It's not only that, you also need reserve for the intermittent sources like wind and solar. I live on an island, we have big batteries that can supply up to 15

It's not only that, you also need reserve for the intermittent sources like wind and solar. I live on an island, we have big batteries that can supply up to 15 MW of power for a period. In the Netherlands we have natural gas plants that are called up when the wind or sun output decreases, lest the grid frequency drop.