What factors affect the maximum output power of photovoltaic modules?

Photovoltaic modules are the core part of photovoltaic power generation systems. Their function is to convert solar energy into electrical energy and send it to batteries for storage or to drive load work. For photovoltaic modules, output power is very important. So, what factors affect the maximum output power of photovoltaic modules?

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 decreases. The peak temperature coefficient of mainstream crystalline silicon photovoltaic modules in the market is approximately -0.38~0.44%/℃. That is, for every one degree increase in temperature, the power generation of photovoltaic modules decreases by about 0.38%. The temperature coefficient of thin-film solar cells will be much better. For example, the temperature coefficient of copper indium gallium selenide (CIGS) is only -0.1~0.3%, and the temperature coefficient of cadmium telluride (CdTe) is about -0.25%, both of which are better than crystalline silicon cells.

2. Aging and attenuation
In the long-term application of photovoltaic modules, slow power attenuation will occur. The maximum attenuation value 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 types of aging attenuation:
1) The attenuation caused by the aging of the battery itself is mainly affected by the battery type and battery production process.
2) The attenuation caused by the aging of packaging materials is mainly affected by the component production process, packaging materials and the environment where it is used. Ultraviolet irradiation is an important cause of performance degradation of main materials. Long-term exposure to ultraviolet rays causes the EVA and backsheet (TPE structure) to age and turn yellow, resulting in a decrease in component transmittance and thus a decrease in power. In addition, cracking, hot spots, wind and sand wear, etc. are all common factors that accelerate the power degradation of components.
This requires component manufacturers to strictly control when selecting EVA and backplanes to reduce component power attenuation caused by the aging of auxiliary materials.

3. Initial light-induced attenuation of components
The initial light-induced degradation of photovoltaic modules means that the output power of photovoltaic modules drops significantly in the first few days of use, but then stabilizes. Different types of batteries have different degrees of light-induced attenuation:
In P-type (boron-doped) crystalline silicon (single crystal/polycrystalline) silicon wafers, illumination or current injection causes the formation of boron-oxygen complexes in the silicon wafers, which reduces the minority carrier lifetime, thereby causing some photogenerated carriers to recombine, reducing the Cell efficiency, causing light-induced attenuation.
On the other hand, the photoelectric conversion efficiency of amorphous silicon solar cells will drop significantly within the first half year of use, and will eventually stabilize at about 70% to 85% of the initial conversion efficiency.
For HIT and CIGS solar cells, there is almost no light-induced attenuation.

4. Dust and rain protection
A power station is a whole composed of many battery panels connected in series and parallel. Middle school physics knowledge tells us that in a series circuit, if one point is broken, the entire circuit will be broken. If one of the parallel circuits is disconnected, the other circuits are still connected. The principle of battery components is the same. In a string of photovoltaic panels, one panel is blocked and the current path is restricted. No matter how much other panels in the string generate electricity, they cannot fully output it.
Using the barrel theory to explain, the amount of water a barrel can hold is determined by the shortest board. The other boards are useless no matter how long they are. The blocked panel is the short board of the barrel, which determines the power generation of the entire string of panels.

5. Mismatch in series connection of components
The mismatch in the series connection of photovoltaic modules can be vividly explained by the barrel effect. The water capacity of the wooden barrel is limited by the shortest wooden board; the output current of the photovoltaic module is limited by the lowest current among the series connected modules. In fact, there will be a certain power deviation between components, so component mismatch will cause a certain amount of power loss.
The above five points are the main factors that affect the maximum output power of photovoltaic cell modules, and will cause long-term power losses. Therefore, the later operation and maintenance of photovoltaic power stations is very important, which can effectively reduce the loss of benefits caused by failures.