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It seems to eminate from the panel itself, but I'll try to measure more accurately when the sun comes out again. I'm not sure what B fields are.

B Fields are the magnetic flux density fields measured in Tesla units...
It says how many magnetic flux lines, e.g. emanating from a permanent magnets are going through an area of space, like in 1 cm x 1 cm.
Hope this helps..
See:

at:
https://www.testandmeasurementtips.com/magnetic-flux-density-and-magnetic-monopoles/