Every Drop Counts

One water conservation solution has the potential to tackle multiple problems, with a promising array of benefits for society and the environment.

By Seabright McCabe, SWE Contributor

Brandi McKuin, Ph.D., is a postdoctoral scholar in the University of California, Santa Cruz department of environmental studies, an environmental engineer-turned-researcher who studies the nexus of food, energy, and water.

“I think it’s really important to think of multipurpose, interdisciplinary solutions,” Dr. McKuin said. “We’re facing big challenges with climate change, and we really need to think in interdisciplinary ways about how to address them.”

Dr. McKuin is lead author of a study in Nature Sustainability, and was technical lead for one such solution, Solar AquaGrid. Her techno-economic analysis shows that covering and shading canals with solar panels can save water; generate clean, renewable energy; and preserve arable land in a cost-effective way.

solar-canals illustration
Illustrating the advantages of solar canals: at top, ground based panels; middle and bottom: truss and suspension cable canal-spanning designs.

Mitigating evaporation loss

The American Southwest is just one region among many facing historic drought. Lake Mead, near Las Vegas, is only 37% full at this writing, with its evaporation rate increasing. Utah’s Great Salt Lake is down by 51%. The Colorado River, where wet and dry periods are normal, has had 17 dry years in the past 22, gravely impacting its watershed.

In California, a network of canals 3,945 miles (6,350 km) long snakes its way from the Sierra Nevada Mountains down the length of the state. The California Aqueduct is the largest water delivery system on Earth, carrying an average of 3 million acre-feet (4.1 million maximum) of water to 35 million people and 5.7 million acres of farmland.

With water at a premium during what’s being called “a return to paleo drought,” covering a canal system that crosses the Mojave Desert makes sense. “Solar canals could save enough water to satisfy the residential needs of 2 million people, or irrigate 50,000 acres of farmland,” Dr. McKuin said, estimating that 65 billion gallons per year could be saved from evaporative loss.

solar aqua grid aerial shot
A rendering of how a working solar canal might look when completed.
Photo Credit: Citizen Group

Solar canals could also help lessen the need for pumping groundwater, which causes land subsidence that threatens buildings, infrastructure, and, in some areas, the concrete canals themselves.

“In a big drought, when you compare the volume saved to the annual water delivery needed, it’s a drop in the bucket,” Dr. McKuin said. “But if we don’t know when a drought is going to end, every drop counts.”

Generating clean power, efficiently

Solar canals could contribute substantially to California’s decarbonization goals, supplying 13 gigawatts of solar power each year, enough to power almost 4 million homes.

Because the water in the canals needs to move, photovoltaic, thin-film panels can’t be simply floated on the surface, but must be engineered to go up and over it. Dr. McKuin and her colleagues studied two designs: a steel truss system and a suspension cable system, both of which have been deployed in India.

Solar canals also provide a cooler microclimate due to their proximity to water, which heats more slowly than solid ground. And while panels prevent evaporation loss, the evaporation that does occur actually cools the panels from underneath. “When panels become too hot, they lose efficiency — there’s a rate of loss per degree of heat increase,” Dr. McKuin explained. “By providing a cooler microclimate, we estimate there could be an enhanced efficiency. In particular, we found that cadmium telluride (CdTe) semiconductors produced 3% more electricity for solar panels over a simulated canal versus a ground-based system.”

Getting power to the grid is complicated, considering the thousands of miles of canal to be wired and connected. Dr. McKuin’s report notes that decentralized microgrids should be an essential consideration for future pilot experiments in the field.

Conserving arable land, biodiversity, cultural landmarks

California is the largest producer of agricultural products in the U.S., and every acre of farmland counts. At the same time, the state has committed to requiring that renewable and zero-carbon energy resources supply 100% of electric retail sales to customers by 2045, which puts solar farms in competition with farmland.

Solar canals can help achieve this goal, by producing clean electricity while reducing the need for acre-consuming, ground-based solar farms. “With this project, we can save arable land for food production and preserve biodiversity by preventing habitat loss and fragmentation,” Dr. McKuin said.

Additionally, canal-spanning solar panels have the potential for taking 15–20 diesel-powered water pumping stations offline per megawatt generated, in some of the worst air-quality areas in the nation.

There’s also a cultural benefit. “For instance, there are some plant communities that are culturally important to Indigenous tribes,” Dr. McKuin said, noting that one large project, the Genesis Solar Energy Center in the Sonoran and Mojave deserts, destroyed or damaged trails, burial sites, and important cultural artifacts, leading to a prolonged legal conflict. “There’s been a lot of discussion about the use of public lands for solar farms,” she said. “Our project could help spare some of that land for continued use by the public, and also protect Native American lands.”

Solar canals haven’t been built yet in the U.S., partly because their cost efficiency hasn’t been proved until now. Dr. McKuin’s report shows that “the cost savings from water conservation, enhanced electricity production, avoided land and permitting costs, and reduced aquatic weed maintenance outweighed the added cost of the canal-spanning system.” The Solar AquaGrid study estimates an annual savings of $40,000 per mile in maintenance costs.

“Covering canals with solar panels won’t solve all of our problems,” Dr. McKuin said. “But it’s among the many solutions we need to be thinking about.”

Brandi McKuin: Applying Systems Thinking to Sustainability

mckuin-brandi headshot

“I was always interested in sustainability. When University of California, Merced opened right in my backyard, I decided to study environmental engineering with a focus on renewable energy.”

Brandi McKuin, Ph.D., was in her 30s and working for a law firm when she decided to become an engineer.

Dr. McKuin counts the book Cradle to Cradle: Remaking the Way We Make Things, which challenges the Industrial Revolution-based notion that industries must by nature be environmentally damaging, as one of her biggest influences. “I felt a need for people to use systems thinking about how to make systems more sustainable.”

Engineering became a springboard to full research. After earning her degree, Dr. McKuin stayed on at UC Merced for her dissertation on the food, energy, and water nexus that became the focus of her work. “I started doing research as a graduate student, and I just haven’t stopped,” she said.

Now pursuing postdoctoral research at the University of California, Santa Cruz, Dr. McKuin encourages women engineers and students who are environmentally focused to “stay curious. There are so many opportunities to apply systems thinking to make things more sustainable.”

The Solar AquaGrid study received development support from the Bay Area agency, Citizen Group, and was underwritten by NRG Energy.