There are 4 quality grades for PV panels: A, B, C and D.
Grade A panels are the highest quality ones. They have no cracks, fractures and discoloration which lead to productivity drop. Usually they look perfect and no difference can be seen when comparing 2 cells. Grade B panels have visible faults like small scratches and discoloration. These panels produce less electricity in comparison with grade A panels but are sold at a lower price. Grade C panels have bigger scratches and fractures and produce noticeably less electricity than higher grades. They have much lower price but should be used with low-voltage batteries only. Grade D panels may have broken parts which can be used for making lower power modules. These panels have fractures, cracks, microbreaks. They are usually re-assembled to get smaller panels with lower power.