Techno-economic Assessment of Geothermal Power Plants Hybridized with Solar Heat and Thermal Storage

Abstract

Geothermal power plants may experience a decrease in power output over time due to a reduction in either mass flow rate, temperature or pressure of the resource. A recent study quantified the temperature drawdown of U.S. double-flash geothermal power plants at 0.8% per year. Hybridizing existing geothermal plants with other renewable power sources to exploit the unused capacity of the geothermal power block has become an area of increasing interest. For instance, a geothermal power plant may be retrofitted with heat from a concentrating solar field. In addition, geothermal may be integrated with solar in a new-build site with the aim of combining the benefits of both technologies – i.e. the baseload generation of geothermal, plus the relatively high efficiency of concentrating solar power. In this article, we give an overview of hybrid geothermal-solar projects undertaken at the National Renewable Energy Laboratory in collaboration with various partners. We investigate the retrofit of double-flash and binary geothermal plants with solar heat. Off-design models are developed and validated with operational data. Annual simulations evaluate the hourly performance, the benefits of thermal storage, and are used to calculate economic metrics. Finally, we discuss the implications of integrating solar and geothermal in a new greenfield site.