The domestic photovoltaic policy has been gradually improved in exploration, and the business environment for investing in photovoltaic power stations is maturing. The new wave of investment in domestic photovoltaic power plants is forming a climate. Under normal circumstances, the normal working life of PV power plants is 20-25 years. During this period, photovoltaic modules inevitably have to withstand various tests. Only with the normal operation of photovoltaic power plants, investors can ensure their own return rate. Therefore, more and more investors are focusing their attention on the selection of component quality. This phenomenon is prompting the development of the domestic photovoltaic industry to move toward rationality.
Frequent quality problems
As the most important basic equipment of a photovoltaic power plant, the quality, power generation capacity, profitability, and value of the power plant are closely related to the components. Components are mainly composed of batteries, packaging materials, backplanes, glass, borders, junction boxes, etc. Among them, the battery is the most important key component, and the external packaging material is to protect its normal and stable operation. Among these key protective materials, the quality of the outermost backsheet is of utmost importance. Once the backsheet fails, the inner packaging material and the cell sheet will disappear with the environment as unprotected flowers.
In the western region of China, rich illumination resources and low land prices have long been an ideal competitive venue for the construction of large-scale photovoltaic power plants. However, in these areas, there are also harsh natural environments such as dry and rainy conditions, serious surface sedimentation, and strong wind and sand activity. With the extension of the outdoor use time of photovoltaic modules, the abrasion of sand and sand will continuously reduce the thickness of the outer skin material of the backplane. This requires the developer to select the outer surface of the backplane and must have strong wear resistance.
“Some polysilicon battery modules have a power attenuation of 3.8%-7.0% for 2-3 years, and amorphous silicon has a power attenuation of 20% for 3 years.†The result of the post-assessment and testing of photovoltaic power stations in Qinghai Province by the Institute of Electrical Engineering of the Chinese Academy of Sciences. According to the survey conducted by the Certification and Certification Center, among the 425 solar power stations that have been surveyed in the country, 30% of the power stations built for more than three years have already experienced varying degrees of problems.
At present, more and more component quality issues are related to the selection of backplanes. The market mainstream backplanes are generally divided into PET backplanes, FEVE backplanes, PVDF films, and PVF backsheets. Among them, the PET back sheet is widely used in Japan, and the outer layer protective material PET Polyester is a non-fluorine material. Non-fluorinated materials have poor weatherability, and the direct exposed polymer chains in the outdoors are easily destroyed by ultraviolet rays and cracking occurs.
This kind of situation is not accidental. PET backplanes began to be used by Japanese manufacturers in the 1990s for roof components that had a 10-year warranty. Some of them were exposed to light and heat yellowing cracks in the open air within a few years, causing the module power to rapidly decay. Cracking of FEVE backings is also more severe, and the same problems have also occurred on PVDF backsheets.
Decay effect rate of return
In recent years due to construction time and cost control factors, the quality of some photovoltaic power plants has yet to be tested.
With the passage of time, component quality problems may occur frequently and eventually affect the sustainable development of the photovoltaic industry. The long-term stable operation of photovoltaic power plants and the reaching of their useful lives have a significant impact on the internal rate of return of the power plant project and the net present value of investment returns.
Taking a 20MW photovoltaic power station in the western part of China as an example, assuming that the annual power attenuation of the module is 0.8% and the service life of the module is reduced from 25 years to 10 years, the internal rate of return of the photovoltaic project will decrease from 11.39% to 4.89%. The present value is reduced by 3.28 yuan/watt.
If the service life of the module is 25 years, the annual power attenuation of the module will increase from 0.8% to 5.0%, the internal rate of return of the project will decrease from 11.39% to 2.02%, and the net present value of investment income will decrease by 4.02 yuan/watt. The fact that the component attenuation rate directly affects the power plant investment return rate becomes an indisputable fact.
Relevant experts believe that the high power attenuation of components is related to the use of new materials that have not been validated outdoors for a long time. Backplanes are the key materials.
The European Union's Joint Research Center (JRC) has conducted more than 20 years of outdoor component empirical research on crystalline silicon modules since the 1980s. It has found that glass-backed components (double-glass components) have significant power fluctuations and fluctuate greatly. 60% is not conducive to long-term stable operation of the power plant. However, in the early days, photovoltaic power plants built abroad used DuPont Solar PVF membrane backsheets (without aluminum membrane). After about 20 years of outdoor use, the power attenuation was less than 20%, and the average annual power attenuation was only 0.3%.
Some domestic research institutes have also conducted relevant research on the long-term power attenuation of domestic photovoltaic systems. Research on the power attenuation of 177 Solarex polysilicon modules of PVF membrane backplanes in Hainan Island by Sun Hui of Sun Yat-sen University also shows that even under hot and humid weather conditions, 23 In these years, the average power attenuation of these components was only 6.1%, and the main reason was due to the drop in short-circuit current due to the yellowing of the encapsulating material EVA.
To ensure the quality of the power station, using a better backplane may be the best and most effective way. The difference between backplane prices is only 0.10-0.12 yuan per watt. This part only needs 25-29 days to recover the cost.
Take DuPont Special Energy PVF film TPx backsheet and single-sided PVDF backsheet as an example, the two are only 0.01-0.02 Yuan/Watt. It only takes 1-4 days to recover the cost difference. The cost of electricity with a good backplane is 0.76 yuan/kWh, but it can bring a net income of 0.14 yuan/kWh. If the material is of low quality and has not been verified by long-term outdoor performance, the useful life may only be 10 years. The cost of 1.07 yuan/kWh will result in a net loss of 0.17 yuan/kWh.
At present, some short-sighted profit-seeking behavior is being corrected. For power plant investors, the selection of proven backsheet materials can ensure the maximum value of the power plant, and the higher returns from better materials selection are also guiding developers to reverse the rational construction of photovoltaic power plants.
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