Is kWh a good measure for battery capacity?

WarpedOne · Jun 9, 2013

Yeah, I know it is a standard way of doing it, but is it good?

Good in a way that TM advertises 60 kWh and 85 kWh versions and the confusion that at least 3/4 ob Model S owners share.
They are a bit familiar with kW from ICE world (don't really know what it means). They now see kWh and don't know what to do with extra h they forget about it and go saying they have a 60 kW model S.

60 kW ICE car is a P*O*S people mover not a luxury car. Yes they are wrong, but that doesn't stop them misrepresenting their car in the eyes of others who know sh*t of physics and cars.
Oh, you have 60 kW? Meh, I have 200 kW!

Yes, advertising batteries in terms of their rated range would be even worse. What would be much better is representing the capacity in the right unit - Joules.

60 kWh battery should be advertised as 216 MJ battery and 85 kWh battery should be advertised as 306 MJ battery. When someone would ask what MJ stands for they could answer it stands for MegaJoules, millions of joules, millions!

Such advertising/designation would be
1. completely right from physics point of view (kWh is also),
2. they would not give misrepresentation hammer into the hands of joe shmoe (as they do with using kWh)
3. and mega is waaay better then mere kilos of whatever

If they don't want to switch kWh for MJ, they could at least stop differentiating between them on kWh. Call the 60 kWh basic battery, and 85 kWh range battery or something similar.

These 60 kW Model S sh*t must stop BEFORE they move to GenIII.

jerry33 · Jun 9, 2013

I don't see the problem. The average person can't describe the difference between a kW and a kg. It's not confusing to most people and everyone grasps that 85 > 60.

AnOutsider · Jun 9, 2013

Hmm I've never come across confusion over an ICE when discussing kwh. Also, if they call it basic and large or whatever, what happens when 120kwh comes into play? Or 60 gets dropped?

I think the current method works well, and is similar to discussing engines in terms of size (v8, v10, etc)

WarpedOne · Jun 9, 2013

A: Ou, you have EV?
B: Yes, it's a 60 kW Tesla
A: Just 60 kW? My honda has 200 kW, yes these EVs are week, slow, ....

bollar · Jun 9, 2013

It may be a question in Europe (the OP is from Slovenia). It's not an issue in the US. We'd probably use mega calories, not mega Joules, anyway.

jerry33 · Jun 9, 2013

The difference is the battery is 60/85 kWh, not 60/85 kW. The energy screen in my 85 goes up to 320 kW. It's the difference between storage capacity and power.

bollar · Jun 9, 2013

The OP's point is that in the metric world, car power is expressed as kW, not HP. He expects confusion between the battery capacity (kWh) and power (kW).

scottf200 · Jun 9, 2013

"kWh" are on folks electric bills so it at least the masses have seen that and can (mostly) relate. New topics about math and units are not the masses strong point. kWh units like gallons of gas seems easily understood by folks I talk to the Volt about. 16 kWh - think in units like gallons of gas.

GSP · Jun 9, 2013

I think the reasons to use MJ have real merit.

However, I buy my electricity in kWh, so I prefer to stick with that.

kWh also make it easier to calculate charging times given a kW power rating on the charger.

GSP

Raffy.Roma · Jun 9, 2013

@WarpedOne

I think that KWh or Wh is a better way of expressing energy when we are talking of electric energy, while KJ or J is a way of expressing energy in general.
That is to say if you want to express the energy stored in a battery you'd better use KWh, while if for instance you want to express the kinetic energy of a car travelling at 100 km/h you'd better use KJ.
It's like this because power rating of chargers are given in KW.

brianman · Jun 9, 2013

WarpedOne said:
A: Ou, you have EV?
B: Yes, it's a 60 kW Tesla
A: Just 60 kW? My honda has 200 kW, yes these EVs are week, slow, ....

I don't think Tesla's volume is anywhere near big enough to require them to market to mentally deficient customers. Maybe in 2020, but not yet.

widodh · Jun 9, 2013

It's just education. Since I see a lot of people doing it wrong, even a Nissan Leaf commercial on the TV here had it wrong: "The Leaf has a 24kW battery and can be charged with up to 6kWh" (!!!!!)

Anyway, even people on this forum get it wrong, they still confuse kW (Power) with kWh (storage), but again, education. People just need to adapt, that's all.

raymond · Jun 9, 2013

WarpedOne said:
What would be much better is representing the capacity in the right unit - Joules.

I want to win the meter vs. yard/feet/mile-debate first. Then I want to bury mr. Fahrenheit, and only *then* might we go after the kWh.

Funny thing: even in the Netherlands most everybody still speaks in horsepower even though ICE power is advertised in kW. In short: this is not going to happen in your lifetime.

- - - Updated - - -

widodh said:
People just need to adapt, that's all.

Yup. And if there's just *one* thing people suck at, it's change.

brianman · Jun 9, 2013

raymond said:
Yup. And if there's just *one* thing people suck at, it's change.

"Okay... so the movie is 11.75 and you gave me a 20...."

deonb · Jun 9, 2013

kWh is one of the more silly units of measurements in the world. It's basically k(J/s)h. Or kilojoules-per-second hour.

It's like saying the cruising altitude of an airplane is 11.1 feet-per-second hour, rather than just 40'000 feet.

Having said that... at least 11.1 feet-per-second-hour is still explainable and easy to convert. What we have in practice today is worse and even more arbitrary (40'000 feet = 7.57 mile).

So I agree with Raymond, I'd rather have yard/feet/miles taken care of first. Oh, and non-ISO paper sizes while we're at it.

WarpedOne · Jun 10, 2013

He expects confusion between the battery capacity (kWh) and power (kW).

I didn't expect it, I'm seeing the confusion is already here. On this forum and elsewhere:

If I was to charge a 60kw model S with a standard outlet aka nema 5-15, how long would it take to charge from empty to full?

If he was just lazy at typing he would/could write 60 or 60k that would be even shorter and not wrong. People tend to loose that h that turns quantity into speed.
Q: How far is your daily commute?
A: 50 mph
Exactly the same nonsense.

I don't expect Tesla will educate people on physics etc only that they would do something to discourage the wrong use like at least not referring to different battery packs in kWh.

Yggdrasill · Jun 10, 2013

The solution to stupid people isn't to dumb things down, the solution is to laugh at them. (Not necessarily right in front of them.)

CapitalistOppressor · Jun 10, 2013

What people in the U.S. understand is Horsepower, Torque, 0-60 times and 1/4 mile times. I've yet to meet an American who looks at those stats for the Model S who doesn't immediately say "Holy Cr@p!!"

kWh, kW or Joules are all utterly incomprehensible to Americans, except for how kWh relates to their electric bill.

brianman · Jun 10, 2013

CapitalistOppressor said:
kWh, kW or Joules are all utterly incomprehensible to Americans, except for how kWh relates to their electric bill.

Gotta love generalizations.

Everyone in my sample set of one thinks it's annoying and unnecessary.

hiroshiy · Jun 15, 2013

I love this thread... Thought calories is easier to understand for most people without scientific degrees. 60 kWh battery has approx 52000 kcal.

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Is kWh a good measure for battery capacity?

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