Can America’s canals double as solar farms?

Some 8,000 miles of federally owned canals snake across the United States, channeling water to replenish crops, fuel hydropower plants and supply drinking water to rural communities. In the future, these narrow waterways could serve an additional role: as hubs of solar energy generation.

A coalition of environmental groups is urging the federal government to consider carpeting its canals with solar panels. The concept was pioneered in India a decade ago and will soon be tested in California for the first time. Early research suggests that suspending solar arrays over canals can not only generate electricity in land-constrained areas but may also reduce water evaporation in drought-prone regions.

Last week, more than 125 climate advocacy groups, led by the Center for Biological Diversity, sent a letter to the U.S. Department of Interior calling on the agency to deploy solar over its 8,000 miles of canals and aqueducts. The agency’s Bureau of Reclamation owns and operates the infrastructure, often in partnership with local irrigation and water districts.

Such a move would potentially generate over 25 gigawatts of renewable energy — enough to power nearly 20 million homes — and reduce water evaporation by tens of billions of gallons, according to the letter. To come up with the national numbers, the groups extrapolated from previous research led by the University of California, Merced that analyzed the potential benefits of covering California’s 4,000 miles of canals.

“We’re trying to elevate this as a good solution that you should be doing,” Brett Hartl, the government affairs director at the Center for Biological Diversity, said about the letter. ​“You don’t have to pave over thousands of acres of land…at the expense of lost habitat.”

The solar-canal campaign reflects a broader tension that’s building as the U.S. transitions away from fossil fuels toward cleaner energy sources.

Sprawling utility-scale solar systems are facing pushback in rural Midwestern communities and in Maine, Texas, Virginia and elsewhere. Local opponents have argued that big solar projects would take farmland out of production, reduce property values and possibly harm wildlife. The American Clean Power Association, an industry trade group, has argued that community opposition is making it harder for solar developers to build projects at the rate that’s needed to address climate change.

The Biden administration is pushing to permit 25 gigawatts of solar, wind and geothermal energy projects on public lands by 2025, the bulk of which will likely include utility-scale projects in the western United States. Solar canals could, in theory, provide a way to meet some of those goals without disturbing ecosystems or affecting communities.

“It builds on the conventional wisdom that you’d better build solar over existing infrastructure first before you take natural lands or productive farmland out of use,” said Roger Bales, an engineering professor at UC Merced who specializes in water and climate research. Existing sites can include rooftops, landfills, parking lots and former industrial lands.

For all their promise, solar canals remain more of an idea than a widely deployed reality. But efforts are underway to start installing and testing projects in water-scarce parts of the country. 

Most notably, Solar AquaGrid, a company based in the Bay Area, is designing a solar array prototype that will cover nearly 2 miles of irrigation canals in the Central Valley, a vast agricultural region where cotton, tomatoes, almonds and hundreds of other crops are grown. The California Department of Water Resources is providing $20 million for the pilot project, and the Turlock Irrigation District, which operates 250 miles of canals through the valley, has volunteered its waterways.

The initiative, known as Project Nexus, is expected to break ground this fall and start operating in 2024, ideally before the next irrigation season begins in the spring. Brandi McKuin, a project scientist at UC Merced, will collect data for two years along with Bales and other UC researchers to see how well the solar array produces electricity, prevents evaporation and improves water quality.

“We need to get to the heart of those questions before we make any recommendations about how to do this more widely,” McKuin told the Associated Press.

McKuin previously led a 2021 study of California’s solar-canal potential, which found that the technology could be an ​“economically feasible” way to help meet the Golden State’s clean energy goals.

As part of that analysis, the California researchers consulted with experts in India, where a handful of solar canals are already operating.

India’s first project, a 1-megawatt array, was completed in 2012 in the western state of Gujarat and uses steel trusses to support thousands of panels over a 2,460-foot stretch of irrigation canal. Another project, a 2.5 MW installation in Punjab state, uses tensioned cables.

Both systems are more expensive and technically complex than conventional ground-mounted solar arrays. Maintaining solar canals also presents its own set of complications, including having to build ramps for technicians to climb and clean solar panels.

But the projects have shown benefits, as well. Putting solar panels above the water helped keep the equipment cool, which in turn improved their efficiency and electricity output. Shade from the panels helped prevent water loss through evaporation and controlled the growth of aquatic weeds, reducing pesticide use and the need for water treatment.

“The study found that, across a wide range of climate conditions, the co-benefits do matter” when it comes to assessing solar canals, Bales said. ​“We’re trying now not to view this as an energy project but as a broader infrastructure investment.”

Outside of California, at least two other solar-canal initiatives are in the early stages of development.

The Gila River Indian Community in south-central Arizona is set to receive up to $233 million from the Inflation Reduction Act and Bipartisan Infrastructure Law for a number of water-conservation projects, including installing solar-panel shade covers over tribal irrigation canals. Salt River Project, one of Arizona’s largest public utilities, is partnering with Arizona State University to collect data from two canal sites to determine whether solar canals might work there.

A $25 million provision in the Inflation Reduction Act also provides funding for the Bureau of Reclamation to design, study and implement projects that put solar panels over ​“water conveyance facilities” like canals.

Hartl of the Center for Biological Diversity said that, while he’s following the California pilot project with interest, he hopes that solar developers and government agencies don’t wait until the project concludes to start pursuing deployments in other places.

“This really checks a lot of boxes,” he said of solar canals. ​“We’re really trying to come to the table with a positive, constructive solution.”