Weighing the Costs and Benefits of Renewables Portfolio Standards:A Comparative Analysis of State-Level Policy Impact Projections

State renewables portfolio standards (RPS) have emerged as one of the most important policy drivers of renewable energy capacity expansion in the U.S. Collectively, these policies now apply to roughly 40% of U.S. electricity load, and may have substantial impacts on electricity markets, ratepayers, and local economies. As RPS policies have been proposed or adopted in an increasing number of states, a growing number of studies have attempted to quantify the potential impacts of these policies, focusing primarily on projecting cost impacts, but sometimes also estimating macroeconomic and environmental effects. This report synthesizes and analyzes the results and methodologies of 28 distinct state or utility-level RPS cost impact analyses completed since 1998. Together, these studies model proposed or adopted RPS policies in 18 different states. We highlight the key findings of these studies on the costs and benefits of RPS policies, examine the sensitivity of projected costs to model assumptions, assess the attributes of different modeling approaches, and suggest possible areas of improvement for future RPS analysis.