Hybrid Geothermal Energy Conversion - a Potential Solution for Low-Temperature Geothermal Resources

Low- to moderate- temperature geothermal resources are typically used for direct heat energy applications, whereas deep, high-temperature, geothermal resources are often used for electricity generation. But deep geothermal resources usually require enhancement of the permeability of the hot dry rock at these depths (4-6 km), which can induce seismicity. Here we present an alternative geothermal energy utilization approach that uses shallower, lower-temperature, naturally permeable formations. Our approach can generate electricity while substantially reducing drilling costs and the risk of induced seismicity. This approach uses geothermal heat to supplement a secondary energy source, thereby potentially enabling the use of geothermal energy for electricity generation in many regions worldwide that are not viable with current approaches. We determine the net power output, energy conversion efficiencies, and economics of these hybrid power plants, where the geothermal power plant uses supercritical carbon dioxide (scCO₂) as the subsurface working fluid. When scCO₂ is used underground, the overall system stores 100% of the injected CO₂, while generating geothermal power, constituting a Carbon Capture Utilization and Storage (CCUS) system. Parameters varied include geothermal reservoir depth (2.5-4.5 km) and turbine inlet temperature (100-220°C). We find that hybrid power plants outperform two individual, i.e., stand-alone geothermal and waste-heat power plants. Furthermore, such hybrid power plants are more economical, and result in lower capital costs per electricity produced ($/kW) than separate power plants.