Pumped Up: Renewables Growth Revives Old Energy-Storage Method
Moving water uphill lets producers of solar and wind power bank energy for use when it is needed most
Forget about Tesla Motors Inc.’s batteries: The hottest way to store energy in the electricity business today is a century-old technology that involves moving water to stash power.
Known as pumped storage, the giant facilities push large volumes of water uphill when there is surplus electricity, and then let gravity move it back down through turbines to generate hydroelectric power when extra kilowatts are needed.
Newer technologies for energy storage—including batteries, flywheels, compressed air and ice—are under development, but the proven, old-school solution of storing water as a proxy for power is attracting renewed respect from utilities and environmentalists aiming to fight climate change. It helps solve a big problem as power companies invest in renewable energy, which doesn’t always produce electricity when it is most needed.
California, for example, set a record for solar-power production in early July. But peak demand for electricity comes in the early evening, long after solar production has peaked. Pumped storage gives producers a way to bank energy for future use.
“We’re seeing just a huge resurgence of interest,” says Jeff Leahey, deputy director of the National Hydropower Association.
Renewable-energy sources produced 10% of the nation’s power last year, and are growing so fast that they are now expected to overtake nuclear energy by 2021 and coal by 2030, according to the Energy Information Administration. Even at existing levels, excess renewable output is disrupting electricity markets, flooding the wires with power during certain times of day and sending wholesale power prices plunging.
When PG&E Corp. and environmentalists brokered a deal last month to shut down the Diablo Canyon nuclear plant by 2025, green activists weren’t just looking to close California’s last remaining nuclear facility and replace it with renewable energy. They also wanted the nuclear plant’s pumped-storage “battery pack” to be even more available for green energy.
Known as the Helms Pumped Storage Plant, the facility built in 1985 consists of two reservoirs linked to a 1,200-megawatt hydroelectric powerhouse in the Sierra Nevada mountains.
“I don’t think people know what a big deal pumped storage is,” says S. David Freeman, a former general manager of the Los Angeles Department of Water and Power who is a senior adviser to Friends of the Earth, one of the environmental groups involved in the deal. “It’s by no means a futuristic thing. It’s been around for decades.”
Helms is one of 42 pumped storage plants in the U.S. Combined, they have a capacity of 23,000 megawatts, equal to about 20 reactors, according to the Energy Department. That may nearly double in coming years: Proposals to add 18,000 megawatts of pumped-storage capacity are currently before the Federal Energy Regulatory Commission.
Pumped-storage facilities are expensive to build. Still, they remain the cheapest form of large-scale electricity storage according to the Energy Department, which estimates they make up about 99% of such storage world-wide.
On the surface, pumped storage makes no sense—there is a net loss of energy from moving water uphill and then generating power. It often takes five units of electricity to pump water that makes four units of power.
But for decades, pumped storage was a cost-effective way to store surplus energy from nuclear plants—which produce the same amount of electricity at all times of day—and convert it into electricity for peak demand during the day.