Solar power development over canals is an emerging response to the energy–water–food nexus that can result in multiple benefits for water and energy infrastructure. Case studies of over-canal solar photovoltaic arrays have demonstrated enhanced photovoltaic performance due to the cooler microclimate next to the canal. In addition, shade from the photovoltaic panels has been shown to mitigate evaporation and potentially mitigate aquatic weed growth. However, the evaporation savings and financial co-benefits have not been quantified across major canal systems. Here we use regional hydrologic and techno-economic simulations of solar photovoltaic panels covering California’s 6,350 km canal network, which is the world’s largest conveyance system and covers a wide range of climates, insolation rates and water costs. We find that over-canal solar could reduce annual evaporation by an average of 39 ± 12 thousand m3 per km of canal. Furthermore, the financial benefits from shading the canals outweigh the added costs of the cable-support structures required to span the canals. The net present value of over-canal solar exceeds conventional overground solar by 20–50%, challenging the convention of leaving canals uncovered and calling into question our understanding of the most economic locations for solar power.
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The SAM simulation outputs, Monte Carlo simulation outputs and bootstrap analysis that support the techno-economic analysis of this study are available from the Dryad Digital Repository76. The data that support the water conservation and diesel irrigation retirement findings of this study are available from the corresponding author (B.M.) upon reasonable request. Source data are provided with this paper.
Cash Receipts by Commodity State Ranking (USDA Economic Research Service, accessed September 2020); https://data.ers.usda.gov/reports.aspx?ID=17844
Liu, Q. Interlinking climate change with water–energy–food nexus and related ecosystem processes in California case studies. Ecol. Process. 5, 1–14 (2016).
Management of the California State Water Project Bulletin 132-14 (California Department of Water Resources, 2015).
Fulton, J. & Cooley, H. The water footprint of California’s energy system, 1990–2012. Environ. Sci. Tech. 49, 3314–3321 (2015).
Welle, P. D., Medellin-Azuara, J., Viers, J. H. & Mauter, M. S. Economic and policy drivers of agricultural water desalination in California’s Central Valley. Agric. Water Manag. 194, 192–203 (2017).
Shobe, B. & Merrill, J. Climate Smart: Saving Water and Energy on California Farms. Recommendations for California’s State Water Efficiency and Enhancement Program (SWEEP) (California Climate and Agriculture Network, 2018).
Crow, F. R. Comparison of chemical and nonchemical techniques for suppressing evaporation from small reservoirs. Trans. ASAE 10, 172–174 (1967).
Cooley, K. R. Evaporation reduction: summary of long-term tank studies. J. Irrig. Drain. Eng. 109, 89–98 (1983).
Gallego-Elvira, B., Martínez-Alvarez, V., Pittaway, P., Symes, T. & Hancock, N. The combined use of shade-cloth covers and monolayers to prevent evaporation in irrigation reservoirs. In International Conference on Agricultural Engineering 1–9 (AgEng, 2010); https://eprints.usq.edu.au/8917/
Martinez-Alvarez, V., Maestre-Valero, J. F., Martin-Gorriz, B. & Gallego-Elvira, B. Experimental assessment of shade-cloth covers on agricultural reservoirs for irrigation in south-eastern Spain. Span. J. Agric. Res. 8, 122–133 (2010).
Bontempo Scavo, F., Tina, G. M., Gagliano, A. & Nižetić, S. An assessment study of evaporation rate models on a water basin with floating photovoltaic plants. Int. J. Energy Res. 45, 167–188 (2021).
Rosa-Clot, M., Tina, G. M. & Nizetic, S. Floating photovoltaic plants and wastewater basins: an Australian project. Energy Procedia 134, 664–674 (2017).
Lee, N. et al. Hybrid floating solar photovoltaics-hydropower systems: benefits and global assessment of technical potential. Renew. Energy 162, 1415–1427 (2020).
Kumar, A. & Kumar, M. Experimental validation of performance and degradation study of canal-top photovoltaic system. Appl. Energy 243, 102–118 (2019).
Kumar, M. & Kumar, A. Performance assessment of different photovoltaic technologies for canal-top and reservoir applications in subtropical humid climate. IEEE J. Photovolt. 9, 722–732 (2019).
Kahn, M. & Longcore, T. A Feasibility Analysis of Installing Solar Photovoltaic Panels Over California Water Canals (UCLA, 2014).
Colmenar-Santos, A., Buendia-Esparcia, Á., de Palacio-Rodríguez, C. & Borge-Diez, D. Water canal use for the implementation and efficiency optimization of photovoltaic facilities: Tajo–Segura transfer scenario. Sol. Energy 126, 168–194 (2016).
Sahu, A., Yadav, N. & Sudhakar, K. Floating photovoltaic power plant: a review. Renew. Sust. Energ. Rev. 66, 815–824 (2016).
Hernandez, R. R. et al. Environmental impacts of utility-scale solar energy. Renew. Sust. Energ. Rev. 29, 766–779 (2014).
Cazzaniga, R. et al. Floating photovoltaic plants: performance analysis and design solutions. Renew. Sust. Energ. Rev. 81, 1730–1741 (2018).
Bryant, B. P. et al. Shaping land use change and ecosystem restoration in a water-stressed agricultural landscape to achieve multiple benefits. Front. Sustain. Food Syst. 4, 138 (2020).
Grodsky, S. M. & Hernandez, R. R. Reduced ecosystem services of desert plants from ground-mounted solar energy development. Nat. Sustain. 3, 1036–1043 (2020).
Bureau of Reclamation Fundamental Considerations Associated with Placing Solar Generation Structures at Central Arizona Project Canal (U.S. Department of the Interior, 2016).
Kougias, I. et al. The potential of water infrastructure to accommodate solar PV systems in Mediterranean Islands. Sol. Energy 136, 174–182 (2016).
Augustin, D., Chacko, R. & Jacob, J. Canal top solar PV with reflectors. In 2016 IEEE International Conference on Power Electronics, Drives and Energy Systems (PEDES) 1–5 (IEEE, 2016).
Sairam, P. M. N. & Aravindhan, A. Canal top solar panels: a unique nexus of energy, water, and land. Mater. Today Proc. 33, 705–710 (2020).
Over Water (P4P Energy, 2019); http://p4penergy.com/products/over-water/
Canal Top Solar PV Projects (Punjab Energy Development Agency, 2020); https://www.peda.gov.in/canal-top-solar-pv-projects
Hidalgo, H. G., Cayan, D. R. & Dettinger, M. D. Sources of variability of evapotranspiration in California. J. Hydrometeorol. 6, 3–19 (2005).
Baldocchi, D., Dralle, D., Jiang, C. & Ryu, Y. How much water is evaporated across California? A multiyear assessment using a biophysical model forced with satellite remote sensing data. Water Resour. Res. 55, 2722–2741 (2019).
Evaporation from Water Surfaces in California Bulletin 73-79 (California Department of Water Resources, 1979).
Craig, I., Green, A., Scobie, M. & Schmidt, E. Controlling Evaporation Loss from Water Storages Publication No 1000580/1 (National Centre for Engineering in Agriculture, 2005).
Perez, R. et al. A new operational model for satellite-derived irradiances: description and validation. Sol. Energy 73, 307–317 (2002).
Drury, E., Denholm, P. & Margolis, R. M. The Impact of Different Economic Performance Metrics on the Perceived Value of Solar Photovoltaics Technical report no. NREL/TP-6A20-52197 (National Renewable Energy Laboratory, 2011).
Hernandez, R. R. et al. Techno–ecological synergies of solar energy for global sustainability. Nat. Sustain. 2, 560–568 (2019).
Da Silva, Pimentel, Diogo, Gardenio & Branco, D. A. C. Is floating photovoltaic better than conventional photovoltaic? Assessing environmental impacts. Impact Assess. Proj. Apprais. 36, 390–400 (2018).
Ravi, S. et al. Colocation opportunities for large solar infrastructures and agriculture in drylands. Appl. Energy 165, 383–392 (2016).
Niblick, B. & Landis, A. E. Assessing renewable energy potential on United States marginal and contaminated sites. Renew. Sust. Energ. Rev. 60, 489–497 (2016).
Majumdar, D. & Pasqualetti, M. J. Analysis of land availability for utility-scale power plants and assessment of solar photovoltaic development in the state of Arizona, USA. Renew. Energy 134, 1213–1231 (2019).
Gorman, W., Mills, A. & Wiser, R. Improving estimates of transmission capital costs for utility-scale wind and solar projects to inform renewable energy policy. Energy Policy 135, 110994 (2019).
Pitt, D. & Michaud, G. Assessing the value of distributed solar energy generation. Curr. Sustain. Renew. Energy Rep. 2, 105–113 (2015).
Friedrich, K. et al. Reservoir evaporation in the Western United States: current science, challenges, and future needs. Bull. Am. Meteorol. Soc. 99, 167–187 (2018).
Diffenbaugh, N. S., Swain, D. L. & Touma, D. Anthropogenic warming has increased drought risk in California. Proc. Natl Acad. Sci. USA 112, 3931–3936 (2015).
Baldocchi, D. & Waller, E. Winter fog is decreasing in the fruit growing region of the Central Valley of California. Geophys. Res. Lett. 41, 3251–3256 (2014).
Kumar, M., Kumar, A. & Gupta, R. Comparative degradation analysis of different photovoltaic technologies on experimentally simulated water bodies and estimation of evaporation loss reduction. Prog. Photovolt. Res. Appl. 29, 357–378 (2020).
Coyle, D. J. Life prediction for CIGS solar modules part 1: modeling moisture ingress and degradation. Prog. Photovolt. Res. Appl. 21, 156–172 (2013).
Jordan, D. C. & Kurtz, S. R. Photovoltaic degradation rates—an analytical review. Prog. Photovolt. Res. Appl. 21, 12–29 (2013).
Lund, J., Medellin-Azuara, J., Durand, J. & Stone, K. Lessons from California’s 2012–2016 drought. J. Water Res. Plan. Man. ASCE 144, 4018067 (2018).
Christian-Smith, J. et al. Maladaptation to drought: a case report from California, USA. Sustain. Sci. 10, 491–501 (2015).
Pauloo, R. et al. Domestic well vulnerability to drought duration and unsustainable groundwater management in California’s Central Valley. Environ. Res. Lett. 15, 44010 (2020).
Jasechko, S. & Perrone, D. California’s Central Valley groundwater wells run dry during recent drought. Earth’s Future 8, e2019EF001339 (2020).
Grantham, T. E. & Viers, J. H. 100 years of California’s water rights system: patterns, trends and uncertainty. Environ. Res. Lett. 9, 084012 (2014).
Nelson, K. S. & Burchfield, E. K. Effects of the structure of water rights on agricultural production during drought: a spatiotemporal analysis of California’s Central Valley. Water Resour. Res. 53, 8293–8309 (2017).
Escriva-Bou, A., McCann, H., Hanak, E., Lund, J. & Gray, B. Accounting for California water. Calif. J. Politics Policy 8, 1–26 (2016).
Hoffacker, M. K., Allen, M. F. & Hernandez, R. R. Land-sparing opportunities for solar energy development in agricultural landscapes: a case study of the Great Central Valley, CA, United States. Environ. Sci. Tech. 51, 14472–14482 (2017).
National Hydrography Dataset (USGS, accessed January 2016); http://nhd.usgs.gov/data.html
Valiantzas, J. D. Simplified versions for the Penman evaporation equation using routine weather data. J. Hydrol. 331, 690–702 (2006).
Wilcox, S. National Solar Radiation Database 1991–2010 Update: User’s Manual Technical report no. NREL/TP-5500-54824 (National Renewable Energy Laboratory, 2012).
Collins, W. D. et al. The community climate system model version 3 (CCSM3). J. Clim. 19, 2122–2143 (2006).
Solar Insolation (1 Month) (NASA Earth Observations, 2016); https://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_INSOL_M
Hijmans, R. J., Cameron, S. E., Parra, J. L., Jones, P. G. & Jarvis, A. Very high resolution interpolated climate surfaces for global land areas. Int. J. Climatol. 25, 1965–1978 (2005).
Historical Climate Information (Western Regional Climate Center, 2016); http://www.wrcc.dri.edu/CLIMATEDATA.html
Carpenter, L. G. The Loss of Water from Reservoirs by Seepage and Evaporation Bulletin No. 45 (State Agricultural College, Agricultural Experiment Station, 1898).
Jensen, M. E. Estimating Evaporation from Water Surfaces. In Proceedings of the CSU/ARS Evapotranspiration Workshop, Fort Collins, CO 1–27 (ASCE, 2010).
Hart, Q. J. et al. Daily reference evapotranspiration for California using satellite imagery and weather station measurement interpolation. Civ. Eng. Environ. Syst. 26, 19–33 (2009).
Reference Evapotranspiration Zones (California Irrigation Management Information System, accessed January 2016); https://cimis.water.ca.gov/App_Themes/images/etozonemap.jpg
Fu, R., Feldman, D. & Margolis, R. U.S. Solar Photovoltaic System Cost Benchmark Q1 2018 Technical report no. NREL/TP-6A20-72399 (National Renewable Energy Laboratory, 2019).
Horowitz, K. A. et al. Estimating the Effects of Module Area on Thin-Film Photovoltaic System Costs Conference paper NREL/CP-6A20-68506 (National Renewable Energy Laboratory, 2018).
Ave, K. Sacramento Municipal Utilities District (SMUD) Proposal for Folsom South Solar Canal Project, WaterSMART: Water and Efficiency Grants for FY2015 (SMUD, 2015).
Gerstle, B., Allbright, M., Lee, C. & Iklé, J. 2019 Padilla Report: Costs and Cost Savings for the RPS Program (Public Utilities Code §913.3) (California Public Utilities Commission, 2019).
How to Calculate PV Performance Ratio and PV Performance Index (Hukseflux Thermal Sensors, accessed August 2020); https://www.hukseflux.com/applications/solar-energy-pv-system-performance-monitoring/how-to-calculate-pv-performance-ratio
Greenfield, B. K., Blankinship, M. & McNabb, T. J. Control costs, operation, and permitting issues for non-chemical plant control: case studies in the San Francisco Bay-Delta Region, California. J. Aquat. Plant Manag. 44, 40–49 (2006).
California Department of Fish and Wildlife Lake and Streambed Alteration Agreements and Fees (California Department of Fish and Wildlife, 2019); https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=162284&inline
UC Cooperative Extension Aquatic Weed and Algae Control (University of California, 2010).
Medellín-Azuara, J. et al. Cost of Ecosystem Management Actions for the Sacramento–San Joaquin Delta (Public Policy Institute of California, 2013).
McKuin, B. et al. Energy and water co-benefits from covering canals with solar panels datasets. (Dryad Digital Repository, 2021); https://datadryad.org/stash/dataset/doi:10.6071/M32H30
McMurray, A., Pearson, T. & Casarim, F. Guidance on Applying the Monte Carlo Approach to Uncertainty Analysis in Forestry and Greenhouse Gas Accounting (Winrock International, 2017).
Canty, A. & Ripley, B. boot: Bootstrap R (S-Plus) Functions (R package version 1.3-25, 2020).
Emission Inventory Methodology, Agricultural Irrigation Pumps – Diesel (California Air Resources Board, 2006).
Burt, C., Howes, D. & Wilson, G. California Agricultural Water Electricity Requirements ITRC Report no. CEC-400-2005-002 (Irrigation Training and Research Center, 2003).
We thank R. Raj and J. Harris for coordinating stakeholder meetings, R. Winston and S. Kurtz for helpful discussions on solar canal development and J. T. Watson for helpful comments on the accessibility of the article to scientists across the broader sustainability scholarship. We thank NRG Energy for support. R.B. and T.P. were funded by the USDA (National Institute of Food and Agriculture grant 2018-67004-24705). J.H.V. was funded by the US Department of Energy US–China Clean Energy Research Center for Water-Energy Technologies (DE-IA0000018).
The authors declare no competing interests.
Peer review information Nature Sustainability thanks Michael Brady, Giuseppe Tina and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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McKuin, B., Zumkehr, A., Ta, J. et al. Energy and water co-benefits from covering canals with solar panels. Nat Sustain 4, 609–617 (2021). https://doi.org/10.1038/s41893-021-00693-8