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Energy and water co-benefits from covering canals with solar panels

Abstract

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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Fig. 1: Locations of California canals and study sites.
Fig. 2: Illustrations and flow diagrams showing the inputs and outputs of three solar PV systems.
Fig. 3: Maps of annual mean evaporation from water surfaces, PV solar resources and county-level numbers of diesel-powered irrigation pumps.
Fig. 4: Financial metrics for three different 1 MW PV system designs across a wide range of California sites.

Data availability

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.

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Acknowledgements

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).

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J.E.C., R.B., J.H.V. and T.P. designed the study. B.M., A.Z. and J.T. conducted the analysis. B.M., A.Z., J.T. and J.E.C. wrote the initial draft. J.E.C., R.B., J.H.V. and T.P. contributed to methodological refinements and conceptual considerations. All authors contributed to completion of the manuscript through comments and edits of the text and figures.

Corresponding authors

Correspondence to Brandi McKuin or J. Elliott Campbell.

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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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Supplementary information

Supplementary Information

Supplementary Figs. 1–5, Tables 1–24, Discussion and Methods.

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Supplementary Data 1

Source Data for Supplementary Fig. 1: QGIS project files (Supplementary_Fig_1a.qgs, Supplementary_Fig_1b.qgs) and associated shapefiles.

Supplementary Data 2

Source Data for Supplementary Fig. 2: Rstudio file (Supplementary_Fig_2.R) and .csv file.

Supplementary Data 3

Source Data for Supplementary Fig. 3: Rstudio file (Supplementary_Fig_3.R) and .csv file.

Supplementary Data 4

Source Data for Supplementary Fig. 4: Rstudio file (Supplementary_Fig_4.R) and .csv file.

Supplementary Data 5

Source Data for Supplementary Fig. 5: Rstudio files (Supplementary_Fig_5a.R, Supplementary_Fig_5b.R) and .csv files.

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Source Data Fig. 1

QGIS project file (Fig_1.qgs), folders containing associated shapefiles, .csv file.

Source Data Fig. 2

Alternative versions of Fig. 2 in .eps and .svg file formats. Note that there is no source data associated with the figure because it is a drawing/flow chart.

Source Data Fig. 3

QGIS project files (Fig3a.qgs, Fig3b.qgs, Fig3c.qgs), associated shapefiles and alternative version of Fig. 3 in.eps file format.

Source Data Fig. 4

RStudio files (Fig4a.R, Fig4b.R), .csv files and alternative version of Supplementary Fig. 4 in .eps file format.

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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

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