Guest Post: Efficiency or Range? You Can’t Have Both.

The i3 is the most efficient production car available today

Every now and then I have a reader send me an article they wrote and ask if I'd like to post it here. Usually it's not exactly what I'm looking for and politely explain why I won't be posting it and thank them for sending it nonetheless.  Occasionally I'll get something interesting though, like the post below which was sent to me by Robert Kasper. I think it's particularly timely since just last week I posted the Tesla/BMW comparison piece and I think this is an interesting follow up to it.  I hope you enjoy:                    

  Efficiency or Range?  You Can’t Have Both.

…But Advanced Technology Can Help.

By Rob Kasper

In the world of electric vehicles, whether Battery Electric Vehicles (BEVs) or Plug-in Hybrid Electric Vehicles (PHEVs), there is a clear trade off between range and efficiency.  For a given technology, efficiency suffers as range increases due to the weight of not only additional battery capacity, but the increased structure and volume to haul that capacity around.  Now that there are a significant number of plug-in vehicles being manufactured, and a recognized standard to test them, we can identify trends.  Consider Table 1 and Figure 1, a plot of efficiency (as measured in EPA MPGe) vs. range in miles for 2014 plug-in electric vehicles measured by the EPA.  They are grouped into Battery Electric Vehicles (BEVs) and Plug-in Hybrid Electric Vehicles, and further identified as either conventional or advanced technology design and construction.  Conventional technology is generally characterized by a manufacturer’s use of an existing gasoline powered platform modified for battery electric drive, steel frame construction and cladding, and standard battery technology.  Advanced technology is generally characterized by a clean sheet, purpose built EV design, extensive use of aluminum or aluminum plus Carbon Fiber Reinforced Plastic (CFRP) for weight savings, higher energy density lithium ion battery packs, with the bonus of performance equivalent to or exceeding the best of conventional technology plug-in vehicles.

Figure 1: Efficiency vs. Range

Table 1: EPA Electric Range and MPGe

Beyond the obvious observation that the price of greater range is lower efficiency within a given technology, it is important to note the significance of advancing technology.  The ground-up EV design, significantly lighter weight construction, and advanced battery technology of the BMW i3 and Tesla Model S push the blue trend line significantly up and to the right of conventional BEVs’ green trend line.  As significant is the single data point (in purple) representing the only advanced technology PHEV currently available – The BMW i3 REx.  Not only is it capable of greater efficiency and far more range than any conventional PHEV (the red trend line), it is more efficient than all but two conventional BEVs, with only slightly less range than all but the most inefficient conventional BEVs.

It is this outlier of a data point, the BMW i3 REx that might best help illustrate why a smart means of increasing the range of an EV may not necessarily be to add more battery capacity.   Battery energy is clean and well suited for powering vehicles for relatively short-range transportation but due to its weight and lengthy charge times, inefficient and inconvenient for long distances.   On the other hand, the benefits of energy density and convenience make gasoline/diesel energy better suited for longer range transportation with the trade-off being greater well to wheel emissions in many parts of the world.  In the case of the BMW i3 REx, each mile of range requires either 0.15 pounds of gasoline, or 5.7 pounds of battery capacity.  At 37 times the mass specific energy density of battery power, very little gasoline is required to extend range for a given tank size, and that tank can be replenished in minutes nearly anywhere in the well developed fossil fuel infrastructure that currently exists worldwide.  This capability requires a 265 pound increase in the weight3 of the vehicle for the REx engine and associated systems, which imposes a 6% decrease in efficiency, but once set, that efficiency does not appreciably decrease as more energy in the form of gasoline is added to increase range.  Increasing battery capacity cannot increase range as efficiently, as not only must the weight of the battery increase by 37 times the weight of gasoline per mile in the first increment, but by the weight of increased structure and volume, as well as even greater battery capacity to offset the reduction in efficiency resulting from the weight increase.  There comes a point where the sacrifice in efficiency may no longer be worth the additional range to be gained.
See figure 2:

Figure 2: EV Energy Storage (and Generation) Weight vs Range for Advanced Technology EVs

1- EPA testing protocol does not account for approximately 4 miles of range remaining after REx fuel exhaustion when publishing a 72 mile battery powered electric range before REx activation, but does account for it in the total range calculation of 150 miles:  72 electric miles + 1.9 gal x 39 mpg + 4 electric miles = 150 EPA range (76 electric + 74 gasoline).  76 miles of range is also the result of dividing the EPA measured total i3 wall to wheel consumption of 22.0 kWh by the i3 REx EPA measured consumption rate of 0.288 kWh/mile.  This value is further corroborated by the CARB BEVx designation awarded to the i3 REx which requires the electric range not only be at least 75 miles, but that it must exceed the gasoline range, neither of which would be possible without accounting for the ~4 miles of range remaining after REx fuel exhaustion.

2- The EPA’s 95 MPGe rating of the Toyota Prius Plug-In Hybrid includes 0.2 gallons of gasoline operation plus 29 kWh of electric operation per 100 miles.  Subtracting the 10 mile of gasoline operation contribution to the total (0.2 gal X 50 mpg) yields 29 kWh per 90 miles, or 32.2 kWh per 100 miles, which results in 105 MPGe for electric only operation. (MPGe = 33,705 divided by watt hours per mile.)

3- While EPA rated at 87 miles of range in its base form, purchasers of the Mercedes-Benz B-Class can choose to pay an additional $600 for the Range Package, which makes an additional 17 miles of range available.  There is no difference in total battery capacity between the two configurations, only the percentage of SOC made available to the driver.

4- The 8 BMW battery pack modules weigh 55 lbs. each, for a total of 440 lbs.  Reference page 17 of the BMW i3 Service Managers Workshop Participant Guide at http://darrenortiz.com/website_pdfs/BMWi3PG.pdf.

5- 265 lbs for the REx engine and all associated equipment is the difference in weight between the i3 BEV and i3 REx as published on BMW’s spec pages:  http://www.bmwusa.com/Standard/Content/Vehicles/2014/i3/BMWi3/Features_and_Specs/BMWi3Specifications.aspx
http://www.bmwusa.com/Standard/Content/Vehicles/2014/i3/BMWi3RangeExtender/Features_and_Specs/BMWi3RangeExtenderSpecifications.aspx.  Adding the 440 lb. battery weight makes the total energy production and storage weight at 76 mile of range 705 lbs.  This increases by 11.4 lbs. of gasoline for every 74 miles driven beyond 76.

6- Widely quoted in other sources, Car and Driver claims the Telsa Model S 85 kWh battery pack weighs 1323 lbs: http://www.caranddriver.com/reviews/2013-tesla-model-s-test-review.  This is exactly 600 kg, making it appear to be an estimate, but it is the only number we have to work with, as Tesla does not publish the spec.

7- Weight of the 60 kWh Tesla Model S battery pack is estimated from the 85 kWh figure to be 60/85 X 1323 lbs. = 934 lbs.

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. :)

Breaking: BEV i3's Arrive At Dealers Monroney Label Revealed

As expected, the i3 is officially the Most Efficient Car in America. The 81 miles per charge range is a bit disappointing though.

BMW has just now released the BEV i3's from the ports and they are en-route to dealers. The i3's with range extenders have not been released and will remain at the ports a little longer. The common belief it that the EPA range certification for the REx hasn't been finalized yet so the REx cars need to wait a little longer at the port.

The BEV i3 is rated at 81 miles per charge, which is somewhat of a disappointment, but the efficiency figures are off-the-charts good. 138 MPGe City, 111 MPGe Highway and 124 MPGe Combined. That makes the BEV i3 the most efficient automobile on the road in America, and by a good margin. More on this later, I just wanted to get this up as it was breaking.

Below are the top 10 most fuel efficient automobiles for 2014 as listed by FuelEconomy.gov

How Much Does it Cost to Charge an Electric Car?

There are many reasons for considering making an electric car the next car you buy or lease. Besides the many environmental benefits, the promise of energy security, the silky-smooth driving experience with instant torque available without delay and low maintenance, one of the best characteristics of electric vehicles is how little they cost to operate. I've covered this topic here before, but this is something that really needs to be driven home. While Electric cars are currently more expensive than their conventionally-powered counterparts, the total cost of ownership over time can certainly be less, and in some cases much less.

Just as with gasoline cars some EV's are more efficient than others, but the average EV needs about 30 kWh’s of electricity to power the vehicle for 100 miles. For example, the EPA rating for the Nissan LEAF is exactly 30 kWh’s per 100 miles. A Tesla Model S 60 is rated at a combined 35 kWh’s per 100 miles and uses a little more energy since it’s heavier and more powerful than a LEAF, while the Chevy Spark EV has a combined consumption rating of 28 kWh’s per 100 miles. The BMW i3’s EPA consumption ratings haven’t been announced yet, but since the i3 is likely to be wear the “most efficient EV” crown, I expect it to be rated somewhere around 26kWh’s per 100 miles. The consumption for all electric vehicles can be viewed at the US Department of Energy’s website: www.fueleconomy.gov

According to Researchers at the University of Michigan Transportation Research Institute, the sales-weighted average fuel economy of all new vehicles sold in the United States in 2013 was 24.8 mpg. The average cost for a gallon of regular gasoline in the US over the past three years was $3.53/gallon. By using 15,000 miles as the average amount of miles a person will drive in a year, the annual cost of gasoline for the average car will be $2,135 per year, using the average cost of gasoline from 2011 through 2013.

Electricity rates vary much more than gasoline across the country, but the cost is much more stable. Unlike with gasoline, there aren’t huge spikes in electricity rates if a refinery has a problem, and neither does the price skyrocket when there is political instability in one of the large oil producing countries as we have seen lately, since all of the electricity we use in America is domestically produced. The average cost of electricity in the US is 12 cents per kWh. Therefore the average person driving an average EV 15,000 miles per year pay about $540.00 per year to charge it. As mentioned, the cost of electricity can vary greatly depending on where you live, but in order to equal the price of the average gasoline car’s fuel costs, the price of electricity would have to be four times the national average, and cost 48 cents per kWh. Nowhere in the US does electricity cost even close to that much. So the average American would save roughly $1,600 per year in fuel alone, and that's if gasoline prices remain around $3.53 per gallon. Gasoline prices do frequently spike up and down, but in the long run they always goes up. Electricity costs do eventually increase also, but not nearly at the pace of gasoline. Plus with fewer moving parts, EV's cost much less to maintain. If you combine the fuel savings with the reduced maintenance costs, it's clear to see an EV will cost you much less in the long run, even if the vehicle costs a little more up front.

Another great thing about electric cars is that you can easily reduce your electric bill by $40 to $50 per month just by being more efficient, and therefore completely eliminate your transportation fuel cost! You really can't use less gasoline unless you drive less or buy a more efficient car, but you can reduce your electricity usage at home and still drive as much as you always have. Simple measures like a programmable thermostat and the use of compact florescent or LED light bulbs can make a big difference. In fact, five 100 watt light bulbs left on continuously for a year use nearly the same amount of energy as it takes to power an electric car 15,000 miles! Here's how: five 100 watt light bulbs use 500 watts per hour. In 24 hours they use 12,000 watts or 12kWh. In 365 days they use 4,380kWh’s. A typical EV that uses 30 kWh’s for every 100 miles will use 4,500 kWh’s to drive 15,000 miles. Simply by turning unnecessary lighting off at your home, you can drastically reduce or completely eliminate your annual transportation fuel cost. Try doing that with a gasser!

How Much Will It Cost To Fuel The i3?

The concept i3 coupe parked with a BMW i branded level 2 wall charger

I get asked all the time "How much does it cost to drive an electric car?" I've also had a fair share of people say " I like the car, but I wouldn't want to see your electric bill". Like gas cars, some electric cars are more efficient than others. The BMW i3 has been purpose built to not only offer the dynamic driving experience BMW customers have come to expect, but to also be a highly efficient car. But what is efficient for an electric car? Everybody understands MPG for gas cars but few really understand how electric cars are measured for efficiency, let alone how that will translate into the cost to operate it.

The ActiveE Monroney sticker

First off lets discuss how the EPA calculates the miles per gallon equivalent(MPGe) for electric cars. Gas cars have the official EPA miles per gallon listed on the window(Monroney) sticker and electric cars have a rating called MPGe. Since one gallon of gasoline creates the same energy as 33.7 kilowatt hours of electricity, electric cars are tested to see how far they can go on 33.7kWh's and that is the official MPGe which is listed on the window sticker of every new EV. The BMW ActiveE I drive has a rating of 107 MPGe. Not bad for a heavy converted gas car, but not especially good as far as electric vehicles go. The Chevy Spark EV, recently was rated at 119 MPGe making it the most efficient EV rated so far as it barely beat out the Honda Fit EV's 118 MPGe rating.

Neither The Fit EV or the Spark EV were purpose built as electric vehicles. They are converted gas cars like the ActiveE. Being purpose built as an EV with a lightweight CFRP body and aluminum frame, the i3 should easily top the Spark's 119 MPGe rating. I'm guessing the i3 may have an MPGe rating as high as 130, which will give it the "most efficient EV" crown, one that it may hold for quite some time as there is really no other EV coming out anytime soon that will challenge it in my opinion.

So lets say the i3 gets a 130MPGe rating for arguments sake. That means it will go 3.86 miles for every kilowatt hour of electricity you use to charge it or need about 26kWh's to drive 100 miles. The average price of electricity in the US is 11 cents per kWh, however that varies greatly from state to state. I pay 18 cents per kWh so for me it would cost $4.68 to drive an i3 100 miles. If I were to drive 15,000 miles per year my annual fuel cost would only be $702! How far can you currently drive on $702 in gas? If your car gets 25 miles per gallon and you pay on average $3.50 per gallon(which is lower than what we have averaged the past year) it would cost you $2,100 in gas to drive the same 15,000 miles! Plus, we all know gas prices will only climb over time. Electricity rates do go up occasionally but historically they are much more stable than gas prices. Plus, many people do have the option of installing a solar array which will guarantee a free supply of electricity for the next 25 to 30 years. There is nothing the gas and oil industry can offer to compete with solar, as the customer supplies, and has control over their own energy.

BMW will offer solar canopies to i3 customers

So whip out your electric bill and find out how much you pay per kWh for your electricity. Then divide the number of miles you drive per year by 3.86 and multiply that by your electricity rate and you'll know how much it would cost you to fuel an i3 for a year. I'm sure you already know how much you dump into the gas pump so calculating your savings won't be too hard. Of course if you want to save even more you can install a solar array at your home like I did and start making your own electricity. Sure there's an initial outlay of cash for the solar system and not everybody can afford it, but if you can it's a fantastic set up and you'll have it paid off in a few years of savings from driving your i3 on sunshine!