Stillwater is the world’s first power plant to combine medium enthalpy, binary cycle geothermal, solar thermal and solar photovoltaic technologies at the same site.
By combining generation technologies of different profiles at one production site, energy availability is increased and energy intermittency reduced. Geothermal and solar (thermal and photovoltaic) are complementary, meaning that production from solar is higher during the sunniest and hottest days of the year, when the thermal efficiency of the geothermal plant is lower.
The increased delivery of power during peak hours also enables a more load-following production profile. At the same time, sharing existing infrastructure enables costs-savings and reduction of the plant’s environmental impact per unit of energy produced and delivered.
In addition, research findings between March and December 2015 confirm that the combination of a 2 MW solar thermal facility with a 33.1 MW geothermal plant increased overall output at Stillwater by 3.6% compared with production from geothermal only. These findings were bolstered by the results of a study of the integration of geothermal and solar thermal. This is the first time empirical data from a commercial hybrid plant validates a theoretical hybrid model.
This work was performed under the framework of the Cooperative Research and Development Agreement (CRADA) with the National Renewable Energy Laboratory (NREL) and Idaho National Laboratory (INL), under the oversight of the U.S. Department of Energy Geothermal Technologies Office.
The Stillwater plant began operation in 2009 with the completion of the geothermal plant. Since then, the site has served as a hub of innovation for Enel Green Power (EGP).
In 2012, the company added a 26.4 MW solar PV unit to the geothermal plant – at the time one of the largest PV systems of its kind in the United States. In 2015, the company developed a solar thermal system to operate in conjunction with the existing Stillwater geothermal power station. By combining three renewable sources at the same location for the first time, EGP was able to fully capitalise on already installed assets, creating a more efficient and productive overall plant.