A week of low solar and low wind is a yearly or every-couple of years event that you definitely need to solve for a completely renewable grid.

▲

fpoling an hour ago | parent [-]

Keeping coal plants around is cheap to cover that. Longer term things like producing ammonia during summer and converting it to electricity in fuel cells will allow to remove needs for fossil fuels completely.

▲

adrianN 41 minutes ago | parent [-]

I’d keep gas plants around, but anyway, you need to cover that case and can’t just handwave it away.

	▲	fpoling 26 minutes ago \| parent [-]
		The main advantage of gas plants is that they support variability. In a world with enough battery storage to last for days that would be irrelevant. And as an insurance against rare events it is better to keep coal plants as transportation and storage of coal is vastly more resilient to interruptions.