In the accelerating wave of global energy transition, solar photovoltaics (PV) have become one of the primary clean energy sources. A PV module must endure outdoor exposure for over 25 years, facing severe tests such as ultraviolet radiation, temperature cycles from -40°C to +85°C, dust erosion, and humid heat aging. Ensuring long-term power generation efficiency and electrical safety is not just about the quality of the solar cells themselves but also hinges on the unseen yet crucial sealing and encapsulation materials. Among these, high-performance silicone rubber stands out due to its outstanding weather resistance, elastic recovery, and electrical insulation properties, making it indispensable for junction box sealing, frame bonding, and edge protection of dual-glass modules—earning it the title of "the invisible guardian under the sun."

I. Key Sealing Requirements in PV Modules

Over 30% of PV system failures are attributed to moisture intrusion, leading to:

Cell corrosion (EVA yellowing, silver grid oxidation);

Insulation failure (Potential Induced Degradation, PID);

Internal short circuits in junction boxes.

Therefore, sealing materials must meet stringent criteria:

Long-term resistance to humidity and heat (85°C/85%RH for over 3000 hours);

UV aging resistance (no chalking after 5000 hours in QUV testing);

Low water vapor transmission rate (WVTR < 10 g·mm/m²·day);

High volume resistivity (>10¹⁴ Ω·cm);

Excellent adhesion to glass, aluminum, and backsheets.

II. Core Application Scenarios of Silicone Rubber

Junction Box Potting and Sealing

Junction boxes serve as points where currents converge; internal diodes and solder joints are prone to moisture-induced failures.

Two-component addition-cure thermally conductive silicone rubber is widely used for potting:

Thermal conductivity: 1.0–2.0 W/m·K, aiding heat dissipation;

Low elastic modulus (0.5–1.5 MPa), providing thermal stress relief;

UL 1703 and TÜV certified, with a flame retardancy rating of V-0.

Compared to polyurethane (PU), silicone does not hydrolyze or crack under humid heat conditions, offering longer service life.

Frame and Backsheet Bonding and Sealing

Elastic sealants are required between aluminum frames and glass/backsheet interfaces to prevent rainwater infiltration.

One-component oxime or alkoxy silicone sealants (RTV-1) are commonly applied on-site:

After curing, they form highly elastic joints capable of accommodating thermal expansion and contraction;

Displacement capacity of ±25%, superior to acrylics or MS polymers;

Excellent weatherability ensures no cracking for up to 25 years.

In frameless dual-glass modules, silicone serves as the primary edge-sealing material.

Edge Protection for Dual-Glass Modules

Dual-sided power generation modules use two layers of glass; edges are susceptible to water ingress through microcracks.

High-flow liquid silicone rubber (LSR) is employed to encapsulate edges, forming seamless seals:

Good transparency does not interfere with backside power generation;

Excellent flexibility withstands wind-induced vibrations.

III. Performance Comparison

表格

Material Polyurethane (PU)       Organic Silicone (Silicone) Modified Silane (MS)

Humidity Resistance   Poor (hydrolyzes) Excellent Moderate

UV Resistance     Moderate (yellows)     Excellent (color stable)      Excellent

Elasticity Retention (25 years)   <60%      >85%      70–80%

Adhesion Versatility    Requires primer   Broad (glass/metal/plastic) Broad

Cost       Low High       Moderate

Despite higher costs, silicone's lifecycle reliability makes it irreplaceable in premium modules.

IV. Industry Standards and Certifications

IEC 61215: Specifies requirements for terrestrial PV modules, including DH2000 (damp heat) and TC200 (thermal cycling) tests for sealing materials;

UL 1703: Sets safety standards for flat-plate PV modules, stipulating flame retardancy and electrical insulation for potting compounds;

TÜV Rheinland / CSA: Require detailed mechanical and electrical performance data before and after aging for silicone certification.

Leading companies like Dow, Wacker, and Huithink New Materials have launched "PV-specific silicone rubber" series, claiming lifespans exceeding 30 years.

V. Challenges and Green Trends

Elimination of Acetic Acid Curing Silicones: These release acetic acid, which corrodes silver electrodes, prompting a shift towards neutral curing (oxime, alkoxy);

Low VOC and Solvent-Free: Compliance with environmental regulations (e.g., REACH, RoHS);

Recyclability Design: Exploring thermally reversible silicones to facilitate glass separation during module disposal.

Conclusion

Behind every ray of sunlight converted into clean electricity lies the silent guardianship of silicone rubber. It doesn't generate power but ensures continuous output; it isn’t flashy but resists the harshest elements. From deep within junction boxes to the edges of modules, this flexible silicon-based material responds to the dual tests of time and nature at a molecular level—because true green energy is not just about generating power but also about safeguarding it.



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