Thermal Performance of a Parabolic Trough Solar Concentrator Coupled with a Modified Flat Plate Collector for Greenhouse Heating

In the present study, a parabolic trough solar collector (PTC) was coupled with a modified flat plate solar collector (FPC) to serve as a greenhouse heating system. The modified FPC was located inside the greenhouse for two purposes: working as the heat exchanger during the night and also generating solar thermal energy during the day. Heat transfer models were established to describe the performance of the system components and a set of experiments were conducted to validate the models. The results showed that there was a fair agreement between the theoretical and experimental data with respect to the correlation coefficient and the root mean square percent deviation criteria. The average thermal efficiency of the PTC decreased when the FPC was engaged. Raising the fluid flow rate through the PTC increased the amount of stored energy at the off-FPC mode while it led to a decrease in stored energy when the system was at on-FPC mode.