At the 2018 PVSEC conference held in Belgium in September, seven researchers from the German Fraunhofer CSP (Fraunhofer Photovoltaic Silicon Research Center) jointly released a research report, Benchmarking light and elevated induced degradation, LETID. The components used for testing this time were randomly purchased by Fraunhofer researchers on the market, not the kind of "golden" samples that are usually made by companies for testing. It can be said that the components selected for testing represent the general characteristics of circulating components in the market.
The report details the LeTID of the single polycrystalline PERC module, which is the "attenuation due to light and high temperature" test results. The results of the report show that the average light attenuation of single-crystal PERC modules exceeds that of polycrystalline PERC modules by more than 1.7%.
They selected a total of 6 different brands of monocrystalline PERC modules and 3 different brands of polycrystalline PERC modules. For each type of brand component, choose two pieces each, a total of 9 pairs of components and 18 samples.
R. Gottschalg, Fraunhofer CSP, 35th EUPVSEC, 2018
Under the same stringent test conditions, they performed attenuation tests on 18 samples (2 in each group, a total of 9 groups). The test results show that the light attenuation of all six samples of three groups of polycrystalline PERC is less than 2%, of which one group has almost no attenuation; while the 12 samples of six groups of single crystal PERC have a maximum attenuation of more than 6%. Polycrystalline average attenuation is about 0.9%, single crystal average attenuation is about 2.6%. The single crystal PERC module's light attenuation average exceeds that of the polycrystalline PERC module by more than 1.7%.
One might ask, is the result of the Fraunhofer Solar Institute credible?
According to Baidu search results, the Fraunhofer Solar Energy Research Institute, established in Germany in 1986, is currently the largest solar testing center in Europe, with a total of 1,200 employees. As of the end of 2016, the institute has a total of 123 PhDs and is a global heavyweight photovoltaic test center. Fraunhofer has been designated by many customers as an authoritative and trusted third-party component testing agency, and its test results are the ultimate basis for many component performance disputes.
Why doesn't PERC technology really solve the serious attenuation problem of single crystal?
The attenuation of conventional single crystals is caused by congenital defects in single crystal silicon materials.
The inherent properties of a single crystal are determined by its semiconductor physical properties.
One of the factors for light attenuation is the oxygen content of the silicon wafer. The higher the oxygen content of the silicon wafer, the greater the light attenuation. Polycrystalline silicon wafers have less oxygen than single crystals.
The oxygen content of polycrystalline silicon wafers is much lower than that of single crystals, so the concentration of "boron oxygen" defects that cause light decay is much lower than that of single crystals. Therefore, the conventional polycrystalline modules have a light decay that is less than that of single crystals. This is reflected in the fact that almost all manufacturers' polycrystalline modules have a first-year attenuation warranty lower than 0.5% compared to single crystals. Therefore, for large and medium-sized power stations that focus on yield, polycrystalline modules are used almost without exception.
While PERC technology improves battery efficiency and component power, the risk of light decay is also greatly increased. Therefore, in the manufacturing process of single crystal PERC and polycrystalline PERC, it is necessary to take anti-light decay treatment of the battery. Common anti-fading treatment measures are through silicon wafer doping changes, battery process optimization, and hydrogen passivation of the battery.
Another important reason for the misunderstanding is that the current light decay test conditions are too loose, and the influence of high temperature on the attenuation of the silicon wafer is not considered, thereby underestimating the light decay risk of single crystal PERC.
As Fraunhofer reports: under the combined effect of light and temperature, the attenuation of single crystal PERC is large, up to 6%.
So how does the light decay performance of polycrystalline PERC components?
Artes' R & D team has conducted in-depth research for more than 5 years on the attenuation mechanism and anti-light attenuation treatment of polycrystalline PERC. They have accumulated a lot of experience and lessons in materials, processes, equipment and attenuation test methods, and also independently Developed technology and process for resisting light decay. AT & S achieved mass production of GW-level low-light decay polycrystalline PERC cells and modules in 2018, and plans to achieve PERC of all polycrystalline products in early 2019.
Our outdoor module test monitoring data show that the light attenuation of AT & S polycrystalline PERC modules is even lower than that of our conventional polycrystalline modules. The average long-term light attenuation is <1%, and the module's power generation performance is very good.
In order to verify the light attenuation results of Canadian Polysilicon PERC modules, we also sent the polycrystalline PERC cells to UNSW for testing at the University of New South Wales, Australia. UNSW's light attenuation test is performed under severe conditions: 1000W / m2, 75 ° C, 200 hours. Under such tightening conditions, the average light attenuation of Artes polycrystalline PERC cells is less than 2%. Dr. Abbott Malcolm, director of the UNSW hydrogen passivation project, said: This is the lowest light decay performance of all polycrystalline PERC cells tested by UNSW.
The test results of UNSW and Fraunhofer have once again proven that AT & S polycrystalline PERC products have very low attenuation and have LCOE advantages over conventional polycrystalline or single crystal PERC.