[rtkwe]

Depending on the renewables mix the grid settles on, selling some back during the night might make sense. Both solar (obviously) and wind (less obviously, at least to me) decrease during the night so we may find we need to supplement the generation with battery reserves during the night for demand peaks.

Nuclear and traditional dammed hydro prefer to be setup to provide extremely consistent power too so there's a gap in the power generation if we completely eliminate fossil fuels. Even if we don't completely eliminate them, peaker plants are extremely expensive to operate because their base costs and ideally low usage means their cost per megawatt is pretty high.