SAN DIEGO — When you think about renewables, it's natural that solar power and wind may come to mind.
But have you ever thought about how to generate energy when the sun is down and the winds are calm?
Neena Kuzmich, with the San Diego Water Authority, explains with big climate goals on the horizon, cities like San Diego are tapping into the world of pumped storage hydropower.
"The issue right now is those renewables are intermittent," Kuzmich said.
This is how it works: a city builds a new holding basin above its current reservoir.
Newly built underground tunnels will connect to an underground powerhouse that will use excess renewables to pump water from the lower reservoir to the upper basin during the day.
At night, the water will come back down through that pipeline, passing through the turbine pump station.
That flow will then generate clean energy to power the city's grid.
"The beauty about pumped storage is that it's proven technology that lasts for 100 years," Kuzmich said.
Pumped storage hydropower is already operating at more than 40 sites in the United States and has been working beautifully for decades, but now, bigger goals are calling for bigger solutions.
"The renewed interest comes from as we start to move towards more and more renewable energy. You need longer duration storage," said Greg Stark, who is the hydropower technical lead for the national renewable energy laboratory.
Many cities like San Diego already have damns and reservoirs in place.
This new project would allow them to be dual-purpose.
"You're hearing the stories about drought. This is truly a drought-proof supply because it is our emergency water," Kuzmich said. "This type of facility would allow us to store that excess energy that's generated by those solar panels during the day, and be able to use that in the evening hours from that 4 p.m. to 9 p.m., which is really the high energy use period of time by the homeowners and the businesses.
"And it's right as the sun is setting, and so all of that solar is going away and that's where pumped storage fits really nicely," Stark said.
Stark explains that cities can be reliant on this technology because of its ability to time shift energy.
"If wind and solar didn't show up, and it was forecasted to show up and they've gotten a lot better at the forecasting but there is still some times where it's not quite there, and historically, what they would do they would fire up a gas turbine to fill up that gap. Well, think about a world where all that stuff has to go away. What's left that you can turn on and off simultaneously? Storage is one, and hydro is the other," Stark said.
If all goes as planned, the San Vicente reservoir will be doing exactly that in about eight to 10 years.
"You need something to essentially look at replacing those natural gas plants that we have because if we truly want to be 100% clean energy we need to have a type of facility that can replace those stable base load facilities and an energy storage facility does that," Kuzmich said.
The next 10 to 25 years are filled with climate action goals and these experts say this is one piece of the puzzle to get there.
"The ability for water to be multi-purpose is really amazing for the average person that may not even realize we can produce energy by using water," Kuzmich said.