Photovoltaic modules are the core part of the photovoltaic power generation system. Their function is to convert solar energy into electrical energy and send it to the 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:
- The attenuation caused by the aging of the battery itself is mainly affected by the battery type and battery production process.
- 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 the selection of 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 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.
Glass panels for photovoltaic cell modules
The panel glass used in photovoltaic cell modules is generally tempered 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 reach more than 90%, the wavelength range of the spectral response is 320-1100nm, and it has a high reflectivity for infrared light greater than 1200nm.
Since the content of iron in solar panel glass is lower than that of ordinary glass, the light transmittance of the glass is increased. Generally speaking, ordinary glass is greenish when viewed from the edge. Since this glass contains less iron than ordinary glass, this glass is whiter than ordinary glass when viewed from the edge of the glass.
In order to reduce the reflection of sunlight and increase the incidence of light, the surface of the solar panel glass is made fluffy by physical and chemical methods. Coating a thin film containing nanomaterials on the surface of the glass, this kind of coated glass can not only significantly increase the light transmittance of the panel glass, but also significantly reduce light reflection, and also has a self-cleaning function, which can reduce rain, dust and other damage to the battery The pollution of the surface of the board keeps it clean, reduces light decay, and improves power generation rate.
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, manufacturers will temper the panel glass, 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.
How to identify the quality of photovoltaic cell components?
Nowadays, solar photovoltaic power generation is widely used not only in cities, but also in villages. As more and more power stations are built on farms, the quality of power stations has become a concern of many owners. For farm users who build photovoltaic power plants, they are not clear about the quality of the equipment, let alone the professional technical knowledge of photovoltaic systems. So how can ordinary users identify the quality of photovoltaic cell components and keep photovoltaic power plants away from hidden dangers?
The most important part of the front end of the power station is the solar cell module, also known as photovoltaic panels, battery panels. Its quality will undoubtedly directly affect the working efficiency and service life of the system. How can a layman distinguish the quality of a battery panel?
1. Look at the merchant.
See component suppliers. See if it is a mainstream brand in the industry. There is a saying that “it is good to enjoy the shade under a big tree”, and the quality assurance and after-sales service of big brand components are guaranteed.
2. Check the welding process.
See if there is any leakage of welding when the cells are connected in series. This can be seen directly from the appearance.
3. Look at the quality of the pressure on the back.
Whether the pressure is uneven, or bubbles, folds, etc. It is not difficult to find air bubbles and wrinkles, they can be seen in sunlight.
4. Look at the frame quality.
Is it strictly rectangular, and is the error too large?
5. Look at the conversion rate.
A high conversion rate is the guarantee of the quality of photovoltaic cell modules! This conversion efficiency is invisible on the surface, and it is necessary to compare the module parameters.
Take the commonly used 60-piece polysilicon photovoltaic module as an example: the conversion efficiency of 250W photovoltaic module is 15.4%; the conversion efficiency of 255W photovoltaic module is 15.7%; the conversion efficiency of 260W photovoltaic module is 16%; The efficiency is 16.3%; the conversion efficiency of 270 W photovoltaic modules is 16.6%; if there is a company that advertises that the conversion rate of polysilicon 60P photovoltaic panels reaches more than 20%, haha! It must be fake!!
Modules are an important part of photovoltaic power plants. Once problems arise, the power generation of photovoltaic power plants built by ordinary people with hard-earned money will not be guaranteed, let alone income. Therefore, no matter in the city or in the countryside, users must learn to self-identify the quality of components and pass the first pass of a good power station.