By Jay Landers

In 2018, the state of California updated its Renewables Portfolio Standard to call for obtaining 60% of its power from renewable energy sources by 2030. At the same time, the state also mandated that its electricity system be powered solely by carbon-free, renewable energy sources by 2045. Meeting these ambitious targets will require no shortage of technological developments, particularly batteries or other means of storing electricity generated by intermittent, renewable energy sources, especially solar and wind power.

As part of its recently enacted budget for 2021-22, California included funding to help foster the development of one such storage method, known as pumped-storage hydropower. In particular, the budget provided $18 million to the city of San Diego and the San Diego County Water Authority for use in advancing their planned joint project known as the San Vicente Energy Storage Facility.

The funding will enable the two entities to issue a request for proposals in September for a private partner willing to develop the project at its own expense.

The roles of pumped storage

Typically, pumped storage entails pumping water from a lower reservoir to a higher reservoir during off-peak hours when electricity demand is low and energy production exceeds demand. During periods of peak demand, the water is released from the upper reservoir to the lower reservoir to generate additional power. As the water flows downhill, it powers turbines that generate electricity, which is then transmitted to the electrical grid.

Increasingly, pumped storage is being viewed as a way to take advantage of excess electricity produced during the day by renewable energy sources, primarily solar and wind. In essence, these hydropower facilities act as giant batteries, storing renewable energy for use during periods when renewable energy generation cannot meet demand. This is the approach that the proposed San Vicente Energy Storage Facility would take.

Project components

The new facility would take advantage of the water stored behind the existing San Vicente Dam, near Lakeside, Calif., says Neena Kuzmich, P.E., the deputy director of engineering for the SDCWA. “The project will build a new upper reservoir that will hold approximately 8,000 acre-ft at a higher elevation,” Kuzmich explains. “There will also be a tunnel system with an underground powerhouse containing four reversible pump turbines that would connect the two reservoirs.”

aerial of dam
The planned 500 MW San Vicente Energy Storage Facility would rely on water stored behind the San Vicente Dam, near Lakeside, Calif. (Courtesy of San Diego County Water Authority)

In 2014, the city of San Diego and the water authority completed a joint effort to raise the city-owned dam by 117 ft, increasing its storage capacity by more than 150,000 acre-ft (see “Vulnerable No More,” Civil Engineering, November 2016, pages 64-71). Today, the San Vicente Reservoir can hold up to 247,000 acre-ft, Kuzmich says. Of this amount, the SDCWA owns 157,000 acre-ft of storage capacity, while the city owns the rest.

Ultimately, the San Vicente Energy Storage Facility could store as much as 500 MW of capacity for eight hours, or the equivalent of 4,000 MW/hr per day of energy, according to a project fact sheet from the city and the SDCWA. “When operating, the project will provide enough energy for about 135,000 households,” the fact sheet states.

The location of the San Vicente Energy Storage Facility is ideal from the standpoint of transmitting energy generated by the project. “San Vicente Reservoir is near major electricity transmission interconnection facilities, which would allow the project to play a central role in integrating solar and wind energy from across the Southwest for use in San Diego County,” according to a July 16 SDCWA news release announcing the state funding for the project.

Next steps

As for funding, the $18 million “will cover the environmental reviews, the preliminary engineering, as well as the activities related to obtaining a (U.S. Federal Energy Regulatory Commission) license” for the project, Kuzmich says. 

These activities are to be conducted by whichever “full-service team” ultimately is selected by the city and the SDCWA to implement the San Vicente Energy Storage Facility, she notes. The selected team also would “prepare an economic pro forma model to determine the required revenues to recover their costs,” Kuzmich says.

Assuming the project goes forward, the selected team “will fund and finance the implementation work” and then own and operate the completed facilities, Kuzmich says. The project developer would accrue the revenues associated with electricity generation. In turn, the city and the SDCWA would lease water from the San Vicente Reservoir to the developer for use in the pumped-storage facility, Kuzmich says. Revenues realized from the leasing arrangement would be split equally between the city and the water authority.

After advertising the RFP in September, the SDCWA expects to hold an interview process “towards the end of the year,” Kuzmich says. The water authority’s board then would approve negotiating with a potential developer. “That would be the basis for developing a project development agreement,” she says. Any completed agreement would have to be approved by the water authority’s board as well as San Diego’s city council, Kuzmich notes. “We’re hoping that by the middle of next year, 2022, that we’ll be able to complete negotiations for the project development agreement,” she says.

The initial activities related to environmental reviews, preliminary engineering, and licensure are expected to “take about four years to complete,” Kuzmich says. Construction is expected to wrap up in 2030. A preliminary estimate put the cost of the facility at about $1.5 billion, Kuzmich says. “But until the developer prepares a detailed cost model, the actual cost is not known,” she notes.

As envisioned by the city and the SDCWA, the energy storage facility would be completed at no cost to themselves. However, energy rates would later be increased to account for the operations of the facility, according to Kuzmich.

Multiple benefits

For the city of San Diego, the San Vicente Energy Storage Facility offers certain key benefits, says Alexandra Berenter, a senior manager of external affairs and water policy within the mayor’s office. “It will help avoid rolling blackouts in our area through on-demand energy production, and it will help meet both state and local climate goals,” Berenter says. “The project also could mitigate costs for water ratepayers across the San Diego region by generating additional revenue to help offset the cost of water purchases, storage, and treatment.”

At the same time, the project is designed to protect against the low reservoir levels that have forced at least one major hydropower facility in California to shut down operations in recent weeks. In early August, the California Department of Water Resources removed the 644 MW Hyatt Powerplant at Lake Oroville from operation because of declining water levels in the reservoir.

“This is just one of many unprecedented impacts we are experiencing in California as a result of our climate-induced drought,” the DWR said in an Aug. 5 statement. “California and much of the western part of the United States are experiencing the impacts of accelerated climate change including record-low reservoir levels due to dramatically reduced runoff this spring.”

Raising the height of the San Vicente Dam increased the extent to which the dam can carry over storage from one year to another. Therefore, the San Vicente Reservoir is less susceptible to annual fluctuations in runoff compared with other reservoirs in the state. For this reason, the reservoir “provides significant reliability,” Kuzmich says. “The additional water volume that was achieved with raising the San Vicente Dam provides enough water to reliably run this energy storage facility,” she notes. “That’s unique about this project.”

If completed, the new pumped-storage facility would be the fifth such plant in California. In fact, the SDCWA owns and operates one of those existing installations. The 40 MW Lake Hodges Pumped Storage Facilities includes a reservoir located below the water authority’s Olivenhain Reservoir. A tunnel connecting the two reservoirs conveys water through an underground pump station housing two pump turbines, each capable of generating 20 MW of electricity.

Although similar in layout, the 500 MW San Vicente Energy Storage Facility would be more than 12 times the size of its Lake Hodges counterpart, Kuzmich notes.