If you have enough installed capacity that the production averaged over a year is sufficient, you can store excess energy as hydrogen or methane and turn it back into electricity while renewable production is insufficient. The amount of storage you need is a function of how much capacity you install, how large the grid is, and how smart e.g. electric car chargers are. Some clever economists probably can figure out the cheapest configuration.

Currently it's much cheaper to just burn fossil fuels or import power from your neighbors than to build hydrolyzers, which is why you don't see many, but pilot facilities in the multiple-MW range exist, so the technology is available.