[blendo]

https://en.wikipedia.org/wiki/Oroville%E2%80%93Thermalito_Co... is in northern California.

"Water released for power in excess of local and downstream requirements is conserved by pumpback operation during off-peak hours through both powerplants into Lake Oroville to be subsequently released for power generation during periods of peak power demand. The Plant has 4 units: 1 generating unit and 3 pumping–generating units, with an installed capacity of 120 MW, maximum flow rate of 17,400 cu ft/s (490 m3/s).[5]"

Summer days are always dry and sunny, so a large solar array might work well here.