Good stuff there Eric. It will take me a while to digest it all, but it looks reasonable. I think you may be a little pessimistic in assuming 250 cycles to 60% for the T-105s, but I don't have any hard data to back up that assertion. At any rate, the general sense sense I'm getting is that for lower power applications lead-acid compares favorably cost-wise, but there is a weight penalty. As you get above a few HP the balance tips in favor of LiFePo. Looks like they are pretty close in the 2KW range where I tend to operate much of the time, and the lower up-front cost is a definite advantage for me. Thanks for the insight.
Jim
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> 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:r
> 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, "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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