TODAY’S STUDY: SOLAR POWER PLANTS AND LAND

Land-Use Requirements for Solar Power Plants in the United States

Sean Ong, Clinton Campbell, Paul Denholm, Robert Margolis, and Garvin Heath, June 2013 (National Renewable Energy Laboratory)

Executive Summary

By the third quarter of 2012, the United States had deployed more than 2.1 gigawatts (GWac1) of utility-scale solar generation capacity, with 4.6 GWac under construction as of August 2012 (SEIA 2012). Continued growth is anticipated owing to state renewable portfolio standards and decreasing system costs (DOE 2012a). One concern regarding large-scale deployment of solar energy is its potentially significant land use. Efforts have been made to understand solar land use estimates from the literature (Horner and Clark 2013); however, we were unable to find a comprehensive evaluation of solar land use requirements from the research literature. This report provides data and analysis of the land use associated with U.S. utility-scale2 ground-mounted photovoltaic (PV) and concentrating solar power (CSP) facilities.

After discussing solar land-use metrics and our data-collection and analysis methods, we present total and direct land-use results for various solar technologies and system configurations, on both a capacity and an electricity-generation basis. The total area corresponds to all land enclosed by the site boundary. The direct area comprises land directly occupied by solar arrays, access roads, substations, service buildings, and other infrastructure. We quantify and summarize the area impacted, recognizing that the quality and duration of the impact must be evaluated on a case-bycase basis. As of the third quarter of 2012, the solar projects we analyze represent 72% of installed and under-construction utility-scale PV and CSP capacity in the United States. Table ES-1 summarizes our land-use results.

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We found total land-use requirements for solar power plants to have a wide range across technologies. Generation-weighted averages for total area requirements range from about 3 acres/GWh/yr for CSP towers and CPV installations to 5.5 acres/GWh/yr for small 2-axis flat panel PV power plants. Across all solar technologies, the total area generation-weighted average is 3.5 acres/GWh/yr with 40% of power plants within 3 and 4 acres/GWh/yr. For direct-area requirements the generation-weighted average is 2.9 acres/GWh/yr, with 49% of power plants within 2.5 and 3.5 acres/GWh/yr. On a capacity basis, the total-area capacity-weighted average is 8.9 acres/MWac, with 22% of power plants within 8 and 10 acres/MWac. For direct land-use requirements, the capacity-weighted average is 7.3 acre/MWac, with 40% of power plants within 6 and 8 acres/MWac. Other published estimates of solar direct land use generally fall within these ranges.

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Both capacity- and generation-based solar land-use requirements have wide and often skewed distributions that are not well captured when reporting average or median values. Some solar categories have relatively small samples sizes, and the highest-quality data are not available for all solar projects; both of these factorsmust be considered when interpreting the robustness of reported results. Owing to the rapid evolution of solar technologies, as well as land-use practices and regulations, the results reported here reflect past performance and not necessarily future trends. Future analyses could include evaluating the quality and duration of solar land-use impacts and using larger sample sizes and additional data elements to enable a thorough investigation of additional land-use factors.

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Introduction

By the third quarter of 2012, the United States had deployed more than 2.1 gigawatts (GWac3) of utility-scale solar generation capacity, with 4.6 GWac under construction as of August 2012 (SEIA 2012). Continued growth is anticipated owing to state renewable portfolio standards and decreasing system costs (DOE 2012a). One concern regarding large-scale deployment of solar energy is its potentially significant land use. Estimates of land use in the existing literature are often based on simplified assumptions, including power plant configurations that do not reflect actual development practices to date. Land-use descriptions for many projects are available from various permitting agencies and other public sources, but we were unable to locate a single source that compiles or summarizes these datasets. The existing data and analyses limit the effective quantification of land-use impacts for existing and future solar energy generation, particularly compared with other electricity-generation technologies.

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This report provides data and analysis of the land use associated with U.S. utility-scale groundmounted photovoltaic (PV) and concentrating solar power (CSP) facilities, defined as installations with capacities greater than 1 MW. The next section (Section 2) discusses standard land-use metrics and their applicability to solar power plants. We identify two major classes of solar plant land use—direct impact (disturbed land due to physical infrastructure development) and total area (all land enclosed by the site boundary)—by which we categorize subsequent results. Section 3 describes our solar land-use data collection and analysis methods. We derived datasets from project applications, environmental impact statements, and other sources and used them to analyze land use based on the capacity and generation of solar plants. Section 4 presents our results. In addition to summarizing PV and CSP land use, we examine relationships among land use, plant configuration, location, and technology. Finally, in Section 5, we identify limitations to the existing solar land-use datasets and suggest additional analyses that could aid in evaluating land use and impacts associated with the deployment of solar energy. Appendices include tables of our solar project data as well as more detailed analyses of specific land-use relationships…

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Conclusions

Table 8 and Table 9 summarize the U.S. utility-scale PV and CSP land-use requirements evaluated in this report. Average total land-use requirements are 3.6 acres/GWh/yr for PV and 3.5 acres/GWh/yr for CSP. Average direct-area requirements are 3.1 acres/GWh/yr for PV and 2.7 acres/GWh/yr for CSP. On a capacity basis, the total-area capacity-weighted average for all solar power plants is 8.9 acres/MWac, with 22% of plants within 8 and 10 acres/MWac. For direct land-use requirements, the capacity-weighted average is 7.3 acre/MWac, with 40% of power plants within 6 and 8 acres/MWac. Solar land-use estimates from the literature generally fall within these ranges. Within the broad technology categories of PV and CSP, land-use metrics are also impacted by specific technology choices, such as cell efficiency, tracking method, and inclusion of thermal energy storage, and are a function of the solar resource available at each site.

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Although our results stem from an empirically based effort to estimate solar land use, several caveats are warranted. Some solar-technology categories have relatively small samples sizes, which must be considered when interpreting the robustness of reported results. Over 26 GWac of PV and CSP are under development as of February 2013 (SEIA 2013), and the results reported in this study must be understood in light of a rapidly growing installed base. Additionally, various data sources were used when gathering information about solar projects. Although we tried to obtain the highest-quality sources (project applications and regulatory documents, referred to as “official documents” in this report), we collected official documents for only 20% of all projects evaluated. Other data sources are expected to have higher levels of uncertainty (although how much higher is unclear), which could contribute to the observed variability in results. With the exception of a few CSP projects, we collected reported capacity of power plants but not annual generation. The generation-based land-use results are expected to have higher levels of uncertainty because annual generation is simulated. Although generation-based results provide a more consistent approach when comparing land-use requirements across technologies, capacity based results are useful for estimating land area and costs for new projects because power plants are often rated in terms of capacity. Finally, owing to the rapid evolution of solar technologies as well as land-use practices and regulations, the results reported here reflect past performance and not necessarily future trends.

We analyze elements that affect the area of solar impact, but we recognize that the duration of use and impact on land quality are also important when considering land use impacts. Future analyses could include evaluating the quality of land impacts, assessing both the initial state of the land impacted and the final states across a variety of factors, including soil quality and overall ecosystem quality. Finally, larger sample sizes and additional data elements would improve the robustness of the conclusions and enable a more thorough investigation of the impacts of additional factors, such as tilt angle, azimuth, PV module technology, CSP solar multiple, and storage technologies.

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