Rows of solar panels stretch to the horizon near Chandrasan, a small village in India's western state of Gujarat. The 1-megawatt solar array snakes through fields flush with crops of cotton and peanuts, but it doesn't encroach on the precious farmland. Instead, the panels hover above a narrow irrigation canal, which replenishes the surrounding fields.
India's first “solar canal," completed in 2012, has since sparked a growing global interest in the unconventional design, owing to its overlapping benefits. When placed over a canal, solar arrays do more than produce electricity in land-constrained areas. They also keep cool, and thus operate more efficiently, thanks to the water down below. Shade from the panels, meanwhile, can reduce evaporation and limit harmful algae growth in the waterway.
A handful of larger-scale solar canals now wind through India's countryside, providing a one-two punch of energy production and water conservation. Recently, researchers in California studied this fledgling network to determine whether such projects would work at home.
Some 6,400 kilometers of public water delivery canals crisscross the Golden State, providing ample airborne real estate for hovering solar panels. “A critical question was whether the infrastructure to span the canals would be cost-prohibitive," Brandi McKuin, the study's lead author and a postdoctoral researcher at the University of California, Santa Cruz, explained in a news release.
For instance, the 1-MW installation in Gujarat uses steel trusses to support thousands of glimmering blue rectangles over a 750-meter stretch of canal. A 2.5-megawatt installation in India's Punjab state uses tensioned cables. Both systems are costlier and more technically complex than traditional ground-mounted designs. It's also more complicated to maintain and operate solar canals, since technicians must build and climb ramps to clean the panels, or use specialized equipment to maintain the underwater support structures.
“While a normal ground-mounted project is a simple project, the canal-top projects are a feat of engineering in themselves," said Manik Jolly, who was involved in the Gujarat pilot project when he worked at SunEdison and is now CEO of Grassroots and Rural Innovative Development, a startup in New Delhi.
Despite the extra expense, California researchers found that solar canals could be an “economically feasible" way to help meet the state's clean energy goals. On paper, the financial benefits—enhanced electricity production, avoided land fees, cost savings from water conservation—ultimately outweighed the higher costs associated with canal-spanning infrastructure, McKuin and her colleagues wrote in the journal Nature Sustainability.
In the real world, projects in India have shown promising results. Thanks to the natural cooling effects of water, panels placed above canals saw their efficiency and output improve by 2.5 percent to 5 percent, according to the Gujarat Energy Research and Management Institute. Canal-top panels also showed no degradation, and their power output stayed stable during a three-year study period. By contrast, ground-mounted solar panels tend to see their output decline at a rate of 1 percent per year.
And since India's irrigation canals run through agricultural areas, covering the waterways with solar panels can also help boost rural electricity supplies, which in turn reduces reliance on far-flung transmission lines and strengthens the local grid.
“Transmission costs are a heavy cost in the electricity business, and there are also massive transmission losses," Jolly said. “So it cuts down on both if we use these canals to produce electricity in the energy-deficient areas of the country." He said the financial savings from avoided transmission losses could cancel out the additional costs of building and operating solar canals.
With 120 major canal systems, India has enormous potential—at least 10,000 megawatts' worth—to bring solar energy into rural areas and beyond, Sudhir Moola, executive director of Premier Energies, recently told PV Magazine. His company built a 1-megawatt solar canal project in Uttarakhand in 2017 using high-tensile steel supports. Spanning 35 meters, the array is the widest canal-top installation in India, he said.
An illustration of a solar panel canal in California. Illustration: Solar AquaGrid LLC
In California, many irrigation canals wind through drought-prone agricultural hubs, which produce more than half of the fruits, vegetables, and nuts grown in the United States and provide a significant amount of global food exports. The University of California researchers pointed to solar canals as a way to conserve the state's vital water supplies in the face of climate change, which is raising the risk of more extreme and enduring droughts. For example, a 10-megawatt solar canal in Gujarat is expected to prevent 90 million liters of water from evaporating every year.
"What we're seeing here is actually some surprising benefits when you bring water and energy together," Elliot Campbell, a senior author on the paper and a professor at UC Santa Cruz, said in the news release.