Concentrated photovoltaic (CPV) is a new kind of solar power generation technology. In the concentrated photovoltaic power generation system, the injection of high light intensity will lead to the generation of high heat (generally 25% to 36% of the incident light is converted into electrical energy), which will increase the temperature of the battery, and the increase in temperature will greatly reduce the output efficiency of the battery. Therefore, it is necessary to effectively cool the battery. The liquid immersion cooling method is used to cool the battery, that is, the solar battery is directly immersed in the insulating medium, and the heat of the battery surface is taken away by the flowing cooling liquid, which can effectively cool the solar battery. . However, the concentrating system works outdoors for a long time, and the light, heat, oxygen, rain, snow and wind in the natural environment are constantly eroding all parts of the system. All parts of the photovoltaic system are required to have a consistent service life to avoid damage caused by one place. The whole system is paralyzed. In order to ensure the reliable operation of the photovoltaic cooling system, it is necessary to investigate the effect of two main factors, high temperature and strong ultraviolet rays, on the cooling medium.
1. Changes in oil properties
1.1 Rate change
1) At 85°C, the silicone oil before the experiment was used as the reference solution, and the silicone oil after each experiment was used as the test solution, and the following spectral transmittance curves were obtained. The transmittance of silicone oil in the 300nm and below bands drops sharply when the experiment time is longer than 800h. During the investigation period, since the silicon cell does not respond to the spectrum before 400nm, the human radiation of the silicon cell immersed in the silicone oil is not reduced. Since the spectral transmittance decreases before 320nm, that is, the absorption of the liquid increases, so the ineffective light incident on the battery is reduced, thereby reducing the battery temperature. For multi-junction concentrating cells, the spectral response range is extended to 300~1800nm, and immersion in this liquid may cause a small amount of incident light loss.
2) In the experiment at 150°C, regardless of whether there is oxygen in the silicone oil or whether there is a battery, the transmittance does not decrease when the spectrum is greater than 400nm; from 400nm, the transmittance decreases rapidly with the decrease of the wavelength, and it can only reach 250nm. 10%. Combined with the 85°C experiment, it can be proved that oxygen and batteries do not increase the attenuation of the silicone oil transmission rate, and temperature is the main factor that reduces the liquid transmission rate. After the coupling experiment, the liquid decreased less than 150°C and more than 85°C. Because the temperature of the liquid in the coupling experiment is close to 85°C, it can be concluded that ultraviolet rays can promote the decrease of the low-band spectral transmittance of silicone oil, and the increase in temperature can also promote decrease in transmittance.
Under ultraviolet irradiation, when the silicone oil is added without a battery, the presence of oxygen has almost no effect on the transmittance of the silicone oil. It greatly promotes the reduction of the low-band spectrum of silicone oil. The reason may be that high-energy ultraviolet photons excite some substances on the surface of the battery, and the dissolution of silicone oil causes a decrease in transmittance. In the presence of oxygen, this effect is more severe. strong. The UV irradiation time (72h) of the coupling experiment is shorter than that of the UV experiment (120h), and the decrease of the silicone oil transmittance after the coupling experiment is also smaller than that of the UV experiment. Therefore, it can be seen that temperature and ultraviolet coupling have no obvious effect on the change of the properties of silicone oil.

1.2 Infrared spectrum test
After the experiment, the position and shape of the characteristic peaks of simethicone oil did not change, especially in the fingerprint area (the fingerprint area is 1300~650cmˉ1). The reflected absorption peaks in all regions will almost overlap, but the intensity is slightly different, which is caused by the different amount of sample added during the test. The convex peak near 3500cmˉ1 after the experiment in the figure is the miscellaneous peak introduced by the incomplete drying of the KBr used to make the tablet during the test, and the peak near 2300cmˉ1 is the Si-H characteristic peak, which should be formed by silicone oil and a small amount of water in KBr. Therefore, the microscopic molecular structure of the silicone oil has not changed from the infrared spectrum experiment.

1.3 Changes in battery characteristics
Battery Electrical Performance Test
The figure shows the change of the electrical properties of the liquid immersion battery before and after the experiment. The open circuit voltage and short circuit current of the battery before and after the experiment change irregularly and the amplitude is very small. The calculated maximum relative change rate of V is 0.0421, and the maximum relative change rate is 0.034. It can be seen that the experiment has almost no effect on the open circuit voltage and short circuit current of the battery, or The effect is too small to be accurately detected. Considering possible test errors, it can be considered that the electrical performance of the silicon battery has not declined after the above experiments. This is because the chemical properties of silicone oil are stable, and the thermal stability is also good. At the same time, the silicon solar cell itself has good physical and chemical stability, so the performance of the cell does not change significantly under the experimental conditions used in this paper.