Gila River Tribes Intend to Float Solar Panels on a Reservoir. Could the Technology Help the Colorado River?

GILA RIVER INDIAN RESERVATION, Ariz.—About 33 miles south of Phoenix, Interstate 10 bisects a line of solar panels traversing the desert like an iridescent snake. The solar farm’s shape follows the path of a canal, with panels serving as awnings to shade the gently flowing water from the unforgiving heat and wind of the Sonoran Desert.

The panels began generating power last November for the Akimel O’otham and Pee Posh tribes—known together as the Gila River Indian Community, or GRIC—on their reservation in south-central Arizona, and they are the first of their kind in the U.S. The community is studying the effects of these panels on the water in the canal, hopeful that they will protect a precious resource from the desert’s unflinching sun and wind. 

In September, GRIC is planning to break ground on another experimental effort to conserve water while generating electricity: floating solar. Between its canal canopies and the new project that would float photovoltaic panels on a reservoir it is building, GRIC hopes to one day power all of its canal and irrigation operations with solar electricity, transforming itself into one of the most innovative and closely-watched water users in the West in the process.

The community’s investments come at a critical time for the Colorado River, which supplies water to about 40 million people across seven Western states, Mexico and 30 tribes, including GRIC. Annual consumption from the river regularly exceeds its supply, and a decades-long drought, fueled in part by climate change, continues to leave water levels at Lake Powell and Lake Mead dangerously low. 

Covering water with solar panels is not a new idea. But for some it represents an elegant mitigation of water shortages in the West. Doing so could reduce evaporation, generate more carbon-free electricity and require dams to run less frequently to produce power. 

But, so far, the technology has not been included in the ongoing Colorado River negotiations between the Upper Basin states of Colorado, New Mexico, Utah and Wyoming, the Lower Basin states of Arizona, California and Nevada, tribes and Mexico. All are expected to eventually agree on cuts to the system’s water allocations to maintain the river’s ability to provide water and electricity for residents and farms, and keep its ecosystem alive.

“People in the U.S. don’t know about [floating solar] yet,” said Scott Young, a former policy analyst in the Nevada state legislature’s counsel bureau. “They’re not willing to look at it and try and factor it” into the negotiations.

Several Western water managers Inside Climate News contacted for this story said they were open to learning more about floating solar—Colorado has even studied the technology through pilot projects. But, outside of GRIC’s project, none knew of any plans to deploy floating solar anywhere in the basin. Some listed costly and unusual construction methods and potentially modest water savings as the primary obstacles to floating solar maturing in the U.S.

A Tantalizing Technology With Tradeoffs

A winery in Napa County, California, deployed the first floating solar panels in the U.S. on an irrigation pond in 2007. The country was still years away from passing federal legislation to combat the climate crisis, and the technology matured here haltingly. As recently as 2022, according to a Bloomberg analysis, most of the world’s 13 gigawatts of floating solar capacity had been built in Asia.

Unlike many Asian countries, the U.S. has an abundance of undeveloped land where solar could be constructed, said Prateek Joshi, a research engineer at the National Renewable Energy Laboratory (NREL) who has studied floating solar, among other forms of energy. “Even though [floating solar] may play a smaller role, I think it’s a critical role in just diversifying our energy mix and also reducing the burden of land use,” he said. 

This February, NREL published a study that found floating solar on the reservoirs behind federally owned dams could provide enough electricity to power 100 million U.S. homes annually, but only if all the developable space on each reservoir were used. 

Lake Powell could host almost 15 gigawatts of floating solar using about 23 percent of its surface area, and Lake Mead could generate over 17 gigawatts of power on 28 percent of its surface. Such large-scale development is “probably not going to be the case,” Joshi said, but even if a project used only a fraction of the developable area, “there’s a lot of power you could get from a relatively small percentage of these Colorado Basin reservoirs.”

The study did not measure how much water evaporation floating solar would prevent, but previous NREL research has shown that photovoltaic panels—sometimes called “floatovoltaics” when they are deployed on reservoirs—could also save water by changing the way hydropower is deployed. 

Some of a dam’s energy could come from solar panels floating on its reservoir to prevent water from being released solely to generate electricity. As late as December, when a typical Western dam would be running low, lakes with floating solar could still have enough water to produce hydropower, reducing reliance on more expensive backup energy from gas-fired power plants.

Joshi has spoken with developers and water managers about floating solar before, and said there is “an eagerness to get this [technology] going.” The technology, however, is not flawless. 

Solar arrays can be around 20 percent more expensive to install on water than land, largely because of the added cost of buoys that keep the panels afloat, according to a 2021 NREL report. The water’s cooling effect can boost panel efficiency, but floating solar panels may produce slightly less energy than a similarly sized array on land because they can’t be tilted as directly toward the sun as land-based panels. 

And while the panels likely reduce water loss from reservoirs, they may also increase a water body’s emissions of greenhouse gases, which in turn warm the climate and increase evaporation. This January, researchers at Cornell University found that floating solar covering more than 70 percent of a pond’s surface area increased the water’s CO2 and methane emissions. These kinds of impacts “should be considered not only for the waterbody in which [floating solar] is deployed but also in the broader context of trade-offs of shifting energy production from land to water,” the study’s authors wrote.

“Any energy technology has its tradeoffs,” Joshi said, and in the case of floating solar, some of its benefits—reduced evaporation and land use—may not be easy to express in dollars and cents.

Silver Buckshot

There is perhaps no bigger champion for floating solar in the West than Scott Young. Before he retired in 2016, he spent much of his 18 years working for the Nevada Legislature researching the effects of proposed legislation, especially in the energy sector. 

On an overcast, blustery May day in southwest Wyoming near his home, Young said that in the past two years he has promoted the technology to Colorado River negotiators, members of Congress, environmental groups and other water managers from the seven basin states, all of whom he has implored to consider the virtues of floating solar arrays on Lake Powell and Lake Mead.

Young grew up in the San Francisco Bay area, about 40 miles, he estimated, from the pioneering floating solar panels in Napa. He stressed that he does not have any ties to industry; he is just a concerned Westerner who wants to diversify the region’s energy mix and save as much water as possible. 

But so far, when he has been able to get someone’s attention, Young said his pitch has been met with tepid interest. “Usually the response is: ‘Eh, that’s kind of interesting,’” said Young, dressed in a black jacket, a maroon button-down shirt and a matching ball cap that framed his round, open face. “But there’s no follow-up.” 

The Bureau of Reclamation “has not received any formal proposals for floating solar on its reservoirs,” said an agency spokesperson, who added that the bureau has been monitoring the technology. 

In a 2021 paper published with NREL, Reclamation estimated that floating solar on its reservoirs could generate approximately 1.5 terawatts of electricity, enough to power about 100 million homes. But, in addition to potentially interfering with recreation, aquatic life and water safety, floating solar’s effect on evaporation proved difficult to model broadly. 

So many environmental factors determine how water is lost or consumed in a reservoir—solar intensity, wind, humidity, lake circulation, water depth and temperature—that the study’s authors concluded Reclamation “should be wary of contractors’ claims of evaporation savings” without site-specific studies. Those same factors affect the panels’ efficiency, and in turn, how much hydropower would need to be generated from the reservoir they cover.

The report also showed the Colorado River was ripe with floating solar potential—more than any other basin in the West. That’s particularly true in the Upper Basin, where Young has been heartened by Colorado’s approach to the technology. 

In 2023, the state passed a law requiring several agencies to study the use of floating solar. Last December, the Colorado Water Conservation Board published its findings, and estimated that the state could save up to 407,000 acre feet of water by deploying floating solar on certain reservoirs. An acre foot covers one acre with a foot of water, or 325,851 gallons, just about three year’s worth of water for a family of four.

When Young saw the Colorado study quantifying savings from floating solar, he felt hopeful. “407,000 acre feet from one state,” he said. “I was hoping that would catch people’s attention.” 

Saving that much water would require using over 100,000 acres of surface water, said Cole Bedford, the Colorado Water Conservation Board’s chief operating officer, in an email. “On some of these reservoirs a [floating solar] system would diminish the recreational value such that it would not be appropriate,” he said. “On others, recreation, power generation, and water savings could be balanced.”

Colorado is not planning to develop another project in the wake of this study, and Bedford said that the technology is not a silver bullet solution for Colorado River negotiations. 

“While floating solar is one tool in the toolkit for water conservation, the only true solution to the challenges facing the Colorado River Basin is a shift to supply-driven, sustainable uses and operations,” he said.

Some of the West’s largest and driest cities, like Phoenix and Denver, ferry Colorado River water to residents hundreds of miles away from the basin using a web of infrastructure that must reliably operate in unforgiving terrain. Like their counterparts at the state level, water managers in these cities have heard floatovoltaics floated before, but they say the technology is currently too immature and costly to be deployed in the U.S.

In Arizona, the Central Arizona Project (CAP) delivers much of the Colorado River water used by Phoenix, Tucson, tribes and other southern Arizona communities with a 336-mile canal running through the desert, and Lake Pleasant, the company’s 811,784-acre-foot reservoir.

Though CAP is following GRIC’s deployment of solar over canals, it has no immediate plans to build solar over its canal, or Lake Pleasant, according to Darrin Francom, CAP’s assistant general manager for operations, power, engineering and maintenance, in part because the city of Peoria technically owns the surface water.

Covering the whole canal with solar to save the 4,000 acre feet that evaporates from it could be prohibitively expensive for CAP. “The dollar cost per that acre foot [saved] is going to be in the tens of, you know, maybe even hundreds of thousands of dollars,” Francom said, mainly due to working with novel equipment and construction methods. “Ultimately,” he continued, “those costs are going to be borne by our ratepayers,” which gives CAP reason to pursue other lower-cost ways to save water, like conservation programs, or to seek new sources.

The increased costs associated with building solar panels on water instead of on land has made such projects unpalatable to Denver Water, Colorado’s largest water utility, which moves water out of the Colorado River Basin and through the Rocky Mountains to customers on the Front Range. “Floating solar doesn’t pencil out for us for many reasons,” said Todd Hartman, a company spokesperson. “Were we to add more solar resources—which we are considering—we have abundant land-based options.”

GRIC spent about $5.6 million, financed with Inflation Reduction Act grants, to construct 3,000 feet of solar over a canal, according to David DeJong, project director for the community’s irrigation district.

“If you can save water in two ways—why not?”

— Scott Young, former Nevada policy analyst

Young is aware there is no single solution to the problems plaguing the Colorado River Basin, and he knows floating solar is not a perfect technology. Instead, he thinks of it as a “silver buckshot,” he said, borrowing a term from John Entsminger, general manager for the Southern Nevada Water Authority—a technology that can be deployed alongside a constellation of behavioral changes to help keep the Colorado River alive. 

Given the duration and intensity of the drought in the West and the growing demand for water and clean energy, Young believes the U.S. needs to act now to embed this technology into the fabric of Western water management going forward.

As drought in the West intensifies, “I think more lawmakers are going to look at this,” he said. “If you can save water in two ways—why not?” 

“We’re Not Going to Know Until We Try”

If all goes according to plan, GRIC’s West Side Reservoir will be finished and ready to store Colorado River water by the end of July. The community wants to cover just under 60 percent of the lake’s surface area with floating solar.

“Do we know for a fact that this is going to be 100 percent effective and foolproof? No,” said DeJong, GRIC’s project director for its irrigation district. “But we’re not going to know until we try.”

GRIC’s panels will have a few things going for them that projects on lakes Mead or Powell probably wouldn’t. West Side Reservoir will not be open to recreation, limiting the panels’ impacts on people. And the community already has the funds—Inflation Reduction Act grants and some of its own money—to pay for the project.

But GRIC’s solar ambitions may be threatened by the hostile posture toward solar and wind energy from the White House and congressional Republicans, and the project is vulnerable to an increasingly volatile economy. Since retaking office, President Donald Trump, aided by billionaire Elon Musk, has made deep cuts in renewable energy grants at the Environmental Protection Agency. It is unclear whether or to what extent the Bureau of Reclamation has slashed its grant programs. 

“Under President Donald J. Trump’s leadership, the Department is working to cut bureaucratic waste and ensure taxpayer dollars are spent efficiently,” said a spokesperson for the Department of the Interior, which oversees Reclamation. “This includes ensuring Bureau of Reclamation projects that use funds from the Infrastructure Investments and Jobs Act and the Inflation Reduction Act align with administration priorities. Projects are being individually assessed by period of performance, criticality, and other criteria. Projects have been approved for obligation under this process so that critical work can continue.”

And Trump’s tariffs could cause costs to balloon beyond the community’s budget, which could either reduce the size of the array or cause delays in soliciting proposals, DeJong said. 

“I know for a fact this is inspiring a whole new generation of water protectors—those that want to come back and they want to go into this cutting-edge technology.”

— GRIC Governor Stephen Roe Lewis

While the community will study the panels over canals to understand the water’s effects on solar panel efficiency, it won’t do similar research on the panels on West Side Reservoir, though DeJong said they have been in touch with NREL about studying them. The enterprise will be part of the system that may one day offset all the electrical demand and carbon footprint of GRIC’s irrigation system.

“The community, they love these types of innovative projects. I love these innovative projects,” said GRIC Governor Stephen Roe Lewis, standing in front of the canals in April. Lewis had his dark hair pulled back in a long ponytail and wore a blue button down that matched the color of the sky.

“I know for a fact this is inspiring a whole new generation of water protectors—those that want to come back and they want to go into this cutting-edge technology,” he said. “I couldn’t be more proud of our team for getting this done.”

DeJong feels plenty of other water managers across the West could learn from what is happening at GRIC. In fact, the West Side Reservoir was intentionally constructed near Interstate 10 so that people driving by on the highway could one day see the floating solar the community intends to build there, DeJong said. 

“It could be a paradigm shift in the Western United States,” he said. “We recognize all of the projects we’re doing are pilot projects. None of them are large scale. But it’s the beginning.”