BMW i3 Confirmed as Most Efficient EV Yet

MAY 7 2014 BY DSCHURIG 49

BMW i3

A Legion Of BMW i3s Waiting For Delivery At A US Port Last Week

Several months ago, I published the results of an analysis to rank BEVs according to several key performance measures that included projections for the then unreleased BMW i3. This is an update to that article using the newly released EPA i3 metrics.

Recently Released EPA Data Puts The BMW i3's Range At 81 Miles With An Efficiency Of 124 MPG2

Recently Released EPA Data Puts The BMW i3’s Range At 81 Miles With An Efficiency Of 124 MPG2

One of the conversations that is rarely if ever included in the EV forum discourse is efficiency. There is as much conversation as you could ever want about range, conveniences, charging protocols, acceleration, regen, interior sound levels, battery life, interior capacity and more but very few words are exchanged about how efficiently EVs propel themselves and their occupants from destination to destination.

Even, one might say especially, in the realm of alternative energy vehicles where reducing the carbon footprint is central to the concept, efficiency remains the true premium since in their presently generated form, all alternative fuels have a carbon cost. Possibly someday in the future we will be swimming in gloriously abundant photovoltaic electricity and the story will be different but we are nowhere near that point yet so we must consider efficiency in our analysis of EV performance.

True, EV drive trains are inherently more efficient than their ICE counterparts but they are currently powered by batteries and energy storage density in batteries is much lower than gasoline as we know. For a given vehicle package with current technology, EVs are heavier than ICEs due largely to battery mass. As we also know, mass is the enemy of motion, or more accurately change in velocity – acceleration, braking, turning, suspension response, handling are all negatively impacted by mass.

The First BMW i3 Was Delivered This Month In The US - In BEV "Electronaut" Trim

The First BMW i3 Was Delivered This Month In The US – In BEV “Electronaut” Trim

The lower battery energy density makes the balance between mass and performance more delicate for EVs than for ICEs – a few more gallons of gas won’t penalize you much in mass but it will provide substantially more energy. Obviously energy can be increased by a larger battery as well but batteries are heavy and a bigger battery necessitates a stronger structure (read heavier) and the return is not linear. The heavier structure also requires stronger (heavier) suspension components which then require a bigger battery which mandates a stronger structure ad infinitum.

But mass isn’t the only story, there are other energy sapping factors to consider in addition to old-fashioned mass including overall size, coefficient of drag, drive train losses, circuitry losses, wheel size/geometry, rolling resistance and more. So achieving higher efficiency is a remarkable balancing act, very sensitive to movement in any direction away from the optimized performance target.

So I thought it would be good to look at EV choices relative to efficiency to see where the market is. I compiled a list of the EVs that have been tested by the EPA with their five cycle test, hoping to result in a data set that is more objective then by using OEM numbers or magazine tests. I recorded the efficiency in kWh per 100 miles for each vehicle from the EPA list (I am only analyzing BEVs so I just don’t want to look at MPGe, too much ICE in it for me).

I then calculated Miles per kWh, the metric I like best for BEVs. I added a few other data points that may be of interest to this discussion and populated them from the OEM websites – 0-60 times came from zeroto60times.com except when it was available on the OEM website.

Sorting on Miles per kWh generated the table below:

EV Miles Per kWh

BEV Miles Per kWh

In this analysis, as we all now know, the BMW i3 is the leader, nearly twice as efficient as the least efficient RAV4. The Bavarians have achieved quite a remarkable result, designing the i3 to the top of the “do more with less” rankings. And of course, this correlates to the lowest annual fuel cost. But does it sacrifice in other important areas? As important as it is, efficiency at the expense of other critical performance criteria does not a great product make so I checked out a few other rankings:

0-60 times:

BEV 0 to 60 Times

BEV 0 to 60 Times (Editor’s Note/Update: The Mercedes B-Class ED Is Also Being Promoted at 7.0 Seconds to 60 MPH)

The Teslas dominate this measure as we all know. The i3 holds its own though, high on the rankings coming in right after the Teslas and apparently in line with its most obvious upcoming competition – the Mercedes Benz B-Class ED, said to have a 0-60 time of 7 seconds as well. The RAV4 is a surprise but it does have that big battery.

Curb Weight:

BEV Curb Weights

BEV Curb Weights

The i3s are not the lightest of the group which may not be surprising considering the diminutive nature of several of the offerings. As small as the small ones are, including a two-seater, as a group they operate on the lower end of efficiency and acceleration spectrum emphasizing that mass is not the only factor in doing more with less. The Teslas are the heaviest by a substantial margin – the SP85 is literally a full ton heftier than the i3 BEV.

Range:

BEV Range Chart (Editor's note/update:  Mercedes-Benz B-Class Is Being Promoted At 85 Miles EPA - although there is no documentation on that as of yet)

BEV Range Chart (Editor’s note/update: Mercedes-Benz B-Class Is Being Promoted At 85 Miles EPA – although there is no documentation on that as of yet)

Again the Teslas own this category with their massive battery packs. They do it with brute force, however, claiming the lowest efficiency and highest mass in the group. The i3 is in the middle of the rankings, generally ahead of other vehicles that offer much less in other function and features.

Conclusion:

The i3 has clearly established a new bar in efficiency demonstrating what is possible with a clean sheet, purpose built design.

It is not the smallest or the lightest or the least utilitarian or the slowest EV from the set the EPA has tested, which one may expect from the vehicle with the highest efficiency. In fact quite the opposite is true – it also exhibits strong performance by other measures including acceleration and with its low curb weight, it should prove to be very nimble and has already been reported to possess great handling. All with seating for four adults and a cargo area. In my opinion, it is the best all around performer due to all of these considerations, the most significant of which is its EV leading, carbon footprint reducing efficiency.

Footnotes for all four tables:
1. Curb weight, Motor, Torque Battery capacity from OEM websites 2. 0-60 times from www.zeroto60times.com. From their website “0 to 60 times and Quarter mile data is gathered from numerous credible sources. There are a great deal of factors that affect 0-60 stats, so different sources may test the same vehicle and each may arrive at a unique 0-60 mph and quarter mile result. Zero to 60 times .com does not guarantee the accuracy or validity of the any of the 0-60 mph times 3. EPA Combined rating as reported on www.fueleconomy.gov 4. 0-60 times for Tesla from www.teslamotors.com, Smart Electric Drive time is for 0-62mph, Toyota 0-60 from www.toyota.com 5. Tesla Model SP 85kWh Curb Weight from www.teslamotorsclub.com 6. Sport Mode 7. Specs from www.wikipwedia.org/Toyota iQ

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49 Comments on "BMW i3 Confirmed as Most Efficient EV Yet"

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Is it even more efficient that a Segway? 😉

+1

I know EPA and NEDC ratings are different but as the Renault Zoe doesn’t have an EPA rating I thought it worth commenting that on the NEDC ratings the Zoe still comes out more efficient than the i3. The i3 in most efficient mode has a rating of either 160km or ‘up to 200km’ (depending who you ask) while the Zoe manages 210km – both on a 22kWh battery pack.

The i3 only uses 18.8 kWh of battery. It does not allow a full charge of 22 kWh, presumably to increase the longevity.

I believe the full 22kWh is available on the BEV, just not the Rex and, either way, the theoretical maximum range used for NEDC is based on the 22kWh.

Personally if I was paying for and hauling around 22kWh worth of battery I’d be a little upset if I was prevented from using more than 10% of it.

As a RAV4 EV owner, I am certain the RAV4 EV gets better than 2.3 m/kWh. I average 3.2 m/kWh in my daily commuting over hilly terrain. Many other owners get better performance than I, but I drive almost exclusively in Sport mode with the AC on and stereo rockin’. And the RAV much bigger than everything else in the list except the Tesla. Maybe a typo?

The EPA methodology measures kWh from the wall, so it includes the battery charging losses. That is the main reason the mi/kWh figure is lower than what the car displays. Also, the EPA figures are “adjusted” for heating and other things that you may seasonally encounter.

Being the most efficient is honorable and worth touting. However you have to consider:

Two extra solar panels will make up the 25% disparity of all EVs.

If you are paying the utility, 50 cents per day saving will never make up the $10,000 premium.

$10,000 delta could more than pay for the solar energy for all the other models in the list except the RAV 4 and the Model S. Then the other models are having a larger green impact than paying the premium for the higher efficiency alone.

I hear what you’re saying, but BMW is going to do something with that $10k also. If they plow it into building more wind energy for their production plants, that’s as good as you buying a solar array on your house. No, we don’t know that they will do that … but we could assume, especially if the i3 sells well, that at least some of that money is going into making a future EV (i3 or otherwise) more efficient – since that’s the “signal” sent by that purchase.

They could try this in WA, where I believe they make the i3:
http://southeastchptap.org/profiles/se_profiles/BMW_Manufacturing-CHP_Project_Profile.pdf

As for fueling costs, the efficiency is kinda pointless. All the EVs are really cheap to drive, even the P85 Tesla.

However, the efficiency matters for getting the best range out of the battery. Since the i3 managed to get a decent range out of a pretty small battery. Of course that helps BMW more than it helps you since it lowers their battery costs.

And for the 100th time . . . I still just don’t understand why they didn’t provide an option for a larger battery pack!?!?!

Darren hi,

Thanks for a detailed post.

I’d like to add that with BEVs, even more than a few % shaved off per-mile efficiency (which the i3 does very well as you demonstrate), the *production* CO2 footprint is important.

A typical ICE compact will emit during its driving life, at least 10x more CO2 than the amount needed to produce it.

For BEVs the factor is much smaller. First the numerator is smaller, especially as the grid becomes cleaner. Second battery-tech being still immature and inefficient, the CO2 emissions in producing BEVs are higher (that’s the denominator).

As a result, a (say) Nissan Leaf driven on Pacific Northwest roads, might take ~10 years to emit from driving, the same amount of CO2 spent in producing it.

And here’s where BMW i3 really shines: at least according to their publications (http://www.bmw.com/com/en/insights/corporation/bmwi/sustainability.html), they put a lot of effort into reducing the production CO2 footprint as well. A 3rd party will be needed to put numbers on that claim, but still hats off to BMW for designing footprint-reduction into the manufacturing process.

Your mileage figures for Tesla Model S are too low. I averaged 348 kWh/mi on my P85 which is 2.9 mi per kWh. During my last annual service, I got a 60kWh loaner and I can easily get 3.6 mi per kWh.

These calculations are wall to wheels, not simply your driving efficiency. The Model S is known to have high charging (vampire) losses than many other EV’s. Probably a lot to do with its robust thermal management system.

Efficiency does not trump Deficiency.

Cost Efficiency

The one efficiency statistic not listed above.

So who cares if i3 is efficient if it costs the consumer nearly the price of an iMiev more than SparkEV or LEAF yet produces even slightly less range?

Sure, it’s fun to sit on our technical high-and-mighty thrones in front of our laptops and pontificate about how efficient i3 or i8 is due to their plastic, coated with a veneer of carbon fiber bodies placed upon aluminum structures…But when the rubber meets the road folks – it’s dollars and sense.

Has anyone written a technical sheet for publication here of how much BMW will charge an i3 owner for a fender, door and hood damaged in an accident?

As techie as we pride ourselves, we must also use the practical side of our brains.

In most cases the costs of repair are actually lower, compared to a conventional body!

‘Only’ the passenger cell and the door frames are made of carbon fiber. The outer skin is made of plastic plates which absorb smaller bumps. And in a case of repair they can be replaced easily.

The body parts you mentioned are cheaper than their counterparts of a conventional 1 series:

Front fender
i3: 200 EUR / 1 series: 250 EUR

Hood
i3: 250 EUR / 1 series: 455 EUR

Even the i3’s front door, which has a carbon fiber frame, is cheaper:

i3: 415 EUR / 1 series: 480 EUR

The tables are using outdated numbers. The actual Nissan Leaf S NA model has a weight of 3,242 pounds.

http://www.nissanusa.com/electric-cars/leaf/versions-specs/

Wish they had an option to fill the Rex area with extra battery capacity. Then they could move up the charts in range.

Amazing. The BMWs actually look *better* with the white protective shipping covering on them!

So for all the Kevlar and custom design i3 is less than 7% more efficient than a similar sized car (though more luggage space)like Fit EV that is basically an ICE conversion done for compliance reasons. That’s pretty disappointing.

…also not sure why the table says i3 has an 18.8KWh battery where it really has a 22KWh battery.

Darren, I had a lot of this data already at kdawg.com on the compare tab. Your #’s look close to mine. I have some data that you do not if you care to update your spreadsheets. I may borrow your miles/kWh data.

One metric you missed (as others pointed out) was cost. You are paying a lot more for a minuscule amount of efficiency gain.

Darren,
we were having this discussion yesterday at GM-Volt.

Do you have a value for the sensitivity of range with respect to vehicle weight??

We have numbers that vary from 10% in wt=4% in range all the way up to 10% in wt =7% in range.

Using the Volt as a baseline at 3850 pounds and using 10% in wt =4% in range:

That means chopping 400# out of the Volt (10%) would increase range by 1.5 miles (4%). at 3 miles/kwh that additional 1.5 miles could be covered by 0.5 kwh hrs of battery.

How much does taking 400 lbs out of the Volt cost?? versus another 0.5 kwh of battery. (another 0.5 kwh of battery is only 250$ or so)

One could make an argument that it is not worth it to overspend reducing weight.

This data makes me want to get a Spark EV. That cheap little car seems to rock.

Smart ED you mean

No way. That is only a 2 seater, the efficiency isn’t good, and it doesn’t have very good range.

I would like to have a spark ev too, mainly because they are so quick off the line.

Nope Tesla is the most efficient

Smart Electric Drive’s 0-60 is invalid and should be updated.

0-60 is 9 seconds using kickdown mode, 11 seconds is non kickdown.

The article mentions weight as an efficiency draw while recuperation makes weight less of an issue.

Exactly the mass momentum drives recuperation so that at 100% efficiency it does not freaking matter how heavy tha car is, they’d all behave exactly the same c.p.

You are using useable capacity for i3 but full capacity for other vehicles. For eg. we know Leaf uses only 21 kWh of the battery.