I don’t think you realize the work involved in integrating a new unreliable power source into the grid. Its a delicate dance to anticipate demand to keep power always available. Having more power than you need is bad for the grid, which is why the costs go negative: power companies want it off the grid ASAP.
Conventional power stations can stay on all the time & that’s awesome for the grid stability. There is no power gap renewables are filling. So to turn solar on we need to turn off a coal powered plant. If this new source cannot match the reliability it hinders to grid than help. So there’s no question of “turn it off when you don’t need it”.
We need to turn off fossil fuel power generation for more renewables, sure, but it doesn’t alleviate their problems right now.