But the air conditioners go on just as the sun starts to drop in the sky — and solar power, one of California’s largest renewable energy sources, starts to wane. There are two different types of solar energy: the kind that comes from large solar power plants in California’s deserts, and the kind that comes from solar panels on rooftops and smaller, private properties. Danielle Mills, director of the American Wind Energy Association, said that, in addition to storage, diversifying California’s electricity system — turning to energy sources like wind or renewable imports — can help alleviate the reliability problems that come with the transition.