Experimental comparison of two PV direct-coupled solar water heating systems with the traditional system

Simple and reliable, PV direct-coupled DC pumps are promising in solar water heating systems (SWHS). However, there is limited experimental data on the performance comparison of PV-coupled SWHS with traditional SWHS. Hence in this study, a comparative test rig is set up to measure and analyze the performance of the PV-coupled SWHS and the traditional system under the same conditions. The experimental results show that on sunny days the PV-coupled SWHS has similar daily thermal efficiency as the traditional SWHS, and slightly higher efficiency after improving the design of the PV module. Under low irradiation, the PV-coupled SWHS gains much more heat than the traditional SWHS, which indicates the potential of the PV-coupled SWHS having much higher efficiency than the traditional SWHS on cloudy days. In order to improve the performance of the PV-coupled SWHS, two different designs of PV module are proposed, and their influence on the pump startup characteristics, the flow rate profile, and the thermal efficiency of the system is investigated. It is found that the modified design of the PV module can reduce the requirement of PV cells and increase the efficiency of the system.