In 2014, the installed capacity of photovoltaic power stations in mainland China could reach 10-12 GW, accounting for one-fourth of the world. Since November, photovoltaic power plants in China have entered the peak of construction. However, the completed photovoltaic power plants have experienced large-scale quality problems. The problem of component decay and large-scale outbreak of snails in large ground power stations is just an example. The author conducted surveys and interviews with owners of some power stations in Qinghai, Tibet, and Zhangjiakou, and discovered that some well-known brand components used in power plants will undergo severe component decay within 1-2 years, and snails will explode in large areas. This is closely related to the quality of the components and the plastic materials used, and will affect the return on investment.
According to relevant person in charge of the Beijing Jian Heng Certification Center, the current problems of photovoltaic power plants mainly focus on equipment quality, power station design, power station construction, and power station operation and maintenance. Through the testing of 425 power stations, the main quality issues of photovoltaic modules are: hot spots, cracking and power attenuation. Taking power attenuation as an example, the center tested 11 large-scale ground power stations operating for about one year last year. After considering the uncertainty of the equipment, it was found that about 50% of the components were attenuated by 5% to 10%, about 30%. The power attenuation of the components exceeds 10%, and the attenuation of 8% of the components has exceeded 20%. This means that component companies generally promise a 20% decline in quality assurance in 25 years. Some products have been close to, or even beyond, the guaranteed bottom line after one year of operation.
The rapid investment in China's photovoltaic industry in the first two years, coupled with the low investment threshold, has led to an outbreak of production capacity, and bad money has driven away good money. Many power station developers do not understand component technology and system technology, and simply use a lot of inexpensive, low-quality components simply to pursue investment returns. According to the review of China's domestic power stations, the attenuation of the power generation per unit of the power plant with better control of attenuation can be controlled at around 0.1%; while the attenuation of some untested module products exceeds 60%. The plastic components in solar photovoltaic modules, including: junction boxes, silicone sealing, backsheets, and EVA film, are the weak points of their quality, and EVA film is the weakest part. EVA film is heated and extruded using EVA resin and additives. Since EVA resin itself is easily hydrolyzed to generate acetic acid, acetic acid is one of the important reasons for power attenuation of the module.
Acetic acid can react with the sodium salt in the glass to cause sodium ion migration to cause power decay of the module (PID decay). It can also induce oxidation of silver in the gate line to cause snails. Japan's Chemitox soaked the cells in a solution of dilute acetic acid at a certain concentration and observed changes in the silver gate lines, demonstrating that acetic acid will gradually erode the silver grid lines on the surface of the cell sheet to narrow it.
Through experiments to simulate the harsh natural environment, it was aged at 85 degrees Celsius, 85% humidity, and applied voltage of 1000 V for 96 hours. It was found that the PV modules using low-priced EVA film had 20% to 60% attenuation. This means that the components produced in mainland China may experience a large-scale power failure within 10 years under the condition that the power station environment is not ideal. However, even if the PV module can pass the 96-hour or 192-hour decay test, it is still unclear whether the 25-year lifetime can be guaranteed. Some photovoltaic power plants with large temperature difference between day and night or near waters are in crisis; these sites are often easily selected as PV power station sites due to low prices or lack of specific uses.
With the development of photovoltaic module technology, many countries have imposed increasingly stringent requirements on the anti-fade performance of components. For example, PVEL has proposed that photovoltaic modules need to pass 600 hours of anti-PID aging test, while Japan's Chemitex requires the surface of the module to test anti-PID attenuation performance while retaining the water film.
For the snail-printing problem of photovoltaic modules, there is currently no standard test method. Most of them are made into a cracked state and then assembled into modules. The heat-aging and exposure tests are alternately performed. Some EVA film makers attributed snails to the use of EVA regrind materials and promised quality without using EVA return materials. However, this is actually a blind assurance that the performance and component structure of EVA resins are not fully understood. Many times of plastic processing will bring natural hydrolysis, but in the production of EVA film, there is rarely the possibility of repeatedly processing EVA resin. The relationship between the quality of snails and cell sheets, the water permeability of the back sheet, the formulation of the EVA film, and the processing technology and component design are all related. For EVA film, it is important to improve the anti-hydrolysis resistance of snails.
The components that currently use the PV module power anti-decay solution can maintain power attenuation within 5% after 85 hours of humidity at 85% humidity and 96 hours of aging at 1000V; and use the anti-PID attenuating EVA adhesive from Hiwin New Materials Co., Ltd. The components of the membrane attenuate less than 2% in the tests of several well-known component factories at home and abroad. In the water film anti-decay test of Japan Chemitex, the anti-PID decay EVA film is an important guarantee for China's domestic component manufacturers to pass the test. Haiyouwei's EVA film can guarantee the longevity of photovoltaic modules in a harsh natural environment.
If the calculation is based on 25 years of service life of the power plant, the PV module with a power attenuation of 0.8% and a decay of 5% will have a 9.4% difference in return on investment. The best EVA materials and the worst EVA materials at present have a difference of only 0.03 yuan per watt, as long as the three days of power generation can be equalized. According to a survey conducted by Wind & Sun's 2.6 KW power station (British's first distributed power station) and the Haifeng Jianfengling power station in the United Kingdom, the attenuation of the power station is mainly caused by EVA yellowing and hot spots caused by lightning strikes. If a high-quality EVA is used, the module lifetime may be Can be more than 25 years. Zhang Xue, a technical engineer at CPTV, believes that the common power station owner's investment believes that the lower the cost of the power plant components, the better, but this concept does not consider the 25-year life cycle of the components and the investment return rate of the power plant. Power plant investors should pay attention to the quality of components, and packaging materials, especially EVA materials, have a great influence on the quality of components. The use of low-quality EVA has led to large-scale outbreaks of lightning strikes and power attenuation at power stations, which have become increasingly apparent with the increase in installed capacity in China. Owners invest in photovoltaic power stations, and the selection of EVA materials needs to be done with caution.
The author believes that although low-quality components reduce the installed cost per watt, it also significantly reduces the service life of the power plant, resulting in a decline in the power plant not reaching its useful life, or even scrapping the plant in advance. Investors in power stations should ignore the cost per watt of construction, pay attention to the cost of electricity, and adopt better quality materials.
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