Friday, June 13, 2014

BMW i3: The Emperor of Efficiency

After a recent 62 mile round trip I finished with a 5.0 mi/kWh consumption rating. I've never achieved such a low consumption rate on any other EV that I have driven. This translates to an astounding 200 Wh's per mile!
When the EPA range and efficiency figures were announced couple months ago, the i3 became the most efficient vehicle available in America. Here in the US, the EPA uses "MPGe" as its official efficiency metric to compare the energy consumption of alternative fuel vehicles. That stands for "miles per gallon equivalent", and unfortunately most people don't really understand what it means or how that really translates to what the vehicle will cost them to operate. The consumption rate, or how many miles the car will travel on one kilowatt of electricity, (mi/kWh) is a metric that I, and many other electric vehicle owners prefer to use.

i3 BEV EPA ratings
Wikipedia describes the MPGe rating as follows:
"The ratings are based on EPA's formula, in which 33.7 kilowatt hours of electricity is equivalent to one gallon of gasoline, and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions."
The BEV i3 received a combined (city and highway) MPGe rating of 124 miles and the i3 REx (like I have) achieved a combined score of  117 miles. I'm not a huge fan of this rating system because all it really does is compare the efficiency of my car to the energy in a gallon of gas. One of the problems with that though, is gasoline engines are very inefficient, and only around 25% of that energy is harnessed to propel the vehicle. The rest is simply wasted. The MPGe metric isn't completely useless though. It does offer a standard rating system to compare all electric cars side by side, and it also calculates the energy use of the vehicle including the charging losses, meaning it is a true "wall to wheels" energy rating. So for a comparison tool, it has its merits.
Two days of combined driving with no real effort to drive efficiently at all. About 60% highway @ ~70mph and 40% secondary roads, with the air conditioning on the entire time and driving in comfort mode.

I've only driven about 1,500 miles so far, but I'm seeing energy consumption figures that I have never achieved on any other electric vehicle that I have driven (And I've pretty much driven them all by now!). Overall, I'm averaging about 4.5 miles per kWh and can easily attain 5 miles per kWh if I make an effort to. Five miles per kWh translates to an extremely low 200 Watt-hours per mile! For comparison, I averaged about 3.6 miles per kWh in my ActiveE under the same driving conditions and ambient temperatures under which I have been driving my i3. I had to really try hard to average 4 miles per kWh with the ActiveE, and with the i3 I would have to intentionally try hard not to do so. Based on the EPA figures I knew it was going to be a tremendously efficient car, but seeing it first hand has been an eye opening experience.

I'm sure I can push the consumption rate up to around 6 miles per kWh if I drive in Eco Pro+ mode, watch my speed and use the regenerative brakes to their full potential. But for now I'm having too much fun getting to know the car. Mashing the accelerator and feeling the instant torque every now and then is difficult to refrain from, but at some point I'll do a real efficiency test and see how low I can go. Now that I've had the car for about a month, I'm starting to get some followers message me ask what I like and don't like about it. I just want to say I have indeed been compiling a "likes and dislikes" list and I have just about enough info for a comprehensive initial review. That will most likely be the next post here so stay tuned. :)

20 comments:

  1. Now if it could only challenge the King of Kilowatts, the Model S : )

    ,CDspeed

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    1. More range would be nice, but personally I wouldn't want a 85kWh battery. If the i3 had a 26kWh to 28kWh battery and a decent DCQC network in the ground it would be perfect. Fast charging is the key, not big batteries IMO.

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    2. Yes. Batteries are the problem, not the solution. We should be asking what is the absolute minimum needed to get the job done.

      http://www.evalbum.com/4525

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    3. This comment has been removed by the author.

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    4. Actually, it beats the that King of Kilowatts by 23% to 31%. At 117 MPGe the i3 compares to 95 MPGe for the 60 kWh Model S and 89 MPGe for the 85 kWh Model S.

      (previous deleted comment corrected for units)

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  2. I agree Tom. I am seeing high 4's and even a 5 also. I remember first first long ride in my AE I hit 4.6 and never saw it again. (Yes I looked at the bottom of the hill :).... I plan on taking that same ride to see what the i3 gets. I wonder how we will do when it's 20 degrees....
    Eddie B

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    1. The consumption rate will obviously get worse in the winter Eddie but how much well see. You have the heat pump on your BEV i3 so that, plus using the heated seats will likely minimize the impact on your range. I would expect it will be much less noticeable than what you witnessed with the ActiveE.

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  3. I second the fun factor of mashing the accelerator from time to time, as I could finally drive an i3 yesterday at JMK... Well worth the few extra kWh wasted... Wonder how much slower the Rex feels to a regular driver vs the BEV (they had no REX for the test drive).

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    1. I was there for a few hours yesterday Alex, sorry I missed you or I would have let you drive mine for a bit to see.

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    2. Sorry, I got there late, after work - and traffic yesterday was terrible. But you've driven both, so what do you think, do you notice the half second difference ? Also the car felt stable enough in turns but I think the wider rear tires and extra weight in the back make the REX even more stable...

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    3. Alex, If I remember correctly all the cars there yesterday for the test drives had the 20" Sport wheels so they had the wider rears on them. It's not BEV/REx specific. All i3's have the staggered size wheels with the sole exception for a base, Mega World BEV. It's hard to really tell the half second or so difference unless you've driven them back to back. The REx is very quick itself, and offers a great driving experience IMO.

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    4. Actually I drove one with 19" & Tera because this is what I have on order. The tires on the 20" Terra next to it looked wider but I actually did not check the size on the wall tire so you may be correct about being 175s on the rear even in 19". Definitely a good driving car, almost as much fun as my current ride but with more inside room and almost 10x !! the mpg (I get 14mpg in the RX8). Has the same door style that I like and the one pedal driving is great, the same as downshifting to first gear, so no learning curve for me. The missing thing is still the tax solution but Manny said they are working on it...

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  4. There's a typo: i3 REx MPGe should be 117, not 177.

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  5. Very Nice! Love the emperor line!

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  6. Hi Tom, thanks for the informations!

    Do you think it would be possible for BMW or thirdparties to build a website similar to www.voltstats.net where you could see various energy and fuel consumption for the i3/i8 users, like MPGe (or miles/Wh) and for i3 REX and i8 the gasoline consumption in MPG and the percentage of electric miles vs total miles. Please tell this to BMW because I think such real world data would motivate to get the i3.

    I think the i3 REX will certainly reach a fleet average of 90% of electric miles and a fuel consumption of 400 MPG, much more than a Volt, due to the bigger battery. I think the i3 is currently the most effective car to minimize the dependency from fossil fuels without range limits (with the only nuisance of a bit small gasoline tank).
    A german i3 REX user reported on the german i3 forum that he took the family (2 adults and 2 children) on a 750miles trip!

    Tom, how many miles have you driven with the i3 already?
    What's the percentage of electric miles and how many gallons of gasoline have you used?
    It would be very interesting if you could post this data each 3000-5000miles.
    I'm sure you will achieve a high electric miles percentage and hundreds of gasoline MPG (= total miles driven / total gallons used)

    Thanks in advance for your numbers!

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  7. I was taking a road trip through Indianapolis and I saw 5 Chevy Volts, 4 Nissan Leafs, and a BMW i3 (the first one I've seen in the flesh!) We also visited the Tesla store in Keystone at the Crossing which was a plus. All in all, it was a really good trip! P.S. Tom, I like how you replicated the "ActiveE Mobility" photo used at the top, but it looks kinda weird with a bright red i3.

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  8. Good Stuff Tom,

    However " I'm not a huge fan of this rating system because all it really does is compare the efficiency of my car to the energy in a gallon of gas. One of the problems with that though, is gasoline engines are very inefficient, and only around 25% of that energy is harnessed to propel the vehicle. The rest is simply wasted."

    This is something the EPA has done right. It's worth comparing like with like. That gallon of gas will propel your Honda Civic or VW Golf say 30 miles ie: 30mpg. which is basically 30 mpge.

    So the stuff about how the engine wastes say 70% of the potential of that gallon of gas is irrelevant to the comparision as your car gets 117 mpge according to the EPA.

    It's a bit like someone comparing an electric motor to a wheel bearing - both are incredibly efficient in themselves but really we shoud, be thinking in terms of how much energy am I using to move this many lbs/kg or weight at this speed (mph/kmh).

    In one sense the fuel becomes irrelevant as a 1000kg car will need the same amount of energy at 60 mph whether it's electric/diesel/gas/cng.......

    However, how that potential electric/diesel/gas/cng is supplied (oil exploration, drilling, refining, transporting or similar for fossile powered power stations plus tranmission losses and cost of electric infrastructure, etc) and burned both globally and locally (exhaust pipes at power station and car) determines much of the energy required is actually wasted.

    Newtons Laws apply to all vehicles in motion!

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    1. The EPA’s conversion equates one gallon of gas to 33.7 kWh of electricity based on the fact that the same amount of heat energy could be produced by both. But that is a measure of the raw energy contained in each and is an idealized comparison. In the real world what’s more important is either the amount of usable energy you can get out, or the total energy that went in. The figure doesn’t factor in that the gasoline can’t produce as much usable energy or that the electricity likely took a lot more heat energy to produce (if it isn’t solar, wind or hydro). The real world gasoline ICE inefficiencies affect the comparison, but the electrical production inefficiencies are outside it and not considered.

      So the 33.7 factor seems biased in favor of electricity, but at least it’s a good hard figure. More relevant comparisons such as gasoline versus electricity costs or a wheel to well analysis give much fuzzier, variable, and arguable figures of comparison.

      I find it interesting that Tom says the EPA sticker includes a “wall to wheels” charging efficiency factor. Just how large is that inefficiency and does it vary by charging rate? One of the tests I’d like to do is to charge off 120V through a kill-a-watt meter to compare what the i3 says it used versus what it actually takes to recharge. It would be harder to meter a 240V L2 charge unless the public chargers normally give you this figure. Since this will be my first electric car, I don’t have a clue about that.

      I have played around with small off grid solar systems and know there are distinct differences between what goes into a battery system and what comes out given several steps with conversion inefficiency. I hear lithium batteries are more efficient at storing power than the lead acid I’ve played with, but the charger electronics play a roll too.

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  9. Interesting reading Tom, thanks! I leased a 2013 Leaf last summer, and it is nearly as efficient - maybe as efficient? - as the numbers you are posting. In mild and warm months here in the Pacific Northwest, I average between 4.7 and 5.1 miles per KW. Driving REAL carefully I can hit 5.5 to 6 (all non freeway driving). The heart of winter is quite a bit different, dropping down into the high 3's to low 4's... Compared to ICE driving, still really inexpensive!

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