Electricity is complicated. Once a power plant is online, it outputs to the grid and there must be matching demand using it. Running a grid is about balancing supply with demand. Then wind starts blowing and you have unpredictable oversupply and nowhere to put it - or vice versa.

The trouble is that you can’t just plug a “reliable power plant” in or off the grid. It takes hours (that’s “quick” here) or days to power on/off.

You need batteries to cope (e.g. hydro power plants) and there’s not enough of them now.