Difference in color of black back panel of photovoltaic panel

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]

Black spots on the surface of photovoltaic panels

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. [pdf]