Re: [Electric Boats] Re: Battery Life and Types

Excellent comparison. Thank you for expending the "cpu" cycles to
deliver this.

Steve Spence
Renewable energy and self sufficiency
http://www.green-trust.org
http://arduinotronics.blogspot.com/

On 09/15/2010 07:38 PM, Eric wrote:
>
>
> Jim,
>
> I'm not sure what number that you're looking for, but here's a bunch of
> data comparing my battery bank to a set of T-105s.
>
> 8kWh bank of LiFePO4 batteries, cost $3600 including BMS, tax and
> shipping, weight 200 lbs. Manufacturers lifespan is > 2000 cycles at 80%
> DoD.
>
> Assuming 1 deep discharge per week for 10 years:
> 6400Wh x 500 cycles = 3,200,000Wh delivered
> 3200kWh / 200 lbs = 16kWh/lb
> $3600 / 200 lbs = $18/lb
> $18 / 16kWh = $1.125/1000Wh delivered
>
>>From what I know about Trojan T-105s
> 11.25kWh bank of 8 T-105 batteries, cost $1200 including tax and
> shipping, weight 500 lbs. Manufacturers lifespan is less than 500 cycles
> at 60% DoD.
>
> Assuming 1 deep discharge per week for 5 years:
> 6750Wh x 250 cycles = 1,687,500Wh delivered
> 1687.5kWh / 500 lbs = 3.4kWh/lb
> $1200 / 500 lbs = $2.4/lb
> $2.4 / 3.4kWh = $0.70/1000Wh delivered
>
> But these numbers aren't the whole story. Because of the different
> battery chemistry and Peukrert's Effect, T-105s deliver much less energy
> under load than the Li batteries do. Assuming a 2kW load, the T-105s
> should deliver 4920Wh in a 60% DoD cycle, the Li batteries will deliver
> 6100Hh in an 80% DoD cycle. Here's the same calcs again:
>
> Assuming 1 deep discharge per week for 10 years:
> 6100Wh x 500 cycles = 3,050,000Wh delivered
> 3050kWh / 200 lbs = 15.25kWh/lb
> $3600 / 200 lbs = $18/lb
> $18 / 15.25kWh = $1.18/1000Wh delivered
>
> Assuming 1 deep discharge per week for 5 years:
> 4920Wh x 250 cycles = 1,230,000Wh delivered
> 1230kWh / 500 lbs = 2.46kWh/lb
> $1200 / 500 lbs = $2.4/lb
> $2.4 / 2.46kWh = $0.98/1000Wh delivered
>
> So for this usage pattern, the lithium batteries cost 20% more per
> delivered watt hour but are only 40% the size and weight of the T-105s.
>
> I don't know how relevant these numbers are, since they are based on a
> broad set of assumptions, but those assumtions are stated here. Change
> the assumptions and the results will change. From my perspective, this
> is a fair comparison.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
> --- In electricboats@yahoogroups.com
> <mailto:electricboats%40yahoogroups.com>, "luv2bsailin"
> <luv2bsailin@...> wrote:
>>
>> Right on Steve, but I suggest running them down more to increase range
> without increasing weight. If you only go to 50%, then half that lead is
> just ballast. Even if they only last 5 years, that's about $200 per year
> at today's prices. I'm sure most power boaters spend more than that on
> maintenance.
>> It would be interesting to compare cost per pound per cycled watt-hour
> or some such bench-mark for various usage patterns. I know there are a
> couple spreadsheet gurus on this site...
>> Cheers,
>> Jim McMillan
>>
>
>

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