Thermo-economic Investigation of a Hybrid Solar/Biomass Multigeneration System for off-grid Communities

orc2019 Tracking Number 81

Multigeneration systems driven by renewables sources are a relevant solution enabling clean, flexible and efficient generation of numerous outputs for different applications. Within this scope, this work aims to evaluate the thermo-economic performances of a renewable energy- based polygeneration system supplying electricity, freshwater, domestic hot water, space heating and cooling requirements for an off-grid community, based on the combination of compound parabolic collectors, a biomass boiler, an ORC and a vapor compression cycle (VCC). Solar collectors are used to preheat the heat transfer fluid (HTF). During highly solar irradiated off-peak periods, a fraction of the preheated HTF is transferred to charge a thermocline thermal energy storage, with the aim to reuse the stored energy during peak-demand periods; whereas the remaining part of the HTF is sequentially transmitted to the biomass boiler, providing the complementary energy to drive the ORC. Rejected heat from the ORC is recovered through a counter-current heat exchanger to meet domestic hot water and space heating requirement of the community. Depending on the community electricity load demand, part of the turbine energy will be used to drive the VCC (summer period) or a reverse osmosis unit (summer and winter periods), allowing a continuous operation of the system. A model of the studied system was built in Ebsilon® Professional and simulations were conducted to assess the plant’s thermodynamic and exergoeconomic performances under both winter and summer modes operation. Results showed that the considered system is able to meet the community requirements in winter mode with a solar field contribution of 29.7 %, an ORC exergy efficiency of 38.8 %, a global exergy efficiency of 6.55 % and a total exergetic cost of 31 €/month/inhabitant, whereas in summer mode solar field’s contribution reaches 17.8 %, ORC exergy efficiency is 37.8 %, global exergetic efficiency is 6.43% and the total exergetic cost is 55 €/month/inhabitant. The obtained results showed that the considered system can be a promising solution to provide basic requirements for isolated communities. Sensitivity analysis will be conducted to assess the impact of main system’s parameters (solar field aperture, storage volume, working fluids) on the plant’s performances.