Thermo-economic investigation of solar-biomass hybrid cogeneration systems based on small-scale transcritical organic Rankine cycles

Abstract

The present study aims at investigating the energy, exergy, and economic performance of an innovative multi-source renewable hybrid energy system for small-scale combined heat and power (CHP) applications. The system is based on a transcritical organic Rankine cycle (ORC) able to exploit solar and biomass sources, through a concentrated solar power unit and a biomass boiler. A thermo-economic model has been developed and a parametric analysis has been implemented to define the proper configuration of the hybrid system balancing energy and economic purposes. The investigation, performed for a residential complex in Southern Italy, highlights that the suitable hybridisation of biomass and solar energy increases the useful production and system flexibility compared to the single-source configurations. The proposed small-scale system guarantees a 48.9% decrease in the biomass consumption compared to the corresponding biomass-only apparatus, increases the exploitation (+8.8% of electric production) of low solar radiations that are not adequate to feed a full-solar ORC, also overcoming the stochastic and intermittent characteristics of the solar source. The comparison with the conventional scenario, where the electric grid and natural gas boilers satisfy the energy demands, separately, demonstrates that the suggested solar/biomass hybrid ORC system guarantees a 24.2% primary energy saving, a 53.5% decrease in the unit electric and thermal production costs, and a 57.7% drop in greenhouse gas emissions, with a payback period equal to 7.5 years.