Monday Study: The Resources Necessary To Close California’s Nuclear
Countdown to Shutdown; California’s Clean Energy Future after Diablo Canyon Closes
Mark Specht, February 23, 2021 (Union of Concerned Scientists)
As California strives to decarbonize its economy, the state’s electrical grid is rapidly evolving. The production of renewable electricity from sources like solar and wind continues to climb, while old natural gas and nuclear power plants continue to shut down. However, with the long-anticipated retirement of the Diablo Canyon nuclear power plant on the horizon, the transition to clean electricity is soon to encounter a speed bump: California will need to replace all of Diablo Canyon’s output with clean energy. The state can overcome this obstacle and carry on toward its clean energy goals, but this will require careful, proactive planning.
California has long been a leader in decarbonizing its economy and transitioning to clean energy. Driving this transformation is the state law requiring global warming emissions reductions to 40 percent below 1990 levels by 2030 (California Legislature 2016) along with an executive order to achieve economywide carbon neutrality by 2045 (Brown 2018). To meet these ambitious goals, nearly every sector of California’s economy will need to evolve, pursuing innovative strategies and new technologies to eliminate global warming emissions wherever feasible.
Decarbonizing California’s electricity sector will be the key to success as other sectors of the economy, such as buildings and transportation, increasingly electrify. To ensure that the state’s electricity sector rapidly transitions to clean electricity, California legislators and regulators have enacted many requirements. Foremost among them is the law requiring the state’s electricity to be 60 percent renewable by 2030 and 100 percent zero-carbon by 2045 (California Legislature 2018a). State regulators at the California Public Utilities Commission have been tasked with overseeing a long-term electrical grid planning process—integrated resource planning (IRP)—which aims to ensure that the state’s electricity sector reduces its emissions enough for California to achieve its economy-wide decarbonization goals.
Taken together, this suite of policies and requirements is driving the transition to clean electricity in California. These policies can ensure that the retirement of Diablo Canyon does not stall, but rather accelerates the transition. However, current planning will not be sufficient to replace Diablo Canyon; without further action, cumulative global warming emissions will be higher over the next decade. In this analysis, the Union of Concerned Scientists (UCS) offers a comprehensive analytical approach that specifically examines the increase in cumulative global warming emissions from Diablo Canyon’s retirement, along with solutions for replacing Diablo Canyon without increasing global warming emissions.
The Upcoming Retirement of California’s Last Nuclear Power Plant
After a long and fraught history of seismic safety concerns due to the discovery of fault lines very close to Diablo Canyon (Lochbaum 2013), in 2018 California regulators approved the request to shut down both of Diablo Canyon’s nuclear reactors, totaling 2,240 megawatts (MW), when their operating licenses expire in 2024 and 2025 (CPUC 2018). The decision to retire Diablo Canyon, California’s last nuclear power plant, marked the beginning of the end for the era of nuclear power in California.
Ultimately, the decision to retire Diablo Canyon was made largely for economic reasons—it would not have been cost-effective to make the investments necessary to keep the power plant running beyond 2025. At the same time, California regulators also made a commitment to prevent an increase in global warming emissions due to Diablo Canyon’s closure (CPUC 2018). Shortly afterward, California legislators codified that commitment into law (California Legislature 2018b)
Replacing the massive Diablo Canyon nuclear power plant without increasing global warming emissions will be no easy feat. By itself, Diablo Canyon accounted for 8 percent of California’s in-state electricity generation in 2019 (CEC 2020) (Figure 1). When the similarly sized San Onofre nuclear generating station unexpectedly and permanently went offline in 2012, natural gas power plants initially filled the gap. As a result, there was a notable uptick not only in global warming emissions from gas plants, but also in air pollution emissions like nitrogen oxides (NOx), which disproportionately affect the health of California’s disadvantaged communities (PSE Healthy Energy 2017). To avoid a similar uptick in global warming and air pollution emissions when Diablo Canyon closes, California regulators and electricity providers must take action now.
The Existing Approach to Replacing Diablo Canyon That Falls Short…Analysis of the Increase in Emissions from Diablo Canyon’s Retirement…
The Path Forward to Replace Diablo Canyon
This analysis demonstrates that California’s current electricity sector emissions pathway fails to meet the requirements of state law because cumulative global warming emissions will be higher over the next decade due to the retirement of Diablo Canyon. Additional action is required to replace Diablo Canyon without significantly increasing global warming and air pollution emissions. Here we outline the types of resources that California will need to deploy to replace Diablo Canyon, as well as specific recommendations for moving forward.
TYPES OF RESOURCES REQUIRED TO REPLACE DIABLO CANYON
Our analysis estimated the incremental resources required to fill the 15.5 MMT cumulative emissions gap in the 46 MMT pathway. In addition, we assessed the overall resources required to replace Diablo Canyon in the 46 MMT, 38 MMT, and 30 MMT pathways.
First, our analysis examined the type and quantity of incremental grid resources required specifically to close the 15.5 MMT cumulative emissions gap in the 46 MMT pathway.9 Closing this emissions gap also included the reduction of 2030 emissions below 46 MMT to 43 MMT (in order to satisfy Renewable Portfolio Standard requirements in addition to fully replacing Diablo Canyon with clean energy). Our findings suggest that, over the course of the next decade, the most cost-effective way to fill this emissions gap is to increase the wind build-out by 3,000 MW while slightly decreasing the solar and battery storage build-out by 600 MW and 300 MW, respectively.10 (The reduction in the total build-out of new solar and battery storage by 2030 is very small, and the total build-out still exceeds 10,000 MW and 8,000 MW, respectively.)
Next, we examined the overall amount of grid resources required to replace Diablo Canyon’s capacity and zeroemissions energy in 2030 in all three emissions pathways (Figure 3). The results show that, generally, a diverse combination of renewable energy and energy storage is the most economic approach to replacing Diablo Canyon, regardless of the 2030 emissions target.
Wind and energy storage are the most cost-effective resources for replacing Diablo Canyon, likely due to their relatively low costs and high grid reliability contributions. However, the quantity and type of Diablo Canyon replacement resources vary based on the 2030 emissions target in large part due to the limited availability of the most cost-effective resources. For instance, wind and energy storage are the main resources that replace Diablo Canyon in the 46 MMT pathway, but there are real-world limitations on the amount of wind and pumped storage (one type of energy storage using reservoirs of water) facilities that can be built. To decarbonize the electricity sector down to the 30 MMT target, essentially all of the available wind and pumped storage must be built regardless of whether or not Diablo Canyon remains online. Therefore, no additional wind or pumped storage resources are available to replace Diablo Canyon in the 30 MMT pathway, and geothermal, battery storage, and solar would be used instead.
ADDITIONAL ACTION REQUIRED TO REPLACE DIABLO CANYON
California regulators could take action in a couple of different ways to ensure that Diablo Canyon’s retirement does not result in increased global warming emissions. One option is to select a lower-emissions pathway than the one the state is currently on, which would address Diablo Canyon’s retirement automatically. Alternatively, regulators could stick with the current pathway and order procurement of clean resources specifically to replace Diablo Canyon, which would necessarily go over and above the procurement that is already required to reach California’s renewable electricity goals. UCS recommends the former option—specifically the adoption of the 30 MMT pathway for California’s electricity sector—because this pathway guarantees the full replacement of Diablo Canyon while also accelerating the decarbonization of the electricity sector, helping to ensure that California achieves its economy-wide decarbonization goals.
With the transition to clean electricity being the linchpin of decarbonizing California’s entire economy, the retirement and replacement of Diablo Canyon is a prime opportunity to accelerate the state’s clean energy progress. By utilizing an analytical approach and taking the actions necessary to fully replace Diablo Canyon by 2030, California can keep its momentum toward a decarbonized economy, setting an example for how to manage the clean energy transition no matter the challenges along the way.