In California, a sprawling 4,000-mile network of canals winds through citrus orchards and fields of tree nuts, delivering irrigation and drinking water to homes and farms across the state. The canals are critical in an increasingly arid part of the country. But what if they could help fulfill another urgent need: renewable energy? To test that idea, researchers, private enterprise and a public utility in the Central Valley are installing solar panels atop the man-made waterways. The pilot program, called Project Nexus, is testing solar canopies that researchers say could generate gigawatts of power and save billions of gallons of water by providing shade that slows evaporation. It could be transformational if scaled up, researchers say, in helping the state to meet its ambitious climate and biodiversity goals.