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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hello Travis,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Just for my $.02….<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I gave up a while ago on the textbook 3 days of autonomy, but
for a slightly different reason (including yours).<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>We would give a battery bank 3 days of autonomy, and then place
all kinds of alarms and load shedding at 50% SOC, but nothing to tell folks
when they have used up one day of their energy. (This is particularly
relevant with small systems with LVD charge controllers.) Consequently,
everyone (we are talking about remote installations in the jungle with no
alternative) keep using the power until the alarm sounds. The panels can
charge back up usually not much more than one day. The battery lives its
(shortened) life out going between 50% SOC and 70% SOC, unless of course the
ever important generator is part of the system.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>There is no magic to 3 cloudy days versus 6, or 8 or 12, so ….
Might as well deal with it sooner rather than later….<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Walt<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>SunEnergy Power International<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Travis
Creswell<br>
<b>Sent:</b> Tuesday, December 01, 2009 2:16 PM<br>
<b>To:</b> 'RE-wrenches'<br>
<b>Subject:</b> Re: [RE-wrenches] Other's thoughts on Autonomy? was concord
batteries, EQUALIZE Them!<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>IMHO, one of the worst design boo-boo’s is going past more
then 2 days of autonomy. Personally, I no longer size much over one day
because it’s my anecdotal observation that most batteries die of old age
and being ignored long before cycles get them. Speaking mostly about
quality deep cycle flooded.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>Lots of good things result;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-50%-75% smaller battery bank means a $20,000 battery bank just
turned into $5,000 bank which frees up a ton of money for more modules and
now-a-days you can buy a lot more PV with that money. More array mean far
less reliance on autonomy. I’ll take the trade all year long.
In the summer we have 3 to 4 weeks of sun and one day of clouds and in the
winter we get 3 to 4 week stretches with 1 sunny day. Autonomy
doesn’t really matter in either case from what I’ve seen. The
larger the bank means more self discharge losses, which on large battery banks
gets significant as they age. 5-15 years later you’ll still have
all that array but no matter what you’re looking at new battery bank.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-If you study the quality deep cycle manufacturers literature
you’ll see that you’ll see that anything over 1 day of autonomy is
too much to allow the array to actually charge the battery bank anywhere near
the recommended amps and just like rust, sulfation never sleeps.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-Less cells to water<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-Less space required<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-Given that a surprisingly high percentage of off gridders totally
screw up on their first bank, no matter how much we all try we might as keep
the stupid tax of replacing a 2.5 yr old battery bank to a minimum.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-All of this discussion about cross paralleling, buss bars, TLC
with a gazillion connections and multiple strings goes away.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>-And the best part is we don’t have to carry all of the lead
into the basement and even better back out of the basement!<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>Just my .02. Feel free to strongly disagree but let’s
be polite about it.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>Travis Creswell<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'>Ozark Energy Services<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:navy'><o:p> </o:p></span></p>
<div>
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<hr size=2 width="100%" align=center>
</div>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>R Ray
Walters<br>
<b>Sent:</b> Tuesday, December 01, 2009 12:44 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] concord batteries, EQUALIZE Them!</span><o:p></o:p></p>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<div>
<p class=MsoNormal><span style='font-size:16.0pt;font-family:"Helvetica","sans-serif";
color:black'>I used to think that one string was optimal; until I had a single
cell failure take out an entire system for weeks. (try operating a 24 v system
at 22v! )<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:16.0pt;font-family:"Helvetica","sans-serif";
color:black'>I now think that 2 parallel strings is optimum, 3 is OK, and
4 is max.<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span class=apple-style-span><span style='font-size:13.5pt;
font-family:"Helvetica","sans-serif";color:black'>At 4 parallel strings, we
start spending more time looking to make sure all connectors are the same exact
length etc. to insure equal operation.</span></span><span style='font-size:
16.0pt;font-family:"Helvetica","sans-serif";color:black'><o:p></o:p></span></p>
</div>
</div>
<div>
<p class=MsoNormal>But of course how do you account for varying internal
resistance of the batteries......??<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>I've done 4 parallel strings at 144 DC of sealed batteries
on an electric vehicle, but we were very careful with our resistances, I even
switched to smaller wire, on closer strings, and calculated out the exact
resistance, so all strings were theoretically equal. This set actually just
died, but achieved its manufacturer's predicted cycle life. (B&B battery,
350 cycles to 80% DOD)<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>So if you're careful, 4 strings can work well.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>Worst I've seen was 20 golf carts paralleled in a 12 v
system, (10 strings) and they didn't pull the main connections from across the
set, just connected to one end.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>The results were very predictable, with the furthest
batteries being chronically under charged, and the closest ones being over
cycled to a premature death.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Ray Walters<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<p class=MsoNormal><o:p> </o:p></p>
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<div>
<p class=MsoNormal>On Dec 1, 2009, at 11:28 AM, <a
href="mailto:Windsun@wind-sun.com">Windsun@wind-sun.com</a> wrote:<o:p></o:p></p>
</div>
<p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p>
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<div>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Calibri","sans-serif"'>You
gotta wonder about why the customer bought such a battery layout, or why the
installer sold that kind of configuration (which ever it was) with so many
small batteries. We would never recommend going over 2 parallel banks, but
sometimes the "customer knows best...".</span><o:p></o:p></p>
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<p class=MsoNormal> <o:p></o:p></p>
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<p class=MsoNormal><o:p> </o:p></p>
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