copper leaching in solar thermal system [RE-wrenches]

[Todd Cory, Mt. Shasta Energy Services]

Yes, dielectric unions at the water heater, the only place where dissimilar
metals meet. The rest of the loop is copper, stainless and brass (all
compatible). The water has very low total dissolved solids and is not acidic
(anodes last forever). There are 2 homes on this well and only the home with
the solar thermal is making the shower green, so I know that is the cause,
for some unknown reason.

I wonder how long the water can contain enough copper to make the shower
green before the potable side of the loop to the heat exchanger is so thin
it starts to leak. The glycol half loop of the loop is buried to another
building where the collectors are located. I have seen PV panels used to
apply power to buried natural gas pipes to prevent some kind of corrosion. I
am not sure why they do that, nor if this might be more of an electrical
(anode/cathode) situation because the glycol part of the loop is buried to
the panels located on a metal roof on another building.

Since the plumbing was done right and the water quality is not the problem
that leaves my question about different electrical potentials on one end of
the glycol loop and the other end of the potable loop. Does anyone have any
ideas how electrical characteristics with burying copper pipes or having
them span possible different electrical potentials might cause them to
corrode? You would think if they are copper (a great conductor) there could
be no dissimilar electrical potential?? This is a mystery to me, but I know
something is wrong because the pipes are leaching their copper into the
water.

Todd

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