<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:12pt">HI Matt:<br> 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.<br> 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.<br><div> 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.</div>Nick Soleil<br>Project Manager<br>Advanced Alternative Energy Solutions, LLC<br>PO Box 657<br>Petaluma, CA 94953<br>Cell: 707-321-2937<br>Office: 707-789-9537<br>Fax: 707-769-9037<div><br></div><div style="font-family: arial,helvetica,sans-serif; font-size: 12pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font size="2" face="Tahoma"><hr size="1"><b><span
style="font-weight: bold;">From:</span></b> Matt Lafferty <gilligan06@gmail.com><br><b><span style="font-weight: bold;">To:</span></b> RE Wrenches <re-wrenches@lists.re-wrenches.org><br><b><span style="font-weight: bold;">Sent:</span></b> Wed, October 28, 2009 4:29:56 PM<br><b><span style="font-weight: bold;">Subject:</span></b> [RE-wrenches] Shade Mitigating DC Device Application<br></font><br>
<meta http-equiv="x-dns-prefetch-control" content="off">
<div><font size="2" face="Arial"><span class="109500522-28102009">Esteemed
Wrenches,</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Your collective
wisdom & conjecture is sought in resolving the following
riddle:</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009">There once was a
home in the hills.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">With morning sun the
roof is filled.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Blasted mountain
rising in the west,</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Makes a shady mess
at very best.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><em></em></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><em>"Onward! Fear
not!</em>",<em> </em>sayeth the man.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><em>"Twenty-four
modules. Not one less!"</em></span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><em>"Black box of
magic for every one."</em></span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">
<div><font size="2" face="Arial"><span class="109500522-28102009"><em>"And string
inverter plus Island of Sun!"</em></span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009">With fifty-one
hundred watts of DC.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Two series strings
of four times three.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Black boxes of
magic, but not by that name.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">At quarter the price
are they really the same?</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">
<div><font size="2" face="Arial"><span class="109500522-28102009">'Tis not the
matter, least not today.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">To you the group...
What do you say?</span></font></div></span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009">For greatest
performance over time to yield...</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">2 balanced
strings of shade and of sun,</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Or put worst
shade all onto one?</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Snake-oil merchants
say not to worry.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font><font size="2" face="Arial"><span class="109500522-28102009">Magical boxes change dark
to light in a hurry.</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">What say ye, from
out in the field?</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009">Balance the strings,
or not?</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><End></span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009">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.
</span></font><font size="2" face="Arial"><span class="109500522-28102009">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?</span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009">I have my theory on
the subject and am interested in yours. <span class="109500522-28102009">Thanks in
advance for any and all feedback. </span></span></font></div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><span class="109500522-28102009"></span></span></font> </div>
<div><font size="2" face="Arial"><span class="109500522-28102009"><span class="109500522-28102009">Pray for
Sun!</span></span></font></div></span></font></div><meta http-equiv="x-dns-prefetch-control" content="on"></div></div></div><br>
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