[RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per string?

[Darryl Thayer]

The temperature correction is the concern.  I have heard lots of stories of inverters dieing when it gets to cold.  Look in the code book 690.7 at the temperature correction table.  Go to weather.com and find your record low temperature.  Find you Tc factor and will your senerios work?  I have heard from a sunny boy rep that it is OK to over power by 1.25% 
darryl

--- On Mon, 4/19/10, Dana <dana at solarwork.com> wrote:


From: Dana <dana at solarwork.com>
Subject: Re: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per string?
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Date: Monday, April 19, 2010, 4:31 PM








Many times we switch to another module manufacturer as one will not fit or another inverter manufacturer. 
PVPowered has a more relaxed window and we have had fine success with them when SMA does not fit. 
Cold is the dictator and the 600 VDC threshold.
 
 

Thanks,  Dana Orzel
 
Great Solar Works, Inc
web - www.solarwork.com
E - dana at solarwork.com
V - 970.626.5253
F - 970.626.4140
C - 970.209.4076
 
"We have been slow to give up on the myth of the Earth's generosity.
Rather grandly, we have overdrawn our accounts."
Barbara Kingsolver - Water is life.
 


From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jim MacDonald
Sent: Monday, April 19, 2010 2:37 PM
To: RE-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per string?
 
For a straight grid-tie system@ 10 degree tilt, 180 azimuth, zero/little shade, NYC avg 4.29 kWh/m²/day.
 
Feed an SMA7000 with (3) strings of 11 Suntech STP275’s [9.075 kWdc]
Or
Do strings of 10, so itd be 8.250 kWdc into the 7 kWac inverter.
 
Strings of 11= 491.7 Voc; 386 Vmp
Strings of 10= 447 Voc; 351 Vmp 
 
The tradeoff would be power clipping at/around noon in the sunny months in the 9.075 kW scenario;
Inverter sleeping late every morning and retiring early in the evenings in the lowered voltage scenario.
 
Trying to figure out which would yield more kWh at the end of the year.
 
Any ideas appreciated,
thanks
 
 
 
 
Jim MacDonald
Solar Energy Systems, LLC
Brooklyn, NY 11222
www.solarEsystems.com
 
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