“Stillwater showcases the pioneering technology innovation of Enel Green Power that is making us so successful in working with governments and business partners around the world to tackle environmental issues and climate change through renewable energy. The lessons we are learning at this advanced geothermal-solar facility will be key to the development of other hybrid plants throughout the world. We will continue to invest in new technological solutions to maximise existing assets and support further growth, maintaining innovation and operational efficiency as a key driver of our strategic plan”
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 hybrid facility received the Geothermal Energy Association Honors award for «Technology Advancement» four times in 2012, 2013, 2014 and 2015.
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). Making the most of its international reach, resources and partners, EGP looked to its own diverse renewable portfolio and the most advanced facilities in the world for more resourceful and innovative ways to maximise plant operations and output.
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.