Solar Thermal and Geothermal Hybrid Power Plant Study

Over the past couple of decades, the concept of integrating solar thermal energy into a geothermal power plant has been studied and documented in various publications. A new concept, to use concentrated solar thermal energy first in a high pressure steam topping turbine, and then as an additional heat source to the Raft River geothermal binary power plant (GBPP) in Idaho, USA was investigated. The approach yielded an economically attractive design through lower capital cost, higher net output and higher efficiency. An unexpected result was the option to incorporate solar thermal storage into the hybrid cycle for 4 or 8 hours at a cost far below battery storage of electrical energy. U.S. Geothermal Inc. (USGeo), the National Renewable Energy Laboratory (NREL), the Idaho National Laboratory (INL), and POWER Engineers (PEI) worked together to investigate the concept. The study was made possible through a 2017 Small Business Ventures Pilot Program grant, funded by the U.S. Department of Energy (DOE) Geothermal Technologies Office.This article is a high-level summary of a detailed study that is pending publication by INL and NREL, and of a geothermal paper that will be presented at the forthcoming October 2018 GRC Annual Meeting in Reno, Nevada.