I wonder if it's not static buildup. If you take a long wire
and place it in the open dry air, it will build up a static
charge that is very impressive. If you have ever installed
electric fence, and make some long runs, you find out that a
10-mph breeze will charge it up pretty good.
On a radio DX trip, a friend and I put 500 feet of #14 wire
(THHN) out on the rock in a straight line to see if we could
hear European AM radio stations. Weather was calm with just
a little movement in the weeds. The wire that was no where
near electrical sources repeatedly shocked both of us. We
measured the voltage on the wire and it read between 300 and
a peak of 465 volts, DC. Current was low. We could light,
and blow out, an NE1 neon lamp. And the voltage would make a
car's brake light (removed from the car) to light very dim.
The voltage was enough of a problem that we had to make up a
static suppression choke out of #12 wire and a piece of PVC
sewer pipe.
It's quite possible that this is what Art is experiencing.
Or it could be induction from both natural magnetic sources,
and manmade sources.
Still, if you think about it, if you could take this "free
energy" and store it in a battery, and if you had devices in
your hole that required very little amperage to run, you
might find that it could be a good way to cut your bills.
However, most homes require a lot of power, especially if
you have electrical heat, hot water tanks, electric stoves,
etc.
BTW, sites like
http://www.homepower.com and
http://www.wind-power.com are good reads.