<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I really studied this at one time, and what's interesting is that if a battery bank is too large, (regular discharges less than 20%) you're not really getting your money's worth, as the # of cycles x amount of discharge is less. Likewise, a battery that is discharged regularly deeper than 70% starts eating life too. It's surprisingly even however, from 20% DOD to around 70%; more cycles less discharge, or less cycles, more discharge, you get about the same total KWH total out of the pack over its life either way. (just take a cycle life chart for most batteries, and start multiplying cycles by DOD at different points)<div>The bottom line is, you might save some money upfront with a smaller battery bank, but it won't last as long. Therefore, the replacement cost ( labor to move out old bats, move in new) is higher with a smaller bank, so the total operating cost over the system life is higher, too.</div><div>Also, the charge rates that battery companies list are really for big, dumb on-grid chargers, not the 3 stage PWM units with temp comp that we use. I've found systems with really low charge rates to actually last a very long time. We're trading possible under charging and sulfation to avoid chronic over charging (and over heating) which is the real killer IMHO. Somewhere between is optimum.</div><div><br></div><div>I still do 5 days storage to 100% DOD, (or 4 days to 80%, same thing) for our avg. off grid systems, and tweak it down if we need to save money. Big systems with a good generator can work fine at less than 3 days. Of course local weather is a factor in this too. We get long spells of cold, cloudy weather followed by a couple of weeks of nice sun.</div><div><br></div><div>For GT w/ backup, I size for more like 8 hours. As was said before, they'll probably die from the float service, not the cycling. Even a really small battery will still work if the grid is out for a longer time, they'll just have to do more when the sun is out, and go to bed early.</div><div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div>R. Walters</div><div><a href="mailto:ray@solarray.com">ray@solarray.com</a></div><div>Solar Engineer</div><div><br class="khtml-block-placeholder"></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span>
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<br><div><div>On Dec 1, 2009, at 3:15 PM, Travis Creswell wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div lang="EN-US" link="blue" vlink="blue" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div class="Section1"><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; 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></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">Lots of good things result;<o:p></o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; 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></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; 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></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">-Less cells to water<o:p></o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">-Less space required<o:p></o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; 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></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; 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></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; 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></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">Just my .02. Feel free to strongly disagree but let’s be polite about it.<o:p></o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">Travis Creswell<o:p></o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; ">Ozark Energy Services<o:p></o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" color="navy" face="Arial"><span style="font-size: 10pt; font-family: Arial; color: navy; "><o:p> </o:p></span></font></div><div><div class="MsoNormal" align="center" style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; text-align: center; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><hr size="2" width="100%" align="center" tabindex="-1"></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><b><font size="2" face="Tahoma"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold; ">From:</span></font></b><font size="2" face="Tahoma"><span style="font-size: 10pt; font-family: Tahoma; "><span class="Apple-converted-space"> </span><a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" style="color: blue; text-decoration: underline; ">re-wrenches-bounces@lists.re-wrenches.org</a><span class="Apple-converted-space"> </span>[mailto:re-wrenches-bounces@lists.re-wrenches.org]<span class="Apple-converted-space"> </span><b><span style="font-weight: bold; ">On Behalf Of<span class="Apple-converted-space"> </span></span></b>R Ray Walters<br><b><span style="font-weight: bold; ">Sent:</span></b><span class="Apple-converted-space"> </span>Tuesday, December 01, 2009 12:44 PM<br><b><span style="font-weight: bold; ">To:</span></b><span class="Apple-converted-space"> </span>RE-wrenches<br><b><span style="font-weight: bold; ">Subject:</span></b><span class="Apple-converted-space"> </span>Re: [RE-wrenches] concord batteries, EQUALIZE Them!</span></font><o:p></o:p></div></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><o:p> </o:p></span></font></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><o:p> </o:p></span></font></div><div><span style="-webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; orphans: 2; widows: 2; word-spacing: 0px; "><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="5" color="black" face="Helvetica"><span style="font-size: 16pt; font-family: Helvetica; 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></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="5" color="black" face="Helvetica"><span style="font-size: 16pt; font-family: Helvetica; color: black; ">I now think that 2 parallel strings is optimum, 3 is OK, and 4 is max.<o:p></o:p></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><span class="apple-style-span"><font size="4" color="black" face="Helvetica"><span style="font-size: 13.5pt; font-family: Helvetica; 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></font></span><font size="5" color="black" face="Helvetica"><span style="font-size: 16pt; font-family: Helvetica; color: black; "><o:p></o:p></span></font></div></div></span></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "></span>But of course how do you account for varying internal resistance of the batteries......??<o:p></o:p></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; ">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></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; ">So if you're careful, 4 strings can work well.<o:p></o:p></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; ">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></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; ">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></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><o:p> </o:p></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; ">Ray Walters<o:p></o:p></span></font></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><o:p> </o:p></span></font></div></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><o:p> </o:p></span></font></div><div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; ">On Dec 1, 2009, at 11:28 AM,<span class="Apple-converted-space"> </span><a href="mailto:Windsun@wind-sun.com" style="color: blue; text-decoration: underline; ">Windsun@wind-sun.com</a><span class="Apple-converted-space"> </span>wrote:<o:p></o:p></span></font></div></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><br><br><o:p></o:p></span></font></div><u1:smarttagtype name="PostalCode" namespaceuri="urn:schemas-microsoft-com:office:smarttags"></u1:smarttagtype><u1:smarttagtype name="Street" namespaceuri="urn:schemas-microsoft-com:office:smarttags"></u1:smarttagtype><u1:smarttagtype name="City" namespaceuri="urn:schemas-microsoft-com:office:smarttags"></u1:smarttagtype><u1:smarttagtype name="address" namespaceuri="urn:schemas-microsoft-com:office:smarttags"></u1:smarttagtype><u1:smarttagtype name="State" namespaceuri="urn:schemas-microsoft-com:office:smarttags"></u1:smarttagtype><u1:smarttagtype name="place" namespaceuri="urn:schemas-microsoft-com:office:smarttags"></u1:smarttagtype><div link="blue" bgcolor="#ffffff" vlink="blue" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Calibri"><span style="font-size: 10pt; font-family: Calibri; ">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></font><o:p></o:p></div></div><div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "> <o:p></o:p></span></font></div></div></div></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 12pt; font-family: 'Times New Roman'; "><font size="3" face="Times New Roman"><span style="font-size: 12pt; "><o:p> </o:p></span></font></div></div>_______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address:<span class="Apple-converted-space"> </span><a href="mailto:RE-wrenches@lists.re-wrenches.org" style="color: blue; text-decoration: underline; ">RE-wrenches@lists.re-wrenches.org</a><br><br>Options & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org" style="color: blue; text-decoration: underline; ">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive:<span class="Apple-converted-space"> </span><a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org" style="color: blue; text-decoration: underline; ">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a><br><br>List rules & etiquette:<br><a href="http://www.re-wrenches.org/etiquette.htm" style="color: blue; text-decoration: underline; ">www.re-wrenches.org/etiquette.htm</a><br><br>Check out participant bios:<br><a href="http://www.members.re-wrenches.org/" style="color: blue; text-decoration: underline; ">www.members.re-wrenches.org</a><br><br></div></span></blockquote></div><br></div></body></html>