This, like normal power plant outages, is fine because in reality the entirety of your power does not come from one specific place, from a specific type of power. Instead we load balance over different places using the grid, and energy sources. It's much much rarer to have an extended period of cloud cover and no wind than an extended period of cloud cover, and an extended period without wind. Compound that with "over the entire electrical grid" and it doesn't happen.

And as a worst case version where the geographical and types-of-power constraints exist... e.g. if you're planning an off grid facility which is too small to justify wind power... backup generators exist.