Enhancement of the Thermal Efficiency of the Evacuated Tubes Solar Water Heater by Adding a Reflector

Evacuated tube solar collector (ETSC) is an efficient means used to harvest direct incident solar energy and convert it into thermal energy. Still always there is a rare area of the tube itself which is not facing the sunshine. Thus, reflectors are used to maximize the collecting area. This study investigated the performance of 21 different configurations of the ETSC system. In this research, three different types of reflective materials were used such as aluminum foil, mirror, and white painting. The aluminum foil was used in five different shapes such as a flat surface, parabolic, V-shape, vertical-zigzag and horizontal-zigzag. While the mirror and white painting were used in a flat shape only. All those types of reflectors were installed at a distance of (0.22, 0.17 or 0.12) m behind ETSC's center. The experiments were conducted during 11th-13th December 2018 under Kerbala, Iraq climate. Each system was compared with a reference one which was set without a reflector. Based on thermal efficiency calculations, the results showed that the flat mirror at a distance of 0.17 m was the best. Also, the orientation of the zigzag surface has a significant effect on efficiency.