Solar arrays floating on man-made bodies of water can now be cost-competitive with ground-mounted solar and offer unique benefits to utilities.

While the technology has a number of advantages, growth in the U.S. has been limited by a lack of definitive data on benefits and financing obstacles due to banks that are reluctant to loan money for projects.

Floating photovoltaic (FPV) solar, sometimes called "floatovoltaics," is still a peculiarity in the U.S., but the technology has been proven commercially viable in over 100 projects globally. The world's first commercial-scale project was built in California, but in the last two years, China has seized the opportunity and now holds over 90% of the world's 1.1 GW installed capacity, according to an October 2018 World Bank report.

FPV could cost-competitively provide almost 10% of U.S. power, according to a December 2018 National Renewable Energy Laboratory (NREL) study. And it offers other unique benefits many U.S. utilities can take advantage of, early movers in the domestic market told Utility Dive.

"A lot of people were waiting to see if our 4.4 MW New Jersey project went as planned because it is almost ten times bigger than any other U.S. floating solar array," Jason Wert, national market lead for engineering firm RETTEW's energy and environmental group, told Utility Dive. "We're nearly there and now five utilities in five states want us to develop new projects totaling 80 MW."

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"Utilities diversifying into renewables do not always have access to affordable land for ground-mounted solar, but may have water on their properties."

Eva Pauley-Bowles

Managing Director, Ciel & Terre

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Floating solar arrays are essentially the same as ground-mounted or building rooftop arrays. But they are sited on water bodies, mostly man-made "wastewater storage ponds, reservoirs, remediation and tailing ponds, and agricultural irrigation or retention ponds," according to NREL.

Using the "extremely conservative assumptions" of only 27% of U.S. man-made water bodies, and only 12% of those bodies' surface area, "we concluded floating solar could produce almost 10% of U.S. electricity," NREL Energy-Water-Land Lead Analyst and report co-author Jordan Macknick told Utility Dive.

Solar and the water it floats on have complementary benefits, he added. The array can reduce the water's evaporation and algae growth and the water can increase the array's output by cooling its solar panels.

Utilities, especially water utilities, often have free access to man-made water body surfaces. And they are starting to work with private developers, U.S. leading developer Ciel & Terre's Managing Director Eva Pauley-Bowles told Utility Dive.

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"As many as 40 countries around the world with limited land and low cost solar are considering projects."

Zuzana Dobratkova

Senior Energy Specialist, World Bank Energy Sector Management Assistance Program

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"Utilities diversifying into renewables do not always have access to affordable land for ground-mounted solar, but may have water on their properties," Pauley-Bowles said. "They are becoming interested in floating solar, but they tend to be risk averse."

NREL's conclusions show utilities have a lot to gain by considering FPV's risk profile and its value as a revenue opportunity. The World Bank report details progress and profit at sites around the world that demonstrate viability. But there are still critical uncertainties.

The numbers

"As of mid-2018, the cumulative installed capacity of floating solar was approaching 1.1 GW," the World Bank reported. That was the U.S. ground-mounted solar installed capacity in 2000.

In 2008, the 477 kW Far Niente Winery irrigation pond array in Napa Valley, California, became the world's first operating commercial-scale system, but the first pilot was in Aichi, Japan in 2007, World Bank Energy Sector Management Assistance Program (ESMAP) Senior Energy Specialist Zuzana Dobratkova told Utility Dive.

Projects over 1 MW "began to emerge in 2013," the World Bank reported. The first over-10 MW project was built in 2016. By 2018, 100 MW-plus plants were operating in China and planned in India and Southeast Asia.

China "has almost 1 GW of installed capacity, most on collapsed coal mines where water has pooled in highly toxic unusable lakes," Dubratkova said. "As many as 40 countries around the world with limited land and low cost solar are considering projects."

Just 1% of the world's man-made water body surfaces could theoretically host over 400 GW of nameplate generation, the World Bank found.

"The most interesting application is on existing hydropower facility reservoirs," Dubratkova said. It is technically difficult and expensive to anchor solar arrays where water levels regularly change as much as 30 meters, but workable hybrid projects could firm solar's day-to-day and seasonal variations and serve as peaking power plants.

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"More and higher-profile projects are needed to create confidence that the technology is reliable and warrants substantial investment."

Jordan Macknick

Report co-author and Energy-Water-Land Lead Analyst, NREL 

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There are 2,666,741 bodies of water in the U.S., according to the United States Geological Survey, and 24,419 of those, totaling 1.3% of U.S. water surface area, could host 2.12 GW of FPV capacity, NREL found.

"Covering only 27% of the surface area of the reservoirs could produce 786 TWh of electricity per year, roughly 9.6% of 2016 electricity production in the United States," NREL reported. "Potential generation would double if 54% of eligible water bodies were to be covered."

A surprise in the report was that "every state has floating solar potential, though the water bodies are diverse and the solar resources are different," NREL's Macknick said. Idaho, Maine, New Mexico and Oklahoma have more floating solar potential than their in-state electricity consumption and could become solar-generated electricity exporters.

"There is more growth outside the U.S. mainly because in countries with renewable energy targets but limited land, innovative approaches become almost inevitable," he added.

Though "established and accepted" outside the U.S., FPV is still an "unknown" to U.S. investors, he said. "More and higher-profile projects are needed to create confidence that the technology is reliable and warrants substantial investment."

Floating solar offers energy-relevant and non-energy benefits, Macknick said. "But we don't have decades worth of data, like there is for land-based systems, to validate those benefits. More fundamental science and standardized studies are needed."

Benefits, limitations, obstacles

The secondary benefits from FPV are "region specific," Macknick said. The FPVs can reduce drinking water evaporation in more arid regions and reduce algae growth in areas with higher levels of humidity.

Another non-energy benefit from FPV is that it does not compete for agricultural land, unlike ground-mounted PVs, alleviating the demand for landowner space and the acquisition costs for utilities, the NREL report noted.

Of seven floating solar projects installed through 2017, six were in Florida and California and the seventh was in New Jersey, all states with "a relatively large amount of potential water surface area, while also having relatively higher-cost land values," according to NREL.

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"[P]ower production gains of 1.5% to 22% have been documented as a result of the cooling effect of water."

NREL report

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An energy-related benefit is that FPV can generate electricity within utility service areas near load pockets with high retail electricity rates at below retail rate costs, the paper reported. FPV also offers cost advantages in site preparation and losses to panel shading.

Another energy-related benefit is that "power production gains of 1.5% to 22% have been documented as a result of the cooling effect of water," NREL reported.

But that indeterminately wide range in the cooling benefit highlights the FPV's biggest barrier, Macknick acknowledged. With few operational U.S. projects, most in service less than two years, there is a "lack of empirical data documenting long-term system performance, financial burdens, operations and maintenance, material science, environmental impacts and other key factors."

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U.S. floating solar is "sort of on the cusp of an expansion that hasn't happened yet."

Jordan Macknick

Report co-author and Energy-Water-Land Lead Analyst, NREL

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Case studies and publicly available data on FPV will follow deployment, NREL reported. But until better data is available, growth will likely be limited by a lack of definitive documentation of FPV benefits and of its "performance and durability in various climates and conditions."

Nevertheless, "floating solar can be cheaper than land-based solar if the land cost is high and access to the water surface is free," Dobratkova said. "The biggest obstacle right now is financing because banks are reluctant to loan. Most projects so far have been built with individual companies' balance sheets."

U.S. developers may soon overcome that obstacle because U.S. floating solar is "sort of on the cusp of an expansion that hasn't happened yet," NREL's Macknick said.

The U.S. experience

It took three years of problem solving to build an FPV array for the Sayerville, New Jersey, water utility's water treatment plant, RETTEW's Wert said. "Every step required consensus building. Environmental permitting took 18 months because the state had to decide whether the energy or water department was responsible."

But in the last six months, utilities "seem ready to embrace floating solar," he said. Though still more expensive than ground-mount solar's $1/watt cost, "it is starting to get down from about $1.90/watt to about $1.50/watt."

The floating solar racking system, inverters, cabling, anchoring and labor cost more, Wert said. But where a power plant or a water treatment plant doesn't have available land, "it is either floating solar or rooftop solar, and floating solar is more cost-effective."

At least three U.S. utilities moved on floating solar in 2018.

The Los Angeles Department of Water and Power approved a feasibility study for an 11.6 MW reservoir project in April. In October, the Kelseyville, California, municipal utility commissioned a 252 kW water treatment pond project and the Walden, Colorado, municipal utility brought a Grid Alternatives-built 75 kW drinking water treatment system online.

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"For utilities and developers, it may be difficult to obtain attractive financing until lenders get comfortable with the technology."

Sam Choi

Manager for Emerging Technologies and Renewables, Orlando Utilities Commission

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The California utilities are working with Ciel & Terre, which leads U.S. FPV developers with 5.2 MW of projects in Florida, New Jersey, Colorado and California, according to Pauly-Bowles.

Ciel & Terre also built the 31.5 kW array for Orlando Utilities Commission (OUC) in 2017, OUC Manager for Emerging Technologies and Renewables Sam Choi told Utility Dive in an email. The project has had "no negative impact" on its environment, imposes "very minimal" O&M expenses, and "has weathered hurricane winds without any problems," Choi said.

OUC found costs high and financing a challenge, he reported. "For utilities and developers, it may be difficult to obtain attractive financing until lenders get comfortable with the technology."

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"Where there are land constraints close to demand centers, use will increase."

Zuzana Dobratkova

Senior Energy Specialist, World Bank Energy Sector Management Assistance Program

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But OUC's cost was $3/watt, Choi said, making Wert's $1.50/watt estimate a 50% cost reduction in one year. As "performance and risks are better understood, you should see a market develop," Choi said.

OUC is now evaluating two "customer-sited floating solar projects," Choi said. One will be "megawatt-scale and coupled with battery storage" and both are planned for commissioning in 2019.

Where the U.S. will go

As utilities expand their renewables portfolios, those with land constraints and available water bodies should pilot floating solar, OUC's Choi said. Megawatt-scale floating solar now rivals "pricing of similar capacity commercial rooftop systems," and, as the technology matures, there will a "tipping point" in favor of floating solar.

Economics will make the behind-the-meter commercial-industrial market of between 1 MW and 5 MW the main U.S. market for the foreseeable future, Ciel & Terre's Pauley-Bowles agreed. "Right now, it is attractive to wineries, industrial sites, mining, and anyone with a man-made reservoir that wants to use on-site generated electricity. With more installations, larger projects may become economic."

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"First, this a proven technology around the world and nothing in the U.S. changes the risk profile. Second, there is little NIMBY pushback because of its reduced environmental impact. And third, that means it will probably get easier and cheaper to build."

Jason Wert

National Market Lead, RETTEW Energy and Environmental Engineering

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Floating solar will not be "a major source of renewable energy" in developed countries in the near term, but "it will be a visible one," the World Bank's Dobratkova said. "Where there are land constraints close to demand centers, use will increase."

U.S. FPV's strength is that it offers both energy-related and non-energy benefits to large and small utilities and economics will allow it to take market share away from larger rooftop projects, RETTEW's Wert said. "We have considered jobs from 400 kW to 38 megawatts, and floating solar beats carport solar almost every day."

Utility CEOs should notice three facts, Wert added. "First, this a proven technology around the world and nothing in the U.S. changes the risk profile. Second, there is little NIMBY pushback because of its reduced environmental impact. And third, that means it will probably get easier and cheaper to build."