Tight Energy Supply Brightens Prospects for Pumped Storage

By Published On: January 12, 2022

California uses lots of electricity to push massive amounts of water from the Bay-Delta rivers to farms, homes and factories in Central and Southern California. A critical portion of that electricity is generated by hydropower at a state dam in Northern California. On really hot days, the Department of Water Resources defers this push of water so that the available power can instead go to the grid to meet soaring energy use.

A provision in Gov. Gavin Newsom’s new proposed budget would increase the power produced at Oroville Dam in Butte County. The proposal provides $240 million to revive two pumped storage plants to allow DWR to send water that has already generated electricity back up to Lake Oroville to be ready to run again through power turbines. The stored water acts like a giant battery on standby.

“DWR is pleased to see that Governor Newsom included $240 million for a temperature management project at Oroville Dam that will allow the Oroville facilities to resume pumped storage operations,” John Yarbrough, DWR Assistant Deputy Director for the State Water Project, said in an email. This storage “will be a critical component of the State’s movement to a carbon free energy grid.”

The pumped storage facilities already exist. But they have been offline since 2006 because the power to lift the released water back behind the dam from the downstream reservoir was too expensive, making operations uneconomic.

Power supply for super peak demand

The two pumped storage operations at Oroville can add an annual average 250,000 MWh during “Super Peak hours,” Yarbrough said.

They also can put to use excess solar energy at midday, absorbing 360,000 MWh of stored sun energy and converting it to water power.

During pump back operations at Lake Oroville, warmer water from the lower reservoir is moved up into the lake, Yarbrough said. But warm water is detrimental to downstream fisheries, including to the Feather River Fish Hatchery. The temperature management project aims to access colder water at lower levels in Lake Oroville and convey it to key downstream locations, according to Yarbrough. If the $240 million budget is approved, the Oroville project will evaluate the feasibility of different strategies for accessing the cold water in the lake and conveying it to critical downstream locations.

Established technology

Temperature management projects vary by location but the technology is well established.

DWR’s State Water Project consumes huge amounts of power, primarily to lift fresh water over the Tehachapi Mountains. But the timing of operations of the water pumping plants and hydropower facilities, which generate about half the needed power, gets altered to help the state grid during times of peak summer demand.

During the rolling blackout in mid-August in 2020, DWR diverted between 560-760 MW to the California Independent System Operator’s grid by maximizing power generation and minimizing consumption at all its facilities. Another 150 MW came from DWR coordinating with the Metropolitan Water District to increase water deliveries through the Devil Canyon hydroelectric power plant in San Bernardino.

In about five years, the two pumped storage projects at Oroville’s Hyatt Power Plant and Thermalito facility will again be powered by water flowing down from the dam through the plant turbines, then recirculated to produce more hydropower, and sold in CAISO’s market.

Last summer, however, the Hyatt hydropower plant, which has 300-440 MW of capacity during “average” precipitation years, went offline because of very low levels at Lake Oroville after two years of drought. It went back online last week, producing little hydropower given the low demand in the cold winter months.

Photo: DWR’s Thermalito pumped storage, source: DWR

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