What are the factors that affect the power generation of photovoltaic power plants?
1. Area and material properties of lighting panels
2. Local lighting time
3. The elevation and orientation of the lighting panel
4. Climate conditions
5. The power, material, conversion efficiency and FF ratio of the solar panel itself
6. The material of the connecting line, the quantity depends on the size of the line loss
7. Covering on the surface.
Next, let's understand and address some of the factors that affect photovoltaic power generation.
1. The influence of temperature
The reasons for the high component temperature:
1. The internal circuit of the component is short-circuited
2. There is virtual welding between the cells inside the module, which means that the welding is not reliable.
3. The module is used in the area where the radiation intensity is too high. There are cells in the module that are cracked and heated by the current impact.
Second, the impact of occlusion
The influence of dust cannot be underestimated. The dust on the surface of the panel has the functions of reflecting, scattering and absorbing solar radiation, which can reduce the transmittance of the sun, resulting in the reduction of the solar radiation received by the panel and the reduction of the output power. The cumulative thickness is proportional. The shade of houses, leaves and even bird droppings on the photovoltaic modules will also have a relatively large impact on the power generation system. The electrical characteristics of the solar cells used in each module are basically the same, otherwise the so-called hot spot effect will occur on the cells with poor electrical performance or shaded. A shaded solar cell module in a series branch will be used as a load to consume the energy generated by other illuminated solar cell modules, and the shaded solar cell module will heat up at this time, which is the hot spot phenomenon, which is serious damage to the solar cell module. In order to avoid the hot spot of the series branch, it is necessary to install a bypass diode on the photovoltaic module to prevent the hot spot of the parallel circuit. A DC fuse needs to be installed on each PV string. Even without the hot spot effect. Shading of solar cells also affects power generation
3. Corrosion Effects
The real power generation of the module is the circuit composed of cells and bus bars. The glass, backplane, and frame are all peripheral structures that protect the internal structure (of course, there are certain functions to increase power generation, such as coated glass). If only the peripheral structure is corroded , it will not have a big impact on the power generation in the short term, but in the long run, it reduces the life of the components and indirectly affects the power generation.
The surface of photovoltaic panels is mostly made of glass. When wet acidic or alkaline dust adheres to the surface of the glass cover, the glass surface will be slowly eroded, resulting in the formation of pits and depressions on the surface, resulting in diffuse reflection of light on the surface of the cover. , the propagation uniformity in the glass is destroyed. The rougher the cover plate of the photovoltaic module, the smaller the energy of the refracted light, and the actual energy reaching the surface of the photovoltaic cell decreases, resulting in a decrease in the power generation of the photovoltaic cell. And rough, sticky surfaces with adhesive residue tend to accumulate more dust than smoother surfaces. Moreover, the dust itself will also absorb dust. Once the initial dust exists, it will lead to more dust accumulation and accelerate the attenuation of photovoltaic cell power generation.
4. Component attenuation
PID effect (Potential Induced Degradation), also known as Potential Induced Degradation, is the encapsulation material of the battery module and the material on its upper and lower surfaces. Ion migration occurs under the action of high voltage between the battery and its grounded metal frame, resulting in the performance of the module. attenuation phenomenon. It can be seen that the PID effect has a huge impact on the output power of solar cell modules, and it is the "terrorist killer" of the power generation of photovoltaic power plants.
In order to suppress the PID effect, component manufacturers have done a lot of work in terms of materials and structures, and have made certain progress; such as the use of anti-PID materials, anti-PID batteries and packaging technology. Some scientists have done experiments. After the decayed battery components are dried at a temperature of about 100 ° C for 100 hours, the decay caused by PID disappears. Practice has proved that the component PID phenomenon is reversible. The prevention and control of PID problems is mainly carried out from the inverter side. First, the negative grounding method is used to eliminate the negative voltage of the negative pole of the components to the ground; by increasing the voltage of the components, all components can achieve positive voltage to the ground, which can effectively to eliminate the PID phenomenon.
5. Detect components from the inverter side
String monitoring technology is to install a current sensor and a voltage detection device at the input end of the inverter component to detect the voltage and current value of each string, and to judge the operation of each string by analyzing the voltage and current of each string. Check whether the situation is obviously normal. If there is an abnormality, the alarm code will be displayed in time, and the abnormal group string will be precisely located. And it can upload fault records to the monitoring system, which is convenient for operation and maintenance personnel to find faults in time.
Although the string monitoring technology increases a little cost, which is still insignificant for the entire photovoltaic system, it has a great effect:
(1) Early detection of module problems in time, such as module dust, cracks, module scratches, hot spots, etc., are not obvious in the early stage, but by detecting the difference in current and voltage between adjacent strings, it is possible to analyze whether the strings are faulty . Deal with it in time to avoid greater losses.
(2) When the system fails, it does not require on-site inspection by professionals, and can quickly determine the type of failure, accurately locate which string, and the operation and maintenance personnel can solve it in time to minimize losses.
6. Component cleaning
cleaning time
The cleaning work of distributed photovoltaic power generation components should be carried out in the early morning, evening, night or rainy days. It is strictly forbidden to choose the cleaning work around noon or during the period when the sun is relatively strong.
The main reasons are as follows:
(1) Prevent the loss of photovoltaic array power generation due to artificial shadows during the cleaning process, and even the occurrence of hot spot effects;
(2) The surface temperature of the module is quite high at noon or when the light is good, so as to prevent the glass or the module from being damaged by cold water shock on the glass surface;
(3) Ensure the safety of cleaning personnel.
At the same time, when cleaning in the morning and evening, it is also necessary to choose a period of time when the sun is dim to reduce potential safety hazards. It can also be considered that cleaning work can also be carried out in sometimes rainy weather. At this time, because of the help of precipitation, the cleaning process will be relatively efficient and thorough.
Cleaning steps:
Routine cleaning can be divided into ordinary cleaning and flushing cleaning.
Ordinary cleaning: Use a small dry broom or rag to remove the attachments on the surface of the component such as dry floating ash, leaves, etc. For hard foreign objects such as soil, bird droppings, and sticky objects attached to the glass, a slightly harder scraper or gauze can be used for scratching, but it should be noted that hard materials cannot be used to scratch to prevent damage to the glass surface. According to the cleaning effect, it is necessary to rinse and clean.
Rinse cleaning: For objects that cannot be cleaned off, such as residues of bird droppings, plant sap, etc., or wet soil, which are closely attached to the glass, they need to be cleaned. The cleaning process generally uses clean water and a flexible brush to remove. If you encounter oily dirt, etc., you can use detergent or soapy water to clean the contaminated area separately.
Precautions
The precautions are mainly to consider how to protect the photovoltaic modules from damage and the safety of cleaning personnel when cleaning the photovoltaic power station. details as follows:
1. Dry or damp soft and clean cloth should be used to wipe photovoltaic modules, and it is strictly forbidden to use corrosive solvents or hard objects to wipe photovoltaic modules;
2. The photovoltaic modules should be cleaned when the irradiance is lower than 200W/m2, and it is not advisable to use liquids with a large temperature difference with the modules to clean the modules;
3. It is strictly forbidden to clean the photovoltaic modules under the weather conditions with wind force greater than level 4, heavy rain or heavy snow.