What are so-called ‘water batteries’?

One of solar energy’s biggest drawbacks is that we only get it when the sun is up, unless we have ways to store what we don’t use to tap into when the sun goes down. One way to do this is to turn water into batteries … of sorts.The San Diego County Water Authority has proposed a project that would use the San Vicente Reservoir to make these water batteries. By building a smaller upper reservoir connected to the main one, the city of San Diego would be able to store 4,000 megawatts of energy per day. That’s enough to light up 135,000 homes when it gets dark and there’s no more solar power to draw on.“During off-peak periods — when power is inexpensive and renewable supplies from wind and solar facilities exceed demand — turbines will pump water to the upper reservoir where it will act as a battery of…

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