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Geothermal Energy

Adding Solar Steam-Topping Turbines to Geothermal Power Plants to Boost Performance

Company Name: U.S. Geothermal, Inc.
Program Office: Geothermal
Location: Boise, ID
Email: Kevin Kitz, Vice President of Project Development;
Award Amount: $150,000
Project Term: 12 months
Project Status: Active
Participating Lab(s): National Renewable Energy Laboratory/Idaho National Laboratory


Faced with high capital costs and increasing competition from inexpensive natural gas and solar power producers, the domestic geothermal industry must find ways to lower the levelized cost of energy (LCOE) for geothermal power.

One solution is for geothermal plants to add solar thermal energy to the plant in order to boost power generation and revenue.

U.S. Geothermal (USGeo) has developed a promising new approach that could boost performance and revenue, but the company has not found the expertise needed to validate the concept in the private sector. In contrast, the Department of Energy's national labs have unique modeling and evaluation technology that can be applied to this exact problem. The labs also have experience doing this type of evaluation.

Through this SBV Pilot, USGeo will work with experts at the National Renewable Energy Laboratory and Idaho National Laboratory to examine the viability of a new geothermal-solar hybridization configuration that could maximize the economics of an existing geothermal resourceand power plant, with applicabililty to other existing plants. The right hybrid approach could also justify the development of new projects with an LCOE that is too high, including some lower-temperature geothermal resources.


Existing geothermal projects integrate solar thermal energy by heating cooled brine back up to the geothermal power plant inlet temperature, or adding heat to the incoming brine. This results in an inefficient 15 percent conversion rate of solar energy, effectively doubling the solar collector's cost per kilowatt-hour compared to conversion in a high-temperature concentrated solar power (CSP) system.

Using USGeo's proposed new thermodynamically efficient approach, high-temperature solar heat (400 °C) will generate power through a topping steam cycle, while the exhaust heat from the topping cycle will boost power generation from the bottoming geothermal binary cycle.

This geothermal/solar hybrid approach would marry the best aspects of both concentrated solar power and geothermal energy to provide a lower LCOE than either technology could achieve alone, thus improving market penetration for both technologies.


A successful project will provide an opportunity to increase output from an underperforming geothermal asset at Raft River in Idaho. Expected private-sector investment at Raft River could be on the order of $10 million.

Strategically, USGeo would be able to develop competitive new geothermal power projects in the western US with a lower LCOE.

Across the geothermal industry, the project findings could help both existing underperforming plants and greenfield construction of new projects. Expanding geothermal and solar deployment helps achieve the DOE's "all of the above" strategy for America's energy independence while reducing both air pollution and greenhouse gas emissions.

Read about additional projects.