The difference in color is due to the composition of the panels. Blue panels are made with monocrystalline silicon cells, while black panels use polycrystalline cells.
[pdf] Monocrystalline silicon consists of silicon in which the crystal lattice of the entire solid is continuous. This crystalline structure does not break at its edges and is free of any grain boundaries.
[pdf] If you see dark spots on your panels, this could be a sign that your panels are undergoing delamination, and you should contact your installer for an inspection.
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