Long-Term Thermal Performance Evaluation of a Solar Heating System of Greenhouse with High Temperature Underground Seasonal Thermal Energy Storage

In this study, we analyzed the long-term feasibility of a solar heating system for a citrus greenhouse to address the financial difficulties facing farms and to reduce greenhouse gas emissions. The solar heating system consisted of an auxiliary boiler, a solar storage tank with a capacity of 100 m and a cylindrical borehole thermal energy system (BTES) with a storage volume of 2,905 m. We installed an evacuated tube collector and flat-plate collector (both with a capacity of 302 m) to measure and compare each solar fraction and thermal storage efficiency. TRNSYS 18 was used as the simulation tool. The annual solar fraction was found to be 83.2%, and the efficiency of thermal storage was 35.7%. In this case, the efficiency of evacuated tube collector and flat-plate collector was 68.7% and 33.2% respectively. This shows that the evacuated tube collector, operating at a relatively high temperature, was more efficient than the flat-plate collector. Despite the high solar fraction, the maximum operating temperature of the solar storage tank was 90° or less, indicating that the tank was less likely to fail due to overheating.