What factors affect the maximum output power of photovoltaic modules?

Photovoltaic modules are the core part of the photovoltaic power generation system. Its function is to convert solar energy into electrical energy and send it to the storage battery for storage, or to drive the load to work. For photovoltaic modules, the output power is very important, so what factors affect the maximum output power of photovoltaic cell 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 rises, 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, the power generation of photovoltaic modules decreases by about 0.38% for every degree of temperature increase. 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%, which are better than crystalline silicon cells.

2. Aging and attenuation

In the long-term application of photovoltaic modules, there will be slow power decay. The maximum attenuation in the first year is about 3%, and the annual attenuation rate is about 0.7% in the following 24 years. 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 battery production process.

2) The attenuation caused by the aging of packaging materials is mainly affected by the production process of components, packaging materials and the environment of the place of use. Ultraviolet radiation is an important reason for the degradation of the main material properties. Long-term exposure to ultraviolet rays will cause aging and yellowing of the EVA and the backsheet (TPE structure), resulting in a decrease in the transmittance of the component, resulting in a decrease in power. In addition, cracking, hot spots, wind and sand wear, etc. are common factors that accelerate component power attenuation.

This requires component manufacturers to strictly control when selecting EVA and backplanes, so as to reduce component power attenuation caused by the aging of auxiliary materials.

3. Initial light-induced attenuation of components

The initial light-induced attenuation of photovoltaic modules, that is, the output power of photovoltaic modules drops significantly in the first few days of use, but then tends to stabilize. Different types of batteries have different degrees of light-induced attenuation:

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, thereby recombining some photogenerated carriers and reducing the cell efficiency, resulting in light-induced attenuation.

During the first half year of use of amorphous silicon solar cells, the photoelectric conversion efficiency will drop significantly, and finally 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 cover

Large-scale photovoltaic power plants are generally built in the Gobi region, where there is a lot of wind and sand, and little precipitation. At the same time, the frequency of cleaning is not too high. After long-term use, it can cause about 8% loss of efficiency.

5. Components do not match in series

The series mismatch of photovoltaic modules can be explained vividly by the barrel effect. The water capacity of the wooden barrel is limited by the shortest board; while the output current of the photovoltaic module is limited by the lowest current among the series components. In fact, there will be a certain power deviation between the components, so the mismatch of the components will cause a certain power loss.

The above five points are the main factors affecting the maximum output power of photovoltaic cell modules, and will cause long-term power loss. Therefore, the post-operation and maintenance of photovoltaic power plants is very important, which can effectively reduce the loss of benefits caused by failures.
How much do you know about the glass panels of photovoltaic modules?

The panel glass used in photovoltaic cell modules is generally tempered glass with low iron content and ultra-white glossy or suede surface. We also often refer to smooth glass as float glass, suede glass or rolled glass. The thickness of the panel glass we use the most is generally 3.2mm and 4mm, and the thickness of building material-type solar photovoltaic modules is 5-10mm. However, regardless of the thickness of the panel glass, its light transmittance is required to be above 90%, the wavelength range of the spectral response is 320-1l00nm, and it has a high reflectivity for infrared light greater than 1200nm.

Since its iron content is lower than that of ordinary glass, the light transmittance of the glass is increased. Ordinary glass is greenish when viewed from the edge. Since this glass contains less iron than ordinary glass, it is whiter than ordinary glass when viewed from the edge of the glass, so this glass is said to be super white.

Suede refers to the fact that in order to reduce the reflection of sunlight and increase the incident light, the surface of the glass is made fuzzy by physical and chemical methods. Of course, using sol-gel nano-materials and precision coating technology (such as magnetron sputtering method, double-sided immersion method, etc.), a layer of thin film containing nano-materials is coated on the glass surface. This kind of coated glass can not only significantly increase the thickness of the panel The light transmittance of the glass is more than 2%, which can also significantly reduce light reflection, and also has a self-cleaning function, which can reduce the pollution of rainwater, dust, etc. on the surface of the battery panel, keep it clean, reduce light decay, and increase the power generation rate by 1.5 %~3%.

In order to increase the strength of the glass, resist the impact of wind, sand and hail, and protect the solar cells for a long time, we have tempered the panel glass. First, the glass is heated to about 700°C in a horizontal tempering furnace, and then cooled quickly and uniformly by cold air, so that uniform compressive stress is formed on the surface and tensile stress is formed inside, which effectively improves the bending and impact resistance of the glass. After tempering the panel glass, the strength of the glass can be increased by 4 to 5 times compared with ordinary glass.