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Batteries are quietly driving down evening electricity prices across the U.S.

Batteries have begun setting electricity prices once controlled by gas peaker plants. Wholesale power now costs less during the hours it used to be most expensive

Eric Thayer / Los Angeles Times via Getty Images

On the hottest of summer days, a natural gas "peaker" usually kicks in to support the wave of air conditioning units turning on at once. It's the electrical grid's lifesaver, a turbine built only for the highest-demand hours of the year, and also one of the most expensive to run. It's what made 7 p.m. electricity so expensive in different parts of the U.S in the first place.

But a shift is taking place. California and Texas are now turning to batteries to power their grids. Power units that were typically used simply to store energy are now being deployed as power sources themselves. California's grid operator has at least 13,000 megawatts of battery capacity, enough to serve several million homes through evening peak hours, and Texas' batteries already power up to 10% of the state's grid at peak.

Electricity customers see the benefits. When batteries set the marginal price instead of gas turbines that cost two to three times as much to run, wholesale power gets cheaper during the hours it used to be most expensive. Gas peakers that already sat idle for more than 86% of the year will eventually lose the few remaining hours that kept them viable, and utilities will likely choose batteries over new gas........

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