Possible causes for these I-V curve's

[Monchichak]

Tested 2 strings today (twice) & each time string 1 had poor fill factor.
Any ideas what may be the cause of this type of result?

 

[Monchichak]

Possibly answering my own question - irradiance was low and there was some shading on some of the panels from a nearby tree during the test. I suspect shading maybe the culprit.