dgpcolorado wrote:While I see your point, I find the unit "kWh/100km" a bit kludgy...
As a general rule of thumb, the larger your sample size the more accurate the estimate. So kWh per 100km gives a better idea of how much energy it will require to take a trip. Wh/KM could be misleading because where was the sample taken?
dgpcolorado wrote:Anyway, comparing EV energy use to the energy equivalent of gasoline seems a bit misleading. The energy content of gasoline expressed in kWh does show how inefficient an ICE is but isn't that well known? And how do you express the efficiency losses of an EV? Charging at 6 kW is perhaps 90% efficient, unless one is preheating, when it could be considerably lower. Charging at 1.4 kW is about 75% efficient. What sort of number do you use for your kWh/100km figure? An EV with a battery Temperature Management System (TMS) has additional efficiency losses, but how could one put a number on them? The point I am trying to make is that a dash number of "kWh/100km" is not really a fair or useful comparison to L/100km, converted to kWh/100km, for an ICE car.
There is nothing misleading about comparing kilowatt hours to gasoline, both units can be expressed accurately as BTU's which means the conversion is straight across and accurate. While my numbers were quickly generated by the guess-oh-meter and the fuel economy for my cars was hand calculated it is sufficient to illustrate the vast difference in energy efficiency between the electric car and the internal combustion engine. I did not including charging losses as part of my calculation, though correcting for losses would not effect the final values dramatically. The Leaf is still the clear winner in energy efficiency.
dgpcolorado wrote:For EVs at this early stage the most important metric is range. Once all EVs have a long range then relative efficiency will become a more interesting number.
Range is not a metric of efficiency, it is the capability of the vehicle and is beyond the scope of this discussion. I'm talking about improving the way that energy efficiency is displayed to the driver.
abasile wrote:I agree. The only reason, I think, for the '100km' in L/100km is that L/km would end up being a small decimal number like 0.095 L/km. Wh/km is cleaner all around.
As mentioned above, the reason for unit of energy per 100km is that a larger sample size has greater accuracy.
abasile wrote:BTW, as one with science training, I am in favor of the US switching to metric units, though I acknowledge some caveats. For instance, the Fahrenheit scale seems more intuitive than Celsius for day-to-day use because 0 is "really cold" and 100 is "really hot", and negatives aren't all that common for most of the US population.
If you truely have science training and you feel the Fahrenheit scale is more intuitive, I suggest you go back for more training.
There is nothing more intuitive than using water as reference. Water at sea level boils at 100C and freezes at 0C. How is that not intuitive?