We examine policy instruments that aim to decarbonize electricity production by replacing fossil fuel energy with intermittent renewable sources, namely, wind and solar power. We consider a model of investment, production, and storage with two sources of energy: one is clean but intermittent (wind or solar), whereas the other one is reliable but polluting (thermal power). We first determine the first-best energy mix depending on the social cost of polluting emissions. We then show that, to implement the socially efficient energy mix without a carbon tax, feed-in tariffs and renewable portfolio standards must be complemented with a price cap and volume-limited capacity payments.