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Tom,<br>
Yes, but if you use individual 2V cells, you can pull one failed
cell out of the string and get by just fine by adjusting setpoints
down by 8% (11/12ths). You'll lose 8% of capacity until a cell is
replaced; or, if the failed cell is the first to go at end-of-life,
just live with the remaining 22V bank while collecting funds for the
replacement set ("You have been setting aside some money each year
for that set, haven't you?"). <br>
<br>
Using two strings is fine, but if the smaller strings are made up of
4V or 6V cases, you no longer can remove just one cell. Rather, you
must disconnect one string and live on 50% capacity (or 67% with two
out of three strings) until a replacement is secured. <br>
<br>
Based on the above, I'd usually go with a single string of the best
batteries I can find. Personally, I like what Chris Worcester wrote:<br>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31, 73,
125);">My one string of 1476 AH IBE 2 V cells went 19 years
before retiring them to a neighbor’s off grid system, where they
are now working. One string has my vote!</span></p>
<span style="font-size: 10pt; font-family:
"Calibri","sans-serif"; color: navy;"></span>as
I just put that exact size of IBE<span style="font-size: 10pt;
font-family: "Calibri","sans-serif"; color:
navy;"></span> 2V cells in my own home. Here's hoping I get
another 18 years and 10 months out of them. <br>
Allan<br>
<br>
<span style="font-size: 10pt; font-family:
"Calibri","sans-serif"; color: navy;"></span>
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<font face="Times New Roman, Times, serif"><b>Allan Sindelar</b></font><br>
<small><a href="mailto:Allan@positiveenergysolar.com"><font
color="#000099" face="Times New Roman, Times, serif"><u>Allan@positiveenergysolar.com</u></font></a></small><font
face="Times New Roman, Times, serif"><br>
<span style="font-size: 10pt;">NABCEP Certified Photovoltaic
Installer<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank"><u>www.positiveenergysolar.com</u></a><o:p></o:p></span></font>
<span style="font-size: 10pt;"> </span> </div>
<br>
On 5/31/2011 5:36 PM, Tom Elliot wrote:
<blockquote cite="mid:04EB96A325B74AB59657E5E13696937C@Haikulaptop"
type="cite">
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<div>From a reliability standpoint I would never want to bet
the farm on one string. All it takes is the failure of one
cell and the system is useless until it is replaced. Three
strings means a cell failure only reduces capacity by 33%
not 100%. I’ve always thought in off-grid systems it is a
good idea to build in as much redundancy as possible
whenever possible. Oh, and always use a buss bar system
with multiple strings, it makes for a far more stable system
with less stress on the batteries.</div>
<div> </div>
<div>Tom</div>
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