First, the attenuation of components:
Photo-attenuation is also called the SW effect. The a-Si:H thin film is irradiated with a strong light or current through a long period of time, and defects are generated in the interior of the a-Si:H thin film, which degrades the performance of the thin film. The StaEbler-Wronski effect (DLStaebler and CRWronski) was first discovered. Personally think that the attenuation of PV modules is actually the attenuation of the performance of silicon wafers. First of all, silicon wafers will undergo slow chemical reactions in the long-term aerobic environment to be oxidized, which will reduce the performance. This is the main reason for long-term attenuation of components; during vacuum forming process Doping boron (holes) and phosphorus (donor) in a certain proportion will increase the carrier mobility of the silicon wafer and thus improve the performance of the module, but boron as the electron-poor atom will react with the oxygen atom (donor) , reducing the carrier mobility, thereby reducing the performance of the components, which is the main reason for the decline of the component in the first year of about 2%.
The attenuation of the component is divided into:
1, due to destructive factors caused by the sudden decline in power components, the destructive factor mainly refers to the component in the welding process, welding, the lack of plastic packaging process, or due to improper handling of components in the assembly process, and even components in use In the midst of violent impact by hail, the inside of the module was cracked, and the battery chip was severely broken.
2. The initial photo-induced attenuation of the module, ie, the output power of the photovoltaic module has dropped sharply within the first few days of initial use, but then it has stabilized, generally below 2%;
3. Aging decay of components, ie very slow power drop during long-term use, annual attenuation of 0.8%, 25 years of attenuation not exceeding 20%; 25-year efficiency warranty has been applied in Japan and Germany. The company's components were confirmed. After 2012, the domestic PV modules have basically met the requirements. The equipment and materials for producing PV modules are basically imported from West Germany.
Second, system efficiency:
(Individuals think that the system efficiency can be reduced without considering, and the efficiency of the system can be reduced. We can meet the requirements through the partial update or maintenance of the equipment. As for thermal power stations and hydropower stations, we do not mention attenuation.
The key factors that affect the power generation are the system efficiency. The main considerations for system efficiency include: dust, reduced efficiency due to rain blocking, reduced temperature-induced efficiency, reduced efficiency due to mismatched component series, power loss of the inverter, and direct current AC cable power loss, transformer power loss, tracking system accuracy, and more.
1) Reduced efficiency due to dust and rain blocking
Large-scale photovoltaic power plants are generally located in the Gobi region, with large wind and sand, and little precipitation. Considering that managers have to manually clean the square elements frequently, use attenuation values: 8%;
2) Temperature-induced reduction in efficiency
The solar cell module will have lower output voltage and higher current due to temperature changes. The actual efficiency of the module will be reduced and the amount of power generation will be reduced. Therefore, the temperature-induced reduction in efficiency is an important factor that must be considered. Consider the voltage caused by temperature changes in the design. Change, and select the number of components in series according to the change, to ensure that the component can work in the maximum tracking power range for most of the time. Consider the power change of 0.45%/K, consider the weighted average of the monthly irradiation calculation, and you can calculate The weighted average is obtained because there are certain differences in the ambient temperature in different regions, and there are certain differences in the system efficiency. Therefore, considering the temperature, the value of the system efficiency reduction is 3%.
3) Reduced efficiency due to component mismatch
Due to production process problems, there is a certain deviation between power and current between different components. A single battery module has little effect on the system, but the photovoltaic grid-connected power station is composed of many battery components in series and in parallel because of the power and current between components. Deviations will have a certain effect on the power generation efficiency of photovoltaic power plants. The efficiency of the component in series is reduced due to inconsistent currents, and the efficiency is chosen to be a 2% reduction.
4) DC cable power loss
According to the design experience, the conventional 20MWP photovoltaic grid-connected power generation project uses about 350km of dedicated cable, and the power cable from the combiner to the DC distribution cabinet (usually the specification model is ZR-YJV22-1kV-2*70mm2) is about 35km. The cable loss of the DC portion is calculated to be 3%.
5) Power loss of the inverter
At present, the efficiency of domestically produced high-power inverters (500kW) has basically reached a system efficiency of 97.5%. The grid-connected inverters are transformerless, and two parallel-connected inverters are isolated by a double-split transformer. The inverters are not internally connected. Considering the transformer efficiency, the inverter power loss can be 97.5%, taking 97.5%.
6) Power loss of AC cable
Because photovoltaic grid-connected power stations generally use on-site boosting for grid connection, AC cables are usually high-voltage cables. The loss of this part is small, and the cable loss in the calculation AC part is about 1%.
7) Transformer power loss
The transformer is a mature product, and a high-efficiency transformer is selected. The transformer efficiency is 98%, that is, the power loss is about 2%.
Integrate the power loss of each part above and measure the efficiency of the system: component dust loss, component temperature efficiency loss, component mismatch loss, line pressure drop loss, inverter efficiency, step-up transformer efficiency, AC line loss, etc., can be calculated PV system efficiency:
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%.
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