Is Geothermal Energy Possible In California?
Geothermal energy is thermal energy generated and stored in the Earth. It is a renewable energy source that utilizes the natural heat within the Earth’s crust to produce steam and hot water that can be used to produce electricity, provide direct heating and cooling, or be used for a variety of industrial purposes.
California has enormous potential for geothermal energy due to its unique geology. The state has active geothermal areas related to tectonic plate boundaries and magma chambers, which provide heat sources close enough to the surface to be harnessed commercially. Significant known geothermal resources exist in the coastal ranges, Sierra Nevada mountains, Cascades, and Mojave Desert. With 48 currently identified geothermal sites, California leads the nation in geothermal power generation and has the potential to expand capacity even further.
Geology of California
California’s tectonic setting along the active margin of the North American and Pacific plates makes it geologically suitable for geothermal energy.[1] The state lies within the Cordillera region, which contains young and seismically active mountains, abundant volcanic activity, and major fault zones. This creates an ideal setting for geothermal reservoirs.
Most of California’s high-temperature geothermal resources are located in the northern Coast Ranges, western Transverse Ranges, and the Modoc Plateau. Key geologic features like the San Andreas Fault system, volcanic centers, sedimentary basins, and young igneous intrusions provide permeable pathways and heat sources for geothermal reservoirs.[2]
Currently identified geothermal reservoirs reside in sedimentary rocks and volcanic rocks. The main sedimentary rock reservoirs are in the Coast Ranges and Transverse Ranges, while volcanic rock reservoirs are mostly found in the Cascades and Modoc Plateau.[1]
Types of Geothermal Resources
There are four main types of geothermal resources that can be used for energy production:
Hydrothermal Reservoirs
Hydrothermal reservoirs involve both heat and water, typically in the form of naturally occurring hot water or steam reservoirs deep beneath the earth’s surface. Water is heated up by hot rocks and collects in cracks and porous rock. Wells can be drilled into these reservoirs to tap the hot water or steam which powers turbines to generate electricity. This is the most common type of geothermal energy production. Examples include The Geysers in California and Wairakei in New Zealand (Source: https://greenesa.com/blog/geothermal-energy-types-uses-advantages).
Geo-Pressured Reservoirs
These reservoirs contain hot water under pressure. The water has not been heated up enough to become steam, but the pressure keeps it from boiling. The pressurized water can be brought to the surface and used to drive turbine generators. Geo-pressured reservoirs are located along the Gulf Coasts of Texas and Louisiana in the US (Source: https://www.energy.gov/sites/prod/files/2014/06/f16/geothermal_energy.pdf).
Magma
Magma is molten rock or lava beneath the earth’s surface. Drilling deep enough to reach magma for energy production is currently not feasible. However, experimental projects are underway to extract heat from magma through deep wells without reaching the magma itself. For example, a pilot project in Iceland is drilling wells to a depth of 2.1 miles to get superheated steam from the magma chamber below (Source: https://www.energy.gov/sites/prod/files/2014/06/f16/geothermal_energy.pdf).
Hot Dry Rock
Hot dry rock reservoirs lack both water and permeability to allow the easy flow of fluid. But wells can be drilled into hot dry rocks and water can be pumped down one well to extract heat from the rocks. The heated water is then drawn to the surface from a second well to generate electricity. An experimental hot dry rock project is being developed at Fenton Hill, New Mexico (Source: https://greenesa.com/blog/geothermal-energy-types-uses-advantages).
Locations of Geothermal Plants
California is home to some of the world’s largest and most productive geothermal fields. The state has 40 operating geothermal power plants located at 21 different sites https://www.energy.ca.gov/data-reports/california-power-generation-and-power-sources/geothermal-energy.
The largest geothermal field in California and the entire world is The Geysers, located in Sonoma, Lake, and Mendocino counties. This complex contains 21 geothermal power plants with an installed capacity of over 2,000 megawatts, making it the largest complex of geothermal power plants globally https://en.wikipedia.org/wiki/The_Geysers. Steam from over 350 wells across 45 square miles is harnessed to generate electricity at The Geysers.
Another major geothermal resource is located in Imperial Valley, which contains the Salton Sea geothermal field. There are currently 11 geothermal plants operating in this area, producing over 340 megawatts of power. The region has the potential for significant expansion of geothermal capacity in the future.
Beyond these two main areas, there are smaller geothermal plants scattered across northern and central California. Locations include Coso in Inyo County, Wendel in Lassen County, Casa Diablo in Mono County, and several others. While small individually, together these plants contribute over 400 megawatts of geothermal capacity for California.
Potential Capacity
California currently has an installed geothermal capacity of about 2,700 MW, providing about 4.5% of the state’s total electricity generation [1]. The largest geothermal power plants are located at The Geysers in Northern California, which provides about 60% of the state’s geothermal capacity. Other key geothermal plants are located at the Salton Sea, Coso, and Imperial Valley.
However, experts estimate the state’s untapped geothermal resource potential to be up to 20,000 MW [2]. New technologies like enhanced geothermal systems could allow access to deeper resources across California. Areas with high potential include Imperial Valley, Coso, the Cascades, and Modoc Plateau.
The 2045 California Public Utility Commission’s modeling projects geothermal capacity to reach 4,000 MW by 2030 and potentially over 5,000 MW by 2045 as more untapped resources come online [1]. Realizing the full 20,000 MW potential could supply almost a third of California’s electricity needs and play a major role in achieving renewable energy goals. However, development faces challenges around policy, technology, economics and environmental impacts that need to be addressed.
Economic Viability
Geothermal energy has become increasingly cost competitive with other renewable energy sources in California. A 2022 study by the California Energy Commission found the levelized cost of energy for geothermal power plants in California ranged from $58-78 per MWh, compared to solar PV at $37-53 per MWh and onshore wind at $54-79 per MWh [1]. While geothermal has a higher capital cost, it provides consistent baseload renewable power compared to the intermittency of solar and wind.
California has several incentive programs to support geothermal development. The Self-Generation Incentive Program (SGIP) provides rebates for new geothermal systems up to $5 million per project. The Geothermal Grant and Loan Program offers grants covering up to 50% of drilling costs to confirm geothermal reservoirs. There are also federal tax credits available covering 10% of project costs. With continued technological improvements and supportive policies, geothermal can play an expanded role in California’s renewable energy mix.
Environmental Impacts
Geothermal energy does have some environmental impacts that need to be considered [1]. Three main areas of concern are land use and habitat, seismicity, and water use.
Geothermal plants require land to be cleared for construction, which can disturb natural habitats. Pipelines also need to be built to transport the hot water. Careful siting and routing of facilities is important to minimize habitat loss [2].
Extracting large amounts of hot water can induce small earthquakes along fault lines. Seismic activity is monitored and geothermal operations adjusted as needed. Most induced earthquakes are minor, but larger ones are possible [3].
Geothermal plants use water for cooling and disposing of brines. Water usage can be minimized by using closed-loop systems. Brines also need to be properly disposed of to avoid contaminating water sources.
Regulatory Framework
Geothermal energy development in California is regulated by the California Department of Conservation’s Geologic Energy Management Division (CalGEM), which oversees the permitting and oversight of geothermal projects in the state.
CalGEM issues permits for the drilling, operation, maintenance, and abandonment of geothermal wells, as specified in the California Code of Regulations Title 14, Division 2, Chapter 4 (18 CCR § 473). All operators must submit monthly production reports and well tests to CalGEM.
Recent policy changes include Assembly Bill 2189, signed in 2018, which required CalGEM to initiate amendments to its regulations to promote the development of geothermal energy and ensure proper management techniques. The regulations are currently under review.
In 2019, Senate Bill 1169 established deadlines for CalGEM to complete its permitting process for geothermal wells to improve efficiency. The bill also extended permitting for certain idle geothermal wells.
Overall, California aims to streamline the permitting and regulatory process to encourage more geothermal development and meet its renewable energy goals.
Challenges and Limitations
Geothermal energy development faces several challenges and limitations in California. One major constraint is geographic. While California has abundant geothermal resources, they are concentrated in specific regions like the Imperial Valley and Geysers area north of San Francisco. Constructing power plants far from transmission infrastructure or population centers increases project costs. Competing land uses also pose barriers. Geothermal plants require large areas of land, which can conflict with agricultural, recreational, or residential zones. According to a 2022 NREL report, projects in Imperial County have faced challenges due to endangered species habitats [1]. Additionally, some local communities have resisted geothermal development out of concern over impacts like noise, viewshed changes, induced seismicity, and greenhouse gas emissions. A 1979 California Energy Commission report found “delays of five to ten years” for geothermal projects due to “local opposition groups” [2]. Overcoming negative public perceptions through engagement and education will be key to unlocking California’s geothermal potential.
Future Outlook
The future looks bright for geothermal energy in California. According to a 2022 report from the California Energy Commission, the state could expand its geothermal capacity from the current 2,700 MW to 8,900 MW by 2045 if policies support its growth[1]. This would allow geothermal energy to play a substantial role in meeting California’s renewable energy goals.
Geothermal power capacity is predicted to grow by around 50% globally by 2026[2]. California is well-positioned to capture a significant share of this growth. The state’s vast geothermal resources, existing plants, and supportive policies make it an attractive location for geothermal development and investment.
Innovations in enhanced geothermal technology could also boost California’s geothermal capacity. Techniques like hydraulic fracturing are enabling access to geothermal resources that were previously unattainable. Further research and development could lead to major expansions of viable geothermal sites in the state.
