In two decades of experience with state renewable portfolio standards (RPSs), the United States has observed immense growth in renewable energy markets, initially in wind energy and more recently in solar power. During this time, RPSs have experienced considerable policy reinvention and increased diversity. Here, we explain how changes in RPS policy design features relate to different market outcomes. We develop a score for measuring RPS stringency and show that a one-point increase in RPS stringency leads to increases of 0.2%, 1% and 0.3% in renewable energy, solar generation and renewable energy capacity, respectively. Other important design features include resource eligibility, planning processes, cost recovery and geographical restrictions. These findings are then reaffirmed through 42 semi-structured phone interviews with experts in the field of RPS implementation from government agencies, including public utility commissions and state energy offices, electric utilities and various renewable energy firms and associations.

在二十年的州可再生能源投资组合标准（RPS）经验中，美国观察到可再生能源市场的巨大增长，最初是风能，最近是太阳能。在此期间，RPS经历了重大的政策改革和多样性的增加。在这里，我们解释RPS政策设计功能的变化如何与不同的市场结果相关。我们得出了衡量RPS严格度的评分，并显示RPS严格度每提高1点，可再生能源，太阳能发电和可再生能源的发电量分别增加0.2％，1％和0.3％。其他重要的设计功能包括资源资格，计划流程，成本回收和地域限制。