This paper develops an empirical approach to estimate the equilibrium value of intermittent renewable energy. We model an electricity system operator who optimizes the amount of generation capacity, operating reserves, and demand curtailment potentially in the presence of large-scale solar facilities. We use generator cha­racteristics, solar output, demand and weather forecast data to estimate parameters for southeastern Arizona. The deadweight loss of a 20% solar mandate is 79%  of its $184/MWh average cost. Unfore­castable inter­mittency accounts for $12.5/MWh. At a $21/ton social cost of CO2 this mandate is welfare neutral if solar capacity costs decrease from $5/W to $1.38/W.