Why not compressed air?

Compressed air energy storage (CAES) is a way to store energy generated at one time for use at another time using compressed air. At utility scale, energy generated during periods of low energy demand (off-peak) can be released to meet higher demand (peak load) periods.^[1] Small scale systems have long been used in such applications as propulsion of mine locomotives. Large scale applications must conserve the heat energy associated with compressing air; dissipating heat lowers the energy efficiency of the storage system.

Simple systems do not retain heat and waste about 60% of the energy.  But that will get better, loses dropping to 30%.  Remember batteries have heat loss and conversion losses also.

I go one better.  Why not cool the air with excess electricity to the point where some of the co2 can be distilled, then release the fresher compressed air result.   Use the retained co2 for heat storage, then ship that off to the bioreactor using excess electricity. So you feed this thing solar during the day.  You get back a stream of CO2 and uniform electricity plus fresh air. You cost is capital maintenance and efficiency.