Pristine Sun installs floating solar panels in wastewater holding ponds and reservoirs in California. (David Gorn/KQED)
When you’re trying to generate a lot more solar power, you’re limited by the size and heft of those big solar panels.
Where can you put them? The answer so far has been the desert, or on rooftops. There have even been efforts to put panels on top of landfill sites.
Solar entrepreneur Troy Helming of the San Francisco-based solar company Pristine Sun has a new idea: floating on water.
Helming isn't thinking about the ocean. Think of all of the wide-open and unused water surfaces across the state, including reservoirs, agricultural holding ponds and wastewater treatment pools. Those areas represent thousands of acres of potential solar sites.
California is leading the nation in setting up floating solar. In Sonoma County, solar panels are about to go online at a wastewater treatment facility. In San Diego County, a project is underway to set up solar panels on a portion of the 200-acre Olivenhain Reservoir.
The solar panel systems look a little like metal grandstand seats at a football game, stretched flat on big orange floats. And unlike remote desert solar arrays, these panels on water surfaces are near urban centers.
That’s a huge plus, says Helming, because it’s the urban centers that use most of the power.
“Finding bodies of water, that we view as an unutilized or underutilized asset,” Helming says, “are a way to get the energy production closer to where it’s being consumed.”
Putting solar panels on water has already been successful in several other countries, including Japan, France, Indonesia and Singapore.
Mark Jacobson, director of the Atmosphere and Energy program at Stanford University, says there are many other benefits of putting solar panels on water -- especially, he says, for drought-conscious California.
“A big source of water loss over reservoirs is evaporation,” Jacobson says. “When you put solar photovoltaics over a reservoir, you reduce evaporation, you trap more of the water and that saves more of the water.”
He ticks some of the other benefits off his fingers: They generate clean energy, are located near existing power transmission lines and cut down on algae blooms at reservoirs.
One of the challenges of desert solar arrays is that it’s hard to keep the panels clean. The dirt can obscure sunlight and reduce efficiency by as much as 20 percent, he says.
When those panels are on reservoirs, water can easily be used to clean the panels, which makes them much more efficient.
Helming adds that having the panels on the water is also cooler, which further increases efficiency.
“These solar panels are semiconductors. Just like a semiconductor in your phone or laptop or tablet, you want them to be cool to be efficient,” Helming says. “So we’re forecasting a 3 percent to 5 percent increase in efficiency, just by being on the water.”
And here’s the kicker: Floating solar on the Olivenhain Reservoir in San Diego County won’t cost taxpayers a penny, according to Kelly Rodgers of the San Diego County Water Authority.
Why? The county gets a monthly fee for leasing the surface of the reservoir, and on top of that gets a share of the energy generated. About 24,000 solar panels will cover about 15 percent of the reservoir’s 200-acre surface to produce about 12,000 megawatt hours a month -- enough to power about 2,000 homes.
Rodgers says other water agencies around the state are watching what happens in San Diego, because the potential benefits also include meeting state standards.
“With the state’s push toward 50 percent renewable portfolio standards going to 100 percent,” Rodgers says, “it’s a great opportunity to offset greenhouse gas emissions.”
The Sonoma County project has already been field-tested and should go online later this year, Helming says. The contract for the San Diego County project was just signed, so there's lots of permitting still to be done. Officials don’t expect the reservoir solar project to be running for another year, and probably two.
But according to officials at the Natural Resources Defense Council, there are likely no environmental problems with floating solar, because they’re on man-made water surfaces.
If this new floating solar technology takes off in California and starts to fulfill its promise, that could significantly raise the state’s alternative energy supplies.
And that could eventually translate into a corresponding dip, maybe, in the future price of energy.