| Solar photovoltaic (PV) is one of the most prospects of renewable energy utilization technology. To develop the solar photovoltaic technology possesses strategic significance under the situation which energy is draining and environmental is degradation.The previous experiments has shown that both crystalline and amorphous silicon solar cell, the photoelectric conversion efficiency are decreasing with temperature rise. Crystalline silicon solar cell’s efficiency reduces 0.35%～0.7% with temperature per rising 1℃. Undoubtedly, this feature is extremely unfavorable to the conversion efficiency of battery which working in the environment of strong radiation and high temperature. Researching how to reduce the temperature working in the environment of strong radiation and high temperature have a great significance to improve the efficiency of battery power, prolong the working life of the solar cell.In this paper, the cooling method of natural evaporative has been studied based on the heat transfer model of solar cell module and the direct cooling principle. A solar cell module with aluminum alloy material as the backboard has been designed and produced and the hygroscopic material was applied directly on the back surface of solar module relying on the siphonage moisture distribute the water to the entire surface of components, Carry out the evaporative cooling experiments to test the validity and practicability using the evaporative cooling method. The main content was studied in this paper as listed below:The first chapter summarizes the research status quo of solar cell module cooling method in recent years and describes briefly principle and effect of various cooling method, and expounds the features of evaporative cooling and part of the existing research results, and proposed to the idea which apply hygroscopic materials on solar cell module evaporative cooling;The second chapter analyses the expounds the heat transfer model and principle of direct evaporation cooling。The heat transfer model is built by applying the thermal network method on the basis of combining the law of energy and mass conservation. Analyzing the cooling condition and particularity of solar cell module, and the convective heat transfer state and heat transfer parameter accord with the condition of this experiment. The theory of evaporative cooling has been analyzed. The steady temperature is computed for understanding preliminary the cooling effect.The third chapter designs the experiment scheme of evaporative cooling for solar cell module. The evaporative pads is chosen with the good character of water absorption and repeat water absorbing, and low water retention rate. The key equipment is chosen and then precision calibration. The content of experiment under the different of irradiation and wind velocity and air temperature and relative air humidity (RH) is determined on basis of analysis to verify the role of evaporative cooling. Then the test-bed is built and to carry experiment.The fourth chapter analys is of experimental results. It is all obvious both cooling and not of the temperature effect. The temperature under condition of cooling is obvious higher than without cooling, and the efficiency is decrease as the temperature rising. The temperature distribution is uneven that the result of the water accumulate on the end of pads affected by gravity. Then the linear equation of efficiency with the temperature change is fitting.The fifth chapter analysis the influence factor of evaporation on impacting on the solar cell conversion efficiency. It includes three factors to influence evaporation cooling rate:the wind speed、the RH、the surface area of fluid. The result that RH influences the conversion efficiency of solar cell is analyzed under constant wind speed and that wind speed influences the conversion efficiency of solar cell is analyzed under constant RH. The results show that conversion efficiency of module drops linearly with the increase of RH under the fixed wind speed; Conversion efficiency of module rise linearly with the increase of wind speed under the fixed RH.Conclusion:1. The evaporative cooling is a good method to the solar cell cooling;2. Three evaporative pads is chosen with the good character of water absorption and repeat water absorbing, and low water retention rate in the five kinds of non-woven fabric through the contrast test. In the experiment, the backboard of solar cell module takes on temperature gradient:the largest temperature different is 5℃ of 1# and 6℃ of 2# and 6.5℃ of 3#. The temperature distribution of cloth 1# is more uniform; 3. The cooling effect is obvious using evaporation cooling. The efficiency of solar cell module after evaporative cooling is higher than before cool and the average of efficiency improving:cloth 1# is 13.6% and cloth 2# is 7.2% and cloth 3# is 6.7%; 4. When the average solar radiation intensity is 670 w/m2, the air temperature is 33℃, the wind speed is 3 m/s, it is concluded that RH 5% every rise, the conversion efficiency decrease 0.8% of solar cell module under cooling condition. When average solar radiation intensity is 740 w/m2, the average air temperature is 33℃, RH is 34%, the wind speed every increase 1 m/s, the conversion efficiency increased by 1.7% withoutcooling, and 2.7% with cooling. It shows that wind speed is more obvious influence on the solar cell conversion efficiency under cooling. |
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