Performance comparison of photovoltaic/thermal solar water heating systems with direct-coupled photovoltaic pump, traditional pump and natural circulation

The photovoltaic/thermal system with direct-coupled photovoltaic pump is different from the one with traditional DC pump or with natural circulation. Because for the photovoltaic/thermal system with photovoltaic pump, when the solar irradiation increased the water flow rate of the photovoltaic pump would increase, which would enhance the heat convection between the water and photovoltaic/thermal collectors, and made the water obtain more thermal energy, and when the solar irradiation decreased the water flow rate would also decrease, which would reduce the thermal loss for the one with traditional DC pump. In order to compare the three systems, in this paper three photovoltaic/thermal systems with different circulation methods were set up and tested. And comparison among them was made to analyze their performances. The results showed that the photovoltaic/thermal system with photovoltaic pump had the best thermal performance among the three systems. The net energy obtained by the system with photovoltaic pump was close to or a little more than the system with natural circulation, but which was significantly higher than that of the system with traditional DC pump. For the three systems, the system with natural circulation obtained the highest energy efficiency of 69.63% and the highest exergy efficiency of 12.84%.

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