A water-based indirect geothermal system uses an organic Rankine cycle (ORC) at the surface to generate electricity from heat (Figure ). Indirect systems are a mature technology where the geofluid does not come in contact with the turbo-machinery. Indirect systems are the current state-of-the-art in geothermal power generation, and are the used in both GETEM and GEOPHIRES. Both GETEM and GEOPHIRES implement ORCs through characterizations of unpublished ASPEN simulation results. For instance, GEOPHIRES has built-in equations which calculate electric power and cost as a function of geofluid production temperature.