Exploiting variation in the hourly production from wind turbines, this paper quantifies the heterogeneity in the marginal impact of renewable electricity on pollution. The results reveal that output from competing renewable capacity additions-e.g., wind turbines versus solar panels-provide different marginal external benefits. This finding suggests that, if governments continue to subsidize renewables, an emphasis should be placed on designing policies that internalize the heterogeneous benefits. More generally, my results highlight that, by incorrectly assuming renewable electricity is a homogenous good, we will understate the relative efficiency of the first-best pollution prices. (JEL L94, L98, Q42, Q48, Q51, Q53, Q58) T he United States generates 70 percent of its electricity from fossil fuels. As a consequence, the electric sector is a major source of several pollutants, including 40 percent of CO 2 , 23 percent of NO X , and 67 percent of SO 2 emitted in the United States. 1 These pollutants increase the risks posed by climate change, lead to the formation of smog and acid rain, and cause severe health problems. To efficiently reduce the flow of pollution, economists have consistently argued that prices should be placed on each pollutant (Pigou 1920;Dales 1968;Montgomery 1972;Baumol and Oates 1988). 2 In practice, however, emission prices have received limited use. 3 Instead, policymakers are focusing on increasing generation from renewable energy sources. For example, 29 states have adopted renewable portfolio standards that mandate minimum levels of renewable generation. In addition, the federal government provides sizable production and investment tax credits for renewables. Combined, these policies have driven a recent surge in investment in renewable capacity (Hitaj 2013). 1 The US Energy Information Administration provides generation and pollution statistics. 2 Palmer and Burtraw (2005) and Fischer and Newell (2008) focus solely on the electric sector. 3 In the US, cap-and-trade programs only cover a subset of pollutants, and often only apply to certain regions or during specific times of the year. Furthermore, when cap-and-trade programs are used, the caps are frequently set at inefficiently high levels.