[RE-wrenches] calculating low string voltage

[Darryl Thayer]

I am on road so I have no texts with me, but the same formula applies about 0.4% per degree (less voltage) or use the module label  voltage coefficent.  However you must use the MPPT voltage and the temperature = (temperature ambient (2% high) plus roof temperature warming)  The roof temperature is hard to find good values because it depends upon spacing between roof and module.  I add 15 deg C for most situations.  
 
Best I can do from memory.
DT
 

________________________________
 From: Kirk Herander <kirk at vtsolar.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org> 
Sent: Tuesday, November 29, 2011 1:48 PM
Subject: [RE-wrenches] calculating low string voltage
 

I am in debate with a PE over calculation of low voltage of a series string on a hot day. He insists that an arbitrary high cell temp is factored in, not just ambient temperature. Could someone please give an accepted formula for this calculation? Thanks. I cannot find a clear reference to low voltage calculation on a hot day (but every reference material is clear on how to calculate high voltage on a cold day).
 
Kirk Herander
VT Solar, LLC
dba Vermont Solar Engineering
NABCEPTM Certified installer Charter Member
NYSERDA-eligible Installer
VT RE Incentive Program Partner
 
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