On 21 Sep 2002 at 2:45, someone wrote:
> According to the site, the current issue is energy density - at
> 25kW/kg. They have some research that gets to 35kW/kg, but expect that
> they would need to get to 50kW/kg to be viable for consumer EVs.
If you mean 25 Kilowatt hours per kilogram (kWh/kg) specific energy, that
would be a sensational figure! Or perhaps you really do mean kW/kg -- a
measure of specific POWER -- also extraordinarily high, as typical golf car
batteries can comfortably deliver around 100 W/kg (not kW).
State of the art in lead acid is around 35watt hours (NOT KILO-watt hours)
per kg, nicad 55 is Wh/kg. Some advanced chemistries run 80+ Wh/kg. There
is NOTHING I know of in the kilowatt hours per kg, except maybe some liquid
fuels.
Not to bash this poster or anyone else, but what's going on here is some
plain vanilla carelessness in nomenclature.
On this list I frequently read kW (kilowatts, a measure of POWER) where the
posters mean kWh (kilowatt-hours, a measure of ENERGY). Recently there was
an exchange in which two people, both of whom are well educated, highly
experienced with EVs, and definitely know better, wrote kW instead of kWh.
In this case, the post quoted above probably meant Wh (watt hours) instead
of kWh (kilowatt hours).
Then there are the posts that refer to batteries as cells. Great heavens,
it's bad enough that Energizer and the others call flashlight cells
"batteries." This misuse is so entrenched that it's futile to fight it.
However, misuse of the terms in EV power systems is fortunately not yet
established and I see no reason not to try to correct it.
For the record, the smallest electrical unit of a battery is a cell (2 volts
is nominal potential in lead acid, 1.2 volts in most alkaline chemistries
such as nicad and NiMH).
The next smallest unit, a group of cells, is a battery or a module
(sometimes called monoblock, especially in alkaline chemistries). There is
some flexibility in expression at this level:
2v lead cell * 6 => 12v battery * 12 => 144v pack
2v lead cell * 6 => 12v module * 12 => 144v battery
1.2v nickel cell * 5 => 6v monoblock * 24 => 144v battery
I know I seem like a fussy old nag, but it doesn't take much to get the
terminology right. With that little bit of extra effort, we'll all know
instantly what you're talking about without having to deduce it from the
context. Thus clarity will be much enhanced.
Thanks for putting up with my rant.
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David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea rider 36vdc
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Thou shalt not send me any thing which says unto thee, "send this to all
thou knowest." Neither shalt thou send me any spam, lest I smite thee.
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