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

Feasibility Study of Economics 

and Performance of Solar 

Photovoltaics at the Ft. Hood 

Military Base Outside Killeen, 

Texas

A Study Prepared in Partnership with the 

Environmental Protection Agency for the 

RE-Powering America’s Land Initiative: 

Siting Renewable Energy on Potentially 

Contaminated Land and Mine Sites

Jesse Geiger, Lars Lisell, and Gail Mosey

Produced under direction of the U.S. Environmental Protection 

Agency (EPA) by the National Renewable Energy Laboratory (NREL) 

under Interagency Agreement IAG-11-01836 and Task No. 

WFM2.1001. 

Technical Report

NREL/TP-6A10-60398

October 2013
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

Feasibility Study of Economics 

and Performance of Solar 

Photovoltaics at the Ft. Hood 

Military Base Outside Killeen, 

Texas 

A Study Prepared in Partnership with the 

Environmental Protection Agency for the 

RE-Powering America’s Land Initiative: 

Siting Renewable Energy on Potentially 

Contaminated Land and Mine Sites

Jesse Geiger, Lars Lisell, and Gail Mosey

Prepared under Task No. WFM2.1001

Technical Report

NREL/TP-6A10-60398

October 2013
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

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or favoring by the United States government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

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at www.nrel.gov/publications.

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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721.

 Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. 
iii

Acknowledgments

The National Renewable Energy Laboratory (NREL) thanks the U.S. Environmental Protection 

Agency (EPA) for its interest in securing NREL’s technical expertise. In particular, NREL and 

the assessment team for this project are grateful to the Ft. Hood facility managers, engineers, and 

operators for their generous assistance and cooperation. 

Special thanks go to Africa Welch-Castle for hosting the site visit.

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
iv

Executive Summary

The U.S. Environmental Protection Agency (EPA), in accordance with the RE-Powering 

America’s Land initiative through the Region 6 contract, selected Ft. Hood Army Base in 

Killeen, Texas, for a feasibility study of renewable energy production. The National Renewable 

Energy Laboratory (NREL) provided technical assistance for this project. The purpose of this 

study is to assess the site for possible photovoltaic (PV) system installations and estimate the 

cost, performance, and site impacts of different PV options. In addition, the report recommends 

financing options that could assist in the implementation of a PV system at the site. This study 

does not assess environmental conditions at the site. 

Ft. Hood Army Base is located just north and west of Killeen, Texas, and 70 miles north of 

Austin. The military base has been in operation since 1942 and is the largest active-duty armored 

post. Home of the III Corps, the base, capable of housing two full armored divisions, currently 

has 79,640 people on post with more returning from deployments. The site has many 

construction projects on and around the base as buildings are upgraded regularly. Any future 

renewable energy projects will need to fit into the existing build-out plans. The base has two

operating PV systems on site: the solar carports outside of the engineering offices and a 700-kW 

system in a residential neighborhood just south of the main cantonment. 

The suitability of a PV system before considering economic factors is dependent on the available 

area for an array, solar resource, distance to transmission lines, and distance to major roads. In 

addition, the operating status, ground conditions, and restrictions associated with future 

development of the base impact the feasibility of a PV system. After an assessment of these 

factors, we concluded that Ft. Hood is suitable for deployment of a large-scale PV system. 

The Ft. Hood site is approximately 159,000 acres; 52 acres of this were investigated for groundmounted PV, with the additional potential to incorporate PV systems on top of existing and new 

buildings. To the north of the main cantonment (MC) is a vast open space used for military 

exercises and not considered for renewable energy development. There are currently 28.6 acres 

designated for a ground-mounted PV system on the western side of the MC and 23.7 acres 

available for a ground-mounted system in West Ft. Hood. 

There are approximately 50 acres available for potential carport roof-mounted PV systems as 

well. The entire area does not need to be developed at one time, due to the feasibility of staging 

installation as land or funding becomes available, so calculations for this analysis reflect the 

solar potential of the roof-mounted PV systems at $750,000 and $1 million funding levels as well 

as if entire designated land areas are used for the ground-mounted systems. It should be noted 

that the purpose of this report is not to determine how to develop the site but to investigate 

options and present the results in an unbiased manner. 

The economics were analyzed using the average Oncor Energy retail rate provided during the 

site visit of $0.0593/kWh, and all power produced was considered to offset purchased power. 

Four incentives were included in the economic analysis of systems installed and owned by a 

third-party developer (taxable entity). Table ES-1 shows the current incentives considered. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
v 

Table ES-1. Summary of Incentives Evaluated

Incentive Title Modeled Value Expected End 

1. Solar and Wind Energy Business 

Franchise Tax Exemption 

100% of corporate tax N/A

2. Renewable Energy Systems 

Property Tax Exemption

100% of property tax N/A

3. Oncor Electric Delivery - PV 

Incentive Program 

Non-residential: $1.50/W

DC-STC; Maximum: 

100 kW

N/A

4. Federal Investment Tax Credit 30% of total investment 12/31/2015

Of the 12 scenarios considered, none had a positive net present value and 2 had a payback in the 

analysis period. Without other factors beyond utility savings, such as grid independence and 

price guarantees, PV systems would not be recommended for the site at the current utility price. 

Table ES-2 summarizes the system performance and economics of potential systems that were 

modeled at Ft. Hood. The table shows the annual energy output from each system along with the 

number of average American households that could be powered off such a system and 

corresponding estimated job creation. This includes the current cost of energy, expected 

installation cost, site solar resource, and existing incentives for the proposed PV system. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
vi 

Table ES-2. Ft. Hood PV System Summary

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
vii 

Table of Contents

1 Study and Site Background................................................................................................................. 1

2 Development of a PV System on an Army Base ............................................................................... 2

3 PV Systems Technology...................................................................................................................... 4

3.1 PV Overview .................................................................................................................................... 4

3.2 Major System Components .............................................................................................................. 5

3.2.1 PV Module .......................................................................................................................... 5

3.2.2 Inverter ................................................................................................................................ 7

3.2.3 Balance-of-System Components ......................................................................................... 8

3.2.4 Operation and Maintenance .............................................................................................. 10

3.3 Siting Considerations ..................................................................................................................... 10

4 Proposed Installation Location Information .................................................................................... 12

4.1 Ft. Hood Site PV System ............................................................................................................... 12

4.2 Carport-Mounted PV Systems ....................................................................................................... 12

4.3 Ground-Mounted Systems ............................................................................................................. 13

4.4 Utility-Resource Considerations .................................................................................................... 17

4.5 Useable Acreage for PV System Installation ................................................................................. 18

4.6 PV Site Solar Resource .................................................................................................................. 18

4.7 Ft. Hood Energy Usage .................................................................................................................. 20

5 Economics and Performance............................................................................................................ 21

5.1 Assumptions and Input Data for Analysis ..................................................................................... 21

5.2 SAM-Forecasted Economic Performance ...................................................................................... 23

5.2.1 Solar Investor Versus Developer Owned .......................................................................... 25

5.2.2 Fixed Plate Versus Single-Axis Tracking ......................................................................... 26

5.2.3 Possible Ways to Improve the Economics Not Modeled .................................................. 26

5.3 Job Analysis and Impact ................................................................................................................ 27

5.4 Financing Opportunities................................................................................................................. 28

5.4.1 Owner and Operator Financing ......................................................................................... 28

5.4.2 Third-Party Developers with Power Purchase Agreements .............................................. 29

5.4.3 Third-Party “Flip” Agreements......................................................................................... 29

5.4.4 Hybrid Financial Structures .............................................................................................. 30

5.4.5 Solar Services Agreement and Operating Lease ............................................................... 30

5.4.6 Sales/Leaseback ................................................................................................................ 30

6 Conclusions and Recommendations ............................................................................................... 31

Appendix A. Assessment and Calculations Assumptions ................................................................... 32

Appendix B. Results of the System Advisor Model .............................................................................. 35

Appendix C. Results of the Jobs and Economic Development Impact Model ................................... 49

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
viii

List of Figures

Figure 1. Generation of electricity from a PV cell ...........................................................................4

Figure 2. Ground-mounted array diagram .......................................................................................5

Figure 3. Mono- and multi-crystalline solar panels .........................................................................6

Figure 4. Thin-film solar panels installed on (left) solar energy cover and (middle/right) 

fixed-tilt mounting system .........................................................................................................6

Figure 5. String inverter ...................................................................................................................8

Figure 6. Aerial view of the areas evaluated for PV carports (comprises only a small section of 

the space available for carports at the MC) .............................................................................13

Figure 7. Aerial view of the area evaluated for ground-mounted PV on the MC at Ft. Hood ......14

Figure 8. Ground view of the 28.6-acre area evaluated for ground-mounted PV on the west side 

of the MC .................................................................................................................................15

Figure 9. Aerial view of the two sites evaluated for ground-mounted PV at the West Ft. Hood 

site ............................................................................................................................................16

Figure 10. Ground view of the area evaluated for ground-mounted PV at the West 

Ft. Hood site .............................................................................................................................16

Figure 11. Location of onsite substation near the MC area evaluated for a ground-mounted 

system ......................................................................................................................................17

Figure 12. Location of onsite substation near the West Ft. Hood area evaluated for a groundmounted system .......................................................................................................................18

Figure B-1. Monthly output for the $750,000 carport system .......................................................35

Figure B-2. Annual cash flow for the $750,000 carport system ....................................................36

Figure B-3. Monthly output for the $1,000,000 carport system ....................................................37

Figure B-4. Annual cash flow for the $1,000,000 carport system .................................................38

Figure B-5. Monthly output for the total carport system ...............................................................39

Figure B-6. Annual cash flow for the total carport system ............................................................40

Figure B-7. Monthly output for the fixed-tilt ground-mounted system in the MC........................41

Figure B-8. Annual cash flow for the fixed-tilt ground-mounted system in the MC ....................42

Figure B-9. Monthly output for the single-axis tracking ground-mounted system in the MC ......43

Figure B-10. Annual cash flow for the single-axis tracking ground-mounted system in the MC .44

Figure B-11. Monthly output for the fixed-tilt ground-mounted system in West Ft. Hood ..........45

Figure B-12. Annual cash flow for the fixed-tilt ground-mounted system in West Ft. Hood .......46

Figure B-13. Monthly output for the single-axis tracking ground-mounted system in West 

Ft. Hood ...................................................................................................................................47

Figure B-14. Annual cash flow for the single-axis tracking ground-mounted system in West 

Ft. Hood ...................................................................................................................................48

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
ix

List of Tables

Table ES-1. Summary of Incentives Evaluated ...............................................................................v

Table ES-2. Ft. Hood PV System Summary .................................................................................. vi

Table 1. Ground-Mounted Energy Density by Panel and System ...................................................9

Table 2. Rooftop Energy Density by Panel .....................................................................................9

Table 3. Site Identification Information and Specifications ..........................................................19

Table 4. Performance Results for 20-Degree Fixed-Tilt PV .........................................................19

Table 5. Performance Results for 20-Degree Single-Axis PV ......................................................20

Table 6. Installed System Cost Assumptions .................................................................................22

Table 7. Summary of Incentives Evaluated ...................................................................................23

Table 8. PV System Summary .......................................................................................................24

Table 9. Breakeven (NPV>$0) Price Points ..................................................................................27

Table 10. JEDI Analysis Assumptions ..........................................................................................28

Table A-1. Cost, System, and Other Assessment Assumptions ....................................................32

Table A-2. Modeling Assumptions ................................................................................................33

Table C-1. Photovoltaic Project Data Summary 16-kW Roof-Mounted System ..........................49

Table C-2. Local Economic Impacts—Summary Results .............................................................50

Table C-3. Detailed PV Project Data Costs ...................................................................................51

Table C-4. PV System Annual Operations and Maintenance Costs ..............................................52

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
1 

1 Study and Site Background

The U.S. Environmental Protection Agency (EPA), in accordance with the RE-Powering 

America’s Land initiative through the Region 6 contract, selected the Ft. Hood Army 

base near Killeen, Texas, for a feasibility study of renewable energy production. The 

National Renewable Energy Laboratory (NREL) provided technical assistance for this 

project. The purpose of this study is to assess the site for a possible photovoltaic (PV) 

system installation and estimate the cost, performance, and site impacts of different PV 

options. In addition, the report recommends financing options that could assist in the 

implementation of a PV system at the site. This study did not assess environmental 

conditions at the site. 

Ft. Hood is located northwest of Killeen, Texas, which is located 70 miles north of Austin

and 160 miles southwest of Dallas. Ft. Hood has a population of 79,640 on post, with 

many more personnel living off base. Ft. Hood experiences summers that are warm and 

humid with high temperatures typically in the 100o

F range. Winters are cool and cloudy 

with low temperatures in the 40oF range. Ft. Hood has on average 187 days of sunshine 

each year. Oncor Energy is the utility that provides electricity to Ft. Hood and is a 

deregulated utility. 

The total site area at Ft. Hood is approximately 158,700 acres. The base is split into four 

main areas: the main cantonment (MC), West Fort Hood, North Fort Hood, and Belton 

Lake. The MC is where the majority of the on-base personnel resides and works and is 

the area targeted for PV development. Currently a small onsite demonstration of PVcovered car ports and a ground-mounted 700-kW system are being used to prove the 

feasibility of PV on base. There are a number of areas available for PV arrays on base;

however, a few areas have been suggested for PV development by site engineers. A 

preferred dual-purpose development plan would be to build carports in the main parking 

areas for barracks and motor pools. West Fort Hood also has an area near a substation 

suggested for PV development. The major limiting factor for feasibility at the Ft. Hood 

site will not be available area but available funding for energy and energy security 

projects. The ability of developers who can offer PPA prices competitive with grid 

electrical rates will also be a consideration. 

The base has three major electrical substations on site and a large number of meters 

around the MC. The areas adjacent to substations are ideal locations for a large PV 

system. A detailed interconnection study will have to be performed through local electric 

utility Oncor Energy to determine the feasibility of utilizing the onsite substation as a tiein point for a PV system. The site has a large load, 465,272 MWh in 2011, some of which 

could be offset using PV. 

Feasibility assessment team members from NREL, the Ft. Hood Directorate of Public 

Works Energy Management Office, and EPA conducted a site visit on Monday and 

Tuesday, September 17 and 18, 2012, to gather information integral to this feasibility 

study. The team considered information, including solar resource, transmission 

availability, community acceptance, and ground conditions. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
2 

2 Development of a PV System on an Army Base

Ft. Hood is an active military base that is interested in increased energy savings and 

energy security onsite. The community of Ft. Hood is planned through the Army’s master 

planning process. PV and other onsite generation options will need to be integrated with 

the site plan as funding allows. The purpose of this study is to analyze plausible options 

so that an informed decision can be made on how to best utilize the site. 

Understanding opportunities studied and realized by other similar sites demonstrates the 

potential for PV system development.

Developing onsite renewable energy supplies can reduce energy cost risk and may 

become an increasingly important strategic opportunity. Renewable energy technologies 

can contribute to enhancing security of the energy supplied to the site while allowing for 

predictable and potentially decreased energy costs and responsiveness to energy-related 

federal or U.S. Department of Defense (DoD) mandates.

The Army is currently working on a pilot initiative to find pathways to have typical 

installations generate energy onsite equivalent to annual use. Army has partnered with 

NREL to assess opportunities for increasing energy security through increased energy 

efficiency (EE) and optimized renewable energy strategies at select installations across 

the Army’s portfolio. 

The Army’s vision is to “appropriately manage our natural resources with the goal of net 

zero installations.”1 Although Ft. Hood is not currently generating a large portion of their 

energy needs, a move toward energy efficiency and onsite energy generation could 

position the installation to become a leader within DoD and improve their strategic 

capabilities.

Ft. Hood has potential renewable energy and energy security prospects beyond the solar 

PV systems proposed in this report. Any potential PV installation should align with the 

master plan and should work to enhance the overall utility of the base. Aside from PV, 

there is opportunity to build up biomass-based fuel production onsite and biomass power 

production. There are also opportunities to build on- and off-site wind turbines that could 

have the ability to directly power the base. Further development of these and other energy 

opportunities at the site could be pursued. 

There are many compelling reasons to consider moving toward renewable energy sources 

for power generation instead of fossil fuels, including: 

• Renewable energy sources offer a grid-independent energy option in the 

broader energy portfolio

• Deployment of renewable energy bolsters national energy independence and 

increases domestic energy security

 

1 Office of the Assistant Secretary of the Army (Installations, Energy & Environment), “Army Vision for 

Net Zero,” February 2010. Accessed January 2012: http://army-energy.hqda.pentagon.mil/netzero/. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
3 

• Fluctuating electric costs can be mitigated by locking in electricity rates 

through long-term power purchase agreements (PPAs) linked to renewable 

energy systems 

• Renewable energy can have a net positive effect on human health and 

the environment. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
4 

3 PV Systems Technology

3.1 PV Overview

Solar PV technology converts energy from solar radiation directly into electricity. Solar 

PV cells are the electricity-generating component of a solar energy system. When 

sunlight (photons) strikes a PV cell, an electric current is produced by stimulating 

electrons (negative charges) in a layer in the cell designed to give up electrons easily. The 

existing electric field in the solar cell pulls these electrons to another layer. By 

connecting the cell to an external load, this current (movement of charges) can then be 

used to power the load (e.g., light bulb). 

Figure 1. Generation of electricity from a PV cell

Source: EPA

PV cells are assembled into a PV panel or module. PV modules are then connected to 

create an array. The modules are connected in series and then in parallel as needed to 

reach the specific voltage and current requirements for the array. The direct current (DC) 

electricity generated by the array is then converted by an inverter to useable alternating 

current (AC) that can be consumed by adjoining buildings and facilities or exported to the 

electricity grid. PV system size varies from small residential (2–10 kW), to commercial 

(100–500 kW), to large utility scale (10+ MW). Central distribution plants are also 

currently being built in the 100+ MW scale. Electricity from utility-scale systems is 

commonly sold back to the electricity grid.

(-)

(+)

-

- -

-

Electron

Current flow

-

Solar cell

- - -

Load

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
5 

3.2 Major System Components

Figure 2. Ground-mounted array diagram

Source: NREL

A typical PV system is made up of several key components, including: 

• PV modules 

• Inverter

• Balance-of-system (BOS) components. 

These, along with other PV system components, are discussed in turn below. 

3.2.1 PV Module

Module technologies are differentiated by the type of PV material used, resulting in a 

range of conversion efficiencies from light energy to electrical energy. The module

efficiency is a measure of the percentage of solar energy converted into electricity. 

Two common PV technologies that have been widely used for commercial- and utilityscale projects are crystalline silicon and thin film. 

3.2.1.1 Crystalline Silicon

Traditional solar cells are made from silicon. Silicon is quite abundant and nontoxic. It 

builds on a strong industry on both supply (silicon industry) and product side. This 

technology has been demonstrated for a consistent and high efficiency over 30 years in 

the field. The performance degradation, a reduction in power generation due to long-term 

exposure, is under 1% per year. Silicon modules have a lifespan in the range of 25–30 

years but can keep producing energy beyond this range. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
6 

Typical overall efficiency of silicon solar panels is between 12% and 18%. However, 

some manufacturers of mono-crystalline panels claim an overall efficiency nearing 20%. 

This range of efficiencies represents significant variation among the crystalline silicon 

technologies available. The technology is generally divided into mono- and multicrystalline technologies, which indicates the presence of grain-boundaries (i.e., multiple 

crystals) in the cell materials and is controlled by raw material selection and 

manufacturing technique. Crystalline silicon panels are widely used based on 

deployments worldwide. 

Figure 3 shows two examples of crystalline solar panels: mono- and multi-silicon 

installed on tracking mounting systems.

Figure 3. Mono- and multi-crystalline solar panels. Photos from (left) SunPower 

Corporation, NREL 23816 and (right) SunPower, NREL 13823

3.2.1.2 Thin Film

Thin-film PV cells are made from amorphous silicon (a-Si) or non-silicon materials, such 

as cadmium telluride (CdTe). Thin-film cells use layers of semiconductor materials only 

a few micrometers thick. Due to the unique nature of thin films, some thin-film cells are 

constructed into flexible modules, enabling such applications as solar energy covers for 

landfills, such as a geomembrane system. Other thin-film modules are assembled into 

rigid constructions that can be used in fixed-tilt or, in some cases, tracking system 

configurations. 

The efficiency of thin-film solar cells is generally lower than for crystalline cells. Current 

overall efficiency of a thin-film panel is between 6% and 8% for a-Si and 11% and 12% 

for CdTe. Figure 4 shows thin-film solar panels.

 

Figure 4. Thin-film solar panels installed on (left) solar energy cover and (middle/right) 

fixed-tilt mounting system. Photos from (left) Republic Services, Inc., NREL 23817, 

(middle) Beck Energy, NREL 14726, and (right) U.S. Coast Guard Petaluma site, 

NREL 17395

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
7 

Industry standard warranties of both crystalline and thin-film PV panels typically 

guarantee system performance of 80% of the rated power output for 25 years. After 

25 years, they will continue producing electricity at a lower performance level.

3.2.2 Inverter

Inverters convert DC electricity from the PV array into AC and can connect seamlessly to 

the electricity grid. Inverter efficiencies can be as high as 98.5%. 

Inverters also sense the utility power frequency and synchronize the PV-produced power 

to that frequency. When utility power is not present, the inverter will stop producing AC 

power to prevent “islanding” or putting power into the grid while utility workers are 

trying to fix what they assume is a de-energized distribution system. This safety feature is 

built into all grid-connected inverters in the market. Electricity produced from the system 

may be fed to a step-up transformer to increase the voltage to match the grid. 

There are two primary types of inverters for grid-connected systems: string and microinverters. Each type has strengths and weaknesses and may be recommended for different 

types of installations.

String inverters are most common and typically range in size from 1.5 kW to 1,000 kW. 

These inverters tend to be cheaper on a capacity basis, as well as have high efficiency and 

lower operation and maintenance (O&M) costs. String inverters offer various sizes and 

capacities to handle a large range of voltage output. For larger systems, string inverters 

are combined in parallel to produce a single point of interconnection with the grid. 

Warranties typically run 10 years. On larger units, extended warranties up to 25 years are 

possible. Given that the expected life of the PV panels is 25–30 years, an operator can 

expect to replace a string inverter at least one time during the life of the PV system. 

Micro-inverters are dedicated to the conversion of a single PV module’s power output. 

The AC output from each module is connected in parallel to create the array. This 

technology is relatively new to the market and in limited use in larger systems due to a 

potential increase in O&M associated with significantly increasing the number of 

inverters in a given array. Current micro-inverters range in size between 175 W and 

380 W. These inverters can be the most expensive option per watt of capacity. Warranties 

range from 10–25 years. Small projects with irregular modules and shading issues 

typically benefit from micro-inverters. 

With string inverters, small amounts of shading on a solar panel will significantly affect 

the entire array production. Shading impacts only that shaded panel if micro-inverters are 

used. Figure 5 shows a string inverter. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
8 

Figure 5. String inverter. Photo by Warren Gretz, NREL 07985

3.2.3 Balance-of-System Components

In addition to the solar modules and inverter, a solar PV system consists of other parts 

called BOS components, which include: 

• Mounting racks and hardware for the panels 

• Wiring for electrical connections. 

3.2.3.1 Mounting Systems

The array has to be secured and oriented optimally to maximize system output. The 

structure holding the modules is referred to as the mounting system.

3.2.3.1.1 Ground-Mounted Systems

For ground-mounted systems, the mounting system can be either directly anchored into 

the ground (via driven piers or concrete footers) or ballasted on the surface without 

ground penetration. Mounting systems must withstand local wind loads, which range 

from 90–120 mph range for most areas or 130 mph or more for areas with hurricane 

potential. Depending on the region, snow and ice loads must also be a design 

consideration for the mounting system. For brownfield applications, mounting system 

designs will be primarily driven by these considerations coupled with settlement 

concerns. 

Typical ground-mounted systems can be categorized as fixed tilt or tracking. Fixed-tilt 

mounting structures consist of panels installed at a set angle, typically based on site 

latitude and wind conditions, to increase exposure to solar radiation throughout the year. 

Fixed-tilt systems are used at many brownfield sites. Fixed-tilt systems have lower 

maintenance costs but generate less energy (kWh) per unit power (kW) of capacity than 

tracking systems. 

Tracking systems rotate the PV modules so they are following the sun as it moves across 

the sky. This increases energy output but also increases maintenance and equipment costs 

slightly. Single-axis tracking, in which PV is rotated on a single axis, can increase energy 

output up to 25% or more. With dual-axis tracking, PV is able to directly face the sun all 

day, potentially increasing output up to 35% or more. Depending on underlying soiling 

conditions, single- and dual-axis trackers may not be suitable due to potential settlement 

effects, which can interfere with the alignment requirements of such systems. 

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9 

Table 1. Ground-Mounted Energy Density by Panel and System

System Type Fixed-Tilt Energy Density 

(DC-Watts/ft2

) 

Single-Axis Tracking 

Energy Density

(DC-Watts/ft2

) 

Crystalline Silicon 4.0 3.3

The selection of mounting type is dependent on many factors, including installation size, 

electricity rates, government incentives, land constraints, latitude, and local weather. 

Contaminated land applications might raise additional design considerations due to site 

conditions, including differential settlement. 

Selection of the mounting system is also heavily dependent on anchoring or foundation 

selection. The mounting system design will also need to meet applicable local building 

code requirements with respect to snow, wind, and seismic zones. Selection of mounting 

types should also consider frost protection needs especially in cold regions, such as 

New England. 

3.2.3.1.2 Roof-Mounted Systems

Installing PV on rooftops has many of the same considerations as installing groundmounted PV systems. Factors, such as available area for an array, solar resource, shading, 

distance to transmission lines, and distance to major roads at the site, are just as important 

in roof-mounted systems as in ground-mounted systems. Rooftop systems can be 

ballasted or fixed to the roof, and it is recommended that the roof be relatively new (less 

than 5 years old) to avoid having to move the PV system in order to repair or replace 

the roof. 

The development plan for roof-mounted PV systems at Ft. Hood is to include PV on any 

newly constructed car ports. There are many relatively easy low-cost/no-cost measures 

that can be taken during the design phase so that the carports are optimally built for 

rooftop PV systems. Design strategies such as orienting the buildings so that the southern 

exposure is maximized and reducing the amount of mechanical equipment on the roof are 

examples of measures that can be taken to optimize rooftop PV systems. A solar-ready 

design guide was published in order to help design teams optimize rooftop PV systems 

when designing buildings.2

Table 2. Rooftop Energy Density by Panel

System Type Fixed-Tilt Energy Density 

(DC-Watts/ft2

) 

Crystalline Silicon 10.0 

Thin Film 4.3 

 

2 Lisell, L.; Tetreault, T.; Watson, A. Solar Ready Buildings Planning Guide, December 2009. Accessed 

October 2012: http://www.nrel.gov/docs/fy10osti/46078.pdf. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
10 

3.2.3.2 Wiring for Electrical Connections

Electrical connections, including wiring, disconnect switches, fuses, and breakers, are 

required to meet electrical code (e.g., NEC Article 690) for both safety and 

equipment protection. 

In most traditional applications, wiring from (1) the arrays to inverters and (2) inverters 

to point of interconnection is generally run as direct burial through trenches. In

brownfield applications, this wiring might be required to run through above-ground 

conduit due to restrictions with cap penetration or other concerns. Therefore, developers 

should consider noting any such restrictions, if applicable, in requests for proposals in 

order to improve overall bid accuracy. Similarly, it is recommended that PV system 

vendors reflect these costs in the quote when costing out the overall system. 

3.2.3.3 PV System Monitoring 

Monitoring PV systems can be essential for reliable functioning and maximum yield of a 

system. It can be as simple as reading values, such as produced AC power, daily kilowatthours, and cumulative kilowatt-hours, locally on an LCD display on the inverter. For 

more sophisticated monitoring and control purposes, environmental data, such as module 

temperature, ambient temperature, solar radiation, and wind speed, can be collected. 

Remote control and monitoring can be performed by various remote connections. 

Systems can send alerts and status messages to the control center or user. Data can be 

stored in the inverter’s memory or in external data loggers for further system analysis. 

Collection of this basic information is standard for solar systems and not unique to 

landfill applications.

Weather stations are typically installed in large-scale systems. Weather data, such as solar 

radiation and temperature, can be used to predict energy production, enabling comparison 

of the target and actual system output and performance and identification of underperforming arrays. Operators can also use this data to identify required maintenance, 

shade on panels, and accumulating dirt on panels, for example. Monitoring system data 

can also be used for outreach and education. This can be achieved with publicly 

available, online displays; wall-mounted systems; or even smart phone applications. 

3.2.4 Operation and Maintenance

PV panels typically have a 25-year performance warranty. String inverters, which come 

standard with a 10-year warranty (extended warranties are available), would be expected 

to last 10–15 years. Micro-inverters are known to have warranties as long as 25 years. 

System performance should be verified on a vendor-provided website. Wire and rack 

connections should be checked annually. This economic analysis uses an annual O&M 

cost computed as $20/kW/year, which is based on the historical O&M costs of installed 

fixed-axis grid-tied PV systems. In addition, the system should expect a replacement of 

system inverters in year 15 at a cost of $0.25/W. 

3.3 Siting Considerations

PV modules are very sensitive to shading. When shaded (either partially or fully), the 

panel is unable to optimally collect the high-energy beam radiation from the sun. As 

explained above, PV modules are made up of many individual cells that all produce a 

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11 

small amount of current and voltage. These individual cells are connected in series to 

produce a larger current. If an individual cell is shaded, it acts as resistance to the whole 

series circuit, impeding current flow and dissipating power rather than producing it. 

The NREL solar assessment team uses a Solmetric SunEye solar path calculator to assess 

shading at particular locations by analyzing the sky view where solar panels will be 

located. By finding the solar access, the NREL team can determine if the area is 

appropriate for solar panels.

Following the successful collection of solar resource data using the Solmetric SunEye 

tool and determination that the site is adequate for a solar installation, an analysis to 

determine the ideal system size must be conducted. System size depends highly on the 

average energy use of the facilities on the site, PPAs, incentives available, and 

utility policy. 

This report is available at no cost from the 

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12 

4 Proposed Installation Location Information

This section summarizes the findings of the NREL solar assessment site visit on 

September 17–18, 2012. 

4.1 Ft. Hood Site PV System

In order to get the most from ground area available, it is important to consider whether 

the site can be improved to better incorporate a solar system. If there are unused 

structures, fences, or electrical poles that can be removed, the un-shaded area can be 

increased to incorporate more PV panels. 

The Ft. Hood site is approximately 158,706 acres, and much of the site that could house a 

PV installation is already designated for use and future buildout. The vast majority of the 

base is used for field training and is not an acceptable building site for PV arrays. Due to 

the lack of electrical infrastructure outside of the cantonment, any PV arrays will be built 

in and near the cantonments. The cantonments could incorporate a large number of small 

and medium-sized ground-mounted and roof systems, with only a few spaces available to 

large systems. 

The PV systems would be built through dual-use applications, such as roof-mounted PV

systems on top of carports for the motor pools and barracks parking. The potential carport

option would serve as shaded cover for personal vehicles while producing power near the 

barracks loads without sacrificing unused land. Another reason this option is preferred is 

because the systems could be built out in small sections as funding becomes available. 

The areas that could be used for large ground-mounted PV arrays consist of gently 

sloping hills, which is good for packing systems together. The ground-mounted systems 

will cost less per installed capacity than the carport systems, and there is the potential for 

larger system sizes in ground systems. 

4.2 Carport-Mounted PV Systems

Figure 6 shows an aerial view of some of the potential areas for PV carports at Ft. Hood 

taken from Google Earth; the feasible area for the carports is shaded in red. Each of the 

parking lots between Old Ironsides Avenue and Hell on Wheels Avenue were measured 

to have adequate solar access. None of the surrounding buildings or trees will result in 

significant shading for a raised PV system. 

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13 

Figure 6. Aerial view of the areas evaluated for PV carports (comprises only a small 

section of the space available for carports at the MC) 

Illustration done in Google Earth

4.3 Ground-Mounted Systems

Three areas on the MC were also evaluated for ground-mounted PV systems—a 28.6-

acre site, a 17.6-acre site, and a 6.13-acre site. Figure 7 shows an aerial view of the 28.6-

acre site taken from Google Earth. The site is near the substation on the west side of the 

MC and just south of Tank Destroyer Boulevard. The hill is south-facing on a gentle 

slope, as seen in Figure 8.

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14 

Figure 7. Aerial view of the area evaluated for ground-mounted PV on the MC at Ft. Hood 

Illustration done in Google Earth

This report is available at no cost from the 

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at www.nrel.gov/publications.
15 

Figure 8. Ground view of the 28.6-acre area evaluated for ground-mounted PV on the west 

side of the MC 

Photo by Jesse Geiger, NREL

Figures 9 and 10 show the final suggested ground-mounted PV sites southwest of the MC 

in West Ft. Hood. The system is near the West Ft. Hood substation on a hill that faces 

east. This area will require more landscape work than the area mentioned above. 

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16 

Figure 9. Aerial view of the two sites evaluated for ground-mounted PV at the West Ft. 

Hood site

Illustration done in Google Earth

Figure 10. Ground view of the area evaluated for ground-mounted PV at the West Ft. Hood 

site. Photo by Jesse Geiger, NREL 

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17 

4.4 Utility-Resource Considerations

The carport rooftop systems should be sized to interconnect with the nearby barracks and 

motor pool meters. The carports should not require a major electrical tie-in, but 

confirmation from Oncor will be needed. The ground-mounted systems will require 

connections to substations onsite. The substations are located next to each groundmounted system. The locations of the two substations (in relation to the ground-mounted 

systems) are shown in Figure 11 and Figure 12. A detailed interconnection study will 

have to be performed through Oncor and Reliant Energy to determine the feasibility of 

utilizing the onsite substations as tie-in points for PV systems. The base has plans to 

expand the current number of buildings, but current onsite electric customers will be able 

to use the electricity produced by a PV system. 

Figure 11. Location of onsite substation near the MC area evaluated for a 

ground-mounted system

Illustration done in Google Earth

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18 

Figure 12. Location of onsite substation near the West Ft. Hood area evaluated for a 

ground-mounted system

Illustration done in Google Earth

4.5 Useable Acreage for PV System Installation 

Typically, a minimum of 2 useable acres is recommended to site commercial-scale PV 

systems. Useable acreage is typically characterized as “flat to gently sloping” southern 

exposures that are free from obstructions and get full sun for at least a 6-hour period each 

day. For example, eligible space for PV includes under-utilized or unoccupied land, 

vacant lots, and/or unused paved areas (e.g., a parking lot or industrial site space and

existing building rooftops). 

4.6 PV Site Solar Resource

The Ft. Hood site has been evaluated to determine the adequacy of the solar resource 

available using both onsite data and industry tools. 

The assessment team for this feasibility study collected multiple Solmetric SunEye data

and found a solar access of 90% or higher. All data gathered using this tool is available in 

Appendix C.

The predicted array performance was found using PVWatts Version 2 for Killeen, 

Texas.

3 Table 3 shows the station identification information, PV system specifications, 

and energy specifications for the site. For this summary array performance information, a 

hypothetical system size of 1 kW was used to show the estimated production for each 

kilowatt so that additional analysis can be performed using the data indicated below. It is 

scaled linearly to match the proposed system size. 

 

3 National Renewable Energy Laboratory. “PVWatts.” Accessed October 17, 2013: 

http://www.nrel.gov/rredc/pvwatts/. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
19 

Table 3. Site Identification Information and Specifications

Station Identification

Cell ID 0213391

State Texas

Latitude 31.0° N

Longitude 97.9° W

PV System Specifications

DC Rating 1.00 kW

DC to AC Derate Factor 0.8 

AC Rating 0.8 kW

Array Type Fixed Tilt

Array Tilt 20°

Array Azimuth 180°

Energy Specifications

Cost of Electricity $0.06/kWh

Table 4 shows the performance results for a 20-degree fixed-tilt PV system in Killeen, 

Texas, as calculated by PVWatts.

Table 4. Performance Results for 20-Degree Fixed-Tilt PV 

Month Solar Radiation

(kWh/m2

/day)

AC Energy

(kWh)

1 3.90 94

2 4.45 95

3 5.37 125

4 5.99 131

5 5.93 131

6 6.24 132

7 6.50 139

8 6.43 138

9 5.66 121

10 5.25 118

11 4.21 94

12 3.72 88

Year 5.31 1,408

Table 5 shows the performance results for a 20-degree single-axis tracking PV system in 

Killeen, Texas, as calculated by PVWatts. 

This report is available at no cost from the 

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at www.nrel.gov/publications.
20 

Table 5. Performance Results for 20-Degree Single-Axis PV

Month Solar Radiation

(kWh/m2/day)

AC Energy

(kWh)

1 4.74 116

2 5.44 117

3 6.71 158

4 7.40 163

5 7.33 164

6 7.93 171

7 8.36 183

8 8.18 178

9 7.17 155

10 6.67 152

11 5.14 117

12 4.52 109

Year 6.64 1,782

4.7 Ft. Hood Energy Usage

The Ft. Hood site currently has buildings on the site that use electricity. There are future

plans to build a significant number of buildings on the site. It is important to understand 

the energy use of the site to enable for a full analysis of whether or not energy produced 

would need to be sold or if it could offset onsite energy use. The onsite electrical provider 

is Oncor Energy, and the power producer is Reliant Energy. The average onsite electrical 

utility cost is currently $0.0593/kWh annually. The contract with the power provider is 

up for renewal this coming year and will be constant for 2013–2014. 

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21 

5 Economics and Performance

The economic performance of a PV system installed on the site is evaluated using a combination 

of the assumptions and background information discussed previously as well as a number of 

industry-specific inputs determined by other studies. In particular, this study uses the NREL 

System Advisor Model (SAM). 4 

SAM is a performance and economic model designed to facilitate decision making for people 

involved in the renewable energy industry, ranging from project managers and engineers to 

incentive program designers, technology developers, and researchers. 

SAM makes performance predictions for grid-connected solar, solar water heating, wind, and 

geothermal power systems and makes economic calculations for both projects that buy and sell 

power at retail rates and power projects that sell power through a PPA. 

SAM consists of a performance model and financial model. The performance model calculates a 

system's energy output on an hourly basis (sub-hourly simulations are available for some 

technologies). The financial model calculates annual project cash flows over a period of years for 

a range of financing structures for residential, commercial, and utility projects. 

SAM makes performance predictions for grid-connected solar, small wind, and geothermal 

power systems and economic estimates for distributed energy and central generation projects. 

The model calculates the cost of generating electricity based on information you provide about a 

project's location, installation and operating costs, type of financing, applicable tax credits and 

incentives, and system specifications. 

5.1 Assumptions and Input Data for Analysis

The cost of a PV system depends on the system size and other factors, such as geographic 

location, mounting structure, and type of PV module. Based on significant cost reductions in 

2011, the average cost for utility-scale ground-mounted systems have declined from $4.80/W in 

the first quarter of 2010 to $2.79/W in the first quarter of 2012. With an increasing demand and 

supply, potential of further cost reduction is expected as market conditions evolve. The installed 

system cost assumptions are summarized in Table 6. For this analysis, the installed cost of the 

baseline fixed-tilt ground-mounted systems was assumed to be $2.79/W, and the installed cost of 

single-axis tracking was assumed to be $3.34/W. For the carport systems a system cost addition 

will be required. This will add 15% to the baseline scenario for this scenario, by conservative 

estimate. Micro-inverters will also be evaluated for the carport scenarios to decrease ground 

space required. This will increase the installed cost by 10% but decrease the O&M costs for this 

scenario. The carport systems will only be able to use fixed-axis mounting. 

 

4 For additional information on SAM, see https://sam.nrel.gov/cost. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
22 

Table 6. Installed System Cost Assumptions

System Type Fixed Tilt 

($/Wp)

Single-Axis Tracking 

($/Wp)

Ground-Mounted System 2.79 3.34

+ Carports (15%) +0.42 N/A

+ Micro-Inverters (10%) +0.28 N/A

Full Carport Installation

(PV Only) 3.49 N/A

These prices include the PV array and the BOS components for each system, including the 

inverter and electrical equipment, as well as the installation cost. This includes estimated taxes 

and a national-average labor rate but does not include land cost. The economics of grid-tied PV 

depend on incentives, the cost of electricity, the solar resource, and panel tilt and orientation. 

It was assumed for this analysis that relevant federal and state incentives are received for taxable 

entities. It is important to consider all applicable incentives or grants to make PV as cost 

effective as possible. If the PV system is owned by a private tax-paying entity, this entity may 

qualify for federal tax credits and accelerated depreciation on the PV system, which can be worth 

about 30% of the initial capital investment. The total potential tax benefits to the tax-paying 

entity can be as high as 45% of the initial system cost. Because state and federal governments do 

not pay taxes, private ownership of the PV system would be required to capture tax incentives. 

For the purposes of this analysis, the project is expected to have a 25-year life, although the 

systems can be reasonably expected to continue operation past this point. A full list of standard 

assumptions can be found in Appendix A-2. For the purposes of modeling how much PV could 

cover carports, it was assumed that coverage could be 4 W/ft2

. PVWatts Version 2 was used to 

calculate expected energy performance for the system. 

Incentives were investigated for the Ft. Hood site using the DSIRE website, which summarizes 

renewable energy incentives at the state level.

5

 Four incentives were found that should apply to 

the Ft. Hood site if PV development on base were done through third-party developers. The list 

of incentives used in this study can be found in Table 7. Any incentives that were not 

immediately and obviously applicable to the Ft. Hood site were not considered in the analysis. 

 

5 DSIRE: Database of State Incentives for Renewables & Efficiency, http://www.dsireusa.org/. 

This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.
23 

Table 7. Summary of Incentives Evaluated 

Incentive Title Modeled Value Expected End 

1. Solar and Wind Energy Business 

Franchise Tax Exemption 

100% of corporate tax N/A

2. Renewable Energy Systems 

Property Tax Exemption 

100% of property tax N/A

3. Oncor Electric Delivery - Solar 

Photovoltaic Standard Offer 

Program

$0.539/W DC-STC and 

$0.41/kWh AC; 

Maximum: 20% of total 

budget

Annually funded: 2013: 

$4.43 million

4. Federal Investment Tax Credit 30% of total investment Through 2015

5.2 SAM-Forecasted Economic Performance

Using varied inputs and the assumptions summarized in Section 5.1, SAM predicts net present 

value (NPV), PPA, and levelized cost of energy (LCOE). Because of the unique funding options, 

scenarios were run to determine: the system size at different price points; carport space and 

ground space utilization; fixed and single-axis tracking for the ground portion; and third-party 

developer versus Ft. Hood ownership. There are multiple factors that go into choosing which 

scenario(s) beyond NPV, PPA, and LCOE including funding and multi-purpose structure. The 

following systems were evaluated:

1. Carport systems

A. A system under $750,000 installed cost 

B. A system under $1 million installed cost 

C. Total proposed carport-PV area 

D. A system under $750,000 installed cost with micro-inverters

E. Total proposed carport-PV area with micro-inverters

F. Best payback case for carport systems (100 kW) 

2. MC ground-mounted system (28.6 acres)

A. Fixed-tilt PV covering the entire area 

B. Single-axis PV covering the entire area 

3. West Ft. Hood ground-mounted system (17.6 + 6.1 acres) 

A. Fixed-tilt PV covering the entire area 

B. Single-axis PV covering the entire area 

C. Best economic case for ground-mounted systems 

4. A theoretical model to determine size and cost of using PV to turn Ft. Hood into a netzero installation.

Table 8 shows the SAM results from these scenarios.

This report is available at no cost from the 

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at www.nrel.gov/publications.
24 

Table 8. PV System Summary

A net-zero scenario was done to determine the maximum appropriate PV installation onsite and 

not as a currently feasible scale project. Ft. Hood would need to build 260,061 kW in solar 

capacity to become a net-zero facility if electricity usage were to remain constant from 2011.

This capacity should be seen as a ceiling for onsite renewable energy production, and when 

coupled with extensive energy storage systems, could maintain continuous operations on Ft. 

Hood during an extended outage of grid power. 

Only the 100-kW single-axis tracking system, which maximizes the potential Oncor Energy 

incentive, has a PPA price below the current utility cost for energy. The site has suitable solar 

This report is available at no cost from the 

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at www.nrel.gov/publications.
25 

resource, but combined with few incentives, prices for larger-scale solar energy onsite are higher 

than that for grid electricity. The prices may be overcome with changing utility prices, energy 

security price add-ons, and decreases to PV installation cost. All of the different options 

investigated have pros and cons that will play in deciding the path forward.

5.2.1 Solar Investor Versus Developer Owned

Using a solar investor to develop a PC system is a more attractive option for Ft. Hood from an 

economic perspective. The choice between going with a solar investor or developer ownership 

will depend on the desire for equipment ownership by Ft. Hood and the Army or ownership by a 

third party. A solar investor would build and finance the project and inherit the risk and profit, 

and Ft. Hood in turn would receive power from the PV system at a rate agreed upon by the site 

and the investor. The major benefits for a solar investor are the potential tax incentives and the 

ability of the developer to finance the project, requiring no upfront capital from the site. As a 

non-taxable entity, Ft. Hood will not be able to take advantage of the many different tax benefits 

that will drive down costs for the PV systems without a private developer partner. The primary 

benefit to ownership of the system to Ft. Hood will be full control over the systems; however, 

contracts can be structured with the solar investor to ensure power delivery to the base for energy 

security purposes. For these reasons, it is the suggestion of the feasibility team to pursue a 

solar investor. 

For the remainder of the analysis, options will be presented from the perspective that a solar 

investor with a tax incentive appetite will own and operate the PV systems.

Federal Prison Industries (FPI) UNICOR provides services, including solar PV development 

activities. Due to the nature of the work force and established process in which UNICOR can 

develop projects, UNICOR can oftentimes offer a lower PPA price than other developers. The 

federal government in general and Ft. Hood specifically may benefit from the overall increased 

efficiency of federal government operations. 

The reasons that FPI increases the overall efficiency for installing renewable energy systems are:

• FPI has the proper contracting authority for contracting for these systems. 

• FPI is staffed and resourced to provide turnkey renewable energy systems as it is 

consistent with FPI mission in general and with its renewable energy device 

manufacturing in particular because this directly enhances FPI's ability to train and 

educate inmates. 

• FPI has established a Multiple Award Contract with 20 renewable energy integrators. 

• FPI has teaming agreements with many of the large U.S. Department of Energy (DOE) 

energy services companies/integrators as well as with small businesses and service 

disabled veterans to provide integration services. 

• FPI has the expertise in the renewable energy field to ensure the requesting agency is 

getting a best value system. 

• FPI has established sources of third-party financing for these projects. 

This report is available at no cost from the 

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at www.nrel.gov/publications.
26 

5.2.2 Fixed Plate Versus Single-Axis Tracking 

For the carport systems, the system must be fixed tilt. For the ground-mounted simulations, the 

single-axis tracking modules are the preferred option because they will produce more energy and 

have a lower PPA. The single-axis tracking system will produce over 20% more energy than a 

fixed-axis system of the same capacity. When space is a limiting factor, single-axis tracking is 

often the more attractive option. Fluctuations in prices at the local level can switch the 

favorability of the system type. For the 2.5-MW system on the west side of the MC, the installed 

price of single-axis tracking modules would need to increase to $0.0362/kW for a fixed-axis 

system to have more favorable economics.

5.2.3 Possible Ways to Improve the Economics Not Modeled

The economics for a PV system at Ft. Hood could be feasible under lower installed prices,

slightly higher value for electricity produced onsite, or more incentives. One incentive that could 

allow for lower prices from a solar investor would be an exemption from sales taxes for solar 

equipment. This would reduce PPA prices for all PV systems by approximately $0.05/kWh. The 

price for energy security should also be considered for determining PV system feasibility. The 

ability to accept a higher price for secure onsite electricity than what Oncor is charging for 

energy will improve the chances for such a project to move forward. Also, the upcoming contract 

renewal with Oncor Energy could be an opportunity to negotiate onsite renewable energy 

systems, secure further incentives for PV, and improve the utility cooperation for projects 

on base. 

Sensitivity studies were done for the modeled systems to each scenario to determine when a 

system would be economically viable. Table 9 shows the panel installed cost and the utility 

price points that would make each scenario become economically feasible with Ft. Hood 

ownership. Each variable was varied independently. The price point for a panel installed cost is 

similar to the price for a third-party developer to offer a PPA price at the $0.0593/kWh current 

utility price.

This report is available at no cost from the 

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at www.nrel.gov/publications.
27 

Table 9. Breakeven (NPV>$0) Price Points

Case Installed Cost [$/W] Utility Price [$/kWh]

Carport System - <$750,000 1.94 0.102

Carport System - <$1 million 1.78 0.107

Carport System - Total area 1.54 0.113

Carport System - <$750,000 w/ microinverters 2.19 0.101

Carport System - Total area w/ micro-inverters 2.03 0.107

Fixed-Tilt Ground System – MC area 1.44 0.103

Single-Axis Ground System - MC area 1.94 0.96

Fixed-Tilt Ground System – West Ft. Hood 

area 1.44 0.103

Single-Axis Ground System – West Ft. Hood 

area 1.94 0.95

The results graphs and summary of inputs to SAM is available in Appendix B. 

5.3 Job Analysis and Impact

To evaluate the impact on employment and economic impacts of the PV project associated with 

this analysis, the NREL Jobs and Economic Development Impact (JEDI) models are used.

6 JEDI 

estimates the economic impacts associated with the construction and operation of distributed 

generation power plants. It is a flexible input-output tool that estimates, but does not precisely 

predict, the number of jobs and economic impacts that can be reasonably supported by the 

proposed facility. 

JEDI represents the entire economy, including cross-industry or cross-company impacts. For 

example, JEDI estimates the impact that the installation of a distributed generation facility would 

have on not only the manufacturers of PV modules and inverters but also the associated 

construction materials, metal fabrication industry, project management support, transportation, 

and other industries that are required to enable the procurement and installation of the 

complete system. 

For this analysis, inputs, including the estimated installed project cost ($/kW), targeted year of 

construction, system capacity (kW), O&M costs ($/kW), and location, were entered into the 

 

6 JEDI has been used by DOE, the U.S. Department of Agriculture, NREL, and the Lawrence Berkeley National 

Laboratory, as well as a number of universities. For information on JEDI, see 

http://www.nrel.gov/analysis/jedi/about_jedi.html. 

This report is available at no cost from the 

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model to predict the jobs and economic impact. It is important to note that JEDI does not predict 

or incorporate any displacement of related economic activity or alternative jobs due to the 

implementation of the proposed project. As such, the JEDI results are considered gross estimates 

as opposed to net estimates. 

For the Ft. Hood site, the values in Table 10 were assumed from a $750,000 limited project. 

Table 10. JEDI Analysis Assumptions

Input Assumed Value

Capacity 204 kW

Placed In Service Year 2013

Installed System Cost $734,316

Location Ft. Hood, TX

Using these inputs, JEDI estimates the gross direct and indirect jobs, associated earnings, and 

total economic impact supported by the construction and continued operation of the proposed 

PV system. 

The estimates of jobs associated with this project are presented as either construction-period jobs 

or sustained-operations jobs. Each job is expressed as a whole, or fraction, full-time equivalent 

(FTE) position. An FTE is defined as 40 hours per week for one person for the duration of a 

year. Construction-period jobs are considered short-term positions that exist only during the 

procurement and construction periods. 

As indicated in the results of the JEDI analysis provided in Appendix D, the total proposed 

system is estimated to support 6.9 direct and indirect jobs per year for the duration of the 

procurement and construction period. Total wages paid to workers during the construction period 

are estimated to be $327,200, and total economic output is estimated to be $889,000. The annual 

O&M of the new PV system is estimated to support 0.1 FTE per year for the life of the system. 

The jobs and associated spending are projected to account for approximately $3,300 in earnings 

and $6,100 in economic activity each year for the next 25 years. 

5.4 Financing Opportunities

The procurement, development, construction, and management of a successful utility-scale 

distributed generation facility can be owned and financed a number of different ways. The most 

common ownership and financing structures are described below. 

5.4.1 Owner and Operator Financing

The owner/operator financing structure is characterized by a single entity with the financial 

strength to fund all of the solar project costs and, if a private entity, sufficient tax appetite to 

utilize all of the project’s tax benefits. Private owners/operators typically establish a special 

purpose entity (SPE) that solely owns the assets of the project. An initial equity investment into 

the SPE is funded by the private entity using existing funds and all of the project’s cash flows 

and tax benefits are utilized by the entity. This equity investment is typically matched with debt 

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financing for the majority of the project costs. Project debt is typically issued as a loan based on 

each owner’s/operator’s assets and equity in the project. In addition, private entities can utilize 

any of federal tax credits offered. 

For public entities that choose to finance, own, and operate a solar project, funding can be raised 

as part of a larger, general obligation bond; as a standalone tax credit bond; through a tax-exempt 

lease structure, bank financing, grant and incentive programs, or internal cash; or some 

combination of the above. Certain structures are more common than others and grant programs 

for solar programs are on the decline. Regardless, as tax-exempt entities, public entities are 

unable to benefit directly from the various tax-credit-based incentives available to private 

companies. This has given way to the now common use of third-party financing structures, such 

as the PPA. 

5.4.2 Third-Party Developers with Power Purchase Agreements

Because many project site hosts have the financial or technical capabilities to develop a capital 

intensive project, many times they turn to third-party developers (and/or their investors). In 

exchange for access to a site through a lease or easement arrangement, third-party developers 

will finance, develop, own, and operate solar projects utilizing their own expertise and sources of 

tax equity financing and debt capital. Once the system is installed, the third-party developer will 

sell the electricity to the site host or local utility via a PPA—a contract to sell electricity at a 

negotiated rate over a fixed period of time. The PPA typically will be between the third-party 

developer and the site host if it is a retail “behind-the-meter” transaction or directly with an 

electric utility if it is a wholesale transaction. 

Site hosts benefit by either receiving competitively priced electricity from the project via the 

PPA or land lease revenues for making the site available to the solar developer via a lease 

payment. This lease payment can take on the form of either a revenue-sharing agreement or an 

annual lease payment. In addition, third-party developers are able to utilize federal tax credits. 

For public entities, this arrangement allows them to utilize the benefits of the tax credits (low 

PPA price, higher lease payment) while not directly receiving them. The term of a PPA typically 

varies from 20–25 years.

5.4.3 Third-Party “Flip” Agreements 

The most common use of this model is a site host working with a third-party developer who then 

partners with a tax-motivated investor in an SPE that would own and operate the project. 

Initially, most of the equity provided to the SPE would come from the tax investor and most of 

the benefit would flow to the tax investor (as much as 99%). When the tax investor has fully 

monetized the tax benefits and achieved an agreed-upon rate of return, the allocation of benefits 

and majority ownership (95%) would “flip” to the site host (but not within the first 5 years). 

After the flip, the site host would have the option to buy out all or most of the tax investor’s 

interest in the project at the fair market value of the tax investor’s remaining interest. 

A flip agreement can also be signed between a developer and investors within an SPE, where the 

investor would begin with the majority ownership. Eventually, the ownership would flip to the 

developer once each investor’s return is met.

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5.4.4 Hybrid Financial Structures

As the solar market evolves, hybrid financial solutions have been developed in certain instances 

to finance solar projects. A particular structure, nicknamed “The Morris Model” after Morris 

County, New Jersey, combines highly rated public debt, a capital lease, and a PPA. Low-interest 

public debt replaces more costly financing available to the solar developer and contributes to a 

very attractive PPA price for the site hosts. New markets tax credits have been combined with 

PPAs and public debt in other locations, such as Denver and Salt Lake City. 

5.4.5 Solar Services Agreement and Operating Lease

The solar services agreement (SSA) and operating lease business models have been 

predominately used in the municipal and cooperative utility markets due to the treatment of tax 

benefits and the rules limiting federal tax benefit transfers from non-profit to for-profit 

companies. Under IRS guidelines, municipalities cannot enter capital leases with for-profit 

entities when the for-profit entities capture tax incentives. As a result, a number of business 

models have emerged as a work-around to this issue. One model is the SSA, wherein a private 

party sells solar services [i.e., energy and renewable energy certificates (RECs)] to a 

municipality over a specified contract period (typically long enough for the private party to 

accrue the tax credits). The non-profit utility typically purchases the solar services with either a 

one-time up-front payment equal to the turnkey system cost minus the 30% federal tax credit or 

can purchase the services in annual installments. The municipality can buyout the system once 

the third party has accrued the tax credits, but due to IRS regulations, the buyout of the plant 

cannot be included as part of the SSA (i.e., the SSA cannot be used as a vehicle for a sale and 

must be a separate transaction).

Similar to the SSA, there are a variety of lease options that are available to municipalities that 

allow the capture of tax benefits by third-party owners, which result in a lower cost to the 

municipality. These include an operating lease for solar services (as opposed to an equipment 

capital lease) and a complex business model called a sales/leaseback. Under the sales/leaseback 

model, the municipality develops the project and sells it to a third-party tax equity investor who 

then leases the project back to the municipality under an operating lease. At the end of the lease 

period, and after the tax benefits have been absorbed by the tax equity investor, the municipality 

may purchase the solar project at fair market value.

5.4.6 Sales/Leaseback

In the widely accepted sales/leaseback model, the public or private entity would install the PV 

system, sell it to a tax investor, and then lease it back. As the lessee, they would be responsible 

for operating and maintaining the solar system as well as have the right to sell or use the power. 

In exchange for use of the solar system, the public or private entity would make lease payments 

to the tax investor (the lessor). The tax investor would have rights to federal tax benefits 

generated by the project and the lease payments. Sometimes, the entity is allowed to buy back 

the project at 100% fair market value after the tax benefits are exhausted. 

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6 Conclusions and Recommendations 

Under current utility and PV cost conditions studied, the inclusion of PV is not attractive solely 

for cost savings; however, deciding whether or not to pursue solar power should also include 

energy security, prices, and the duel benefit of solar and carport construction. There is also an 

opportunity to lower costs through an agreement with UNICOR as described in Section 5.2. As 

summarized in Section 5, the current PPA prices that could be attained from solar investors at a 

15% internal rate of return would be near $0.1176/kWh. Because Ft. Hood may be able to obtain 

better costs and PPA prices than what is found in this study, it is suggested that this report be 

used as a starting point for acquiring and comparing quotes from vendors. Table 10 lists some 

cost conditions that would make solar energy an economically attractive option.

The option with the highest likelihood to succeed identified in this study would be to 

incrementally build carport systems at the various funding limits allowed. Multiple factors make 

this the best option: many different small systems can maximize the capacity-based credit 

offered by Oncor; the multipurpose carports have a better chance to overcome poor economics; 

and the PV systems would be able to tie into meters already in place at the barracks. Considering 

all of these factors, the carports are the closest to becoming viable projects. 

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Appendix A. Assessment and Calculations 

Assumptions

Table A-1. Cost, System, and Other Assessment Assumptions

Cost Assumptions

Variable Quantity of 

Variable

Unit of Variable

Cost of Site Electricity 0.0593 $/kWh

Annual O&M (fixed) 20 $/kW/year

Inverter Replacement 10 for 15 years $/kW/year

System Assumptions

System Type Annual energy 

kWh/kW

Installed Cost 

($/W)

Energy Density 

(W/sq. ft.)

Ground Fixed 1,408 $2.79 4.0

Ground Single-Axis 1,782 $3.35 3.3

Carport-Mounted PV Systems 1,408 $3.21 4.0

Carport-Mounted PV With MicroInverters1,408 $3.49 4.0

Other Assumptions

1 acre 43,560 ft2

1 MW 1,000,000 W

Ground 

utilization

90% of available 

area

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Table A-2. Modeling Assumptions

Item PPA/Investor

Municipal 

Purchase Notes

Analysis period 

(years) 25 25

Inflation 2.50% 2.50%

Real discount rate 5.85% 3%

Federal tax rate 35% 0%

State tax rate 8% 0%

Insurance (% of 

installed cost) 0.50% 0.50%

Property tax 0 0

Construction loan 0 0

Loan term 15 25 25-year bonds

Loan rate 6% 6% May be lower for bonds

Debt fraction 55% 100%

45%-60% PPA, 100% 

municipal ownership, DSCR of 

~1.3 (>1.2)

Minimum IRR 15.00% 15.00%

PPA escalation 

rate 1.50% 1.50%

Federal

depreciation

5-year MACRS w/ 

50% 1st-year bonus N/A N/A for municipal ownership 

State depreciation 5-year MACRS N/A N/A for municipal ownership

Federal ITC 30% N/A N/A for municipal ownership

Payment 

incentives 0 0

Degradation 0.50% 0.50%

Availability 100% 100%

Cost - fixed axis 

per KW $2.79 - $3.20 $2.79 - $3.20

Cost - single-axis 

tracking per kW $3.35 - $3.84 $3.35 - $3.84

Cost - landfill 

ballasted per kW $3.49 - $4.00 $3.49 - $4.00

Grid 

interconnection

cost $ - $ - 

Land cost $ - $ - 

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O&M

$30/kW/yr first 15 

yrs & $20 yrs 16-25

$30/kW/yr first 15 

yrs & $20 yrs 16-

26

Derate factor 0.8 0.8

Fixed tilt 20° 20°

Single-axis tilt 0° 0°

Acres per MW 

fixed 5.74 5.74 

Acres per MW 

tracking 6.96 6.96 

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Appendix B. Results of the System Advisor Model

Figure B-1. Monthly output for the $750,000 carport system

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Figure B-2. Annual cash flow for the $750,000 carport system

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Figure B-3. Monthly output for the $1,000,000 carport system

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Figure B-4. Annual cash flow for the $1,000,000 carport system

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Figure B-5. Monthly output for the total carport system

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Figure B-6. Annual cash flow for the total carport system

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Figure B-7. Monthly output for the fixed-tilt ground-mounted system in the MC

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Figure B-8. Annual cash flow for the fixed-tilt ground-mounted system in the MC

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Figure B-9. Monthly output for the single-axis tracking ground-mounted system in the MC

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Figure B-10. Annual cash flow for the single-axis tracking ground-mounted system in 

the MC

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Figure B-11. Monthly output for the fixed-tilt ground-mounted system in West Ft. Hood

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Figure B-12. Annual cash flow for the fixed-tilt ground-mounted system in West Ft. Hood

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Figure B-13. Monthly output for the single-axis tracking ground-mounted system in West 

Ft. Hood

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Figure B-14. Annual cash flow for the single-axis tracking ground-mounted system in West 

Ft. Hood

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Appendix C. Results of the Jobs and Economic 

Development Impact Model

Appendix C shows the JEDI results from installing a 204-kW single-axis system. Other 

PV system sizes will be relative to this.

Table C-1. Photovoltaic Project Data Summary 16-kW Roof-Mounted System

Project Location Texas

Year of Construction or Installation 2013

Average System Size - DC Nameplate Capacity (kW) 204.0

Number of Systems Installed 1

Project Size - DC Nameplate Capacity (kW) 204.0

System Application Large 

Commercial

Solar Cell/Module Material Crystalline 

Silicon

System Tracking Single Axis

Total System Base Cost ($/kWDC) $3,430 

Annual Direct Operations and Maintenance Cost 

($/kW)

$20.00

Money Value – Current or Constant (Dollar Year) 2012

Project Construction or Installation Cost $699,637

 Local Spending $465,690

Total Annual Operational Expenses $83,220

 Direct Operating and Maintenance Costs $4,080

 Local Spending $3,754

 Other Annual Costs $79,140

 Local Spending $102

 Debt Payments $0

 Property Taxes $0

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Table C-2. Local Economic Impacts—Summary Results

Jobs Earnings Output

During Construction and Installation Period $000 (2012) $000 (2012)

 Project Development and Onsite Labor Impacts

 Construction and Installation Labor 0.9 $55.2

 Construction- and Installation-Related Services 1.6 $79.5

 Subtotal 2.5 $134.7 $249.0

 Module and Supply Chain Impacts

 Manufacturing Impacts 0.0 $0.0 $0.0

 Trade (Wholesale and Retail) 0.5 $31.3 $94.7

 Finance, Insurance, and Real Estate 0.0 $0.0 $0.0

 Professional Services 0.5 $20.1 $73.0

 Other Services 0.5 $34.9 $129.0

 Other Sectors 1.1 $37.8 $83.4

 Subtotal 2.6 $124.1 $380.1

 Induced Impacts 1.8 $68.3 $260.0

 Total Impacts 6.9 $327.2 $889.0

Annual Annual

Annual Earnings Output

During Operating Years Jobs $000 (2012) $000 (2012)

 Onsite Labor Impacts

 PV Project Labor Only 0.0 $2.3 $2.3

 Local Revenue and Supply Chain Impacts 0.0 $0.7 $2.3

 Induced Impacts 0.0 $0.4 $1.5

 Total Impacts 0.1 $3.3 $6.1

Notes: Earnings and output values are thousands of dollars in year 2012 dollars. Construction and operating 

period jobs are full-time equivalent for one year (1 FTE = 2,080 hours). Economic impacts "during 

operating years" represent impacts that occur from system/plant operations/expenditures. Totals might not 

add up due to independent rounding.

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Table C-3. Detailed PV Project Data Costs

New Mexico Purchased Manufactured

Installation Costs Cost

Locally 

(%) Locally (Y or N)

Materials and Equipment

 Mounting (rails, clamps, fittings, etc.) $37,203 100% N

 Modules $211,088 100% N

 Electrical (wire, connectors, breakers, etc.) $6,044 100% N

 Inverter $38,099 100% N

 Subtotal $292,433

Labor

 Installation $55,229 100%

 Subtotal $55,229

Subtotal $347,663

Other Costs

 Permitting $89,718 100%

 Other Costs $36,620 100%

 Business Overhead $207,360 100%

 Subtotal $333,697

Subtotal $681,360

Sales Tax (materials and equipment purchases) $18,277 100%

Total $699,637

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Table C-4. PV System Annual Operations and Maintenance Costs

Cost Local Share

Manufactured 

Locally 

(Y or N)

Labor

 Technicians $2,448 100%

 Subtotal $2,448

Materials and Services

Materials and Equipment $1,632 100% N

 Services $0 100%

 Subtotal $1,632

Sales Tax (materials and 

equipment purchases) $102 100%

Average Annual Payment 

(interest and principal) $79,038 0%

Property Taxes $0 100%

Total $83,220

Other Parameters

Financial Parameters

Debt Financing

 Percentage Financed 80% 0%

 Years Financed (term) 10

 Interest Rate 10%

Tax Parameters

 Local Property Tax 

(percent of taxable value) 0%

 Assessed Value (percent 

of construction cost) 0%

 Taxable Value (percent of 

assessed value) 0%

 Taxable Value $0

 Property Tax Exemption 

(percent of local taxes) 100%

 Local Property Taxes $0 100%

 Local Sales Tax Rate 6.25% 100%

 Sales Tax Exemption 

(percent of local taxes) 0%

Payroll Parameters Wage Per Hour

Employer Payroll 

Overhead

 Construction and 

Installation Labor

 Construction 

Workers/Installers $21.39 45.6%

 O&M Labor

 Technicians $21.39 45.6%

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