GeoZone | Sonoma Clean Power

Geothermal Opportunity Zone

Accelerating development of local resources to address the climate crisis

About the GeoZone

Sonoma Clean Power, Sonoma County, and Mendocino County are exploring local geothermal development. Our region is home to a world-class geothermal resource at the Geysers. The need for geothermal power is growing as California pursues ambitious clean energy targets. Natural gas plants are being retired and replaced with intermittent resources. The state will also retire its last nuclear power plant in 2025. Battery storage is serving an important role in shifting intraday supply to match load. But a baseload resource like geothermal is necessary to provide year-round reliability.

The Geothermal Opportunity Zone (GeoZone) creates a public-private partnership for local geothermal development. Member counties will engage the community to identify values for new geothermal development. Sonoma Clean Power will contract for power generated from new resources. Private partners will provide the technology and capital to enhance geothermal capacity in our region.

The ultimate goal of the GeoZone is to build 500 MW of incremental local geothermal capacity. Initial deployments will likely need grant funding to be competitive. At-scale, development will bring down the cost of new geothermal capacity. The GeoZone offers the promise of providing a sustainable and affordable source of reliable clean energy.

Public Engagement

Early public engagement in the GeoZone enables the community to share concerns, questions, and preferences that can positively impact the design of new geothermal development. To that end, Sonoma Clean Power started pro-active engagement of stakeholders in 2022 as part of its selection process for private partners.

Linked below are resources from Sonoma Clean Power’s public engagement for the GeoZone. Sonoma Clean Power will continue to facilitate public engagement for the GeoZone as project design and development progresses. Please contact us at if you have any questions, input, or want to be added to an e-mail list of GeoZone stakeholders.

Geothermal Power

The earth has a constantly regenerating source of heat in its core. This heat transfers from the core to areas near the surface by conduction and the flow of magma underground. There are areas in the world where magma exists particularly close to the surface leading to elevated temperatures. This condition exists in our region due to a thermal anomaly associated with the Clear Lake Volcanic Field.

Geothermal resources generate power from fluid produced through wellbores targeting hot rock. At the Geysers today, produced steam expands through a turbine that spins to generate electricity.

Other technologies exist today that generate power using a separate fluid and power cycle. A heat exchanger transfers heat from produced fluids to the power cycle fluid. These "binary" systems allow development of resources with lower temperatures than the Geysers. Binary systems also limit geologic emissions and water usage.

Geothermal Graphic

A Growing Need

Geothermal power makes up a significant part of Sonoma Clean Power’s current supply portfolio. Sonoma Clean Power currently contracts for 50 MW from the Geysers. This energy provides clean and reliable electricity to all customers. It is also essential in enabling EverGreen to provide 100% local and renewable 24/7 service.

California regulators recognize the importance of geothermal energy in meeting state climate goals. Last year, the California Public Utilities Commission (CPUC) ordered 1,000 MW of new baseload renewable capacity by 2026. The CPUC expects a need for over 1,500 MW of new geothermal resources by 2045.

Recently, there has been minimal growth in geothermal capacity in our region. Near-term increases in geothermal capacity will likely come from Nevada or the Imperial Valley. Long-term, the GeoZone’s goal is to enable our region to significantly contribute to the state’s need for more geothermal.

Currently, the Geysers generations around 750 MW of the state’s 1,600 MW of geothermal capacity. The state is relying on our region to sustain current geothermal capacity. Opportunities to improve the sustainability of current resources is within the scope of the GeoZone.

California Statewide

Private Partner Solicitation

Sonoma Clean Power issued a Request for Information (RFI) to select private partners in pursuing the objectives of the GeoZone in Spring 2022. Responses from the solicitation have been reviewed by a technical team including Sonoma Clean Power staff and experts from the geothermal industry and a local permitting agency.

Finalists in the solicitation participated in a public stakeholder engagement meeting in June 2022. Input from stakeholders will inform Sonoma Clean Power’s decision on which finalists to include in a public-private partnership to develop new resources in the GeoZone.

Key GeoZone Documents

Below are links to important documents and records from the GeoZone initiative. These include resolutions formalizing the creation and membership of the GeoZone, the solicitation for private partners, and agreements with other agencies.