[DrDavid]

A likely source of the “excess energy” is the oxidation of the metal electrodes.

[Wonder Warthog]

"A likely source of the “excess energy” is the oxidation of the metal electrodes."

Nope. WAY too much energy output for that to account for it. Read up on Celani's recent INVITED demonstartion at NIWEEK (National Instrument's "cross-fertilization" symposium).