Minimizing the levelized cost of electricity production from low-temperature geothermal heat sources with ORCs: Water or air cooled?

• System optimization of organic Rankine cycles powered by low-temperature geothermal heat.
• Models of heat exchangers, dry and wet cooling and axial turbines.
• Minimization of the levelized cost of electricity.
• Combined optimization of the configuration of the cycle and of the components.

A system optimization of ORCs cooled by air-cooled condensers or wet cooling towers and powered by low-temperature geothermal heat sources is performed in this paper. The configuration of the ORC is optimized together with the geometry of all the components. The objective is to minimize the levelized cost of electricity (LCOE) and the performance of ORCs with different types of cooling systems are compared to each other. The results show that it is economically more interesting to use mechanical-draft wet cooling towers instead of air-cooled condensers. The difference in performance is especially large for a low brine-inlet temperature. The investment cost of wet cooling towers is much lower than the one of air-cooled condensers, so the discount rate has less influence on the former type of cooling. The effect of the water price and the climate conditions on the economics of ORCs is also investigated. Both the brine-inlet temperature and the dry-bulb temperature of the surroundings have a strong influence and values of the optimized LCOE between about 55 and 185 €/MW h are obtained.