The electricity doesn't need to be free. We've had range of interesting business models and regulations taking advantage of off-peak energy for decades.
Anyone looking to take business advantage of solar should be looking at predictably below average prices for most of the day, rather than only when it hits zero.
edit to add:
An example, yesterday on CAISO in California they broke records for solar generated, and battery discharge, but the price never hit 0 and batteries were charging from 6am to 6pm and making good money meeting evening demand:
Anyone looking to take business advantage of solar should be looking at predictably below average prices for most of the day, rather than only when it hits zero.
edit to add:
An example, yesterday on CAISO in California they broke records for solar generated, and battery discharge, but the price never hit 0 and batteries were charging from 6am to 6pm and making good money meeting evening demand:
https://www.gridstatus.io/live/caiso?date=2024-06-20
And it's possible to argue that the price didn't hit zero in part because of the batteries knowing they could sell it for more later.