Study reveals roadmap for carbon-free California by 2045

A 2022 California law mandates net-zero greenhouse gas emissions by 2045 and negative emissions every year thereafter. The state can achieve this but will have to act quickly and thoroughly, and success will require new technologies for sectors difficult to decarbonize, a new Stanford University study finds. The state will need to decarbonize not only cars and electricity but also trucks, trains, planes, agriculture, and factories, while slashing pollution from its oil refineries.

The research team created a new model that projects emissions, society-wide economic costs, and consumption of energy resources under many scenarios for California to reach net-zero emissions by 2045. The model uses data from U.S. federal agencies, national laboratories, California state agencies, past studies, and various other online public sources. (Data sources are provided in the study’s Appendix B.) The model forecasts that 170 gigawatts of new generation and 54 gigawatts of storage will be needed by 2045, compared with California’s current generation capacity of 80 GW, as transportation, buildings, and industry transition from fossil fuels to low-carbon sources of electricity. The expansion of electricity will be needed despite expected gains in energy efficiency in many technologies.

The study, published this week in the journal Energy Policy, provides a detailed roadmap for meeting California’s net-zero mandate. First, commercially available technologies can slash the state’s emissions in half. Technologies proven at pilot scale that need commercial development and lower costs could address another 25%. The final quarter will rely on inventions still being worked on in laboratories.

“One key to success will be building an emission-free power grid using a combination of solar, wind, batteries, and sources of clean, firm power like natural gas with carbon capture and storage or nuclear power,” said the study’s senior author, Sally Benson, the Precourt Family Professor of energy science and engineering in the Stanford Doerr School of Sustainability.

The study, which was funded by several industry associations and trade unions impacted by the state’s move to net-zero emissions, also examines some policy and economic implications for the state.

“We will need to build this infrastructure at an unprecedented pace to put proven technologies to work at the scale we need,” added Benson, who was the chief strategist for the energy transition at the White House Office of Science & Technology Policy from 2021 to 2023.

First 52%: Commercial technologies

The necessary technologies already in commercial use that could halve California emissions include renewable electricity generation, batteries for storing that energy, electric passenger vehicles, heat pumps, and machines that produce methane fuel from wastewater, manure, and food and plant waste.

However, significant administrative and logistical barriers could stymie deployment of these technologies at the required speed and scale. The state is already experiencing overwhelmingly long queues to connect new renewable energy generation and grid-scale energy storage to the grid. Local ordinances frequently block permits for new power plants. Other obstacles include the early termination of federal tax credits for EVs and home solar, federal challenges to California banning sales of gas-powered cars in 10 years, elevated financing costs, and supply chain disruptions.

“California can build the infrastructure it needs to meet the 2045 mandate, but the state must implement policies to overcome regulatory and logistical barriers,” said the study’s lead author, Joshua Neutel, a PhD student in civil and environmental engineering, a joint department of Stanford’s School of Engineering and Doerr School of Sustainability.

Several readily available measures save more money than they cost to implement, after accounting for state and federal incentives – many of which are slated to end in the coming months. The authors estimate electric passenger vehicles, solar and wind power, reduced in-state oil production, and replacement of fossil-based gas with methane fuel made through anaerobic digestion could eliminate 44% of the state’s greenhouse gas emissions (based on estimated 2045 emissions if the state were to continue business as usual).

Next 25%: Early-stage technologies

The authors estimate a quarter of emissions abatement could come from technologies in the early stages of commercialization, including zero-emission heavy-duty vehicles, clean industrial heating from electricity and hydrogen, and carbon capture and sequestration (CCS).

Eliminating carbon emissions from heavy-duty vehicles could reduce California emissions 12%. However, emission-free trucks still need to improve their range and cargo capacity while reducing charging time and purchase price. Another area in early-stage deployment involves switching several industries from fossil fuels to carbon-free electricity and green hydrogen. This accounts for 5% of emission reductions in the authors’ projections.

CCS entails capturing carbon dioxide directly at the source, such as at gas-fired power plants and factories, and securely sequestering the emissions deep underground. In some hard-to-decarbonize sectors, like oil refining and producing cement, hydrogen, and some electricity, CCS may be the most viable option in the near and medium term, according to the authors. The study confirms prior findings that a limited amount of natural gas power paired with CCS (34 of 170 gigawatts, or about 20% of new generation capacity) could vastly reduce the number and costs of wind and solar farms. Pairing bioenergy with CCS could remove another 2% of emissions from 2019 levels to reach net-zero emissions.

Final 23%: Research-phase technologies

Nascent technologies still in the research phase include decarbonized trains, planes, and boats; low-emission refrigerants; and carbon dioxide removal (CDR) from the atmosphere. Replacing fossil fuels for planes, trains, and boats with electricity, hydrogen, and renewable fuels faces challenges from their weight, cargo capacity, costs, and the limited availability of clean fuels.

Traditional refrigerants are powerful greenhouse gases up to 2,000 times more potent than CO2 during their first 100 years in the atmosphere. Climate-friendly alternatives, possibly including CO2 as a refrigerant, are still in the early stages of development.

CDR will play a significant role, with the researchers’ model projecting that California will need to sequester about 45-75 million tons of CO2 annually by 2045 through CDR, in line with the state’s 2022 forecast. Explored CDR options include bioenergy with CCS and direct air capture plants. The prior emits but then sequesters biogenic CO2 through industrial processes like hydrogen and electricity generation. The latter extracts CO2 directly from ambient air and stores it underground.

“If net-zero by 2045 is a binding constraint, then large amounts of CDR will be needed,” said study co-author Sarah Saltzer, managing director of the Stanford Center for Carbon Storage. Current methods for extracting carbon dioxide from ambient air remain costly and energy intensive.

Political and economic implications

The study recommends several policy changes, including streamlining the permitting of, and grid connections for, new generation, energy storage, and power lines. This year, the state has taken initial steps to do this.

The research advises that California should consider incentives for adding CCS to existing natural gas-fired power plants. For example, it could qualify such power plants as one way for utilities to meet the state’s renewable portfolio standard. This could prevent expensive overbuilding of solar power plus batteries.

This work also supports maintenance of the state’s EV sales mandate for 100% clean vehicles by 2035 and consideration of similar policies for building appliances. Policymakers could develop roadmaps for advancing “renewable natural gas” and “renewable diesel,” which are chemically equivalent to fossil-based natural gas and diesel but made from biological feedstocks, said the researchers. These fuels have a limited global supply but could be vital for decarbonizing hard-to-abate sectors.

“Reaching net-zero by 2045 is not so much a challenge in cost,” said Benson, “but a challenge in getting the necessary technologies available in time and establishing the social, political, and economic environment to deploy these technologies rapidly and broadly.”