Liquid encapsulation replaces conventional EVA layers, allowing PV modules to be opened and separated into individual components at the end of their service life
One-cell crystalline silicon modules achieved efficiencies of up to 22.6%, matching reference EVA-encapsulated modules
The concept enables material recovery and reuse, supporting circular PV module design, though further work is needed to scale the approach
Conventional crystalline silicon PV modules typically employ ethylene vinyl acetate (EVA) sheets to encapsulate solar cells. EVA is effective for protection and optical coupling, but is difficult to remove at the end of life. This limits the recovery of materials such as glass, silicon, and silver, raising concerns.
Researchers at Delft University of Technology, in collaboration with PV recycling company Biosphere Solar, proposed a liquid-filled PV module design. The concept replaces conventional polymer encapsulation with a liquid-filled architecture that aims to improve recyclability without compromising performance.
To address this challenge, the researchers developed a circular module concept in which silicon solar cells are encapsulated using a liquid and sealed at the edges with a polyisobutylene (PIB) sealant, rather than laminated with polymer sheets. The design allows the module to be opened, drained, and separated into individual components at the end of life.
For the experiment, the researchers used standard tempered float glass instead of specialized solar glass. One-cell prototypes were built using 25 cm × 25 cm glass. Larger demonstrator modules used 50 cm × 50 cm glass with circular openings. The modules were assembled with commercially available n-type BC crystalline silicon solar cells.
The study evaluated 8 selected liquids using optical, electrical, thermal, and safety criteria. These included silicone oil, ester oil, glycol-based liquids, glycerol, and deionized water. Optical measurements showed that several liquids have refractive indices close to glass. Silicone oil and ester oil exhibited stable performance, while deionized water and some glycol-based liquids caused corrosion or compatibility issues.
Liquid-encapsulated one-cell crystalline silicon modules reached efficiencies of 21.9% to 22.6%. Silicone-oil-filled modules achieved 22.6%, comparable to EVA-encapsulated references, whereas air-filled modules showed lower efficiency.
Modules filled with silicone oil and ester oil showed stable performance over 1,300 hours of damp-heat testing and 200 thermal cycles. Liquids like deionized water and certain glycol-based formulations, were excluded after exhibiting corrosion or compatibility issues with module components under prolonged stress. Electroluminescence(EL) imaging revealed no new cracks or hotspots in the best-performing liquid-filled modules after testing.
Beyond performance and reliability, the primary advantage of the liquid encapsulation concept is end-of-life handling. The researchers showed that liquid-filled modules can be opened by cutting the edge sealant. This allows the liquid, glass, cells, and interconnections to be separated without shredding or high-temperature processing.
Recovered glass and silicon cells were reused to fabricate new modules with similar efficiency. Most major components could be repurposed, although the PIB sealant was not reused. The results suggest that liquid encapsulation could offer a viable pathway toward circular PV module design, combining competitive performance with easier disassembly and material recovery. The authors also note that the approach may be relevant for emerging technologies such as perovskite-silicon tandem solar cells, where moisture protection remains a key challenge. The design still needs to be scaled beyond one-cell prototypes. Liquid-sealant compatibility must also be improved for outdoor use. The results indicate that circularity can be improved without loss of efficiency or reliability.
The research was published in Progress in Photovoltaics: Research and Applications under the title “Liquid PV Module Encapsulation to Enable Circular Design”.
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