A Flat Plate Solar Collector with a Backup Electric Heater for Heating Greenhouses in Egypt

Providing optimal temperatures in greenhouses is essential for cultivating high-temperature-demand crops in winter. Therefore, this study aimed to investigate the feasibility of utilizing a flat plate solar collector (FPC) for heating greenhouses. A field experiment was conducted, complemented by simulations using the PolySun V2023.11 software. The FPC system comprised two collectors, each with an aperture area of 2.24 m2, connected to a 300 L hot water tank. The water tank had an internal electric backup heater (2 kW) and a thermostat to regulate the hot water temperature. The experiment consisted of two greenhouses, each with an area of 50 m2. The first unheated greenhouse (UHGH) was used as the control, while the second heated greenhouse (HGH) was heated by a closed-loop system comprising copper pipes installed along the internal perimeter. Results revealed that the FPC significantly increased air temperature by 2.7 °C, and reduced relative humidity by 9.7% in the HGH compared to the UHGH. Simulated results showed that the annual generated energy of the FPC was 4830 kWh with a reduction of CO2 emission by ≈2.9 tones. The average thermal efficiency of the FPC was 44%, with a payback period of 8.5 years. In conclusion, the FPC could protect plants from low temperatures in winter.