Retrofitting a Geothermal Plant with Solar and Storage to Increase Power Generation

Solar hybridization using concentrating solar power (CSP) can be an effective approach to augmenting the power generation and cycle efficiency of a geothermal power plant which exploits a resource with a declining fluid mass. Thermal storage can further increase the dispatchability of a geothermal/solar hybrid system, which is particularly valued for a regional grid with high renewable penetration. A hybrid plant design with thermal storage is proposed based on the requirements of the Coso geothermal field in China Lake, California. This study models one Coso plant turbine running at a load that is about 7.5 MW_e less than the design load of 30 MW_e. The objective is to increase the power production by 4 MW_e. In this system, a portion of the injection brine is heated with the solar heat-transfer fluid, before being mixed with the production well fluids. In the solar heating loop, the brine should be heated to at least 155°C to increase the net power. The solar field and storage were sized based on solar data for China Lake. Thermal storage is used to store excess power at the high solar-irradiation hours and generate additional power during the evenings. The solar-field size, type and capacity of thermal storage, and operating temperatures are critical factors in determining the most economic hybrid system. Further investigations are required to optimize the hybrid system and evaluate its economic feasibility.