A CO₂-based direct geothermal system (CPG) circulates CO₂ through the subsurface and directly expands the CO₂ in a surface turbine to generate electricity (Figure ). The CO₂ system is a single power cycle circuit between the reservoir and surface, which has the advantages of both utilizing the low viscosity of the CO₂ within the porous media and eliminating the heat transfer irreversibilities that occur when transferring heat from geofluid to the organic fluid.