One of the biggest challenges is improving infrastructure and developing new technologies to accommodate significantly higher levels of renewable energy on the grid. California will need to massively expand and upgrade its transmission infrastructure to transport electricity from remote locations where many renewable resources, like solar and wind farms, are available to population centers where energy demand is highest. This will require building thousands of miles of new high-voltage transmission lines, which often face local opposition and require extensive environmental reviews and permits. More battery storage technologies will also need to be deployed to store excess renewable energy produced during certain times and discharge it when the sun is not shining or wind is not blowing. Developing very large, cost-effective battery storage systems at a massive scale remains an engineering challenge.

Reliably meeting seasonal and daily peaks in electricity demand as reliance on renewables increases is another major challenge. Some renewables like solar energy only produce power when the sun is available, but demand does not dissipate at night and during winter when there is less sunlight. This requires either overbuilding renewable capacity well beyond average demand to account for variability or relying more on resources that can provide power around-the-clock, like geothermal, hydroelectric or biomass. Developing sufficient dispatchable zero-carbon resources to fill in the gaps when the wind is not blowing and sun is not shining is a critical need but costly.

Retrofitting the existing natural gas power plant infrastructure to operate as backup power providers rather than base load suppliers is an economic challenge. Natural gas power plants currently provide a bulk of California’s electricity, but these must transition over time to only operating intermittently as renewable penetration increases. Adapting the business models of power plant owners and securing ongoing capital for plant upgrades to allow flexible part-time operation introduces transition costs. Mothballing or decommissioning gas plants that cannot adapt to this role will require expensive demolition work.

Developing sufficient zero-carbon fuel sources for end uses like long-haul trucking, aviation and shipping is crucial but technically difficult to achieve at scale by 2045. Renewables alone may not be able to fully electrify California’s entire economy, necessitating breakthroughs in technologies like green hydrogen, advanced biofuels or sustainable fuels synthesized from captured carbon. Ramping up production of alternative fuels that have zero lifecycle greenhouse gas emissions to displace fossil fuels in hard-to-electrify sectors will need massive investments.

Ensuring grid reliability as the penetration of intermittent renewables increases also poses operational challenges. Greater complexity is introduced in maintaining second-by-second supply-demand balance on the grid as more weather-dependent power comes online. This requires more sophisticated data analytics capabilities for improved forecasting of energy production and demand as well as faster and more nimble resource dispatch technologies to maintain grid stability. Developing stringent reliability and resiliency standards for the clean grid may be necessary which involves additional costs.

Transitioning to 100% renewable energy by 2045 in the most populous US state requires coordination across many state and local agencies, private industries, investors and other stakeholders. Developing unified strategies, clear policies and long-term market signals to attract sufficient investments within a short time frame while balancing diverse interests poses governance and political economy challenges. Maintaining strong public and political support for the bold climate targets through potential economic disruptions and high costs of transition will be crucial to success. Achieving California’s renewable energy goals will require overcoming each of these challenges through significant technological innovation, investments, policy reforms and stakeholder cooperation over the next two decades. The stakes of success or failure in this ambition could have global implications for clean energy transition.