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<div class="moz-cite-prefix">William,<br>
Years ago I designed a large SB/SI system for a high-mountain
lodge but never got the job, so this is not tempered by
experience. (Years later I was hired as a third-party consultant
to review the suggested upgrade to the installation when it didn't
work as contracted, but that's another story.) John Berdner was my
SMA design resource at that time. He recommended including a
relatively small amount of DC-coupled battery charging through a
charge controller, specifically to provide protection aginst the
situation you have identified.<br>
Allan<br>
<br>
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<p class="MsoNormal"><b>Allan <span class="SpellE">Sindelar</span></b><br>
<span style="font-size:10.0pt"><a
href="mailto:Allan@positiveenergysolar.com"><u><span
style="color:#000099">Allan@positiveenergysolar.com</span></u></a></span><br>
<span style="font-size:10.0pt">NABCEP Certified PV
Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder, <b>Positive Energy, Inc.<o:p></o:p></b></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt">A
Certified B <span class="SpellE">Corporation<sup><span
style="font-size:7.5pt">TM</span></sup></span><br>
<st1:address w:st="on"><st1:street w:st="on">3209
Richards Lane</st1:street><br>
<st1:city w:st="on">Santa Fe</st1:city>, <st1:state
w:st="on">New Mexico</st1:state> <st1:postalcode
w:st="on">87507</st1:postalcode></st1:address><br>
<b>505 424-1112 office 780-2738 cell</b><br>
<a href="http://www.positiveenergysolar.com/"
target="_blank"><u>www.positiveenergysolar.com</u></a><o:p></o:p></span></p>
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style="mso-spacerun:yes"> </span></span></p>
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On 2/9/2014 1:50 PM, <a class="moz-txt-link-abbreviated" href="mailto:william@millersolar.com">william@millersolar.com</a> wrote:<br>
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<p class="MsoNormal">Friends:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have inherited an off-grid install gone
wrong. This is a mini-grid with Sunny Islands and Sunny boy
inverters. All of the PV is connected in AC coupled mode.
There is no direct DC battery charging through a standard
charge controller. Is there any downside to this?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thinking through possible scenarios, I see
a problematic situation: The generator is out of order and
the batteries are depleted. The loads are all turned off to
allow the batteries to recharge, but the battery voltage is so
low that the Sunny islands will not start up. Therefore there
is no grid and therefore the Sunny Boys will not start and
provide PV.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is this scenario valid? Any other
“gotchas” I have not described?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks again to all of you out there. It
seems my work flow is such that I come up with a quantity of
questions all at once and I feel bad I am periodically loading
the forum. I always try to research and think these things
out before I come to the group. I found this and it seems to
reinforce my suppositions above: <a moz-do-not-send="true"
href="http://www.solarindustrymag.com/digitaleditions/Main.php?MagID=3&MagNo=54">http://www.solarindustrymag.com/digitaleditions/Main.php?MagID=3&MagNo=54</a>
I think the bottom line is that the most reliable system will
have a majority of the PV AC Coupled with have a modest RE
component DC coupled.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Sincerely,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">William Miller<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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