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

[Jim MacDonald]

Im sorry, I meant to write “11 modules per string” below..
Been a long day..

From: Jim MacDonald
Sent: Monday, April 19, 2010 7:41 PM
To: RE-wrenches
Cc: Jason Szrom
Subject: RE: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per string?

SB8000US only good for 480 Vac, we’re tying in at 208.

11 strings [11 modules per string] has been calc’d to be OK (<600vdc) for record low -4 fahrenheit (-20 celsius).

I think the big concern as mentioned is getting the Voc high early in the AM to wake the inverter up, also maintaining the Vmp later in the day to keep it running for as long as possible into the late afternoon/ evening.
Will those extra kWh gleaned in the early AM/ late PM over the course of 365 days be more than the kWh clipped during peak production times with the 9.075 kWdc?
NYC average summer highs between 79 and 84 fahrenheit early june-late august.  Sunlink rack @ 10° on a silver-painted built-up roof.

Time-of-use utility $ peak-shaving is not an issue here.

Thank you




From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Darryl Thayer
Sent: Monday, April 19, 2010 5:58 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per string?

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<http://www.solaresystems.com/>


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