I have quite several 72 cells solar panels with cracked glass taking punch during the handling. The designated Voc is a little over 45V and almost all of the cracked solar panels (20pcs) generates Voc above 44V. However the Isc measured are all over the places from 2A to 6A. The designated Isc is about 9A. I measured around 9am and the sun generates over 1000W/m**2. I guess the low Isc is directly related to the damage the panel received. However I don't quite understand why Isc is much lower while there is almost no loss with Voc. Is there something I didn't do right or missing with measurement?
The panel is a series/parallel arrangement of solar cells. The open circuit voltage is determined by the type of cell and the number of them in series, regardless of quality. With no load, they build up tension close to their mathematical limit. Your cracked cells are still cells in series, but their other properties(current generation/series resistance) are messed up. There may be one or more series chains of cells within that are entirely nonfunctional. To get full open circuit voltage, only one full series chain must survive. Under load (short circuit) the cells are not producing their full current and likely have to work through higher resistance, with the end result being much lower output.
Even slight/partial shading of solar cells (anything less than totally even illumination) can cause a severe drop in power output, depending on how the panel is wired. It's possible that's all you're seeing. You could try removing and replacing the broken glass, or filling the crack with some kind of filler that matches the refractive index of the glass to minimize shading (probably some kind of epoxy.) Of course in either case you run the risk of doing further damage to the panels but it sounds like you don't have much to lose.