Module reliability and service lifetime are critical factors in improving photovoltaic system performance and reducing the levelized cost of electricity (LCOE). Soldering and lamination of the cell impart residual stresses that persist over time and superimpose additional loads during operation. This paper demonstrates the use of X-ray Topography (XRT) to image in-situ the dynamic response of a glass/backsheet mini-module upon drying at elevated temperature after saturation at humidity levels compatible with accelerated testing. The local water content in the encapsulant is also determined in-situ over time via Water Reflectometric Detection (WaRD), with diffusion of water in the front (glass side) and rear (backsheet side) resolved. As water diffuses out from the back of the glass/backsheet module, the cell curves towards the backsheet concomitantly. Here we find that the cell edges deflect 40μm out-of-plane with respect to its center while the encapsulant dries, compared to ~100 μm deflection when heating from 25°C to 85°C. The local cell deflections (changes in cell orientation) are correlated with the dynamic loss of water in the backside encapsulant. We conclude that the observed cell deflections are the result of hygroscopic stress induced by the encapsulant upon moisture outdiffusion. Therefore, the cell experiences a continually changing stress state and curvature dependent on local humidity and temperature. Depending on cell architecture and interconnection, this “breathing” mode of the cell may induce wear out and fatigue of the interconnects, affect the electrical connection of cracked pieces or cause failure near the interconnected edges of two cells.
Slauch, Ian M., et al. "In-situ determination of moisture- and temperature-driven deflection of an encapsulated Si photovoltaic cell." Solar Energy Materials and Solar Cells, vol. 254, no. C, Feb. 2023. https://doi.org/10.1016/j.solmat.2023.112262
Slauch, Ian M., Gandhi, Hir, Kumar, Rishi E., Sidawi, Tala, Tracy, Jared, Choudhury, Roy Kaushik, Meier, Rico, Fenning, David P., & Bertoni, Mariana I. (2023). In-situ determination of moisture- and temperature-driven deflection of an encapsulated Si photovoltaic cell. Solar Energy Materials and Solar Cells, 254(C). https://doi.org/10.1016/j.solmat.2023.112262
Slauch, Ian M., Gandhi, Hir, Kumar, Rishi E., et al., "In-situ determination of moisture- and temperature-driven deflection of an encapsulated Si photovoltaic cell," Solar Energy Materials and Solar Cells 254, no. C (2023), https://doi.org/10.1016/j.solmat.2023.112262
@article{osti_2424776,
author = {Slauch, Ian M. and Gandhi, Hir and Kumar, Rishi E. and Sidawi, Tala and Tracy, Jared and Choudhury, Roy Kaushik and Meier, Rico and Fenning, David P. and Bertoni, Mariana I.},
title = {In-situ determination of moisture- and temperature-driven deflection of an encapsulated Si photovoltaic cell},
annote = {Module reliability and service lifetime are critical factors in improving photovoltaic system performance and reducing the levelized cost of electricity (LCOE). Soldering and lamination of the cell impart residual stresses that persist over time and superimpose additional loads during operation. This paper demonstrates the use of X-ray Topography (XRT) to image in-situ the dynamic response of a glass/backsheet mini-module upon drying at elevated temperature after saturation at humidity levels compatible with accelerated testing. The local water content in the encapsulant is also determined in-situ over time via Water Reflectometric Detection (WaRD), with diffusion of water in the front (glass side) and rear (backsheet side) resolved. As water diffuses out from the back of the glass/backsheet module, the cell curves towards the backsheet concomitantly. Here we find that the cell edges deflect 40μm out-of-plane with respect to its center while the encapsulant dries, compared to ~100 μm deflection when heating from 25°C to 85°C. The local cell deflections (changes in cell orientation) are correlated with the dynamic loss of water in the backside encapsulant. We conclude that the observed cell deflections are the result of hygroscopic stress induced by the encapsulant upon moisture outdiffusion. Therefore, the cell experiences a continually changing stress state and curvature dependent on local humidity and temperature. Depending on cell architecture and interconnection, this “breathing” mode of the cell may induce wear out and fatigue of the interconnects, affect the electrical connection of cracked pieces or cause failure near the interconnected edges of two cells.},
doi = {10.1016/j.solmat.2023.112262},
url = {https://www.osti.gov/biblio/2424776},
journal = {Solar Energy Materials and Solar Cells},
issn = {ISSN 0927-0248},
number = {C},
volume = {254},
place = {United States},
publisher = {Elsevier},
year = {2023},
month = {02}}