Floating solar arrays — they are often referred to as “floatovoltaics,” a term trademarked by one company — also have advantages over solar plants on land, their proponents say. Renting or buying land is more expensive, and there are fewer regulations for structures built on reservoirs, water treatment ponds and other bodies of water not used for recreation. Unlike most land-based solar plants, floating arrays can also be hidden from public view, a factor in the nonprofit Sonoma Clean Power Company’s decision to pursue the technology.

“Sonoma County boasts some of the most beautiful rolling hills, and people don’t want to see them covered by solar panels,” said Rebecca Simonson, a senior power analyst for the renewable energy developer, which has signed purchasing agreements for floating solar arrays to be built on six treated water ponds in the county. The solar panels, she said, would not be visible from the road.

The floating arrays have other assets. They help keep water from evaporating, making the technology attractive in drought-plagued areas, and restrict algae blooms. And they are more efficient than land-based panels, because water cools the panels.

“The efficiencies are what motivated us to look at this,” said Rajesh Nellore, the chief executive of Infratech Industries, which has completed the first section of a floating solar plant in Jamestown, Australia, that will eventually cover five water treatment basins. The installation, which went into operation last year, is constructed so that it generates up to 57 percent more energy than a rooftop solar plant. (The finished plant is expected to generate up to 20 percent more energy than a land-based array.)

The panels are specially coated to prevent corrosion, and set on a tracking system that moves them to maximize sunlight during the course of a day. The company is working on a similar project in Holtville, a small city in Southern California, which has suffered from years of drought.