California is widely regarded for environmental leadership, especially around clean energy policy. The state has set an ambitious goal of achieving 100% renewable energy by 2045. Decarbonizing its electric power sector requires new approaches and ways of thinking to meet carbon reduction goals, all while minimizing land use, emissions, and cost. One promising approach is power-to-gas (PtG) technology.

PtG technology uses surplus renewable energy (for example, wind and solar) to produce renewable fuels such as carbon-neutral synthetic methane or carbon-free hydrogen. What makes this technology particularly attractive is its ability to cost-effectively produce weeks to months of fuel volumes for use by thermal units. The combination of stored fuel and thermal capacity yields a long-duration energy storage system that acts like a gigantic distributed “battery.” This long-term storage system can be coupled with traditional, shorter-term storage technologies (less than 12 hours duration) to meet seasonal MWh demand when renewables are variable, and to ensure a reliable and secure supply of electricity during periods of extreme weather.

Renewable synthetic methane can directly interface with existing natural gas infrastructure to generate on-demand power using gas-fired generators that utilities already own. This is significant because it minimizes overbuild of wind, solar, and battery storage solely for reliability purposes while allowing for targeted, strategic investment in fast-start flexible thermal generation, which is essential in the transition to a 100% renewable energy future.

California’s current plan for decarbonization includes a renewable portfolio standard (RPS) that sets a 60% carbon-free target by 2030 before transitioning to 100% clean energy by 2045. To meet these targets, the state is relying on carbon-free energy sources: solar, wind, and hydropower. All three are subject to daily and seasonal variability, so careful consideration must be given to building out a 100% renewable power system that optimizes these resources, maintains reliability, and minimizes cost and environmental impact. Key to this process will be the design and implementation of long-term energy storage systems. This is where PtG technology can play a critical role in California’s clean energy future.

A Wärtsilä whitepaper, “Path to 100% Renewables for California,” explores a pathway for California to decarbonize its electricity sector between 2020 and 2045, and compares it to alternatives, including the state’s current plan. This new pathway, the “optimal path,” looks at PtG technology, specifically power-to-methane (PtM), as a long-term storage alternative. The study’s results show the optimal path would enable California to meet its goal of 100% clean electricity by 2040—five years ahead of schedule. That’s not the only benefit. Relative to California’s current plan, the optimal path emits 124 million tons less CO2; requires less land for solar and wind development (on the order of 600 square miles versus the current plan’s 900 square miles); and provides $8 billion in savings.

Another significant benefit is that the optimal path leverages existing thermal technology for power generation. Methane that is produced via PtM can be stored and transported in existing natural gas infrastructure and used by any thermal unit that burns natural gas. In California, leveraging the state’s existing gas storage capacity and distribution systems would provide approximately 8 TWh of reliable, fully dispatchable renewable energy storage while using only 15% of California’s existing gas storage capacity. This is beneficial for a couple of reasons. First, it alleviates concerns around “stranded assets.” Flexible thermal capacity can shift at any time to burn renewable methane, even before 2045. Second, it minimizes overbuild of excess renewable or battery capacity by retaining flexible thermal units that have the highest effective load-carrying capability. This will save GWs of thermal capacity and infrastructure that ratepayers have already paid for from becoming “climate stranded,” while maintaining reliability in a cost-effective manner.

In addition to PtM, the whitepaper explored the potential of power-to-hydrogen (PtH) as an alternative optimal path. PtH shares many of the same advantages as PtM. It reaches 100% clean electricity by 2040 and full net-zero compliance by 2045, minimizes cumulative CO2 emissions, requires less land for renewable development, provides weeks of long-term energy storage, and costs $3 billion less than California’s current plan. PtH does face some challenges, most notably a lack of hydrogen infrastructure. Thermal power plants that are designed to burn methane typically cannot burn 100% hydrogen. In addition, existing gas storage facilities, pipelines, compressor stations, and distribution lines cannot support 100% hydrogen without significant upgrades or replacement.

The path to decarbonizing California’s power systems by 2045 depends on decisions made today. No policy-level mechanism exists to provide assurance that the state will recognize synthetic methane from PtG coupled with flexible thermal assets as “renewable generation.” Such a policy would allow utilities to strategically install flexible thermal as needed while assuring these assets contribute to a net-zero power system. With support from policymakers, California can accelerate its path to a 100% renewable energy future.

This article was originally published on, republished here with permission.