values considered than the $300/ton 

line). For example, at a productivity target of 30 g/m2

/day, MBSP increases from $300/ton at a 

pond system cost of ~$1k/acre up to $430/ton, $550/ton, and then $700/ton at $30k/acre,

$57k/acre, and $90k/acre, respectively, and then more dramatically to $1,000/ton at $157k/acre. 

We will show later that two primary requirements in driving down costs for algal pond systems 

are (1) making use of large ponds to capitalize on economy of scale benefits (see Sections 4.1.3 

and 5.5) and (2) avoiding the use of fully lined ponds, as are typical in today’s demonstration or 

commercial facilities (see Section 6.1). For small fully lined ponds that may be more typical for 

such facilities today, calculated costs would be on the order of $75-120k/acre. 

As cultivation pond costs can be reduced to reasonable levels, ideally <$30k/acre (consistent 

with larger ponds with minimal lining as shown in Figures 8-9), other considerations start to 

become the dominating contributor to MBSP such that even when ponds are nearly “free,” it is 

difficult to reduce biomass selling price below roughly $300–$350/ton unless productivity can be 

improved to aggressive target values greater than 30 g/m2

/day. This is evidenced later in Section 

5.5, which shows that costs attributed to CO2 and nutrients alone make up more than $110/ton of 

biomass based on the combination of inputs and assumptions employed in the “bottom-up” 

analysis of Section 4 at a 25 g/m2/day annual average productivity. In any case, this analysis 

supports prior conclusions that algal biomass (and therefore biofuel) economics are strongly 

dependent on achievable cultivation productivity, where for example biomass selling price could 

reduce from $1,000/ton to $430/ton by improving productivity from 10 g/m2

/day up to 35 

g/m2

/day while maintaining cultivation pond cost near steady at $40–$45k/acre. Although a 
17 

productivity of 35 g/m2

/day may be slightly optimistic to achieve over an annual year-round 

basis, pond costs may plausibly be reduced below $40k/acre if designed for large pond sizes to 

maximize economy of scale benefits; this could allow achieving costs near the $430/ton goal at a 

lower productivity in the 25–30 g/m2/day range, which is more reasonable as a projection to 

achieve by 2022. Thus, while a cost as low as $300/ton remains a challenge to substantiate 

through TEA, this analysis validates that an MBSP target near $430/ton (or more conservatively, 

at most limited to under $500/ton) is in fact achievable with a number of improvements beyond 

today’s current performance and high-cost pond configurations. This assumes that other key 

contributors such as CO2 or nutrient demands are not given credit for recycle possibilities that 

may be enabled by downstream integrated conversion processes; however, our prior analyses 

have instead given credit for such recycles by reducing biofuel selling prices accordingly, rather 

than biomass selling prices [1] (thus doing so here would double-count for such a credit). 

Alternatively, consideration of value-added coproduct opportunities from the algal biomass 

could also relax the requirement for extremely low-cost ponds and aggressive productivities, by 

providing a means to valorize the biomass and garner higher values relative to biomass 

production costs, and to supplement algal fuel production. 

Figure 5. "Top-down" scan for minimum biomass selling price (MBSP) as a function of both 

cultivation pond system capital costs (agnostic of specific pond design details) and achievable 

annual biomass productivity. (Y-axis for “pond system costs” includes capital costs for civil work, 

concrete, mixing equipment and motors, lining or other leakage/erosion control costs, circulation piping, 

and electrical costs.)

15 25 35 45 55 65

$0

$50,000

$100,000

$150,000

$200,000

$250,000

$300,000

10 15 20 25 30 35 40 45 50

Productivity (ton/acre/year at 330 days/year)

Pond System Capital Costs ($/Wetted Acre)

Productivity (g/m2/day)

$1000/US Dry Ton

$700/US Dry Ton

$550/US Dry Ton

$430/US Dry Ton

$300/US Dry Ton
18 

4 “Bottom-Up” Integrated Model: Process Design and 

Capital Cost Estimation Details

Moving beyond the generic cost scans presented in Section 3, the remainder of this report 

documents the details of a “bottom-up” analysis conducted to incorporate a number of discrete 

pond designs furnished to NREL into an integrated model that includes delivery and circulation

of water, nutrients and CO2, inoculum propagation, and downstream algal biomass dewatering. 

Under this approach, we consider a combination of operations and conditions that represent one 

plausible set of targets to be achieved by 2022, but reiterate that this may not represent the most 

optimal possible scenario, nor a (as of yet) fully commercially demonstrated design as it 

represents future process goals projected onto a set of design configurations as understood today. 

Furthermore, the goal of this assessment is not to reach a previously prescribed MBSP target, but 

rather to present the implications on MBSP for a number of design and processing scenarios 

using a consistent modeling framework, and thereby help inform near-term research and 

engineering directions. This section describes the process as modeled and discusses the influence 

of specific R&D goals in the decision-making process. 

As the cultivation step represents the most critical and cost-intensive area of the process, a 

number of experts in the field were consulted in order to provide a more comprehensive survey 

of inputs for cultivation designs and costs, rather than relying on a single basis for this 

information. As discussed in Section 4.1, four independent sources were consulted to solicit 

detailed inputs on pond designs and costs; namely, two engineering subcontractors (Leidos and 

Harris Group), a commercial developer (Global Algae Innovations [“GAI”]), and a consultant 

group with industry expertise (MicroBio Engineering [“MicroBio”]). NREL gratefully 

acknowledges these sources for providing critical support to establish detailed cost projections 

across a range of individual pond sizes, layouts, and circulation methods for the key cost 

elements related to pond operations and bulk fluid handling. Beyond this step of the process, 

inputs and assumptions for other operations considered in the integrated model—including 

delivery and on-site circulation of CO2 and water, inoculum production, and dewatering—were 

based on inputs from literature, additional vendors, and engineering software (e.g., Aspen Plus 

and ACCE [24]). Design configurations and processing details for these additional operations 

beyond the production pond systems were maintained consistently across all individual pond 

design scenarios in the baseline model framework. While the specific cultivation and processing 

options evaluated here do not constitute an exhaustive survey of the published literature for all 

promising designs, they establish a benchmark against which additional scenarios and associated 

costs may be compared, as the primary objective is to set goals for both costs and performance 

attributed to each area of the process moving forward as the industry progresses. 

4.1 Area 100: Biomass Production

4.1.1 Overview

This section describes the design and cost details for a number of pond sizes and configurations 

made available to NREL through subcontracts, consultations with industry stakeholders, and 

literature. In total, eight discrete pond scenarios are considered within the integrated technoeconomic model for their implications on resulting biomass selling price. In all cases, ponds are 

grouped into 100-acre modules with each module including feed and harvest pipes between 

individual ponds and common headers, with the harvest lines typically drawn off of pond sumps 
19 

controlled by slide gates or valves and delivered to primary dewatering (in-ground gravity 

settlers, discussed in Section 4.5) located within the 100-acre module blocks. The harvested 

material from primary settling is routed to harvest channels for delivery to central dewatering, 

while the clarified effluent is routed back to pond feed header lines along with additional recycle 

water from central dewatering and fresh makeup water. 

The individual pond scenarios span a wide range of sizes, including two 2-acre estimates (with 

paddlewheel mixing), which may be viewed as a standard basis for today’s demonstration- or 

commercial-scale facilities [10,47,48]; four 10-acre estimates (three mixed by paddlewheels and 

one by pumping), which historically have been viewed as an upper bound for pond operability in 

the context of standard paddlewheel raceway designs [17,22]; and two hypothetical 50-acre 

estimates (both based on novel configurations without paddlewheels) primarily for illustrative 

purposes to demonstrate economy of scale ramifications. By considering such a large dataset 

beyond a single design basis, it may be demonstrated that cultivation pond costs are more 

strongly divided by economy of scale differences than by design details or differences of opinion 

in cost elements (see Figures 8 and 9), which is an important conclusion in light of commonly 

held beliefs that cultivation pond costs are too widely scattered to conclude with any certainty 

what commercial ponds would “actually” cost in an nth-plant commercial design. Of course, 

more simplistic pond designs are possible with minimal agitation and therefore lower achievable 

productivity, but such designs are not typically envisioned for production of low-price

commodity products such as algal biofuels and are not considered here. A key point to 

emphasize is that moving beyond currently available 2-acre pond sizes up to 10 acres or more 

carries additional processing risk particularly for today’s strain performance which typically may 

experience frequent contamination and culture crash events, which would be substantially more 

detrimental for a single 10-acre pond than a single 2-acre pond; consequently, it remains a 

critical research priority to develop highly robust strains that withstand culture crashes in order 

to enable the practical use of larger-size ponds. 

High-level schematic layouts for the three different pond design configurations are shown in 

Figure 6. Cultivation process details were applied consistently across all pond designs 

considered, including seasonal biomass productivity targets, evaporation rates, and harvested 

biomass density. Additionally, all base case pond designs avoid the use of fully-lined ponds 

given significant cost premiums that pond lining incurs, but rather only utilize plastic liners 

sparingly on small targeted areas of the ponds for erosion control.

Figure 6. Schematic layouts for the three pond configurations considered over multiple size 

ranges. (Left = paddlewheel raceway; center = GAI pond system with pump circulation; right = Leidos 

gravity flow serpentine pond.)

Typical Sump Location

(varies by design)

1% Elevation 

change

Weir every 

2nd channel

Paddlewheel 

Station

Circulation 

Pump

Circulation 

Pump

0.1% Slope
20 

4.1.2 Design Basis

Process Assumptions

The process begins with algal biomass grown and harvested from the production ponds under 

continuous steady-state conditions. For initial startup and occasional re-inoculation when 

necessary, the production ponds are inoculated with biomass provided from the inoculum system 

at a starting culture density of 0.1 g/L (see Section 4.2). Under normal conditions, the ponds are 

operated under a continuous mode of harvesting to minimize fluctuations and over-design (and 

therefore cost) that the downstream dewatering equipment must accommodate [17]. Biomass is 

harvested at a fixed culture density of 0.5 g/L AFDW for processing through primary settling. 

Biomass productivity is a key parameter, with two important facets—annual average 

productivity (g/m2

/day) and the degree of variation by season (maximum versus minimum 

range). For the former parameter, the overall annual average productivity is set at 25 g/m2/day 

(AFDW basis) as a projection targeted to be achieved by 2022. This is slightly more conservative 

than prior BETO 2022 targets documented in MYPP reports at 30 g/m2

/day that were implicitly 

attributed to 2022 fuel yield goals of 5,000 gallons per acre per year [45,46]. Furthermore, this 

appears to be an achievable target in light of published performance from industry at large-scale, 

currently demonstrated to be as high as 23 g/m2/day (coupled with a very high 40% lipid content 

in one publication) [43], although that was based on favorable year-round climatic conditions in 

Hawaii coupled with a higher use of PBR systems to supplement pond growth, and is 

considerably higher than other currently achieved values more typically observed at 10–15 

g/m2/day based on sustained values averaged over the course of a year [49-52]. In any case, a 

target of at least 25 g/m2

/day is critical in achieving reasonable biomass costs, as evidenced by 

the strong economic sensitivity to this parameter shown in Section 6.1. At this productivity 

coupled with the assumed steady-state biomass density of 0.5 g/L, the mean residence time for 

all pond scenarios is 5 days (i.e., 20% of the pond is harvested each day) on an annual average 

basis. Equally important is the associated lipid content and other compositional attributes that 

influence fuel yields during downstream conversion (particularly pertinent for ALU conversion, 

but also HTL), with the base case set at 27% lipids as FAME (54 wt% C) for the Scenedesmus

strain considered here, as discussed in Section 2.3. These growth rate and compositional 

assumptions translate to an overall biomass energy conversion efficiency (energy contained in 

the biomass versus total full-spectrum solar irradiance) of 3.9%, compared to maximum limits of 

~14% based on the methods published in Weyer et al. and Beal et al. [53,54]. During external 

peer review of this report, the majority consensus among 20 expert stakeholder reviewers was 

that this combination of productivity and compositional targets stipulated here is (and must be) 

achievable by 2022 even if only demonstrable at small scales, and will likely require improved 

strains relative to today’s wild-types.

Seasonal variability in cultivation productivity is a function of both site location and 

biology/strain robustness. Maintaining consistency with the harmonization modeling activities 

discussed previously, the same collection of site locations located along the U.S. Gulf Coast is 

assumed here as was identified during the 2012–2013 harmonization analyses, based on 

optimization to maximize productivity and minimize net water demand (i.e., net evaporation 

rate) [23,42]. The most recent harmonization assessment presented a modeled swing in 

productivity of roughly 5:1 between the summer and the winter as an average across these site 

locations, attributed to current baseline performance expected for the cultivation of a freshwater
21 

Chlorella strain known as DOE 1412 [42,55]. In light of the unfavorable design constraints and 

associated economics such a high variability incurs on downstream conversion processing [1,2], 

this variability is targeted to be reduced by 40% in the present analysis to a range of 3:1 between 

the summer and winter seasons (an aspirational goal to achieve by 2022). Beyond favoring site 

locations with low variability in seasonal temperatures and solar insolation, such a reduction may 

also be achieved through engineered strain improvements or by employing strain rotation 

strategies to make use of a strain more tolerant to cold temperatures during cold season months. 

Indeed, algal growth modeling work being conducted at PNNL has identified that merely by 

employing strain rotation to make use of (for example) Sphaeropleales during cool seasons with 

Chlorella 1412 used in warm seasons, preliminary unpublished estimates suggest that seasonal 

production variability could be reduced by more than 50% to a level near 2:1 relative to today’s 

performance for Chlorella 1412 alone used year-round [56]. Furthermore, year-round cultivation 

data observed elsewhere suggest current swings in productivity observed lower than the 5:1 

basis. For example, the ATP3 Test-Bed Consortium has observed seasonal productivity ranges 

typically between 2:1-3:1 for year-round cultivation of Nannochloropsis across the majority of 

its five test-bed sites, with a site in Florida (most closely representing the Gulf Coast region out 

of the ATP3 sites) limited to a range near 2:1 [49,57]. A similar range also has been observed 

under ATP3 for year-round cultivation of Chlorella, limited to a maximum variability of 2.4:1 for 

the same Florida site [57]. In light of the above considerations, we feel a maximum variability

range in productivity of 3:1 is a reasonable projection, particularly as a target to achieve by 2022. 

The resulting individual seasonal productivity values attributed to this variability range are 

shown in Table 3, and model sensitivity to the range of variability itself is evaluated in Section 

6.1. The “shape of the curve” establishing the seasonal productivity values shown in Table 3 was 

developed based on: (1) limiting peak (summer) growth rate to a maximum of 35 g/m2/day; (2) 

setting minimum (winter) growth rate a factor of three lower (11.7 g/m2/day); and (3) setting 

spring and fall growth rates to support the annual average value of 25 g/m2/day while 

maintaining the same ratio of spring:fall as the most recent 2013 harmonization basis (1.15:1, 

translating to 28.5 and 24.9 g/m2/day respectively).

For seasonal water balance considerations, all assumptions related to water losses (primarily via 

pond evaporation and blowdown removal) were maintained consistently with the 2013 

harmonization work [42], which presented a net water evaporation rate of 0.09 cm/day as an 

annual average across the selected Gulf Coast site locations (after accounting for precipitation), 

with seasonal values shown in Table 3. Net seasonal water evaporation losses shown here are 

based on historical weather and precipitation data gathered by PNNL and could differ 

significantly for other regions of the country. Both previous harmonization studies assumed the 

use of freshwater strains, given sufficient freshwater resources available particularly in the U.S. 

Gulf Coast region, to satisfy cultivation facilities totaling to 5 BGY of biofuel production 

capacity, coupled with environmental and logistical concerns related to the use of saltwater in 

land-based open ponds and large-scale salt disposal for land-locked facilities not located in close 

proximity to the coast [23,58]. Water management costs for such facilities could be considerably 

higher for saline species than for freshwater species; this is briefly investigated in Section 6.1 for 

the use of Nannochloropsis as an alternative saline strain, with costs for blowdown brine 

disposal adding roughly $32/ton to overall biomass cost. The 2013 harmonization assessment did 

still include considerations for salt levels expected to be present in local freshwater resources (set 

here to 250 mg/L for incoming freshwater [59,56]), which required the inclusion of a small 

blowdown stream removed from the primary dewatering clarified effluent recycle line to 
22 

mitigate buildup of salt and other inorganics to an acceptable level for freshwater strains (no 

more than 4,000 mg/L in the ponds, although the maximum observed in the current model is 

2,000 mg/L). The same assumptions for blowdown are also maintained in the present model, set 

as shown in Table 3. As the blowdown streams taken off from the primary settler recycle line 

contain very low salt levels, we do not assume any treatment or disposal costs for their inclusion. 

Finally, building from previous work, nutrient requirements for the inoculum and production 

operations are assumed to be met using diammonium phosphate (DAP) for phosphorous 

requirements, and anhydrous ammonia (NH3) for nitrogen requirements, after accounting for the 

amount of nitrogen available in DAP. Previous models had assumed that these nutrient 

components were delivered in stoichiometric amounts to meet the harvested biomass elemental 

composition without any additional allowances; however, such an idealized scenario may be 

overly-optimistic even for a future optimized commercial facility, as some level of nutrient loss 

may always be expected, e.g., through system losses (volatilization, percolation into soil, etc.) or 

uptake by competing organisms (given that the open environment does not allow for a 

monoculture in the pond). Thus, the model was adjusted to allow for 20% excess nutrient levels 

beyond stoichiometric biomass compositional demands, the majority of which remains in the 

recirculation loop between growth and primary dewatering (dictated by a large fraction of 

water/solubles being removed during primary dewatering and recirculated back to the ponds). 

Likewise, CO2 is also provided to the inoculum and production stages based on stoichiometric 

requirements plus an additional amount to account for retention/uptake efficiency losses 

(discussed in Section 4.3). The stoichiometric quantities are specific to the strain’s elemental 

composition at harvest, set in the base case to 54.0% C, 1.8% N, and 0.22% P by mass (AFDW 

basis), as shown in Table 2. As noted earlier, to ensure applicability to any downstream biomass 

conversion/processing schematic, no credit is taken here for recycle of nutrients or CO2 from 

downstream conversion operations back to the production ponds, as doing so would require 

selecting a specific conversion technology and operating sequence; instead, any such recycle 

credits may be applied to the back-end process for example to reduce fuel costs. 

Table 3. Assumptions for Seasonal Biomass Productivities, Pond Evaporation, and Blowdown 

Rates Used for the Base Case Models

Metric Summer Fall Winter Spring

Annual 

Average

Biomass Productivity 

(g/m2/day AFDW) 35.0 24.9 11.7 28.5 25

Productivity Variance 

versus Summer Peak NA (1:1) 1.4:1 3.0:1 1.2:1 NA

Pond Evaporation 

(cm/day) 0.090 0.035 0.035 0.189 0.087

Blowdown (MM L/day) 7.3 2.8 2.7 12.4 6.3

Pond Design Scenarios

The pond design configurations made available to NREL for use in this analysis span three 

discrete sizes as defined by wetted cultivation area, namely 2-acre and 10-acre sizes to represent 

a range of what may be reasonable for today’s most “accepted” design based on paddlewheelmixed raceway ponds, as well as a hypothetical 50-acre size, which may be plausible for more 

novel configurations that do not make use of a paddlewheel. It should be noted that although all 
23 

designs considered here fall into one of those three size categories, they are not always exactly 

these dimensions, as in some cases the original source based their estimate on a hectare basis 

(i.e., 1 ha pond = 2.47 acres or 4 ha pond = 9.9 acres), while other sources considered specific 

dimensions that translated to a cultivation acreage slightly off from the given category (i.e., 2.2 

acres, 48.4 acres, etc.); these are identified accordingly in the discussion below. For all three size 

categories, ponds are assumed to be constructed with minimal spacing between ponds except for 

allowances for roads and piping as indicated in Figure 7. 

Ponds are grouped into sectional modules as described in Section 2.2, where each module 

represents 100 acres of wetted cultivation area and is graded to be level, based on the inclusion 

of site preparation and grading/leveling costs provided within each respective source for the 

pond designs. Thus, a varying number of individual ponds are located within a single 100-acre 

module based on the given pond size category, which incurs economy of scale cost penalties for 

the smaller pond scenarios, given the requirement for additional concrete, mixing stations, 

motors, electrical and piping runs to individual ponds, and valves/fittings to control harvest flows 

from individual ponds. In reality, electrical supply constraints may limit module size and 

geometry as well as equipment locations within the modules, but a detailed electrical design is 

beyond the scope of this analysis and is not assumed to preclude the placement of ponds and 

other equipment as described here. A schematic of the individual pond layouts within a given 

100-acre module is shown below in Figure 7 (including piping hookups to common headers for 

overall facility culture circulation discussed in Section 2.2), followed by a discussion of the 

designs furnished by the various sources. 

Feed Water Pipeline from Dewatering Facility

Clarified Water Pipeline from Settler to Ponds

Drain Pipes to Channels

Channels to Dewatering

Primary Settler

950'

(290m)

5570'

(1698m)

1370'

(417m)

70'

(21m)

4588'

(1398m)

2264'

(670m)

196'

(60m)

1070'

(326m)

1320'

(402m)

2412'

(735m) 50-acre Pond 1 50-acre Pond 2

2700'

(823m)

2-acre Pond

10-acre Pond

50-acre Pond

Figure 7. Schematic of pond layout within 100-acre modules. (See Figure 4 for overall facility layout).
24 

Leidos Pond Designs

Leidos Engineering is an engineering firm with expertise in the design and construction of algal 

cultivation ponds. Through a subcontract placed between Leidos and NREL, Leidos provided 

design and cost estimates for three pond configurations all based on optimal (but still realistic) 

cost structures for procurement and construction. These configurations included paddlewheel 

raceway systems of 2.2 and 10 acres in size, intended to represent realistic scenarios that are 

either built and operational today (2-acre systems) or may be readily constructed and verified to 

be operable in the near future (10-acre systems), as well as gravity-driven serpentine ponds 48.4 

acres in size based on total wetted cultivation area (intended strictly for illustrative purposes to 

demonstrate one possible means of achieving additional economy of scale benefits for larger 

ponds exceeding the 10-acre threshold). 

All Leidos pond scenarios included considerations for a number of different leakage control 

options, with the lowest-cost option selected for the base case as in-situ clay with minimal plastic 

lining only on specific areas of the pond, as required for erosion control (pond turns in this case), 

rather than fully lining the pond with plastic liners or other alternatives for leakage control. A 

similar approach dictating the use of minimally lined ponds is maintained for all other 

pond scenarios as well (i.e., MicroBio, Harris, and GAI ponds), with complete pond liners 

evaluated as sensitivity scenarios in Section 6.1. As will be seen from these sensitivity cases and 

has been shown in prior work [23,17,12], the requirement to fully line algae ponds with standard 

high-density polyethylene (HDPE) or similarly priced plastic liners adds substantially to capital 

costs and resulting biomass selling price, and would pose significant challenges in achieving cost 

viability for commodity fuel products produced from algal biomass. In reality, the requirement 

for pond liners will depend on factors including soil characteristics and governing regulatory 

policies. On this point, it is noteworthy to mention that one of the largest algal pond systems 

constructed to date at roughly 3.1 acres, located in Christchurch, New Zealand, was constructed 

with 5 mm liners only covering the pond berms but without lining the pond base, and has 

successfully demonstrated soil self-sealing without any noted operability problems due to the 

lack of full pond liners; moreover, this is for an algal pond treating wastewater [47]. This has 

also been demonstrated in use by other algal wastewater treatment systems of varying sizes for 

several decades. Additional long-term production trials and soil studies are required to further 

support this stipulation and to substantiate mechanisms for soil self-sealing and unlined pond 

operation. Furthermore, future work should consider assessing locations with sufficient soil 

characteristics to support unlined ponds, e.g., as part of screening criteria considered in Resource 

Assessment modeling. Such future studies would be particularly pertinent as focus turns to saline 

cultures or engineered organisms.

The Leidos 2-acre design (nominally 2.2 acres in wetted cultivation area) was based on an actual 

developer design already constructed, extrapolated to optimal low-cost construction quotations 

that would be reasonable today under nth-plant conditions. The given 100-acre module plots each 

contain 44 ponds with 100 acres of total cultivation area, shown in Figure 7. Each raceway pond 

is 417 m long with channels that are 10.7 m wide. Within the 100-acre facility there are four 

columns of 11 ponds. It is assumed that the site of the facility contains native in-situ clay and has 

a natural 1% slope, which is level graded within the 100-acre modules. Additional land in the 

100-acre module includes roads between every other column of ponds, as well as piping and 

channel footprints. The module has 100 wetted acres of cultivation but actually takes up 121 

acres of land. The land is prepared by removing surface vegetation and top soil not suitable for 
25 

compaction. In total, 15 cm (6 in) of overburden is removed. The land is then scarified to 30 cm 

(1 ft) deep. Soil from clearing, grubbing, and overburden removal is stock-piled on site and used 

for berm creation. Berms and ponds are created and compacted. The berm walls are 61 cm (24 

in) high, while the separation walls within the raceways are 41 cm (16 in) high. Under the 

“marginally lined” base case noted above, geo-membrane liners are only present on the pond 

turns to control erosion and weeds. For all Leidos pond cases (2-acre raceway, 10-acre raceway, 

and 50-acre serpentine), the geo-membrane liner costs $7.11/m2

. The total liner footprint per 

pond is 233 m2

, which includes allowances for liner overlap and trimming of the liner; this 

translates to 2.5% liner coverage for the Leidos 2-acre design. The normal pond water depth is 

23 cm (9 in). Turning vanes are not included, based on Leidos’ experience that they offer little 

benefit to justify their added expense (though a cost-benefit analysis should be done on a case by 

case basis to consider actual observed productivity or operational tradeoffs versus the use of 

turning vanes). Formed concrete is used to create paddlewheel support structures and a concrete 

sump. For each 100-acre module, 477 m3 of formed concrete is required, of which 20 m3 is used 

for the sump while the remainder is for the paddlewheel support structure. An additional 752 m3

of non-formed concrete is used to create piping stays for the underground piping within the 100-

acre modules. 

The 2-acre raceway ponds use paddlewheels to circulate the culture. Each paddlewheel is 

coupled to a 5.6 kW (7.5 hp) motor, but the actual power consumed is 2.8 kW per paddlewheel 

(operating as such 24 hours/day); this equates to a 10% paddlewheel efficiency at a channel 

velocity of 20 cm/s, which Leidos validated with a developer based on operational data for ponds 

of this size. Electrical runs to the paddlewheels are included, with 10 gauge-3 conductor wire 

routed to each pond, resulting in a total of 5,486 m of wire run for each 100-acre module

(including a 5% additional contingency). Although Leidos considers water piping for the whole 

facility, this design report estimates the cost of piping outside the 100-acre modules separately 

(i.e., circulation piping and aqueducts to and from central dewatering as discussed in Section 4.4, 

applied consistently across all eight pond scenarios). Thus, only the circulation piping originally 

quoted by Leidos that would be located within the 100-acre module is included within the “pond 

cost” category here, i.e., piping required to bring water to and from the individual ponds and a 

central point (in this case, primary harvesting settlers on the pond outlet header and tie-ins to 

facility circulation manifolds on the pond inlet side, respectively). The pertinent piping includes 

an 18-inch diameter, 800-foot (244 m) PVC pipe that takes the water from the main line to 

within the 100-acre module. The 18-inch pipe feeds into a 16-inch PVC sub-header pipe that is 

used to fill the individual ponds. Each 16-inch pipe feeds two columns of ponds. Therefore, two 

16-inch pipes are required to fill all the ponds in a 100-acre module. One 16-inch pipe runs 

between pond columns 1 and 2, and the other runs between columns 3 and 4. The total length of 

the feed 16-inch pipe for a 100-acre module is 2,170 m. The harvest takeoff from a given pond is 

controlled with a slide gate, which is opened and the algae medium enters an 8-inch PVC pipe. 

The 8-inch pipe runs 12 m from each pond to the main header, totaling 585 m in a 100-acre 

module. Similar to the 16-inch feed header, the drain header has a total of two pipes running inbetween pond columns 1 and 2 and pond columns 3 and 4. The 16-inch drain header totals 670 m 

and feeds into a drain channel. As the costs provided from Leidos did not originally include 

harvest/external circulation pump costs (as was also the case with most other design scenarios as 

well), additional pumps to move the water between the harvest manifolds and the primary 

settling units were added to this and all other pond designs, based on cost estimates generated 
26 

from ACCE. Finally, the design also includes CO2 diffusers located in the pond sumps to allow 

for CO2 sparging. 

The Leidos 10-acre pond design is similar to the 2-acre basis, with the most notable exception 

being a reduction in channel size and increase in pond depth around the paddlewheel to control 

costs for very large paddlewheels and supports (which also may bring an added benefit of 

increased paddlewheel efficiency). The 10-acre ponds are 670 m long with 30 m channels. The 

channels narrow from 30 m to 20 m wide at the paddlewheels. When the channels narrow they 

also deepen to maintain a consistent velocity throughout the ponds; this also more fully

submerges the paddlewheel and increases the efficiency of the paddles to move water. However, 

higher head and resistance from additional paddlewheel supports for the larger 10-acre design 

would be expected to at least somewhat offset this efficiency gain, thus for lack of operational 

data to validate actual paddlewheel efficiencies for a design this large, Leidos maintained the 

assumption of 10% efficiency consistent with the 2-acre basis. The resulting power consumption 

for paddlewheel circulation is 11.8 kW for every 10-acre pond, maintaining channel velocity at 

20 cm/s. 

Relative to the 2-acre basis, economy of scale benefits are incurred for the larger 10-acre design 

in that the amount of civil work, liners, paddlewheel equipment, electrical, and piping are all 

reduced per 100-acre module footprint. As seen in Figure 7, in a 100-acre module there are two 

columns of ponds with five 10-acre ponds per column, totaling 10 ponds. Additional land is used 

for roads, piping, and channels, translating to a total footprint of 112 acres for a given 100-acre 

module. Civil grading and overburden removal costs were based on consistent assumptions as 

employed in the 2-acre design, including grading from a 1% starting slope, 15 cm (6 in) of 

surface vegetation and overburden removal, and land scarifying to 30 cm (1 ft) deep. Because the 

ponds are larger than their 2-acre counterparts, the berms and center dividers have a smaller total 

footprint in the 100-acre module. The smaller footprint of berms reduces the amount of cut and 

fill and total compaction for the facility. The height of the berm walls and the separation walls 

are the same as the 2-acre case, at 61 cm (24 in) and 41 cm (16 in), respectively. The normal 

water depth for the 10-acre ponds is 25 cm (10 in). Paddlewheel supports and sump stations are 

again formed with concrete, with additional non-formed concrete used for underground piping 

stays. The ponds are lined in the same fashion as the Leidos 2-acre pond case, namely, lining the 

pond turns but not pond bottoms. In addition, for the 10-acre case the berm wall is also lined 

when the channels narrow from 30 m to 20 m and when the channels expand from 20 m to 30 m 

(for further erosion protection). The berm liner total footprint is 40 m2 per pond, with another 

584 m2 per pond allotted for pond turns. In all, 1.5% of each Leidos 10-acre pond is lined. 

Similar to the Leidos 2-acre ponds, the 10-acre ponds do not have turning vanes. For this and all 

pond designs, storm surge capacity has not been considered as a factor in setting berm heights or 

overall module configurations, and would be an important issue to investigate in the future 

(although this would also be highly location-specific depending on frequency and severity of 

storms).

For a 100-acre module there are also fewer paddlewheels needed in the Leidos 10-acre case

compared to the 2-acre basis. For the 2-acre case, 44 paddlewheels are needed with 5,490 m of 

electrical wiring, whereas for the 10-acre case, only 10 paddlewheels are needed with 2,888 m 

(including an extra 5%) of 10 gauge-3 conductor wire. The paddlewheels are larger and therefore 

more expensive per unit for the 10-acre case, but the lower total number of paddlewheels 
27 

outweighs this effect and results in a lower net cost for paddlewheels in a 100-acre module. 

Piping layout inclusions are similar to the 2-acre case, where the ponds are fed from the main 

facility circulation manifold via a 712 m (2,335 ft) 18-inch pipe running in between the two 

columns. The ponds are again harvested by opening a slide gate and entering an 8-inch pipe that 

runs 12 m to the main drain header. The drain header is 18 inches wide and 350 m long and runs 

to a drain channel, ultimately routed to primary settling. Harvest pumps are again added 

externally based on estimates generated from ACCE. 

In addition to the two raceway pond designs described above, Leidos also considered an 

aspirational serpentine pond design. This design was more hypothetical in nature without 

supporting operational details from any currently constructed system to validate pond operability 

for this configuration (particularly at the assumed size), thus it is stressed that this design is 

primarily intended to serve as an illustrative scenario to further demonstrate economy of scale 

benefits that may be gained by moving beyond 10-acre ponds, which would require moving 

away from a paddlewheel-based system (unless multiple paddlewheel stations were employed in 

a single pond which would mitigate economy of scale benefits for larger ponds). Each serpentine 

pond is 48.6 acres and two ponds cover a 100-acre module (illustrated in Figure 7). Each 

serpentine pond has 134 channels which are 3.7 m wide and 418 m long, with spacing included 

for access to each set of channels, additional berms, and precise grading. Serpentine ponds 

exploit the natural land slope to promote gravity circulation (maintaining the previous Leidos 

scenario assumptions of a 1% slope), with the channels designed to provide a 78-hour residence 

time from the top to the bottom of the ponds at a 20 cm/s velocity. Such a long single-pass 

residence time could pose a danger of becoming carbon or nutrient limited, and could require 

multiple points of CO2 and nutrient injection along the channel length (this was not considered 

here). Again, in this scenario, in-situ clay soil is specified with the use of partial plastic liners, in 

this case installed at the ends of each channel and on earthen weirs to control erosion. To ensure 

proper coverage an additional 0.6 m (2 ft) of liner extends beyond the weir and 15 cm (6 in) of 

liner is buried at the channel’s bottom. Within a given 100-acre module, a total of 9,897 m2 of 

liner is used for the Leidos serpentine design, which is less than the 2-acre case at 10,252 m2 but 

greater than the 10-acre case at 6,244 m2

. Liner coverage for the Leidos serpentine design 

represents 2.4% of total pond area. The civil work includes removing 15 cm (6 in) of 

overburden, scarifying down 30 cm (1 ft), compacting, cut and fill, and fine grading. Access 

roads and a piping footprint are included in the 100-acre modules, which translates to a total 

module footprint of 149 acres. 

To maintain a specific velocity the serpentine ponds not only require a graded layout, but also 

make use of earthen weirs to control the medium height from one set of channels to the other. 

Every two channels make a set, and an earthen weir is placed in between two sets of channels. If 

variations exist in the grade of the pond then the weir heights can be varied to maintain desired 

culture depths. Additionally, weir heights could also be varied to optimize circulation and the 

water column to maximize light capture as cultures get denser. The medium flows from the 

highest elevation channel to the next channel, until it reaches the bottom channel at which point a 

portion of the flow is harvested and routed to primary settling (set by the seasonal productivity 

while maintaining the fixed 0.5 g/L harvest density as stipulated above for the raceway pond 

scenarios). The medium that is not sent to settling is re-circulated back to the top channel by 

flowing into one of two water return pipes. With only two ponds to service per every 100-acre 

module, the piping for a given module only requires two 12-inch PVC pipes each running 1,067 
28 

m. These pipelines also connect to the recirculation manifold from central dewatering. The 12-

inch pipes include a 7.3 m (24 ft) elevation gain from the bottom channel to the top with an

additional 10% head loss included for fittings. As pumps were not included in the Leidos work 

scope, positive displacement pumps on the recirculation pipes were modeled separately in Aspen 

based on providing this required head, resulting in a circulation pumping power of 0.8 kW/acre

over a 24-hour day (when translated to a cultivation acre basis for consistency with other 

scenarios’ circulation power estimates). The pond harvested fraction is assumed to feed directly 

into a drain channel, without requiring additional harvest pipes. Harvest pump costs were 

maintained consistently with the other pond scenarios, based on estimates generated from ACCE. 

The recycle pumps and pipelines were also based on estimates from ACCE, routing the fraction 

of the culture which is not harvested back to the top of the serpentine pond. 

Relative to Leidos’ 2-acre and 10-acre raceway pond cases, the 50-acre serpentine pond design 

requires a larger footprint of channel separation walls. This translates into a larger cut and fill 

requirement, as well as compaction to create the channel walls. However, the penalty in civil 

work cost for this design is made up for in economies of scale given such a large area for a single 

pond, and the associated benefits in reduced equipment, electrical, and piping requirements. 

Namely, paddlewheels are not required, which also greatly reduces electrical and concrete 

demands (neither paddlewheel supports nor sumps are included in this design). Concrete is still 

used for underground piping stays, however with smaller total pipe distances in the 100-acre 

module, fewer stays are required. Compared to the 133 m of 12-inch pipe included for the 

serpentine ponds, the Leidos 10-acre pond design uses a total of 2,495 m of pipe. The lower total 

pipe distance for the serpentine case is attributed to the lower number of ponds and associated 

individual feed/harvest lines. Additionally, the 10-acre ponds have a total of 121 m of pipe 

leading to the drain channels whereas the two 50-acre serpentine ponds do not. Consequently, 

while this 50-acre serpentine design is more speculative and raises questions as to the operability 

of such a large system, it does demonstrate economy of scale benefits that may be gained beyond 

even large paddlewheel systems attributed to low costs for circulation equipment, electrical, 

concrete, and piping, which outweigh additional liner and civil costs that this design incurs. 

MicroBio Pond Designs

The comprehensive literature report published in 2010 by Lundquist et al. [17] considers the 

economics of a 100-hectare raceway pond system with 4-hectare (9.9-acre) individual ponds. 

The analysis, conducted by several co-authors who now make up the consulting company 

MicroBio Engineering, presented a thorough cost model for a number of algal production 

scenarios based on aggressive cost minimization measures justified by taking an approach to 

system design and costing more consistent with simplistic low-cost agricultural engineering 

practices than higher-cost industrial engineering approaches commonly assumed for most other 

algal processing analyses. This literature basis formed the baseline for the 2012 Algae 

Harmonization Model described previously [23]. For the present analysis, the coauthors of the 

Lundquist report were contacted to solicit additional details related to the original 4-ha (9.9 acre) 

pond system described in that report, as well as to provide a second cost estimate for a smaller 

design similar in size to the Leidos 2-acre pond system, both of which were furnished to NREL 

in support of this report as the basis for the MicroBio scenarios. 

The MicroBio 4-ha (“10-acre”) pond design will not be discussed in detail in the present report 

as all design and cost details for this case are consistent with the information as originally 
29 

presented in depth in the above-cited Lundquist report [17], but will be briefly summarized here. 

In short, the ponds are designed as a standard single-loop system with channel dimensions 30 m 

wide by 690 m long and 30 cm deep. Each pond has a paddlewheel mixer, sump with baffle, and 

gas diffuser. The paddlewheel mixer includes a motor and gearbox, and concrete is used for the 

sump station and paddlewheel support. At the point of paddlewheel mixing the pond channels 

are reduced from 30 m to 20 m (similar to the Leidos 10-acre pond design discussed above). The 

mixing velocity is 20–25 cm/s, and 2.0 kW of power per hectare of cultivation area is consumed 

by the paddlewheel as an average over the course of a 24-hour day (higher during daylight hours, 

and lower at night). This paddlewheel power was calculated from standard engineering equations 

to optimize for daytime versus nighttime mixing and channel velocity requirements, based on a 

paddlewheel motor and drive system efficiency of 40%.

The MicroBio base case 10-acre design again stipulates minimally lined ponds, with a partial 

liner used this time only on the pond berms (a similar concept to the Leidos design although 

based on lining the berms of the straight channel sections rather than the pond turns as in the 

Leidos design). The liner cost for both of the MicroBio pond designs is $4.49/m2. For the 2-acre 

pond, 25% of the pond is lined, which reduces to 24% for the 10-acre pond. A fully lined pond 

was also estimated by MicroBio, which is considered as a sensitivity in Section 6.1. The land is 

assumed to contain in-situ clay such that again the pond bottom is left unlined aside from native 

soil compaction. For building the ponds, civil work includes excavation, trenching, compaction, 

and fine grading to build the berms 0.9 m high. Water piping to and from the ponds and a central 

point (dewatering) is included for a 100-hectare footprint in the original published report. We 

assume the same cost per acre for the water piping for each 100-acre module in the present 

design as was originally presented for a larger 247-acre (100-ha) facility. Costs for electrical runs 

and instrumentation were also presented in the original Lundquist report, which were further 

broken down to the portion allocated strictly to ponds for the present design, based on further 

discussions with the MicroBio engineers [25]. 

Beyond the published 10-acre design basis, MicroBio furnished an additional design scenario to 

NREL focused on smaller ponds closer to the 2-acre size considered by Leidos, specifically 1-ha 

(2.5-acre) ponds [25]. As in the Leidos case, the MicroBio “2-acre” ponds are similar in design 

to the larger 10-acre versions, based on paddlewheel-driven raceway ponds with sloped berms, 

concrete sumps and paddlewheel support stations, and plastic lining covering only the sloped 

berms (in-situ clay otherwise forming the pond bottoms). The 2-acre pond scenario was 

developed based on the same overall cultivation footprint for a 100-ha integrated facility as had 

been assumed in the published base case for 10-acre ponds, thus still includes considerations for 

feed/harvest and circulation piping as well as electrical requirements for a grouping of individual 

2-acre ponds. Consistent with the MicroBio 10-acre case, we assume the resulting rolled-up 

dollar-per-acre costs furnished by MicroBio for all elements (ponds, civil, lining, piping, and 

electrical) remain the same between the 247 acre (100-ha) facility basis from MicroBio to the 

100-acre modules assumed in the present work. 

Relative to the 10-acre design, the MicroBio 2-acre design maintains the same cost per acre for 

grading, but fourfold higher for excavation and trenching (i.e., this cost element linearly 

increases as pond size decreases). The smaller 2-acre ponds require roughly 6% more plastic 

lining for pond berms, given the higher ratio of berm area to wetted cultivation area for smaller 

ponds. Electrical costs per acre increase by roughly threefold (similar to Leidos), while piping 
30 

costs increase by roughly 20% (given the use of more piping runs to individual ponds, which are 

partially offset by smaller diameter pipes). The number of paddlewheels and motors increases 

linearly for the smaller ponds, but costs 60% less each, thus translating to roughly 60% higher 

cost per acre for these elements. Finally, concrete requirements increase substantially at roughly 

4.3 times more total concrete required on a per-acre basis compared to the larger 10-acre ponds, 

dictated by a similar total concrete requirement between the two pond sizes. Paddlewheel 

circulation power demand is roughly 30% higher for the smaller ponds per unit cultivation area, 

at 2.6 kW per hectare over a 24-hour day. 

Harris Pond Design 

Harris Group (“Harris”) is another engineering firm with expertise in algal pond design, whose 

assistance was also solicited through a subcontract to provide design and cost estimates for 

raceway pond systems and other downstream processing equipment. Harris was instructed to 

provide independent cost estimates, based on their own vendors, for a paddlewheel raceway 

pond identical in dimensions and overall layout/design as the MicroBio 10-acre (4-ha) case 

discussed above and presented in Lundquist et al. [17]. As such, the Harris design assumes a 

base case with native in-situ clay and pond liners again limited to covering the straight channel 

berms, as well as concrete used for paddlewheel support and sump stations. The liner costs 

$4.49/m2 and covers 14% of the pond. A civil contractor provided Harris with the required civil 

work and associated costs including pond excavation, compaction, and grading; in this case, 

grading costs were low as the contractor assumed nearly flat land to start with. A second vendor 

provided Harris with estimates for concrete requirements/costs for the paddlewheel and sump 

stations, as well as water circulation piping. The water circulation piping was originally based on 

a level 10,000-acre (4,050-ha) overall facility; however, the large majority of the piping was 

attributed to pond feed/harvest and circulation lines, thus the present design maintains the same 

piping estimate on a dollar/acre basis to be applied strictly to the level 100-acre modules (with 

external circulation piping to and from central dewatering considered separately as consistent 

with the other pond scenarios and discussed in Section 4.4). Harris estimated the paddlewheel 

circulation power demand for the 10-acre pond design at 2.4 kW/ha over a 24-hour day, which 

falls between the estimates from MicroBio and Leidos for paddlewheel ponds of the same size. 

One small deviation in the Harris design relative to the other pond scenarios described above is 

the inclusion of turning vanes at the ends of the ponds for the Harris case. However, because 

turning vanes are not included in the other raceway pond designs as they either are not expected 

to represent a significant cost (input from MicroBio) or otherwise are not anticipated to offer 

enough benefit to warrant their inclusion (input from Leidos), the turning vanes originally 

included in the Harris pond design were removed for this analysis to maintain consistency in 

projecting costs for similar pond designs. The turning vanes would add an additional $4,100/acre 

to the cost of the Harris ponds, which would translate to $23/ton in terms of resulting MBSP

impacts. The Harris estimate did not include the cost for electrical equipment. Thus, electrical 

equipment for the Harris 10-acre ponds is added based on the Leidos 10 acre system design. 

Global Algae Innovations Pond Designs 

Global Algae Innovations Inc. (GAI) is a commercial developer and operator of an algal 

production and processing facility located in Kauai, Hawaii [60]. GAI takes a focused approach 

to process design based on engineering optimization, with a number of unique features including 
31 

pond configuration, dewatering system, and CO2 injection. The GAI facility consists of open 

ponds of varying sizes up to a maximum of 3.2 acres, configured as a “hybrid” between raceway 

ponds (each pond consists of two channels separated by a center divider) and serpentine gravityflow ponds (the channels are continuously sloped to induce circulation by gravity). Starting at 

one end of the pond, channels are continuously sloped over a gradual grade of roughly 0.1%, 

turning back at the far end and continuing down over a similar graded slope in the second 

channel. Culture movement is imparted by gravity flow following the graded channel slope. 

Rather than paddlewheel stations on one end of the pond, circulation is provided by pumping 

from the lower to the upper channel. GAI provided NREL with design and cost details for this 

pond configuration over a range of sizes, ranging from a minimum of 10 acres for envisioned 

commercial-scale operation up to a maximum of 200 acres which GAI views as still being 

plausible given the gravity-assisted design, where larger pond sizes of 50 acres or more would 

likely include a circulation pump on both ends of the pond to assist in circulation over large 

distances [61]. For purposes of consideration in the present analysis, we selected the 10-acre and 

50-acre designs for incorporation into the TEA models. 

In addition to typical economy of scale benefits enabled by larger pond sizes of 10 acres or more 

(i.e., lower costs for piping, electrical runs, and circulation equipment needed on each individual 

pond as documented above for the Leidos and MicroBio paddlewheel designs), the GAI pond 

design brings a number of additional benefits beyond standard paddlewheel-driven raceway 

ponds. This includes replacing low-efficiency paddlewheels with pumps, including associated 

concrete supports, as well as avoiding the use of concrete sumps as are typically included in most 

pond designs (including all paddlewheel scenarios described above). In contrast to flat 

paddlewheel ponds, which typically include sumps both to provide a low point in the pond for 

harvesting and to allow for CO2 gas sparging, the GAI design already includes a “low point” at 

the lowest elevation near the circulation pump (to which harvesting pipelines also may be 

connected), and avoids CO2 delivery to individual ponds by instead injecting CO2 into closed 

carbonation stations located on water circulation manifolds. For the GAI pond designs 

considered here, CO2 was similarly assumed to be injected into the pumped recirculation pipeline 

between the bottom and top channels of the pond. Culture circulation is accomplished at GAI 

with the use of aqueducts, which have the potential to reduce circulation costs relative to 

pipelines; but at a quoted price of $5,000/acre representing costs for both harvest and feed 

circulation lines [61], the resulting costs for circulation aqueducts within a given 100-acre 

module are similar for the GAI 10-acre scenario as standard pipeline costs quoted by the other 

pond scenario sources discussed previously. 

Circulation pumping power demand for the GAI pond design is on average approximately 0.75 

kW/acre (1.9 kW/ha), estimated to be equally applicable to both the 10- and 50-acre sizes; this is 

comparable to the low range of paddlewheel power consumption estimates discussed above (for 

example the MicroBio 10-acre pond at 2.0 kW/ha). Pumping is done using low-shear axial flow 

pumps. The GAI facility shuts circulation down at night (which would result in considerable 

energy savings compared to other pond scenarios, at 9 kWh/acre over a 24-hour day or 22 

kWh/ha/day) and indicated that this protocol does not detrimentally impact culture stability or 

productivity; however, for incorporation into the present TEA model framework which assumes 

continuous 24-hour harvesting as noted previously, the original basis of 0.75 kW/acre was 

maintained over a 24-hour day. The currently operating GAI ponds are fully lined, and GAI 

indicated that in the near term they continue to plan for fully lined ponds. However, there is no 
32 

fundamental reason why the ponds must be lined (assuming that suitable soil with in-situ clay is 

present); thus, to enable consistent comparison against all other pond scenarios that stipulate 

minimal liners only where necessary to control erosion, for the present assessment the GAIfurnished pond liner costs were reduced by assuming the same fraction for partial versus full 

liner areal coverage as provided by Leidos for their 10-acre pond design. Thus, both the 10- and 

50-acre GAI pond scenarios assume the presence of in-situ clay soil with minimal use of plastic 

liners (with dollar-per-acre partial liner costs applying equally to 10- or 50-acre ponds), while 

fully lined ponds are considered in the sensitivity analysis shown in Section 6.1. The liner cost 

for the 10- and 50-acre cases is $7.11/m2, with liners covering 1.5% of total pond area for both 

cases. Finally, civil costs were provided by GAI, in this case estimated to scale linearly by pond 

size, and corresponded to similar values furnished for other pond scenarios. Remaining pond 

equipment costs were also provided, which primarily include circulation pumps and electrical 

costs rolled together; these costs were estimated as roughly twofold higher per individual pond 

for the 50-acre pond design relative to the 10-acre basis. A smaller per-acre pumping cost for the 

50-acre design is a function of the fact that the primary points for head loss and therefore 

pumping demands occur at pond turns, which become a smaller fraction of overall pond volume 

as ponds get larger. 

4.1.3 Cost Estimation

Table 4 shows the capital costs attributed to a 100-acre module for each of the eight pond 

designs, as furnished by Leidos, MicroBio, Harris, and GAI. Based on inputs from each of these 

sources, the module costs are broken down into five categories wherever possible: civil work, 

liner costs, piping, electrical, and other pond costs. The civil category incorporates all costs 

associated with land preparation and grading, such as overburden removal, scarifying, 

compaction, etc. The liner category represents the cost of a partial plastic liner either on the pond 

berm or pond turns (specific to the given design). Piping includes pond harvest, feed, and 

circulation piping located within the 100-acre module as well as harvest pumps (costed in ACCE 

and applied consistently to all scenarios) to move the medium from pond harvest headers to 

primary in-ground settling. The electrical category accounts for the electrical runs to individual 

ponds and associated instrumentation. Finally, “other pond costs” account for remaining pond 

equipment and other cost elements, primarily paddlewheels or circulation pumps (in the case of 

GAI and Leidos serpentine ponds), motors, and concrete (for paddlewheel supports and sumps 

where applicable). In some cases, cost breakouts into the respective categories are imperfect as 

some or all of the cost for a given element is accounted for elsewhere, thus the primary value of 

note is the total summation of all cost elements. All costs presented here are indexed to 2011 

dollars, as discussed in Section 5.1. Beyond capital equipment costs, other costs including labor, 

variable expenses, and land, are discussed later in Sections 5.2-5.4. Additional design and cost 

details for the Leidos pond cases (which were provided to NREL in the highest level of detail 

and thus warrant presenting this additional detail here) may be seen in Appendix B. 
33 

Table 4. Pond Cost Details for all Designs Considered in TEA Model, Attributed to a Single 100-

Acre Module

Pond 

Design a 

Pond 

Size 

(acres)

Circulation 

Power 

(kWh/ 

ha/day)

Installed Capital Cost, $/100-acre module (2011$)

Civil

Other Pond 

Costs Liner Piping Electrical Total

Leidos R 2.2 75.5 $1,170,000 $2,490,000 $70,000 $1,430,000 $430,000 $5,590,000

MicroBio 2.5 63.0 $420,000 $1,640,000 $450,000 $890,000 $870,000 $4,270,000

Leidos R 10 70.0 $1,110,000 $980,000 $40,000 $830,000 $140,000 $3,100,000

MicroBio 9.9 48.0 $220,000 $720,000 $430,000 $820,000 $290,000 $2,480,000

Harris 9.9 58.2 $800,000 $1,980,000 $250,000 $1,000,000 $140,000d $4,170,000

GAI 10 44.0 $910,000 $1,160,000b $40,000c $800,000 INCLb $2,910,000

Leidos S 48.6 41.5 $1,310,000 $140,000 $70,000 $700,000 Negligible $2,220,000

GAI 50 44.0 $910,000 $470,000b $40,000c $330,000 INCLb $1,720,000

a Letter designations for Leidos designs: R = raceway, S = serpentine. b Electrical included with “other pond costs” for GAI system. c Original GAI costs were for full pond liners; adjusted here for in-situ clay with partial liners based on the ratio for 

partial versus full liner coverage for Leidos 10-acre ponds. d Based on Leidos electrical cost for a 10-acre pond (Harris electrical costs were outside design scope). 

A number of clarifying details are warranted with respect to the values presented in Table 4. 

First, although self-explanatory, the costs are shown here for a grouping of the given number of 

ponds and supporting equipment that make up an individual 100-acre module considered in the 

integrated facility process, rather than costs for a single pond. This is presented this way given 

the inclusion of piping and electrical, whose costs are more appropriate to present for the full 

100-acre module than attributed to a single pond of varying size. Additionally, of all scenarios 

shown in Table 4 the only one published previously is for the MicroBio 10-acre pond design; 

however, costs shown here, even when divided by 10 for a single 10-acre (4-ha) pond, do not 

match up exactly with the published values for this scenario [17]. This is due both to cost 

indexing from 2009 to 2011 dollars, as well as removal of roughly 12% of the originally 

published MicroBio pond cost, which was confirmed with the co-authors to represent inclusion 

of inoculum system costs, which are considered separately in the present analysis (see Section 

4.2). Similarly, the circulation piping and electrical costs shown in Table 4 are lower on a peracre basis than the originally published values for the MicroBio 10-acre pond, as they represent 

strictly the portion of those elements attributed to cultivation ponds rather than the overall 

processing facility. Next, the Harris 10-acre pond design did not originally include 

considerations for electrical, which were excluded from the subcontract design scope. Thus, to 

include an allowance for electrical costs in the Harris case, the same cost was applied as the 

Leidos 10-acre pond design. Finally, as noted previously, GAI supplied costs for only a fully 

lined pond; therefore to maintain consistency, the fully lined cost was adjusted by scaling by the 

ratio of partial versus full pond liner coverage as estimated by Leidos for the 10-acre pond 

design. Also as noted previously, the GAI “piping” costs primarily consist of aqueducts and 

channels for circulation within the 100-acre modules. 

As can be seen from Table 4 there are two ranges of liner costs: (1) $40,000–$70,000/100 acres 

and (2) $250,000–$450,000/100 acres. The distinction between these ranges is attributable to the 

assumption of where on the pond plastic liner coverage is required. The lower cost range is 

associated with the Leidos and GAI designs (when scaling GAI full liner costs to a partial liner 

scenario) only stipulating lining pond turns, which are a substantially smaller fraction of the 
34 

pond area than the straight channel berms as assumed for the MicroBio and Harris designs

(roughly 2% of total pond area for designs that line pond turns versus up to 25% for lining 

straight channel berms). In addition to the categorized pond cost, Table 4 also shows the 

circulation power demand for each scenario. For the paddlewheel ponds, the MicroBio designs 

tend toward lower circulation power while Leidos power estimates are on the high side for a 

given pond size; a key contributor to these differences is likely the paddlewheel efficiency, at 

40% for the MicroBio designs and 10% for the Leidos designs. Paddlewheel power demand 

tends to decrease per cultivation area as pond size increases (between 2 and 10 acres); however, 

it could be argued that the 10-acre cases are more speculative as a pond of this size has not been 

constructed to validate optimal circulation demands, whereas the 2-acre cases are consistent with 

currently operating ponds of this size. Moving beyond paddlewheel designs, circulation power 

demands further decrease for systems that make use of pumps instead of paddlewheels, including 

both the GAI and Leidos serpentine design. However, while the GAI circulation pumping power 

demand is consistent with real-world operating data for a 3-acre pond, the larger 10- and 50-acre 

GAI ponds, as well as the Leidos 50-acre serpentine pond, are more speculative and will depend 

strongly on onsite grading conditions and circulation rates. 

The cost breakouts from Table 4 are shown graphically in Figure 8, translated to a per-wettedacre basis for ease of comparison against Figure 5 (Section 3). To further demonstrate cost 

alignment based on pond size, two additional data points were added to Figure 8 based on 

literature for currently operating “small” ponds slightly larger than 2 acres; these include a 2.5-

acre pond published by Beal et al. [10] and a 3.1-acre pond published by Craggs et al. [47] (again 

indexed here to 2011 dollars for consistency with the other cases). Although these additional 

sources also represent realistic cost projections, they were not considered in the present TEA 

model for implications on MBSP. While the Craggs design is based on marginally lined raceway 

ponds consistent with the other scenarios described above, the Beal design as published was for a 

fully lined pond. To estimate the cost for a similar pond with only minimal lining, the original 

Beal cost was scaled according to partially lined versus fully lined pond costs based on the 

Leidos 2-acre pond case, with the resulting allocated costs for liners and “other pond costs” 

combined together. As noted previously, the GAI pond cost allocations combine electrical and 

“other pond costs” together as well. For the majority of pond cases shown in Figure 8, the 

combination of civil and “other pond costs” (typically circulation device, motor, and concrete) 

represent the largest contributors (>50% of total cost) with the exception of the Beal 2.5-acre 

case (37% contribution), and the MicroBio 10-acre case (38% contribution). For these two cases, 

piping represents the largest cost driver, which is still a significant contributor for the other cases 

as well. Liner and electrical costs are the least significant cost drivers for all ponds, specific to 

the use of minimally lined ponds (fully lined pond costs are explored in Section 6.1). 

While the allocated pond cost details are insightful, the primary point to emphasize is that ponds 

are, in fact, seen to cluster reasonably well as a function of pond size when categorized into 

small (2-acre), medium (10-acre), or large (50-acre) ponds, consistently demonstrating economy 

of scale benefits for moving toward increasingly large ponds. This point is delineated more 

clearly in Figure 9, which presents the rolled-up overall pond costs per wetted cultivation acre, 

categorized into the three size classifications. Total installed costs range from $43k–$56k/acre 

($48k/acre average) for small 2- to 3-acre pond designs, from $25k–$42k/acre ($32k/acre 

average) for medium 10-acre designs, and from $17k–$22k/acre ($19k/acre average) for 

large 50-acre designs. 
35 

Figure 8. Capital cost details for all eight pond design scenarios considered in TEA model, plus 

two additional values from literature for comparison

a Additional data points were not modeled in the present design report but were added to this plot to further 

demonstrate cost alignment by pond size. b The installed cost shown here for the Beal design estimates the cost for a minimally lined pond scenario 

compared to the original cost for this case which assumed a fully lined pond [10]. If a fully lined pond were used 

for the Beal case, total installed cost would be $114,000/acre.

c GAI cases include electrical costs under “other pond costs”. 

Figure 9. Overall installed pond system capital costs categorized by size groupings

a Additional data points were not modeled in the present design report but were added to this plot to further 

demonstrate cost alignment by pond size (shown in orange). b The installed cost shown here for the Beal design estimates the cost for a minimally lined pond scenario 

compared to the original cost for this case which assumed a fully lined pond [10]. c Legend for numerals: [i] MicroBio 2.5-acre pond, [ii] Leidos 2.2-acre pond, [iii] Beal et al. 2.5-acre pond [10], [iv]

Craggs 3.1-acre pond [47], [v] MicroBio 10-acre pond, [vi] Leidos 10-acre pond, [vii] Harris 10-acre pond, [viii] GAI

10-acre pond, [ix] Leidos 50-acre pond, and [x] GAI 50-acre pond. 

$0

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

Installed Capital Cost ($/acre, 2011$)

Electrical

Piping

Liner

Other Pond Costs

Civil

[ii]

[iii]

[iv]

[v]

[vi]

[vii]

[viii]

[ix]

[x]

[i]

$0

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

0 10 20 30 40 50 60

Pond Capital Cost ($/acre in 2011$)

Pond Size (acres)

a,b

a
36 

4.2 Area 200: Inoculum System

4.2.1 Overview

The inoculum system produces algae starter cultures used to re-inoculate the production ponds. 

Production ponds can require re-inoculation after scheduled pond downtime, culture crashes, and 

other events that require the pond to be drained and restarted with new culture, although under 

normal facility operation, ponds are envisioned to operate continuously, thus negating the need 

for large inoculum systems designed for continuous re-inoculation, e.g., daily or weekly. Culture 

crashes can be caused by a variety of weather and pest/predator/pathogen-related events, such as 

freezing in the winter or incursion by invasive species. Similar to other envisioned commercial 

designs, inoculum propagation occurs over a series of increasingly larger cultivation steps 

beginning in closed photobioreactors and moving to small ponds [17,43]. Following the concepts 

proposed by Lundquist et al. and Huntley et al., a closed PBR is used as the first stage of 

inoculum grow-out, followed by covered (enclosed) ponds of a significantly larger cultivation 

footprint than the PBRs, and then lined open ponds with a larger footprint than the covered pond 

stage [17,43]. Figure 10 provides a simplified schematic of the inoculum system. 

H2O + CO2

+ Nutrients

Seed Train (from lab)

Photobioreactor

Covered Pond Lined Pond

H2O Evaporation Loss

To Cultivation Ponds

H2O 

+ CO2

+ Nutrients

H2O 

+ CO2

+ Nutrients

Figure 10. Simplified schematic diagram of the inoculum production system

4.2.2 Design Basis

The on-site inoculation system covers a separate area beyond the 5,000 wetted acres dedicated to 

the main production ponds. Area 200 is sized by assuming that any given cultivation pond must 

be re-inoculated on average every 20 days during peak summertime production, meaning that 5% 

of the cultivation ponds in the facility are re-inoculated any one day (primarily to recover from 

contamination events). Based on this frequency, the inoculum system is sized to target an initial 

algae concentration of 0.1 g/L AFDW in the main cultivation ponds. Table 5 provides a 

summary of the key assumptions used to set the design for each stage of the inoculum system. As 

shown in Table 5, the areal productivity of the PBRs, covered ponds, and lined ponds are set to 

match the seasonal productivity of the main cultivation ponds shown in Table 3 of Section 4.1.2. 
37 

Table 5. Design Parameters for Each Stage of the Inoculum System

Parameter Units PBR

Covered 

Pond

Lined 

Pond Total

Annual Average Productivity g/m2/day 25 25 25 -

Initial Concentration g/L 0.1 0.1 0.1 -

Harvest Concentration g/L 1.5 0.5 0.5 -

Areal Footprint Coverage acres 8.7 a 23 116 147.7

Area Coverage Percent of Total 

Biomass Cultivation Area % 0.2% 0.5% 2.3% 3.0% 

Work for Blowers and Mixing kW/acre 3.9 b 1.3 c 1.3 c -

Heat Removed by Chillers GJ/day 83.4 333.7 - 417.1 a Includes footprint for spacing between tubes 

b Assumption based on [10,43] c Assumption derived from the Leidos 2-acre pond system (Section 4.1.2)

The design of the PBR is based on the PBR system described in detail by Beal et al. and Huntley 

et al. [10,43]. This PBR design has been developed for commercial application and is of the 

horizontal tubular variety with airlift driven mixing [43]. It has a higher volume-to-area ratio 

than other typical tubular PBR systems due to its large diameter (0.38m) [7,43,62,63]. The 

design has 250m2 of lit area and a total areal footprint of 371m2

 for every 50m3 cultivation 

volume. The PBR design from Beal was originally based on a 50% harvest, whereas this process 

assumes a much smaller daily harvest of 5%. Although Beal et al. set forth a baseline 

productivity of 24 g/m2/day for the PBR system based on commercial performance achieved in 

Hawaii, the PBR here is instead sized based off of this design report’s summer productivity 

target of 35 g/m2/day (Table 3). Accordingly, the volumetric productivity of the PBR for this 

design report is 0.2 g/L/day in the summer (based on cultivation area). 

Both the covered and lined ponds are designed based off of the Leidos 2-acre pond design 

described previously. Briefly, the pond design includes civil work, paddlewheel equipment, 

electrical and instrumentation equipment, concrete, and water piping. CO2 piping was 

determined separately, and it is accounted for in the total CO2 distribution cost for the facility. 

Additionally, both the covered ponds and the open lined ponds are fully lined with a 40-mil

geomembrane. One fully lined 2-acre pond requires 44,266 m2 of the liner. The covered pond 

also is enclosed by a plastic hoop air-supported greenhouse [17]. 

Because of the enclosed design of the PBRs and covered ponds, it is assumed that no CO2 is lost 

to outgassing in either of these stages. Ten percent of the CO2 pumped into the open lined ponds 

is assumed lost due to outgassing. Additionally, water evaporation only occurs in the open lined 

ponds, matching the seasonal pan evaporation rate for the main production ponds shown 

previously in Table 3. With no water evaporation to help regulate the temperature of the two 

enclosed systems, a chiller is used to remove heat accumulated in these systems. The amount of 

solar irradiation absorbed as heat is calculated based on the information provided by Bosma et al. 

and Bechet et al. [63,64], assuming that these closed systems will absorb similar irradiation on an 

areal basis as the tubular PBR described by Bosma. It is assumed that the PBR and closed pond 

absorb 14.4 GJ/acre/day of heat with total footprint coverage of 29 acres (lit cultivation area). 

Table 5 shows the assumed heat absorbed by the PBRs and covered ponds, which must then be 

removed using the chiller system. In total, 417 GJ/day of heat is removed for the entire system. 

This translates to 0.08 GJ/acre/day for the 5,000 acre cultivation area, and is a minimal cost of 
38 

less than 1% of the total facility. Cooling demands may be reduced or eliminated depending on 

the specific species and the location of the facility. Nutrients are supplied to each step of the 

inoculum system assuming the same demands for 120% of stoichiometric minima based on 

biomass elemental composition as described previously for the main production ponds. 

Paddlewheel mixing occurs both in the covered pond and the lined pond. Based on the Leidos 2-

acre pond design, the paddlewheel power demand is assumed at 31.2 kWh/acre/day for both the 

covered and open lined ponds. The PBR uses an airlift system for mixing with a power demand 

of 93.6 kWh/acre/day [10]. Table 5 shows the power demand for each inoculum stage. 

4.2.3 Cost Estimation

As with the design of the PBR, the cost of the PBR system is also based on Beal et al. at 

$18.22/m2

 for the Gulf Coast [10]. The costs for both the covered and open lined ponds are based 

on the 2-acre pond design quoted by Leidos. Leidos’ quote includes civil work (i.e., clear and 

grub, strip and stockpile the overburden, scarify, compaction, cut and fill, and fine grade), the 

paddlewheel, electrical instrumentation, concrete, and water piping. However, in this case, the 

“marginally lined” designs providing only berm liner coverage were not assumed as were 

stipulated for the main production ponds, as both inoculum pond stages are fully lined. The 

installed cost for the inoculum pond stages, excluding lining and pond coverings is $53,656/acre 

of cultivation area. The installed cost for lining adds an additional $30,626/ acre of cultivation 

area, based on the Leidos estimate for a fully lined 2-acre pond. For the covered pond stage, an 

air-supported plastic hoop greenhouse was assumed based on cost estimations from Lundquist et 

al., at $142,115/acre of cultivation area [17]. Table 6 provides the inoculum areal coverage, 

installed cost per acre of wetted cultivation area, and the total installed cost for the present design 

model. Finally, as noted above there is a small utility requirement for chiller cooling on the PBR 

and covered pond stages. Recognizing that in reality this “front-end” portion of the facility 

would likely be integrated with “back-end” conversion operations on site (which typically have 

inclusions for utility cooling and heating systems), as well as the fact that the chiller duty 

requirement is marginal given such a small inoculum footprint relative to the total facility, the 

required chilled water is costed here as a material operating cost rather than constructing a chiller 

system; the associated utility price for chilled water was set at $5/GJ [65]. 

Table 6. Inoculum System Capital Costs and Areal Coverage

Stage of Inoculum Areal Coverage for 

Inoculum Stage (acres)

Installed Cost 

($/acre of cultivation area)

Installed Cost 

($MM; 2011$)

1 – Photobioreactor 5.8 $109,000 $0.65 

2 – Covered Pond 23 $233,000 $5.41 

3 – Open Lined Pond 116 $87,000 $10.06 

Total 144.8 NA (varies by stage) $16.12 
39 

4.3 Area 300: CO2 Delivery

4.3.1 Overview

This section describes the assumptions related to CO2 delivery to the site, storage, and injection 

to the culture media. It is well established that in order to promote high biomass growth rates 

required to achieve economical production of commodity fuel products, supplemental CO2 must 

be delivered to the cultivation system beyond merely relying on CO2 transfer from ambient air

[66,67]. The two primary means of providing CO2 to algal systems are either via bulk flue gas 

transported and sparged into ponds at low pressure, or concentrated CO2 captured and purified 

out of flue gas, and transported and delivered to the facility under high pressure. In either case, 

the flue gas is primarily envisioned to be sourced from a coal- or natural gas-fired power plant, 

though other opportunities exist for co-location with ethanol plants, ammonia plants, or other 

(non-fossil) CO2 sources. While prior harmonization modeling activities focused on transport 

and delivery of bulk flue gas via low-pressure pipeline transport [23,42], this option requires a 

significant number of assumptions related to specific facility siting, layout, proximity to the 

power plant, flue gas rate and composition, etc., which tend to introduce subjectivity and a 

higher degree of uncertainty in the expected cost of delivered CO2. Instead, for the base case 

considered in this report, we focus on purified CO2 from flue gas carbon capture (i.e. amine 

scrubbing, membrane purification, etc. which may be expected to provide CO2 at >99% purity), 

which reduces uncertainty by treating CO2 as a material operating expense with substantial 

literature documentation for appropriate pricing. The alternative of low-pressure flue gas 

transport and delivery is considered as an alternative sensitivity scenario in Section 6.1. Under 

the purified CO2 base case scenario, CO2 is delivered to the facility under high pressure, stored 

in spherical storage tanks, and distributed and sparged into individual ponds during daylight 

hours. 

4.3.2 Design Basis

Similar to nutrient requirements discussed previously, the CO2 demand for the facility is 

determined by the algal biomass carbon content at harvest, set to 54 wt% C for the base case 

strain on an AFDW basis as shown in Table 2. The CO2 demand is further weighted by a 90% 

culture utilization factor, which accounts for a 10% outgassing loss consistent with observed 

losses of pure CO2 in sparged sumps [22,68]. In contrast, CO2 outgassing losses are typically 

higher at 15%–25% for sparging low-pressure bulk flue gas (with significant levels of nitrogen) 

directly into pond sumps [69,70], which is one of several logistical challenges attributed to a 

low-pressure flue gas scenario, in addition to another major challenge being the use of very large 

ductwork networks routed to numerous locations spread over such a large facility footprint. As 

CO2 is only delivered to the culture during the daylight, the CO2 storage and pond distribution 

systems are designed to deliver the total daily demand (based on peak summertime daily biomass 

productivity) in 12 hours, assuming a consistent CO2 uptake efficiency. 

In the base case design, pure CO2 enters the plant via pipeline and is stored in a pressurized 

storage sphere. Typical pipeline CO2 conditions for purified CO2 from carbon capture operations 

are supercritical at 130 bar and 40°C, thus this is the assumed condition for CO2 entering the 

facility; CO2 pipeline transport does not necessarily have to be under supercritical conditions, but 

could also be lower pressure as long as the CO2 is high purity. The incoming CO2 is throttled to 

50 psig (4.4 bar) for storage as a liquid. Electric immersion heaters in the sphere slowly vaporize 

the liquid CO2 to maintain pressure in the tank. CO2 for the facility is then taken from the vapor 
40 

space and distributed under moderate pressure. The storage sphere is sized with a 45-ft diameter,

enough to hold one day (12 hours) of CO2 demand for the entire facility. The sphere is 

constructed from carbon steel that has been Charpy impact-tested for cold performance. 

The on-site CO2 piping network consists of a 20 inch trunk line from the sphere to the opposite 

end of the facility. The trunk line supplies 12 inch branch lines running down the aisles between 

100-acre module plots (see Figure 4), which reduce to 8 inch midway. Within each module, a 

network of 3 inch piping delivers the CO2 to the sumps in individual ponds. All piping was 

designed as HDPE to reduce capital costs. With sufficient thickness, HDPE pipe can have 

pressure ratings up to several hundred psig; the current design pressure is 75 psig. HDPE is 

suitable for carrying gaseous CO2 though it should be noted that liquid CO2 must be transported 

in steel for safety reasons. If liquid CO2 is exposed to atmospheric conditions, it will form dry ice 

at -79°C, which is lower than the minimum allowable temperature for HDPE (-50°C). 

4.3.3 Cost Estimation

The existing CO2 commodity market supplies gaseous CO2 in large amounts for use in enhanced 

oil recovery (EOR). The majority of currently available CO2 for industrial use is sourced from 

naturally occurring CO2 reservoirs, ammonia production plants, and ethanol production plants. 

The availability of CO2 and ease of transportation is heavily dependent on locality; multiple 

pipelines serve the Permian basin and Gulf Coast in response to the extensive EOR operations in 

those areas, and proximity to the ethanol industry provides an abundant CO2 source to the 

Midwest region [71]. Although the production facility assumed here (which is not tied to a 

specific single location but is modeled based on leveraging work from prior harmonization 

efforts that focused on the Gulf Coast region) may have an opportunity to tap into existing CO2

pipeline infrastructure, e.g., dedicated EOR operations, many such algal facilities likely would 

not be able to rely on existing CO2 resources, and more importantly making use of EOR CO2

from underground reservoirs would ultimately constitute a fossil CO2 emissions pathway once 

combusted as fuel (in contrast to CO2 from power plant flue gas emissions which represents CO2

recycling and does not release new CO2 to the atmosphere, see Section 6.2). Thus, the current 

design case assumes that CO2 is purchased as a product from a power plant point source 

implementing carbon capture and storage technology (CCS). This approach for CO2 sourcing 

was taken given the relatively large and continuous CO2 requirement for the facility at the given 

productivity rates (Table 3) and biomass carbon content (Table 2). The average CO2 demand for 

the facility is 1,148 tonne/day, which can be supported by a single power plant that may be 

expected to emit over 11,000 tonne/day CO2 for a typical 500 MW coal-fired power plant (see 

Section 6.1). 

For the base case, the cost of CO2 including purification, compression, and transportation via 

pipeline is set at $45/metric tonne CO2 (~$41/U.S. ton), which includes all parasitic energy

demands placed on the power plant CCS system; thus, power demand for the CCS operations is 

considered outside the current model scope and is not explicitly included in the facility power 

balance, but rather is rolled up in the delivered CO2 price for the algae facility. In other words, 

the algae facility takes on the cost burden for implementing a CCS system into a power plant 

including integration of the CCS heat and power requirements with power plant operations, 

resulting in an amortized cost of the captured CO2 at $45/metric tonne, which accounts for 

diverting this required heat and power from the power plant to the CCS system. This parasitic 

energy demand for CCS is estimated explicitly in Section 6.2 for purposes of evaluating 
41 

sustainability metrics, based on CCS literature. Recognizing this design case is specific to a 2022 

target timeframe, the $45/tonne CO2 cost represents an average future projected price estimate 

for feasible carbon capture cost from power plant flue gas sources based on three separate 

technologies and studies: ammonia post-combustion capture in a pulverized coal plant, physical 

solvent pre-combustion capture in an integrated gasification combined cycle (IGCC) plant, and a 

membrane process for a supercritical pulverized coal plant; pipeline transport up to a distance of 

80 km was also included in the cost for one of the studies [72-74]. This price also is consistent 

though slightly more conservative compared with DOE’s targets for carbon capture via secondgeneration technologies, at a goal of $40/metric tonne CO2 in the 2020–2025 timeframe [75]. 

Industry estimates place the current cost of existing pipelined CO2 supplies at $0.75 per thousand 

cubic feet ($15/metric tonne) with forecasts up to $4.00 per thousand cubic feet ($80/metric 

tonne) by 2030, further supporting the assumed basis for dedicated CCS sourcing to supply the 

algal facility considered here [71]. Sensitivity to CO2 price is presented in Section 6.1. Capital 

costs for the HDPE piping network and storage sphere/immersion heaters were developed in 

ACCE, costing roughly $5MM and $2MM installed, respectively. 

4.4 Area 400: Makeup Water Delivery + On-Site Circulation to/from 

Dewatering

4.4.1 Overview

Area 400 represents the transfer circulation pipelines between the 100-acre modules and the 

central dewatering facility, as well as makeup water pipelines bringing in fresh water from 

outside the facility boundaries. Although in other design reports focused on biorefinery 

conversion operations such piping would typically be costed based on indirect capital cost 

factors [44,76], in this case the piping is more critical as it covers a large land footprint and the 

details related to piping dimensions, frictional losses, and elevation change have a large bearing 

on other modeled parameters such as pumping power demand, thus this overall facility 

circulation piping is considered explicitly as its own process area section here. As Area 400 is an 

integral part of the overall facility design and layout, Section 2.2 is referenced often in the 

following paragraphs. In each 100-acre module the harvested material from the ponds is drained 

to channels, which flow to the settler ponds, assisted by harvest pumps. The partially thickened 

stream exiting primary settling is drained to aqueduct channels sent to central dewatering, which 

represents the boundary where Area 400 begins (at the take-off point from the settler outlet). 

Water removed during the second and third dewatering stages in central dewatering is sent back 

uphill to the 100-acre modules via a pipeline system. In addition to water circulation, Area 400 

also brings in makeup water from a nearby groundwater resource outside the facility. 

4.4.2 Design Basis

Figure 4 in Section 2.2 shows the aqueduct channels in green and the distribution pipelines in 

blue. The distance that the aqueducts and pipelines travel is specific to the pond size considered

in the 100-acre modules. Table 1 shows the size variations for the circulation pipeline segments 

as well as the distances that the pipelines travel for each pond size scenario. There are four 

aqueduct channels, and the algae medium at the highest point of each channel flows, on average, 

4,907 m, 4,328 m, and 4,267 m for the 2-acre, 10-acre, and 50-acre cases, respectively. The total 

channel distance in the facility is 10.9 km (6.8 miles) for the 2-acre pond designs, 9.8 km (6.1 

miles) for the 10-acre pond designs, and 9.7 km (6.0 miles) for the 50-acre pond designs. The 

aqueduct channel design and cost assumed here was provided by an estimate furnished by GAI 
42 

who make use of aqueducts for circulation of their cultivation systems [61]. Only 5% of the 

water entering the primary settling ponds is contained in the thickened slurry that enters the 

aqueducts. During the summer, the water flow rate leaving a single 100-acre module is 1,044 

L/min (276 gal/min), which translates to 13,105 L/min (3,462 gal/min) in each of the four 

aqueduct trunks. After consulting with GAI, it was determined that this does not constitute a very 

large flow and could be handled simply with a dug and compacted trough, particularly given the 

1% slope assumed for this facility, which would prevent settling through the aqueducts [61]. 

The clarified water from the central dewatering facility is routed back to the 100-acre modules 

via the pipeline shown in Figure 4 in Section 2.2. Table 1 in Section 2.2 shows the pipeline 

dimensions and lengths for each of the pond size scenarios. The main pipeline header is 34 

inches in diameter when the water first enters. As water is split to each of the vertical columns it 

reduces from 34 inches to 26 inches and then to 20 inches. When the pipeline turns against the 

elevation grade to move uphill it is 16 inches wide in each of the four pipelines, and then further 

decreases in size as it rises in elevation until it reaches 12 inches in diameter at the top. All 

pipelines estimated in ACCE are buried 4 ft underground. The horizontal feed line into each of 

the 100-acre modules is estimated in Area 100 and is specific to the pond design. Based on the 

modeled flow rates and pipe dimensions, Aspen calculates the circulation pumping power 

demand to move the clarified water recycle through the pipeline network and up the facility 

grade, based on maintaining positive pressure at all points in the pipeline. The pump efficiency 

for the facility pipeline is set at 67% (combined pump and motor efficiency). For the 2-acre pond 

facilities, the pump outlet pressure leading into the pipeline from central dewatering is 5.3 atm. 

Similarly, for the 10-acre facility the outlet pressure is 5.4 atm. The 50-acre pond facilities 

require a pumping outlet pressure of 8.3 atm to overcome the larger elevation change. This 

translates to an annual average of 390, 400, and 650 kW of pumping power for the three pond 

size scenarios, respectively, for the overall facility (i.e. not per single module). Only a single 

pipeline network as described here is included in the facility design for normal water circulation, 

i.e., a second pipeline system is not included to accommodate events such as pond crashes and 

drainage/disposal; instead, it is assumed that the contaminated pond would be isolated with 

proper valving on feed and harvest lines, and the pond would be drained and disposed by truck. 

The assumptions for makeup water pipeline delivery from off site were maintained based on the 

previously described harmonization models, the most recent of which (2013) considered 

transporting fresh water from local groundwater resources. Pipeline distance from source to 

facility gate varied by individual site, with an average distance of 1,287 meters (0.8 miles) and 

108 meters of total pumping head based on inputs from PNNL’s Biomass Assessment Tool 

model as reasonable average values for the consortium of sites considered along the U.S. Gulf 

Coast [58]. Costs were included for the off-site makeup water pipeline and pumps, but at a 0.8-

mile pipeline distance these costs are small compared to costs for on-site pipeline circulation, 

which is spread over a much larger total distance (10.1 miles total recirculation pipeline distance 

for the 10 acre pond scenarios). Pump efficiency for the off-site makeup water pipeline also was 

maintained at 67%. 

4.4.3 Cost Estimation

Based on the given harvested/partially concentrated stream flow rate to central dewatering 

coupled with the assistance of the 1% land slope, GAI estimated the costs for the aqueduct 
43 

channels to central dewatering as approximately $100/wetted cultivation acre for a large facility 

of this size [61]; this includes marginal pumping costs to assist in moving the material down the 

elevation grade and across the level terraces. This is an estimation that is specific to this facility 

design and layout, and could increase significantly for either a less (downhill) sloped grade or 

higher volumetric flow rates, as might be seen if primary dewatering were also to be done 

centrally at the bottom of the facility grade (i.e., increasing total harvested flow rates by a factor 

of 22). The uphill circulation piping costs for this portion of the facility pipelines were 

determined from ACCE based on the use of HDPE pipes at the designated pipe diameters in 

Table 1 of Section 2.2 [24]. The costs for the makeup water pipeline and pumps were maintained 

based on the previously-discussed harmonization report (ultimately also costed using ACCE 

[23]). Additional piping and pump costs within the 100 acre module boundaries are considered 

separately and are not included in Area 400. 

4.5 Area 500: Dewatering

4.5.1 Overview

Harvesting and dewatering algal biomass is challenging due to the small size of algal cells, 

density similar to water, and dilute initial concentration (typically around 0.5 g/L from open 

pond systems). As a result, for some dewatering options the energy input required to harvest 

algal biomass can approach or exceed the energy content of the biomass [77], and can account 

for 20% to 30% of the overall cost of renewable fuel production [78] when considering standard 

approaches taken today, such as centrifugation by itself. Many harvesting and dewatering 

strategies have been investigated and are currently under development, including settling and 

gravity sedimentation, screen filtration, membrane filtration, flocculation, centrifugation, 

dissolved air flotation, filter presses, electrocoagulation, magnetic separation, and ultrasonic 

separation. A full review of all harvesting and dewatering options and associated advantages and 

challenges is beyond the scope of this report, but has been well-documented elsewhere (for 

example, [78,79]). This report describes the dewatering operations included in the Aspen Plus 

model, either in forming the base case or evaluated as alternative sensitivity scenarios. The terms 

“harvesting” and “dewatering” are sometimes used interchangeably, although typically 

harvesting refers to removing the algal biomass from the pond, and sometimes also to primary 

(first-stage) concentration, where dewatering then refers to secondary concentration steps. In this 

section, all unit operations that concentrate algal biomass are referred to as dewatering. 

Recognizing that a large number of dewatering technologies are currently under investigation 

and development, for this modeling effort a comprehensive literature review was conducted and 

a number of vendors, technology developers, and consultants were contacted to discuss and 

ultimately select a series of promising and cost-effective methods (based on considerations 

including capital and operating cost, power consumption, technology readiness level, proven 

experience based on processing algae, and effect on product and coproduct options downstream). 

The operations selected to form the base case are in-ground gravity settlers, followed by hollow 

fiber membranes, and then centrifugation to ultimately concentrate the harvested biomass from 

0.5 g/L (0.05 wt%) to 200 g/L (20 wt%) AFDW basis (see Figure 11). However, it should be 

emphasized that algal biomass dewatering is still a relatively new and broadly varied research 

area spanning numerous existing and novel concepts, and it is premature to dictate what “the 

best” strategy will be. Thus, for purposes of projecting future 2022 cost targets, the dewatering 

steps selected here are most appropriately viewed as goals for both dewatering performance (i.e., 
44 

retention efficiencies, power demand) and cost (capital and operating expenses) that any 

technology option may aspire to. Another important factor that influenced the decision to select 

these three operations was to maintain downstream flexibility as much as possible, in terms of 

being agnostic to biomass conversion pathways or fuel/product purity limitations that may 

become challenged with the introduction of foreign chemicals such as flocculants or metal ions, 

which are not introduced for any of the steps selected for the base case. Beyond the baseline 

dewatering configuration, three alternative dewatering strategies were also evaluated with cost 

implications on MBSP presented in the sensitivity analysis (Section 6.1). These alternative 

scenarios include: (1) replacing membranes with a dissolved air flotation (DAF) system 

employing chitosan flocculant, (2) replacing the membranes with electrocoagulation technology, 

and (3) replacing the membranes and centrifuges with a belt filter press.

From ponds

0.5 g/L

0.05 wt%

10 g/L

1.0 wt%

Biomass 

to upgrading

200 g/L

20.0 wt%

Recycle to ponds

0.4 g/L

0.04 wt%

130 g/L

13.0 wt%

Recirculation to ponds

0.1 g/L

0.01 wt%

Blowdown

0.1 g/L

0.01 wt%

Settlers are located in 

100-acre pond modules

Membranes and centrifuges are located 

in the central dewatering facility

Settlers Centrifuges

Membranes

Figure 11. Block flow diagram of dewatering strategy considered for the base case. All g/L 

concentration values are based on AFDW biomass.

4.5.2 Design Basis

Base Case

The dewatering process begins with primary settling ponds, placed at one end of each 100-acre 

plot. Settling units are characterized by low energy demand, as power is required only for pumps 

and in some designs scraping equipment. Settling performance can be improved if flocculants 

and lamina separators are employed, although both add cost, and lamina separators are 

advantageous for applications where space (equipment footprint) is a constraining factor, which 

is not applicable here. The high water content of the material harvested from ponds (99%–

99.5%) translates to tremendous volumetric flow rates that must be processed through first-stage 

dewatering on the order of 9 MM gal/day during peak summer flows in a single 100-acre 

module, or 445 MM gal/day for the full facility (based on 24-hour pond harvesting to minimize 

harvest flows as much as possible). Consequently, it is critical to target the simplest and lowestcost option possible for this first-stage operation in order to both control costs for primary 

dewatering, as well as to reduce subsequent throughputs and therefore costs for further 

dewatering requirements. On the latter point, gravity settlers can be used to increase algal 

biomass concentration by a factor of 20–40, which even for a twentyfold concentration reduces 

the operating capacity of expensive secondary dewatering equipment by 95%. However, gravity 

settlers have only been demonstrated to achieve outlet biomass concentrations up to 1.5%–2% in 
45 

the most optimistic scenarios found in literature [43], therefore one or more subsequent steps are 

necessary to reach 20 wt% to 25 wt% as typically targeted for downstream conversion processes 

[1,2]. In any case, although spontaneous gravity settling (also termed bioflocculation) requires 

further supporting data to demonstrate consistent performance at commercial scales, this 

operation (or an alternative equivalent in cost) is a prerequisite to achieving cost viability for 

algal biomass and biofuel production, thus it is maintained here consistent with prior efforts [23]. 

A limited number of large-scale operations have recently been shown to support the efficacy of 

bioflocculation, including commercial operations at Cellana as published by Huntley et al. [43], 

as well as algal settling ponds installed and operating at a wastewater treatment facility located in 

Delhi, California, that utilizes algal biomass for treating wastewater [25]. Bioflocculation 

efficacy is highly strain-specific, and is known to work well for Scenedesmus (another 

supporting factor in selecting this strain for the base case), but may not be as effective for other 

strains such as Chlorella or Nannochloropsis. 

The primary settlers concentrate the algal biomass from 0.5 to 10 g/L (0.05 to 1.0 wt% AFDW), 

reducing the volume of water flowing to the central dewatering facility by a factor of 20. 

Economic sensitivity to the initial harvest density exiting the ponds and processed through 

primary settling is considered in Section 6.1. Following consultation with MicroBio Engineering 

[25] based on a similar design published in Lundquist et al. [17], the primary settlers were 

designed as simple in-ground settling ponds based on low-cost agricultural engineering practices, 

rather than higher-cost above-ground steel tanks as typically utilized for industrial wastewater 

processing (sludge thickening). The in-ground design consists of long trenches with sufficient 

volume to provide four hours of residence time serving the entire 100-acre module at steady state 

flow. The targeted concentration and residence time are in line with other known data for largescale bioflocculation operations, including >1% concentration through a two-stage settling 

sequence (the first being done in the ponds themselves after suspending circulation) over a 

period of “several hours” [43], as well as 1.5%–2% concentration achieved with a 4–6 hour 

residence time [25,17]. Open settling ponds may lead to accumulation of ash in the concentrated 

product stream, which could increase total throughputs (and therefore costs) for further 

downstream dewatering operations, as well as cleaning/maintenance for the membrane units. 

This is not considered here, but would not likely impact economics to any significant degree 

given the relatively low overall costs for the second and third dewatering steps. 

The settler trenches are 440 feet in length, and trapezoidal in profile: 75 feet wide at the top, 3 

feet wide at the bottom, and 15 feet deep. The bottom of the trench is concrete and the sides are 

lined with geosynthetic membrane. A continuous raking system moves along the bottom of the 

trench to push the settled biomass into six evenly-spaced collection sumps. The biomass is 

removed from these sumps by positive-displacement pumps. The clarified water is recirculated 

back to the production ponds through a 22-inch pipeline and return pump (costed here as part of 

the dewatering section, but included in the Figure 7 overall module piping depiction as the 

clarified water pipeline from settlers to ponds), less blowdown necessary to mitigate buildup of 

salts and other inorganics. The blowdown rates vary by season and were set consistent with prior 

harmonization models as presented in Table 3 to ensure salt accumulation remains below 4,000 

mg/L [42]. Being based on a freshwater system, the blowdown rates are relatively low and 

translate to a maximum loss of algae of 0.1%. The dewatering efficiency of the settling step is 

targeted at 90%, meaning 10% of the biomass remains in the clarified water stream recirculated 

to the ponds. However, given the low blowdown loss, 99.9% of algal biomass produced during 
46 

cultivation ultimately is recovered in the dewatered product available for downstream conversion 

(given that the clarified water streams from second- and third-stage dewatering are also fully 

recycled to the ponds). As noted previously, the choice to locate the primary settling unit 

distributed on each 100-acre module rather than centrally with the secondary and tertiary 

dewatering steps was made in order to minimize pumping and circulation costs to move large 

volumes of water up the overall facility grade. Similar to caveats raised in prior modeling efforts, 

one potential challenge with recovering and recycling nearly all of the unrecovered algal biomass 

present in the clarified effluent from dewatering is that it could enrich the culture for variants that 

do not readily settle; a potential mitigation measure for this issue may be to place a trickle bed 

filter or other mechanism on the recycle line to reduce the amount of recycled biomass or, 

alternatively, to increase the blowdown rate to remove more of the recirculated biomass.

After primary settling, the partially concentrated material is sent to central dewatering for further 

concentration. The second concentration step takes place using hollow fiber membrane 

technology, which was selected primarily in light of favorable performance and cost results 

attributed to a commercial-scale membrane system currently installed and operating at the GAI 

facility [61]. Beyond favorable operational data furnished to NREL by GAI, in general, 

membrane technology offers several advantages over competing dewatering strategies, including

high reliability, direct scalability, and simple thermal, mechanical, and chemical management 

demands [80]. Additionally, membrane technology produces a filtrate product suitable for 

recycle, and does not add chemicals to the algal biomass that must be removed later or may 

negatively impact the value of coproducts [80]. Historical arguments against the use of 

membrane systems for algal dewatering primarily have been based on fouling and 

maintenance/reliability issues that have been observed for other membrane types [77]; however, 

GAI indicated that maintenance and fouling are not typically problematic or costly issues for 

their process, based on a daily cleaning protocol for the membrane modules. Still, such issues 

could be both strain- and location/media-dependent and could pose challenges depending on 

factors such as membrane material, organic (biological) contaminants growing on the membrane 

surface, or inorganic (silica/ash) contaminants depositing on the surface and blocking pores [77]. 

The performance and cost inputs assumed in the integrated model for the membrane system were 

based on guidance from GAI associated with details made available for their process. Namely, 

the operation employs hollow fiber membrane units that receive algae at 1% (10 g/L) from the 

settling ponds and concentrate the biomass to 13% (130 g/L); the system as operated at GAI 

processes a lower inlet biomass concentration than the 1% value modeled here, but can 

accommodate 1% or higher incoming solids content levels, and can also achieve higher outlet 

concentration levels as well. Dewatering efficiency is very high at near-100% biomass retention

(modeled here at 99.5%) with low turbidity in the clarified filtrate. The overall power 

consumption for the membrane system is 0.04 kWh/m3 based on feed rate to the unit. 

Approximately 4% additional installed capacity is added to allow for daily maintenance of 

membrane modules, performed on a rotating hourly basis. Due to the proprietary nature of the 

membrane system, the membrane material and operating techniques were not disclosed to NREL 

and are not reported here. The membrane dewatering performance furnished by GAI and 

incorporated in the base case, specifically power demand, is significantly better than values 

found elsewhere in peer-reviewed literature, as in Bilad et al. [77], which presents power 

consumption values roughly an order of magnitude higher than the basis utilized here. However, 

GAI has subsequently improved even more on the 0.04 kWh/m3 basis to further reduce this value 
47 

and validate that the basis applied here is in fact reasonable. The filtrate (clarified water) from 

the membranes is combined with clarified water from the centrifuge and is fully recycled to the 

production ponds. 

Following secondary dewatering via membranes, centrifugation is used as the final dewatering 

step due primarily to its ability to achieve high biomass concentration (20 wt% or greater [81]) 

and high technology readiness level with widespread commercial use across many industries. 

Centrifuges have been used to concentrate algae for years at laboratories and small scales, and 

centrifuges represent a mature technology that has been used commercially for decades. 

Although costly if implemented as the sole dewatering technology or otherwise processing more 

dilute biomass feed streams, as a tertiary dewatering step centrifugation is not a significant cost 

driver or power consumer. Performance and cost estimates for a bowl centrifuge design were 

provided by subcontractor Harris Group, based on a vendor quotation. The centrifuge

concentrates algae from 13% to 20% (200 g/L), with a dewatering efficiency of 97% (3% of 

algal biomass is removed with the clarified water), although again 100% of the clarified water 

from this step is recycled back to the ponds. Power consumption for the centrifuge is estimated at

1.35 kWh/m3 based on feed to the centrifuge step. At a final dewatered concentration of 20% 

AFDW, the slurry will be considerably more viscous than the material harvested from the ponds; 

however, NREL’s experience working with Scenedesmus at 20% solids in small pilot trials is 

that the material still behaves as a flowable slurry and thus does not likely require conveyors for 

transfer to product storage. The performance of the dewatering steps selected for the base design 

case is summarized in Table 7. 

Table 7. Summary of Base Case Dewatering Steps

Inlet Flowrate, 

m3/day a 

Outlet Concentration, 

wt% AFDW

Separation

Efficiency

Energy Demand,

kWh/m3

Settling Ponds 1,685,000 1 90% Negligible b 

Membranes 76,000 13 99.5% 0.04

Centrifuges 6,000 20 97% 1.35

Overall 20 86.9% c 0.006 d

a Flowrates shown are for peak summer season, which sets the design basis for equipment capacity.

b Primary power demand for settlers is for inlet/outlet pumping, but this is not reflected here for operational 

power of the settler pond itself. A small power demand for a raking mechanism is expected, but is anticipated 

to be marginal.

c Overall separation efficiency = mass flowrate of algae leaving final dewatering step (centrifuges) divided by 

mass flowrate of algae into first dewatering step (settlers); >99% of algae “lost” to clarified effluent streams is 

recycled back to ponds and ultimately recovered in final product, less a small fraction removed as blowdown. d Total dewatering power divided by total volumetric flow into the primary settling ponds. 

Alternative Scenarios

A number of alternative dewatering scenarios were also considered beyond the selected base 

case sequence, which are briefly described here but whose resulting implications on MBSP are 

presented in the sensitivity analysis (Section 6.1). One alternative strategy is to replace the 

membranes with a DAF system employing a flocculant. This option was considered as an 

alternative design because DAF systems have been used extensively in wastewater treatment 

applications for sludge thickening and algae removal, and therefore have a high technology 

readiness level. DAF was also previously considered in the base case during prior harmonization 

modeling activities given its longer history being researched for algal dewatering [7,23]. 
48 

However, the power requirements for generating air bubbles (dissolved air) can be substantial. 

Also, flocculants can significantly increase operating costs and introduce foreign materials, such 

as metals, that can negatively impact the value of products or coproducts [82] or interfere with 

conversion processing equipment. Flocculants work by blocking the negative surface charge 

surrounding the algal cell, allowing the cells to adhere to each other [82]. Dissolved air flotation 

aids in flocculation by creating small air bubbles that attach to algal cells, causing them to float 

to the surface where they can be collected with a mechanical skimming device. Chitosan was 

selected as the flocculant for consideration here (consistent with prior harmonization modeling 

approaches) due to its organic, non-toxic properties and ability to break down in downstream 

operations such as anaerobic digestion. The design and cost basis for the DAF system was 

provided by Harris Group. The DAF system receives algae from the settling ponds at 1% and 

concentrates to 6%, with a separation efficiency of 95%. Power consumption for the DAF, 

including air compression, is maintained consistent with prior harmonization modeling 

assumptions, which in turn were based on standard processing conditions for wastewater sludge 

thickening, estimated at 0.133 kWh/kg of algae removed. The chitosan loading rate is targeted at 

40 mg/L based on Heasman et al. [83]. Optimal chitosan loading can vary from 2 to 200 mg/L 

depending on the algal species [84], therefore chitosan loading and cost are further explored in 

the sensitivity analysis (Section 6.1). 

The second alternative dewatering scenario explored is replacing the membranes with 

electrocoagulation technology. In electrocoagulation, the surface charge of the algae cell is 

altered by generating an electric field between two electrodes. Coagulation of the algal cells is 

enhanced by the release of metal ions from the reactive metal electrode into the water through 

electrolysis. In effect, the metal ions act as chemical flocculants [78]. Compared to chemical 

flocculation employed in the DAF process, electrocoagulation reduces raw material costs by 

eliminating chemical treatment, although metal electrodes are continuously consumed and 

therefore must be continuously replaced. Power demand for electrocoagulation systems is 

generally greater than other dewatering techniques [78]. Performance and cost estimates for the 

electrocoagulation design were provided by an equipment vendor. The electrocoagulation units 

receive algae directly from the settling ponds at 1 wt% and concentrate the material up to 6 wt%, 

with 95% separation efficiency. The power demand is set at 0.7 kWh/m3 of feed to the 

electrocoagulation units, based on vendor input; however, performance and power demand for 

this operation may vary significantly depending on fresh versus saline media (e.g., water salinity 

and thus conductivity) [85]. 

The third alternative scenario replaces the membranes and centrifuge with a belt filter press. The 

belt filter press was considered as another viable alternative dewatering option based on 

accompanying publications by Huntley et al. and Beal et al. [10,43], who showed that gravity 

settling followed by a belt filter press compared favorably against other dewatering routes 

(including DAF followed by centrifugation) based on models extrapolated from literature. Belt 

filter presses may allow for dewatering algae to higher concentrations of 25 wt% to 30 wt%. A 

belt filter press works by applying mechanical pressure to the algae slurry between two tensioned 

belts that pass through a serpentine series of rollers of decreasing size. The algal biomass is 

effectively sandwiched between the belts, which are porous enough to allow water to pass 

through, but retain algal biomass as a cake that builds up. The belt filter press modeled for this 

alternative scenario is based on the design described in the Supplemental Information of Beal et 

al. [10]. The filter press receives algae directly from the settling ponds at 1 wt%, and 
49 

concentrates the material to 20 wt%, with 98% separation efficiency. The power demand for the 

filter press is 0.3 kWh/m3 of algal slurry into the filter press [10], which was confirmed with the 

equipment manufacturer. 

4.5.3 Cost Estimation

Base Case

Excavation and grading costs for the primary settler and material costs for the concrete bottom 

and lined sides were taken from the Leidos cost details for these elements (which originally were 

developed for shallower raceway ponds, but apply equally to this in-ground settler operation if 

the volume of earthwork and concrete are known). Estimated costs for the sumps and raking 

mechanism were obtained from discussions with MicroBio [25]. For purposes of model scaling, 

the overall capital costs were normalized by settler volume, which translates to $34,300 per 

1,000 m3 in 2014$ (comparable to costs developed separately by MicroBio at $36,700/1000 m3

in 2009$ as published in Lundquist et al. [17]). The diameter of the settler return pipeline is a 

constant 22 inches as the total liquid volume does not change with pond design. The pipeline 

length varies per pond size with 1,852 m (6,078 ft) required for the each module in the 2-acre 

case, 1,025 m (3,364 ft) for the 10-acre case, and 411 m (1,350 ft) for the 50-acre case. This 

results in a cost variation of $20MM, $11MM, and $5MM for the 2-, 10-, and 50-acre cases, 

respectively, based on extrapolating from a similar 22-inch PVC pipeline cost quoted for the 2-

acre case by Leidos and scaled by pipe length required for each design. Corresponding settler 

water return pumps on this pipeline were costed in ACCE.

Capital and operating costs for the membrane system were provided by GAI based on their 

installed commercial process [61]. Costs for the membranes alone constitute roughly 40% of the 

total installed cost for the unit (scaling linearly with feed rate based on a fixed membrane flux), 

while the remaining 60% of the installed cost is associated with other supporting items such as 

membrane housing, pumps, and piping (scaling with a 0.6 factor given economy of scale 

accommodations for varying flow rates associated with this portion of the membrane system). 

Operating costs for this system are primarily driven by power demands (discussed previously) 

and maintenance costs, which were set at 3% annually of Area 500 installed capital expenses.

Capital costs and power requirements for the centrifuge were provided by Harris Group. The

purchased capital cost was scaled from an original quote for a bowl centrifuge capable of 

processing a throughput of 154 m3

/hr at a cost of $747,500 in 2013$. Operating cost for the 

centrifuge is primarily power demand, discussed previously. 

Alternative Scenarios

Capital costs for the DAF system were also provided by Harris Group. The purchased capital 

cost was scaled from an original quote for a DAF unit capable of processing 1,531 m3/hr at a cost 

of $560,000 in 2013$ (total cost including DAF tank and mechanism), which translates to 

$366/m3/hr of capacity. The chitosan cost is estimated to be $18/kg based on information from 

industrial grade chitosan suppliers [86]. At the chitosan loading of 40 g/L assumed for the DAF 

scenario, the chitosan costs constitute a significant operating cost; furthermore, given limited

availability of chitosan at large industrial scales (particularly to support numerous commercial 

algal production facilities), this may not ultimately be the best choice for flocculant but was 

maintained here given the data availability for flocculant use in algal dewatering. 
50 

Capital and operating costs for electrocoagulation are based on quotes from discussions with a 

vendor. The purchased capital cost for electrocoagulation equipment was set at $16,667/m3

/hr of 

operating capacity. This value is based on a pilot-scale unit, and electrocoagulation is not a 

mature technology, therefore it is reasonable to anticipate capital costs will decrease with further 

development and scale-up toward commercialization. Power requirements and operating costs 

were obtained from personal quotes and vendor product literature, set at 0.7 kWh/m3 of feed into 

the electrocoagulation unit [87]. Operating costs not including power are primarily attributed to 

electrode replacement costs, which are estimated at roughly $24 per MM gal of feed to the unit. 

This figure is significantly less than the standard 3% of installed capital cost assumed for A500 

maintenance expenses, therefore the electrode replacement costs (except power demand) are not 

considered as a separate operating expense, but rather are assumed to be accounted for in the 

maintenance cost allowance. 

The capital and operating cost for the filter press dewatering operation are based on results 

presented in Beal et al. [10]. The purchased capital cost for the filter press was quoted to NREL 

at $5,300/m3/hr of operating capacity based on information provided by a filter press 

manufacturer. 

The installed capital costs of all baseline and alternative dewatering technologies are summarized 

in Table 8, scaled to a per-volume-feed rate basis to the given unit operation for summer season 

flowrates. However, it is important to note that installed capital costs represent only a portion of 

the cost impact attributed to each dewatering technology. For example, the capital costs for the 

DAF scenario are relatively low, but flocculant (chitosan) operating costs are significant, and 

power demand may also be significant as well (potentially higher than the basis currently 

considered based on industry feedback). Also, different outlet concentrations achievable for each 

dewatering technology confound making direct comparisons. DAF and electrocoagulation 

concentrate to 6% solids, leaving more concentration requirements (and therefore costs) for the 

centrifuge step to achieve the final concentration of 20%. Membranes are assumed to concentrate 

to 13%, while filter presses are assumed to concentrate all the way to 20%, allowing elimination 

of the centrifuge step altogether. Another cost consideration not reflected here is the potential 

impact of coagulant and metal ion contaminants on product and co-product values, resulting 

from DAF and electrocoagulation operations. The installed capital costs presented in Table 8 are

based on the peak summer season capacities modeled for the process scenarios. Capital cost 

scaling exponents and installation factors are different for each dewatering technology, therefore 

the scaled, installed costs shown here apply only to the base case.

Table 8. Installed Capital Costs for Dewatering Technology Options, 

Per Volume Feed Rate to Unit

Installed Capital Cost, 

$/(m3/day)

Base Case:

Settling Ponds $5.80

Membranes $178

Centrifuges $478

Alternatives:

DAF $29

Electrocoagulation $157

Filter Press $70
51 

4.6 Area 600: Storage

4.6.1 Overview

Bulk storage for process chemicals and the dewatered biomass product is provided in this area of 

the plant. Specific tanks that are costed include the algae product tank, makeup water, and water 

for fire suppression. Additional tankage for chemicals (primarily nutrients) is included as a 

balance of plant factor. All assumptions for storage costs and logistics are set consistently with 

other recent design report practices. It also should be noted that storage for CO2 is included 

separately in Area 300, to provide more clarity on costs attributed to CO2 delivery, storage, and 

injection for the base case focused on captured/purified CO2, and for sake of comparison against 

the alternative scenario considering bulk flue gas considered in the sensitivity analysis.

4.6.2 Design Basis

The three primary storage tanks include storage for the algae product, makeup water, and fire 

suppression water (summarized in Table 9). The algae product tanks are sized to have at least 24 

hours of storage (varies seasonally), whereas the makeup water tanks were scaled to have at least 

6 hours of storage. The fire water storage tank was scaled from NREL’s 2013 design report 

according to the dry algae product rate (summer capacity case). While fire suppression may not 

be a concern for the majority of the facility footprint made up of numerous algae ponds, it still 

may be required for other uses e.g. land or structure fires. Storage of the dewatered algal biomass 

material at 80% moisture content in standard storage tanks without refrigeration may pose a risk 

of product degradation losses (such as fermentation and degassing) if not processed quickly. As 

the facility is envisioned to be integrated with downstream conversion operations, the biomass 

product should be sent immediately to the conversion facility and it is not anticipated that the 

product would be stored for more than a few hours under normal operation; still, a 1% 

degradation loss of the stored product was added to the model to account for marginal biomass 

yield losses during storage. 

Table 9. Storage Requirements for Major Tanks

Material Size

Algae product Sufficient to contain >24 hours of production: 2 carbon steel tanks @ 600,000 gal 

Makeup water Sufficient to contain >6 hours of production: 4 carbon steel tanks @ 500,000 gal

Fire water 4 hours of fire suppression @ 2,500 gpm: 1 glass-lined carbon steel tank @ 

600,000 gal (scaled on dry algae product flow rate) 

Other supplemental tanks and pumps were not considered explicitly here, but were costed based 

on a 20% balance of plant factor relative to the total cost of the major tanks listed above, based 

on the same methodology detailed in NREL’s 2014 ALU design report [1]. 

4.6.3 Cost Basis

The costs for the A600 storage section were based on prior NREL design reports [44,4] with

costs scaled according to the new material flows to estimate new prices of the tanks. 
52 

5 Process Economics

The ultimate purpose for developing the process designs, simulation models, and cost estimates 

described above is to determine the economics of algal biomass production and processing for 

delivery to downstream conversion/upgrading operations. This information is used either as an 

absolute cost to assess the implications on cost drivers for an integrated algal biorefinery or to 

provide a means for “valorizing” the biomass based on converting constituent components into 

higher-value products, or as a relative cost that can be used to guide research by examining the 

change in production cost associated with a process modification or other core research activity. 

The total capital investment (TCI) is first computed from the total equipment cost. Next, variable 

and fixed operating costs are determined. With these costs, we use a discounted cash flow 

analysis to determine the minimum biomass selling price (MBSP) required to obtain a zero net 

present value (NPV) with a finite internal rate of return (IRR) (for the given IRR target, NPV is 

zero after the end of the 30-year facility lifetime). Even though the resulting MBSP is most 

appropriately viewed as a “transfer price” for delivery to downstream conversion operations, 

which are likely to be co-located and integrated with the production facility (at a dewatered 

biomass moisture content of 80 wt% which precludes it from being transported over substantial 

distances to a remote conversion facility), approaching the financial analysis in this way would 

ultimately yield the same minimum fuel selling price (MFSP) for a downstream conversion 

facility applying the MBSP projected here for its biomass feedstock cost as if a single integrated 

facility were modeled, including both the biomass production and biomass conversion operations 

together. The following section summarizes the assumptions made in completing the discounted 

cash flow analysis, with more details and supporting description available in previous NREL 

design reports for assumptions that remain unchanged [1,44,76]. 

Our analysis does not take into account any policy factors such as subsidies, mandates, or carbon 

credits, because these would be purely speculative. The purpose of this analysis is to demonstrate 

the process requirements needed to achieve specific cost projections, and to demonstrate how the 

technology pathway described here is able to achieve such costs on its own merits (through 

bottom-up TEA modeling) and, if it cannot otherwise achieve a prescribed cost goal, to give 

stakeholders a sense of the magnitude of incentive required to make it so. 

Finally, while the MBSP cost results for all eight pond design scenarios considered in the TEA 

model (described in Section 4.1) are presented individually here in Section 5.5, for ease of 

discussion in Sections 5.2–5.4 related to capital and operating costs as applied to cash flow 

calculations, it is appropriate at this point to establish a single “base case” representing system 

costs and concomitant MBSP goals for a 2022 target projection. As equipment designs and costs 

for all other process areas excluding production ponds (Areas 200–600) are essentially identical 

for any pond design configuration, the primary variables between the pond scenarios are capital 

costs and power demand for Area 100. For purposes of selecting a base case, we demonstrate 

below and in Section 4.1.3 that 2-acre ponds, while serving as “today’s standard” commercially 

available design, are too costly to enable favorable biomass production costs given economy of 

scale challenges, while 50-acre ponds although more economical than 2- or 10-acre ponds are 

currently too large to justify selecting such a design as the base case without operational data to 

validate their practicality. Thus, the 10-acre size is selected as the most reasonable design for a 

2022 target base case. As all four 10-acre pond cases are based either on detailed engineering 
53 

designs or currently constructed systems furnished by experts in the field, rather than selecting a 

single “winner,” we take the average of the capital costs and (circulation) power demands 

attributed to the four designs to represent a single “base case” for projecting an aspirational 

system to be demonstrated by 2022. These average costs are used as the basis for discussing cash 

flow calculations, total capital investment, etc. in the following sections, but all individual pond 

scenarios were also run through the same methodology independently to arrive at MBSP 

estimates for each case as presented in Section 5.5.

5.1 About Cost-Year Indices

The cost-year of 2011 was chosen for this analysis to provide more updated and relevant cost 

output information relative to the 2007-year basis, which had been utilized for a number of years 

in prior analyses. This new basis is being applied consistently across all DOE-BETO platforms 

for which similar “design case target” reports are being established during 2013–2015 efforts, 

and it is expected that performance goals and TEA outputs will remain in 2011 dollars through 

2017 to permit comparison of future feedstocks, conversion technologies, and other alternative 

scenarios. However, the present equipment costs were originally provided in cost-years ranging 

between 2009 (primarily for the MicroBio pond costs as published in Lundquist et al. [17]) and

2015 (for the most recent pond estimates furnished by Leidos and GAI, as well as a number of 

vendor costs for dewatering operation scenarios). Cost-years for chemicals range from 2003 to 

2014. 

The methods used for determining MBSP in another year’s dollar value and for scaling capital, 

operating, and labor cost estimates to a desired target year remain similar to those described in 

prior design reports. Thus, the details will not be repeated here, but will be summarized briefly. 

Capital costs provided in a year other than 2011 dollars were adjusted using the Plant Cost Index 

from Chemical Engineering Magazine [88] to a common basis year of 2011. The final cost index 

for a given year is generally not made available until the spring of the following year. Therefore, 

for the small number of equipment items that were quoted in 2015 dollars, we assumed the same 

Plant Cost Index value from 2014 (all cost quotes that fall in this category were provided in the 

first half of 2015). Consistent with methods utilized for all other recent design reports, costs are 

not inflated over the 30-year facility lifetime (i.e., inflation is kept constant over the modeled 

facility lifetime). Employee salaries were scaled using the labor indices provided by the U.S. 

Department of Labor Bureau of Labor Statistics [89]. Finally, for chemical costs we also 

maintain a similar approach for cost-indexing as in prior design reports [1], including the use of 

the Industrial Inorganic Chemical Index formerly published by SRI Consulting up through 2011 

[90]. For new chemical cost values between 2012–2014, following a change in the SRI (now 

IHS) Chemical Index methodology, we make use of the Producer Price Index industry data for 

chemical manufacturing published by the Bureau of Labor Statistics [91], which tracked the 

SRI/IHS Chemical Index values through 2011. The general formula for converting nominal 

values to real values and for adjusting dollars to a common basis is:

2011 Cost = (Base Cost)

2011 Cost Index

Base Year Index
54 

5.2 Total Capital Investment (TCI) 

Section 4 of this report describes the details of the conceptual “bottom-up” process design model 

and how the purchased cost of the equipment was determined. The next step is to determine the 

installed cost of that equipment where applicable, although a number of process areas such as the 

production pond systems (Area 100) are already largely given as installed costs. The installation 

cost can be determined by performing a detailed study of everything required to install the 

necessary equipment and make it operational (e.g., foundation, piping, and wiring). This type of 

detail is not warranted at this level of analysis, and a factored approach in which multipliers are 

applied to the purchased equipment cost is considered satisfactory. The methodology and 

rationale for applying unit-level installation costs remains the same as described in prior design 

reports [1,44,76], and again further detail can be found there which will not be repeated here. In 

summary, each type of equipment utilizes a different installation factor to scale the given direct 

equipment purchased cost to a final installed cost, with these factors generally varying between 

1.3 and 2.0. A complete listing of the equipment is provided in Appendix A, along with 

equipment purchased and installed costs. Similar to prior design reports, a number of equipment 

items such as dewatering operations were quoted as a package which includes all supporting 

equipment. The installation factor for such packages can be relatively low because most of the 

engineering is already included in the price. Additionally, equipment designed as a pre-fabricated 

skid generally has a lower construction cost. Equipment costed in ACCE (primarily pipelines, 

pumps, and tanks) also includes estimates for both purchased and installed costs, thus separate 

installation factors are unnecessary for this equipment.

The cost for a given component reflects a baseline equipment size. As changes are made to the 

process, the required equipment size may be different than what was originally designed. Instead 

of re-costing in detail, an exponential scaling expression was used: 

New Cost = (Base Cost)

New Size

Base Size

In this equation, the scaling exponent n varies depending on the type of equipment to reflect 

economy of scale dependencies. The basis for scaling is typically some characteristic of the 

equipment related to production capacity, such as flow or heat duty. Some equipment does not 

follow such a scaling-factor approach, namely when the capacity for a given operation is 

exceeded and requires multiple units in parallel (thus losing economy of scale benefits, which are 

captured in the exponential expression above). More detail on reasonable scaling values for 

different types of equipment is provided in NREL’s 2011 ethanol report [76], which describes 

this approach, but for a different biomass feedstock. In summary for the present case, ponds and 

inoculum equipment scale linearly for a given pond size (i.e. many individual production and 

inoculum ponds are employed in the facility), and primary settling units also scale linearly based 

on a given dollar-per-volume basis applied here (see Section 4.5.3). Costs scale exponentially for 

downstream dewatering equipment (membranes and centrifuges) which may vary in capacity for 

a given unit as throughput changes. Cost and scaling details for all processing equipment are 

provided in Appendix A. 

Once the total equipment cost has been determined in the year of interest, several direct and 

indirect costs are added to determine the total capital investment (TCI). First, direct cost factors 
55 

are applied relative to the installed costs to determine the total direct cost (TDC) and include 

warehouse allowances, site development, and additional yard piping (i.e., piping for downstream 

operations beyond the piping explicitly considered in Areas 100 and 400). Indirect cost factors 

including project contingency, field expenses, home-office engineering and construction 

activities, and other construction-related costs are then computed relative to TDC and summed to 

yield the fixed capital investment (FCI). Finally, the FCI is combined with working capital and 

land costs to give the TCI. In prior NREL design reports, application of direct and indirect cost 

factors was relatively straightforward and followed a standard methodology applicable to most 

biorefinery systems focused on the conversion of biomass into fuels and coproducts [1,44,76]. 

For the current design, while the cost factor categories remain the same, the methodology for 

estimating these factors has been modified to reflect significant differences in the present process 

(comprised largely of “farming” operations and pipeline networks spanning thousands of acres) 

relative to standard biorefineries (comprised of conversion and upgrading units similar to ethanol 

or petrochemical facilities constrained to ~100 acres of land footprint). In prior biorefinery 

design cases, direct and indirect factors were handled based on separating out costs attributed to 

process areas falling inside battery limits (ISBL) and outside battery limits (OSBL) of the 

facility. For the current effort, installed costs and associated cost factor estimates were divided 

into three categories: cultivation (Areas 100 and 200), dewatering (Area 500), and OSBL (Areas 

300, 400, and 600). Table 10 presents a summary of the direct and indirect factor cost allowances 

as applied to each of the three facility categories, followed by a discussion on the rationale for 

the assumptions employed to select the given cost factor values. 
56 

Table 10. Additional Costs for Determining Total Capital Investment (TCI)

Item Description Dewatering Cultivation OSBL

Additional direct costs

Warehouse Includes on-site storage of equipment and 

supplies.

4% of A500 

installed cost

1.2% of A100

and A200 

installed cost 

0%

Site development Includes fencing, curbing, parking lot, roads, well 

drainage, rail system, soil borings, and general 

paving. This factor allows for minimum site 

development assuming a clear site with no 

unusual problems such as right-of-way, difficult 

land clearing, or unusual environmental problems. 

9% of A500 

installed cost

Included in 

pond cost 

estimate

$1,534/acre

(roads and 

fences)

Additional piping To connect ISBL equipment to storage and 

utilities outside the battery limits.

4.5% of A500 

installed cost

Included in 

pond cost 

estimate

0%

Indirect costs % of A500 

Total Direct 

Cost (TDC)

% of A100 and 

A200 TDC

% of OSBL 

TDC

Prorateable 

expenses 

Includes fringe benefits, burdens, and insurance 

of the construction contractor. 

10% of TDC 4% of TDC 1% of TDC

Field expenses Consumables, small tool and equipment rental, 

field services, temporary construction facilities, 

and field construction supervision. 

10% of TDC 4.5% of TDC 1% of TDC

Home office and 

construction 

Engineering plus incidentals, purchasing, and 

construction. 

20% of TDC 10.3% of TDC 1% of TDC

Project 

contingency 

Extra cash on hand for unforeseen issues during 

construction. 

10% of TDC 10% of TDC 10% of TDC

Other costs Start-up and commissioning costs; land, rights-ofway, permits, surveys, and fees; piling, soil 

compaction/dewatering, and unusual foundations; 

sales, use, and other taxes; freight, insurance in 

transit and import duties on equipment, piping, 

steel, and instrumentation; overtime pay during 

construction; field insurance; project team; and 

transportation equipment, bulk shipping 

containers and plant vehicles. 

10% of TDC 2.6% of TDC 1% of TDC

As presented in Table 10, for the dewatering section (Area 500), percentage allocations for direct 

and indirect cost allowances were set equal to those typically utilized in prior biorefinery design 

cases [1] as this process area shares similarities with equipment utilized in biorefinery processes, 

e.g., the use of equipment for solids handling and separations that must be engineered, 

fabricated, and shipped to the facility for installation, which requires warehousing for storage of 

spare parts, etc. The OSBL process areas including CO2 delivery (whose equipment consists of 

storage tanks, pipelines, and valves), facility circulation pipelines and aqueducts, and tankage, 

are simplistic and are not envisioned to require substantial allowances for additional indirect 

factors to escalate their expenses dramatically beyond the installed costs primarily quoted in 

ACCE, thus all indirect factors for the OSBL equipment were set at 1% with the exception of 

contingency allowances which were maintained at the standard 10% (see Table 10). Direct cost 

factors for both warehouse and additional piping were excluded, as warehouse costs are not 

anticipated to be necessary for this equipment and essentially all piping in this portion of the 

facility is costed explicitly. However, an allowance for “site development” is included in the 
57 

OSBL category, costed at approximately $1,530/acre representing the cost for roads and fences 

[17]. 

The final category with a separate set of cost factor allocations is cultivation (Areas 100 and 

200). Both site development (representing a large fraction of pond civil work) and piping costs 

were included in the pond construction cost estimates obtained for all eight pond scenarios 

considered, with inoculum system costs primarily extrapolated from pond costs plus additional 

elements such as full pond liners, hoop houses for covered ponds, and PBR “system” costs (see 

Section 4.2). Therefore, only the warehouse line item applies for additional direct cost inclusions 

within the cultivation process areas. To help estimate warehouse direct cost allowances as well 

as the various indirect cost factors as pertinent to algal cultivation systems, three detailed capital 

cost breakdowns reported in literature [10,17,92] were analyzed and cost factors were calculated 

relative to the cultivation capital cost in each case. When available, the average of all three 

sources was selected for use here, with the exception of contingency, which was fixed at the 

standard 10% value, and field expenses, which were set at 4.5% of cultivation TDC. Table 11 

shows the cultivation factors back-calculated from literature as well as those selected for use in 

this report, along with standard factors typically used in biorefinery design models as well as the 

wastewater industry for comparison. Relative to standard biorefinery processes, the selected 

warehouse direct factor is smaller for the cultivation areas reflecting the smaller and standardized 

parts inventory required to maintain raceway ponds compared to refinery units (i.e., spare 

paddlewheels and motors). The home office and construction factor is also lower owing to pond 

modularity and lack of detailed engineering/procurement necessary for raceway pond 

development for many repeating pond units. Similarly, prorateable expenses and field expenses 

are smaller due to lower requirements for scaffolding, cranes, and other temporary on-site items. 

The “other costs” category is also considerably smaller due to the inclusion of surveys, pilings, 

soil compaction/dewatering, and foundations already accounted for in the pond cost estimates, 

thus leaving fewer remaining items such as transportation and permit costs alone. 

Finally, land costs at $3,000/acre were applied to the total facility footprint (see Section 2.2), 

consistent with prior algae TEA efforts [7,23]. This cost is lower than typical land costs applied 

for biorefinery conversion facility design reports (for example $14,000/acre as presented in the 

the 2014 ALU design report [1]); however, it is appropriate for use here, given the emphasis on 

the use of low-value land not otherwise suitable or intended for crop production or other 

industrial uses. A land price of $3,000/acre is a conservative estimate for such land, applicable to 

both the Gulf Coast as well as the Southwestern United States (both attractive regions for algal 

production), based on performing a statistical analysis of land prices in Louisiana and Arizona 

[93]. Based on the details described above, Table 12 shows the application of all applicable cost 

factors to obtain the TCI for the base case (where the “base case” is taken here based on 

averaging the installed capital costs for all four 10-acre pond designs as discussed previously). 

Applying the cost factor assumptions discussed above and summarized in Table 10 for all three 

process categories, the resulting ratio for FCI to installed costs is 1.3 for cultivation (Areas 100 

and 200), 1.9 for dewatering (Area 500), and 1.8 for OSBL (Areas 300, 400, and 600), resulting 

in an overall total FCI to total installed cost ratio of 1.5. As expected for reasons discussed 

above, this is slightly lower than ratios typically seen for biorefinery design models at 1.7–1.8 

[1,44]. 
58 

Table 11. Cost Factors Pertinent to Algal Cultivation Systems Deduced from Literature [10,17,92], 

and Selected for Use Here. (Standard factors for typical biorefinery designs and wastewater processing 

are also provided for comparison.)

Cost Factor Selected

Beal 

et al.

Lundquist 

et al.

Alabi 

et al. Wastewater

Biorefinery 

“Standard”

% of Cultivation Cost % of Total Direct Cost

Warehouse 1.2% 1.3% 2.0% 0.3% - 4%

Prorateable Expenses 4.0% 0.03% 8.4% - 4% 10%

Field Expenses 4.5% 4.5% 25.1% - 12% 10%

Home Office & Construction 10.3% 8.4% 10.4% 12.2% 5% 20%

Other Costs (Start-Up, Permits, etc.) 2.6% 1.4% 5.2% 1.4% 2% 10%

Table 12. Project Cost Worksheet Including Total Direct Costs and Total Capital Investment (base 

case for 10-acre average pond costs a; all costs in 2011 dollars)

Purchased 

Cost b

Installed Cost b

Total Installed 

Cost Process Area Cultivation Dewatering OSBL b

Area 100: Production Ponds

 (average of 10-acre cases c) $158,500,000 $158,500,000 $ - $ - $158,500,000

Area 200: Inoculum Ponds $16,100,000 $16,100,000 $ - $ - $16,100,000

Area 300: CO2 Delivery $6,100,000 $ - $ - $6,500,000 $6,500,000

Area 400: Makeup Water 

Delivery + On-Site Circulation $5,400,000 $ - $ - $7,200,000 $7,200,000

Area 500: Dewatering $41,700,000 $ - $43,900,000 $ - $43,900,000

Area 600: Storage $4,000,000 $ - $ - $5,300,000 $5,300,000

Totals $231,900,000 $174,600,000 $43,900,000 $19,000,000 $237,500,000

 Warehouse $2,100,000 $1,800,000 NA $3,900,000

 Site Development NA $3,900,000 $11,700,000 $15,600,000

 Additional Piping NA $2,000,000 NA $2,000,000

Total Direct Costs (TDC) $176,800,000 $51,500,000 $30,700,000 $259,000,000

 Prorateable Expenses $7,100,000 $5,200,000 $300,000 $12,500,000

 Field Expenses $7,900,000 $5,200,000 $300,000 $13,300,000

 Home Office & Construction Fee $18,300,000 $10,300,000 $300,000 $28,900,000

 Project Contingency $17,700,000 $5,200,000 $3,100,000 $25,900,000

 Other Costs (Start-Up, Permits, etc.) $4,700,000 $5,200,000 $300,000 $10,100,000

Total Indirect Costs $55,600,000 $30,900,000 $4,300,000 $90,800,000

Fixed Capital Investment (FCI) $232,300,000 $82,500,000 $35,000,000 $349,800,000

 Land $22,800,000

 Working Capital $17,500,000

Total Capital Investment (TCI) $390,200,000

Lang Factor (TCI/Purchased Equipment Cost) 1.5

TCI per Annual Ton $2080/Ton (AFDW) a Total facility size for 10 acre “base case” is 7,600 acres (5,000 acres production pond area), subdivided into 100-

acre modules each consisting of ten 10 acre ponds.

b Capital costs are based on peak summer production capacity. 

c Pond capital costs shown are the average of all four 10-acre pond design cases. The installed capital cost for each 

individual 10-acre case is $208,900,000 for Harris, $146,400,000 for GAI, $155,300,000 for Leidos, and 

$123,500,000 for MicroBio. 
59 

5.3 Variable Operating Costs 

Variable operating costs, which include CO2, other raw materials, and power demand, are 

incurred only when the process is operating. For the algal processing facility modeled here, 

variable operating costs by definition also vary as seasonal biomass productivities and associated 

harvest rates and equipment throughputs fluctuate, in contrast to fixed operating costs (and 

equipment capital costs), which do not. Variable costs for nutrient inputs (CO2, NH3, and DAP) 

scale proportionately with seasonal biomass productivity rate, but power demand is less strongly 

tied to this metric, given a large fraction of facility power consumption attributed to pond mixing 

which remains fixed across the year for a given pond design. Quantities of raw materials used 

were determined using the Aspen material balance, based on running individual Aspen models 

for each season and then taking the average of all four seasons in setting the net annual operating 

expenses, power demand, and product yields. Table 13 documents the costs and sources of 

chemicals used in the process and Table 14 summarizes the variable input flow rates on a perseason basis, as well as the resulting variable costs on a per-year and per-ton-of-biomass basis. 

Material costs for the present model consist of CO2, ammonia and DAP nutrients, and utilities. 

The base case model assumes the use of purified CO2 produced from flue gas carbon capture 

sourced from a nearby power plant, with a cost set at $45/metric tonne representing 2022 

technology goals as discussed in more detail in Section 4.3. As noted previously, this was done 

both to reduce uncertainty and subjectivity in CO2 cost contributions relative to more speculative 

modeling scenarios for bulk flue gas transport and distribution, as well as the fact that the latter 

approach based on flue gas poses significant logistical challenges and raises questions as to its 

practicality for a facility of this size (these issues, as well as cost implications associated with a 

flue gas scenario, are presented in Section 6.1). Ammonia and DAP prices were updated in this 

report relative to assumptions employed in previous work, to make use of market fertilizer 

pricing published by the USDA as the most appropriate basis for large-scale use of fertilizers for 

biomass production [94]. Given significant fluctuations in the prices for both fertilizers over 

recent years, average prices were taken for years 2011–2014 (the most recent year currently 

available). The resulting prices for ammonia and DAP are $772/ton and $630/ton, respectively, 

after indexing to 2011 dollars. As discussed previously, ammonia and DAP nutrient demands are 

set in the model based on nitrogen and phosphorous elemental content of the biomass at harvest 

(Table 2) plus an additional 20% excess allowance present in the circulated culture. While the 

biomass composition has also been measured to contain a small level of elemental sulfur, a cost 

for “sulfur delivery” is not included in the base case model. This is because sulfur is likely to be 

present in more than sufficient quantities in bulk flue gas delivered to the ponds, and even 

potentially in the captured CO2 basis scenario depending on affinity of the carbon capture 

technology for sulfur species (e.g., SO2). Even if sulfur were not present in sufficient amounts 

with the delivered CO2, if it were to be costed as an external nutrient (SO2) it would add a 

negligible amount to MBSP on the order of $1/ton. 

Utility costs include power and marginal chilled water demands. The electricity price was set at 

6.8 ¢/kWh, based on the EIA 2011 average industrial retail price [95]. As discussed previously, 

given that chilled water demand is relatively low in this design (required for seasonal cooling in 

the PBR and covered pond inoculum operations) coupled with the fact that this facility is likely 

to be integrated with downstream biorefinery conversion operations (which typically include 

utility systems for chilled water, cooling water, and steam), chilled water demands were costed 
60 

in this design based on a utility operating expense rather than constructing a dedicated chiller 

system on site, which would likely be duplicative with the downstream conversion facility. A 

chilled water utility “transfer price” was thus utilized, at a value of $5/GJ [65]. Consistent with 

prior harmonization models [23,42], makeup process water to primarily make up for evaporation 

and blowdown losses was not costed as an operating expense, but rather was costed based on 

pipeline, pumping, and power demands attributed to bringing water to the facility from a nearby 

local groundwater resource located 1,287 meters (0.8 miles) from the facility boundary, 

including 108 meters of pumping head (see Section 4.4). The resultant total facility operating 

costs translate to $5,400/cultivation acre for the base case (10-acre average scenario), which 

agrees closely with $5,000/cultivation acre described in Beal et al. and Huntley et al. [10,43]. 

Table 13. Chemical/ Utility Costs and Sources

Component Cost (2011$) Source

Inputs

CO2 $0.0204/lb [72-74] ($45/metric tonne)

Ammonia $0.3862/lb [94] (average of 2011–2014)

Diammonium phosphate $0.3150/lb [94] (average of 2011–2014)

Power $0.0682/kWh [95]

Chilled water utility price $5.00/GJ [65]

Process water NA

Water is sourced from a nearby local water resource; costs 

are accounted for via pipelines, pumps, and pumping power 

to bring makeup water on site. 

Table 14. Variable Operating Costs (includes seasonal flow rates and resulting annual costs) a 

Process 

Area

Stream Description Summer 

Usage

(kg/h)

Fall 

Usage 

(kg/h)

Winter 

Usage 

(kg/h)

Spring 

Usage 

(kg/h)

Annual 

Average 

(kg/h)

MM$/yr 

(2011$)

$/Ton AFDW

Algae

(2011$)

Raw materials

A100 

and

CO2 66,908 47,600 22,366 54,482 47,839 17.05 90.90

Ammonia 603 428 201 491 431 2.91 15.49

A200 Diammonium Phosphate 292 208 98 238 209 1.15 6.13

A600 Electricity (kW) b 11,620 9,581 7,130 10,683 9,753 5.27 28.09

Chilled Water Utility (GJ/h) 17 17 17 17 17 0.69 3.66

Process Water 1,222,975 520,358 460,576 2,261,033 1,116,236 NA NA

Total variable operating costs 27.06 144.27

a All costs shown are for the base case average of the 10-acre designs. Values for Harris 10-acre, Leidos 10-acre, 

GAI 10-acre, and MicoBio 10-acre ponds match the values provided, excepting electricity. b The Harris 10-acre case, Leidos 10-acre case, GAI 10-acre case, MicroBio 10-acre case, and overall average 10-

acre case have variable electricity demands because of different paddlewheel or circulation pump requirements. The 

average 10-acre case electricity usage is shown in the table. The annual average power demand for the individual 

10-acre design cases is 10,000 kW for Harris, 11,000 kW for Leidos, 8,850 kW for GAI, and 9,150 kW for MicroBio. 

5.4 Fixed Operating Costs

Fixed operating costs are generally incurred in full whether or not the plant is producing at full 

capacity. These costs include labor and various overhead items. Again as with indirect cost 

factors discussed above, staffing requirements and resulting labor costs were modified for this 

effort relative to standard assumptions employed in recent biorefinery conversion pathway 

design reports [1,44]. A number of labor cost assumptions were maintained with these prior 

analyses where appropriate, including the plant manager, lab manager, maintenance supervisor, 

shift supervisors, and clerks/secretaries. Additionally, maintenance and lab technicians and 

associated salaries were also maintained, but the required number of each employee type was 
61 

adjusted to vary depending on pond size and thus number of total ponds in the facility that must 

be monitored and maintained (shown in Table 15 for each of the three pond size scenarios). As 

pond size decreases and thus total number of individual ponds increases, the number of each of 

these technicians required to service the ponds increases. A similar modification was made for 

production pond operators, which represent the most costly labor category based on the large 

number of pond operators required for such a large facility (between 33 for the large 50-acre 

pond designs up to 73 for the 2-acre pond designs). Pond operator salaries were set based on data 

from the Bureau of Labor Statistics (BLS) for an “agricultural equipment operator” [96]. 

Likewise, operators for the inoculum system (fixed at eight total operators regardless of 

production pond scenario) and the dewatering section (fixed at nine total operators) were also 

adjusted using BLS data, in this case matching employee categories for “water and wastewater 

treatment plant operators” and “separating, filtering, clarifying ... and still machine operators” 

[97]. Finally, engineering labor costs were also increased, based on assuming two each of civil 

and environmental engineers also based on BLS salary data [98,99]. 

The resulting employee requirements and associated labor costs are shown in Table 15, with the 

10-acre base case selected for presenting the annual labor expenses. The estimated labor costs 

are in line with other published TEA studies for algal biomass production after adjusting for 

facility size [10,17,92]. These estimates suggest a considerable difference in total labor costs 

depending on individual pond size considered for the facility, further adding to economy of scale 

benefits for moving toward larger pond size designs. For the 2-acre pond case, the total burdened 

labor cost is estimated at $8.4 MM/yr, which decreases to $7.0 MM/yr and $5.5 MM/yr for the 

10- and 50-acre pond cases, respectively. 

Table 15. Fixed Operating Costs

Position 2011 

Salary # Required 2011 Cost a MM$/yr (2011$) a 

$/Ton 

(2011$) a 

 Labor & Supervision (based on pond size scenario; 10-acre base case is shown for $MM/yr costs)

2-acre 10-acre 50-acre

Plant Manager $ 155,400 1 1 1 $ 155,400 

Plant Engineer (civil) $ 81,935 2 2 2 $ 163,871 

Plant Engineer (environmental) $ 83,244 2 2 2 $ 166,487 

Maintenance Supervisor $ 60,257 1 1 1 $ 60,257 

Maintenance Technician $ 42,286 15 12 7 $ 507,432

Lab Manager $ 59,200 1 1 1 $ 59,200 

Lab Technician $ 42,286 4 1 1 $ 42,286

Shift Supervisor $ 50,743 4 4 4 $ 202,972 

Module Operator – Production $ 26,872 73 56 33 $ 1,504,856

Module Operator – Inoculum $ 44,038 8 8 8 $ 352,307 

Module Operator – Dewatering $ 38,536 9 9 9 $ 346,825 

Clerks & Secretaries $ 38,057 3 3 3 $ 114,171 

Labor Total 123 100 72 $ 3,676,065 3.68 19.60

Labor Burden (90%) $ 3,308,459 3.31 17.64

 Other Overhead

Maintenance 3% of Area 500 + 0.5% of Areas 100–400 $ 2,257,731 2.26 12.04

Property Insur. & Tax 0.7% of FCI $ 2,448,790 2.45 13.06

Total Fixed Operating Costs 11.69 62.33 a Annual costs shown in the three right columns reflect base case average of the four 10-acre pond designs.
62 

A 90% labor burden is applied to the salary total and covers items such as safety, general 

engineering, general plant maintenance, payroll overhead (including benefits), plant security, 

janitorial and similar services, phone, light, heat, and plant communications. The 90% estimate is 

the median of the general overhead range suggested in the 2008 PEP Yearbook produced by SRI 

Consulting (now IHS) [90]. Annual maintenance costs were estimated as 3% of the installed cost 

for the dewatering section plus 0.5% of the installed costs for Areas 100, 200, 300, and 400, 

which consist of cultivation ponds and supporting equipment or circulation piping and tankage, 

which are expected to incur much lower maintenance requirements than “standard” biorefinery 

type equipment and machinery. Property insurance and local property tax were estimated at 0.7% 

of the fixed capital investment, based on the 1994 Chem Systems report described in NREL’s 

2011 ethanol report [76]. 

5.5 Discounted Cash Flow Analysis and the Minimum Selling Price of 

Biomass

Discount Rate

For this analysis, the discount rate (which is also the internal rate of return [IRR] in this analysis) 

was set to 10% and the plant lifetime was set to 30 years. This discount rate is standard for all 

BETO design reports, and was based on the recommendation in Short et al. [100] on how to 

perform economic evaluations of renewable energy technologies for DOE. His view was that, 

“In the absence of statistical data on discount rates used by industrial, transportation and 

commercial investors for investments with risks similar to those of conservation and renewable 

energy investments, it is recommended that an after tax discount rate of 10%...be used.” 

Equity Financing

For this analysis, it was assumed that the plant would be 40% equity financed. The terms of the 

loan were taken to be 8% interest for 10 years. The principal is taken out in stages over the 3-

year construction period. Interest on the loan is paid during this period, but principal is not paid 

back (this is another nth-plant assumption, which says that this cash flow comes from the parent 

company until the plant starts up). This is all consistent with the assumptions used in recent

NREL design reports since 2011. Figure 12 illustrates the sensitivity of minimum biomass 

selling price to the percentage of equity financing and the after-tax discount rate (the IRR), 

associated with the above-discussed “base case” average for the four 10-acre pond designs. 
63 

Figure 12. Sensitivity of MBSP to IRR and % equity (8% interest on a 10-year loan)

Depreciation

To determine the capital depreciation amount for the calculation of federal taxes to be paid we 

used the IRS Modified Accelerated Cost Recovery System (MACRS). Within the MACRS 

system is the General Depreciation System (GDS), which allows both the 200% and 150% 

declining balance (DB) methods of depreciation. This offers the shortest recovery period and the 

largest tax deductions. According to IRS publication 946 [101], a biorefinery plant would fall 

under Asset Class 49.5, “Waste Reduction and Resource Recovery Plants.” This class uses a 7-

year recovery period, not including any power plant (i.e., gas or steam turbine) equipment. 

Again, all assumptions employed here are maintained consistently with prior design reports. 

Taxes

The federal corporate tax rate used in our analysis is 35%. Income tax is averaged over the plant 

life and that average is calculated on a per-ton-biomass basis. The amount of income tax to be 

paid by a potential biomass (or fuel) producer varies annually due to changes in the volume of 

product produced and the allowable depreciation deduction. In fact, no income tax is paid in the 

first eight years of operation because the depreciation and loan interest deductions are greater 

than the net income. State taxes are not considered, primarily because the location of the plant is 

not specified (to a state level) and tax rates vary from state to state (from 0% to 12%); this is 

consistent with previous design report practice standards and is applied consistently here as well. 

As noted previously, applying factors such as income taxes and IRR to both the models for 

biomass production and biomass conversion to fuels will ultimately yield the same minimum 

fuel selling price as a single integrated facility model.

Construction Time

The construction time is important to the cash flow analysis because no income is earned during 

construction but large sums of money are being expended. Construction time assumptions were 

left unchanged from other recent design reports. Perry and Green [102] indicate that small 

$400

$450

$500

$550

$600

$650

$700

$750

$800

$850

$900

0% 20% 40% 60% 80% 100% 120%

Minimum Biomass Selling Price 

($/Ton AFDW)

Equity %

10% IRR

15% IRR

20% IRR
64 

projects (less than $10 million investment) can be constructed in fewer than 18 months and that 

larger projects can take up to 42 months. An overview of petroleum refining economics indicates 

that large refineries (on the order of a $1.5 billion investment) can be constructed in 24 months 

[103]. Certainly this algal biomass facility is less costly than such a petroleum refinery, so using 

a construction time of 24 months fits within these references, although the present facility is 

significantly different in terms of land footprint size and type of equipment being installed. In 

any case, the present design consists largely of many modular pond systems of identical 

configuration, which are envisioned to allow for relative ease and speed of construction. Table 

16 summarizes the schedule for construction and the cash flow during that time. Twelve months 

are added before construction for planning and engineering.

Table 16. Construction Activities and Cash Flow

Project 

Start 

Month

Project 

End 

Month

Activity Description

% of 

Project 

Cost

0 12 Project plan and schedule established; conceptual and basic 

design engineering and permitting completed; major equipment 

bid packages issued, engineering started on selected subpackages, P&IDs complete, and preliminary plant and equipment 

arrangements complete. 

8%

12 24 All detailed engineering including foundations, structure, piping, 

electrical, and site complete; all equipment and instrument 

components purchased and delivered; all site grading, drainage, 

sewers, rail, fire pond, foundation, and major structural 

installation complete; 80% of all major process equipment set (all 

except longest-lead items); all field-fabricated tanks built; and the 

majority of piping and electrical materials procured. 

60%

24 36 Complete process equipment setting, piping, and instrumentation 

installation complete; all electrical wiring complete; all building 

finishing and plumbing complete; all landscaping complete; precommissioning complete; and commissioning, start-up, and initial 

performance test complete. 

32%

TOTAL 100%

Start-Up Time

Perry and Green [102] indicate that for a moderately complex plant, start-up should be about 

25% of the construction time, or 6 months in this case. The start-up period is not completely 

wasted, however. We expect that an average of 50% production could be achieved during that 

period while incurring 75% of variable expenses and 100% of fixed expenses. 

Working Capital

Peters and Timmerhaus [104] define working capital as money available to cover (1) raw 

materials and supplies in inventory, (2) finished product in storage, (3) accounts receivable, (4) 

cash on hand for monthly payments such as wages and maintenance supplies, (5) accounts 

payable, and (6) taxes payable. The present analysis applies the same basis for working capital as 

was used in prior work, namely 5% of fixed capital investment. 
65 

Table 17 summarizes the parameters used in the discounted cash flow analysis. Using these 

parameters, plus the cost information in Table 12, Table 14, and Table 15, the resulting 

minimum biomass selling price for the base case (average of the four 10-acre pond designs) is 

$491/ton (2011 dollars, AFDW basis). It is worthwhile to distinguish this MBSP result, based on 

10% IRR and other economic inputs noted above, from the cost of production (i.e., breakeven 

cost to cover capital and operating expenses at 0% IRR), as these terms are often incorrectly used 

interchangeably; the associated cost of production for this case is estimated at $309/ton. Table 18 

summarizes the yields and processing costs for the base case model. According to the 

methodology of Cran [105], the expected accuracy of the TCI analysis is +/- 25%. If we apply 

this uncertainty to the TCI, the impact on the MBSP is +/-$73/ton. The complete discounted cash 

flow summary worksheet is shown in Appendix C. The contributions to the base case MBSP are 

broken down into major cost drivers as shown in Figure 13, along with individual MBSP results 

for each of the eight discrete pond designs. 

Table 17. Discounted Cash Flow Analysis Parameters

Plant life 30 years

Discount rate 10%

General plant depreciation 200% declining balance (DB)

General plant recovery period 7 years

Federal tax rate 35%

Financing 40% equity

Loan terms 10-year loan at 8% APR

Construction period 3 years

 First 12 months’ expenditures 8%

 Next 12 months’ expenditures 60%

 Last 12 months’ expenditures 32%

Working capital 5% of fixed capital investment

Start-up time 6 months

 Revenues during start-up 50%

 Variable costs incurred during start-up 75%

 Fixed costs incurred during start-up 100%

Table 18. Summary of Yields, Rates, and Processing Costs (base case 10-acre average)

Facility size 5,000 acres (2,023 ha) wetted cultivation area

CO2 demand 417,700 ton/yr

On-line time 7,920 h/yr (330 days/yr, i.e., 90% on-line factor)

Biomass production rate 0.19 MM ton/yr (AFDW)

Biomass yield 37.5 ton/acre/yr (84.1 tonne/ha/yr AFDW)

Total installed equipment cost $238 MM

Total capital investment (TCI) $390 MM

TCI per annual ton biomass $2,080

Minimum Biomass Selling Price $491/ton AFDW

 Contribution from cultivation system $278/ton

 Contribution from CO2 + nutrients $112/ton

 Contribution from remainder $101/ton
66 

Figure 13. MBSP results for each pond scenario broken out by major contributions. (Figure also 

shows “base case” selected for presentation of cost details shown in Sections 5.2–5.4, attributed to 

average of the four 10-acre pond designs representing 2022 design and cost targets.) 

Figure 13 reiterates the primary conclusion presented in prior analyses [23] that the cost of algal 

biomass (which in turn dominates the cost of algal biofuels) is driven most strongly by the cost 

for cultivation systems, even for both a reasonably high targeted annual productivity at 25 

g/m2/day combined with low-cost pond systems with only marginal inclusions for plastic liners 

in small targeted areas of the pond for erosion control. As either productivity decreases or pond 

costs increase, system costs and biomass selling price increase (see Figure 5) driven primarily by 

pond costs becoming an even larger fraction of overall selling price. Within the pond cost 

category itself, more specific cost drivers are presented in Figure 8. Inoculum costs account for 

$25/ton across all pond designs (between 9-19% of total pond costs). Beyond this, although 

major cost drivers vary by pond design, generally for the 10-acre cases the largest contributors to 

pond costs are the “other” category (e.g. paddlewheels, motors, and concrete), followed by civil 

work and then piping. Given otherwise consistent assumptions for algal biomass productivity 

and composition, harvest density, dewatering performance and costs, and overall facility layout, 

all cost contributions to MBSP are nearly identical across the eight pond system designs 

considered, except of course for the costs attributed to ponds (including partial pond liners) and 

inoculation system equipment, which vary inversely proportional with individual pond size as 

presented in Figure 9. While intuitively this is to be expected, given economy of scale benefits 

discussed previously (attributed to fewer individual feed and harvest pipelines, pipe 

fittings/control valves, electrical runs, and circulation equipment required for fewer ponds of 

$576

$649

$452

$491

$545

$475 $491

$419 $392

$0

$100

$200

$300

$400

$500

$600

$700

Algal biomass selling price ($/ton AFDW)

OSBL

Dewatering

Ponds + Inoculum

Fixed OPEX Costs

Other Variable OPEX

Nutrients

CO2
67 

larger size), the results presented in Figure 13 provide quantitative implications on MBSP for 

this important attribute. 

The 2-acre pond cases, while based on today’s standard commercially available designs and 

demonstrated operability, are too costly to support cost viability for algal biomass production 

(particularly when focused on conversion of the biomass to commodity fuel products), at an 

average MBSP cost of $122/ton higher than the average cost for the 10-acre designs. 

Alternatively, the large 50-acre pond designs enable even lower MBSP costs than the 10-acre 

designs considered, at an average of $85/ton lower than the 10-acre averages. However, the 

improvements become limited by diminishing returns, at an average 17% cost reduction 

associated with a fivefold pond size increase. Given the fact that such a large size for a single 

pond drastically exceeds the largest ponds currently constructed and operating today, the 50-acre 

pond designs are viewed more as example scenarios to further quantify economy of scale trends 

than to conclude that such a design is “the best” or most optimum configuration to target without 

supporting operational data. Consequently, the 10-acre pond designs are projected here to be the 

most optimum practical size to target for construction and demonstration by 2022, with an 

average MBSP of $491/ton algal biomass across the four given 10-acre pond configurations. As 

noted previously, the practicality of ponds as large as 10 acres is contingent on the development 

of highly robust algal strains resistant to contamination and culture crash events, which would be 

much more detrimental on system yields and costs in a single 10 acre pond than a 2 acre pond 

(i.e. five-fold higher loss in biomass present in a given pond). 

Beyond cultivation system cost allocations to MBSP, varying between $172–$261/ton for the 10-

acre pond designs, the next largest cost drivers are CO2 ($91/ton), fixed operating costs ($60–

66/ton) driven primarily by labor costs, which also somewhat follow economy of scale trends 

based on the total number of individual ponds that must be operated and serviced in the facility, 

and dewatering at $53/ton. Sensitivities to all three of these parameters are investigated in the 

next section.
68 

6 Analysis and Discussion

6.1 Cost Sensitivity Analysis

Single-Point Sensitivity Analysis 

A single-point sensitivity analysis was performed using the variables and limits shown in Table 

19. The baseline for all variables used in the design case is described previously in this report. 

Reasonable minima and maxima for each variable were chosen to understand and quantify the 

resulting cost impact on overall MBSP, using the “base case” pond design projection based on 

the average capital costs and power demand attributed to the four 10-acre pond scenarios. Each 

variable was changed to its maximum and minimum value with all other factors held constant. 

The results of the sensitivity analysis are displayed as a tornado plot in Figure 14. 

Table 19. Assumptions Varied in the Sensitivity Analysis (baseline = base case 10-acre average)

Area Assumption Min Baseline Max

Biomass Production Annual average evaporation rate, cm/day 0.06 0.09 0.12

Paddlewheel work, kWh/ha/day 48 55 75

Cultivation area, acres 1,000 5,000 10,000

Biomass composition - HCSD HPSD

Leakage control - In-situ clay Fully lined

Seasonal variability (summer:winter) 1 3 5

Recirculation method - Gravity flow 

one direction

Pumping both 

directions

Average productivity, g/m2/day 15 25 40

Composition + productivity, g/m2/day HLSD @ 15 HCSD @ 25 HPSD @ 35

Inoculum Inoculum system design basis, summer days 

between inoculation 10 20 40 

CO2 Delivery CO2 utilization efficiency 85% 90% 95%

Co-located flue gas versus purchased CO2 Flue gas CO2 -

Dewatering Centrifuge power, kWh/m3 0.7 1.45 2.0

Membrane power, kWh/m3 0.02 0.04 0.4

Overall (combined) dewatering efficiency “net” 90.0% 99.9% -

Operating Costs Sulfur “nutrient” cost, $/lb - $0 $0.14

Phosphorus recycle a - 0% 50%

Nitrogen recycle a - 0% 90%

CO2 recycle a - 0% 30%

CO2 price, $/tonne $0 $45 $100

Power cost, $/kWh - $0.068 $0.100

Financial/Other Labor costs -50% 0% +50%

Dewatering CAPEX -50% 0% +50%

On-stream factor, days/year 300 330 365

Pond CAPEX, million dollars $124MM $159MM $197MM

Total capital investment (TCI) -25% 0% +25% a Recycle of N, P, and CO2 is not considered in the model base case as it is intended to be given credit on the 

downstream processing side for biomass conversion. Parameters are included here in sensitivity analysis strictly for 

purposes of demonstrating economic benefit for conversion pathways that allow for nutrient/CO2 recovery.

As shown in Figure 14, cultivation productivity exhibits the strongest cost driver on MBSP of all 

parameters considered, particularly if achievable productivity were lower than 25 g/m2

/day 

(annual average). Both the strong sensitivity to productivity in general and the trend for 

diminishing economic returns between 15 and 25–30 g/m2/day versus 25–30 and 40–45 g/m2/day 
69 

are consistent with trends shown in prior harmonization efforts [23,42] and reiterated here in 

Figure 16; namely that costs reduce dramatically between an initial benchmark productivity near 

15 g/m2/day (representing today’s estimated “state of technology” performance) to roughly 25–

30 g/m2/day, at which point further cost reductions begin reaching asymptotic limits between 30–

50 g/m2/day. In this case, if productivity could be further increased from an annual average of 25 

to 35 g/m2/day (40% improvement), MBSP could be further reduced by roughly $90/ton. 

Although such an improvement is still significant relative to most other sensitivity parameters, it 

is much less dramatic than a $220/ton MBSP penalty incurred for a 40% reduction in 

productivity to 15 g/m2/day, dictated by the fact that ponds are costed on a dollar-per-acre basis 

and do not scale with biomass productivity; thus, particularly when productivity is low, the 

“capital utilization efficiency” of the ponds is poor. Thus, it is critical when projecting future 

targets that annual average productivity increase to at least 25-30 g/m2

/day, both from an 

economic standpoint as well as in reaching a more “stable”/less sensitive (uncertain) portion of 

the curve in setting TEA cost estimates.

The second line in Figure 14 attempts to investigate the combination of both productivity and 

biomass composition at harvest. As discussed in Section 2.3 and shown in Table 2, relative to the 

mid-harvest Scenedesmus (HCSD) strain selected for use in the base case model, the biomass N 

and P demands are higher for early-harvest biomass (HPSD), as required to keep the biomass 

nutrient-replete in the active growth phase. If such a higher nutrient supply for HPSD biomass 

hypothetically enabled a 40% productivity improvement to 35 g/m2

/day relative to the HCSD 

base case at 25 g/m2/day, any MBSP reductions would be offset by an associated 4.8-fold 

increase in nutrient costs resulting in an MBSP nearly equivalent to the base case. If instead lateharvest/high-lipid biomass (HLSD) were desired but required a 40% reduction in productivity to 

15 g/m2

/day, MBSP would increase by a similar $220/ton magnitude as for the original 15 

g/m2/day sensitivity parameter investigated by itself (noted above), given that N and P content 

differences are much smaller between mid- and late-harvest biomass and thus do not play a 

significant role like they do for the difference between early- and mid-harvest biomass. These 

results are based on hypothetical differences in productivity attributed to each biomass 

composition/harvest point and require experimental data to quantify actual tradeoffs between 

nutrient loading and achievable productivity. However, if they were to follow similar variances 

in productivity as assumed here, this is an interesting result which suggests that it may not be 

“worth” strictly targeting the highest productivity possible if it requires significant nitrogen 

loading at substantial cost, relative to later-harvest biomass under mildly nutrient-deplete 

conditions (particularly given downstream dependencies on conversion yields to fuels which 

may be significantly improved, e.g., for high-carbohydrate/mid-lipid [HCSD] biomass relative to 

high-protein/low-lipid [HPSD] biomass). Additionally, it is imperative to stress that these results 

are drawn based on meeting 100% of nutrient demands with fresh makeup fertilizers, without 

any credit given for downstream recycling (which is intended to be taken on the “back end” 

conversion models to reduce final product costs). In reality, for fuel-based processes it is critical 

to achieve high rates of nitrogen and phosphorus recycle for both economic and sustainability 

reasons [23], and indeed a number of conversion pathways have been posited which may 

reasonably achieve >50% P recycle and >80% N recycle [1,2]. In such scenarios with high 

nutrient recycling, the economic effects of one biomass compositional profile (namely C:N:P 

ratio) compared to another would be significantly diminished, either for a single strain over 

multiple harvest points or for different strains altogether. For example, Figure 14 demonstrates a 
70 

credit of roughly $14/ton for 90% N recycle, if it were to be credited here on the front end to 

biomass costs instead of to fuel costs on the back end. 

Similar arguments apply as discussed above for the “productivity + composition” parameter as 

for the “biomass composition” parameter alone in Figure 14 (7th line from the top of the plot), 

which shows a nearly $80/ton increase in MBSP in going from the HCSD basis to the highnutrient HPSD biomass, when considering economic implications for biomass compositional 

changes in isolation without considerations for productivity tradeoffs. The MBSP for HLSD 

biomass is similar (actually marginally higher) than for the HCSD case, again when isolating the 

focus only to compositional changes and associated nutrient costs, because N and P levels 

remain similar to HCSD, but carbon content is further increased (due to the higher lipid content) 

and thus CO2 costs are higher for the HLSD case. However again, the same caveat applies that 

the magnitude of the impacts would be considerably diminished for fully integrated processes 

which enable high N and P nutrient recycling. More details on compositional impacts to MBSP, 

for both the base case Scenedesmus strain and for two alternative strains, are provided in the 

following section. 

Beyond productivity considerations, the strongest sensitivity attributed to system costs is the 

method employed for pond leakage control. As discussed above, the basic assumptions for all 

eight pond scenarios stipulate the use of in-situ clay soil to mitigate percolation issues, with the 

use of plastic pond liners only on small portions of the ponds (typically either channel berms or 

pond turns, depending on the individual pond design) as required for erosion control. If instead 

ponds were fully lined across the full 5,000 acres of cultivation, the MBSP would increase 

substantially by $126/ton for the 10-acre average base case. Furthermore, this assumes the liner 

does not need to be replaced within the 30-year facility lifetime, beyond standard maintenance 

costs; if full liner replacement were required, this would add another $126/ton. This reiterates the 

point that achieving low-cost algal biomass and biofuels depends strongly on siting the facility in 

a location with sufficiently high clay soil, and on any applicable regulatory policies that allow for 

the use of unlined ponds. The individual MBSP results for each discrete pond design based on 

fully lined ponds are shown in Figure 15. 

Next, CO2 price also is shown to carry significant impact, with an MBSP increase of $111/ton 

associated with a CO2 price of $100/metric tonne representing an upper range of projected CO2

costs for carbon capture technologies [72,71]. Alternatively, MBSP would reduce substantially 

by $91/ton if high-purity CO2 were available at no cost (aside from costs still included for on-site 

storage and distribution). A limited number of such opportunities may exist for example by colocation with ethanol, ammonia, or natural gas processing facilities. As an alternative to purified 

CO2, pipeline transport and delivery of bulk flue gas from a nearby power plant were also 

considered, which may be viewed as “free” for the CO2 itself but requires substantial costs for 

large-diameter pipelines for gas transportation both off site and on site. This scenario is 

discussed in more detail in the next section, given its importance on both costs and ramifications 

on the power plant. In summary, a co-located flue gas scenario appears to offer the potential to 

reduce MBSP by roughly $44/ton relative to concentrated CO2, however the logistics for a flue 

gas scenario are very challenging and raise questions as to the practicality of this scenario for 

such a large facility size.
71 

Algal retention efficiencies across the dewatering steps were next investigated on a “net” 

efficiency basis. Here, the net retention represents the overall fraction of biomass produced from 

the cultivation ponds, which is ultimately recovered in the final dewatered product stream and 

available for downstream conversion. In the base case, this is very high at 99.9% with the only 

loss from the system occurring in the blowdown stream removed from the primary settler 

clarified water recycle. If this loss were increased to 10% (90% net retention), whether through 

increased blowdown or otherwise routing a fraction of the clarified water streams from 

dewatering away from the ponds (for example, to downstream anaerobic digestion in the 

conversion facility as was done in the 2012 harmonization model [23]), MBSP would increase 

by $107/ton. Note that the “gross” dewatering efficiency is considerably lower, as the raw 

product of the three individual dewatering steps (90×99.5×97% = 87%). However, variances in 

individual retention efficiencies and therefore gross dewatering efficiency carry little economic 

impact assuming high recycle of clarified effluent streams and resultant net efficiency. 

The final sensitivity parameter worth mentioning is the facility size based on wetted cultivation 

acreage. Beyond the economy of scale implications for individual pond size and configuration 

discussed previously, we also investigated how changing the assumed overall facility size 

impacts MBSP. For this parameter, the same 100-acre module layout for pond groupings was 

maintained, but total number of modules were either increased or decreased, which carries 

implications on circulation piping and pumping costs across the full facility, as well as total flow

rates that the dewatering operations must accommodate. Figure 14 shows that if total facility 

cultivation footprint is doubled from 5,000 to 10,000 acres, there may be a fairly marginal 

savings in MBSP of roughly $16/ton. However, if the size is reduced to 1,000 acres, MBSP costs 

increase more substantially by $102/ton, driven by economy of scale losses for dewatering 

equipment (mainly central dewatering, as primary gravity settler dewatering scales linearly as 

individual module count is changed). The remaining sensitivity parameters are largely selfexplanatory.
72 

Figure 14. Tornado plot presenting results of the single-point sensitivity analysis on MBSP cost 

($491/ton reference case)
73 

Figure 15. MBSP results for alternative scenario based on fully lined ponds.

Figure 16. Scan of MBSP vs. Productivity for the Base Case (10-acre average pond costs)

$667

$813

$537

$651 $644 $635 $617 $584 $552

$0

$100

$200

$300

$400

$500

$600

$700

$800

$900

Algal biomass selling price ($/ton AFDW)

OSBL

Dewatering

Full Pond Liners

Ponds + Inoculum

Fixed OPEX Costs

Other Variable OPEX

Nutrients

CO2

$300

$400

$500

$600

$700

$800

$900

10 20 30 40 50

Algal biomass selling price ($/ton AFDW)

Productivity (g/m2/day)
74 

Alternative Scenarios

In addition to the single-point sensitivity analysis considered above, a number of additional 

alternative scenarios were also evaluated, which either do not fit with the tornado plot format or 

otherwise warrant further discussion and context. These additional scenarios are presented here, 

and include: (1) replacing purified CO2 with bulk flue gas (expanding on the single-point 

analysis discussed briefly above), (2) considering two alternative strains and biomass 

compositions for their impacts on MBSP, and (3) evaluating alternative dewatering options 

beyond the combination of the three operations utilized for the base case.

Flue Gas CO2 Sourcing

We first present a more detailed discussion related to the option to utilize bulk flue gas in the 

modeled pond facility. A key benefit of algae cultivation is its potential for capture and reuse of 

CO2 from point emitters including power plants. Indeed, the baseline CO2 cost of $45/metric 

tonne discussed in Section 4.3.3 is derived from cost estimates of flue gas CO2 separation, 

compression, and transportation at pulverized coal power plants. Likewise, the CO2 distribution 

system described previously assumes pure CO2 is delivered to the facility under pressure. Direct 

feeding of flue gas to algae ponds, on the other hand, is a commonly proposed design alternative. 

This section examines direct flue gas feed and its associated techno-economic challenges.

To first compute the volume of flue gas required, a stoichiometric carbon balance of the algal 

culture indicates that the steady-state, summer CO2 demand of the production ponds in this 

report is approximately 1,440 tonne/day. In the base case for pure CO2, uptake and utilization 

was assumed to be 90%, with CO2 sparged into deep sumps in each individual pond. Due to the 

relatively low CO2 concentration in flue gas, outgassing losses are typically set to 15%–25% for 

sparging low-pressure bulk flue gas (with significant levels of nitrogen) directly into pond sumps 

[69,70]. If we therefore conservatively assume 75% CO2 uptake from directly sparged flue gas, 

the summer CO2 requirement is 1,920 tonne/day or 43,630 kmol/day. For a typical 500 MW 

coal-fired power plant producing 0.95 tonne CO2 /MWh [106], this is equivalent to 16% of the 

plant’s total CO2 production. The flue gas composition was taken to be (vol%): 13.47% CO2, 

2.38% O2, 15.5% H2O, 0.8% Ar, and 67.85% N2. The water content of this mixture represents 

saturation at atmospheric pressure and 55°C (131°F), typical stack conditions of coal flue gas 

following desulfurization [72]. The total peak flue gas requirement for the algal culture is 

therefore 324,000 kmol/day. While the majority of the facility, including harvest from ponds 

through dewatering, operates on a 24-hour-per-day basis, as the culture itself is only growing and 

utilizing CO2 during daylight hours, the flue gas delivery equipment must be designed to deliver 

the full daily amount in 12 hours, a rate of 27,000 kmol/h. At stack conditions, this is a total gas 

volume of 815,000 actual m3/h (481,000 ACFM).

At such a large volume, pipeline delivery from a power plant to the facility over any significant 

distance is infeasible. Using Aspen HYSYS and Aspen Process Economic Analyzer, we obtained 

a rough CAPEX estimate of $135MM (installed) for a three-stage centrifugal compressor system 

to raise the flue gas to 200 psia (13.6 atm). At this pressure, the compressed flue gas can be 

delivered up to 15 km (roughly 9 miles) in a 36-inch pipe before choking; the pipeline adds 

another $15MM CAPEX. The instantaneous power demand for this compressor is 80 MW. 

Although flue gas delivery only takes place for half of the day, electrically-connected equipment 

of this scale cannot be simply powered up and down on a daily basis. In practice, the compressor 
75 

would continue to run overnight to maintain pressure in the pipeline; we estimated a daily 

average of 75 MW. It must be stressed that at 0.95 tonne CO2/MWh, this is more power than is

generated along with the 1,440 tonne/day of CO2 actually being utilized (63MW). Furthermore, 

assuming this power demand and a 13% annual capital charge (consistent with the standard 

DCFROR methods), the cost of CO2 delivered over the relatively short distance of 15 km is 

$49/tonne, or 10% larger than the baseline $45/tonne assumption for pure CO2. Economically 

and energetically, pressurized flue gas delivery is not a competitive alternative to CO2 separation

over any significant distance. 

If flue gas cannot be economically transported any significant distance by pipeline, then direct 

flue gas feed requires that the algae facility be co-located with the power plant. To that end, we 

considered a flue gas distribution system to replace the pure CO2 distribution system described 

earlier, using large-diameter HDPE pipes and induced-draft fans. The flue gas was assumed to be 

available at the saturated conditions described above, in the same location in the facility as the 

dewatering section. HDPE was chosen primarily for corrosion resistance. As noted above, the 

flue gas is saturated with water vapor at 55°C. As all of the piping runs are several kilometers 

long, water will condense from the flue gas as it cools. Condensate from flue gas is acidic due to 

dissolved CO2 and will damage steel pipe and ducts over time if not mitigated.

Figure 17 shows the layout of flue gas piping and fans. Piping was sized at either 60 inches or 48 

inches, depending on flow. It was impractical to combine the gas flow to the more distant 

branches in a single pipe (as was done for pure CO2 distribution), because the diameter required 

was prohibitive. Each fan was assumed to have an outlet pressure of 15 inches of water gauge 

(INWG). Fans were spaced along the runs to boost gas flow where the pressure approached zero, 

however again as noted previously the realistic constraints imposed by power distribution and 

availability at any given location in the facility could preclude placing fans in these specific 

locations along the runs. Centrifugal blowers connected to the headers serve each 100-acre 

module to ensure sufficient pressure to deliver flue gas to the spargers in each pond. Each 

blower’s outlet pressure was 82 INWG (3 psig). 

Figure 17. Layout of flue gas piping and fans for the 50-module system

Flue gas 

source

60"

60"

60"

48"

Centrif. Blower

ID Fan
76 

Cost estimates for the HDPE piping runs, fans, and blowers were developed in ACCE. The 

installed capital cost for the system shown in Figure 16 is roughly $52MM, more than 8 times

the capital cost of the baseline pure CO2 distribution costs. The combined annual average power 

draw for the fans and blowers is 7,100 kW. For TEA purposes, we assumed this instantaneous 

power demand would only be drawn for half of each day. After removing the costs for pure CO2

and its distribution capital from the base case, the resultant biomass cost was approximately 

$447/ton (shown previously in Figure 14).

As a TEA exercise, direct feed of power plant flue gas to the algae culture appears to be a viable 

alternative to the baseline of pure CO2 feed, as it has the potential to reduce the most significant 

material operating cost essentially to zero (excluding consideration of power costs for either 

scenario). However, we have demonstrated that compression of whole flue gas at 13%–14% CO2

into a reasonably sized pipeline, even for short distances, is infeasible as it can require more 

electricity to deliver a given amount of flue gas CO2 than was generated with that CO2 in the first 

place. We further demonstrated that a plant-adjacent co-located algae facility can work, but in 

reality the practicality of this scenario is more questionable given the requirement to find a 

suitable area with such a large available footprint for the combined facility (and particularly so 

for numerous such facilities as would be required to meet a national scale fuel production rate of 

5 billion gallons per year, as was considered in prior harmonization efforts [23,42]). Flue gas 

delivery in a co-located facility is also significantly more capital-intensive than pure CO2 feed, 

which is a disadvantage from a capital utilization standpoint, as the delivery system is only used 

for half the day. Considering the robust field of flue gas CO2 capture research, and DOE’s 

interest in the topic, pure CO2 feed is the more likely practical scenario for the foreseeable future 

at least for a large commercial facility near the size considered here. Other alternatives also exist, 

for example a system that GAI employs noted previously which is based on injecting flue gas 

CO2 into a closed carbonation system consisting of an absorption scrubber located on a 

circulation loop external to the pond; GAI indicated favorable operating performance for this 

system, including high CO2 retention efficiencies (with the inclusion of bicarbonate to regulate 

pond alkalinity) and lower/more favorable results for both CO2 costs and LCA profile attributed 

to this method for CO2 delivery than the pure CO2 results presented here [61]. Such a design is 

plausible here as well, but would be dependent on numerous factors including water 

chemistry/alkalinity, biomass growth rates versus circulation rates, and overall size/number of 

ponds a single carbonation station serves. 

Alternative Strains and Compositions 

As described in Section 2.3, the strain and compositional details selected for use in the base case 

model was based on Scenedesmus biomass harvested under mildly deplete nutrient conditions at 

ASU and subjected to thorough compositional analysis at NREL. This strain and compositional 

profile was selected to (1) remain as agnostic as possible to the downstream conversion pathway, 

with both component and elemental compositions available to a high degree of mass closure for 

use in downstream conversion models, (2) set a reasonable lipid content (27 wt%) that is not 

overly-aggressive to justify the concomitant productivity targets projected in the model (25 

g/m2

/day AFDW annual average), and (3) make use of a strain with commercial relevance and 

application. Beyond the mid-harvest, high-carbohydrate/mid-lipid Scenedesmus (HCSD) 

biomass considered in the base case, two other strains also have been analyzed over a similar 

harvesting regime and varying states of nutrient depletion, including a freshwater Chlorella and a 

saline Nannochloropsis strain. These additional strain/composition scenarios were also 
77 

considered in the model for their impact on MBSP, primarily through differences in nutrient 

costs dictated by biomass elemental composition (see Table 2), but also to enable consideration 

of a saline scenario for the Nannochloropsis case. For all strains and compositions considered 

here, seasonality effects were maintained with seasonal biomass productivities held constant as 

described in Section 4.1.2; downstream dewatering performance and cost assumptions were also 

left unchanged, but it is noted that in reality the efficacy of any given dewatering operation can 

be highly strain-dependent [79,107,108]. Thus, to better inform this scenario analysis, 

experimental data is needed for both biomass productivity tied to compositional analysis, as well 

as dewatering performance conducted in an integrated process for a range of strains. 

A total of eight strain/composition scenarios were run through the biomass production model 

beyond the HCSD base case, with results shown in Figure 18. All strain details and identifying 

acronyms are shown in Table 2 (Section 2.3), but in summary, “HP,” “HC,” and “HL” denote 

high-protein (early harvest/high-nitrogen), high-carbohydrate (mid-harvest/nitrogen limited), and 

high-lipid (late-harvest/nitrogen deficient) harvesting regimes, respectively, according to the 

original protocols for growing and harvesting biomass employed at ASU, while “SD,” “CZ,” and 

“NC” denote Scenedesmus acutus (LRB-AP 0401), Chlorella vulgaris (LRB-AZ 1201), and

Nannochloropsis granulata, respectively. Requirements for CO2, ammonia, and DAP were set 

following the same approach as discussed for the base case model, based on a 20% excess of the 

stoichiometric N and P demands for the given biomass composition at harvest, and 

stoichiometric C demands (plus additional CO2 to account for retention efficiency losses). 

Blowdown splits were left unchanged from the base case model for both the SD and CZ 

freshwater cases, in all cases maintaining circulation salt content below 4,000 mg/L with an 

incoming salt content of 250 mg/L in the makeup freshwater. The blowdown for the NC case 

was adjusted given both higher incoming salt content of the makeup saline/brackish water (7,700 

mg/L) and salt tolerance of the NC strain (up to 34,000 mg/L) based on typical values employed 

in PNNL’s Resource Assessment model for Nannochloropsis grown in the general Gulf Coast 

region [109]. The high salt concentration of the blowdown streams for the saline 

Nannochloropsis case incurs an additional cost for salt/brine disposal. The brine disposal cost 

was set at $2.64/m3 associated with brine deep well injection [110]. This disposal cost translates 

to a $32/ton increase in MBSP for the Nannochloropsis cases, which is a non-trivial cost penalty 

and further supports the choice of a freshwater base case (if the facility were nearby a coast such 

a disposal cost may not be required). The off-site makeup saline water delivery assumptions for 

the NC case were left unchanged relative to the freshwater cases (i.e. 108 m total head for 

bringing makeup water to the facility from a nearby resource).

As noted in the previous section for the single-point sensitivity analysis, the given SD biomass 

composition translates to a considerably higher MBSP for the early-harvest/high-protein case, 

given a nearly fivefold higher cost for NH3 and DAP nutrients relative to the mid-harvest HCSD 

basis (again noting the important caveat that this is before accounting for any potential nutrient 

recycles from downstream). On the other hand, late-harvest HLSD biomass results in a nearly 

identical MBSP (in fact marginally higher) as the amount of savings in N/P nutrients is much 

smaller, which is offset by a higher cost for CO2 given a 6% higher carbon content for HLSD 

relative to HCSD. Thus, purely based on considerations of nutrient loading tradeoffs associated 

with maintaining a culture in rapid growth phase (N-replete) versus lipid accumulation phases 

(N-limited or N-deficient), the HCSD basis appears to offer an optimum. This may or may not be 

the case when also considering the associated implications on the biomass productivity rate for 
78 

these scenarios, as discussed in the single-point analysis above. The trends for the Chlorella

biomass mirror those of the Scenedesmus strain across the various compositional profiles, but 

shifted up between $2–$8/ton for any given compositional basis. The Nannochloropsis results 

are somewhat different than either of the first two cases, with costs increasing in order of HL, 

HC, and HP compositions, given a more dramatic decrease in N and P composition moving from 

the HC to HL scenarios, combined with a large reduction in ash content, which is much higher in 

general for the Nannochloropsis biomass (being a saline strain) than for either of the freshwater 

cases. The ash content is not assumed to detrimentally impact process performance for any of the 

facility operations, but it does increase total throughputs and thereby costs, particularly as 

biomass AFDW solids content begins to increase in the later dewatering steps. There was not a 

noticeable impact on MBSP attributed to dramatic differences in blowdown removal, as the 

blowdown fraction did not need to be substantially adjusted given the higher salinity tolerance of 

the strain. The HCNC basis result for the mid-harvest Nannochloropsis is estimated to increase 

MBSP by $67/ton relative to the HCSD baseline for Scenedesmus. While these results are 

insightful, they would benefit further from experimental data for cultivation productivity 

attributed to any of the given compositional scenarios. Furthermore, again as noted previously, if 

downstream conversion processing operations allowed for a high degree of N and P recycle in a 

fully integrated facility, the nutrient cost penalties for HP vs HC compositions or for NC vs SD 

strains would be diminished (although the general comparative trends would still be applicable). 

Figure 18. Modeled MBSP for three strains across three growth/harvesting regimes. (SD = 

Scenedesmus (freshwater), CZ = Chlorella (freshwater), NC = Nannochloropsis (saline); HP, HC, and HL 

represent early-harvest/high-protein, mid-harvest/high-carbohydrate, and late-harvest/high-lipid biomass, 

respectively, based on original growth conditions used to generate biomass for analytical 

characterization. See Section 2.3, Table 2. Base case reference points are represented by HC cases; 

MBSP values are $491/ton, $494/ton, and $558/ton for HCSD, HCCZ, and HCNC, respectively).

Alternative Dewatering Scenarios

Beyond the baseline dewatering configuration utilized for the base case, three alternative 

dewatering strategies were also evaluated for cost implications on MBSP. These alternative 

scenarios include: (1) replacing the secondary dewatering step utilizing membranes with a 

dissolved air flotation (DAF) system employing chitosan flocculant, (2) replacing the membranes 

HP

HP HP

HC HC

HC

HL HL

HL

$470

$490

$510

$530

$550

$570

$590

SD CZ NC

MBSP ($/ton AFDW Algae)
79

with electrocoagulation technology, and (3) replacing the membranes and centrifuge (second and 

third dewatering steps, respectively) with a belt filter press. A more detailed explanation of each 

alternative scenario and its process design and cost assumptions is presented is Section 4.5. For 

both the base case dewatering system and the alternative scenarios, a number of single-point 

sensitivities were performed on key parameters to capture the range of variability for each 

parameter as presented in literature. The results are displayed in Figure 19. 

Figure 19. MBSP implications for alternative dewatering scenarios

First, the base case dewatering assumptions were examined with respect to settling time as 

required for the first-stage gravity settling step and for the power demand required for the 

second-stage membrane step. Settling time in primary settlers can vary significantly depending 

on factors such as algal species and settler design. The baseline value for settling time was 

assumed at 4 hours, based on feedback from MicroBio [25] who supported 4–6 hours as being 

reasonable for simplistic in-ground gravity settlers based on their operating experience with these 

units. Additionally, large-scale trials have demonstrated settling velocities of 1 m/hr [43], which

supports settling times of 4–6 hours for the 15-foot deep settler design. The high sensitivity value 

of 6 hours considered here represents a settling velocity of slightly less than 1 m/hr, while the 

low sensitivity value of 2 hours would represent an optimistic settling time that is likely 

achievable only using a shallower design. The results of the sensitivity study on settling time 

$300

$350

$400

$450

$500

$550

$600

$650

$700

$750

$800

Base Case (Membranes)

Settling Time, hrs

(2 : 4 : 6)

Membrane Power, kWhr/m3

(0.02 : 0.04 : 0.4)

Centrifuge

(No : Yes)

DAF Scenario

Flocculant cost, $/kg

(12 : 18 : 36)

Flocculant Loading, mg/L

(10 : 40 : 150)

Electrocoagulation Scenario

EC Capacity, m3/hr

(36 : 18 : 9)

Filter Press scenario

Filter Press Capacity, m3/hr

(400 : 200 : 100)

Floculant

(No : Yes)

Algal biomass selling price ($/ton AFDW)

$493

$474

$553

$493

$490

$499

$483 $474

$537

$469

$482

$486

$503

$503

$737

$531

$620

$484

$491 $491
80

indicate a relatively small impact on MBSP, with the total MBSP range limited to $16/ton 

between 2–6 hours. The power required to operate the base case membrane system also was 

examined. GAI has demonstrated an operational power demand for this unit of 0.04 kWh/m3 of 

feed to the membranes, and has subsequently improved on this result further with an expected 

“best case” power demand of 0.02 kWh/m3 [61] (set as the low sensitivity point here). However, 

such values are considerably lower than those reported elsewhere, as in Bilad et al. [77], which 

estimates the power consumption for this operation to be roughly an order of magnitude higher, 

therefore the high sensitivity value was set to 0.4 kWh/m3. While this may be expected to carry 

larger implications on overall facility power demand and associated sustainability metrics, the 

resulting impact to MBSP is marginal with only a $3/ton difference between the high- and lowpower estimates. A final “aspirational” sensitivity assumed that the membranes are capable of 

achieving 20% solids, compared to the baseline case of 13%, thereby eliminating the centrifuges 

altogether (supported by feedback from GAI who indicated further optimization allowing for 

outlet concentrations beyond 13%). This scenario would result in a cost savings of $7/ton. 

Relative to the use of hollow fiber membranes for secondary dewatering, two of the three 

alternative dewatering options resulted in similar MBSP estimates while the third was noticeably 

higher. Namely, the DAF scenario is the most expensive of the options considered, primarily as a 

result of high operating costs due to flocculant requirements as assumed for the basis DAF 

design. This translates to an estimated MBSP roughly $60/ton higher than the membrane base 

case. The electrocoagulation alternative to DAF or membranes as a secondary dewatering step 

translates to a similar MBSP at $3/ton above the membrane basis. This is primarily due to high 

capital cost per unit volume processed for this operation. While this technology has recently 

gained in attention and research focus as a promising candidate for algal biomass dewatering 

(this was considered as a leading candidate by the National Alliance for Advanced Biofuels and 

Bioproducts (NAABB) consortium [51]), performance data for this unit is still lacking, 

particularly as may be required to support projecting targets for the technology out to 2022 for 

large commercial-scale operations. The filter press option results in a marginally lower MBSP 

estimate by $17/ton relative to the membrane plus centrifuge base case, which is within the 

margin of uncertainty, and it also does not have a lengthy history (as supported by literature) 

specific to processing algae as much as other options, thus the reason it was restricted to 

consideration as an alternative scenario early on in the work. This operation would benefit from 

additional experimental validation to support its efficacy and cost potential for the use of algal 

biomass dewatering. 

The DAF scenario was further evaluated for MBSP implications attributed to both cost and 

loading of flocculant, given considerable ranges for either parameter based on public 

information. The use of chitosan is maintained as the flocculant material (consistent with prior 

harmonization modeling efforts) as discussed previously in Section 4.5, primarily in an attempt 

to remain agnostic toward downstream processing operations or product/coproduct specification 

issues, which could become challenged with the use of an inorganic flocculant such as alum. 

Chitosan costs were set based on information from commercial vendors [86]. The value for low, 

baseline, and high chitosan costs are $12, $18, and $36 per kg, respectively. Over this price 

range (which is wide enough that it also may be viewed as representative for flocculant costs in 

general), MBSP costs are impacted significantly with a $89/ton range in MBSP between the lowprice and high-price estimates. Required flocculant loading is also an operating parameter that 

can vary based on algal species and cell concentration [82]. Optimal chitosan dosage, 
81

specifically, was seen to vary widely between 2 to 200 mg/L in one study, dependent on the algal 

species [84]. Dosages of 2 and 200 mg/L are otherwise at the far fringes of the spectrum for what 

would be reasonable, therefore low and high values for chitosan dosage were adjusted to 10 and 

150 mg/L, respectively. The baseline value of 40 mg/L was reported in Heasman et al. [83]. As 

can be seen in Figure 19, flocculant loading has a significant impact on MBSP, more so than all 

other dewatering sensitivities. Increasing chitosan loading from 40 to 150 mg/L increases the 

MBSP by $184, while reducing it to 10 mg/L decreases MBSP by $22. This carries significance 

both for the use of DAF (which normally requires a flocculant to operate with good 

performance), but also for any other dewatering technique that may require flocculant usage, 

with the primary point being that flocculants are costly and their use should be minimized as 

much as possible, particularly for early operations with very low solids.

Neither electrocoagulation nor filter press technologies have been proven for dewatering algae at 

demonstration-scale for extended trials, and consequently the processing capacity of either 

option is relatively uncertain for a commercial scale model such as this. Estimating capacity 

improvements that may be plausible in the future is difficult, but conversations with equipment 

vendors provided information necessary to make initial estimates. Filter presses often employ a 

dewatering table as an inexpensive “pre-dewatering step” prior to the filter press. The dewatering 

table can concentrate the slurry by a factor of 3–5, although no research on dewatering tables 

used for algae was found in the literature. Nevertheless, a dewatering table followed by a filter 

press provides the potential to significantly increase capacity versus a filter press alone, while 

adding little in capital cost, therefore the high capacity case for the filter press sensitivity was set 

to 120 m3

/hr, 200% of the baseline capacity of 40 m3/hr. There are opportunities to reduce the 

cost of electrocoagulation technology, but a 200% increase in capacity for the same capital cost 

is likely overly optimistic for this case, therefore the high-capacity case for electrocoagulation 

was set at 36 m3/hr, 100% greater than the baseline capacity of 18 m3/hr. The low-capacity case 

for both the filter press and electrocoagulation scenarios was set to 50% of baseline capacities. 

The resulting impact on MBSP tied to processing capacity is relatively minor, at $13/ton for the 

filter press and $18/ton for electrocoagulation. A final sensitivity considers the addition of 

flocculant for the filter press operation. Filter presses often employ flocculant to enhance 

separation, therefore the filter press scenario was also evaluated with the use of chitosan at the 

same cost and dosage levels assumed in the DAF scenario. Adding chitosan flocculant to the 

filter press operation increased MBSP by $64/ton. 

To summarize, the dewatering sensitivity analysis supports that membranes offer a cost-effective 

strategy for the important secondary dewatering step (moving between low-cost but still lowconcentration gravity settling and third-stage centrifugation, which is inexpensive if the initial 

concentration is around 10%), and membrane dewatering efficacy has also been proven at large

scale over sustained operations. Filter presses offer potential as well, but require further 

experimental investigation and validation to support their use specific to algal processing. Of all 

parameters considered, flocculant loading and cost exhibit much stronger drivers on MBSP than 

other variables, if their use is required (e.g., for DAF or otherwise). Assuming that flocculants 

are not used, dewatering operations do have room for improvement and certainly have more 

room for large-scale experimental validation across multiple strains, but do not appear to offer 

potential cost reductions of the same magnitude as the production pond area. 
82

6.2 Sustainability Metrics for Base Model

Following standard practice for recent design reports, here we provide an estimate of life-cycle 

resource consumption and environmental emissions. LCA provides a framework from which the

environmental sustainability of a given process may be quantified and assessed. This section 

presents the sustainability metrics of the current conceptual process across the feedstock 

production and dewatering stages, with a focus on the greenhouse gas, fossil energy, and 

consumptive water use profiles for the modeled process. Although sustainability metrics are 

presented here in keeping with other recent design report practices for cellulosic feedstock 

pathways [44], it is imperative to note that the results presented here are strictly confined to the 

upstream cultivation and dewatering steps of the process, which is otherwise inherently 

integrated with downstream algal biomass conversion operations (e.g., ALU, HTL, or other 

processing configurations). Although it is reasonable to consider sustainability metrics for the 

feedstock and the conversion stages independently for terrestrial biomass pathways, algal 

processes are more inter-dependent between feedstock production and logistics operations 

(cultivation and dewatering) and downstream conversion steps, including numerous recycles and 

power integration across the process boundaries. As such, presentation of sustainability metrics 

attributed to only the cultivation and dewatering stage for algal processes do not carry as much 

meaning as for a fully integrated facility and pose a danger of being misinterpreted, particularly 

given the possibility for a high degree of CO2 and nutrient recycles from back-end conversion 

steps which must be accounted for in the associated conversion biorefinery LCA, if not reflected 

here. A complete LCA of the fully integrated process, incorporating the details from this model 

as well as pertinent downstream operations, is required to better understand and quantify the 

complete sustainability profile of this technology pathway; this is the subject of planned and 

ongoing investigation with partners at ANL, who coordinate “official” LCA models for algal 

processing pathways using GREET modeling tools under the BETO platform [111]. Therefore, 

the results presented here represent preliminary estimates of the sustainability metrics attributed 

to the modeled algal biomass facility, but may be superceded in the future with ANL GREET 

models. 

Facility input and output streams, water consumption, and other process-related metrics were 

derived from the algal biomass production process model described above. SimaPro v.8.0.2 

software [112] was used to develop and link units quantifying life-cycle impacts as previously 

documented by Hsu et al. [113]. Ecoinvent v.2.2 processes were used to fill the data gaps and 

modified to reflect U.S. conditions [114]. The material and energy flows of the cultivation and 

inoculation steps capture the impacts of input raw materials and outputs, such as air emissions 

and water loss predicted by the process model, as shown in Table 20. This life-cycle inventory 

(LCI) table and subsequent discussion of sustainability metrics considers the base case (average 

of the four 10-acre pond designs) for the HCSD biomass basis, including use of the average

pond circulation power demand across the four 10-acre designs (55 kWh/ha per 24-hour day).

Additionally, the LCI data presented in Table 20 are translated to an annual average daily basis; 

the daily values shown here (such as tonne/day) do not reflect actual daily rates for any season of 

the year, but rather are the average of the rates across all four seasons.
83

Table 20. Input and Output Data for Modeled Production Facility (10-acre average base case).

(Note: Daily rates shown below are based on annual averages over all modeled seasons.)

Products

Annual Average Rates, 

tonne/day

Algal biomass (AFDW) a 516

Algal biomass (total including ash) 528

Water in biomass product stream 2,082

Resource Consumption

CO2 (counted as biogenic in origin) 1,148

Ammonia 10

DAP 5

Total process water input b 26,790

Electricity demand, kWh/day c 234,084

Output Streams

Water lost to blowdown 6,272

Algae lost in blowdown 0.33

Air Emissions

Water lost to evaporation 18,060

CO2 outgassing from ponds (counted as biogenic) 114

O2 from ponds 890 a Final product rate after 1% loss assumed for biomass degradation in storage. b Total water input, including the amount contained in the biomass product stream sent to conversion (in 

many cases, a large fraction of this water is ultimately recycled back to ponds from downstream 

conversion steps); water “loss” from the system is 24,331 tonne/day (evaporation plus blowdown). c Based on average circulation power demand attributed to all four 10-acre pond designs; facility power 

demand for the individual 10-acre pond scenarios is 212,490 kWh/day for GAI, 219,700 kWh/day for 

MicroBio, 240,100 kWh/day for Harris, and 286,390 kWh/day for Leidos. Power demand shown here is 

for ISBL power only and does not include the power consumption implicit in the CO2 delivered from offsite flue gas carbon capture (this is accounted for separately in SimaPro under captured CO2).

Details on contributions to greenhouse gas (GHG) emissions and fossil energy consumption for 

the modeled biomass facility are shown in Table 21, which correspond to the information in 

Table 20. Fossil GHG emissions associated with the base case model are estimated to be 0.73 kg 

CO2-eq/kg biomass. Both the CO2 input and “emissions to the air” from the cultivation ponds 

(attributed to CO2 retention efficiency losses) shown in Table 20 are treated as biogenic in 

nature, following accepted methodologies for CO2 accounting in algal biofuels LCA which 

dictate that although the CO2 originates from fossil power plant flue gas, the power plant is 

operated to generate power and not to provide CO2, which otherwise would be emitted to the 

atmosphere and then later could be utilized in dilute form as biogenic CO2 for growing a 

different biomass resource [115] (this stipulation is specific to CO2 sourcing via power plant flue 

gas, and would not apply for other sources such as EOR pipeline operations sourcing fossil CO2

from underground reservoirs). Biogenic CO2 does not contribute to the increase of GHG in the 

atmosphere [116] and is not considered in the IPCC global warming methodology [117]. Hence, 

the contributions to GHG at the cultivation stage are predominantly driven by the methods used 

to capture, purify, and transport the CO2 feed in concentrated form.

In this case, the material and energy inventories representative of the carbon capture technology 

operation were based on averages from four literature sources that presented these details for 

current pulverized coal post-combustion capture processes integrated with the power plant 
84

[72,118-120]. The resulting averaged inputs for the carbon capture process were 1.78 MEA 

(monoethanolamine) and 582 MJ energy demand per metric tonne of CO2 captured, as well as an 

output represented by ammonia emissions of 147 g NH3/metric tonne CO2 captured. The 

parasitic energy demand, which accounts for additional coal burned to generate the extra steam 

and electricity for the integrated carbon capture system, was specified in SimaPro as 100% coal 

generated energy. This approach represents today’s current carbon capture technology whereas 

the proposed algal facility model assumes a second-generation carbon capture system implicit in 

the $45/tonne CO2 cost target by 2022, which could reduce the GHG penalty associated with this 

CO2 feed stream. The remaining balance represents the GHG profile associated with the 

underlying LCI processes (namely NH3 and DAP nutrient inputs), and the required ISBL process 

electricity. For the latter, the U.S. average electricity mix from the grid was applied consistently 

with the basis from Argonne National Laboratory’s GREET model software [111]; this includes 

a GHG emission factor of 0.65 kg CO2e/kWh and fossil energy consumption of 7.46 MJ/kWh.

At 0.4 kg CO2-eq /kg AFDW biomass, it is evident that indirect GHG emissions due to carbon 

capture from flue gas contributes the most to the overall GHG emissions, with the above caveat 

that this is for the use of today’s energy-intensive MEA amine carbon capture technology used as 

the basis for this factor. The second major factor is ISBL process electricity with a total GHG 

profile of 0.3 kg CO2-eq/kg biomass. Fossil energy consumption associated with the production 

facility is estimated to be 8.8 MJ/kg AFDW biomass, again largely attributed to the carbon 

capture process and facility electricity demands. Allocations for facility power demand broken 

down by process area are shown graphically in Figure 20. As noted above, were the downstream 

conversion process integrated with the upstream biomass facility modeled here, a number of 

benefits would likely be observed including (1) recycle of a fraction of CO2 anywhere between 

10%–40% (depending on downstream conversion steps and yields), which would reduce 

incoming makeup CO2 demands by a similar fraction, (2) recycle of a substantial fraction of 

nutrients on the order of 50% P and 50%–90% N (dependent on similar factors as noted for 

CO2), and (3) in some cases, the generation of a net electricity coproduct in the downstream 

conversion facility which would partially offset the power demand shown here for the biomass 

production facility [1].

Table 21. Greenhouse Gas (GHG) Emissions and Fossil Energy Consumption (FEC)

Associated with Producing 1 kg of Algal Biomass (AFDW)

GHG 

(kg/kg)

FEC 

(MJ/kg)

CO2 capture and delivery 0.38 4.4

Ammonia 0.04 0.8

DAP 0.02 0.2

Electricity (ISBL) 0.30 3.4

Total 0.73 8.8

Table 22 summarizes the key sustainability metrics for the modeled biomass production facility 

base case (10-acre average scenario). On a mass basis, the GHG emissions for the cultivation 

stage are 0.73 ton CO2e/ton biomass product produced. The net fossil energy consumption is 

7,962 MJ/ton biomass product (translated to a MJ/U.S. ton basis in this case given the focus on 

the biorefinery conversion stages typically presented in MJ/GGE at a given GGE/ton fuel yield). 

In addition to GHG emissions and fossil energy consumption discussed above, water 

consumption (i.e., net water use during the production and dewatering operations) and total 
85

annual biomass yield are reported in Table 22. The net water consumption is estimated at 12,450

gal/ton biomass, which includes water maintained with the dewatered product at 80 wt% 

moisture, evaporation from production and inoculum ponds, and water lost to blowdown. 

Roughly 8% of this consumption (970 gal/ton) is water contained in the biomass product stream, 

the majority of which may ultimately be made available for subsequent recovery and recycle

back to the ponds from downstream conversion operations [1,2]. Either way, this is similar to 

water consumption estimated during prior harmonization efforts focused on the same U.S. Gulf 

Coast region (e.g., roughly 10,100 gal/ton projected in the 2012 harmonization study [23]). It is 

also substantially lower than published water demands for corn and soybean production, at 

45,000 gal/ton and 63,000 gal/ton, respectively, based on average U.S. irrigation values [121].

The water footprint associated with algal biomass production is to be expected, given the use of 

thousands of acres of cultivation ponds open to atmospheric evaporation. While this may prove 

more challenging in the U.S. Southwest given water availability constraints in that region (and 

higher expected evaporation rates than those modeled here associated with the Gulf Coast), the 

original harmonization work assessed through PNNL’s Resource Assessment model, which set 

the precedent for algal facility site screening and prioritization, was based on ensuring that no 

more than 5% of mean annual flows for the local watershed resources were consumed by the 

algal facilities, thus alleviating concerns for algal cultivation water demands becoming too taxing 

on local water resources in the region [23]. Additionally, water usage can also be mitigated 

through the use of saltwater or brackish water cultivation with more aggressive blowdown 

strategies. The breakouts for facility water consumption are shown graphically in Figure 20.

Table 22. Summary of Sustainability Metrics for the Process (average 10-acre pond base case)

Metric Result

GHG emissions (U.S. ton CO2e/ton AFDW biomass product) 0.73

Process water consumption (m3/day) 26,790

Process water consumption (gal/ton AFDW biomass product) 12,450

Total biomass productivity (AFDW ton/acre/yr) 38

Net fossil energy consumption (MJ/ton AFDW biomass product) 7,962

Figure 20. Allocations for ISBL facility power demand broken down by process area (left) and 

water consumption broken down by source of water loss (right)
86

7 Concluding Remarks

7.1 Summary

The present report establishes a plausible case for achieving a modeled cost under $500/ton 

AFDW for algal biomass production and processing, based on targets envisioned for 

demonstration by 2022 for improvements to both process performance and system design beyond 

the current state of the art. The integrated process pathway is based on a single set of sequential 

operations upstream and downstream of the cultivation step, including the use of high-purity CO2

delivered to the facility under pressure and sparged to individual ponds; utilization of nutrients 

based on demands set by biomass compositional analysis plus a small (20%) excess; inoculum 

production based on sequential scale-up from a PBR to enclosed ponds to open fully lined ponds 

of increasingly larger cultivation volumes; a three-step dewatering process based on low-cost inground gravity settlers followed by hollow fiber membranes followed by centrifugation to 

concentrate the harvested biomass up to 20 wt% AFDW; and culture circulation throughout the 

5,000-acre facility (based on wetted pond area) utilizing a series of pipelines and aqueduct 

channels. The key cultivation step is based on algal biomass production in open ponds and does 

not consider PBR cultivation (beyond that utilized for inoculum propagation) given the limited 

availability of cost and design details for commercial PBR systems, as well as to focus the scope 

of analysis from becoming too large for a single report; PBR cultivation will be a subject of 

future assessment. Given continuing wide disagreement in public literature around the “true” 

cost of algal biomass/biofuel production and a relatively large dataset of detailed pond designs 

made available for our use over the past two years, rather than considering a single pond design 

on which to base the modeled MBSP, the present analysis considers eight separate pond cost 

estimates furnished by four separate sources considered experts in the field across three discrete 

pond sizes.

The techno-economic analysis makes a number of important assumptions for future performance 

projections related to cultivation productivity and seasonal variability, which play a critical role 

in the resulting MBSP estimates. These include: (1) a target for cultivation biomass productivity 

at 25 g/m2

/day (AFDW) based on annual average rates across individual seasons; (2) maximum 

seasonal variability in productivity of 3:1 between peak summer and minimum winter season 

performance (this value is particularly important for downstream conversion facility design); (3) 

an associated harvested biomass composition targeting a mid-level lipid content near 27% for a 

representative strain Scenedesmus; and (4) an nth-plant target of 330 days/year for facility on-line 

time, e.g., 35 days/year downtime allowing for culture crashes, pond freezes, and planned 

maintenance. Based on these assumptions, the analysis conducted here presents a modeled 

MBSP ranging from $576–$649/ton AFDW (average = $612/ton) of dewatered biomass for the 

two 2-acre pond designs considered in the integrated model, compared with an MBSP range 

between $452–$545/ton (average = $491/ton) for the four 10-acre designs, and $392–$419/ton 

(average = $406/ton) for the two hypothetical 50-acre designs. These distinctive groupings 

highlight the important role that maximizing economy of scale plays in guiding optimum pond 

design for a large commercial algae farm; most importantly, increasing individual pond sizes 

from 1–3 acres (as currently exist today) up to 10 acres for commercial scale-up is estimated to 

reduce biomass cost on the order of $120/ton or more, which is critical to enable cost viability 

for biofuels through downstream conversion. While 10-acre ponds represent a considerable 

increase in size beyond today’s current standard, all four expert sources we consulted for 
87

establishment of the pond designs agree that such a size is plausible even if representing an upper 

limit of operability for “standard” paddlewheel raceway systems. Thus, the average of the four 

10-acre cases is selected as the “base case” for purposes of making use of a single MBSP target 

number, at $491/ton AFDW in 2011 dollars. While this is a slightly higher cost result than the 

original BETO 2022 target of $430/ton projected in recent MYPP reports [45,46], it validates 

that a target of such a level is not unrealistic (e.g., less than $500/ton), and, in fact, reaching a 

$430/ton cost would still be within reach for example through slightly higher productivities than 

those projected here.

The modeled MBSP selling prices are strictly representative of nth-plant assumptions regarding 

facility design, operation, and financing, and are not intended to reflect first-of-a-kind or earlyentry commercial facilities. The MBSP projections presented here are also most appropriately 

viewed as a “transfer price” for subsequent delivery to downstream biorefinery processing for 

conversion of the biomass into fuels and/or coproducts, as the high 80% moisture content of the 

biomass product is likely to limit economical transport of the material over any significant 

distance. Compared to terrestrial cellulosic biomass such as woody or herbaceous feedstocks 

(e.g., corn stover and switchgrass), which are typically projected at $80/ton for future cost targets 

[46], the base case MBSP of $491/ton projected here is significantly higher and highlights the 

primary challenge for algal biofuels attributed to costly biomass production and processing 

logistics for aquatic biomass. However, this premium for algal biomass is largely offset by the 

potential for significantly higher fuel yields from downstream conversion operations, on the 

order of 120–140 GGE/ton for either HTL or ALU algal conversion pathways, compared to 

roughly 50–80 GGE/ton projected for all terrestrial biomass conversion pathways considered in 

MYPP reports to date (including both thermochemical and biochemical conversion pathways 

from woody or herbaceous feedstocks) [1,44,46]. 

Still, at a $430/ton biomass price for either the ALU or HTL conversion pathway, the “best case” 

fuel cost for either pathway design case is currently projected at $4.35–$4.49/GGE if focused 

exclusively on fuel production. In order to further reduce fuel costs to an ultimate BETO target 

of $3/GGE, either (1) biomass feedstock costs would need to reduce to a level of $300/ton or less 

without sacrificing compositional quality or (2) the conversion pathways would need to consider 

opportunities for high-value coproducts. On the former point, we show in Sections 3 and 6.1 that 

reducing biomass cost to a level closer to $300/ton would be challenging, although not 

impossible, requiring (for example) the pursuit of very large 50-acre pond designs, further 

improving productivity beyond 25 g/m2

/day annual average, and exploiting opportunities to 

utilize lower-cost CO2 sources. While some of these may be possible to a degree, a more readily 

achievable approach would likely be to consider opportunities for high-value coproducts 

produced alongside algal biofuels to reduce fuel costs. In the context of the ALU pathway, which 

is based on selective fractionation and isolation of biomass into its constituent lipid, 

carbohydrate, and protein fractions, there are many such opportunities for conversion of one or 

more of these constituents into an array of possible coproducts [122-124], which will be a subject 

of future research. For HTL conversion to fuels, costs may also be reduced by co-processing 

algal biomass with less expensive feedstocks (for example, terrestrial biomass or waste 

fats/greases), which may also reduce seasonal variability effects by increasing blended feeds 

during winter months [2].
88

Beyond the base case assumptions employed here, a number of alternative sensitivity scenarios 

were considered to quantify resulting impacts to MBSP. As expected, the strongest driver to 

overall economics was seen to be the achievable annual productivity, with substantial impacts to 

MBSP particularly if productivity were reduced below 25 g/m2/day (while maintaining the same 

compositional assumptions). Interestingly, if nutrient feeding strategies were adjusted to 

maintain the culture under a nutrient-replete, rapid-growth state (translating to a 4.8-fold increase 

in N and P nutrient costs based on the given compositional details), the resulting increase in 

productivity for pursuing this strategy would need to be more than 40% (e.g., more than 35 

g/m2/day versus the 25 g/m2/day baseline) for this strategy to pay off compared to the lowernutrient base case at a higher state of lipid accumulation; however, this excludes any credits for 

nutrient recycle from downstream conversion operations, which could considerably reduce cost 

differences attributed to variations in composition and therefore fresh makeup nutrient costs. In 

any case, the resultant biomass product for such a strategy would likely be much less valuable 

for downstream conversion, as it would be high in protein and nitrogen but low in lipid content, 

carbohydrates, and overall carbon content. 

The model exhibited a relatively low degree of cost sensitivity to most dewatering parameters for 

the low-cost dewatering strategies considered in the base case, but a higher degree of sensitivity 

for alternative dewatering options and particularly so for dissolved air flotation with the use of a 

flocculant. Finally, two critical sensitivities were considered with respect to the use of pond 

liners and the opportunity to utilize bulk flue gas in place of concentrated CO2. For the former 

parameter, the analysis reiterates that it is critical to make use of unlined ponds located on sites 

with high native clay content of the soil (or soil that otherwise supports physical or biological 

sealing), where adding full plastic pond liners would add over $120/ton on average to the MBSP 

for the 10-acre pond designs, costing approximately as much as the pond systems themselves. If 

high-clay soil is not available, alternatives may exist for pond “self-sealing” by allowing a layer 

of algal or bacterial biomass to accumulate on the pond floor. Regarding CO2 delivery, the 

analysis found that in theory the use of bulk flue gas may provide the opportunity to reduce 

MBSP relative to the use of purified CO2 at $45/tonne (sourced from flue gas carbon capture), 

however the logistics for flue gas pipeline transport at 10vol%–15 vol% CO2 are highly 

challenging and likely would require co-location of the algal facility with a flue gas point source 

(e.g., coal-fired power plant) for this scenario to even be plausible. Even then, it would still be 

limited in practicality for large flue gas pipelines feeding to individual ponds over such a large 

facility footprint.

In addition to providing an economic analysis, the present report also considers sustainability 

metrics for the base case scenario (i.e., the average of the 10-acre pond designs), by tracking and 

reporting on greenhouse gas emissions, fossil energy demand, and consumptive water use at the 

modeled production facility (production stage only, excluding downstream conversion). The 

sustainability analysis for the baseline scenario indicates a fossil GHG profile of 0.73 ton 

CO2eq/ton AFDW biomass, fossil energy consumption of 7,962 MJ/ton, and water demand of 

12,450 gal/ton (driven primarily by seasonal pond evaporation losses). An important caveat for 

these results, however, is that both the GHG and fossil energy profiles are driven strongly by the 

assumed LCA inventory attributed to the CO2 carbon capture technology occurring off site, 

which is based on today’s technology for MEA amine capture, whereas the $45/tonne CO2 price 

represents a 2022 target that may be more appropriate as a second-generation carbon capture 

technology. Additionally, these sustainability metrics are only representative of a partial process 
89 

focused on only the biomass production operations in an otherwise inherently integrated process 

with downstream conversion, thus the values carry somewhat limited meaning and a full TEA 

and LCA is required for the overall well-to-wheel integrated process including downstream 

conversion operations, in order to present a more complete understanding of such metrics. This 

will be a subject of continued modeling consideration moving forward between NREL and 

partner laboratories. 

It is worthwhile to reiterate that algal production processes are still arguably in an early stage of 

development and understanding, relative to other terrestrial/cellulosic technology pathways. 

Thus, the absolute cost values established here, as well as the timeframe required to achieve 

these outcomes, inherently carries a somewhat higher degree of uncertainty given the nascent 

stage of research as presented in the public domain for operational data over sustained 

timeframes at large scales. This said, the economic potential for algal biomass production (i.e., at 

a cost target below $500/ton) validates that a path forward exists to achieve a viable algal 

biofuels industry. 

7.2 Future Work

Moving forward, to ultimately achieve cost goals and reduce uncertainty in key areas for the 

algal production and processing pathway in the context of a fully integrated process with 

downstream conversion, a number of important bottlenecks, uncertainties, and areas for further 

development are summarized below. Some of these points are repeated from NREL’s recent 

technical memo for the algal lipid upgrading (ALU) process [125], with a common theme being 

the need for data, particularly for a fully integrated process at meaningful scale. More open data 

flow between modelers and commercial practitioners of these technologies would greatly 

improve our understanding of the current state of technology.

Validate algae growth rates and biomass compositional analysis based on data from 

large-scale demonstrations: In order to validate realistic, achievable goals related to 

algal cultivation and corresponding biomass quality (i.e., composition), a sound 

understanding of the initial baseline is first required. While NREL and other partners 

have done substantial analysis on this subject [23,42], these two key parameters still 

largely remain limited to modeled or semi-empirical data for today’s current 

performance. Among a number of entities working to address this issue, the ATP3 and 

RAFT consortia programs are focused on this goal as a critical priority, working to 

provide publicly available data for cultivation test-bed sites located in regions across the 

United States. Data made available from these efforts will be leveraged in NREL’s 

models to better quantify today’s “state of technology” costs. 

Improve cultivation performance: To ultimately realize economic viability for algalderived biofuels regardless of the conversion technology, substantial improvements in 

both performance and cost will be required. For cultivation performance, this will depend 

to a large extent on both locality and strain specifics, with high-cost sensitivities on the 

downstream conversion process to seasonal variability factors. Minimizing seasonal 

variability to no more than 3:1 between peak and minimum productivities as modeled 

here will be important to demonstrate, whether by choice of strain(s) or location, or 

employing crop rotation strategies to utilize cold- and warm-temperature strains. 

Improving overall productivity remains a critical goal (albeit while controlling nutrient 
90 

costs), and will likely require strain improvement efforts relative to current wild-type 

strain performance. Additionally, continued attention must be afforded to protection of 

crop yield against culture crashes (losses to grazers and pathogens) through improving 

strain robustness and systems design [126]; this is particularly critical in enabling the 

practical use of large size ponds called for in this report. 

Reduce cost for cultivation: In addition to improving cultivation performance, costs 

must be reduced at the same time. Primary means for reducing cultivation costs for open 

pond systems include avoiding pond liners (which will depend on local soil 

characteristics with suitable clay content, strain employed, and local regulatory policies) 

and constructing suitably large ponds, e.g., 10 acres or more for an individual pond 

configuration to maximize economy of scale benefits gained by reducing individual feed 

and harvest pipes, electrical runs, circulation equipment, and concrete, which are strong 

contributors to overall pond costs. Future work should consider production trials, soil 

studies, and resource modeling to identify areas with suitable soil characteristics to 

support the use of unlined ponds. Alternatively, further room for investigation exists to 

understand pond “self-sealing” mechanisms (e.g. by algal or bacterial biomass) in 

locations without high-clay soils. Biomass valorization to identify high-value coproduct 

opportunities also provides a way to offset cultivation costs. 

Reduce cost and increase efficiency of dewatering steps: While the performance for all 

three dewatering operations are supported to varying degrees by operational data based 

specifically on algae processing and concentration, they have not been demonstrated in 

an integrated way, nor for their specificity to a range of strains. The sequence of 

dewatering technologies employed in this design case are envisioned to aggressively 

reduce costs for this processing step, relative to more typical operations utilized today, 

such as centrifugation and/or the use of added flocculants. 

Identify opportunities for lower-cost carbon and nutrient sources: Costs for CO2 and 

nutrient inputs in the base case account for roughly $112/ton out of the $491/ton average 

10-acre MBSP results (over 22% of total MBSP). One means of reducing these costs is to 

target conversion processes downstream that allow for a high degree of recycle back to 

the ponds (any such credit for recycle was not accounted for here, as instead it was 

accounted for in the ALU conversion design case by reducing final biofuel costs). 

Utilizing bulk flue gas in place of captured CO2 may provide an opportunity to reduce 

CO2 cost; however, this option may be limited to sites where co-locating an algal facility 

directly with the power plant is possible, and even then may be limited in overall facility 

size for flue gas delivery to ponds. Additional opportunities exist for integration with 

other process technologies, such as corn or cellulosic ethanol facilities, and warrant 

further investigation. Costs also may be reduced by considering the use of lower cost 

carbon/nutrient sources such as wastewater, which may at least reduce the need for 

dedicated CO2 or fertilizer nutrients and may also provide additional incentives for 

simultaneous wastewater treatment [17].
91

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Appendix A. Individual Equipment Cost Summary

The following table shows abbreviated specifications, purchased cost, and installed cost for each 

piece of equipment in this process design, with all capital costs set based on the maximum 

throughput design case, i.e., summer season flows. Although each piece of equipment has its 

own line, many were quoted as part of a package. NREL would like to acknowledge the 

equipment vendors and external consultants who assisted us with the cost estimation effort for 

this design report.
100

Mechanical Equipment List Scaled Installed Costs

EQUIPMENT TITLE DESCRIPTION

NUM REQD

$ 

Year of 

Quote

Purch Cost 

in Base Yr 

Scaling 

Variable

Scaling Val

Units

Scaling Exp

Inst Factor

New Val

Size Ratio

Scaled 

Purch Cost 

Purch Cost 

in Proj 

Year 

Inst Cost in 

Proj Year 

A100: Leidos 10-acre raceway ponds

Clear and grub $167,960 2014 $167,960 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $8,398,000 $8,537,942 $8,537,942

Strip (overburden) and stockpile $221,269 2014 $221,269 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $11,063,450 $11,247,809 $11,247,809

Scarifying $3,888 2014 $3,888 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $194,400 $197,639 $197,639

Total compaction (1 foot lays) $133,500 2014 $133,500 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $6,675,000 $6,786,231 $6,786,231

Total cut and fill (short runs) $155,170 2014 $155,170 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $7,758,500 $7,887,786 $7,887,786

Fine grade $408,980 2014 $408,980 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $20,449,000 $20,789,758 $20,789,758

Berm pond liner 40 mil geomembrane $43,687 2014 $43,687 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $2,184,350 $2,220,750 $2,220,750

Paddlewheel $640,000 2014 $640,000 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $32,000,000 $32,533,241 $32,533,241

Paddlewheel motor INCLUDED 2014 INCLUDED - - -

Paddlewheel gearbox INCLUDED 2014 INCLUDED - - -

Paddlewheel support INCLUDED 2014 INCLUDED - - -

Electrical to ponds, 3 conductor, 10 gauge 

wire $58,020 2014 $58,020 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $2,901,000 $2,949,342 $2,949,342

Instrumentation $79,000 2014 $79,000 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $3,950,000 $4,015,822 $4,015,822

Pond Concrete (sump and slide gate) (21 

cy/pond) $156,959 2014 $156,959 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $7,847,950 $7,978,726 $7,978,726

Non formed concrete work (piping "stays") $171,829 2014 $171,829 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $8,591,450 $8,734,616 $8,734,616

CO2 Diffusers $10,000 2013 $10,000 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $500,000 $516,217 $516,217

Slide Gates $58,510 2014 $58,510 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $2,925,500 $2,974,250 $2,974,250

PVC pipe 18-inch diameter Pond fill main header $396,649 2014 $396,649 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $19,832,450 $20,162,933 $20,162,933

PVC pipe 18-inch diameter Ponds drain header to harvest $47,778 2014 $47,778 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $2,388,900 $2,428,708 $2,428,708

PVC pipe 8-inch diameter Pond drain to drain header $11,580 2014 $11,580 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $579,000 $588,648 $588,648

Pumps from ACCE 100 $144,409 2012 $144,409 smix.A110.A100.13 7182 gpm 0.80 1.15 6180 0.86 $12,805,331 $12,829,426 $14,792,010

Leidos 10 acre pond total $151,044,281 $153,379,844 $155,342,428

A100: Harris 10-acre raceway ponds

Site Excavation Includes Labor and Materials $4,761 2013 $4,761 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $2,408,389 $2,486,504 $2,486,504

Backfill Includes Labor and Materials and Equipment $14,284 2013 $14,284 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $7,225,673 $7,460,033 $7,460,033

Spoil Includes Labor and Materials and Subcontractor $120 2013 $120 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $60,703 $62,672 $62,672

Trench Excavation Includes Labor and Materials $564 2013 $564 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $285,304 $294,557 $294,557

Trench Backfill and Tamp Includes Labor and Materials $627 2013 $627 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $317,173 $327,460 $327,460

Excavation machinery Dozer D9, Dozer D51, Compactor, Trk 300, Trk 200, Loader $56,325 2013 $56,325 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $28,492,442 $29,416,576 $29,416,576

Berm Liner 24 mil HDPE From Harris Group Quote $24,300 2013 $24,300 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $12,292,345 $12,691,039 $12,691,039

Paddlewheel $52,000 2013 $52,000 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $26,304,607 $27,157,780 $27,157,780

Paddlewheel Bearings INCLUDED 2013

Paddlewheel Drive INCLUDED 2013

Paddlewheel Motor hookup, Conduit etc. INCLUDED 2013

CO2 Baffle Wall-concrete $36,500 2012 $36,500 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $18,463,811 $18,498,553 $18,498,553

Sump+paddlewheel FND-concrete $102,023 2013 $102,023 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $51,609,134 $53,283,042 $53,283,042

Electrical to ponds, 3 conductor, 10 gauge wire $58,020 2014 $58,020 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $2,901,000 $2,949,342 $2,949,342

Instrumentation $79,000 2014 $79,000 SIZEFAC 100 wetted acres 1.00 1.00 5000 50 $3,950,000 $4,015,822 $4,015,822

Water Piping $68,800 2014 $68,800 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $34,803,019 $35,382,969 $35,382,969

Pumps from ACCE 100 $144,409 2012 $144,409 smix.A110.A100.13 7182 gpm 0.80 1.15 6180 1 $12,805,331 $12,829,426 $14,792,010

Harris 10 acre pond total $201,918,932 $206,855,774 $208,818,359

A100: MicroBio 10-acre raceway ponds

Civil Work Includes excavating and trenching, and fine grading $4,892 2009 $4,892 SIZEFAC 1 ha wetted area 1.00 1.00 2023 2023 $9,898,614 $11,108,676 $11,108,676

Pond Includes Paddlewheel Equipment and concrete $15,778 2009 $15,778 SIZEFAC 1 ha wetted area 1.00 1.00 2023 2023 $31,925,700 $35,828,477 $35,828,477

Berm Liner Partial Berm Liner $9,430 2009 $9,430 SIZEFAC 1 ha wetted area 1.00 1.00 2023 2023 $19,080,957 $21,413,521 $21,413,521

Fine Bubble Spargers $5,182 2009 $5,182 SIZEFAC 4 ha wetted area 1.00 1.00 2023 506 $2,621,355 $2,941,805 $2,941,805

Water Piping Pond piping (excludes yardpiping) $10,176 2009 $10,176 SIZEFAC 1 ha wetted area 1.00 1.00 2023 2023 $20,590,437 $23,107,528 $23,107,528

Electrical for Ponds $19k/ha for full facility, ponds are 1/3 of $19k/ha $6,300 2009 $6,300 SIZEFAC 1 ha 1.00 1.00 2023 2023 $12,747,617 $14,305,958 $14,305,958

Pumps from ACCE 100 $144,409 2012 $144,409 smix.A110.A100.13 7182 gpm 0.80 1.15 6180 1 $12,805,331 $12,829,426 $14,792,010

MicroBio 10 acre pond total $109,670,012 $121,535,392 $123,497,976

A100: GAI 10-acre ponds

Grading This is a rolled up cost for all earthwork (clearing, grading, berms, 

etc.) including contractor fees, etc. $9,000 2014 $9,000 SIZEFAC 1 acre 1.00 1.00 5000 5000 $45,000,000 $45,749,870 $45,749,870

Partial Liner $0.65 2014 $0.65 SIZEFAC 1 ft^2 1.00 1.00 3360500 3360500 $2,184,325 $2,220,724 $2,220,724

Pump Equipment Cost $36,690 2014 $36,690 SIZEFAC 10 acre 1.00 3.12 5000 500 $18,345,000 $18,650,697 $58,190,174

Channel (aqueducts) GAI design. Includes cost of excavation and compaction. $5,000 2014 $5,000 SIZEFAC 1 acre 1.00 1.00 5000 5000 $25,000,000 $25,416,594 $25,416,594

Pumps from ACCE 100 $144,409 2012 $144,409 smix.A110.A100.13 7182 gpm 0.80 1.15 6180 0.86 $12,805,331 $12,829,426 $14,792,010

Global Algal Innovations 10 acre pond total $103,334,656 $104,867,311 $146,369,373

A100: Production Ponds Base Case (Average of 10-acre pond designs)

AVERAGE of 10-acre Costs Average of installed cost for 10-acre cases 

(Leidos, Harris, MicroBio, GAI) $158,506,910 2011 $158,506,910 SIZEFAC 5000 acre 1.00 1.00 5000 1.00 $158,506,910 $158,506,910 $158,506,910

Area 100: Production Ponds Total $158,506,910 $158,506,910 $158,506,910
101

Mechanical Equipment List Scaled Installed Costs

EQUIPMENT TITLE DESCRIPTION

NUM 

REQD

$ 

Year of 

Quote

Purch Cost in 

Base Yr Scaling Variable

Scaling 

Val

Units

Scaling 

Exp

Inst 

Factor

New Val

Size 

Ratio

Scaled Purch 

Cost 

Purch Cost 

in Proj Year 

Inst Cost in 

Proj Year 

A200: Inoculation Pond Scheme (Does not include additional flue gas equipment and flue gas piping)

Tubular Photobioreactors Horizontal tubular, serpentine, airlift-driven design. Cost information from Beal et. al 2015 $18.22 2014 $18.22 APBR2 1 m^2 1.00 1.00 35242 35242 $642,116 $652,816 $652,816

Covered inoculum ponds Pond Cost From 2.2 Acre system minus berm lining. Quoted by Leidos $5,427,316 2014 $5,427,316 ACOVPON 100 wetted acres 1.00 1.00 23 0.23 $1,260,377 $1,281,380 $1,281,380

Open inoculum ponds Pond Cost From 2.2 Acre system minus berm lining. Quoted by Leidos $5,427,316 2014 $5,427,316 ALINEPON 100 wetted acres 1.00 1.00 116 1.16 $6,301,885 $6,406,898 $6,406,898

Lining for covered inoculum ponds 40 mil geomembrane. Quoted by Leidos $3,097,827 2014 $3,097,827 ACOVPON 4765888 ft^2/100 acres 1.00 1.00 1106775 0.23 $719,404 $731,391 $731,391

Air Supported Greenhouse Covering for inoculum ponds. Quoted by MicroBio. $3.00 2014 $3.00 ACOVPON 1 ft^2 1.00 1.00 1112746 1112746 $3,338,237 $3,393,865 $3,393,865

Lining for open inoculum ponds 40 mil geomembrane. Quoted by Leidos $3,097,827 2014 $3,097,827 ALINEPON 4765888 ft^2/100 acres 1.00 1.00 5533873 1.16 $3,597,018 $3,656,957 $3,656,957

A200: Inoculation Pond Scheme (Does not include additional flue gas equipment and flue gas piping) $15,859,036 $16,123,308 $16,123,308

Mechanical Equipment List Scaled Installed Costs

EQUIPMENT TITLE DESCRIPTION

NUM 

REQD

$ 

Year 

of 

Quote

Purch Cost in 

Base Yr Scaling Variable

Scalin

g Val

Units

Scalin

g Exp

Inst 

Factor

New 

Val

Size 

Ratio

Scaled Purch 

Cost 

Purch Cost 

in Proj Year 

Inst Cost in 

Proj Year 

A300: CO2 Piping

Pipeline CO2 Storage Sphere 45' Diameter 1.0 $1,400,800 2014 $1,400,800 strm.A110.A100.57 68550 kg/h 0.60 1.25 65057 0.95 $1,357,530 $1,380,151 $1,725,189

Storage tank immersion vaporizers 15’ X 200 W $70,500 2014 $70,500 strm.A110.A100.57 68550 kg/h 1.00 1.76 65057 0.95 $66,908 $68,023 $119,720

Trunk line 27100' length x 20” Diameter $1,661,900 2014 $1,661,900 strm.A110.A100.57 68550 kg/h 1.00 1.00 65057 0.95 $1,577,225 $1,603,507 $1,603,507

Branch line 4 x $912,300 2014 $912,300 strm.A110.A100.57 68550 kg/h 1.00 1.00 65057 0.95 $865,818 $880,245 $880,245

Within-plot piping 6250' 50 $44,200 2014 $44,200 strm.A110.A100.57 68550 kg/h 1.00 1.00 65057 0.95 $2,097,399 $2,132,349 $2,132,349

Supply to Inoculum area 1000' $59,300 2014 $59,300 strm.A110.A100.57 68550 kg/h 1.00 1.00 65057 0.95 $56,279 $57,216 $57,216

A300: CO2 Piping total $6,021,158 $6,121,493 $6,518,228

Mechanical Equipment List Scaled Installed Costs

EQUIPMENT TITLE DESCRIPTION

NUM 

REQD

$ 

Year of 

Quote

Purch Cost in 

Base Yr Scaling Variable

Scaling 

Val

Units

Scaling 

Exp

Inst 

Factor

New 

Val

Size 

Ratio

Scaled Purch 

Cost 

Purch Cost 

in Proj Year 

Inst Cost in 

Proj Year 

A400: Makeup Water Delivery + On-Site Circulation

Channel (aqueducts) GAI design. Includes cost of excavation and compaction. $100 2014 $100 SIZEFAC 1 acre 1.00 1.00 5000 5000 $500,000 $508,332 $508,332

34 in Diameter Pipe Primary distribution pipe costed in ACCE $872,158 2012 $872,158 LPIPE36 5883 ft 1.00 1.51 5883 1.00 $872,158 $873,799 $1,322,784

DPIPE36 34 Inches 1.40 34 1.00

26 in Diameter Pipe Primary distribution pipe costed in ACCE $852,949 2012 $852,949 LPIPE28 9426 ft 1.00 1.48 9426 1.00 $768,891 $770,337 $1,139,228

DPIPE28 28 Inches 1.40 26 0.93

20 in Diameter Pipe Primary distribution pipe costed in ACCE $469,386 2012 $469,386 LPIPE20 9990 ft 1.00 1.72 9990 1.00 $436,868 $437,690 $754,930

DPIPE20 20 Inches 1.40 19 0.95

16 in Diameter Pipe Module column distribution pipe costed in ACCE $416,554 2012 $416,554 LPIPE18 9360 ft 1.00 1.58 9360 1.00 $416,554 $417,338 $661,342

DPIPE18 16 Inches 1.40 16 1.00

14 in Diameter Pipe Module column distribution pipe costed in ACCE $321,593 2012 $321,593 LPIPE16 9360 ft 1.00 1.63 9360 1.00 $321,593 $322,198 $525,487

DPIPE16 14 Inches 1.40 14 1.00

12 in Diameter Pipe Module column distribution pipe costed in ACCE $267,709 2012 $267,709 LPIPE14 9360 ft 1.00 1.67 9360 1.00 $267,709 $268,213 $448,542

DPIPE14 12 Inches 2.00 12 1.00

Make-up water Pipeline 1 mile pipeline to allowable water source $2,638,100 2009 $2,638,100 WPIPEID 36 Inches 1.40 1.00 22 0.61 $1,323,914 $1,485,757 $1,485,757

Make-up Water Pump centrifugal pump $705,500 2009 $705,500 smix.A600.Make-up 10626 MM gal/yr 0.60 1.00 2575 0.24 $301,423 $338,271 $338,271

A400: Makeup Water Delivery + On-Site Circulation total $5,209,110 $5,421,935 $7,184,674

Mechanical Equipment List Scaled Installed Costs

EQUIPMENT TITLE DESCRIPTION

NUM 

REQD

$ 

Year of 

Quote

Purch Cost in 

Base Yr Scaling Variable

Scaling 

Val

Units

Scaling 

Exp

Inst 

Factor

New 

Val

Size 

Ratio

Scaled Purch 

Cost 

Purch Cost 

in Proj Year 

Inst Cost in 

Proj Year 

A500: Dewatering

22-inch Diameter Pipe Clarified water return pipe. Quoted by Leidos $284,880 2014 $284,880 LPIPE22 4300 LF 1.00 1.00 168199 39 $11,143,368 $11,329,058 $11,329,058

Pumps from ACCE Pump for clarified water pipeline $121,905 2012 $121,905 smix.A110.A100.REC 6653 gpm 0.80 1.15 5874 0.88 $5,517,028 $5,527,409 $6,364,943

Primary Settler (4 hr residence) Includes excavation, berm liners, concrete base, sumps, and mechanical rake 50 $34,300 2014 $34,300 smix.a110.a100.TOSET 1000 m3 1.00 1.00 5587 279 $9,582,398 $9,742,077 $9,742,077

Hollowfiber Membrane Separation Unit Rolled up cost for complete unit $12,864,000 2014 $12,864,000 smix.A500.207 20000000 gal/day 0.75 1.00 20147352 1.05 $13,320,465 $13,542,434 $13,542,434

Centrifuge Bowl type centrifuge. Quoted by Harris $2,242,500 2013 $2,242,500 smix.A500.226 463 m3/hr 0.60 1.80 252 0.54 $1,555,198 $1,605,640 $2,890,152

A500: Dewatering Total $41,118,550 $41,746,714 $43,868,844

Mechanical Equipment List Scaled Installed Costs

EQUIPMENT TITLE DESCRIPTION

NUM 

REQD

$ 

Year of 

Quote

Purch Cost in 

Base Yr Scaling Variable

Scaling 

Val

Units

Scaling 

Exp

Inst 

Factor

New 

Val

Size 

Ratio

Scaled Purch 

Cost 

Purch Cost 

in Proj Year 

Inst Cost in 

Proj Year 

A600: Storage

Product Storage Tank Actual 600,000 gal, 24 h storage 2.0 $418,795 2009 $418,795 smix.A600.PRODUCT2 750000 gal 0.60 1.14 512481 0.68 $666,502 $747,978 $855,149

Firewater Pump 2500 gpm, 150 FT TDH 1.0 $15,000 2009 $15,000 strm.A600.713 8343 kg/h 0.80 3.10 11051 1.32 $18,783 $21,079 $65,345

Firewater Storage Tank 600,000 gal - 4 hrs @2500 gpm 1.0 $803,000 2009 $803,000 strm.A600.713 8343 kg/h 0.70 1.70 11051 1.32 $977,637 $1,097,149 $1,865,154

Make-up Storage Tank Actual Tank 500,000 gal and 6 hours storage 4.0 $418,795 2009 $418,795 smix.A600.Make-up 750000 gal 0.60 1.14 487756 0.65 $1,294,036 $1,452,226 $1,660,301

Tankage BOP 20% of BOP factor (BC2013 model) $591,392 $663,687 $889,190

A600: Storage Total $3,548,349 $3,982,119 $5,335,139
102

Appendix B. Additional Design and Cost Details for 

Leidos Pond Scenarios

Raceways with Paddlewheels Raceways with Paddlewheels Serpentine Pond

In-situ Clay, with partial liner, 10 acre In-situ Clay, with partial liner, 2.2 acre In-Situ Clay, with partial liner, 48.6 acre

DIRECT POND COSTS Quantity Unit Cost Units Total Cost Quantity Unit Cost Units Total Cost Quantity Unit Cost Units Total Cost

Civil Work Feet of overburden to remove: 0.5 feet Feet of overburden to remove: 0.5 feet Feet of overburden to remove: 0.5 feet

Clear and grub 130 $1,292 acres $167,960 130 $1,292 acres $167,960 130 $1,292 acres $167,960

Strip (overburden) and stockpile 104867 $2.11 CY $221,269 104867 $2.11 CY $221,269 104867 $2.11 CY $221,269

Scarifying 629200 $0.01 SY $3,888 629200 $0.01 SY $3,888 629200 $0.01 SY $3,888

Total Compaction (1 foot lays) 267000 $0.50 CY $133,500 286000 $0.50 CY $143,000 363716 $0.50 CY $181,858

Total cut and fill (short runs) 59000 $2.63 CY $155,170 76500 $2.63 CY $201,195 116361 $2.63 CY $306,029

Fine Grade 629200 $0.65 SY $408,980 629200 $0.65 SY $408,980 629200 $0.65 SY $408,980

Civil Work Total $1,090,767 $1,146,292 $1,289,985

Leakage Barrier

Truck in Material, Clay n/a n/a n/a

Blend clay with native soil n/a n/a n/a

Mix-in Soil Amendment n/a n/a n/a

Pond Liner, Liner, 40 mil geomembrane 67210 $0.65 SF $43,687 110350 $0.65 SF $71,728 106530 $0.65 SF $69,245

Leakage Barrier Total $43,687 $71,728 $69,245

Paddlewheel / Motor / Gearbox / support 10 $64,000 ea $640,000 44 $38,800 ea $1,707,200 n/a

Paddlewheel Total $640,000 $1,707,200 $0

Electrical and Instrumentation

Electrical to ponds, 3 conductor, 2 gauge wire 6850 $8.47 LF $58,020 15600 $4.55 LF $70,980 n/a

Instrumentation (number of panels) 10 $7,900.00 ea $79,000 44 $7,900.00 ea $347,600 n/a

E&I Work Total $137,020 $418,580 $0

Piping

PVC Piping Pipe, LF Fittings Pipe, LF Fittings Pipe, LF Fittings

22-inch; Harvest to harvest return pond 4300 $13,980 $63.00 LF $284,880 4900 $13,980 $63.00 LF $322,680 n/a

18-inch, Pond fill main header 2335 $305,584 $39.00 LF $396,649 800 $9,542 $39.00 LF $40,742 n/a

16-inch; Pond fill sub-header 0 $27.00 LF $0 7120 $437,832 $27.00 LF $630,072 n/a

18-inch; Ponds drain header to harvest channel 1150 $16,728 $27.00 LF $47,778 2200 $63,856 $27.00 LF $123,256 n/a

8-inch; Pond drain to drain header 400 $4,780 $17.00 LF $11,580 1920 $10,516 $17.00 LF $43,156 n/a

12-inch, Harvest Return piping n/a n/a 7800 $15,400 $25.00 LF $210,400

HDPE Piping

2-inch; CO2 individual pond lines 400 $15,850 $8.49 LF $19,246 1760 $69,740 $8.49 LF $84,682 5600 $70,752 $8.49 LF $118,296

6-inch; CO2 feeder lines in pond columns 0 $0 $13.00 LF $0 5000 $8,644 $13.00 LF $73,644 5000 $19,244 $13.00 LF $84,244

8-inch; CO2 line 3500 $1,612 $17.70 LF $63,562 1600 $417 $17.70 LF $28,737 1400 $2,232 $17.70 LF $27,012

Others

CO2 diffusers 10 $1,000 ea $10,000 44 $500 ea $22,000 140 $500.00 ea $70,000

Slide Gates 10 $5,851 ea $58,510 44 $5,851 ea $257,444 n/a ea $0

Piping Work Total $892,205 $1,626,413 $509,952

Concrete

Pond concrete - paddlewheel, motor, supports, 

slide gate, inlet pipe 209 $751.00 CY $156,959 624 $751.00 CY $468,624 n/a

Non formed concrete work (piping "stays") 0 $274.00 CY $171,829 2621 $274.00 CY $269,270 252 $274.00 CY $69,170

Concrete Work Total $328,788 $737,894 $69,170

TOTAL DIRECT POND COSTS $3,132,466 $5,708,107 $1,938,351

SUMMARY METRICS $/acre Total Cost $/acre Total Cost $/acre Total Cost 

Total Direct Pond Cost (excluding land) $32,360 $3,132,466 $58,968 $5,708,107 $20,024 $1,938,351

Civil Work $11,268 $1,090,767 $11,842 $1,146,292 $13,326 $1,289,985

Leakage Control $451 $43,687 $741 $71,728 $715 $69,245

Paddlewheel $6,612 $640,000 $17,636 $1,707,200 $0 $0

E&I $1,415 $137,020 $4,324 $418,580 $0 $0

Piping $9,217 $892,205 $16,802 $1,626,413 $5,268 $509,952

Concrete $3,397 $328,788 $7,623 $737,894 $715 $69,170
103

Appendix C. Discounted Cash Flow Rate of Return 

Worksheet

Year -2 -1 0 1 2 3 4 5

Fixed Capital Investment $11,194,467 $83,958,499 $44,777,866

Land $22,843,635

Working Capital $17,491,354

Loan Payment $31,280,730 $31,280,730 $31,280,730 $31,280,730 $31,280,730

 Loan Interest Payment $1,343,336 $11,418,356 $16,791,700 $16,791,700 $15,632,577 $14,380,725 $13,028,725 $11,568,564

 Loan Principal $16,791,700 $142,729,448 $209,896,247 $195,407,217 $179,759,063 $162,859,058 $144,607,052 $124,894,886

 Algal Biomass Sales $69,037,774 $92,050,366 $92,050,366 $92,050,366 $92,050,366

 By-Product Credit $0 $0 $0 $0 $0

Total Annual Sales $69,037,774 $92,050,366 $92,050,366 $92,050,366 $92,050,366

Annual Manufacturing Cost

Feedstock - CO2 Cost $12,787,023 $17,049,364 $17,049,364 $17,049,364 $17,049,364

 Other Variable Costs $8,759,231 $10,010,549 $10,010,549 $10,010,549 $10,010,549

 Fixed Operating Costs $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044

Total Product Cost $33,237,298 $38,750,957 $38,750,957 $38,750,957 $38,750,957

Annual Depreciation $0 $0 $0 $0 $0

General Plant Writedown 14.29% 24.49% 17.49% 12.49% 8.93%

 Depreciation Charge $49,990,290 $85,672,652 $61,184,756 $43,693,402 $31,239,558

 Remaining Value $299,836,789 $214,164,138 $152,979,381 $109,285,979 $78,046,421

Steam Plant Writedown 3.75% 7.22% 6.68% 6.18% 5.71%

 Depreciation Charge $0 $0 $0 $0 $0

 Remaining Value $0 $0 $0 $0 $0

Net Revenue ($30,981,513) ($48,005,820) ($22,266,072) ($3,422,718) $10,491,286

Losses Forward $0 ($30,981,513) ($78,987,333) ($101,253,405) ($104,676,123)

Taxable Income ($30,981,513) ($78,987,333) ($101,253,405) ($104,676,123) ($94,184,837)

Income Tax $0 $0 $0 $0 $0

Annual Cash Income $4,519,746 $22,018,678 $22,018,678 $22,018,678 $22,018,678

Discount Factor 1.2100 1.1000 1.0000 0.9091 0.8264 0.7513 0.6830 0.6209

Annual Present Value $224,475,459 $4,108,860 $18,197,255 $16,542,959 $15,039,054 $13,671,867

Total Capital Investment + Interest $42,811,539 $104,914,540 $79,060,920

Net Present Worth $0

Year 6 7 8 9 10 11 12 13 14

Fixed Capital Investment

Land

Working Capital

Loan Payment $31,280,730 $31,280,730 $31,280,730 $31,280,730 $31,280,730 $0 $0 $0 $0

 Loan Interest Payment $9,991,591 $8,288,460 $6,449,078 $4,462,546 $2,317,091 $0 $0 $0 $0

 Loan Principal $103,605,747 $80,613,476 $55,781,824 $28,963,639 $0 $0 $0 $0 $0

 Algal Biomass Sales $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366

 By-Product Credit $0 $0 $0 $0 $0 $0 $0 $0 $0

Total Annual Sales $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366

Annual Manufacturing Cost $0 $0 $0 $0 $0 $0 $0 $0 $0

Feedstock - CO2 Cost $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364

 Other Variable Costs $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549

 Fixed Operating Costs $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044

Total Product Cost $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957

Annual Depreciation

General Plant Writedown 8.92% 8.93% 4.46%

 Depreciation Charge $31,204,575 $31,239,558 $15,602,288

 Remaining Value $46,841,846 $15,602,288 ($0)

Steam Plant Writedown 5.29% 4.89% 4.52% 4.46% 4.46% 4.46% 4.46% 4.46% 4.46%

 Depreciation Charge $0 $0 $0 $0 $0 $0 $0 $0 $0

 Remaining Value $0 $0 $0 $0 $0 $0 $0 $0 $0

Net Revenue $12,103,242 $13,771,391 $31,248,043 $48,836,863 $50,982,318 $53,299,409 $53,299,409 $53,299,409 $53,299,409

Losses Forward ($94,184,837) ($82,081,594) ($68,310,204) ($37,062,161) $0 $0 $0 $0 $0

Taxable Income ($82,081,594) ($68,310,204) ($37,062,161) $11,774,702 $50,982,318 $53,299,409 $53,299,409 $53,299,409 $53,299,409

Income Tax $0 $0 $0 $4,121,146 $17,843,811 $18,654,793 $18,654,793 $18,654,793 $18,654,793

Annual Cash Income $22,018,678 $22,018,678 $22,018,678 $17,897,533 $4,174,867 $34,644,616 $34,644,616 $34,644,616 $34,644,616

Discount Factor 0.5645 0.5132 0.4665 0.4241 0.3855 0.3505 0.3186 0.2897 0.2633

Annual Present Value $12,428,970 $11,299,064 $10,271,876 $7,590,301 $1,609,592 $12,142,726 $11,038,842 $10,035,311 $9,123,010

Total Capital Investment + Interest
104

Year 15 16 17 18 19 20 21 22

Fixed Capital Investment

Land

Working Capital

Loan Payment $0 $0 $0 $0 $0 $0 $0 $0

 Loan Interest Payment $0 $0 $0 $0 $0 $0 $0 $0

 Loan Principal $0 $0 $0 $0 $0 $0 $0 $0

 Algal Biomass Sales $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366

 By-Product Credit $0 $0 $0 $0 $0 $0 $0 $0

Total Annual Sales $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366

Annual Manufacturing Cost

Feedstock - CO2 Cost $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364

 Other Variable Costs $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549

 Fixed Operating Costs $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044

Total Product Cost $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957

Annual Depreciation

General Plant Writedown

 Depreciation Charge

 Remaining Value

Steam Plant Writedown 4.46% 4.46% 4.46% 4.46% 4.46% 4.46% 2.23%

 Depreciation Charge $0 $0 $0 $0 $0 $0 $0

 Remaining Value $0 $0 $0 $0 $0 $0 $0

Net Revenue $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409

Losses Forward $0 $0 $0 $0 $0 $0 $0 $0

Taxable Income $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409

Income Tax $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793

Annual Cash Income $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616

Discount Factor 0.2394 0.2176 0.1978 0.1799 0.1635 0.1486 0.1351 0.1228

Annual Present Value $8,293,646 $7,539,678 $6,854,253 $6,231,139 $5,664,671 $5,149,701 $4,681,547 $4,255,952

Total Capital Investment + Interest

Year 23 24 25 26 27 28 29 30

Fixed Capital Investment

Land

Working Capital

Loan Payment $0 $0 $0 $0 $0 $0 $0 $0

 Loan Interest Payment $0 $0 $0 $0 $0 $0 $0 $0

 Loan Principal $0 $0 $0 $0 $0 $0 $0 $0

 Algal Biomass Sales $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366

 By-Product Credit $0 $0 $0 $0 $0 $0 $0 $0

Total Annual Sales $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366 $92,050,366

Annual Manufacturing Cost

Feedstock - CO2 Cost $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364 $17,049,364

 Other Variable Costs $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549 $10,010,549

 Fixed Operating Costs $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044 $11,691,044

Total Product Cost $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957 $38,750,957

Annual Depreciation

General Plant Writedown

 Depreciation Charge

 Remaining Value

Steam Plant Writedown

 Depreciation Charge

 Remaining Value

Net Revenue $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409

Losses Forward $0 $0 $0 $0 $0 $0 $0 $0

Taxable Income $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409 $53,299,409

Income Tax $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793 $18,654,793

Annual Cash Income $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616 $34,644,616

Discount Factor 0.1117 0.1015 0.0923 0.0839 0.0763 0.0693 0.0630 0.0573

Annual Present Value $3,869,047 $3,517,315 $3,197,559 $2,906,872 $2,642,611 $2,402,374 $2,183,976 $1,985,433

Total Capital Investment + Interest ($2,311,540)
105

Appendix D. Process Flow Diagrams

High-level stream table information from Aspen Plus modeling output follows, for key streams 

associated with each process operation area. The stream table values are associated with the 

HCSD biomass base case scenario, for the summer season which is used to set the basis for the 

facility design capacity. This is followed by high-level PFDs for the associated process areas. As 

the stream table information focuses primarily on the high-level overall process and does not 

include every individual modeled stream within each process area, mass balance closure around 

a given unit area may not be 100%. 
106

A100

BIOMASS PRODUCTION

A400

MAKEUP WATER 

DELIVERY + ON-SITE 

CIRCULATION

A300

CO2 DELIVERY

DEWATERING 

ALGAE BIOMASS 

CONVERSION TO 

BIOFUELS

(not modeled here)

A600

STORAGE

JULY 2015 PFD-001

OVERALL PROCESS:

ALGAL PRODUCTION PROCESS

CO2

(From outside of facility)

A500

Primary 

Settler

Nutrients

120

130

500 520 600

160

100

140

300

610

150 Evaporation 510 Blowdown

CO2

RECYCLE WATER

ALGAE 

(1 wt% solids)

ALGAE PRODUCT 

(20 wt% solids)

ALGAE PRODUCT 

(20 wt% solids)

ALGAE 

(0.05 wt% solids)

Clarified water

Physically co-located within individual modules 

INOCULUM ALGAE 

(0.05 wt% solids)

Makeup Water 110

620

Storage Loss

A200

INOCULUM SYSTEM

Nutrients 200

220

230 Evaporation

CO2

Makeup Water 210

Figure 21. Overall process schematic for Aspen stream tables
107

Aspen Plus mass balance information for key stream tables:

COMPONENT UNITS 100 110 120 130 140 150 160 200 210

Total Flow kg/hr 863 1,202,718 2,909 66,420,622 65,057 815,493 3,000,092 31 20,258

Percent Solids Wt % 0 0 29.4 0.0054 0 0 0.037 0 0

Temperature °C 25 25 25 25 32 25 25 25 25

Pressure atm 1 1 1 1 4 1 1 1 1

Ammonia kg/hr 581 0 4 139 0 0 6 21 0

DAP kg/hr 282 0 2 67 0 0 3 10 0

O2 kg/hr 0 0 0 0 0 50,400 0 0 0

CO2 kg/hr 0 0 0 0 65,057 6,506 0 0 0

Salt (NaCl) kg/hr 0 301 225 80,892 0 0 3,653 0 225

Water kg/hr 0 1,202,417 1,821 66,335,960 0 758,588 2,995,308 0 20,032

Algae (AFDW) kg/hr 0 0 857 3,478 0 0 1,096 0 0

Ash kg/hr 0 0 0 86 0 0 27 0 0

COMPONENT UNITS 220 230 300 500 510 520 600 610 620

Total Flow kg/hr 1,851 19,231 66,908 69,877,491 304,135 3,152,731 152,640 152,336 303

Percent Solids Wt % 0 0 0 0.051 0.005 1.0 20.4 20.2 100

Temperature °C 25 25 40 25 25 25 25 25 25

Pressure atm 1 1 128 1 1 1 2 2 2

Ammonia kg/hr 0 0 0 146 0.6 7 0.3 0.3 0

DAP kg/hr 0 0 0 71 0.3 3 0.1 0.1 0

O2 kg/hr 0 1,463 0 0 0 0 0 0 0

CO2 kg/hr 1,851 151 65,057 0 0 0 0 0 0

Salt (NaCl) kg/hr 0 0 0 85,063 370 3,801 148 148 0

Water kg/hr 0 17,617 0 69,756,413 303,747 3,116,702 121,396 121,396 0

Algae (AFDW) kg/hr 0 0 0 34,939 16 31,445 30,349 30,046 303

Ash kg/hr 0 0 0 859 0.4 773 746 746 0
108

AMMONIA 

FROM STORAGE

DAP

FROM STORAGE

CO2 VAPOR

From CO2 INJECTION PIPELINE

PFD-004

BIOMASS PRODUCTION PONDS

INOCULUM ALGAE

From INOCULUM SYSTEM

PFD-003

PADDLEWHEEL STATION

POND MAKEUP WATER

FROM STORAGE

EVAPORATION

To Atmosphere

SETTLING TANK

1% SOLIDS

0.05% SOLIDS

THICKENED ALGAE

To DEWATERING

PFD-005

CLARIFIED WATER

To BLOWDOWN

Clarified water + CO2

RECYCLED WATER

FROM DEWATERING

PFD-005

JULY 2015 PFD-002

AREA 100: BIOMASS PRODUCTION

A500
109

INOCULUM ALGAE

To BIOMASS PRODUCTION

PFD-002

Ammonia

From STORAGE

Carbon Dioxide

From CO2 DELIVERY

PFD-004

Water

From STORAGE

DAP

From STORAGE

ALGAE STRAIN

PHOTOBIOREACTORS

COVERED PONDS

LINED PONDS

EVAPORATION

To Amosphere

JULY 2015 PFD-003

AREA 200: INOCULUM SYSTEM
110

PURCHASED CO2

FROM CCS PIPELINE

STORAGE SPHERE

CO2 VAPOR

To UNIT MODULE INJECTION POINTS

CO2 VAPOR 

TO PRODUCTION POND

PFD-002

UNIT MODULE INJECTION POINT

(one per module)

JULY 2015 PFD-004

AREA 300: CO2 DELIVERY
111

THICKENED ALGAE

From SETTLER

PFD-002

BIOMASS PRODUCT

TO STORAGE

CENTRIFUGES

RECYCLE WATER

TO BIOMASS PRODUCTION

PFD-002

1% SOLIDS 13% SOLIDS 20% SOLIDS

MEMBRANE

SEPARATORS

JULY 2015 PFD-005

AREA 500: DEWATERING
112

Appendix E. TEA Summary Worksheets for Individual 

Pond Scenarios

The following worksheets present additional cost and process details for each of the eight 

individual pond design cases evaluated in the TEA models.

MBSP (Minimum Biomass Selling Price): $576 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $353 /US Dry Ton

Other Production $112 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (MicroBio Raceway Pond, SIZE 2-acre) $214,000,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $7,600,000 Power $31

Dewatering $53,000,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $76

Capital Depreciation $78

Total Installed Equipment Cost $302,500,000 Average Income Tax $49

Average Return on Investment $226

Added Direct + Indirect Costs $183,700,000

 (% of TCI) 38%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $486,200,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $1,613 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $2,592 Power $5,900,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $14,300,000

Term (years) 10 Capital Depreciation $14,700,000

Capital Charge Factor (Computed) 0.136 Average Income Tax $9,200,000

Average Return on Investment $42,400,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$576 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: MicroBio Raceway Pond, SIZE 2-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
113

MBSP (Minimum Biomass Selling Price): $649 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $430 /US Dry Ton

Other Production $107 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (Leidos Raceway Pond, SIZE 2-acre) $279,100,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $7,600,000 Power $34

Dewatering $53,000,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $81

Capital Depreciation $94

Total Installed Equipment Cost $367,600,000 Average Income Tax $58

Average Return on Investment $266

Added Direct + Indirect Costs $209,500,000

 (% of TCI) 36%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $577,100,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $1,960 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $3,077 Power $6,400,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $15,200,000

Term (years) 10 Capital Depreciation $17,600,000

Capital Charge Factor (Computed) 0.136 Average Income Tax $10,900,000

Average Return on Investment $49,900,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$649 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: Leidos Raceway Pond, SIZE 2-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
114

MBSP (Minimum Biomass Selling Price): $452 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $235 /US Dry Ton

Other Production $105 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (MicroBio Raceway Pond, SIZE 10-acre) $123,500,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $7,200,000 Power $26

Dewatering $43,900,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $60

Capital Depreciation $54

Total Installed Equipment Cost $202,500,000 Average Income Tax $36

Average Return on Investment $160

Added Direct + Indirect Costs $138,800,000

 (% of TCI) 41%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $341,300,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $1,080 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $1,820 Power $4,900,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $11,200,000

Term (years) 10 Capital Depreciation $10,100,000

Capital Charge Factor (Computed) 0.137 Average Income Tax $6,800,000

Average Return on Investment $30,000,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$452 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: MicroBio Raceway Pond, SIZE 10-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
115

MBSP (Minimum Biomass Selling Price): $491 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $278 /US Dry Ton

Other Production $101 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (Leidos Raceway Pond, SIZE 10-acre) $155,300,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $7,200,000 Power $32

Dewatering $43,900,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $62

Capital Depreciation $61

Total Installed Equipment Cost $234,300,000 Average Income Tax $40

Average Return on Investment $180

Added Direct + Indirect Costs $151,400,000

 (% of TCI) 39%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $385,700,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $1,249 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $2,056 Power $5,900,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $11,600,000

Term (years) 10 Capital Depreciation $11,500,000

Capital Charge Factor (Computed) 0.137 Average Income Tax $7,500,000

Average Return on Investment $33,800,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$491 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: Leidos Raceway Pond, SIZE 10-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
116

MBSP (Minimum Biomass Selling Price): $545 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $336 /US Dry Ton

Other Production $96 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (Harris Raceway Pond, SIZE 10-acre) $208,800,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $7,200,000 Power $29

Dewatering $43,900,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $66

Capital Depreciation $74

Total Installed Equipment Cost $287,800,000 Average Income Tax $47

Average Return on Investment $213

Added Direct + Indirect Costs $172,600,000

 (% of TCI) 37%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $460,400,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $1,534 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $2,455 Power $5,400,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $12,400,000

Term (years) 10 Capital Depreciation $13,900,000

Capital Charge Factor (Computed) 0.136 Average Income Tax $8,800,000

Average Return on Investment $40,000,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$545 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: Harris Raceway Pond, SIZE 10-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
117

MBSP (Minimum Biomass Selling Price): $475 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $261 /US Dry Ton

Other Production $102 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (GAI Pond, SIZE 10-acre) $146,400,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $7,200,000 Power $25

Dewatering $43,900,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $61

Capital Depreciation $59

Total Installed Equipment Cost $225,400,000 Average Income Tax $39

Average Return on Investment $175

Added Direct + Indirect Costs $147,800,000

 (% of TCI) 40%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $373,200,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $1,202 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $1,990 Power $4,800,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $11,500,000

Term (years) 10 Capital Depreciation $11,100,000

Capital Charge Factor (Computed) 0.137 Average Income Tax $7,300,000

Average Return on Investment $32,800,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$475 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: GAI Pond, SIZE 10-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
118

MBSP (Minimum Biomass Selling Price): $419 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $211 /US Dry Ton

Other Production $96 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (Leidos Serpentine Pond, SIZE 50-acre) $111,300,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $8,200,000 Power $26

Dewatering $37,100,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $49

Capital Depreciation $49

Total Installed Equipment Cost $184,500,000 Average Income Tax $33

Average Return on Investment $146

Added Direct + Indirect Costs $127,500,000

 (% of TCI) 41%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $312,000,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $984 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $1,663 Power $4,800,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $9,200,000

Term (years) 10 Capital Depreciation $9,200,000

Capital Charge Factor (Computed) 0.137 Average Income Tax $6,200,000

Average Return on Investment $27,400,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$419 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: Leidos Serpentine Pond, SIZE 50-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)
119

MBSP (Minimum Biomass Selling Price): $392 /US Dry Ton (AFDW)

Contributions: CO2 and Nutrients $112 /US Dry Ton

Cultivation $180 /US Dry Ton

Other Production $100 /US Dry Ton

Total Biomass Production (AFDW Basis) 0.19 MM US Ton/yr

Total Biomass Yield (AFDW Basis) 37.5 US Ton/acre/yr

84.1 Metric tonne/ha/yr

Internal Rate of Return (After-Tax) 10%

Equity Percent of Total Investment 40%

Capital Costs Manufacturing Costs ($/US Ton AFDW Biomass product)

Production ponds (GAI Pond, SIZE 50-acre) $86,000,000 CO2 $91

Inoculum Ponds $16,100,000 Ammonia $15

CO2 Delivery $6,500,000 Diammonium Phosphate $6

Makeup Water Delivery + On-Site Circulation $8,200,000 Power $25

Dewatering $37,100,000 Chilled Water Utility $4

Storage $5,300,000 Fixed Costs $47

Capital Depreciation $43

Total Installed Equipment Cost $159,200,000 Average Income Tax $30

Average Return on Investment $131

Added Direct + Indirect Costs $117,500,000

 (% of TCI) 42%

Manufacturing Costs ($/yr)

Total Capital Investment (TCI) $276,700,000 CO2 $17,000,000

Ammonia $2,900,000

Installed Equipment Cost/Annual US dry ton biomass $849 Diammonium Phosphate $1,100,000

Total Capital Investment/Annual US dry ton biomass $1,475 Power $4,700,000

Chilled Water Utility $700,000

Loan Rate 8.0% Fixed Costs $8,800,000

Term (years) 10 Capital Depreciation $8,100,000

Capital Charge Factor (Computed) 0.138 Average Income Tax $5,600,000

Average Return on Investment $24,600,000

Specific Operating Conditions

Algal Productivity (g/m^2/day) 25

3:1

41

5000

Total footprint (acres; includes processing, storage, etc.) 7615

$392 /US Ton Biomass MBSP

Algal Biomass Production Process Engineering Analysis

CO2 Price ($/US ton)

All Values in 2011$

Production Pond Design: GAI Pond, SIZE 50-acre

Facility size (acres, cultivation pond only)

Maximum seasonal variability (productivity)