Wouldn't Miles/Wh Make More Sense?

[PianoAl]

Wouldn't it make more sense to report efficiency in miles per watt-hour* instead of kilowatt-hours per mile? People are used to miles per gallon, and the bigger the number, the better the efficiency.

*Wh instead of kWh because people are afraid of decimals.

 

[GtiMart]

A watt-hour is very small, you would have fractions of miles. You might report miles / kWh, it's just the inverse of Wh/mile. You can use Wh in that case because there will be a couple hundred used per mile, that number is relatable. On the other side, 250Wh/mile would become 0.004 miles per Wh, not great. If you use kWh then it's 4 miles/kWh, a much more manageable number.

Some report kWh/100km, which could be on miles too... 250wh/mile would become 25kWh/100 miles.

In the end it's all the same consumption though.

 

[GSP]

It is better to report “fuel consumption,” as in Wh/mi or L/100 km, instead of ”fuel efficiency,” as in mi/kWh or mpg. The reasoning is that it is much easier to understand the cost implications when comparing vehicles. Intuitively it seems that the difference between an 80 mpg car and a 40 mpg one is huge, and the difference between a 15 mpg and 10 mpg vehicle is not as significant. In reality, the opposite is true. Putting the fuel cost in the numerator, instead of the denominator, makes the difference in fuel cost intuitive. EPA had some info in this on their fueleconomy dot gov website, explaining why they added “gal/100 mile” fuel consumption to their car comparisons. Other sources, including the Society of Automotive Engineers, have also published the advantage of using fuel consumption instead of mpg.

GSP

 

[UncertainTimes]

All people look at is range when they’re shopping. Range anxiety or whatever. No one looks at the fuel tank capacity when shopping for ice cars.

 

[PianoAl]

A watt-hour is very small, you would have fractions of miles. You might report miles / kWh, it's just the inverse of Wh/mile. You can use Wh in that case because there will be a couple hundred used per mile, that number is relatable. On the other side, 250Wh/mile would become 0.004 miles per Wh, not great. If you use kWh then it's 4 miles/kWh, a much more manageable number.

Some report kWh/100km, which could be on miles too... 250wh/mile would become 25kWh/100 miles.

In the end it's all the same consumption though.

Right. I realized my mistake after posting and actually expected more abuse before I got a chance to fix it.

I still think that a number that's analogous to mpg would be best, a larger number being a better thing. That's what people are used to.

To make the values palatable, it would have to be something like miles per milliwatt, but that would be too confusing to the average Joe.

In that case, 250 Wh/mile would correspond to 4 miles per milliwatt. In any case, we're stuck with what we have.

 

[PianoAl]

All people look at is range when they’re shopping. Range anxiety or whatever. No one looks at the fuel tank capacity when shopping for ice cars.

True. I'm thinking more of people trying to improve their efficiency. Right now, it's "I drove conservatively, and got my efficiency to 230 Wh/mile!" or "I put a cargo box on the rack, and ..."

 

[Rocky_H]

People are used to

That's what people are used to.

"That's what [AMERICANS] are used to."
There. Fixed that for you.

The distance per fuel amount is the American system. As @GtiMart mentioned above, liters per 100 km is what is used in Europe, and it's a consumption figure of fuel over distance, like the Tesla wh/mi is.

But I think mainly this does come down to people's instinctive attraction to whole numbers, and how the mind just trails off when it hits a decimal point and forgets everything after that.

So people can kind of remember numbers like 250, 270, 280, 312, etc. if they want to use them. But if you did the miles per kWh, it might be somewhere near 3 or somewhere near 4, and it would be: three point something somethingsomethingsomething I forgot the rest of it. And people get frustrated/overwhelmed with trying to decide how many numbers after the decimal point are important to look at and try to remember. Is one enough? Do I need three? Or four? Anything with decimals is going to have that frustration. But if it can always be formatted to a three digit integer--easy peasy and it sticks in the mind better.

It's kind of the same thing when people say that house electricity bills should be done in Joules, since that's the real unit of energy. The problem is a Joule is freaking tiny, so people don't want to see units in quadrillions.

 

[GtiMart]

KWh/100km (or miles) might gain popularity then. It's energy per distance as @GSP indicates, and similar to gas equivalents. We measure that way here for gas... It gets big enough that decimals are not that important. It would be 25 (kWh/100miles) in my example.

 

[father_of_6]

Miles per 1.21 gigawatts.

 

[3sr+buyer]

Wouldn't it make more sense to report efficiency in miles per watt-hour* instead of kilowatt-hours per mile? People are used to miles per gallon, and the bigger the number, the better the efficiency.

*Wh instead of kWh because people are afraid of decimals.

For miles/Wh, you may get something like 0.003-0.004 miles/Wh. That is why miles/kWh can make more sense, with numbers like 3-4 miles/kWh.

However, Wh/mile is easier to report on the energy screen, because it has no discontinuity at infinity when driving downhill at just the correct grade to be consuming 0 Wh.

On a car with an energy screen reporting miles/kWh, you might see something like this going down a hill (from 2017 Chevy Bolt Review Part 2 (CleanTechnica Exclusive) ):

(Yes, the Model 3 energy screen is better in other ways, but using Wh/mile is one of the improvements in that it avoids the infinity discontinuity.)

 

[cwerdna]

Many US-market BEVs use miles per kWh in the US. That's been true of my all I've owned/leased (current and my previous three, first two being the same model).

 

[cwerdna]

BTW, re: miles/kWh, this sorta relates to a energy efficiency in commercial building class I took years ago. For some unit, someone (not in the class) told the instructor (who is behind writing numerous standard/codes: Building Energy Efficiency Standards - Title 24), "this is America. Bigger is better".

That goes along miles per gallon and miles per kWh. And, since a gallon of gasoline as 33.7 kWh of energy content, miles/kWh makes sense/goes in line w/that.

Anyway, w/the above EVs (from 3 unrelated automakers), we talk about figures like 3.x to say 4.x miles/kWh... maybe 5.x if you drive slow. People with Bolts who have drive in below freezing weather w/cars cold-soaked outside might not even reach 2.0 miles/kWh.

 

[miimura]

In Europe they use liters/100km for efficiency. To them Wh/km makes sense. In America, everyone is used to miles/gal so mi/kWh makes sense to us.

To me they both make sense.

The one that makes no sense is when a German car is trying to show you the consumption while parked and they display kWh/h.

 

[GtiMart]

Yeah, that's because they showed liters/h before at idle, which did make some sense. They just changed the energy unit.

 

[davewill]

KWh/100km (or miles) might gain popularity then. It's energy per distance as @GSP indicates, and similar to gas equivalents. We measure that way here for gas... It gets big enough that decimals are not that important. It would be 25 (kWh/100miles) in my example.

That's the same thing as Wh/mile or Wh/km, just with the decimal point shifted by one.

 

[acarney]

I don't like the 25kWh per 100 miles type thing because I feel like it's harder then if you have 17kWh left figuring out how many miles that would be.

If it's 300 wh/mi I know roughly 3 miles will use 1 kWh which means I have 3 * 17 miles left, 51 miles. Just seems like you can estimate faster and easier when you know how much energy is used in a mile.

 

[BigNick]

In the USA we do MPG, miles per gallon, so Wh/mile seems "backwards" to many of us here. If you are good at doing math in your head, it's not too bad going from Wh/mile to miles/kWh. (Or Wh/km to km/kWh.)

In Australia and I think (most of) Europe, they do L/100km (liters per 100 km). My GTOs, which were re-badged Holden Monaros sold in the USA, displayed L/100km for fuel economy when Metric was selected and I could never get that damn number under about 9.5... and I had to drive like an old man to get that.

Also, MPG <=> L/100km is harder to calculate in your head due to the English-Metric conversions! 3.785 liters in a gallon, 1.609 km in a mile, 62.15 miles in 100 km, and now my brain hurts and I need a calculator.

Once my flux capacitor is ready, I'll be able to measure years per 1.21 gigawatt-seconds.

 

[AdamVIP]

If you switch to miles / energy you have to use kWh because Wh are too small and no one like decimals. The problem with that is that you still have low single digit miles per kWh and when you try to compare cars it wont be all that different without bringing out with more decimals. W/mi is the easiest way to compare across different EVs.

 

[3sr+buyer]

The one that makes no sense is when a German car is trying to show you the consumption while parked and they display kWh/h.

They couldn't just say kW ?

 

[miimura]

They couldn't just say kW ?

Obviously, yes. That was the point of the facepalm.