The head of California’s electric grid said Wednesday he is “guardedly optimistic” that the state will avoid rotating blackouts this summer, but warned that voluntary cooperation during Flex Alerts will be necessary.

Elliot Mainzer, president and CEO of the California Independent System Operator, said utilities throughout the state have built up power reserves and invested in new technology like battery storage to prevent blackouts like the ones in 2020.

But recent record heat in California and the Pacific Northwest combined with a drought that will reduce hydropower give him cause for concern.