Abstract: California's renewable portfolio standard requires a rapid de-carbonization of the state's electricity supply by 2045. Despite renewables' falling fixed costs, increased reliance on intermittent, primarily solar, generation creates two challenges for California's grid operator. First, maximum solar generation does not coincide with peak demand during the day. Second, locations with the greatest generation potential are distant from the state's demand centers. The spatial and temporal mismatch between renewable supply and demand increases the frequency of line congestion, causing localized curtailment despite the willingness to pay elsewhere. Utility-scale storage promises to mitigate the inefficiencies of intermittent generation by allowing owners to arbitrage electricity across time and space. My research investigates whether batteries operating in California's wholesale electricity market have increased the productivity of renewables, indicated by reductions in curtailment, and whether these impacts varied with batteries' location. I find that the marginal MWh of electricity used to charge batteries at noon in California resulted in a 0.5 MWh reduction in solar curtailment, which was largely driven by storage capacity additions near solar generators.

Abstract: The increased penetration of variable renewable energy has flooded wholesale electricity markets with clean electricity generated at zero marginal cost. Previous work established that the resultant reduction in average wholesale prices diminished the revenues of conventional baseload generators, increasing the reliance on flexible but emissions-intensive combustion turbines. In recent years, the growth in renewable generation capacity has been accompanied by investments in utility-scale electricity storage, particularly lithium-ion batteries. By arbitraging electricity, batteries smooth the supply of renewably generated electricity and demand throughout the day, potentially decreasing the dependence on high marginal cost combustion turbines. In this paper, I document the reduction in generation and emissions from combustion turbines in California, where storage capacity has grown expeditiously. By quantifying unit-specific changes in generation and NOx emissions, I find that the largest reductions in air pollution occurred in California's population-dense urban areas, benefiting historically disadvantaged communities.  

With co-author, Kevin Novan, we examine the changes in the generation sources and imports from neighboring balancing authorities during battery charging hours to estimate the carbon content of stored electricity. We argue that lithium-ion battery storage facilities should not be treated as zero-carbon generation sources in California's Cap-and-Trade market when there is evidence that they draw imports from regions generating electricity with fossil fuels.