This March 24, 2017 photo released by Arizona Public Service Co., shows large, building-size APS energy-storage battery installed in Buckeye, Ariz. Arizona Public Service Co., Arizona's biggest electric utility plans to spend hundreds of millions of dollars to add large, building-size batteries to the power grid, aiming to use their capacity to store surplus power available early in the day when solar power plants are productive. One megawatt is approximately enough energy to power 250 homes, meaning that 850 megawatts of the batteries APS plans could supply about 212,500 homes for three to four hours. (Arizona Public Service Co. via AP)
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