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Jamie,<br><br>
Thanks for the reply. That does make sense as to how the AC Voltage
might affect an inverter. It would certainly seem a likely issue
with the Sunny Boy line of inverters up to the 7000, which have a maximum
MPP DC Voltage of 250 V. The SB 8000 is a 300 V MPP unit. I
wonder if the Sunny Design tool is correct about the concern. I
also wonder why the SB 8000 went to 300 V DC.<br><br>
Drake <br><br>
<br>
At 01:17 PM 5/12/2011, you wrote:<br>
<blockquote type=cite class=cite cite="">Drake,<br>
<br>
The sunny boy design tool assumes a max grid voltage of 240 (I have
version 1.56 that allows you to select 250vAC as the max on screen #2),
if your grid voltage exceeds the grid design voltage then the minimum mpp
design voltage needs to increase along with it in order to maximize your
kWh production. <br>
<br>
I forget what the difference is between grid and minimum mpp, IIRC it is
10vDC+ above Grid Voltage so 240vAC would require 250vDC as the minimum
mpp. You would need to check the installation manual for the sunny
boy inverter that you are installing.<br>
<br>
At high temps, the mpp voltage drops (calculate this as %/deg c above 25
deg c from your module manufacturer supplied temp coef) and may drop
below the minimum designed mpp needed for 240vAC or 250vAC. If this
happens then either the mppt will adjust below the knee of the power
curve in order to increase the voltage (less efficient), or the mpp
voltage will drop below the minimum needed and the inverter may shut
off. I have seen both happen.<br>
<br>
<br><br>
<b>Jamie Johnson<br>
NABCEP Certified PV Technical Sales Professional<br>
NABCEP Certified Solar PV Installer<br><br>
General Manager<br>
SOLAR POWER ELECTRIC<br>
<img src="cid:.0" width=226 height=210 alt="[]"></b><br>
<br>
<br>
<dl>
<dd>-------- Original Message --------<br>
<dd>Subject: [RE-wrenches] SMA High AC Voltage vs MPP<br>
<dd>From: Drake
<<a href="http://drake.chamberlin@redwoodalliance.org>">
drake.chamberlin@redwoodalliance.org></a>;<br>
<dd>Date: Thu, May 12, 2011 12:27 pm<br>
<dd>To: RE-wrenches
<<a href="mailto:re-wrenches@lists.re-wrenches.org">
re-wrenches@lists.re-wrenches.org</a>><br><br>
<dd>Hello Wrenches,<br><br>
<dd>Using the Sunny Design tool, I got a message saying the design was
conditionally compatible. The message said:<br><br>
<dd><font color="#0000FF">"In case of increased grid voltage, the
operating point of the PV generator may slightly deviate from its MPP if
the module temperature is high. This design can therefore only be
recommended if the expected average grid voltage at the inverter will not
exceed the value used in the calculation."<br><br>
</font>
<dd>The SMA tech rep I talked to thought the design was good, but
couldn't really answer the questions I had. These are:
<dd>What is the design AC voltage?
<ul>
<li>Is it 240 VAC or the maximum voltage the inverter allows, which is
264 VAC?
<li>There is no input for design AC voltage.
</ul>
<li>Why does the max AC voltage affect the MPP at high temperature?
<ul>
<li>Since it apparently does, how much does it affect it?
</ul>
<li>If the grid voltage got to 250 VAC, would that be a problem?
<ul>
<li>I see that range pretty regularly around here.
</ul>
</ul>
<dd>Any help with these questions would be appreciated. <br><br>
<dd>Thank you, <br><br>
<dd>Drake <br><br>
<dd><font size=2>Drake
Chamberlin<x-tab> </x-tab>
<br>
<dd>ATHENS ELECTRIC<br>
<dd>OH License
44810<x-tab> </x-tab><br>
<dd>CO license 3773<br>
<dd>NABCEP Certified PV<br>
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<font size=2>Drake
Chamberlin<x-tab> </x-tab>
<br>
ATHENS ELECTRIC<br>
OH License
44810<x-tab> </x-tab><br>
CO license 3773<br>
NABCEP Certified PV<br>
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