Natural gas overtook coal as the top fuel for making electricity in the U.S. two years ago. But its brief reign is under assault in some parts of the country. State regulators, renewable-energy advocates and environmental groups are arguing that some existing and proposed gas plants aren’t needed or should be replaced by renewable energy. In states including Arizona, Michigan and Massachusetts, the future of gas plants is being questioned. But nowhere is gas under more fire than in California, where regulators are saying no to new gas plants and looking to get rid of older ones. Earlier this year, the California Public Utilities Commission directed the state’s largest utility, Pacific Gas & Electric Co. PCG 2.06% , to solicit bids for renewable energy and storage projects to replace three costly gas plants. PG&E Corp. , parent of Pacific Gas & Electric, said it currently has no plans to […]