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I have a related question to this. Does setting up a pair of Outback
GVFXs with the balancing transformer and allowing one inverter to go
to sleep at lower AC output improve efficiency? It seems we would
be reducing electronic loads, but adding transformer losses. Any
comments? I have a recently commissioned double Outback system with
200 AH @48v battery bank. He's reporting efficiency at 77% DC in to
AC out. I'd love to improve that, as his aging array of Sharp
modules seems to be under performing as well, (4.08 KW STC rated, 3
Kw actual out) I haven't gone back and done testing with my
insolation meter, so I'm not sure exactly what is happening, but his
overall efficiency (STC rated to AC out) is only 56% .<br>
<br>
Ray<br>
<br>
On 1/4/2012 7:55 PM, Maverick Brown [Maverick Solar] wrote:
<blockquote cite="mid:A4F08B3A7C2746219FA24FD632D8CB46@MSE002"
type="cite">
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<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">Please use the 90% of
the CEC or PTC rating of the PV module at most.</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">Among several systems
that I monitor daily, I have an example 11.760kw (STC)
system that has a 500Ah battery bank and it peaks at 77-80%
of the STC rating each day.</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">Peak is defined as the
top of the bell curve that forms from the graphing watts
output versus nameplate watts.</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">If I use the CEC
rating (10.54kw), it peaks at 86-90% of the CEC rating each
day.</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">If I go to the CEC
list and copy & paste into a spreadsheet and enter the
values for the STC versus PTC, I <em>might</em> find I
would loose 10% (or more) in the PV rating.</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2"><a
moz-do-not-send="true"
href="http://www.gosolarcalifornia.org/equipment/pv_modules.php">http://www.gosolarcalifornia.org/equipment/pv_modules.php</a> (go
ahead, find your modules and divide PTC by Nameplate).</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">I also have a
grid-interactive system that has a very large battery bank
(2600Ah @ 48V, with 9kw STC Array) and it only has a peak
efficiency rating of 69% because of the load of the
batteries. The larger the battery bank, the happier
customers are for outage situations, but the larger the
battery bank, the more current goes into "Floating" the
batteries during selling. For that system, I may lower "Grid
Support/SellRE" and use Auto EQ to keep the batteries
fresh...</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">Anyway, keep in mind
that you cannot simply assume:</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">12kw Array x 6 hours
of sun = 72kwh of generation each day. The brand of PV, the
size of the battery bank and even the charge controller's
Absorb & Float settings can greatly reduce what the
inverter thinks it can sell. With multiple inverters and
charge controllers it gets even more complicated (worse).</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span><span
class="683282302-05012012"></span><span
class="683282302-05012012"><font color="#0000ff" face="Arial"
size="2">Good luck,</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"><font
color="#0000ff" face="Arial" size="2">Maverick</font></span></div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<div dir="ltr" align="left"><span class="683282302-05012012"></span> </div>
<br>
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lang="en-us">
<hr tabindex="-1">
<font face="Tahoma" size="2"><b>From:</b>
<a class="moz-txt-link-abbreviated" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a class="moz-txt-link-freetext" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On
Behalf Of </b><a class="moz-txt-link-abbreviated" href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a><br>
<b>Sent:</b> Wednesday, January 04, 2012 5:14 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] DC to AC derate<br>
</font><br>
</div>
On 1/4/2012 3:01 PM, All Solar, Inc. wrote:
<blockquote
cite="mid:B5CBE3E26B764CC9987DB55BA8FD7972@SrvcTagGV13VB1"
type="cite">
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<div><font face="Arial" size="2">Wrenches,</font></div>
<div><font face="Arial" size="2">Once again I am trying to size
a grid tie w/battery system and I struggle a little with the
efficiencies of them.</font></div>
<div><font face="Arial" size="2">With PV Watts (v.1), is
changing the DC to AC derate an accurate method for getting
the output?</font></div>
<div> </div>
<div><font face="Arial" size="2">Thanks in advance!</font></div>
<div> </div>
<div><font face="Arial" size="2">Jeremy</font></div>
</blockquote>
<br>
<br>
If you keep the batteries charged to a voltage just above their
resting voltage,<br>
say, 52 volts for a 48V system, and the battery bank isn't too
large, (~225 A-hours,<br>
maybe a bit more), about 90% PV to grid AC efficiency is in the
ball park.<br>
<br>
That's what we figured in the early days of GFX inverters at OB.
That's giving<br>
5% for the electronics and 5% for keeping up the batteries.<br>
Different and/or more accurate information may have come along
since<br>
that time.<br>
<br>
boB<br>
<br>
</blockquote>
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