The Los Angeles Department of Water and Power wants to spend $3 billion to pump back the water that's flowing through Hoover Dam -- so it can flow through again later, during periods of peak energy demand. This generates a net profit for the dam's operators -- the pumping stations are powered by cheap solar and wind energy, while the dams are currently operating at just 20% of their capacity. An anonymous reader quotes Clean Technica: The problem is that California has so much renewable energy available now, thanks in large measure to aggressive state mandated policies, that much of it is "constrained." That's utility industry speak for having to give it away or simply let it go to waste. In some cases, utilities in California actually pay other utility companies to take the excess electricity off their hands. Why not store it all in some of Elon Musk's grid scale batteries? Simply put, pumped hydroelectric storage is cheaper than battery storage, at least for now. Lazard, the financial advisory and asset management firm, estimates utility scale lithium-ion batteries cost 26 cents per kilowatt-hour compared with 15 cents for pumped hydro storage. "Hoover Dam is ideal for this," Kelly Sanders, an assistant professor of civil and environmental engineering at the University of Southern California tells the New York Times. "It's a gigantic plant. We don't have anything on the horizon as far as batteries of that magnitude."
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