General Motors Co. says it's boosting solar power at its plants. The Detroit automaker said Tuesday that it's adding three acres of new solar arrays at two Michigan facilities: an engine plant in Flint and processing center in nearby Swartz Creek. The ground-mounted solar arrays are expected to generate a combined 400,000 kilowatt hours of renewable energy annually. That's equivalent to the annual energy of use of 25 homes. The installations are expected to be completed this fall.