Achieving 50 Percent Renewable Electricity in California

The report analyzes the impact of raising California's Renewables Portfolio Standard (RPS) to 50 percent by 2024. It finds that while this transition reduces GHG emissions and production costs, it increases renewable curtailment, primarily driven by downward reserve and regional generation requirements. The study concludes that non-fossil flexibility—including electricity storage, advanced demand response, and allowing renewables to provide reserves—is significantly more effective at reducing curtailment and emissions than increasing the flexibility of natural gas power plants.

• Increasing the RPS from 33 percent to 50 percent without additional grid changes reduces GHG emissions from electricity generation by 22 percent and production costs by 20 percent, but increases renewable curtailment to 4.8 percent of available generation.
• Downward reserve and regional generation requirements are the primary drivers of renewable curtailment, together accounting for 80 percent of curtailment in the 50 percent RPS base scenario.
• Allowing wind and solar facilities to provide operating reserves, particularly downward reserves, would reduce renewable curtailment by 44 percent.
• Deploying 3 GW of additional non-generation flexibility (comprising 1 GW each of advanced demand response, electricity storage, and net export capability) reduces renewable curtailment by 70 percent, as well as GHG emissions and production costs.
• Among natural gas plant modifications, reducing the minimum power level of combined-cycle gas turbine (CCGT) plants is the most effective way to reduce curtailment, whereas increasing ramp rates does not provide significant benefits.
• Non-fossil flexibility solutions are more effective than increasing gas plant flexibility; a combination of 3 GW of non-generation flexibility and renewable reserves reduces curtailment to 1.1 percent (a 77 percent drop), while a highly flexible gas fleet only reduces it by 37 percent.
• Natural gas plants remain necessary for providing power and capacity during peak net demand hours through 2024, as renewables and other resources cannot fully ensure reliability during some peak periods.

APA

Nelson, J. H., & Wisland, L. M. (2015). Achieving 50 Percent Renewable Electricity in California. Union of Concerned Scientists. https://www.ucs.org/sites/default/files/attach/2015/08/Achieving-50-Percent-Renewable-Electricity-In-California.pdf

Chicago

Nelson, James H., and Laura M. Wisland. Achieving 50 Percent Renewable Electricity in California. Union of Concerned Scientists, 2015. https://www.ucs.org/sites/default/files/attach/2015/08/Achieving-50-Percent-Renewable-Electricity-In-California.pdf.

Wikipedia

{{cite report |last1=Nelson |first1=James H. |last2=Wisland |first2=Laura M. |title=Achieving 50 Percent Renewable Electricity in California |publisher=Union of Concerned Scientists |date=August 2015 |url=https://www.ucs.org/sites/default/files/attach/2015/08/Achieving-50-Percent-Renewable-Electricity-In-California.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{nelson2015achieving, author = {Nelson, James H. and Wisland, Laura M.}, title = {{Achieving 50 Percent Renewable Electricity in California}}, institution = {Union of Concerned Scientists}, year = {2015}, month = aug, url = {https://www.ucs.org/sites/default/files/attach/2015/08/Achieving-50-Percent-Renewable-Electricity-In-California.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }