Solar photovoltaic systems have become one of the most promising systems due to their low environmental impact. Despite the long-term reliability of photovoltaic solar systems under field conditions, with low degradation and failure rates, they are still susceptible to faults such as corrosion and delamination. Among the common reliability issues, the potential-induced degradation (PID) effect of photovoltaic modules can lead to catastrophic failures under field conditions.
PID effect is defined as the power degradation caused by applying high voltage between solar cells and the frame of photovoltaic modules. The composition of crystalline silicon photovoltaic modules is as shown in the diagram below.
The PID effect not only leads to degradation of photovoltaic modules but also results in the failure of crystalline silicon solar modules, causing irreversible losses in practical production applications and having a significant impact on capacity. The PID effect has been demonstrated to cause severe power degradation and rapid shutdown issues in bifacial photovoltaic modules and systems.
Causes of PID Effect
The causes of PID effect are complex and mainly include the following factors:
1. The grounding installation method of photovoltaic module frames in solar power plants results in high potential between solar cells and the ground.
2. External conditions such as temperature, humidity, voltage, light exposure, and grounding conditions on the glass surface.
3. Whether the module has a frame.
4. Different levels of Na+ movement induced by the actual application of materials such as glass, encapsulation films, solar cells, and back panels in photovoltaic modules.
The stability of EVA encapsulation films is greatly influenced by environmental factors, especially ultraviolet, infrared radiation, and humidity. The failure modes induced by the aging of EVA encapsulation films can be summarized as three types: discoloration, delamination, and corrosion. Aging of EVA encapsulation films can lead to optical decoupling due to discoloration (yellowing, browning), resulting in power loss, decreased adhesion, delamination, and corrosion of metal parts caused by acetic acid. The aging of EVA encapsulation films triggers the deacetylation reaction to generate acetic acid, as shown in the diagram below, thereby reducing the film’s pH and accelerating the corrosion of the component’s surface; the acid ions produced by aging cause the migration of Na+ ions in the glass layer, thereby inducing the PID effect.
EVA deacetylation reaction
Research Progress on PID-resistant Modification of EVA Encapsulation Films
In response to the mechanism of PID effect induced by Na+ migration in crystalline silicon modules, PID-resistant modification of EVA encapsulation films mainly involves two aspects: first, inhibiting EVA aging; second, reducing the internal ion migration rate of EVA encapsulation films to prevent the PID effect induced by Na+ migration.
Regarding the former, high-performance anti-aging EVA encapsulation films can be developed through modification. Regarding the latter, because EVA encapsulation films with high volume resistivity imply low ion migration rates within the film, mitigating phenomena such as leakage due to poor insulation can be achieved by increasing the volume resistivity.
COACE R2120 is a silane-grafted photovoltaic-grade EVA used in EVA photovoltaic films to enhance post-aging adhesion, especially to improve the pass rate of PCT aging tests, reduce monomer residue, and improve the yield of encapsulated products.
COACE RM211A is an amino-functionalized acid-resistant additive for EVA photovoltaic films, aimed at enhancing the aging resistance and acid resistance characteristics of EVA films under high temperature and high humidity conditions.
COACE RM210A is an inorganic type of EVA acid-resistant masterbatch. Its advantages include low addition amount, high efficiency, easy dispersion, and minimal impact on transparency.
COACE RM208 is an organic-type acid-resistant masterbatch, relatively similar to the inorganic type, with no impact on transparency. It not only resists acid but also can capture cations, providing some resistance against PID.
COACE R2320 is an epoxy-functionalized EVA anti-PID additive.
Optimal combination schemes:
1- RM210A: 1% + R2320: 4%.
2- RM208: 2% + R2320: 3%.
