Yep, I didn't include the lifespan in doing the cost comparison, because I don't expect to put 500 deep cycles on my batteries in 10 years. Long term costs (over decades) were not even covered in my analysis, so I'm not sure what you're disagreeing with. I am certainly not counting on a lifespan of more than 10 years from my LiFePO4 cells regardless of cycle count, but if they last longer, it will be a pleasant bonus. But as I mentioned, if one expects to delve into the upper ranges of deep cycle lifespans "replacement costs may need to be factored in."
For most of the people that are considering an electric conversion, the up-front investment is a higher priority than costs averaged over a decade or more. At least that's what most of them have said in posts in this group.
Given your typical usage, do you really expect to average more than 4 deep discharges a week (greater than 60% depth of discharge) for the next 10 years? That usage is well within the projected lifespan of LiFePO4 cells. If that is your actual usage than Lithiums will be cheaper than the other chemistries. But for those that average less than two deep cycles a week for a decade (like me), AGM might be cheaper in the long run.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Robert Lemke <robert-lemke@...> wrote:
>
> Eric,
> I agree with your math and the Puekert, DOD, and weight short comings of AGM and flooded. I respectfully disagree on the long term cost, asÂ
> LiFePO4 is the hands down winner when cycle life is entered into the equation. With proper care, 500 cycles is about it for AGM and less for flooded, but at the present time you will get 2000 cycles from LiFePO4 .
> Bob
>
> --- On Thu, 9/6/12, Eric <ewdysar@...> wrote:
>
> From: Eric <ewdysar@...>
> Subject: Re: [Electric Boats] battery cost comparison
> To: electricboats@yahoogroups.com
> Date: Thursday, September 6, 2012, 10:17 AM
>
> Hi Don,
>
> I'm not sure what physics lesson that you're looking for, but here is a detailed comparison between battery chemistries by cost, weight and range.
>
> ---------------------------------------------
> This is what I posted on April 20 this year in post #21398
> "Hi Capt. Todd
>
> Perhaps you mean something like this post that I made back in Jan 2012 (post#20750) and reposted in this month (post #21237). I directly compared the weight and cost of the same usable capacity of different battery types. Peukert's has already been factored in. You can read the whole post here http://groups.yahoo.com/group/electricboats/message/21237
>
> You said "Additional concerns are that the estimated Puekert coefficients might be 1.0 for Lithium, 1.1 for AGM, and 1.3 for Flooded. Estimated safe discharge levels might be 80% for Lithium, 60% for AGM, and 50% for Flooded."
>
> In case you want to check my math, for my calcs I used a PE of 1.03 for Li (no battery is 1.0), 1.1 for AGM and 1.25 for FLA. And you can see that I used discharge levels of 80%, 70% and 60% respectively.
>
> -- Excerpt from post #21237 -----------------------------------
> Let's do the math for a battery pack that has a usable 2.5 hour range at 2500W (6.25kWh used).
>
> FLA â€" 14.25kWh to 60% DoD at 2500W = 2.5 hours = 633 lbs, cost about $1500
> AGM â€" 10.5kWh to 70% DoD at 2500W = 2.5 hours = 520 lbs, cost about $2500
> LiFePO4 â€" 8.25kWh to 80% DoD at 2500W = 2.5 hours = 200 lbs, cost about $3500
>
> So now the lithiums are 2.3 times the cost of the FLA T-105s but they are less than 1/3 the weight for the same range at this load. So for most boaters, I recommend AGMs as a good balance of price to range.
> ------------------------------------
>
> Another point to consider is that the math is dependent on the load. Because of Peukert's Effect, higher load/capacity ratios favor Lithium, but lower load/capacity ratios make AGM and flooded look better. Aiming for the same amount of energy consumed, here's a similar chart at 4000W for 1.5 hours (6kWh used)
>
> FLA â€" 15.1kWh to 60% DoD at 4000W = 1.5 hours = 670 lbs, cost about $1600
> AGM â€" 10.5kWh to 70% DoD at 4000W = 1.5 hours = 520 lbs, cost about $2550
> LiFePO4 â€" 8kWh to 80% DoD at 4000W = 1.5 hours = 200 lbs, cost about $3400
>
> Here's the another chart at 1500W for 4 hours (6kWh used)
>
> FLA â€" 12.5kWh to 60% DoD at 1500W = 4 hours = 550 lbs, cost about $1350
> AGM â€" 9.6kWh to 70% DoD at 1500W = 4 hours = 475 lbs, cost about $2350
> LiFePO4 â€" 7.8kWh to 80% DoD at 1500W = 4 hours = 195 lbs, cost about $3300
>
> Looking at 6kWh usable at both 4000W and 1500W, we can see that FLA cost 40% of Li at 1500W and 47% of Li at 4000W, mostly because of Peukert's Effect. You can see where this is trending.
>
> I haven't even thrown battery life into the mix, but since I'm still working I don't put as many cycles into my boat as I would like. With proper maintenance and charging, I believe that I could get all of these battery banks to last 10 years. But that's just the way that I use my boat. For someone that cycles their pack more often, replacement cost may need to be factored in.
>
> I hope that this helps.
>
> Fair winds,
> Eric
> Marina del Rey, CA
> -----------------------------------
>
>
> --- In electricboats@yahoogroups.com, donald bland <dlblandjr@> wrote:
> >
> > so to answer you retoric question , sounds great , cept , I think I need 48 v ,
> > for a E.Y. system as I understand it .
> > so . . . we have Mike , and George , whom we can , thankfully ask , for a wee
> > physics lesson then mates!
> > perhaps maybe this other fellow, Aaron Vivian , will sign in as he said he would
> > and further enlighten our little minds , eh ?
> > weeel , I must indulge my better half in going out to dinner , so we must resume
> > this convo on the morrow , eh mates?
> >
> >
>
>
>
>
> ------------------------------------
>
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