MIXED PANEL ARRAY'S [RE-wrenches]

[Steve Willey, Backwoods Solar]

I did a like test a few years ago with parallel connection of a  30 cell
"self regulating" and a 36 cell panels.  In normal charge, the battery holds
both to a same operating voltage. When the series type controller
disconnects the battery, these panels go to open circuit in parallel. I
noted fairly high reverse flow and perceptibly higher temperature in the
lower voltage panel.  My conclusion was that a panel in sunlight has lower
resistance to reverse flow than a panel at night, where reverse flow is
actually very small.  I did not further test by shading the panel and
observing, or letting it cool to night temps. It could be related to the
much higher daytime operating temperature, or to the fact that it was
powered by sunlight and so forward biased at the same time the reverse
voltage was applied from the higher voltage panel.

Steve Willey   www.backwoodssolar.com
Backwoods Solar Electric Systems

----- Original Message -----
From: Kurt Nelson, SunWise <sunwise at win.bright.net>
To: <RE-wrenches at topica.com>
Sent: Tuesday, August 15, 2000 7:04 PM
Subject: Re: MIXED PANEL ARRAY'S [RE-wrenches]


> Greetings Wrenches,
> Down at the "Shop", I have an array composed of a some Arco 16-2000 33
cell
> panels, as well as a couple 36 cell panels.  This year, I added an SP-75
to
> the system that is mounted on the inside of the door in such a fashion
that
> I swing it out and flip it up when I open the shop.  I then have some
meters
> (volts/amps) and a couple switches that allows the visiting folks to play
> with Solar by switching through some loads (water pump and such) or back
to
> the main shop/battery system to learn about solar.  I have noticed that
when
> the new Siemens panel is on the system, and the charge regulator
> (down-stream) regulates, the amp meter that is on the SP75 indicates about
> one amp output.  Is this feeding back into the 33 cell panels?  Initially
I
> decided this was the case, but is this a factor of higher (Voc) voltage?
If
> any such panel (12VDC nom. into 12VDC battery) is connected directly to a
> battery, we see something in the way of 35mA out of the array at night.
> Does the PV start to see increased reverse current flow when subjected to
a
> higher voltage than the panel's rated voltage or even PPP voltage?  Why
> would I be seeing something approaching 20 watts going back into this
little
> 33 cell array when a twelve volt battery doesn't put but a trickle back?
>
> Thanks for your responses,
>
> Kurt Nelson
>
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 michael.welch at homepower.com
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