Perhaps you missed this post in which I show how to produce over 5v from a collection of metal and soil on my kitchen table.
Actually I have not missed it. I even commented under it six days ago, and you replied to it. At first I have not thought that these two are actually the same technique.
Ah yes! So sorry. Of course you did. I get confused sometimes.
And I understand your question now. It's a good one in fact and I don't have an answer. What I can tell you is that I've not been able to measure any kind of voltage from the spirals or coils. Perhaps they need to be bigger for this? Or perhaps this kind of energy is not measurable with this kind of meter?
Will let you know if I discover more on this.