California Built Solar Panels Over Its Canals and Stopped Losing the Water
Put a roof of solar panels over an irrigation canal and you ask one structure to do several jobs at once: make electricity, keep the sun off the water, and hold back the weeds. A pilot in California’s Central Valley has now run a full season and measured all three.
The project is called Project Nexus, a $20 million state-funded experiment run by the University of California, Merced, the Turlock Irrigation District, and a developer called Solar AquaGrid. Its canopies span two canals south of Modesto and together put out about 1.6 megawatts. When the crews tallied a full irrigation season under the panels, the electricity was almost the least interesting part. In the shade, evaporation fell by as much as 70 percent. And the channels stayed markedly cleaner: the aquatic weeds and algae that usually clog a canal grew up to 85 percent less.
That second number is the one canal operators tend to sit up for. Scraping weeds and algae out of a working canal is grinding, expensive, year-round maintenance, and a canopy that holds them down takes a permanent line off the budget while it also saves water and makes power. Because solar canopies cost more to build than panels bolted to open ground, it may be these side benefits that decide whether the whole idea pays for itself.
The power benefits from the setup, too. Solar panels lose efficiency as they heat up, and the water running beneath them works like a long, free radiator. Arizona has already seen the effect. A project the Gila River Indian Community finished in 2024, running panels along Interstate 10 south of Phoenix, is producing about 1.5 megawatts, roughly a quarter more than anyone forecast. Over 3,500 feet of shaded canal there, the water cooled by a degree and grew no algae at all. Gujarat, in western India, has been covering its canals this way for over a decade.
The obvious next thought is to do it everywhere, and researchers have already run that number. A 2021 UC Merced study estimated that shading all 4,000 miles of the state’s major canals could add about 13 gigawatts of capacity, close to half the new solar California needs for its 2030 targets, and save some 63 billion gallons of water a year, enough for two million people or 50,000 acres of farmland. The scientist who led that work spends most of her breath tempering it. “It’s probably unrealistic to assume that we’re going to cover all 4,000 miles of California’s canals,” Brandi McKuin told The New York Times, and the economics, she added, are unsettled: “It’s still really early to say what the economic feasibility of this is.”
For now, the plan stays small on purpose. Roger Bales, a UC Merced engineer, thinks the canals might one day supply as much as a gigawatt, but only after the first stretch proves itself. “We have to get to a hundred miles,” he told the Times, “and then it might take off.” The idea is to begin where a canal already runs beside something that wants the electricity, a pumping station or a highway charger, and let the numbers argue for the next stretch. So far the argument rests on two canals south of Modesto: less water lost to the air, channels that stay clear, and steady power off the panels that shade them.ment rests on two canals south of Modesto: less water lost to the air, channels that stay clear, and steady power off the panels that shade them.
