Investigation of energy and financial performance of a novel CO2 supercritical solar-biomass trigeneration system for operation in the climate of Athens

Abstract

The ever-growing increase of the energy demand required to satisfy the needs of society has aroused considerable interest regarding the investigation of polygeneration systems that employ renewable energy sources. In the present work, the concept of installing a supercritical CO2 trigeneration system to cover the needs of a refrigerated warehouse in Athens with simultaneous production of power and heating is studied in terms of energy performance, and its financial benefits compared to the solution of an ejector refrigeration-only system are analyzed and assessed. The trigeneration system utilizes solar energy in parabolic trough collectors and biomass energy as the supplementary source, in order to increase the temperature of high-pressure CO2 and produce power in the turbine which is coupled to a generator. Regarding the collectors, the installation of zero up to four solar modules that exploit the solar power is examined, while the rest energy input needed in order to achieve the selected operating conditions is supplied by a biomass boiler. Since all the trigeneration cases require the same amount of energy input to reach the desired conditions, the trigeneration system for every combination of solar modules is found to produce 185.59 MWh annually, while the refrigeration-only system is found to consume 172.94 MWh during a year. The power production efficiency, the combined power and refrigeration production efficiency and the total trigeneration efficiency for the selected nominal conditions are calculated 11.77 %, 66.09 % and 163.70 % respectively. The case of a trigeneration system with four solar collectors displays a payback period of 4.0 years compared to the refrigeration-only case, providing financial savings equal to 542 k€ for the duration of the project lifetime. The same case compared to that of trigeneration system using only biomass boiler and no solar collectors exhibits payback period of 13.5 years, achieving financial savings of 22.9 k€ for the considered lifetime of the project.