Exergoeconomic Optimization of an Organic Rankine Cycle for Low-Temperature Geothermal Heat Sources

An exergoeconomic analysis of a geothermal power generation for a low-temperature resource is performed. An Organic Rankine Cycle (ORC) with isobutane and isopentane as working fluids is considered as binary power plant. A systematic parameter variation is done for the minimum temperature difference in the evaporator and condenser. The most suitable design parameters are evaluated under exergetic, economic and exergoeconomic criteria. The specific costs of electricity generation are minimal for the use of isobutane as working fluid and minimal temperature difference of 3 K at evaporation and 7 K at condensation. The most suitable concept for isopentane leads to only 0.4 % higher specific costs although the second law efficiency is 4.75 % lower. The exergoeconomic analysis permits to consider important criteria, like design and operating parameters in the fluid selection for ORC applications.