Glass is a very challenging material to study. Under minor deformation, its macroscopic properties are reversible, while its microscopic configurations are irreversible. In simple terms – repetitive heat cycling and/or mechanical deformation of glass weakens the material in ways that cannot be measured without inducing failure. As a result, large format solar panels – greater than our prior commercial standard of roughly 2m2 (roughly 6.5’ by 3.25’) – have questions of longevity to be answered.
Results of the inhomogeneous snow load test have been released for the LONGi Hi-MP solar panel. The test simulates a beamless racking installation, in which the glass back of the module floats under its own strength and does not gain support from the racking structure.
The larger format solar panels – 2.6 m2 (28 ft2)- were able to reach or exceed 6400 pascals (Pa) of force before failing (130 lb/ft2) The press release notes five units were tested, and one of the units reached 7400 Pa.
Per an internet search of ‘what does the water in snow weigh’, light snow might weigh 7 lb/ft2, whereas compacted drift snow – which might build at the base of a solar panel – could weigh 20 lb/ft2 or more.
One limit to a standard mechanical stress test is that it doesn’t specifically focus pressure in the ‘lower’ half of the solar panel, whereas in real world settings that load shifts toward the edge with the deepest snow accumulation. Thus, the creation of the inhomogeneous snow load test, which places increasingly larger weights on the panel, in this case, installed at at 37°.
As module size increases, the local pressure and bending moment begins to increase exponentially. LONGi also tested a 3.1 m2 module – the size of a large format 210 mm solar cell based module – which failed at 4,600 Pa. LONGi recently announced that they had come to a sizing standardization agreement with JA Solar and Jinko Solar for 182mm solar cell based panels. The standardization agreement, among other items, sets the size of 72-cell products at 2,278 × 1,134mm (2.58 m2), with 78-cell panels set at 2,465 × 1,134mm (2.79 m2).
The press release from LONGi is part of the ongoing discussion amongst manufacturers as they settle in on the next generation of solar cell and panel sizing
LONGi included a table sharing the amount of glass deformation that would occur before the module actually breaks. Panel deformation matters because it can crack solar cells, and cracked solar cells lower module performance.
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