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.

Contract No. DE-AC36-08GO28308

Life Cycle Assessment of a 

Parabolic Trough Concentrating 

Solar Power Plant and Impacts 

of Key Design Alternatives

Preprint

Garvin A. Heath and Craig S. Turchi 

National Renewable Energy Laboratory

John J. Burkhardt III 

Abengoa Solar Inc.

To be presented at SolarPACES 2011

Granada, Spain

September 20 - 23, 2011

Conference Paper

NREL/CP-6A20-52186

September 2011
NOTICE

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Addendum 

Please see the following reference, and its supporting information, for more complete description of the 

methods and results reported here:

Burkhardt, J., G. Heath, and C. Turchi. 2011. Life Cycle Assessment of a Parabolic Trough Concentrating 

Solar Power Plant and the Impacts of Key Design Alternatives. Environmental Science & Technology. 45: 

2457–2464. http://dx.doi.org/10.1021/es1033266
1 

LIFE CYCLE ASSESSMENT OF A PARABOLIC TROUGH 

CONCENTRATING SOLAR POWER PLANT AND

IMPACTS OF KEY DESIGN ALTERNATIVES

Garvin A. Heath1

1 PhD, Senior Scientist, National Renewable Energy Laboratory, 1617 Cole Blvd, MS RSF300, Golden, 

CO 80401-3393 USA, 1-303-384-7460, 

*

, John J. Burkhardt III2 and Craig S. Turchi3

garvin.heath@nrel.gov, 2 MSME, Research Analyst, National 

Renewable Energy Laboratory; Current position: Performance Analyst, Abengoa Solar Inc., 3 PhD, 

Senior Engineer, National Renewable Energy Laboratory

Abstract

Climate change and water scarcity are important issues for today’s power sector. To inform capacity expansion 

decisions, life cycle assessment is used to evaluate a reference design of a parabolic trough CSP facility located 

in Daggett, California along four sustainability metrics: life cycle (LC) greenhouse gas (GHG) emissions, water 

consumption, cumulative energy demand (CED), and energy payback time (EPBT). This wet-cooled, 103 MW

plant utilizes mined nitrates salts in its two-tank, thermal energy storage (TES) system. Design alternatives of 

dry-cooling, a thermocline TES, and synthetically-derived nitrate salt are evaluated.

During its life cycle, the reference CSP plant is estimated to emit 26 g CO2eq per kWh, consume 4.7 L/kWh of 

water, and demand 0.40 MJeq/kWh of energy, resulting in an EPBT of approximately 1 year. The dry-cooled 

alternative is estimated to reduce LC water consumption by 77% but increase LC GHG emissions and CED by 

8%. Synthetic nitrate salts may increase LC GHG emissions by 52% compared to mined. Switching from twotank to thermocline TES configuration reduces LC GHG emissions, most significantly for plants using 

synthetically-derived nitrate salts. CSP can significantly reduce GHG emissions compared to fossil-fueled 

generation; however, dry-cooling may be required in many locations to minimize water consumption.

Keywords: LCA, water consumption, greenhouse gas, GHG, energy payback, EPBT

1. Introduction 

Operational carbon dioxide (CO2) emissions from the United States electric power sector constituted 40% of 

energy-related CO2 emissions in 2009, 98% of which was from combustion of coal and natural gas (1). 

Thermoelectric power was also responsible for 41% of all U.S. freshwater withdrawals in 2005, the largest enduse sector (2). Furthermore, water scarcity and drought will likely become more widespread during the 21st 

century as a result of climate change (3). An important challenge is to identify technologies that deliver 

electricity services while minimizing both greenhouse gas (GHG) emissions and use of locally finite freshwater 

resources. To inform capacity expansion decisions, this research quantifies the GHG emissions and water 

consumption of a representative parabolic trough (trough) concentrating solar power (CSP) plant.

Life cycle assessment (LCA) is recognized as a holistic and standard approach for quantifying environmental 

impacts of energy technologies, including those that use renewable resources. LCA accounts for the impacts 

resulting from up-stream and down-stream activities over the life cycle of a power plant. In this paper we 

evaluate a reference design for a parabolic trough CSP facility located in Daggett, California. This wet-cooled, 

103 MW plant utilizes mined nitrates salts in its two-tank, thermal energy storage (TES) system. This is the first 

LCA of a CSP plant in the U.S. in over a decade and reflects modern plant designs.

The goals of this study are to use hybrid LCA to expand on the limited literature that estimates the environmental 

impacts of CSP plants and, for the first time, to compare the environmental performance of several important 

design alternatives for trough CSP plants and quantify the plant’s life cycle water consumption. Quantified 

metrics of environmental performance include life cycle GHG emissions, water consumption, cumulative energy 

demand (CED), and the resultant energy payback time (EPBT). The design alternatives evaluated and compared 

herein include: wet versus dry cooling, two-tank indirect versus thermocline indirect TES systems, and mined 

versus synthetically-derived nitrate salt storage media.
2 

2. Methods

2.1.Scope

The temporal vintage of the CSP plant design is year 2010 and the geographic reference is Daggett, California, 

U.S., whose annual direct normal irradiation (DNI) is among the highest in the U.S. (approximately 2,700 

kWh/m2) [4]. The plant is assumed to operate for 30 years [5]. Following the guidelines described in the 

international standard series ISO 14040-44 [6], our hybrid LCA evaluates the following life cycle phases of the 

hypothetical trough plant: material and component manufacturing, plant construction, operation and maintenance 

(O&M), plant dismantling, and materials disposal. Infrastructure used in the transportation of materials, 

construction, and dismantling of the plant is amortized over the infrastructure element’s useful lifetime. Impacts 

are allocated to four CSP systems: heat transfer fluid (HTF), solar field, TES, and power plant.

SimaPro v7.1 [7] LCA modeling software and the EcoInvent life cycle inventory (LCI) database [8] were used 

throughout this study. Employing engineering judgment, materials specified in the reference plant design have 

been paired with an EcoInvent process to provide GHG emissions, energy flows, and embodied water when 

primary data was not available. An EIO LCA tool [9] was used to estimate life cycle burdens of select 

components and systems, including pumps, compressors, turbine generator set, and miscellaneous controls and 

electronic equipment. Costs of these components were extracted from primary data sources [5] and used as 

inputs to the U.S. 2002 Industry Benchmark EIO-LCA model [9].

Life cycle metrics are normalized to a functional unit of 1 kWh generated. The method by which each life cycle

metric is evaluated is described below:

• GHGs: Emissions of individual GHGs from the CSP plant life cycle are presented as the sum of each 

GHG weighted by its 100-year global warming potential (GWP) [3], divided by the total kWh generated by the 

plant over its lifetime, to obtain grams of CO2 equivalents (g CO2eq/kWh).

• Water Consumption: life cycle water consumption is calculated by summing the volume of surface and 

ground water consumed in all life cycle stages per unit of electricity generated (L/kWh). Water consumption is 

defined as the amount of water that is “evaporated, transpired, incorporated into products or crops, consumed by 

humans or livestock, or otherwise removed from the immediate water environment” [2]. 

• CED & EPBT: CED is the sum of all primary energy supplied by both RE and non-RE sources across 

the life cycle of the CSP plant (based on [7, 10]). Units are in megajoule equivalents per unit of electricity 

generated (MJeq/kWh). EPBT is defined as the length of time required to generate as much energy as is 

embodied in its life cycle (i.e., CED). EPBT is calculated as CEDtot / (α * Enet), where, CEDtot is total life cycle

CED of the CSP plant (MJeq), Enet is annual net output of the CSP plant (MJ/year), and the constant α is the ratio 

of source-to-site energy of average U.S. grid electricity (dimensionless). The constant α ensures that numerator 

and denominator are commensurate in terms of primary energy. (Note: It is unclear if all inputs to this equation 

are reported on a consistent heating value basis, i.e., higher or lower. However, the impact of potential 

inconsistency should not change the conclusions of this study.) The average value of α for years 2001-2005 for 

the United States has been reported as 3.34 [11]. 

2.2. Reference Plant Design and Data Sources

The hypothetical trough CSP plant, on which this LCA is based, was designed by a major CSP plant contract 

engineering firm, WorleyParsons Group (WPG), and is intended to be representative of actual plants being 

designed and built today in the U.S. [5]. This plant has a net capacity of 103 MW, incorporates 6.3 hours of 

storage (using a two-tank indirect configuration and mined salts), and is wet cooled. Hereafter we refer to this 

plant as the “reference plant”. To evaluate impacts of switching the reference plant design to one using drycooling technology, WPG also reported all necessary modifications required to maintain the reference plant’s 103 

MW net output [5, 12]. Table 1 lists the main specifications of the wet- and dry-cooled CSP plants. WPG 

provided mass and composition of materials embodied in subsystems of each plant, manufacturing locations of 

the aforementioned materials, and material- and energy-related information regarding O&M activities [12]. 
3 

Wet Dry Units

Gross Capacity 118 120.5 MW

Parasitics (at design 

point) 15 17.6 MW

Net Capacity 103 103 MW

Rankine Cycle 

Efficiency 37.4 35.4 % 

Annual Generation 426,700 438,800 MWh

Capacity Factor 0.47 0.49

Grid Electricity 

Consumption 3,700 3,990 MWh/yr

Natural Gas 

Consumption 8,900 15,600 MMBtu/yr

Solar Field Aperture 

Area 987,500 1,063,000 m2

HTF Mass 4,270 4,600 metric ton

TES Storage Capacity 1,990 2,140 MWhth

Total Plant Fenceline 

Area 4,100,000 4,140,000 m2

Table 1. Specifications of Wet- (Reference Plant) and Dry-Cooled Designs [5]

Primary data were obtained from manufacturers of several CSP plant components. Manufacturers of glass 

mirrors [13], heat collection elements (HCE) [14], and mined salts [15-17] provided detailed information on 

embodied materials, transportation methods, energy flows, and direct GHG emissions of manufacturing 

processes. Solutia, Inc. provided proprietary data regarding direct and indirect emissions resulting from in-house 

manufacturing processes and transportation of their high-temperature HTF, Therminol® VP-1 (“Therminol” is a 

registered trademark of Solutia, Inc.) [18]. To complete the life cycle accounting, the quantity of raw materials 

required to manufacture HTF and their associated impacts was estimated. Data regarding consumption of water 

during manufacturing processes were provided for the glass mirrors. For all other materials, direct and indirect 

water consumption was estimated employing EcoInvent processes of closely related materials.

The two-tank and thermocline TES systems were modeled using design parameters found in TES studies [19-22]

and personal communication with an industry expert [23]. Impacts resulting from manufacture of synthetic salts 

are approximated using reactions obtained from industrial chemical literature and LCI data from EcoInvent [8]. 

We assume that synthetic potassium nitrate is produced by reacting potassium chloride with nitric acid [24], and 

that synthetic sodium nitrate is produced by neutralizing nitric acid with sodium hydroxide [25]. 

3. Results and Discussion

3.1. Results for Reference Plant

Life cycle GHG emissions of the reference plant are estimated to be 26 g CO2eq/kWh. Table 2 reports life cycle

impacts by system and life cycle phase for both wet- and dry-cooled plant designs. The manufacturing phase is 

responsible for 46% of life cycle GHG emissions. The largest contributors to manufacturing-phase emissions are 

the solar collector assemblies (SCAs) and the HTF. The SCAs, which consist of mirrors, HCEs, and frames, 

contribute 33% of manufacturing emissions, or 15% of life cycle emissions. Embodied GHG emissions of these 

SCAs are considerable, owing to the large masses of energy-intensive materials in the solar field. Because of the 

large volume required and its relatively high normalized impacts, the HTF is the next largest contributor to 

manufacturing GHG emissions (15% of manufacturing phase or 7% of life cycle emissions).

The O&M phase is responsible for 39% of life cycle GHG emissions. Consumption of grid electricity used to 

satisfy the parasitic loads during hours with no electricity generation accounts for 67% of these emissions; this 

value is dependent upon the regional electricity generation fuel source mix and is reduced if the plant 

incorporates more TES. Natural gas consumption, which is used during daily system start-up and for HTF freeze 
4 

protection activities, and manufacture of replacement components are the next largest contributors to O&M phase 

GHG emissions, at 18% and 13% of operational emissions, respectively. Note that grid electricity consumed by 

all CSP plant systems contributes 6.8 g CO2eq/kWh to total life cycle GHG emissions. This value is dependent 

upon the regional electricity generation fuel source mix and is reduced if the plant incorporates more TES.

Life cycle water consumption of the reference plant is estimated to be 4.7 L/kWh. Eighty-nine percent can be 

attributed to the O&M phase (4.2 L/kWh). The power block is responsible for 3.5 L/kWh from cooling tower 

make-up, blowdown quench, and steam cycle make-up water (71%, 14%, and 8% of life cycle water 

consumption, respectively). Cooling water consumed by regional power plants that generate the grid electricity 

used by the CSP plant accounts for 0.24 L/kWh (5% of life cycle consumption), while mirror washing accounts 

for 0.12 L/kWh (3% of life cycle consumption). The majority of the remaining water consumption is attributed 

to water consumed during the manufacturing phase (10% of life cycle, or 0.47 L/kWh).

CED of the reference plant is estimated to be 0.40 MJeq/kWh. The two largest contributions to life cycle CED 

are from the manufacturing and O&M phases (48% and 42%, respectively). Because GHG emissions are largely 

proportional to energy use, SCAs and HTF were also found to significantly contribute to manufacturing phase 

CED (33% and 20%, respectively). Main contributors to O&M phase CED are electricity consumption, natural 

gas combustion, and the manufacture of replacement components. Over its 30-year lifetime, the reference plant 

generates an estimated 12.8 x 109 kWh, which, multiplied by the CED of 0.40 MJeq/kWh, yields a CEDtot = 

5.12x109 MJeq. The resulting EPBT of the reference plant is 1.0 year.

3.2. Results for Design Alternatives

The dry-cooled power block is estimated to reduce life cycle water consumption by 77% (and operational power 

block water consumption by 96%) but increase life cycle GHG emissions and CED by 8%. Of the GHG 

emissions attributable to switching from wet to dry cooling, 46% result from the O&M phase, 45% from the 

manufacturing phase, and 9% from the remaining phases. The increase in manufacturing-phase GHG emissions 

mainly arises from the addition of the air-cooled condenser, the greater number of SCAs required, and the larger 

resulting volume of HTF compared to the wet-cooled design. Higher O&M emissions of the dry-cooled system 

are primarily due to additional natural gas consumed in the auxiliary boiler and additional electricity consumption 

used to meet the larger parasitic load [5]. 

Three combinations of alternative designs of the TES system and salt type are compared to the reference plant 

design. First, by switching from a two-tank to a thermocline TES design but still assuming mined salts, 

significantly less material is required due to the reduced tankage requirement and two thirds reduction of salt 

mass [21]. As a result, total life cycle GHG emissions and CED of the thermocline-based reference plant are 

estimated to be 7% lower than the two-tank designed reference plant (to 24 g CO2eq/kWh and 0.37 MJeq/kWh, 

respectively) and water consumption is estimated to be reduced by about 2% (to 4.6 L/kWh).

Second, if synthetic salts are used instead of mined salts within the reference plant’s two-tank TES configuration, 

GHG emissions are estimated to increase by 52%, CED by 24%, and water consumption by 3% (to 39 g 

CO2eq/kWh, 0.50 MJeq/kWh, and 4.9 L/kWh, respectively) compared to the reference plant. GHG emissions 

increase considerably because nitrous oxide (N2O; GWP=298) emissions resulting from synthetic salt production 

are significantly higher than those resulting from mined salts. The majority of N2O emissions result from the 

production of ammonia, which is subsequently reacted to produce the nitric acid used in salt production reactions 

[26, 27]. Although absorption of N2O with water is a part of the manufacturing process, a small fraction is 

unavoidably emitted to the atmosphere [27]. 

Lastly, if both synthetic salts and a thermocline configuration are used, negative effects of the synthetic salts are 

attenuated by the reduced salt requirement of the thermocline system. Under this scenario, life cycle GHG 

emissions of the reference plant are estimated to increase by only 10% (to 28 g CO2eq/kWh) while water 

consumption and CED are effectively unchanged.
5 

Life Cycle 

Phase Plant System

GHG WATER CED

[g CO2eq / kWh] [L / kWh] [MJeq / kWh]

Wet Dry Wet Dry Wet Dry

Manufacturing

HTF 2.5 2.6 0.10 0.10 0.051 0.053

Power Plant 1.9 2.4 0.076 0.085 0.033 0.037

Solar Field 4.6 4.8 0.15 0.16 0.071 0.074

TES 2.7 2.8 0.15 0.15 0.037 0.038

Construction

HTF 0.14 0.15 0.0012 0.0012 0.0018 0.0018

Power Plant 0.19 0.21 0.0041 0.0030 0.0032 0.0034

Solar Field 0.77 0.81 0.022 0.023 0.012 0.013

TES 0.64 0.67 0.0054 0.0057 0.010 0.011

Operation

HTF 2.2 2.3 0.081 0.085 0.039 0.041

Power Plant 6.2 6.9 4.0 0.29 0.10 0.12

Solar Field 0.61 0.64 0.14 0.14 0.010 0.011

TES 0.99 1.03 0.029 0.030 0.016 0.017

Dismantling

HTF 0.018 0.018 0.000079 0.000077 0.00027 0.00027

Power Plant 0.014 0.014 0.000062 0.000061 0.00021 0.00021

Solar Field 0.090 0.088 0.00039 0.00038 0.0013 0.0013

TES 0.0019 0.0018 0.0000080 0.0000079 0.000028 0.000028

Disposal

HTF 0.50 0.52 0.00087 0.00090 0.00025 0.00025

Power Plant 0.14 0.08 0.00021 0.00022 0.00010 0.00012

Solar Field 0.77 0.81 0.0013 0.0013 0.00063 0.00066

TES 0.68 0.71 0.0048 0.0050 0.0088 0.0093

Life Cycle Phase Subtotals Wet Dry Wet Dry Wet Dry

Manufacturing 12 13 0.47 0.50 0.19 0.20

Construction 1.7 1.8 0.033 0.033 0.028 0.029

Operation 10 11 4.2 0.55 0.17 0.19

Dismantling 0.12 0.12 0.00053 0.00053 0.0019 0.0018

Disposal 2.1 2.1 0.0071 0.0074 0.0098 0.010

Grand Total 26 28 4.7 1.1 0.40 0.43

Table 2. Life Cycle Impact Metrics Disaggregated by Phase and System for Wet- (Reference Plant) and 

Dry-Cooled Designs
6 

3.3 Discussion

The results of this study pertain to the specific hypothetical plant design employed here. However, given the 

robustness of the set of estimates of life cycle GHG emissions from this and previous research, it is likely that life 

cycle environmental impacts for a reasonably diverse set of plant designs will be similar. Regarding the 

applicability of these results to plants in other locations, as a first approximation, it is reasonable to assume that a 

change in DNI will proportionally affect the plant’s power output and therefore inversely proportionally affect 

the life cycle impacts per unit electricity generated. However, other characteristics relating to location, such as 

monthly average wet- and dry-bulb temperatures, can affect plant performance and design in ways that will make 

the final results differ from a strictly inversely proportional relationship to DNI. Therefore, further research 

would be required to achieve a more precise estimate for other plant locations.

As this is the first estimation of life cycle water consumption for CSP, with uncertainty in certain inputs (e.g., 

water consumed for production of HTF and salts), additional research is necessary to confirm and expand on the 

results reported here. Measurement of water consumption both at the plant and in the production of input 

materials, would be particularly beneficial. Moreover, an additional cooling method—hybrid cooling—which 

uses a combination of wet and dry cooling, should be evaluated to quantify the impacts of a more complete 

portfolio of cooling options for solar developers and policymakers.

4. Conclusion

Based on this and previous analysis (e.g., [28, 29]), CSP can significantly reduce GHG emissions compared to 

fossil-fueled generation, although dry-cooling may be required in many locations to minimize water 

consumption. However, life cycle GHG emissions of CSP plants with TES are strongly dependent upon the 

source of salts. In the event that synthetic salts must be used, it would be beneficial to utilize a thermocline 

design.

Acknowledgements

Funding for this project was provided by the U.S. Department of Energy’s Solar Energy Technologies Programs. 

The authors thank the contributions of Mikael Hajjar, the manufacturers who provided us with primary data, staff 

of WPG (Ryan Bowers, Jeff Jantos, Dylan Ross, John Straubinger, and Michael Nietch), and Margaret Mann of 

NREL.

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This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08-GO28308 with the 

National Renewable Energy Laboratory.