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 Environmental 

Impacts Resulting from the 

Manufacture of the Heliostat 

Field for a Reference Power 

Tower Design in the United 

States

Preprint

G. Heath, J. Burkhardt, and C. Turchi 

Presented at SolarPACES 2012

Marrakech, Morocco

September 11-14, 2012

Conference Paper

NREL/CP-6A20-56452

October 2012
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1 

Life Cycle Environmental Impacts resulting from the Manufacture 

of the Heliostat Field for a Reference Power Tower Design in the 

United States

Garvin A. Heath1, John J. Burkhardt III2, and Craig S. Turchi3

1 PhD, Senior Scientist, Technology Systems and Sustainability Analysis Group, National Renewable Energy Laboratory, 15013 Denver West 

Parkway, Golden, CO 80401-3393 USA, garvin.heath@nrel.gov. 

2 Research Analyst, National Renewable Energy Laboratory, MSME (now private consultant in Boulder, CO)

3 Senior Engineer, Concentrating Solar Power Program, PhD

Abstract

Life cycle assessment (LCA) is recognized as a useful analytical approach for quantifying environmental impacts of 

renewable energy technologies, including concentrating solar power (CSP). An LCA accounts for impacts from all 

stages in the development, operation, and decommissioning of a CSP plant, including such upstream stages as the 

extraction of raw materials used in system components, manufacturing of those components, and construction of the 

plant. The National Renewable Energy Laboratory is conducting a series of LCA studies for various CSP 

technologies. This paper contributes to a thorough LCA of a 100 MWnet molten salt power tower CSP plant by 

estimating the environmental impacts resulting from the manufacture of heliostats. Three life cycle metrics are 

evaluated: greenhouse gas emissions, water consumption, and cumulative energy demand. The heliostat under 

consideration (the 148 m2 Advanced Thermal Systems heliostat) emits 5,300 kg CO2eq, consumes 274 m3 of water, 

and requires 159,000 MJeq during its manufacture. Future work will incorporate the results from this study into the 

LCA model used to estimate the life cycle impacts of the entire 100 MWnet power tower CSP plant.

Keywords: life cycle assessment, concentrating solar power, heliostat, power tower, greenhouse gas emissions, 

water consumption, cumulative energy demand

1. Introduction

The electric power sector constituted 40% of all energy-related carbon dioxide (CO2), a major greenhouse gas 

(GHG) contributing to anthropogenic climate change, emissions in 2009 [1]. As a means to reduce the nation’s

carbon footprint, the installed capacity of renewable energy technologies has been on the rise over the past decade 

and electricity generation from non-hydropower renewables has more than doubled since 1990 [2]. As the 

renewable energy sector’s contribution to the nation’s total electricity generation continues to grow, it is important 

to understand the potential environmental benefits associated with technologies such as concentrating solar power 

(CSP). Because operational environmental burdens are typically small for renewable energy technologies, life cycle 

assessment (LCA) is recognized as the most appropriate analytical approach for determining their environmental 

impacts of these technologies, including CSP. An LCA accounts for impacts associated with all stages in the life 

cycle (typically a 30-year period) of a CSP plant, which includes the extraction of raw materials, manufacture of 

components, plant construction, operation, and decommissioning. 

The National Renewable Energy Laboratory (NREL) is undertaking a series of LCAs of modern CSP plants. In 

2011, NREL published an LCA of a reference parabolic trough CSP plant design based in Daggett, CA [3]. The life 

cycle inventory of materials and performance data of the reference plant design, which has a 103 MWnet, wet-cooled 

power block and 6.3 equivalent full load hours (EFLH) of molten salt thermal energy storage (TES), were provided 

by WorleyParons Group (WPG). The three life cycle environmental metrics evaluated in the 2011 study were GHG 

emissions, water consumption, and cumulative energy demand (CED). Various design alternatives, including an 
2 

alternate power block cooling method, TES configuration, and storage medium, were evaluated to develop a robust 

range of life cycle impact values that could be expected from similar parabolic trough plants being developed in the 

United States.

Analogous to our analysis of a reference parabolic trough design, NREL is completing a thorough LCA of a molten 

salt power tower CSP plant design based in Tucson, AZ. A detailed life cycle inventory (LCI) and annual 

performance data for the reference design will again be provided by WPG. The power tower will employ a 100 

MWnet, dry-cooled power block and 6 EFLH of molten salt storage. As a part of this work, NREL has estimated the 

environmental impacts resulting from the manufacture of the heliostat to be used in the reference power tower plant 

design using published life cycle inventory data. This work represents an important step in the completion of the 

whole-plant LCA as the environmental impacts of the heliostat field have been shown in previous research to 

represent roughly half of the material inventory of a power tower CSP plant design and nearly the same percentage 

of life cycle GHG emissions [4]. 

2. Methods

2.1 LCA methodology

There are three common methods used to conduct an LCA: 1) a “process-based” approach in which a system is 

modeled from the “bottom up” using individual component masses and process energy flows, 2) a “top down” 

approach where categories of costs are translated to environmental impacts through the use of economic inputoutput (EIO) matrices and national-average emissions data for each affected industry, and 3) a combined, or 

“hybrid” approach. This work described herein uses the hybrid LCA method to evaluate the impacts of the heliostat 

of a power tower CSP plant based upon three metrics: GHG emissions, life cycle water consumption, and CED. As 

the environmental impacts associated with CSP plant construction, operation and decommissioning are generally 

small, this analysis focuses on estimating the GHG emissions, water consumption, and CED embodied in the 

production of the materials used in heliostats (i.e., extraction of raw materials and manufacturing of components). 

The impacts associated with the remaining components (i.e,. power block, thermal energy storage, and tower 

systems) and life cycles phases (i.e., construction, operation, and decommissioning) will be accounted for the in the 

whole-plant LCA to follow this work.

Emissions of individual GHGs that result from the upstream process during the manufacturing of the heliostat 

components are presented as the sum of each GHG weighted by its 100-year global warming potential (GWP) [5] to 

obtain kilograms of CO2 equivalents (kg CO2eq). Likewise, the total water consumption is calculated by summing 

the volume of surface and groundwater consumed in all upstream processes during this stage of the heliostat’s life 

cycle. As used here, 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” [6]. Finally, CED is calculated as the sum of all primary energy supplied by both renewable and 

non-renewable sources during the life cycle phase under consideration. The life cycle metrics evaluated herein have 

been normalized to two functional units for ease of comparison: 1 heliostat and 1 m2 of heliostat aperture area (e.g. 

kg CO2eq/heliostat and kg CO2eq/m2

). Our LCA methodology is consistent with the guidelines outlined in the 

international standard series ISO 14040-44 [7].

2.2 Material and life cycle inventory data

The heliostat being considered for the reference power tower plant design is the Advanced Thermal Systems (ATS) 

148 m2 glass/metal heliostat (see Figure 1). The ATS heliostat has operated successfully at the National Solar 

Thermal Test Facility (NSTTF) in Albuquerque, NM for over 20 years and yet is still considered a current low-cost 

baseline heliostat design in the US [8]. A thorough description of the ATS heliostat design and embodied materials 

are provided in a heliostat cost reduction study conducted by Sandia National Laboratories [8]. The study also 

provided the cost of the major electrical and control systems used for heliostat operation. The material and cost data 

were extracted from the heliostat cost reduction study and are being used as inputs for the LCA model. 
3 

SimaPro v7.122 LCA modeling software [9] and the EcoInvent LCI database [10] were used to estimate upstream 

GHG emissions, energy flows, and embodied water for minimally processed or bulk materials (e.g. carbon steel and 

concrete). The internet-based EIO LCA tool provided by the Green Design Institute of Carnegie Mellon University 

[11] was used to model impacts of components in two situations: 1) where the materials inventory for a specific 

component was not available, and 2) where we deemed that the environmental impacts resulting from a product’s 

manufacture could not be accurately evaluated by summing the cumulative impacts of constituent raw materials. 

The latter situation occurs for what we call “highly manufactured components” like motors, pumps, heaters, and 

turbines. For these highly manufactured components, one must consider not only the energy required to manufacture 

the raw materials, which are embedded in the component, but also the energy required to process those raw 

materials and assemble the final product. EIO LCA models are able to capture this additional energy because the 

environmental impacts of an entire industry (e.g., pump and pumping equipment manufacturing) are accounted for, 

which includes process and assembly energy.

Fig. 1. A visual interpretation of the 148 m2 ATS heliostat shown from different angles. All dimensions are 

approximate and are based on data from [8] 

4. Summary of results

The heliostat has been broken into six main subsystems: cross bracing structure and attachments, gear drive, mirror 

module assemblies, pedestal assembly, torque tube assemblies, and trusses and attachment plates. The life cycle 
4 

impacts have also been disaggregated by major components within each subsystem. The total cost and embodied 

masses of each of these subsystems have been provided in Table 1, along with the estimated GHG emissions, CED, 

and water consumption associated with their manufacture. Due to limited information, the environmental impacts 

resulting from the concrete foundation, controls and cabling, drive motors and limit switches, and field wiring have 

not yet been estimated. The contractor (WPG) will provide materials and cost data for the aforementioned 

components such that the heliostat LCI is made complete.

Model Inputs

Model Outputs

ProcessBasedCostBasedMassBasedCostBasedMassBasedCostBased

Subsystems/Componentsb Massc

[kg]

Cost

[2006$]

GHG

[kgCO2eq]

Water

[m3]

CED

[MJeq]

Cross Bracing Structure and Attachments 247 - 393 - 7.65 - 5,970 -

Beams 150 - 239 - 4.64 - 3,620 -

Brackets 7.26 - 11.5 - 0.225 - 175 -

Fasteners 10.0 - 15.9 - 0.309 - 241 -

Long Diagonals 52.2 - 83.0 - 1.62 - 1,260 -

Short Diagonals 16.3 - 25.9 - 0.505 - 394 -

Stabilizers 6.35 - 10.1 - 0.197 - 153 -

Wind Ties 4.99 - 7.93 - 0.154 - 120 -

Gear Drive 5.44 4,000 8.65 2,230 0.168 108 131 33,800

Azimuth Subassembly - 3,000 - 1,670 - 81.1 - 25,300

Elevation Subassembly - 1,000 - 557 - 27.0 - 8,440

Fasteners 5.44 - 8.65 - 0.168 - 131 -

Mirror Module Assemblies 2,330 80.0 2,530 - 64.0 - 46,800 -

Adhesived 72.6 - 333 - 18.6 - 6,480 -

Assembly - 80.0 - - - - - -

Cross Members 68.0 - 108 - 2.11 - 1,640 -

Fasteners 36.3 - 57.7 - 1.12 - 876 -

Glass Mirror Facetse 1,500 - 999 - 22.0 - 22,100 -

Hat Sections 649 - 1,030 - 20.1 - 15,700 -

Pedestal Assembly 1,550 52.0 2,470 50.1 48.1 1.95 37,500 660

Flange 62.1 - 98.7 - 1.92 - 1,500 -

Pedestal Pipe 1,490 - 2,370 - 46.1 - 36,000 -

Machine Flat Surface - 10.0 - 9.64 - 0.375 - 127

Drilling (12 holes per pedestal) - 12.0 - 11.60 - 0.451 - 152

Welding - 20.0 - 19.30 - 0.751 - 254

Misc. Machining - 10.0 - 9.64 - 0.375 - 127

Torque Tube Assemblies 975 - 1,550 - 30.2 - 23,500 -

Fasteners 10.9 - 17.3 - 0.337 - 263 -

Flange 64.4 - 102 - 1.99 - 1,550 -

Torque Tube Pipe 900 - 1,430 - 27.9 - 21,700 -

Trusses and Attachment Plates 454 - 721 - 14.0 - 11,000 -

Mounting Adaptor Plate 33.6 - 53.4 - 1.04 - 811 -

Truss Subassembly 420 - 668 - 13.0 - 10,100 -

Subtotal - - 7,670 2,280 164 110 125,000 34,400

Grand Total (per heliostat) - - 9,950 274 159,000

Grand Total (per m2 of aperture area) 67.2 1.85 1,070

a: The values under columns labeled “Process-Based” represent the impacts resulting from using material masses and the processbased LCA approach to estimate the component’s environmental impacts. The values under columns labeled “Cost-Based” 

represent the impacts resulting from the EIO LCA approach, using component cost data from [8] and the EIO LCA model [11] 

provided by Carnegie Mellon University.

b: Subsystem subtotals are provided in bold.

c: Unless otherwise noted, the material composition of each component is carbon steel. The EcoInvent process used to estimate 

the component’s environmental impacts is “Reinforcing steel, at plant/RER with US electricity U” [10].

d: The EcoInvent process used to estimate the impacts of “Adhesive” is “Adhesive for metals, at plant/DE with US electricity U” 

[10].

e: The EcoInvent process used to estimate the impacts of “Glass Mirror Facets” is “Solar glass, low-iron, at regional storage/RER U” 

[10].

Table 1. Environmental Impacts resulting from the Manufacture of One 148 m2 ATS Heliostat
5 

5. Comparison to other work

Lechón and colleagues have also conducted an LCA on both parabolic trough and power tower CSP systems for a 

location in Spain [4]. Enough information has been provided in the study to approximate the impacts on a per 

heliostat or per aperture area basis. In addition, Lechón and colleagues also evaluate two of the three life cycle 

metrics considered here: life cycle GHG emissions and CED. Lechón and colleagues estimate that the 

manufacturing of the solar field in the power tower plant design contributes 5.61 g CO2eq/kWh to the total life cycle 

GHG emissions, with the contributions from its construction, operation, and decommissioning considered 

separately. If we assume that the majority of these emissions result from the heliostat structure alone (i.e., ignoring 

cabling and other ancillary solar field components as we have for the ATS heliostat analysis), each heliostat in [4] 

emits 5,300 kg CO2eq during its manufacture, or 55.1 kg CO2eq per m2 of aperture area (based on a lifetime electricity 

production value of 2,600 GWh, 2,750 heliostats, and 264,825 m2 of aperture area [4]). Likewise, one heliostat from 

[4] requires 75,600 MJeq during its manufacture, or 785 MJeq per m2 of aperture area. See Table 2 for a summary of 

the comparison between the heliostat assumed in [4] and the 148 m2 ATS heliostat evaluated here.

Lechon et al. 

2008 [4]

Current Study (148 

m2 ATS heliostat) % Change

Aperture Area per Heliostat [m2] 96.3 148 54% 

GHG Emissions [kg CO2eq/heliostat] 5,300 9,950 88% 

GHG Emissions [kg CO2eq/m2] 55 67 22%

CED [MJeq/heliostat] 75,600 159,000 110%

CED [MJeq/m2] 786 1,070 36%

Table 2. Comparison of Environmental Impacts Resulting from the Manufacture a Heliostat

One should note that the embodied emissions and CED associated with the manufacture of each 148 m2 ATS 

heliostat are significantly greater (88% and 110% greater, respectively) than the heliostat evaluated in [4]. A key 

contributor to this increase in manufacturing impacts is likely due to the significant increase in size of the heliostat; 

the 148 m2 ATS heliostat has a 54% larger aperture area than the heliostat used in [4]. It is not unreasonable to 

assume that the mass of embodied materials, and therefore embodied GHG emissions and CED, will increase 

proportionally to aperture area; however, this would not explain the entire increase in manufacturing impacts.

A more informative metric to refer to for this comparison would be the GHG emissions and CED required per 

aperture area, which increase by 22% and 36%, respectively. An increase in this metric showcases key differences 

in LCI and LCA assumptions in each study. Our work assumes a U.S.-based plant location and that the U.S. 

electrical grid is used in the manufacturing processes of most embodied materials. The plant location assumed in [4] 

is southern Spain and, although not explicitly stated, it is likely that the Spanish (or European average) electrical 

grid is used in the majority of the manufacturing processes used in the study. The U.S. electrical grid emits 10% 

more CO2 per unit of electricity generated when compared to European electrical grid, or 18% more when compared 

to the Spanish electrical grid [12, 13]. The larger carbon intensity of the U.S. electrical grid may further lend an 

explanation to why the GHG emissions per aperture of heliostat are 22% larger than that reported in [4]. In addition 
6 

to differences the electrical grid, our work uses hybrid LCA to evaluate the impacts of the heliostat, while [4] may 

only use a process-based approach to evaluate the impacts of their heliostat. The use of EIO LCA typically results in 

higher impacts as it captures process energy and other ancillary activities that occur upstream in the value chain that 

are not captured in the process-based approach. Finally, it is reasonable to assume that the heliostat used in [4] may 

require less material per m2 of aperture area due to advances in heliostat design and material science; recall, the 148 

m2 ATS heliostat has been in operation for over 20 years, while power tower plants in Spain, and the work published 

by Lechón and colleagues, have been completed much more recently.

5. Conclusions and future work

The National Renewable Energy Laboratory is conducting a series of LCA studies for various CSP technologies. 

The current paper. contributes toward the completion of a full LCA of a 100 MWnet molten salt power tower CSP 

plant to be built in Tucson, AZ. Using published life cycle inventory data [8], this analysis provides estimates of the 

GHG emissions, water consumption, and CED required to manufacture one 148 m2 ATS heliostat. The heliostat 

under consideration emits 5,300 kg CO2eq, consumes 274 m3 of water, and requires 159,000 MJeq during its 

manufacture. Annual performance data and a detailed life cycle inventory of the remaining subsystems for this 

reference plant design will be provided by an engineering consulting firm. Future work will incorporate the results 

reported here into a detailed LCA model used to estimate the life cycle impacts of the entire power tower plant. In 

addition, the life cycle impacts resulting from the heliostat will be carefully compared to other estimates (such as 

that provided in [4]) in order to identify and resolve key differences in the LCA and heliostat design assumptions.

References

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