California's solar canals cut evaporation and add power — but don't scale everywhere

California’s Project Nexus is testing whether covering irrigation canals with solar panels can solve two problems at once: shading water to slow evaporation while generating clean electricity on land that’s already been disturbed. Backed by a $20 million state grant and run with the Turlock Irrigation District, UC Merced, and the state Department of Water Resources, the pilot deploys three panel designs over canals of different widths. Early results support the concept — UC Merced’s Roger Bales estimates that panels over 100 miles of Turlock’s canals could save water for thousands of households and generate hundreds of megawatts, while building on developed land avoids the permitting delays that stall projects on open space (110 days versus 621 on average).

The co-benefits are real but modest in scale. Shading cut algae and weed growth, improving water quality and reducing maintenance, and the current installation is a proof of concept generating just 1.7 megawatts — a fraction of the district’s 56-megawatt desert solar farm. The site doubles as a research platform, instrumented to measure temperature, humidity, radiation, and evaporation directly.

The bigger lesson is that the approach isn’t universal. Turlock works partly because it’s one of only four California districts providing both water and retail power, and because its cleaning equipment requires panels mounted high above the water — unlike lower installations in India and Arizona. Urban districts like Contra Costa, where canals thread through backyards and parks and need constant access, are opting to pipe their water instead. Coordinating land, water, and power across overlapping agencies remains the hard part of getting to an idea that otherwise ‘just makes sense.’