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For decades, politicians, planners and policy experts have tossed around an idea that, on its face, could help address two problems: Water scarcity and the growing demand for electricity. The pitch is simple enough. Put more solar on top of irrigation canals.
From there, the benefits are cascading:
Save water through reducing (often significant) evaporation loss from canals.
Generate renewable power on land that is permitted with existing rights-of-way.
Reduce vegetation/algae growth in canals, a considerable maintenance cost.
Build renewable energy in a low-conflict way by utilizing built environments.
The idea has flowed in and out of the public sphere, only to usually disappear. But in recent years, it’s started to gain traction at a time when consecutive years of drought have amplified structural water issues and at a time when Western states are working to add more renewable energy to the grid. At the end of last year, the Arizona Republic reported on a pilot project to cover ~3,000 feet of the Gila River Indian Community’s canals with solar. Their engineering project is one of the first case studies in the U.S.
And it is not alone. In California, the Turlock Irrigation District, in partnership with UC Merced, the Division of Water Resources and Solar Aquagrid, are piloting a canal retrofit (Project Nexus) to test the promise of solar on canals. I recently talked with some of the people involved to better understand the promises and the challenges.
A test case: The Turlock Irrigation District is, in some ways, a natural place to test this technology. It already delivers water and power to its customers, giving it needed expertise in both worlds. The oldest irrigation district in California, its water from the Tuolumne River is sent out to about 4,700 growers over roughly 150,000 acres. But it needs more renewable energy to meet the state’s goals, and a lot of that comes down to finding land for solar. Because water is fairly abundant, purchasing acreage for a project or taking land out of production can be costly. So as much as the solar canal pilot project promised to save water from evaporation, the agency became interested in it from a “land use” perspective, according to Josh Weimer, a district spokesperson.
“We like to wade into the unknown if we think there is a long-term potential benefit and run into all the issues. It’s what happens anytime with the first innovation. You have to run through all those obvious barriers, and even those that are not so obvious and hopefully come out the other side and show everybody that it’s worthwhile to do.”
After the idea of putting solar on canals came across the Turlock Irrigation District’s radar, the district’s general manager called UC Merced, which was already studying the concept. That led to a pilot project on two sections of canal. In the first section, the project team will cover 1,400 feet on a canal 20-feet wide. The other section will cover about 120 linear feet on a much wider canal, stretching across roughly 110 feet.
The narrower project is expected to go online in November 2024, with the full design slated to go live in 2025. But that’s only the end of the beginning. From there, they will be watching to see if the concept pencils out — and what lessons can be learned.
The promises: Brandi McKuin, a researcher at UC Merced, has been leading the team looking at covering canals and aqueducts with solar panels. Her research was initiated after Solar Aquagrid, an advisory and advocacy firm, approached the university about looking at the potential and feasibility for the state to cover its thousands of miles of canals with solar. In 2021, McKuin led a paper in Nature Sustainability on the benefits of putting solar on canals. The researchers estimated that reducing evaporation loss alone — if about 4,000 miles of canals in California were covered — could save about 63 billion gallons of water, enough for 2 million people or 50,000 acres of farmland.
That number is an upper limit, McKuin notes. The research assumes the use of shade cloth, which can be far more efficient than solar panels. And from a physical, safety and operations perspective, not every mile of canal can be covered. Yet the point is still an important one. At scale, solar on canal projects can help save a lot of water.
“We hope to build off that estimate,” McKuin said. “We we're doing a more rigorous analysis of the canal systems to characterize both the water surface area of the canal and to really have a more refined estimate of the water savings potential.”
She identified a number of other benefits. From a land perspective, solar canals can serve a dual purpose. In doing so, they could offset the economic and environmental costs of building on land needed to support local ecosystems or to grow food. Solar canopies reduce light, potentially reducing vegetation and algal growth in canals (a maintenance/treatment cost for water utilities). And of course, the benefit of bringing more renewable energy onto the grid as utilities look to meet the state’s benchmarks.
The challenges: There’s a reason people have been hesitant to try this.
There are physical constraints. Solar panels cannot line every foot of canal. There are takeouts and infrastructure that make it physically difficult. Utilities need to maintain access for canal upkeep, too. And canals are constructed differently to varying widths, so the corresponding solar canopies also have to come in different templates.
There are also less tangible constraints: The time it takes to plan and build out these solar projects — and the expertise needed to keep them maintained and running. This is especially true in cases (maybe most cases) where an irrigation district is not also a power provider. In those cases, you’d need a third-party energy provider to come in.
But the big one is the cost. In many cases, these projects, at first glance, have seemed cost-prohibitive to those who might go about implementing them. On its website, the Central Arizona Project (CAP) cites cost as a major impediment to putting solar on its 336-mile canal, which delivers Colorado River across the state. One estimate for solar above the canal would have quadrupled the initial $4 billion cost of the CAP project.
Is the saved water worth the cost? Is the opportunity to build solar here, as opposed to in other places, worth the cost? Combined, do the benefits of the energy generation and the water savings outweigh the costs? All of those questions are important ones.
Right now, the Turlock Irrigation District project is getting its funding from the state of California, which is testing the viability of the concept, the physics, economics and long-term feasibility. Many solar developers (from my experience covering and talking with them) want to build at large scales, often on untouched land near transmission lines. Building on disturbed land, whether it is an abandoned mine or a canal, always seems to be a larger sell than building on undeveloped land, despite the biodiversity and environmental advantages of the former. And yet: Project proponents say costs could vary over time, as land is harder to find and water is more scarce. And when all the co-benefits are added up and accounted for, the right projects in the right place could pencil out for districts. It all depends on what is valued and how it is valued.
Getting more data: It’s one of the things that the pilot project hopes to unpack, said Robin Raj, a co-founder of Solar Aquagrid. “What we talk about is a holistic view of those costs. Is ground-mount cheaper than solar over water? Probably yes. But what’s the delta? But when you factor in the true value — meaning saved land costs, water savings and water quality — we might find there is more bang for the buck?”
For almost a decade, Raj has been working to test this concept in the real-world.
“It is a process of patience, iteration, persistence,” he said. “But glass half-empty, half-full. We are really lucky to live in a state that values climate solutions and is putting a priority on it now that the pendulum has shifted — our reality has shifted.”
Now that solar panels are being deployed in a pilot project, he said there are seven or eight categories that the team is looking at to think about scaling. Getting more data is important because the team has received interest nationally and internationally. At the same time, each utility has different needs, constraints and challenges to consider.
“Our goal is to study in order to scale and develop a solution set” he added.