(1) The influence of solar irradiance
Since the photo-generated current of the solar cell and the solar irradiance show a roughly linear change trend, the DC output power of the photovoltaic power generation system also shows a corresponding linear change with the solar irradiance. The output power of the system increases exponentially with the solar irradiance.
(2) The influence of the installation inclination of the module
In the design of grid-connected photovoltaic power stations, the design software that calculates the best local inclination angle based on the meteorological data of the NASA database is usually used. However, when there is no NASA meteorological collection point, the closest meteorological collection point to the area will be used. For meteorological data, the best inclination angle calculated by this method is not actually the best inclination angle in the area.
In addition, certain errors will occur during the construction process, such as the installation of photovoltaic brackets, and the deviation may reach 3°~5° or even higher, resulting in the inclination of the photovoltaic array after the construction is not the optimal inclination, which will affect The output power of the photovoltaic power generation system.
(3) The influence of the mismatch loss of the photovoltaic array
The mismatch loss of the photovoltaic array refers to the output power loss of the entire photovoltaic array caused by the inconsistent output power of the cells that make up the photovoltaic module or the inconsistent output power of the photovoltaic modules in the same photovoltaic array.
1) The influence of the shading effect on the output power of the photovoltaic array.
It is very common for photovoltaic power stations to affect the output performance of photovoltaic power stations due to the occlusion of obstructions during operation. The obstructions are generally other square arrays, clouds, trees around the photovoltaic power station, buildings, lightning protection facilities, bird droppings, dust, etc. These obstructions will form a certain shadow on the photovoltaic module, which will affect the performance of the module, and then This leads to a decline in the output performance of the entire photovoltaic power generation system, as shown in Figure 2 and Figure 3.
2) The influence of hot spot effect.
When the photovoltaic module is partially shielded, the photo-generated current of the shielded part of the battery becomes smaller, which is smaller than the current of the unshielded battery in the same module. At this time, the shielded part will be equivalent to the load and consume the output of other batteries. With the continuous increase of energy consumption, a large amount of heat will be generated here, forming a “hot spot”, that is, the “hot spot effect”. The long-term existence of hot spots can cause serious damage to the components. Therefore, in the current photovoltaic modules in the photovoltaic market, a certain number of cells are connected in parallel with a reverse bypass diode. When this part of the cell is partially shielded and the reverse bias voltage reaches the level of the bypass diode connected in parallel with this part of the cell When the voltage is turned on, the bypass diode is turned on, and this part of the battery will be bypassed. Figure 3 Output curve of shaded and unshaded components
The generation of hot spots is avoided, and the component only loses the power of the battery string, as shown in Figure 4.
3) The impact of cracks and fragments of photovoltaic modules.
The phenomenon of hidden cracks and even fragments of the cells in photovoltaic modules may occur during the production and manufacturing of photovoltaic modules and the construction or later operation of photovoltaic power stations. The picture shows the electroluminescence (EL) test chart of the fragmentation phenomenon of photovoltaic modules and the thermal infrared formation of the fragmentation phenomenon as shown in Figure 6.
In Figure 6, cell fragmentation occurred in the circled part. During operation, this part of the electric application will have a ball effect, which will affect the output performance of the entire photovoltaic power generation system.
4) The influence of the PID effect of photovoltaic modules.
During the operation of photovoltaic modules, serious power attenuation may occur-the potential induced degradation (Patential Indueed Degradation, PID) effect of photovoltaic modules. The PID effect refers to the leakage current between the glass, encapsulation material, aluminum frame and the cell in the photovoltaic module, which causes a large amount of charge to accumulate on the surface of the cell, which causes the cell fill factor, open circuit voltage and short circuit current to decrease, resulting in battery power and The phenomenon of component power attenuation. The power generation performance and durability of photovoltaic modules with PID effect are seriously affected; because the leakage current mainly exists between the cells and the packaging material and the aluminum frame, the attenuation degree of the cells near the aluminum frame is relative to that of the central part of the module. The cell is more serious, and the electroluminescence (EL) test chart can clearly show that the brightness of the cell near the module frame is dim. Figures 7 and 8 show the electroluminescence (EL) test diagrams of normal photovoltaic modules and typical photovoltaic modules with PID effect. The component output power is severely reduced, which in turn affects the output performance of the entire system.
When the PID effect occurs, it is necessary to find a way to restore the components. In the laboratory, the general practice is to place the single or if the module in the aging experiment box, and the positive and negative output terminals of the module are short-circuited and connected to the +1000V terminal of the single (multiple) channel PID recovery power supply. The module frame Connect with the ground terminal of the power supply, as shown in Figure 9.
|temperature||25℃||65℃||Impact situation||Temperature coefficient/(1/℃)|
|Maximum power/W||50||40||﹣20%||﹣ 0.5%|
|Peak voltage/V||17.3||14.7||﹣ 15.0%||﹣ 0.38%|
|Peak current/A||2.89||2.72||﹣ 2.9%||﹣ 0.147%|
|Open circuit voltage/V||21.5||18.2||﹣ 15.3%||﹣ 0.38%|
|Short circuit current/A||3.05||3.13||＋2.6%||＋0.065%|
5) The influence of temperature on components.
The higher the temperature of the solar cell module, the lower the working efficiency of the module. As the temperature of the module rises, the working voltage will decrease and the maximum power will also decrease. Take a 50Wp module as an example to illustrate the influence of temperature on module parameters. When its temperature rises from 25°C to 65°C, other conditions remain unchanged. The performance parameters change are shown in Table 1.