Mixing electricity and water is often not a good idea, but floating solar panels on water is one of the most rapidly expanding sectors in the solar-power market. Worldwide, floating solar projects have grown more than 100-fold in less than four years, to 1,100 MW by September 2018 from 10 MW at the end of 2014, according to an October report by the World Bank and the Solar Energy Research Institute of Singapore.
The growth of floating solar in the United States has been slower, but that is starting to change. Ciel & Terre says it will install about 5 MW of floating solar projects in the U.S. this year. Next year, “we could have more than 25 MW of floating solar projects,” says Chris Bartle, U.S. development manager for the French company, which also manufactures pontoons used to float solar panels. The company has focused solely on floating solar projects since 2011.
D3Energy, Hialeah, Fla., partnered with Ciel & Terre on a 31.5-kW floating solar project for the Orlando Utilities Commission that was energized last year. In California, Ciel & Terre and local developer North Coast Solar built a 252-kW floating solar project at a wastewater treatment pond in Kelseyville and a 10-kW floating solar project for the Kunde Family Winery in Kenwood.
In the crowded corridor around Boston, the Braintree Electric Light Department is exploring a 10-MW floating solar project on a reservoir. “Braintree is very urban. We don’t have the open space,” says William Bottiggi, general manager of the municipal utility. On land, a 1-MW solar project would require about five acres. On water it would need 2.5 acres.
Among the challenges Braintree is facing is that the reservoir is used for drinking water. “One of the hardest parts of the puzzle is water quality,” says Scott Anderson, principal engineer at AECOM and one of the authors of a report on “floatovoltaics” prepared for Braintree.
Several tests have shown the high density polyethylene of the Ciel & Terre pontoons are chemically stable and present little danger of leaching harmful chemicals into water, Anderson says, noting that HDPE is widely used for pipes to carry drinking water and in containers to package food. Nonetheless, Bottiggi says Braintree is going to conduct independent investigations using local water quality standards. AECOM is now looking at cutting up some pontoons to subject them to a leachability test.
In addition to making use of scarce land, the floating solar panels provide shade and inhibit algae growth and slow evaporation. And the cooler temperatures under panels can increase their electrical output.
A floating solar project is slightly more expensive, but the higher output and panel density balance out those costs and put floating solar on par with ground mounted solar, says Lowell Dunn II, CEO and president of D3Energy. Likewise, the higher cost of floating solar equipment is offset by the fact that land does not need to be cleared nor foundations set. No heavy equipment is needed to bolt the pontoons together. All that is needed is about 100 ft of open shoreline. As a string of pontoons is bolted together, it is pushed into the water. A crew of about 10 workers can install as much as 100 kW a day, says Dunn.
Dunn is looking forward to a “steady rollout” of floating solar projects. In a soon to be released report, the National Renewable Energy Laboratory looked at man-made, non-navigable bodies of water and found over 24,000 in the contiguous 48 states that could host floating solar arrays. That comes to about 5 million acres, says Jordan Macknick, a National Renewable Energy Laboratory analyst. He estimates solar panels on those sites could generate enough power to supply about 10% of the nation’s needs. Dunn says, “2019 is going to be the year of floating solar. It is going to make a huge splash.”