Electric Vehicle Energy Efficiency Rating

[BMWBoss]

I recently read a very interesting article on vehicle energy efficiency written by Tesla Motors and found here:

http://www.teslamotors.com/goelectric/efficiency

At the bottom of the article there is a graph that rates the Tesla as a 2.18 in electric vehicle energy efficiency (very impressive when compared to other cars)

I was wondering what the BMW i3 energy efficiency rating would be. Does anyone here at the BMW i3 forum know of a chart that shows all electric vehicle energy efficiency ratings side by side. Now that would be really cool data to see.

 

[bluebeetle]

The range BMW i3 is supposed to have is 150 km.

 

[QORW]

Ok so can some-one please translate that into kWh per Mile (or kWh per kilometer for the rest of the world)!? kWh stands for Kilo watt hours, the electrical equivalent to a gallon of fossil fuel

We all measure our car's running costs by Gallon per Mile which is easy to translate into Dollar per Mile if you know the gallon cost but I have NOT seen an electric vehicle running cost figure anywhere!?

kWh per Mile can easily be translated into Dollar per Mile if you know what your Utility charges you per kWh to charge your EV's battery! Q.E.D!

P.S. There will of course be some heat losses in the process so what you drive out in kWh is not wot u put in da "tank"!

 

[Northwestern]

QORW: Gasoline prices right now average $3.68/gallon and electricity costs used to calculate EVs empg are based on a national average of about 14 cents/kwh. So based on an ICE at 25 mpg the cost is about 14.7 cents/mile. For the i3, I'm using 96 miles per 22 kwh and assuming a 10% loss between the charger and the battery; so it takes about 24 kwh to fully charge a 22 kwh battery. It's about 3.5 cents/mile to run an i3.

Now in my world there are complications. I can only use 100 kwh per month before I hit the 29 cents/kwh tier. There is no reason for me to buy an i3 and pay 29 cents/kwh. I can buy a "time-of-use" meter so I can charge at night at 14 cents/kwh. But the installation of the meter isn't cheap. I'm better off with an i3 with 16 kwh and a range extender so I don't have to install a TOU meter. One would think car manufacturers could eventually tailor the battery capacity to our individual needs instead of offering one size fits all.

 

[QORW]

Ok northwest, thanks for that, it makes sense looking at the Tesla website refered to at the start of this thread.

However, if I understand BMW i3's website correctly, they claim a 125kW output so assuming one drives it flat out, and the car can do 80 miles at full steam 100 miles an hour that comes to 80/100= 0.8 hours driving time which means 0.8 x 125kW = 100kWh consumed (not taking into account road losses etc). So at your 14c per kWh that would be $14 per 80 miles which is 17.5c per mile! Way more than the 3.5 cents/mile you got??

Ok so I guess one would NOT drive it flat out, but that would just extend the range and not the efficiency??

Where am I going wrong?

 

[Northwestern]

QORM: I think you are asking questions above my pay grade. That said, I think you are confusing megajoules and horsepower. I think at full power (125 kw) of output you are using about 57 kw per hour of battery, so you can go 22/57 times 100 mph or about 39 miles out of the i3, which is 8.6 cents per mile. Even if this "guess" is wrong, the important point is range is severely impacted by speed. The i3 may not be the car for 80+ mph drivers.