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re: 12 volt vs 6 volt
19 aug 1998
ed gray wrote of:
>...gc-2 6 volt [230 ah] deep cycle batteries at sam's club... for
>$39.95 plus 6% sales tax... "loosely" rated at 400-600 discharges...
>at 50% discharge cycles or 80% discharge cycles?
that kind of information doesn't seem easily available, but it seems
to me the manufacturers should have it somewhere. maybe there's a data
sheet or a sam's club purchasing spec. i'd like to see it in writing,
in the form of measured performance or an estimate, as an average,
maximum, or guaranteed specification.
alternative energy engineering says the optimum discharge depth for
trojan t105-220s is 1200 60% cycles, ie they store 1200x0.6x6vx220ah/1000
= 950 kwh over their lifetime, making their life-cycle cost $60/950 kwh
= $0.063/kwh, if they cost $60. (aee's 1998 catalog price is $85.)
a gc-2 might provide 500 65% discharges, storing 500x0.65x6vx230ah =
449 kwh over its lifetime, at a cost of $42.35/449 = $0.094 per kwh.
>i spent a considerable time looking up the prices of "trojan" and a
>number of other batteries and figuring cost per amp hour per discharge...
i do this in cost/kwh, eg 6.3 cents or 9.4 cents/kwh above, if the
batteries wear out over a fairly short time. another part of the cost
has to do with the time value of money, ie the interest on the money
used to buy the batteries. discharged 60% every day, t105-220s will
apparently last 1200/365 = 3.3 years; $60 invested at a 10% interest
rate for 3.3 years becomes $60(1+0.1)^3.3 = $82.18, so a more accurate
estimate of the cost of owning a t105-220 might be $82.18/950 kwh
= $0.086/kwh, ie 8.6 cents per kwh, vs $42.35x1.1^1.3/449 = $0.107/kwh
or 10.7 cents per kwh for a gc-2. if the calendar lifetime is longer,
with the same discharge lifetime, ie the batteries are not discharged
so much every day, eg in a backup or small-scale parallel cogeneration
system using a couple of diehards and a trace 4024 inverter that makes
the meter go backwards, the battery life-cycle cost per kwh increases.
>if one is going to a large amount of power such as say 600 amp hours and
>greater other choices even though more expensive may be the way to go...
we might well keep in mind that power is measured in watts, and energy
is measured in watt-hours or kwh. amp-hours don't have much to do with
either. why not use kwh as a measure of energy storage capacity? that
way we can more easily compare systems with different voltages, and
on- and off-grid systems.
nick
nicholson l. pine system design and consulting
pine associates, ltd. (610) 489-0545
821 collegeville road fax: (610) 489-7057
collegeville, pa 19426 email: nick@ece.vill.edyou
computer simulation and modeling. high performance, low cost, solar heating
and cogeneration system design. bsee, msee. senior member, ieee. registered
us patent agent. web site: http://www.ece.vill.edu/~nick
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