Thermo-economic optimization of a novel hybrid renewable trigeneration plant

This work presents a novel renewable trigeneration plant powered by solar, geothermal and biomass energy, producing simultaneously electricity, heat and cool. The developed system includes a 193 m2 photovoltaic field, a 159 kWh lithium-ion battery, a 30 kWe organic Rankine cycle, a 350 kWth biomass auxiliary heater, a geothermal well at 96 °C and a 80 kW single stage H2O/LiBr absorption chiller. The Organic Rankine Cycle is mainly supplied by the geothermal well, producing electricity. An additional amount of electricity is produced by the photovoltaic panels. A detailed dynamic simulation model was developed in TRNSYS environment in order to calculate both energy and economic performance of the plant. The model includes algorithms validated versus literature and experimental data. The model of the renewable trigeneration plant is used for a suitable case study, a residential building in the Campi Flegrei (Naples, South Italy) area, a well-known location for its geothermal sources and good solar availability. The proposed plant exhibits promising energy performance achieving a primary energy saving of 139%, mainly due to the obtained excess energy. From the economic point of view, the proposed plant gets a limited profitability, showing a payback period of about 19 years, mainly due to the high capital cost of the employed technologies. A thermo-economic optimization is also implemented, considering photovoltaic field and battery capacities as independent variables. The results of the optimization suggest increasing the area of the photovoltaic field and to limit the capacity of electric energy storage system, due to the high specific capital cost of the lithium-ion battery. Finally, a multi-objective optimization is also carried out, aiming at calculating the set of the optimal design variables of the proposed trigeneration plant.