The California Independent System Operator says the so-called Flex Alert will be in effect from 2 p.m. to 9 p.m. Tuesday.
Energy demand for the day is forecast to exceed 48,000 megawatts, which would be the highest demand on the grid so far this year.
Officials urge consumers to particularly conserve in the late afternoon because that’s when air conditioners typically at peak use.
“We’ve had several days of persistent hot temperatures, which has already driven demand up very high,” Cal ISO spokesman Steven Greenlee told KCBS.
“We had a couple of big generators (that) broke on us yesterday evening and that tightened up supplies for today,” he added.
Major appliances should be used before or after the Flex Alert period and air conditioners should be set at 78 degrees or higher.
“We just need to ease up on demand in order to help demand,” he summed up the situation.