Performance analysis and exergo-economic optimization of a solar-driven adjustable tri-generation system

Solar-driven trigeneration system producing cooling, heating and power (CCHP) is an effective way to increase the utilization rate of solar energy. Here, a novel adjustable CCHP system is proposed by employing parabolic trough collectors (PTC), Organic Rankine Cycle (ORC), absorption chiller (AC) and electrical chiller/heater (EC/H) to meet building cooling and heating demand. A full thermal simulation model of the system is constructed and validated. The thermal and adjustable performance of a hybrid system with variable solar irradiance and solar thermal allocation ratio is explored by carrying out energy, exergy and heat to electricity ratio. Considering the energy levels of products and investment recovery coefficient of units at the end of service life, a modified exergo-economic method is utilized to optimize the thermal allocation ratio among the system components based on a specific working condition converted from yearly building parameters. The thermal analysis shows that except for the energy efficiency with increasing allocation ratio, the irradiance and allocation ratio have positive impacts on energy, and exergy performance, and the proposed system has a higher adjustable performance with a higher heat to electricity ratio than other studies. The exergo-economic optimization shows that 86% of the solar heat is fed to the ORC-unit at optimum point with an unit exergy cost of 0.826 $/kWh. Compared to conventional exergo-economic method, the specific costs of the products are lower owing to the function of cost recovery coefficient. This research illustrates a new way to effectively utilize solar thermal energy for district energy systems.