I consider an economy with fossil fuels, intermittent renewable energy, and energy storage, identify the conditions under which energy storage is optimal, and analyze the long-run tendencies of the economy energy variables. The findings are twofold. First, the amount of energy stored in the economy is highly dependent on the shape of the demand and supply schedules. In particular, energy storage is fostered by the convexity of the marginal utility, the marginal cost function for fossil fuel energy, and the degree of volatility in renewable energy. Second, considering a low level of renewable energy capacity, storing energy is not welfare improving when the unit cost of providing fossil fuel energy is constant. By showing the influence that energy storage can have on energy generation decisions, I believe that the current work can be influential in a more generous treatment of energy supply in future energy-economy models.