Ormat’s Mammoth Geothermal Complex - Award Winning Facility


The Mammoth Geothermal Complex is nestled in the magnificent Eastern Sierra. Located near the intersection of Highway 395 and State Route 203 in Mono County, CA, the facilities were designed to blend into the landscape.

In fact, many visitors who come to Mammoth Lakes to enjoy skiing as well as other outdoor recreational and sporting activities never even notice the geothermal facilities. This is a tribute to the design that minimizes the visibility of these power plants.

We’re proud of this renewable geothermal complex, but seeing is believing! That’s why we offer tours to interested individuals and groups who want to know more about how we generate clean, renewable electricity. 

If you're interested in taking a tour of the facility, please email mammothtours@ormat.com.

Key Project Data

Location: Mammoth Lakes, CA
Plant Site: 10 acres
Production Wells: 10 (500 feet deep)
Injection Wells: 5 (2000-2500 feet deep)
Geothermal Fluid: 339 deg. F on average
Major Equipment: Two new OECs and six Turbo-expanders together with the Balance of Plant equipment
Turbine Type: 3-stage axial and six single stage radial expanders


Generating Clean Power 

The power plants in the Mammoth Geothermal Complex transform heat from geothermal fluid (hot water from underground) into clean, renewable electricity. The energy is produced by three separate power plants, using hot water from the same source. The three facilities are: G1 (MP1) with 6 MW generating capacity, G2 (MPII) with 11 MW and G3 (PLES-1) with 12 MW generating capacity. All totaled, the facilities generate enough power for approximately 22,000 homes. The power from G2 is sold to Southern California Edison and the power from G1 and G3 is sold to Pacific Gas & Electric under long-term contracts.

There are two geothermal technologies used to convert the geothermal fluid’s thermal energy (or heat) into electricity: “flash” and “binary.” Mammoth utilizes the binary technology, which emits no CO2 or geothermal emissions into the atmosphere. Mammoth Geothermal Complex’s G1 facility was the world’s first air-cooled geothermal facility to incorporate two closed-loop systems and the first binary power plant in California. Here’s how the binary system at Mammoth Geothermal Complex work:

Geothermal fluid is pumped from the ground (see red) in a primary binary loop. This hot water passes through heat exchangers (to heat the secondary loop, shown as green in this diagram) before being immediately returned to the earth with no loss of fluid. In the secondary binary loop, isobutane or n-batane fluid is indirectly heated in the heat exchangers to produce a high-temperature, high-energy, gas vapor that drives the turbine-generator to produce electricity.

The gas vapor is then cooled back to a liquid by air condensers (cooling fans) and pumped back to the heat exchangers for continued use or “recycling”. Throughout the process, operations data is transmitted real time to a control room for monitoring. Staffed 24 hours a day, the control room contains the starters and controls for all electrical motors and switchgears in the plant. 

Construction of Mammoth Geothermal Complex's evaporative cooling project.

Our Reputation for Innovation

Since the start of operations, Mammoth Geothermal Complex has developed an industry-wide reputation for innovation and cutting-edge technologies. The facilities regularly participate in  research projects in cooperation with agencies such as the U.S. Department of Energy, National Renewable Energy Lab, Idaho National Environmental Engineering Laboratory, Lawrence Livermore National Laboratory, Brookhaven National Laboratory, Duke University and the California Energy Commission. The projects evaluate innovative technologies such as high temperature polymer production pump bearings, the use of reclaimed water for cooling purposes, the use of geothermal water for cooling purposes, mineral recovery, supersaturated vapor expansions in turbines, membrane-based non-condensable gas removal systems, micro-earthquake analysis, and corrosion resistant heat exchanger coatings - all with the purpose of improving operations and efficiency. In 2013, NASA conducted a probe test for the possible future study of fumaroles on other planets at Mammoth Geothermal Complex. Click here

For a story published by “The Sheet” about how the team collected data from the probe as the first stage in the development of a robotic sensing tool that could descend on its own into underground cavities and fumaroles."

Because of our reputation as an industry leader, people from all over the world travel to Mammoth Lakes to see our facilities. We’ve given tours to people from countries including the Philippines, Japan, Indonesia, Iceland, Israel, Italy, Kenya, Portugal and New Zealand.

Mammoth Geothermal Complex Awards and Recognition

Mammoth Geothermal Complex has been recognized by elected officials, trade associations and community groups for its outstanding record on environmental protection and operations excellence.

CDOGGR award presented to John Bernardy and Jack Truschel

Since the start of commercial operations, the California Department of Conservation’s Division of Oil, Gas and Geothermal Leases has presented numerous awards to the Mammoth Geothermal Complex for its outstanding record of environmental protection, resource management, and safety. In 2015, Mammoth Geothermal Complex received the award for the 14th time since 1989.

"Mammoth Geothermal Complex consistently exceeds our strict standards, and it serves as a model for others in the industry," says Elizabeth Johnson, Geothermal District Engineer for the California Department of Conservation’s Division of Oil, Gas and Geothermal Resources. "We present this award in recognition of Mammoth Geothermal Complex’s outstanding commitment to environmental stewardship, resource management, and safe operations" continued Johnson, who personally inspects the facilities throughout the year as a part of her regulatory duties.

Dan Lyster from Mono County accepting the GEA Honors Award from Garl Gawell of the GEA

In 2014, the Geothermal Energy Association (GEA) recognized the Mono County Board of Supervisors for demonstrating outstanding environmental achievement in the geothermal industry for a GEA Honors Award. The winners were selected in categories including Technological Advancement, Economic Development and Environmental Stewardship.

The Mono County Board of Supervisors was awarded for "their creation of the Long Valley Hydrologic Advisory Committee, the Mono County Board of Supervisors has played a key role in the evaluation of hydrologic monitoring data, proprietary geothermal production and injection data, and in the siting and permitting of multiple exploration and development projects in the Long Valley caldera in Mono County, California for almost 30 years."

For additional information on the Long Valley Hydrologic Advisory Committee, please click here.