Influence of the match of PV and DC pump on the performance of a PV direct-coupled solar water heating system

Solar water heating system (SWHS) is one of the most energy-saving systems for space and water heating. However, traditional SWHS has operational instabilities which lead to system malfunctions. Then, the SWHS using PV direct-coupled DC pumps is presented, since the flow rate requirement of the heat transfer fluid has a natural relationship with the availability of solar energy and these SWHSs are simple and reliable. In this study, a simulation model for a PV direct-coupled SWHS is presented and validated against experimental results, and a design method of the match of PV module and DC pump is suggested. The simulation is conducted to investigate the influence of the match of PV module and DC pump on the performance of the system, with emphasis on the pump startup characteristics and the pump flow rate profile. Different designs of PV modules, different pumps, and different weather data obtained by measurement are used in the analysis. The results are used to optimize the PV direct-coupled SWHS. It’s found that the direct-coupled SWHS should be designed to has a flow rate varying significantly with solar irradiation, with a threshold irradiation of about 180 W/m². The modified design of PV module could lead to less requirement of PV cells and better flow rate profile, compared with the conventional PV module designs.