Thermal/electrica energy stroage in geothermal powerplants

Geothermal energy is one of America’s best choices as a lowcost renewable energy resource for power generation. Adding energy storage capability to geothermal resources enables the power produced/offset to be dispatched as necessary based on changing grid conditions, expanding the usage and utility of geothermal energy. The proposed energy storage system for capture of both electrical energy in a nonbattery system and lowtemperature thermal energy ≤ 150oC would be an ideal extension to the capabilities of existing geothermal powerplants. Deployment of flexible power production and storage of geothermal energy storage contributes to grid reliability, flexibility, resilience and security, and the DOE’s Grid Modernization Initiative. The Phase I project successfully demonstrated flexible power generation, as well as thermal and electrical energy storage. Thermal energy was stored in concentrated osmotic polymeric solutions, while electrical energy was stored in concentrated ionic solutions. These solutions produced flexible power generation in a Pressure Retarded Forward Osmosis PRFO system, converting their osmotic potential to hydraulic pressure on dilution with water across membranes. The system essentially works as a miniaturized hydroelectric plant, when combined with a hydroturbine. In Phase I, special osmotic polymers were developed, used in the power generation, and re converted back to their concentrated form by utilizing thermal energy. The ionic polymers were re converted back to their concentrated by using electrical energy in a modified electrodialysis CEDI system. In addition, special polymers were developed which are capable of CO2 absorption 250 g CO2 absorbed per ml of solvent and decarbonization of geothermal plants, as well as low boilingpoint osmotic polymers 30oC which can be used for both osmotic power production and additional power production in an Organic Rankine Cycle ORC engine. In the proposed Phase II project, the osmotic engine from Phase I will be coupled with an ORC engine for additional power production in series, increasing the total power generated, and adding to the thermal storage capability. Additionally, a steam electrolysis system will be developed, using the lowtemperature exhaust steam ≤ 125oC from a geothermal powerplant steam turbine effluent to create “green hydrogen”. This green hydrogen will also serve as an electrical energy storage medium. Both systems will be capable of flexible power generation and storage, with grid connectivity. The systems and technologies developed can be used for flexible power generation, with thermal/electrical energy storage, in geothermal applications, as well as lowtemperature waste heat and solarthermal applications, to be commercialized in Phase III with industrial partners. Additional benefits will be decarbonization of waste effluents and production of “green H2” at lower costs than current “green H2” technologies.