Chronar's are getting pretty old now. Is it used, or New Old Stock?
Assuming it is thin film, they wear out, and were not very well sealed against moisture.
Try it with a lower battery, like 12.2V. You should get 80% Isc if everything is right.
Maybe try it with a 6V battery, or 5 AA NiCDs, without a controller.
Could try the head light test, and check the amps into the head light, and the voltage.
Glass backed? Hold it up to a bright light.
Can you see any areas of the film just "missing"?
Especially look at the edges, where nearly a whole single stripe is damaged.
If so, there is a good chance it is worn out or damaged. Not repairable.
May be worth peeling the tape over the terminals back to check for a corroded connection.
G-