Temperatures are predicted to be 10 to 20 degrees above average in many places.
Customers are urged to use less energy from 4 p.m. to 9 p.m. by the grid operator.
Making small changes, such as turning off the lights and cranking up the thermostat, can have a massive effect.
Reduced energy use between 4 p.m. and 9 p.m. by enrolled consumers will resulting in a bill credit.
By signing up for PG&E's SmartAC programme, customers can also contribute to reducing the amount of power used on the grid during a Flex Alert.
Customers that participate will be compensated for the energy that their Powerwalls use.