FOLSOM, Calif. (AP) – California’s power grid operator is calling for voluntary conservation of electricity as high heat grips the state. The California Independent System Operator has issued a Flex Alert from 3 p.m. to 10 p.m. Thursday due to an expected increase in electricity demand, primarily from use of air conditioning. Late afternoon and early evening is when the grid is most stressed and solar power production falls. The heat is being produced by a ridge of high pressure covering the entire West and extending into Alaska. In mid-August, a heat wave strained the grid to the point that the operator ordered utilities to implement rolling blackouts.