In genGEO, an organic Rankine cycle (ORC) is used for electricity generating in water-geothermal power plants. The ORC configuration and methodology are identical to that used in Adams et al. (2015), namely, we use a single-pressure, sub-critical ORC with no superheating. An example ORC power cycle used in genGEO is shown in Figure for a 100°C geofluid temperature. The water temperature in the counter-flow heat exchanger is overlain in blue in Figure . The water outlet temperature from the ORC is ~62°C. The genGEO organic Rankine cycle does not use superheating. Superheating is commonly used in power cycles to guarantee vapor throughout the turbine. However, the shape of the R245fa vapor dome is unusual in that the entropy of saturated vapor decreases at temperatures below 124°C. As the entropy increases throughout the turbine, the fluid will remain gaseous in the turbine so long as the turbine is constrained to saturated vapor below 124°C. The isobutane vapor dome has a similar shape and feature. Thus, we instead imposed a maximum boiling temperature constraint for the organic fluid at the temperature with maximum saturated vapor entropy.