In defense of lead acid, the detailed picture painted by Eric is a bit optimistic on the side of Li and pessimistic on the side of Pb.
Lifespan: Few of the LiFePO4 batteries now in EVs have been in that use for more than 3yrs. I doubt you can find a single EV that has had these batteries powering it for 10yrs. The first of these Chinese batteries (Thundersky) to arrive in the U.S. and put into use in EV’s were here in Portland and imported by a friend of mine, Victor Tikhonov. The battery quality was terrible, capacity dropped like a rock and the company refused to accept any returns or make good for the customer. Internal corrosion problems due to poor quality and process control as I recall was to blame. Many of those early adopters refuse still to trust any of these Chinese batteries since they never admitted blame or made good to their clients. Lots of money was lost as these cells were more expensive than today’s cell prices. I believe these were LiIon batteries and not the LiFePO4 batteries now being deployed.
There’s no guarantee that any of today’s LiFePO4 batteries will last 5yrs, let alone 10yrs. It remains to be seen with today’s late adopters of these 2nd generation cells if product quality will withstand time or not. Noone knows. Contrast this with PbA---there’s over a century of data, theory and evidence to be able to have confidence in cycle life, actual life and quality. And while not disputing that an average T105 battery might not deliver more than 250 cycles at 80% DOD for 5 yrs, for our boating use where it might be more typical to charge/discharge 25 times per year, the T105’s, if treated well, can indeed deliver power for 10yrs or more (I still have 4 T105 batteries from 1999 as part of my 14-battery pack that powers my 1920 Milburn Light Electric car ). Sure, they’re tired as are the 8 that I purchased in 2002 and the 2 unknown history ($20ea) ones, but I have confidence and have demonstrated 16+ mile range with that car, which is all I need. My boat also has T105’s powering it (6 of em)---as these are also of unknown history ($20ea) sure they’re tired, but they provide the limited range I need and despite being probably 6 yrs old, they will probably go another 6 years before I have to retire them. Even if I could find used LiFePO4 batteries as cheap as the used PbA batteries I use, could I trust them?
Bottom Line: PbA has been demonstrated to last 10yrs or longer if treated well and not cycled deeply or often. It remains to be seen if long life will be realized for LiFePO4 batteries in EV applications regardless of cycle frequency.
Cost: Given there’s reason to disbelieve the life claims of LiFePO4 batteries, particularly if the cells aren’t tested carefully and screened by the importer before being sold to the customer, then there’s doubt that the cycle life difference between PbA and Li will justify paying the added cost for Li. If they both last 10yrs for a given low cycle rate per year, with LiFePO4, you paid 2-3x as much as you could have paid with PbA. As I see it, you need to use your boat at least 25 times per year to come close to justifying the cost of Li based on energy/$. If you don’t see using it that often but still are considering Li, you need to focus on the other factors which make LiFePO4 the better choice for you---weight and volume savings are big.
One final consideration: While you can draw LiFePO4 batteries down to deep discharge levels without penalty while PbA pays in cycle life, in the limit, a PbA battery that gets drained to 100%DOD can live to charge/discharge many more times, while the Lithium battery may have delivered its last charge. A Battery Monitoring and Management system is essential for Lithium rechargeables----without one, you can almost be guaranteed you’ll have to replace cells far earlier than you’d like.
-Myles Twete, Portland, Or.
The Reach Of Tide 26ft Columbia River barge cruiser
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Eric
Sent: Thursday, September 16, 2010 9:59 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: Battery Life and Types
Jim,
The 250 cycles for the T-105s is based on a 5 year lifespan and the 500 cycles of Li is based on a 10 year lifespan. Realistically, I don't know that I would even get 50 deep cycles a year from my boat, but I had to pick something. The 500 cycles of Li is less than 1/4 the rated lifespan, but I don't think that the batteries will last 40 years. I haven't heard anything to make me believe that 10 years is unreasonable from the LiFePO4 prismatic cells. My experience has been that even when I take reasonable care of flooded cells, their performance starts to drop off noticably by 5 years, regardless of the cycle count. Other people may be more successful than I have been.
I did read somewhere that deeper cycles on FLA batteries don't really reduce the lifetime delivered Wh. Over simplified, the idea is that a battery that is discharged to 40% will last twice as many cycles as one discharged to 80%. Half the cycles, but twice the energy delivered in each cycle results in the same lifetime delivered Wh. There was no empirical data to back this up, and I'm guessing that the relation is not perfectly linear, but this might be true within 10 or 20%.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@...> wrote:
>
> 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
>
No comments:
Post a Comment