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 exergeticand exergoeconomic analyses are presented in this paper. The plant is designed in order to supplyelectrical, thermal and cooling energy and fresh water for a small community, connected to a districtheating and cooling network. The hybrid system is equipped with an Organic Rankine Cycle fueled bymedium-enthalpy geothermal energy and by a Parabolic Trough Collector solar field. Geothermal brineis also used for space heating and cooling purposes. Finally, geothermal fluid supplies heat to aMulti-Effect Distillation unit, producing also desalinized water from seawater. Dynamic simulations wereperformed in order to design the system. The overall simulation model, implemented in TRNSYSenvironment, includes detailed algorithms for the simulation of system components. Detailed controlstrategies were included in the model in order to properly manage the system. An exergetic andexergoeconomic analysis is also implemented. The exergetic analysis allows to identify all the aspectsthat affect the global exergy efficiency, in order to suggest possible system enhancements. Theaccounting of exergoeconomic costs aims at establishing a monetary value to all material and energyflows, then providing a reasonable basis for price allocation. The analysis is applied to integral valuesof energy and a comparison of results between summer and winter season is performed. Results are analyzedon different time bases presenting energetic, exergetic, economic and exergoeconomic performancedata. Results show that global exergy efficiency varies between 40% and 50% during the ‘‘ThermalRecovery Mode” operation and between 16% and 20% during the ‘‘Cooling mode” operation. It was alsofound that electricity, chilled water, cooling water and desalinated water exergoeconomic costs varyrespectively in the ranges 0.1475–0.1722 €/kW h, 0.1863–0.1888 €/kW hex, 0.01612–0.01702 €/kW hexand 0.5695–0.6023 €/kWhex.