Measured Wall-to-Wheels Consumption

After I first got my iMiEV it took me about a month to get the TED 5000 energy monitor up and working properly (had to return one of its modules). Since early March I've been meticulously recording the amount of energy drawn by my iMiEV, whether at home or at a public charging station (and I no longer opportunity-charge at friends' homes with the iMiEV).

Every once in a while I charge to 100% and I then add up all the intermediate charge amounts since the last 100% and figure out what the miles/kWh, kWh/mile, and kWh/100miles were for that interval. This is the actual wall-to-wheels energy consumption, but note the tire pressure caveat at the end of this discussion.

Happy to report the following summary of our everyday normal driving energy consumption for 2 March through 13 May. If you're a purist, you can round off appropriately and recognize that the TED monitor is a consumer product (but it was within 1% of my Kill-A-Watt), and the mileage is off the iMiEV's odometer (which is also within about 1% of the GPS):

Miles driven: 1937.3
Energy consumed: 442.813kWh
Yielding:
4.375miles/kWh
0.2286kWh/mi
22.86kWh/100mi

Which is significantly better than the 30kWh/100mi (27 City, 34 Highway) EPA Monroney sticker.

Using the EPA's conversion of 33.7kWh/gallon, this would yield 147.4MPGe. Not too shabby, even if I disagree with their metrics.

Now, with this information, if you know how much you're paying for electricity in cents/kWh and if you know how much you drive per month or year, you can quickly figure out what your monthly or yearly costs are.

For example, if I didn't have solar and had to pay the going rate for my off-peak (PG&E E-7) of $0.08/kWh, this would yield 0.08*0.2286 = 1.8 cents/mile! If we compare this to a subcompact that gets 30mpg, with gas costing $4.50/gal around here nowadays, that subcompact's fuel costs would be 4.50/30 = 15 cents/mile. Fair to say that our iMiEV's "fuel" cost is an order of magnitude less than an average US vehicle.

Some more tidbits from my data-taking:

Best Range Remaining (RR) after top-up: 98 miles
Worst RR after top-up: 57 miles
Best energy use recorded: 5.32miles/kWh (18.8kWh/100mi) over 113.2 miles
Worst energy use recorded: 3.64miles/kWh (27.5kWh/100mi) over 87.5 miles

The EPA says that the iMiEV's all-round range is 62 miles. By comparison, if I arbitrarily say that our 16kWh battery has an effective usable non-stressing capacity of, say, 14kWh, this would mean for us this averages out to a non-stressing range of 14*4.375 = 61.3 miles ... I just calculated this and, frankly, am surprised that it's so close to the EPA number. In case you're interested, full capacity would be 16kWh*4.375mi/kWhr=70miles.

These numbers come from a combination of my wife's driving (she's a featherfoot) and my own, which ranges from unabashed leadfoot to hypermiling depending on how far I'm going on any particular trip. Average springtime temperature probably around 65degF and altitudes ranging from sea-level up to 2000'. I would guess an overall 50/50 mix of city/highway - sorry I'm not more accurate, as this is the major consumption determining factor. The only "modification" to the car is that I'm running the tires at 55psi, as I perceive that this not only improves mileage but handling as well (I run high tire pressures in all my cars).

Hopefully this puts some mileage speculation to bed. If anybody wants, I can publish the summary spreadsheet as well. I'll occasionally update this as I'm still diligently recording the consumption.

Finally, as they say, YMMV.

Thanks for those stats. I've only had mine three days, and I am planning on tracking my electric usage with a Kill-a -watt until I can establish some norms.

JoeS,

This is great stuff, thanks! I don't know if I've shared this on this forum before, but the Union of Concerned Scientists just came out with a report entitled "Electric Vehicles’ Global Warming Emissions
and Fuel-Cost Savings across the United States". You can find the report here:

http://www.ucsusa.org/clean_vehicle...issions-and-charging-costs-electric-cars.html

They used an assumed ev efficiency of .34 kwh per mile, so your numbers show that in reality a MiEV reduces greenhouse gas emission much more dramatically than the report estimates. I live in upstate NY, one of the "best" places to switch to an ev. I'm picking up my MiEV this Friday and really looking forward to it.

Tony

tonymil, I'm still wading through the UCS report and their new metric of MPGghg. Yes, my iMiEV is running closer to 23kWh/100mi instead of their assumed 34kWh/100mi. :mrgreen:

Now that I've covered over 4100 miles, time for an update since I started my methodical datataking -

Miles driven: 3058.3
Energy consumed: 714.856kWh
Yielding:
Average 4.2782miles/kWh
Median 4.2080miles/kWh
Average 0.2337kWh/mi
Median 0.2376kWh/mi
Average 23.37kWh/100mi
Median 22.76kWh/100mi

This shows that we continue to consistently significantly beat the average EPA rating of 30kWh/100mi.

Best Range Remaining (RR) after top-up: 98 miles
Worst RR after top-up: 48 miles
Best energy use recorded: 5.32miles/kWh (18.8kWh/100mi) over 113.2 miles
Worst energy use recorded: 3.37miles/kWh (29.66kWh/100mi) over 34.9 miles

All the comments in the first entry of this thread still apply, although one of the datapoints was when I opportunity-charged at a friend's house not using a meter, but I recorded the exact amount of time I was plugged in with my EVSE and measured the voltage so the scaled/derived energy input for that session I feel was quite accurate. If anyone wants a copy of the spreadsheet with the data summary just send me a PM.

The only caveat is that I am now running 60psi in the tires instead of the specified 36psi.

This should give any prospective iMiEV owner a reasonable idea of what your operating costs would be as all you need to do is know your electricity cost. For example, say your electricity cost is ten cents / kilowatt-hour, then

0.10 * 0.234 = 2.3 cents/mile 'fuel' use

Fantastic numbers JoeS. Even your worst calculated energy usage, 29.66kWh/100mi or .30kWh per mile, is better than the UCS assumed efficiency of .34kWh per mile. Whenever I tell someone about the MiEV, the eyes stop rolling and they become very interested once I tell them how much money I'm saving by not using gas. But for me, the reduction in carbon footprint is just as important and each reduction in kWh per mile is further reduction in carbon beyond what's in the UCS report. Great stuff.

At the end of 5154 miles yesterday, time for an update since I started my methodical datataking -

Miles driven: 4095.6
Energy consumed: 959.428kWh
Yielding:
Average 4.2688miles/kWh
Median 4.1765miles/kWh
Average 0.2343kWh/mi
Median 0.2394kWh/mi
Average 23.43kWh/100mi
Median 23.94kWh/100mi

All the caveats of my 6/15/12 posting (above) apply and haven't beaten my worst/best records. My new 240vac wattmeter and my old Kill-A-Watt corroborate the T.E.D. readings pretty well.

I'm beginning to suspect that the EPA ratings do not take regen properly into account ... need a separate thread to discuss this.

Thanks JoeS! Your numbers look a lot like mine. I only have about 300 miles so far but I will post when I get more data under my wheels. I have an excel spread sheet full of (useful / useless, can't decide) information. Good to have a comparison!

JoeS said:

After I first got my iMiEV it took me about ...

Now, with this information, if you know how much you're paying for electricity in cents/kWh and if you know how much you drive per month or year, you can quickly figure out what your monthly or yearly costs are.

For example, if I didn't have solar and had to pay the going rate for my off-peak (PG&E E-7) of $0.08/kWh, this would yield 0.08*0.2286 = 1.8 cents/mile! If we compare this to a subcompact that gets 30mpg, with gas costing $4.50/gal around here nowadays, that subcompact's fuel costs would be 4.50/30 = 15 cents/mile. Fair to say that our iMiEV's "fuel" cost is an order of magnitude less than an average US vehicle.
.

Click to expand...

JoeS - trying to resurrect this topic and hoping you might take a look at this web tool in beta mode to help current and more importantly, potential EV owners estimate their costs to drive on electricity:

http://plugwizblog.blogspot.com/ (Reposted as initial link was bad) :roll:

We are hoping for feedback so we can refine and bring it to the masses. Thanks for the consideration.

At the end of 6230 total miles (10026km) yesterday, time for an update since I started my methodical datataking. Since the average and median numbers are so close, I'm not bothering to post the median readings any more, and you can round off the numbers as you see fit.
For the benefit of the rest of the world, I'm now including kilometers as well (a change the US should have implemented a century ago!)

Distance driven with measurements: 5171.1mi (8322.1km)
Energy consumed: 1216.055kWh
Yielding:
Average 4.2524miles/kWh (6.8435km/kWh)
Average 0.2352kWh/mi (0.1461kWh/km)
Average 23.52kWh/100mi
Average 14.61kWh/100km

All the caveats of my 6/15/12 posting (above) apply and I haven't beaten my worst/best records.

Not a lot of miles yet but this is what I have so far:
428 miles (689km)
79kWh used
80% of the driving is 20-35 mph (32-56 kmph).

Average 5.4miles/kWh (8.7km/kWh)
Average 0.185kWh/mi (0.116kWh/km)
Average 18.46kWh/100mi
Average 11.56kWh/100km

OMG joev, your average energy consumption is better than my 'best' measured interval! Just goes to show how well the iMiEV performs if the speeds are kept low. Whereabouts are you located and what are you using to make your measurements?

To Joes:
Best on one charge was 6.1m/kWh (9.8km/kWh)
Worst on one charge was 4.5m/kWh (7.2km/kWh)

Located: Long Island (South Shore), NY (nice and flat here but I do see some slight grades in the road).

I have a current transformer with a digital readout inline to my level 2 charging station. The CT was used in my PV grid tied system for 12 year and is quite accurate. It gives instant and cumulative info and is resettable. I can't chart the whole charge time in a graph but I know the watt rate varies throughout the charge especially in the beginning and at the end.

LOW SPEED = MORE RANGE/kWh no denying it.

Let me know if you want more info on my data collecting.

joev said:

I have a current transformer with a digital readout inline to my level 2 charging station. The CT was used in my PV grid tied system for 12 year and is quite accurate. It gives instant and cumulative info and is resettable. I can't chart the whole charge time in a graph but I know the watt rate varies throughout the charge especially in the beginning and at the end.

Click to expand...

joeev, thank you for that information.

I use a TED 5000 which gives me computer graphing of instantaneous power and cumulative kWhr (by hour, day, month). Unlike you, my power consumption readings are very constant (e.g., 906W at 120vac +/- just a few watts) and even vary very little with line voltage changes. The charger usually takes exactly a ten-minute break at some point in the charging cycle (to check cell sag is my guess) and at the very end there is a measured power reduction which lasts about 1/2-hour as the cells are top-balanced (my guess).

Joes:
Sounds correct about the charge cycle.
Mine starts at ~ 3.3kw then settles in at ~ 3.2kw

There is a period that it drops off for about 10 minutes.

At the end of the charge cycle it slowly tapers off to about .2kw then shuts off.

Like I said this is just from observing the read out at different times. I really don't care what its doing; I just want to know the amount of energy it is using to recharge.

I've wondered how much the hill Joe lives on 'costs' him in juice - It takes some extra for him to get up to where he lives everytime he returns home . . . . and he doesn't get all of that energy back by regenning going back down the hill when he leaves. I would expect anyone who lives on relatively flat ground should have slightly better numbers . . . . and then lower speeds really help too - How far did you compute the car would go at a steady 22 mph Joe? I recall it was something over 400 miles on one charge, wasn't it?

Don

joev said:

Not a lot of miles yet but this is what I have so far:
428 miles (689km)
79kWh used
80% of the driving is 20-35 mph (32-56 kmph).

Average 5.4miles/kWh (8.7km/kWh)
Average 0.185kWh/mi (0.116kWh/km)
Average 18.46kWh/100mi
Average 11.56kWh/100km

Click to expand...

Status quo, all my averages are just about the same as last month.
730 miles (1175km) lifetime
134kWh used lifetime

I am now driving in "B" mode (was driving in "D" and "Eco" in the above stats) and I can see a slight increase in efficiency.
I would not call it a hyper-mile technique but instead of just coasting to a stop I control the braking (slowing the car down) by adjusting the pressure on the accelerator pedal. If I need a greater stopping distance I keep some pressure on the pedal; less stopping distance I ease off the pedal and get more regen.

I keep a monthly and cumulative lifetime average so I will report next month if the "B" mode makes any difference.

Don said:

...How far did you compute the car would go at a steady 22 mph Joe? I recall it was something over 400 miles on one charge, wasn't it?

Click to expand...

Don, yes, on this thread I had calculated 533 miles at 22mph based on the actual battery current drawn by the controller/motor:
http://myimiev.com/forum/viewtopic.php?p=2857#p2857
I also allowed that even if I was off by a factor of two, three, or even four that going really slowly would still result in a huge "get-home" distance if one had to...
Thinking further about it, what I had only measured was the current going to the motor controller. In addition to this, there's the (not insignificant) current going to the dc-dc converter to run the rest of the car's systems, plus, IIRC, the traction battery supplies some other loads directly as well(?). One of these days we'll have to measure all those loads...

joev, your continued terrific efficiency is a reflection of your hypermiling abilities plus your low average speeds and the flat area that you live in. I'll be interested in seeing how this changes while driving in B. For myself, you'd think I was driving a stick shift as I'm constantly moving through the various modes (including a lot of N) depending on conditions, with many spurts showing that the iMiEV is no slouch. This is counteracted by my wife's featherfooting and consistency.

I have no way (yet) of measuring anything, but I seem to be getting about the same 'mileage' as JoeS - ~4.5 miles per Kwh, only in my case, it's including running the A/C 90% of the time. When I'm fully charged, my RR always reads between 75 and 85 miles, depending on what I did previously. It will be interesting to see here in another couple months what changes when we no longer need the A/C

Mostly flat here (I think that helps a bunch) and other than a 2 mile stretch at 45 mph leaving and coming back home, all speeds are well below that - An average of 30 to 35 I would guess, and we know lower speeds really helps

My worst 'tank' was when we went to another city and back on the freeway - About 65 miles total and I barely made it home . . . . turned off the A/C for the last 20 miles or I don't think I would have. Currently, we have ZERO recharging stations around here, so it's charge at home and that's it

Don

Have now covered over 7300 miles (almost 12000km) and here's the latest actual measured energy consumption from the wall summary since I started keeping track (it's gone up slightly as we've been doing a fair amount of freeway driving lately):

Distance driven with measurements: 6223.8mi (10016.2km)
Energy consumed: 1468.535kWh
Yielding:
Average 4.238miles/kWh (6.821km/kWh)
Average 0.236kWh/mi (0.1466kWh/km)
Average 23.60kWh/100mi
Average 14.66kWh/100km

All the caveats of my 6/15/12 posting apply and I haven't beaten my worst/best records.

My methodology is to keep track of all the energy consumed by the iMiEV on a daily basis, but only incorporate it into my summary spreadsheet after fully charging the car which only occurs every few weeks. Using an iMiEV-dedicated T.E.D (The Energy Detective) sensor and corroborated by Kill-A-Watt (L1) and a kWhr meter (L2). I've recently started keeping track of whether it's L1 or L2 as I was curious what percentage of our charge actually comes from each (eyeballing it, L1 predominates for our everyday overnight charging but L2 is used if recharging during the day is needed).

7/31/12
Not a lot of miles yet but this is what I have so far:
428 miles (689km)
79kWh used
80% of the driving is 20-35 mph (32-56 kmph).

Average 5.4miles/kWh (8.7km/kWh)
Average 0.185kWh/mi (0.116kWh/km)
Average 18.46kWh/100mi
Average 11.56kWh/100km

8-31-12
Status quo, all my averages are just about the same as last month.
730 miles (1175km) lifetime
134kWh used lifetime

I am now driving in "B" mode (was driving in "D" and "Eco" in the above stats) and I can see a slight increase in efficiency.
I would not call it a hyper-mile technique but instead of just coasting to a stop I control the braking (slowing the car down) by adjusting the pressure on the accelerator pedal. If I need a greater stopping distance I keep some pressure on the pedal; less stopping distance I ease off the pedal and get more regen.

I keep a monthly and cumulative lifetime average so I will report next month if the "B" mode makes any difference.

9-30-12
And the winner is......B mode. It did make a slight improvment overall.
Averages for the month:
Average 5.7miles/kWh (9.17km/kWh)
Average 0.176kWh/mi (0.109kWh/km)
Average 17.6kWh/100mi
Average 10.9kWh/100km

1303 miles (2097km) lifetime
235kWh used lifetime