two arrays [RE-wrenches]
Bill Brooks
bill at brooksolar.com
Tue Apr 26 14:39:33 PDT 2005
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Travis,
The 125% number Darryl mentioned has to do with the ratio of Voc/Vpmax.
Normally I would express it the other way around--Vpmax is 70-80% of Voc at
any condition. This is a good rule of thumb since you can walk up to any
array, test the Voc and know the range that Vpmax should be in once the
inverter believes it has reached max power. Without this knowledge, it is
almost impossible to know if an inverter is max power tracking properly.
The conservative way to estimate highest voltage is to use the coldest
recorded temperature and the NEC table 690.7. This table covers large
temperature ranges so manufacturer's temperature coefficients are better to
use, but sometimes impossible to find. An aging array will have lower specs
and many modules are 5% below Voc at STC rating out of the box.
Bill.
-----Original Message-----
From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net]
Sent: Tuesday, April 26, 2005 2:23 PM
To: RE-wrenches at topica.com
Subject: RE: two arrays [RE-wrenches]
Whoa ....
What does the 125% derate have to do with voltage? That's for amps, isn't
it?
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