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Empirical evaluation of the stringency and design of renewable portfolio standards

Nature Energyvolume 3pages754763 (2018) | Download Citation


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.

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We acknowledge research assistance provided by J. Amadon, D. Baldwin, C. Davis, V. Luman, M. McKay, N. Mitchell, D. Olson, J. Williams, M. Williams and R. Woolston. Library research support was provided by S. Darais, R. McPhail and F. Murphy.

Author information


  1. School of Public and Environmental Affairs, Indiana University, Bloomington, IN, USA

    • Sanya Carley
    •  & Nikolaos Zirogiannis
  2. S.J. Quinney College of Law, University of Utah, Salt Lake City, UT, USA

    • Lincoln L. Davies
  3. Texas Law, University of Texas at Austin, Austin, TX, USA

    • David B. Spence


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S.C. and L.L.D. conceived of the research question and gathered all quantitative data, along with research assistants. L.L.D., along with assistance, conducted the interviews. S.C. and N.Z. conducted the quantitative analyses. S.C., L.L.D., D.B.S. and N.Z. wrote the article.

Competing interests

The authors declare no competing interests.

Ethics statement

This research involved human subjects. It was approved with exempt status by the University of Utah, under protocol number 00063847. In accordance with this protocol, informed consent was provided by all study participants

Corresponding author

Correspondence to Sanya Carley.

Supplementary information

  1. Supplementary Information

    Supplementary Notes 1–2, Supplementary Tables 1–10, Supplementary References

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