1. Temperature characteristics of photovoltaic modules
Photovoltaic modules generally have three temperature coefficients: open circuit voltage, short circuit current, and peak power. When the temperature increases, the output power of photovoltaic modules will decrease. The peak temperature coefficient of mainstream crystalline silicon photovoltaic modules in the market is about -0.38~0.44%/℃, that is, as the temperature increases, the power generation of photovoltaic modules decreases. In theory, for every degree of temperature increase, the power generation decreases by about 0.38%.
It is worth noting that as the temperature increases, the short-circuit current is almost unchanged, while the open-circuit voltage decreases, indicating that the ambient temperature will directly affect the output voltage of the photovoltaic module.
2. Aging decay
In long-term practical applications, the components will experience slow power decay. As can be seen from the two figures below, the maximum attenuation in the first year is about 3%, and the annual attenuation rate in the next 24 years is about 0.7%. Based on this calculation, the actual power of photovoltaic modules after 25 years can still reach about 80% of the initial power.
There are two main reasons for aging attenuation:
1) The attenuation caused by the aging of the battery itself is mainly affected by the battery type and the battery production process.
2) The attenuation caused by the aging of the packaging material is mainly affected by the component production process, the packaging material and the use environment. Ultraviolet radiation is an important reason for the deterioration of the performance of the main material. The long-term irradiation of ultraviolet rays causes the EVA and the back sheet (TPE structure) to age and turn yellow, resulting in a decrease in the transmittance of the module and a decrease in power. In addition, cracking, hot spots, sand abrasion, etc. are all common factors that accelerate the power attenuation of components.
This requires component manufacturers to strictly control the selection of EVA and backplanes to reduce the power attenuation of components caused by the aging of auxiliary materials. As one of the first companies in the industry to solve the problems of light-induced attenuation, light-induced high temperature attenuation and potential-induced attenuation, Hanwha Q CELLS relies on its Q.ANTUM technology to provide anti-PID, anti-LID and anti-LeTID, hot spot protection, and quality tracking. Tra.QTM's quadruple power generation guarantee has won wide recognition from customers.
3. Component initial light-induced attenuation
The initial light-induced attenuation of the module, that is, the output power of the photovoltaic module has a relatively large drop in the first few days of use, but then tends to be stable, and the degree of light-induced attenuation of different types of cells is different:
In P-type (boron-doped) crystalline silicon (single crystal/polycrystalline) silicon wafers, light or current injection leads to the formation of boron-oxygen complexes in the silicon wafers, which reduces the minority carrier lifetime, so that some photogenerated carriers are recombined, reducing the cell efficiency, causing light-induced attenuation.
However, the photoelectric conversion efficiency of amorphous silicon solar cells will drop sharply in the first half a year of use, and eventually stabilize at about 70% to 85% of the initial conversion efficiency.
4. Dust cover
Large-scale photovoltaic power plants are generally built in the Gobi region, where there is relatively large sandstorms and less precipitation. At the same time, the frequency of cleaning is not too high. After long-term use, it can cause an efficiency loss of about 8%.
5. Component series mismatch
The mismatch of components in series can be explained by the barrel effect. The amount of water in the barrel is limited by the shortest wooden board; and the output current of the photovoltaic module is limited by the lowest current in the series module. In fact, there will be a certain power deviation between components, so the mismatch of components will cause a certain power loss.