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<div class="moz-cite-prefix">I'd go for using that extra module with
the damaged frame. What is the frame damage going to do to the
system?<br>
Is it bad enough that the module could quit working later (bad
edge seal)?<br>
The voltage mismatch isn't the end of the world either, but your
over all year round performance will be better with that extra
module than not. <br>
The thing to remember is that MPP is going to vary all the time
with insolation and temperature, so predicting actual performance
impact from the mismatch is not just a simple calculation. I have
software that can model one way or another, but it can't model the
strings together, and what the inverter is going to actually do in
various situations.<br>
If the module damage is just cosmetic, as they say "if you can't
see it from the ground.....", while the loss in performance will
be visible. To make the customer feel good, sell him the damaged
module at salvage cost or just throw it in, explaining you just
want the system to work well, but you don't like selling damaged
goods......<br>
We sell used stuff quite a bit, and folks actually like saving a
buck when they can. I'd let the customer have the final say, then
you're off the hook either way.<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 4/28/2013 10:02 AM, Kirk Herander wrote:<br>
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<p class="MsoNormal"><span style="font-size:14.0pt">Hello
everyone,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">I am at
present adding to a -20- panel array of old Sanyo HIT
“lipped” 200 watt panels. They are configured in -4- series
strings of -5- panels, with a string MPP voltage of 279 vdc
(55.8 v, 3.6 a each). The customer wants to add another
nominal 2 kw using the (now) Panasonic 235 watt HIT’s which
have an MPP of 43.0 vdc, 5.5 a. I am locked in to an
existing SMA 6000US inverter. Obviously I cannot get all the
strings to the same voltage. But I can get relatively close
by rewiring:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">String 1:
-7- 200 watt @ 55.8 ea. = 390.6 v MPP<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">String 2:
same as string 1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">String 3:
-6- 200 watt @ 55.8 plus -1- 235 watt @ 43.0 = 377.8 v MPP<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">String 4:
-9- 235 watt @ 43.0 = 387 v MPP<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">Under this
scenario there is a delta of about 12 vdc between high and
low MPP. I assume the entire array will operate at the 377.8
V MPP. I know that the 235 watt panel will be current
limited also in string 3. Am I missing anything obvious in
doing it like this? How will the inverter arrive at an
operational MPP voltage?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">PS. In a
pinch I could install a leftover 200 watt HIT I have in the
shop. That way I could have -3- strings of -7- 200’s @ 390.6
v MPP, and one string of 235’s @ 387v MPP. But I would
prefer not to use this panel since the frame is damaged.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">Kirk
Herander<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">VT Solar,
LLC<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">dba Vermont
Solar Engineering<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">NABCEP<sup>TM
</sup>Certified Inaugural Certificant<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">NYSERDA-eligible
Installer<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">VT RE
Incentive Program Partner<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt">802.863.1202<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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