The all-day photoelectric and thermal efficiencies obtained by the simulation are larger than those obtained by the experiment, and RE is less than 10%. Analyses of transient performance and performance showed that the error is small. This result verifies the accuracy of the simulation model. When the volume of the circu-lation water tank is 80 L, the all-day photoelectric efficiency is reduced 0.35%, however, the all-day thermal efficiency and the overall efficiency is improved by 1.73%, 1.38%, respectively. Besides, the outlet temperature of the tank increases. For the volume of the circulation water tank of 80 L the all-day photoelectric, thermal efficiency and the overall efficiencies is improved by 0.22%, 0.37%and 0.59%, respectively. The volume of the circulation water tank is 80 L, the overall efficiency of the system is the highest to be about 67.5%. The above-mentioned data show that the 80 L is the best among the three volumes.