The dust on the surface of the module can affect the actual radiation receiving capacity of the module. This is obviously also known. In order to increase the radiation receiving capacity of the module, people are also willing to clean the surface of the module assembly.
Is the component that has just been cleaned completely absorbed radiation without hindrance?
It's a pity. It's not.
Where is the problem?
Some people will point out that the reason is the glass on the surface of the component! Because the glass has light transmittance, actually light is not 100% through the glass. This answer is correct 50%, but it does not say the source of the problem.
If just because of the light transmittance, when the component is under power test under the condition of STC, the light itself also passes through the glass, so the nominal power of the component should be considered to be the transmittance of the glass.
However, we noticed that when the component is tested, the light tested is perpendicular to the component. However, in actual projects, the light is irradiated to the surface of the component at various angles. The vertical condition is only a very small part. The source of the problem: Incident angle.
Light enters the glass from the air and reaches the surface of the cell after EVA. During this process, light enters the optically dense medium as shown in Figure 1. In this case, the light transmittance and reflectance are With the change of the incident angle i: When the incident angle i is 0 (normal incidence), the light transmittance is the highest and the reflectivity is the lowest; and as the incident angle i increases, the light transmittance gradually decreases. The reflectivity gradually increases. We call this phenomenon the radiation loss caused by the incident angle loss, also known as IAM (IncidenceAngleModifier) loss
As the incident angle i changes from 0° to 90°, the curve of the transmittance of light in the glass is shown in Fig. 2. It can be seen that the incident angle is about 0~60°, and the decrease of the transmittance is relatively gentle; When the incident angle is between 80 and 90°, the transmittance of the light is almost straight down. However, such a large incident angle usually occurs when the amount of radiation is low in the morning and in the evening. Therefore, from the whole year, the incident angle changes on the photovoltaic The radiation absorption of the components did not cause very serious effects, but it was not so low as to be negligible.
For PV modules with conventional fixed brackets installed with the best inclination angle, the incident angle loss is generally around 1%~3%. Because with the increase of latitude, the height angle of the sun will be reduced as a whole during the year, resulting in an increase in the incident angle. As the time is increasing, the incident angle loss at high latitudes is generally higher than that at low latitudes. However, for the tracking type support, since it tracks the sun in the direction of 1 to 2 axes, it can effectively reduce the incident angle. The incident angle loss is also generally lower than the fixed stent.
In any case, the incident angle loss is a non-negligible part of the PV system's power generation estimation. It is recommended that when calculating the PV system power generation, PVWS and other professional software should be used to analyze the incident angle loss in order to enable more accurate estimation. Power generation.
