Exergetic and exergoeconomic analysis of a novel hybrid solar–geothermal polygeneration system producing energy and water

A dynamic simulation model of a novel solar–geothermal polygeneration system and the related exergetic and exergoeconomic analyses are presented in this paper. The plant is designed in order to supply electrical, thermal and cooling energy and fresh water for a small community, connected to a district heating and cooling network. The hybrid system is equipped with an Organic Rankine Cycle fueled by medium-enthalpy geothermal energy and by a Parabolic Trough Collector solar field. Geothermal brine is also used for space heating and cooling purposes. Finally, geothermal fluid supplies heat to a Multi-Effect Distillation unit, producing also desalinized water from seawater. Dynamic simulations were performed in order to design the system. An exergetic and exergoeconomic analysis is also implemented. Results are analyzed on different time bases presenting energetic, exergetic, economic and exergoeconomic performance data. Results show that global exergy efficiency varies between 40% and 50% during the “Thermal Recovery Mode” operation and between 16% and 20% during the “Cooling mode” operation. It was also found that electricity, chilled water, cooling water and desalinated water exergoeconomic costs vary respectively in the ranges 0.1475–0.1722 €/kW h, 0.1863–0.1888 €/kW hex, 0.01612–0.01702 €/kW hex and 0.5695–0.6023 €/kW hex.