[RE-wrenches] Shade Mitigating DC Device Application

[Nick Soleil]

HI Matt:
    The way I deal with it is normally to put the shaded modules onto one string.  This morning, I finalled an inspection on a system with two strings of 12- BP SX-3200Bs (200 w) to 2- GT-3.3 inverters.  We arranged one string in the morning shade, and one out of it.  Inverter 1 was producing 1400 watts, while inverter 2 was producing only 100 watts.  Luckily, this only goes on during winter months, because Inverter 2 is producing 20% less per day now.
    The question I always ask myself is, how many modules does it take to run the inverter.  I calculate how many modules will be in the sun when the string is shaded. If the shade is enough to shut off a string, but dividing the shade onto two strings will allow both strings to continue to operate in the inverter's voltage window, then divide it up between the strings, so that each string stays on.   If the typical shade is so much that it will shut off two strings then put only one string in the shaded area.

     At my site this morning, the Inverter requires 11-16 modules to stay in the window, and my string was only 12 modules long, so even a small amount of shade can severely impact my arrays output.  My site had 6 of the 12 modules mostly shaded, so I was glad it was only on one string.Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC
PO Box 657
Petaluma, CA 94953
Cell:   707-321-2937
Office: 707-789-9537
Fax:    707-769-9037




________________________________
From: Matt Lafferty <gilligan06 at gmail.com>
To: RE Wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Wed, October 28, 2009 4:29:56 PM
Subject: [RE-wrenches] Shade Mitigating DC Device Application

 
Esteemed 
Wrenches,
 
Your collective 
wisdom & conjecture is sought in resolving the following 
riddle:
 
There once was a 
home in the hills.
With morning sun the 
roof is filled.
Blasted mountain 
rising in the west,
Makes a shady mess 
at very best.
 
"Onward! Fear 
not!",sayeth the man.
"Twenty-four 
modules. Not one less!"
"Black box of 
magic for every one."
"And string 
inverter plus Island of Sun!"
 
With fifty-one 
hundred watts of DC.
Two series strings 
of four times three.
Black boxes of 
magic, but not by that name.
At quarter the price 
are they really the same?
'Tis not the 
matter, least not today.
To you the group... 
What do you say?
 
For greatest 
performance over time to yield...
2 balanced 
strings of shade and of sun,
Or put worst 
shade all onto one?
Snake-oil merchants 
say not to worry.
Magical boxes change dark 
to light in a hurry.
What say ye, from 
out in the field?
Balance the strings, 
or not?
<End>
 
Some factors to 
consider.... The site is shade-challenged, primarily in the afternoon. There 
will be two strings of 12 modules each feeding a single inverter. Enphase is 
off the table for now. Homeowner specifically wants to do back-of-module 
DC shade mitigation. The array layout is such that configuring the strings 
so there is a dominant sunny one and dominant shady one is possible. It is also 
possible and almost as easy to configure the strings so they are more balanced 
with each other. Assuming that each module is equipped with a black box, will it 
make any difference which configuration gets used?
 
I have my theory on 
the subject and am interested in yours. Thanks in 
advance for any and all feedback. 
 
Pray for 
Sun!


      
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20091028/a69fab76/attachment-0004.html>