Wh/M - Watt-hours per Mile

[Gigi]

I left the office today with 23 miles range showing.  Driving only in EV mode, I arrived home after 12.4 miles with 15 miles range remaining.  It is downhill from my office to home, a change of -64 feet elevation on surface streets with speed limits of 35-45. Ambient temperature was 59 degrees.

 

It took 2.4 kWh to drive 12.4 miles, which is 194 Watt-hours per mile.  (kWh used divided by miles driven = Watt-hours per mile)

 

We bought the car in November and have been looking at Wh/M figures in a cold winter with the heater running and the battery not being as efficient as it can be.  I am amazed that this car can get such good Wh/M.  I am supposing that temperature has a lot to do with this. 

 

What kind of Wh/M are others getting?  Perhaps comparing only trips longer than 10 miles 100% EV would be most helpful.

[larryh]

You can find measurements of power required to go various speeds here: 

 

http://www.fordfusionenergiforum.com/topic/1020-reported-trip-energy-used-vs-energy-required-to-recharge-car/?p=5711

 

To compute kWh/mile, divide the power by the speed.  So, for example, the power required to go 50 mph is 10.8 kW.  The kWh/mile is then 10.8 / 50 = 0.216 kWh/mile.

Edited March 6, 2014 at 09:44 AM by larryh

[Gigi]

So, larryh, in that thread you were discussing kW of power used to move the car at different rates of speed expressed in miles per hour - kW per mile per hour, actually, not kW-hours per mile as you suggest above.  I see that you are discussing how how it takes more kW of instantaneous power to move the car at a higher rate of speed vs fewer kW of power to move it at a lower rate of speed, making the Wh/mile consumption rate higher for higher speeds.  Very interesting.

 

My observation is regarding a different and perhaps simpler subject, having to do with how much energy is consumed in moving the car at any speed over some distance expressed in Watt-hours of energy consumed per mile of distance traveled.

 

What I was remarking on is how surprised I am by the difference ambient temperature seems to have made since spring has started here in Atlanta on the number of Watt-hours it takes to go a mile.  I have been accustomed to seeing energy consumption rates for both Energi and Electric being in the 300s and 400s of Watt-hours per mile when it was in the teens and 20s of winter temperatures here.  Seeing a trip average under 200 Wh/mile amazes me. 

 

The MyFord Mobile web page for "trip and charge log" for Electrics shows the calculation for Wh/mile for trips in the same spot on the page where it shows the calculation of MPG for Energis.  kWh consumed divided my miles driven for a trip (Wh/mile) is the fuel consumption rate that people on the Electric forum discuss instead of MPG of gasoline.  Since my wife started driving our Electric and I started driving the Energi, I have been driving the Energi almost entirely on electricity.  In this situation, MPG of gasoline has become almost irrelevant as a rate of consumption and I've begun to pay more attention to Wh/mile consumed in the Energi.  It is still gratifying to see someone's reaction when I tell them that I'm averaging 140 mpg on my current tank of gas.

Edited March 6, 2014 at 02:22 AM by Gigi

[larryh]

Traveling at 50 mph requires about 10.8 kW of power.  If you do that for an hour, you will have used 10.8 kWh of Energy and have gone 50 miles, and used energy at the rate of 10.8 kWh / 50 miles = 0.216 kWh / mile.  These measurements were taken at 70 F.  If you are interested in the effect of temperature on mileage, see:

 

http://www.fordfusionenergiforum.com/topic/1446-cold-weather-observations/?p=10225

 

Note that 150 MPGe corresponds to 1 / 150 = 0.0067 equivalent gallons / mile, or 33.705 (kWh/equivalent gallon) * 0.0067 (equivalent gallons/mile) = 0.225 kWh / mile.   The 0.2 kWh / mile that you achieved corresponds to 168 MPGe.

Edited March 6, 2014 at 10:16 AM by larryh

[Gigi]

Perhaps my question is not clear.

 

What kind of difference are you seeing in your actual Watt-hours per mile driven now that the weather has begun warming up?  My question is about actual trips of varying speeds and distances in present weather conditions compared to winter conditions.

 

I am not asking how many kWh of energy are consumed going at a set speed on flat terrain for a set period of time.  That is an interesting question and a useful and interesting answer, but it is not my question.