Multiple Benefits are Possible with Photovoltaic Panels
by Dustin Mulvaney
Energy sprawl from utility scale solar projects is a leading cause of land use conflict across the American West. These projects can be very large facilities with footprints on the order of square miles; the Desert Sunlight Solar Farm in Desert Center California is six square miles (3,800 acres), while the Gemini Solar Project in Nevada is over eleven square miles (7,100 acres). Some solar projects have damaged cultural resources – geoglyphs, cremation sites, and spiritually important locations. Others have resulted in significant local ecological impacts to habitat of important species such as desert tortoise, kit fox, bighorn sheep, fringe-toed lizard, Joshua trees, and Mojave ground squirrel. There is a wide spectrum of impacts from large utility scale projects, and many of the worst impacts can be avoided by taking advantage of land with existing industrial uses. Although the Western Solar Plan1 adopted by the Bureau of Land Management attempts to direct projects onto previously disturbed or lower conflict sites, the sprawl onto “green field” or otherwise undeveloped sites continues unabated.
The opportunities to avoid habitat degradation through better land use selection are widespread. In addition to incentives to increase distributed energy resources in the built environment, there are several other solutions advocated by researchers and practitioners that could offer fewer land use conflicts over utility-scale solar power. Many of these projects offer multiple benefits in addition to solar power: water savings, agro-ecosystem enhancement, more productive land uses, and carbon sequestration – in addition to avoided habitat loss.
Land-sparing Solar Opportunities
The idea of “land-sparing” utility-scale solar installations was introduced by University of California researchers.2 Recognizing the impacts of big solar projects on habitat, this research identified land-sparing sites such as contaminated agricultural lands, abandoned landfills and mines, brownfields, and other previously disturbed sites and found that there was enough of these parcels to supply enough power to the United States many times over, with over 800 thousand square kilometers (>309,000 square miles). Total power demand for the United States would require on the order of 5,800 to 14,600 square miles of solar development (15,000 to 38,000 km2) according to a 2021 Princeton Net Zero Study to decarbonize energy by 2050.3 The task of integrating solar projects into existing and proposed infrastructures cost-effectively is a major challenge on its own, but land-sparing projects show potential for an enormous supply of renewable energy with minimal impacts to ecosystems of the American West.
The Environmental Protection Agency launched a program, RE-Powering America’s Lands, which assessed contaminated or brownfield opportunities for solar development and which included a screening process to ensure the lands have the appropriate slope, aspect, and absence of shade to be viable sites for solar.4 The EPA has inventoried are over 17,000 square miles of these lands. Many of the sites of former industrial activity are near electrical transmission facilities. The same goes for abandoned mine lands, of which there are between 80,000 and 250,000 sites according to the U.S. General Accounting Office.5 There are also numerous new examples of Superfund hazardous waste sites converted to solar projects. In one example in Sacramento, California, the municipal utility district built a 6 MW solar project on lands contaminated by rocket fuel and where manufacturing had ended in 1993. Finally, a legacy of industrial agriculture in California’s Great Central Valley has resulted in the contamination of land by salts like selenium. These lands might also have habitat characteristics like foraging areas for raptors or ground squirrels, which would suggest caution with some developments, but in general salt-contaminated, abandoned agricultural lands represent another important area that could supply solar power with fewer land use conflicts.
Integrating Agriculture and Solar Power with Agrivoltaics
Integrating photovoltaics into agriculture can be a productive idea. Agriculture covers about 1.4 million square miles in the United States, and it is one of the most intensive and impactful land uses in human civilization. The United States for example grew 87.6 million acres of soy beans and 92.1 million acres of corn crop, with the latter sending 40% to ethanol production. Imagine instead of supplying a transportation fuel (ethanol is generally 10% of gasoline in the U.S.), some small fraction of these corn and soybean lands were converted to solar farms producing energy for electric vehicles. The U.S. corn and soybean fields could produce 25 terawatts of solar power, more power than used by humans today. Only a fraction would be needed, but solar projects sited on former farmlands and developed with an emphasis on ecological restoration could yield multiple benefits. Recent research finds grassland restoration at solar farms in the Midwestern United States (mostly lands formerly dedicated to corn/soybean row crops) increases pollinators, sequesters carbon, reduces sediment loss, and retains water in soils.6
Agrivoltaics – a play on agriculture integrated with photovoltaics – are one way to produce energy and crops from the same land. Rows of crops and solar panels contribute side by side, yielding less than either would alone in a field, but more in total, especially with crop quality improvements or reduced input costs. The partial shading that agrivoltaics can provide reduces water stress; these system offer water savings and can even improve crop quality. Recent research from South Korea shows that the color of broccoli and cabbage improved when grown in agrivoltaics. Water can be the limiting factor for some crops, and the solar arrays’ shade can make microclimates that improve soil moisture.
Center-pivot agriculture is a type of irrigated agriculture where the watering system rotates around a single point, resulting in fields of crops that are circular. The lands surrounding these fields in the corners of square parcels could be another space that could be utilized with minimal impact. Another paper led by UC Davis Professor Rebecca Hernandez found this could supply 8,100 square miles (1,350 GWh) in the US, mostly in the western states where irrigated agriculture is most common.7
Floating Solar Power and Canal-solar
A recent study in Nature found covering 10% of the world’s reservoirs that generate hydropower with floating solar panels would install nearly 4,000 gigawatts (GW) of solar capacity.8 For context, global power demand today is on the order of 20,000 GW. These kinds of deployments also offer multiple uses, including aquaculture or integration with other coastal or energy infrastructures. But they also require study and best practices to ensure they do not result in unintended negative impacts to birds or to aquatic and benthic species.
The water saving opportunities for floatovoltaics are straightforward. Research on water savings found that a “4,500 square meter-floatovoltaics covering the entirety of the reservoir produces 425,000 kWh and saves 5,000 cubic meters of water via avoided evaporation per year.”9 In the land-sparing paper written led by the UC scientists in 2017, the team estimates 39 TWh/year of energy potential over 40 square miles (104 km2) of agricultural reservoirs in California’s Central Valley. This could contribute 15% of California's annual electricity supply and save 31 billion gallons (0.12 km3) of water per year.
Floating solar will also encounter many use conflicts as water bodies are used for navigation and flood control. In May 2002, China’s Ministry of Water Resources banned wind and solar floatovoltaics from freshwater bodies to protect the hydrological integrity of water bodies and flood management.10 They claimed solar and wind projects can obstruct the steady flow of water and damage river banks and dikes, which are key to protecting communities and agriculture.11 As a result of the new rule, the massive 1GW/$1.2 billion Tiangang Lake floating solar project in Jiangsu province will be dismantled. The social and environmental impacts of these infrastructures need to assessed to make sure projects are done right.
A Better Solar Future for Land Use
Solar still can get the land question right, but it will require convincing politicians, environmental organizations, and the public that these alternatives are viable and worthy of resources. It is a false choice to frame conservation in opposition to renewable energy when other alternatives are available. In addition to emphasizing rooftop solar and parking lot canopies and coordinating them as microgrids, there are many other opportunities to be strategic about where to put even utility-scale solar facilities that do not disturb important habitat. Some of these require further research, but we have already identified and characterized many multifunctional and synergistic deployment strategies. It is time to design and implement policy and procurement incentives from buyers of renewable energy that ensure that proper land use receives top consideration. We might only have one chance to get this right.
Dustin Mulvaney, Professor of Environmental Studies, San Jose State University, author of Solar Power: Sustainability, Innovation, Environmental Justice published by the University of California Press, 2019, and Sustainable Energy Strategies: Socio-ecological Dimensions of Decarbonization, with Palgrave-MacMillan/Nature-Springer, 2020. Dustin is on the board of advisors to Basin and Range Watch. www.dustinmulvaney.com Twitter: @DustinMulvaney
2) Hoffacker, M. K., Allen, M. F., & Hernandez, R. R. (2017). Land-sparing opportunities for solar energy development in agricultural landscapes: a case study of the Great Central Valley, CA, United States. Environmental Science & Technology, 51(24), 14472-14482.
6) Walston, L. J., Li, Y., Hartmann, H. M., Macknick, J., Hanson, A., Nootenboom, C., Loonsdorf, & Hellmann, J. (2021). Modeling the ecosystem services of native vegetation management practices at solar energy facilities in the Midwestern United States. Ecosystem Services, 47, 101227.
7) Hernandez, Rebecca, Alona Armstrong, Jennifer Burney, Greer Ryan, Kara Moore, Ibrahima Diedhiou, Steven M. Grodsky, Leslie Saul-Gershenz, Davis R., Jordan Macknick, Dustin Mulvaney, Garvin A. Heath, Shane B. Easter, Brenda Beatty, Michael F. Allen, and Daniel M. Kammen. (2019). Techno–ecological synergies of solar energy for global sustainability. Nature Sustainability, 2(7), 560-568. https://doi.org/10.1038/s41893-019-0309-z.
8) Almeida, R. M., Schmitt, R., Grodsky, S. M., Flecker, A. S., Gomes, C. P., Zhao, L., ... & McIntyre, P. B. (2022). Floating solar power could help fight climate change—let’s get it right.
9) Trapani, K., & Redón Santafé, M. (2015). A review of floating photovoltaic installations: 2007–2013. Progress in Photovoltaics: Research and Applications, 23(4), 524-532.
10) S&P Global. China restricts solar, wind power projects in inland waters, cites flood control. June 9, 2022. https://cleanenergynews.ihsmarkit.com/research-analysis/china-restricts-solar-wind-power-projects-in-inland-waters-cit.html.
11) China Dialogue. Wind and Solar projects banned from freshwater bodies. June 1, 2022. https://chinadialogue.net/en/digest/wind-and-solar-projects-banned-from-freshwater-bodies/