It's almost definitely not free energy. Someone's most probably paying for that in some way. I'm not exactly calling this cap quite yet, but if you are getting energy from that thing, it's probably absorbing waves, and if it's doing that, you're gonna get a visit from some interesting people. FCC, probably. 😮 antennae can also do similar wave absorbing to see it on a voltometer, also its not free its like stealing someone elses wave electricity from the air they are using, but your converting what comes to you into usable electricity and thats very inefficient. Unless I'm missing some other phenomenon.