The San Diego County Water Authority has an unusual plan to use the city’s scenic San Vicente Reservoir to store solar power so it’s available after the sun goes down. The project, and others like it, could help unlock America’s clean energy future.
Maybe in a decade, if all goes well, big underground pipes will connect this lake to a new, much smaller reservoir built in a nearby canyon about 1100 feet higher. When the sun is high in the sky, California’s abundant solar energy will pump water into this upper reservoir.
It is a way of storing electricity. When the sun goes down and the solar power disappears, operators would open a valve and the force of 8 million tons of water, falling back through those same pipes, would drive turbines capable of generating 500 megawatts of electricity for up to at eight o’clock. That’s enough to power 130,000 typical homes.
“It’s a water battery!” says Neena Kuzmich, deputy director of engineering for the water authority. She says energy storage facilities like these will be increasingly vital as California begins to rely more on wind and solar power, which generate electricity on their own schedules, without being disturbed by consumer demands.
Californians learned about it during a heat wave last summer. “I believe everyone in the state of California got a text at 5:30 p.m. to turn off their devices,” Kuzmich says. The sun was setting, solar generation was disappearing, and the remaining power plants, many of which were burning gas, could not keep up with demand. The alert worked; People stopped using so much energy and the network survived.
Yet earlier that same day, there was so much solar power available that the grid couldn’t absorb it all. Grid operators have “cut back” or withheld more than 2,000 megawatt hours of electricity that solar generators could have provided, enough to power a small town. This electricity was wasted and there was no way to store it for later when grid operators desperately needed it.
“We have a problem if we’re going to have these continuous heat waves,” Kuzmich says. “We need a facility to store energy so we don’t have to turn off our devices.”
Pumped hydropower has a story
The technology proposed by San Diego, called pumped hydroelectric energy storage, is already operational at more than 40 sites in the United States. Some of the largest, which can generate more than 1,000 MW for up to eight hours, were built in the 1970s and 1980s to store the electricity that nuclear power plants produced overnight. But few new factories have been built in the last 30 years in the United States. China continued to build such factories.
Today, the need to store energy from renewable sources is rekindling interest in this ancient technology in the United States.
“In the past few years alone, 92 new projects have entered the development pipeline,” said Malcolm Woolf, president and CEO of the National Hydropower Association. Most projects, however, are in the planning stage and still need regulatory approval and funding.
Thanks to the climate bill that President Biden signed in August, these projects now enjoy the same 30% tax credit that solar and wind projects enjoy. “It’s a complete game-changer,” says Woolf. “A number of these projects that have been in the pipeline for a number of years are suddenly much more bankable.”
Water batteries have many competitors when it comes to storing energy. Some companies, including automaker GM, are exploring ways for the power grid to draw backup power from the batteries of millions of private electric cars. Others are working on ways to store electricity by compressing air or making hydrogen. Still others focus on ways to manage electricity demand rather than supply. Electric water heaters, for example, could be remotely controlled to operate when electricity is plentiful and turn off when it is scarce.
However, pumping water has some advantages. It is a proven way to store huge amounts of energy. The San Vicente project would store about as much electricity as the batteries of 50,000 long-range Tesla cars. Water batteries also don’t require hard-to-find battery materials like cobalt and lithium, and plants can keep running for over a century.
The biggest problem with them, at least according to some, is that it’s hard to find places to build them. They need large amounts of water, topography that allows construction of a lower and upper reservoir, and regulatory permission to disturb the landscape.
Woolf, however, says that the perception of the limited prospects of pumped hydro “is a myth that I strive to disabuse people of.” Pumped hydroelectric installations, he says, need not be as massive as those of the last century, and they need not disturb free-flowing streams and rivers. Many proposals are for “closed-loop” systems that use the same water over and over again, moving it back and forth between two large ponds, one higher than the other, like sand in an hourglass.
Three of the proposed projects in the United States that seem closest to failure, in Montana, Oregon and southern California, would all operate in a closed loop.
Kelly Catlett, director of hydropower reform at American Rivers, an environmental advocacy organization that has highlighted the environmental damage caused by dams, says that “there are good pumped storage projects, and there are less good pumped storage projects”.
His group will not support plans to build new dams on streams and rivers, disrupting sensitive aquatic ecosystems. But San Diego’s plan, she says, “looks like something we could potentially support” because it uses an existing reservoir and doesn’t disturb any waterways. Additionally, she says, “I am not aware of any opposition from Indigenous nations, which is another very important factor, as they have suffered much of the impacts of hydroelectric development over the decades.” .
The San Diego County Water Authority Board of Directors and the San Diego City Council are expected to vote soon on whether to proceed with a detailed engineering design for pumped hydroelectric storage at the San Vicente Reservoir. The State of California is injecting $18 million. The design work, followed by regulatory approvals, financing and actual construction, will likely take a decade or more.
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