Hot Tech, Cool Concept: Solarizing California’s Irrigation Canals

Sep 23, 2022 • by Clint Wilder

It’s no exaggeration to say that water systems engineering created the state of California as we know it. For better and for worse, building the state’s gargantuan water infrastructure – one of the world’s largest systems of dams, reservoirs, power plants, pumping plants and some 4,000 miles of canals and aqueducts – was one of the great engineering marvels of the 20th century. The system irrigates 5.7 million acres of some of the most productive agricultural land on the continent and supplies water in a semi-arid climate to some 35 million people.

Can this massive system ­– the largest single user of electricity in the state – help tackle the 21st century existential challenges of climate change, drought, and depleted aquifers? At the epicenter of these challenges, in the heart of California’s Central Valley, one innovative project may help us find out.

By early next year, the principals of the pilot program Project Nexus plan to start construction in an ambitious plan to install solar photovoltaic (PV) canopies over irrigation canals. With $20 million in funding from the state, the project is a partnership of diverse stakeholders: the local community-owned utility Turlock Irrigation District (TID), the state Department of Water Resources (DWR), Solar AquaGrid, and the University of California-Merced. Solar AquaGrid originated the pilot project after first commissioning a study by UC-Merced researchers in 2015, which was published in the journal Nature Sustainability last year. Part of the study assessed the results of a solar-over-canals demonstration project in Gujarat, India that went online at that time. 

In ambitious and innovative climate-tech projects with BHAGs (big hairy audacious goals) like this one, studies and research are a good first step, but the only way to really learn, and answer the key questions, is by doing. Some of those key questions are:

Will it work?

Will it scale?

And who will pay for it?

But let’s not get ahead of ourselves. At the outset, let’s take a look at the benefits of this solar-over-canals concept. It offers potential win-wins across a swath of issues, among them clean energy deployment, water conservation, land use, cost savings, and air quality.

•  Water savings from reduced evaporation. Covering and shading the state’s 4,000 miles of canals with solar panel canopies could save more than 63 billion gallons of water a year, according to the UC-Merced study. That’s enough to meet the needs of two million people, or irrigate up to 50,000 acres of cropland.

•  Clean energy generation. The Full-Monty, 4,000-mile scenario envisioned by Project Nexus could create solar generating capacity of an eye-popping 13 gigawatts, doubling California’s current nation-leading solar capacity of 13.8 GW – and enough to power 9.75 million households. That’s a huge chunk of a carbon-free electricity to help meet the state’s 2045 goal of 100% clean power (and the State Water Project’s near-term goal of 75% clean energy by 2030).

•  Land use. Even in a state that arguably supports renewable energy more than any other, finding appropriate places to site large solar or wind farms can be challenged by the need for habitat protection, other environmental concerns, or good old-fashioned NIMBY. The land alongside canals is considered “already disturbed,” thereby not negatively impacted by the installation of solar mounting systems.

•  Aquatic growth. Creating “roofs” over canals not only reduces evaporation, it slows the growth of weeds and algae that thrive on sunlight. That cuts down on maintenance hassles and costs. You could say you’re using those sunlight photons to grow electrons instead of feeding weeds.

•  Air quality. Using clean solar energy to power irrigation pumps can replace diesel engines, a notable pollution source in a region with perennial air quality issues.

•  More productive solar panels. Since so much of large-scale solar power generation comes from the hot deserts of California and the Southwest, it’s a surprise to many that heat actually reduces the productivity of solar panels. You want light, not heat; given equivalent sunlight, a panel on a clear summer day in Seattle will crank out more juice than one in Phoenix. So what does this have to do with Central Valley canals? The water in the canal is significant cooler than the surrounding land, so that’s a cooler “habitat” for the solar panels above it. At the Gujarat project in India, researchers found a 3% power output increase from the above-water panels. Project Nexus may even experiment with “bi-facial” panels, with a PV underside that can potentially pull additional power from sunlight reflecting off the canal.

The large-scale aggregation of these myriad benefits offers a potentially very rosy scenario in California’s battle against climate change and dwindling water resources. But in order to go big, you have to start small. Project Nexus participants plan to break ground early next year in two pilot canal locations that present different engineering challenges: a long skinny one (one mile long, 20-25 feet wide) and a short wide one (a 500-foot stretch of the TID Main Canal that’s 110 feet wide). Throughout the pilot process, Project Nexus facilitator Solar AquaGrid and its ongoing research partners at UC-Merced is committed to collecting data on all the potential positive metrics in water conservation, clean energy generation, and environmental benefits.

Both pilot locations are in the service territory of the TID, the state’s oldest publicly owned irrigation district (founded in 1887) and one of only four providing both water and electricity services. TID already has a strong commitment to clean energy, with its power mix including 203 megawatts of hydroelectric generation and 54 MW of solar energy from a power purchase agreement with the Rosamond utility-scale solar farm near Edwards Air Force Base in Kern County. TID also walks the walk with a 70.7-kilowatt rooftop solar array on the parking structure at its Turlock headquarters.

•     So – will the Project Nexus solar canopies do what they’re promised to do – and do it affordably? Josh Weimer, TID’s external affairs department manager, told The Hill that the biggest challenge is finding a viable, cost-effective way to engineer the solar panel mounting techniques. The design and engineering solutions must also ensure that the canopies don’t obstruct access to canals for maintenance. 

But trial and error is the name of the game, and this game has pretty impressive upside potential for California’s leadership in clean energy growth, water conservation, and carbon reduction. We’ll be watching closely.

Veteran clean tech journalist and analyst Clint Wilder is editorial director at Clean Edge, co-author of The Clean Tech Revolution and Clean Tech Nation, and a contributing writer at Environmental Entrepreneurs (E2).