# Electric Cars: swappable batteries

• posted
A co-worker and I discussed the feasibility of swapping out batteries
of electric cars in an effort to reduce charging time (from hours to
minutes). Curious, I searched the web (and newsgroup) to see if this
has been discussed before, and it has:

Let's do a preliminary economic analysis. Got some numbers to crunch.
For a hypothetical service station between SF and LA, assume:
(1) 10 cars can be serviced simultaneously
(2) 15 minutes needed per battery change/fillup (i.e. full-service
attendants on forklifts)
(3) each car battery holds 100 kW-hrs (3.6E8 J)
(4) each charging station in the "charging warehouse" will be 10 ft by
10 ft.
(5) attendants are paid \$20/hr (burden rate: workers comp, OASDI, SS,
income taxes etc.)
(6) \$0.15/kw-hr electricity
10 cars every 15 minutes is 40 changes per hour. Let's assume the
"charging warehouse" must hold double this: enough for 80 batteries.
At 10' by 10' per charging station, that's 100 ft^2 x 80 batteries =
8000 ft^2, or about 90 ft by 90 ft of charging warehouse.
Charging 80 batteries per hour, at 100 kW-hr per battery:
3.6E8 J/charge x 80 charges/hr x 1 hr/3600s = 8 megawatts of electric
power needed.
For 15 minutes of service per customer, the station spends \$5 (at
\$20/hr employee burden rate), cost passed on to the customer.
With electricity at \$0.15/kw-hr, 100 kw-hr/battery is \$15 per battery.
So, the customer spends a minimum of \$5 + \$15 = \$20 per battery
change.
This amount excludes any profit, and also excludes loan amortization
for the charging equipment, "charging warehouse"
engineering/construction and forklifts.
Any thoughts?
Mike Darrett
• posted
What about the battery costs and replacement every 3 to 4 years?
• posted
A neighbor of mine has a large deep cycle lead acid battery (probably about 10"x10"x20", maybe 150 lbs) that can supply 2.5 kWh (I think that's right, but maybe I'm misremembering). If this is typical then one needs 3 tons of batteries that take up a volume of about 1.3 cubic meters. Double that if the batteries are only allowed to cycle to 50% of their capacity to make them last longer. There's going to be a significant cost in buying all those batteries (and replacing them when they start failing) as well as in tricking out vehicles that can carry that kind of weight.
Ken Muldrew snipped-for-privacy@ucalgazry.ca (remove all letters after y in the alphabet)
• posted
major snip
Battery amortization.
With different folks driving different amounts you can't reasonably build in the price of the batteries wearing out into the recharging sequence.
You pick up your brand new car from the dealer and drive it for a week. You go in to the charging station and they swap out the battery, taking your brand new one and intalling some old clunker that dies after 2 days of little driving.
Whose battery is this?
• posted
On a sunny day (26 Sep 2003 11:13:39 -0700) it happened snipped-for-privacy@darrettenterprises.com (Mike Darrett) wrote in :
Good work, don't forget that they will tax that electricity with a terrible rate as soon as it becomes main stream. JP
• posted
That this juncture, gasoline is a better deal. I can fill up for about fifteen dollars and go 320 miles which is about 20 miles to the dollar. I don't think an electric car can do this well.
On the other hand if going electric will remove us from the thrall of the Ayrab oil lords, it may be worth the extra cost.
Bob Kolker
• posted
At current (no pun intended) energy costs, electricity is less per mile, but range is less, too because power density isn't as high as gasoline.
• posted
That can be factored in per fillup. Assume, say, that the battery will last for 1,000 charges. At \$5,000 per battery, say, charge an extra \$5 per fillup. Expired batteries then get sent to the manufacturer to recover lead parts, and make new batteries.
Hmm... this gets very expensive very quickly...
Mike
• posted
E*L*E*C*T*R*I*C cars used for corporate car carpooling (who would be stupid enough to pay for it out of their own pockets?) lost as much as 50% of battery capacity after only 6 months. Lead-acid batteries hate deep discharge/sizzle recharge. 6 months comes to (5 days/week)(26 weeks) ~ 130 charges.
1000 charges? Ha ha ha.
You will note that even Official enthusiasm for the E*L*E*C*T*R*I*C car died in less than a year. The battery packs cost \$thousands. There was no hiding from physical reality - exactly as Uncle Al predicted.
• posted
You can make a much faster and cheaper swap by having a standard pallet of batteries that are fitted from under the car on an automated system. The battery pack should have an onboard monitoring system that will bill you for damage done to the battery (by excessive charge or discharge rates), and will charge you for the net energy difference over the period of use of that battery. ie if you return a fully charged battery then you will only be charged for battery damage, not electricity.
The Japanese hybrids seem to have good handle on increasing the number of cycles the battery can take, at the expense of using a VERY restricted capacity - typically they only use around 50% of the capacity of the battery.
Cheers
Greg Locock
• posted
Have a look at this URL

Its a battery that can be recharged by pumping a re-charged electrolyte into it. At this point it is aimed at large stationary plants ( load levelling,renewable energy etc) but perhaps in the future ????
Tom Miller
Mike Darrett wrote in message ...
• posted
Very interesting link, thank you for posting it.
A few questions:
1. What are the anode and cathode composed of in this battery system? The article didn't seem to mention any specifics.
Mike
• posted
In sci.physics, Mike Darrett
wrote on 28 Sep 2003 13:05:59 -0700 :
Second question first: Vanadium is apparently cheap enough to be classified as a "minor metal" (as opposed to a "precious metal" such as gold or silver). However, since I'm not a member of a metals exchange I'm having some difficulty locating an approximate price quote therefor. I'm assuming it's cheaper than silver but that's about all I know at this point.
is interesting but I don't read Chinese. It does have a list of prices, presumably in yuan.)
However, a Google on "vanadium price" actually did work (picky beast!) after several other unsuccessful tries, and got me two websites: one that suggests vanadium is about \$5.75/lb for an 80% ferrovanadium variant (whatever *that* is), and another webpage gives a quote of \$11.60-\$11.80/kg, which is apparently slightly cheaper. These are of course merely approximate as far as I'm concerned; presumably people make their livings based on trading commodities to the Nth decimal place, and the price does fluctuate.
A third website, thanks to about.com, gives me prices to compare to; vanadium is about 7x the price of copper (\$0.82/lb) and almost 9x the price of aluminum (\$0.65/lb). [*] However, nickel is just a tetch cheaper at \$4.65/lb.
The federationgroup link as given is slightly borked. I'm not sure if it's a browser or server problem at this time but I was able to get the PDF brochure at
The positive electrolyte is vanadium sulphate, in state 5 (V). During discharge it mutates into state 4 (IV). The negative electrlyte is vanadium sulphate, in state 2 (II). During discharge it mutates into state 3 (III).
Apparently that's about as specific as they're willing to get.
[*] NASAAC is apparently a specialized aluminum alloy and is slightly cheaper as of this writing, at \$0.62/lb. The exchange lists things down to 1/100 of a cent but I just want an overall feeling.
• posted
Whatever happened to the aluminum sulfer battery under development that held 10 times more energy/weight.?
Bret Cahill
• posted
I distinctly remember this one was Al-Su.
Bret Cahill
• posted
Dunno about any aluminum batteries except the aluminum-air battery (or more correctly a cell). The sodium-sulphur cells use an aluminum electrolyte between the liquids.
• posted
Ah ok. My mistake. I thought I read an article in my general chem book about aqueous vanadium pentoxide (catalyst for sulfuric acid manufacture) going for about \$100,000 per liter. But after looking through that general chem book last night, I couldn't find the article.
Maybe I was just having a nightmare about chemical prices at the time.
Cheers
Mike
• posted
If you mean the sodium sulphur battery, the factory burnt down.
Cheers
Greg Locock

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