Photovoltaic Module Reliability. John H. Wohlgemuth

Photovoltaic Module Reliability - John H. Wohlgemuth


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of the cells, conductors, connectors and diodes resulting in failed or degraded modules. The PV module package provides for the following functions:

       Mechanical support – holding the cells in place pointing toward the sun.

       Dielectric protection – keeping the high voltage away from people and keeping current from flowing out of the array circuit (to ground or in a loop) where it has the potential to cause a fire.Table 1.2 Typical commercial module constructions.Glass Superstrate: Cry‐Si CellsGlass/encapsulant/cry‐Si cells/encapsulant/backsheetGlass/encapsulant/cry‐Si cells/encapsulant/glassGlass Superstrate: Thin Film CellsGlass/thin film cells on front glass/encapsulant/glass with edge sealGlass/thin film cells on front glass/encapsulant/backsheetGlass/encapsulant/thin film cells on back glass/substrateFlexible substratesTransparent frontsheet/encapsulant/thin film cells/flexible substrateTransparent frontsheet/encapsulant/cry‐Si cells/encapsulant/flexible substrate

       Protection of the cells, diodes and interconnects from the weather (UV, rain, humidity, hail, etc.)

       Coupling of the maximum amount of light energy possible into the solar cells (at all angles at the wavelengths that the cells can utilize).

       Cooling of the cells to minimize their temperature increase.

Cross-sectional drawing of glass/encapsulant/cry-Si cells/encapsulant/backsheet module, with arrows marking the cells, backsheet, and encapsulant. Cross-sectional drawing of glass/encapsulant/cry-Si cells/encapsulant/glass module, with arrows marking the encapsulant and cells. Cross-sectional drawing of flexible cry-Si module, with arrows marking the transparent frontsheet, C–Si cells, flexible or rigid substrate, and encapsulant. Cross-sectional drawing of front glass/thin film cells/encapsulant/back glass modules, with edge seal, thin film PV, front glass, back glass, and encapsulant labeled. Cross-sectional drawing of front glass/encapsulant/thin film cells/substrate modules, with glass, substrate, edge seal, thin film PV, and encapsulant labeled. Cross-sectional drawing of module structures for thin film wafer like cells, with arrows marking the transparent frontsheet, thin film PV on substrates, flexible or rigid substrate, and encapsulant.

      There are only a handful of materials that appear in these drawing so let's briefly take a look at the properties required and those typically selected for use in PV modules.

      Glass: When glass is used as the superstrate, one of the properties of interest is the optical transmittance over the wavelength range, that solar cells can effectively use the photons, from about 300 nm to 1100 nm for cry‐Si for example. To maximize performance without significantly increasing the cost,


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