Component attenuation
Light-induced attenuation is also called the S-W effect. After a long period of strong light irradiation or current passing through the a-Si: H thin film, defects will be generated inside it and the performance of the thin film will be reduced, which is called the StaEbler-Wronski effect (D.L.Staebler and C.R.Wronski first discovered. Personally think that photovoltaic modules The attenuation of the silicon wafer is actually the attenuation of the performance of the silicon wafer. First, the silicon wafer will undergo a slow chemical reaction and be oxidized in a long-term aerobic environment, thereby reducing the performance.
This is the main reason for the long-term attenuation of the component; Doping boron (hole) and phosphorus (donor) can increase the carrier mobility of the silicon wafer, thereby improving the performance of the component, but boron, as an electron-deficient atom, will undergo a recombination reaction with oxygen atoms (donor), reducing the current carrying capacity. Sub-mobility, thereby reducing the performance of the module, which is the main reason why the module decays by about 2% in the first year.
The attenuation of components is divided into:
1. Sudden attenuation of component power due to destructive factors. The destructive factors mainly refer to poor welding of components during the welding process, lack of glue in the packaging process, or improper operation of components during handling and installation, or even components during use. During the severe impact of hail, the internal cracks of the components and the severe shattering of the cells were caused;
2. The initial light-induced attenuation of the module, that is, the output power of the photovoltaic module drops significantly in the first few days of use, but then tends to be stable, generally below 2%;
3. The aging and attenuation of components, that is, the extremely slow power decline phenomenon in long-term use, the annual attenuation is 0.8%, and the attenuation in 25 years does not exceed 20%. confirmed on the company’s components. After 2012, domestic photovoltaic modules basically met the requirements, and the equipment and materials for the production of photovoltaic modules are basically imported from West Germany.
System efficiency
(Personally, I don’t think system efficiency attenuation needs to be considered. For system efficiency reduction, we can meet the requirements through partial updates or maintenance of equipment. Just like thermal power stations and hydropower stations, the term attenuation is not mentioned.
The key factor affecting power generation is system efficiency. The main considerations for system efficiency are: efficiency reduction caused by dust and rain occlusion, efficiency reduction caused by temperature, efficiency reduction caused by series mismatch of components, power loss of inverter, DC AC cable power loss, transformer power loss, tracking system accuracy, etc.
1) Efficiency reduction caused by dust and rain blocking
Large-scale photovoltaic power plants are generally located in the Gobi area, with strong wind and sand and little precipitation. Considering the frequency of manual cleaning of square array modules by managers, the attenuation value is used: 8%;
2) Efficiency reduction due to temperature
Due to temperature changes, the output voltage of solar cell modules will decrease, the current will increase, the actual efficiency of the components will decrease, and the power generation will decrease. Therefore, the efficiency decrease caused by temperature is an important factor that must be considered. The voltage caused by temperature changes should be considered in the design. change, and select the number of modules connected in series according to the change, to ensure that the modules can work within the maximum tracking power range for most of the time, considering the power change of 0.45%/K and calculating the weighted average value of the monthly radiation, it can be calculated The weighted average value is obtained. Due to certain differences in ambient temperature in different regions, there are certain differences in the impact on system efficiency. Therefore, considering the temperature-induced reduction in system efficiency, the value is 3%.
3) Efficiency reduction caused by series mismatch of components
Due to production process problems, there is a certain deviation in power and current between different modules. A single battery module has little impact on the system. However, a photovoltaic grid-connected power station is composed of many battery modules connected in series and parallel. Due to the power and current differences between modules Deviations will have a certain impact on the power generation efficiency of photovoltaic power plants. If the modules are connected in series, the efficiency will be reduced due to the inconsistency of the current. The efficiency is selected as a 2% reduction.
4) DC cable power loss
According to the design experience, the amount of dedicated photovoltaic cables used in conventional 20MWP photovoltaic grid-connected power generation projects is about 350km, and the amount of power cables from the combiner box to the DC power distribution cabinet (generally used specification model is ZR-YJV22-1kV-2*70mm2) is about 35km , the calculated cable loss of the DC part is 3%.
5) Power loss of the inverter
At present, the efficiency of domestically produced high-power inverters (500kW) basically reaches a system efficiency of 97.5%. Consider the transformer efficiency, that is, the inverter power loss can be 97.5%, take 97.5%.
6) Power loss of AC cables
Since photovoltaic grid-connected power stations generally adopt the local boost method for grid connection, the AC cables are usually high-voltage cables, and the loss in this part is relatively small. The calculated cable loss in the AC part is about 1%.
7) Transformer power loss
The transformer is a mature product, and a high-efficiency transformer is selected. The efficiency of the transformer is 98%, that is, the power loss is about 2%.
Based on the power loss of the above parts, the efficiency of the system can be calculated: component dust loss, component temperature efficiency loss, component mismatch loss, line voltage drop loss, inverter efficiency, step-up transformer efficiency, AC line loss, etc., can be calculated Efficiency of photovoltaic power plant system:
System efficiency: η=(1-8%)*(1-3%)*(1-2%)*(1-3%)*(1-2.5%)*(1-1%)*(1- 2%)=80.24%.
After the above analysis, it can be concluded that the system efficiency of photovoltaic grid-connected power plants is usually 80%.
At the same time, there will be cracks in the entire photovoltaic module from the silicon wafer to the installation of the power station components. If it cannot be found in advance, the components made of the cracked material will cause very large losses. The EL detector is in this process. The internal defect test is carried out in the process, including problems such as virtual soldering, broken grid, hidden cracks, low-efficiency chips, edge leakage, and over-cutting.