A more complicated solution would be having different markets and prices for different sources of electricity. It's not like these companies are price gouging, the renewables simply can't cover the demand, so electricity cost a lot. But it doesn't cost a lot for these companies to make, so they pocket the difference, incentivizing them to perpetuate similar conditions in the future, holding back supply. With a windfall tax the government takes that profit from you, removing the incentive. Problem solved.
This is yet another example of why the free market alone can't function without intervention by the government.