A blue lagoon is located outside of Sayreville, NJ, within a lush preserve of spruce, maples and oaks. The 14-hectare basin houses part of the city's water supply, which requires enormous amounts of electricity to pump and treat. A few years ago, local officials decided to install an array of solar panels to power the water treatment plant. They just couldn't decide where to put it.
Some 160 hectares of forest surround the treatment facilities in Sayreville, a suburban city of 43,000 people south of New York City. To build a solar plant large enough to meet its electricity needs, the city's water department would need to clear about 6 hectares of trees. "It's not very green," said David Samuel, a Sayreville consulting engineer who worked on the solar initiative.
Samuel had heard of a new solar project in California's Napa Valley, where panels floated above a vineyard irrigation pond. After visiting the site, Sayreville began searching for its own aquatic array in 2015. The project ended in October, and the city is now operating a 4.4-megawatt floating solar plant, the largest of its kind in North America. A glistening blue grid of 12,000 solar panels covers the lagoon, which draws water from the nearby South River. It is expected to save the town $ 1 million in electricity costs over the next 15 years.
"I think it will be a trendsetter, now that people know it can be done successfully," Samuel said.
Present and future of floating solar panels
Floating solar energy is a small but growing segment in the solar energy industry. About 1,100 megawatts of projects are floating in waters around the world, or less than 1 percent of total global solar installations. Most floating solar panels are in East Asia, where countries have ambitious targets for solar power but limited land to install panels. The world's first floating solar array was launched in Aichi, Japan, in 2007. French company Ciel & Terre completed the world's largest project, a 70-megawatt system, at an abandoned coal mining site in China's province of Anhui earlier this year.
Until recently, the US floating solar market has been slower to develop, in large part because floating systems are even more expensive and less familiar than ground-mounted and rooftop solar projects. Analysts don't yet have the long-term data to show how the floating panels will perform for decades, or how the arrays could affect water quality and the natural habitats where they are installed.
"There are still a lot of uncertainties about how these systems work in the long term because it's such a new technology," said Alexandra Aznar, project leader at the National Renewable Energy Laboratory, or NREL, in Golden, Colorado.
Still, as projects emerge globally, Aznar says he is hearing more from state and local governments, utilities and federal agencies interested in placing panels on surfaces that would not otherwise be used. In total, NREL estimates that there are 24,000 man-made lakes, ponds, and reservoirs that could host floating solar panels throughout the continental United States. Combined, these projects have the potential to produce enough solar energy to equal nearly 10 percent of the country's annual electricity production.
In Sayreville, the $ 7.2 million floating solar array resembles a zig-zag puzzle piece. Its solar panels are the same as those used in ground projects. But instead of traditional metal racks and supports, these panels are attached to hollow plastic floats, which are joined together like Lego pieces to form a raft. The equipment is designed to withstand strong winds and waves, as well as damage from ultraviolet light from the sun.
Power cables connect the solar array to equipment on the ground, delivering electricity directly to the water treatment plant. If the solar panels produce more electricity than necessary, the excess goes to the local grid. On cloudy or cloudy days, the water treatment plant can still draw power from the grid to keep running. Through a New Jersey solar incentive program, floating panels also earn financial credits for every kilowatt-hour of electricity produced.
Among the biggest challenges with floating solar projects (other than piles of bird droppings) is ensuring that the panels don't drift too far in the water. Anchoring the Sayreville project was particularly challenging, due to the long distance between the parent and one of the reservoir's banks, said Chris Bartle, US business development manager for Ciel & Terre, who designed the floating structure used at Sayreville. To make it work, the engineers laid a cable parallel to the north edge of the array and then tied the ties to that line.
"There are always growing pains, technological hurdles to overcome," Bartle said. The company, which has built 350 megawatts in floating solar projects around the world, is working on a 1.8 megawatt project in California along with smaller arrays in Florida and New Jersey.
Sayreville's floating solar system may have other benefits in addition to producing clean electricity and reducing utility bills, Samuel said. By protecting the surface of the lagoon, the raft could help limit harmful algae growth, reduce water evaporation, provide shade for fish, and keep the water below cool. Cooler water temperatures can prevent solar panels from overheating and operating less efficiently.
Aznar said more data is needed to determine how and if such "co-benefits" will actually develop over time. If researchers can quantify these benefits, it could help cities and developers justify paying more to put solar panels in water rather than on the ground or in buildings, he added.
Farmers in drought-prone California, for example, might be willing to install expensive arrangements in irrigation ponds if they could prevent water supplies from evaporating in the heat. According to NREL, many potential US floating solar sites are in water-scarce areas where utility prices are high and land is expensive.
For developers like Ciel & Terre, municipal reservoirs and agricultural ponds are an obvious place to start deploying floating solar power, because these projects end up being relatively small and close to existing power lines, Bartle said. The company wants to build on much larger bodies of water - large quarry lakes, tailings ponds, hydroelectric dams - that could contain dozens or hundreds of megawatts of floating solar panels.
"The biggest obstacle so far in the United States has been the fear of being first," Bartle said. With the Sayreville matrices and other matrices released in the United States, "I think we'll see a lot more."