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<DIV>That 284 volt number is if the panel is at 25 degrees C. If the panels are
in full sun and with little wind, they can be higher temperature than that even
in cold weather.</DIV>
<DIV> </DIV>
<DIV>An easy way to get a rough check on that is to disconnect the panels and
temporarily haywire an extra panel in series from another string. I suspect the
array might have to be rewired for 2 x 12.</DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=august@luminalt.com
href="mailto:august@luminalt.com">August Goers</A> </DIV>
<DIV><B>Sent:</B> Thursday, February 03, 2011 5:01 PM</DIV>
<DIV><B>To:</B> <A title=re-wrenches@lists.re-wrenches.org
href="mailto:re-wrenches@lists.re-wrenches.org">RE-wrenches</A> </DIV>
<DIV><B>Subject:</B> [RE-wrenches] Odd Inverter Behavior</DIV></DIV></DIV>
<DIV> </DIV></DIV>
<DIV
style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none">Hi
Wrenches -
<DIV> </DIV>
<DIV>We were called out today to check out an under performing system installed
by another contractor. This is an odd case. </DIV>
<DIV> </DIV>
<DIV>The system has 24 Suntech 180s in three strings of 8 and a SMA Sunnyboy
4000us. Open circuit voltage for each string was about 330 Volts and we verified
that everything appeared to be wired in correctly. There is no DC side grounding
at all. Just a positive and negative coming down off the roof for each
string.</DIV>
<DIV> </DIV>
<DIV>With all modules in direct light the inverter is only pumping out about 250
Watts steady state. We noticed that when we turn it off and on again that the
power went up to about 1500 Watts as it started tracking the max power point.
Then it slowly veers off course and settles out at about 250 Watts and is
running very close to the open circuit voltage of about 330 volts. I would
expect the MPP voltage to be closer to ~280 Volts. The inverter MPP tracking
range goes down to 250 Volts so I don't think that's the problem.</DIV>
<DIV> </DIV>
<DIV>Anyone ever seen anything like this before? What might be causing the
inverter to get confused? The only thing I can think of is that something fishy
is going on with the lack of a DC side ground and that certainly needs to be
fixed anyway. </DIV>
<DIV> </DIV>
<DIV>All thoughts welcome.</DIV>
<DIV> </DIV>
<DIV>Best,</DIV>
<DIV> </DIV>
<DIV>August</DIV>
<DIV> </DIV>
<DIV> </DIV>
<P>
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