GeoZone | Sonoma Clean Power

Sonoma-Mendocino Geothermal Opportunity Zone

Your community-owned power provider is accelerating development of local geothermal resources to improve power reliability, protect air quality and the climate, and add high-quality jobs

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About the GeoZone

Sonoma Clean Power is leading a two-county effort to build new geothermal power to improve California’s electric reliability in partnership with Sonoma County, Mendocino County, Chevron New Energies, Cyrq Energy, and Eavor Inc. The State has recently extended the operation of many of the dirtiest natural gas power plants to keep the lights on in hot summer evenings, at night and all through the winter. Solar with batteries will largely solve California’s summer evening problem, but round-the-clock renewable resources like geothermal are needed to end our dependency on fossil fuel power because of the long stretches of dark in the winter when solar output is low and batteries are empty.

Our region is already home to a world-class geothermal resource at the Geysers, but the need for geothermal power is growing as California pursues ambitious clean energy targets.

The Geothermal Opportunity Zone (GeoZone) creates a public-private partnership to support local geothermal development. With State agencies issuing mandates to build new clean reliability resources, new geothermal development will be done in our region. SCP’s goal is to engage and organize our community to help our region steer the State’s development in ways that protect our environment, our quality of life, and create meaningful jobs. To attract private partners to care about respecting our community’s values, SCP is offering to contract for some of the power generated from new resources and work with our public power counterparts across the State to buy the rest.

The goal of the GeoZone is to build 600 MW of incremental local geothermal capacity, starting with initial projects of up to 60 MW to prove the economics and viability of some new technologies targeting low water use, flexible output and methods for shrinking the surface footprint. At-scale, our goal is to lower the cost of new geothermal capacity and show it is viable in more locations. 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, ask questions, and establish preferences that can steer the design of new geothermal development. To that end, Sonoma Clean Power started the pre-project engagement of stakeholders in 2022 as part of its selection process for private partners. SCP also includes an update to the GeoZone project in each monthly meeting of its Community Advisory Committee and invites the public to join and provide input. Updates from past meetings are available at the webpage linked below. As part of the GeoZone partnerships, SCP’s GeoZone partners are required to develop projects that are responsive to community values.

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

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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 deep underground. There are areas in the world where magma exists particularly close to the surface leading to elevated rock temperatures. This condition exists in our region.

Geothermal resources generate power from water contacting hot rocks deep underground, turning into steam and transferring that heat to turbines at the surface. At the existing Geysers facilities, steam expands and spins turbines to generate electricity.

Newer technologies may be appropriate in the GeoZone that generate power with lower temperatures through the use of a heat exchanger at the surface. These "binary" systems allow development of resources with lower temperatures than the Geysers. Binary systems can also limit natural geologic gas emissions and water usage.

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 – producing about the same amount of energy as produced by all the solar power facilities in Sonoma and Mendocino Counties. This energy provides clean and reliable electricity to all customers. It is also one of the essential sources in enabling SCP’s EverGreen to provide 100% local and renewable service for every hour of the year.

As SCP’s load grows from electric cars and the growing use of heat pumps, the demand for clean “firm” resources like geothermal will grow quickly – particularly since the alternative is to continue extending the operation of the State’s dirtiest natural gas fired power plants. Firm resources are available whenever you need them and enable the growth of solar, wind and battery storage by filling in the gaps at night and through the dark and still periods in the winter. SCP expects 40% of its energy will need to come from geothermal resources by 2038 to stay on track with its climate goals. California regulators are also seeing a need for significant growth: the California Public Utilities Commission included 2,037 MW of new geothermal by 2035 in its latest portfolio for transmission planning—more than doubling existing capacity.

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 in Southern California. Long-term, the GeoZone’s goal is to enable our region to significantly contribute to the state’s need for more geothermal power.

Private Partners

Sonoma Clean Power issued a Request for Information (RFI) to select private partners in pursuing the objectives of the GeoZone in Spring 2022. After a comprehensive evaluation process that included review by industry experts and a public stakeholder round, staff recommended three finalists.

Selection of finalists was discussed in the September 15, 2022 Community Advisory Committee meeting, where the Committee ultimately recommended the Board proceed with negotiating cooperation agreements with all three of the finalists to lower the risk associated with any one of the firm’s approaches. The Board agreed and directed staff to negotiate the cooperations agreements. Draft agreements were presented in the February 16, 2022 Community Advisory Committee.

On March 2, 2023, the Board of Directors voted to approve cooperation agreements with each of the three finalists. Each agreement shares a similar structure: SCP and the partner agree to collaborate on deploying up to 20 MW of demonstration capacity before deciding whether to commercially scale-up to 200 MW. Below is a brief description of each partner’s plan for the GeoZone:

Chevron New Energies

Chevron New Energies is a subsidiary of Chevron Corporation focusing on lower carbon energy—particularly technologies that leverage its expertise as a global energy company. SCP found that Chevron’s experience with oil and gas wells had a number of valuable transferrable skills in the geothermal industry, and further identified that materially encouraging a large fossil fuel company to pursue cleaner technologies had value. In the GeoZone, Chevron has proposed a “pilots to projects” approach. Depending on results of exploration or pilot work, Chevron may develop using conventional horizontal technology, deep Enhanced Geothermal Systems (EGS), or Advanced Closed Loop (ACL). Chevron plans to deploy its subsurface modeling expertise, well factory approach to cost reductions, financing capability, and California operating experience to achieve GeoZone objectives. The SCP Board, staff and some community stakeholders all expressed the need for SCP to work diligently to ensure SCP retains all of the environmental attributes of any eventual geothermal power to guard against the more serious risks of potential “greenwashing” by an oil and gas company.

Cyrq Energy

Cyrq Energy is an established geothermal operator and development company in the Western US. Cyrq Energy plans to deploy thermal storage technology at existing geothermal power plants at the Geysers to improve their flexibility and reliability contribution to the grid; in short, to make more power when we need it and less when we don’t need it. Cyrq’s thermal storage system is heated from electric power during hours when the grid has significant solar production, and then discharged to superheat steam entering geothermal plants when the grid needs more power—increasing their output by about 45%.


Eavor is a Canadian geothermal technology company with an Advanced Geothermal System (AGS) technology called Eavor-Loop. Eavor’s technology involves drilling and connecting two deep multilateral wellbores to circulate water through deep granitic base rock. Eavor’s technology is enabled by significant technological advancements in the capability and efficiency of drilling. Eavor’s wells produce heated water that flows through a heat exchanger at surface to transfer the heat to a turbine loop and then re-injected in a closed loop with no operational emissions. Eavor’s technology can target areas without permeability or groundwater as long as heat and rock conductivity are present. A video walkthrough of Eavor’s technology is available here