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| John spending some time with the i3's carbon fiber big brother, the BMW i8 |
Below is a guest post from a fellow BMW ActiveE Electronaut who went on to get an i3 REx, just as I did. John and I have had quite a few discussions about the i3's range extender implementation for the North American market. In fact, he almost didn't get the car because of it. As you will read below, he's given a lot of thought to how BMW has implemented the REx to achieve the California Air Resource Board's BEVx designation and why he believes CARB should reconsider the strict requirements they have imposed. This will be the first part of his contribution here. Next week I'll publish the second part which will summarize his "SF Bay Area to Tahoe" road trip to see how the range extender fared on this strenuous, 7,000+ ft climb up to Donner Summit.
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My name is John Higham and I was Born Electric on June 2, 2014. I am an aerospace engineer with expertise in designing spacecraft and have 11 U.S. patents on various aspects of spacecraft design, control and operations. When I'm not EVangelizing the benefits of electric vehicles I enjoy cycling, hiking and pretty much anything else that includes fresh air and sunshine. I have also traveled extensively and have written several magazine articles and one book on world travel.
You can determine where an individual’s passion lies by discovering what upsets them. The reasoning is simple -- if you simply don’t care about, say, bicycle racing, you’re unlikely to be perturbed by what Lance Armstrong may or may not have done to win the Tour de France. But if bicycle racing is your passion, you’re not only well versed on the history of Lance’s doping scandal, but also know the nuance of who knew what when; more importantly you are outraged over the loss of sportsmanlike competition from 1999 to 2005.
It is with that understanding that I go on record to say the BMW i3 REx makes me absolutely crazy. Before I indulge that proclamation, I would like to state what is admirable about the i3. Then the remainder of this post is to document what makes me crazy about the i3 REx -- complete with numbers and graphs.
I love the fresh thinking that BMW bestowed on the i3. I love the carbon fiber. I love the environmental responsibility that was engineered into the i3’s cradle-to-grave lifecycle. I love the Colin Chapman-esque “add lightness” mind set. I love the low center of mass. I love the open, light and airy interior. I love the taut suspension and go-kart like handling. Did I mention the carbon fiber? Love that. Perhaps most of all, I love the optional Range Extender (REx).
Ah, yes. The REx. There’s the rub. In concept the REx is brilliant, at least from my point of view. In its execution, the US spec'd REx is at best an opportunity lost. This is not BMW’s fault. Not entirely, anyway, but let’s leave that aspect of the discussion for another post. But first, let me lay the groundwork on why the REx is both important and game-changing for electric vehicles, then we'll discuss how the REx (in US spec) is an opportunity lost.
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| John & his Solar Orange i3 REx |
Cars and Why We Love Them
People buy a car for a multitude of reasons, but I think it is reasonable to say that two very big factors are first, fulfilling the mundane task of getting from “A” to “B” and second, to enable spontaneity. An electric vehicle does the former brilliantly for the vast majority of use cases.
Why then are electric vehicles shunned by the masses? I submit it’s because they do a poor job of the latter. In fact, saying an electric vehicle doesn’t enable spontaneity is being too kind. In truth, an electric vehicle kills spontaneity.
Who can forget the heady days after receiving one’s driver’s license, keys in hand and a full tank of gas -- it’s a breath of pure freedom into the soul of every teenager. Fast-forward a few years and by the time that teenager has acquired a mortgage and is considering a new car purchase for their commute, the practical side of automobile ownership looms large. An electric vehicle may seem like a practical choice. But no grown-up can completely suppress the siren song of the freedom car ownership gives. Spontaneity isn’t always fun and games, as I learned scraping the last few lithium ions off my BMW ActiveE’s cathode taking an unplanned detour to a hospital emergency room. Everyone who has ever owned an electric vehicle knows that driving has to be managed.
What the heck? Manage? Manage is the antithesis of spontaneity. Can any EV driver think of coming home on a Friday after a long commute home from their day job, to discover their spouse wants to go out on the town for an evening and just grab the keys and go?
Perhaps the Tesla drivers can do this, but no other EV is capable of this simple feat. And while Tesla is a fine car, it just isn’t the package I’m looking for. There is something about hauling around an extra 1,000 pounds of battery whose capability goes untouched much of the time that just doesn’t sit well with me. And I know I’m not alone.
The reason that the public eschews EVs can be summed as in one word -- range. First, the lack of range for those occasional cross-country drives and second, the potential to simply be out of range and out of luck at the end of the day when there are errands to run or fun to be had.
This is the reason why the accusation that electric vehicles are the playthings of the rich is frankly accurate more often than not. Because while an electric vehicle makes a great second car, it is often a poor choice as an only car for many families and individuals.
The REx changes all this. Let me explain.
A Transitional Electric Vehicle
For the EV to live up to its potential of being the only car a driver would ever need exactly one thing needs to happen -- the ability to add energy as thoughtlessly and effortlessly as the plain old Internal Combustion Engine vehicle. Fast chargers go a long way to fill that role, but fast chargers are still too slow and not nearly plentiful enough to be practical for many legitimate use cases. Until the “time to charge” issue is resolved a bridge needs to be built. I give you the REx -- it has the potential to bridge the gap between EV and ICE.
The California Air resources Board (CARB) created a category of vehicle called the Transitional Zero Emission Vehicle (TZEV) as a way to help both the public and auto manufacturers to make the transition to a purely zero-emission vehicle such as a Battery Electric Vehicle (BEV), the implication being that this group of vehicles serves as a transition to a pure BEV. TZEVs are further defined into sub-categories, one being the Plug-in Hybrid Electric Vehicle (PHEV) and another called the Battery extended Electric Vehicle (BEVx). The BMW i3 falls into the BEVx category.
What does all this mean? Glad you asked.
The Genius of CARB’s BEVx Classification
Two of the more popular PHEVs are the Chevy Volt and the Toyota Plug-in Prius. It has been said that PHEVs are a gateway drug to BEVs. My anecdotal evidence suggests this is true; everyone I know with a Chevy Volt or Plug-in Prius wishes they had more electric range and has stated their next electric car will at a minimum have increased electric range over their current car.
According to the website voltstats.net the Chevy Volt community drives nearly 80% of its miles all electric; one driver has managed over 30,000 miles on a single tank of gas.
This simple statistic reveals a powerful fact; once experienced, people love to drive electric. The reasons are manifold and range from cost savings, to the quiet smoothness, to the adrenaline rush of instant torque. Some even drive electric to be environmentally conscious.
But Volt drivers aren't exactly gobbling up BEVs as their leases expire. Why is that?
It's because the Volt can be the only car a driver ever needs. The Volt can drive across country without blinking an eye and it can indulge your last-second whim to go out to dinner, even when its battery is flat.
CARB engineered the Battery extended-range Electric Vehicle (BEVx) classification to increase the electric miles driven for PHEV-class cars like the Volt from the current 80% to over 90%. I submit that the BEVx is much more than that. It has the potential of bridging the gap between EV and ICE and being the only car a driver needs. That's the genius of the BEVx.
A PHEV's All Electric Range (AER) is typically 40 miles or less. Its engine is what one might call a normal size and it is mechanically connected to the driving wheels via a transmission just like any ICE-mobile.
The BEVx classification is differentiated from the PHEV, like the Volt, by virtue that the engine may not even be an engine. The classification allows for an Auxiliary Power Unit (APU) that may or may not be an ICE. The APU is not mechanically connected to the driving wheels, rather its purpose is to generate electricity to extend the AER beyond what the manufacturer engineered in. For an EV to be classified as BEVx under CARB's official designation, one important factor is that the available range while operating with the APU for the range must be less than or equal to the AER.
If the difference were simply that, I would have no need to be writing this. The other important difference is that the APU is constrained by regulation to turn on only when the battery falls below 6% SOC, shutting off once its SOC rises above 6%. This artificial constraint on how the APU manages the SOC means that BEVx class cars come close to being the only car a driver may ever need, but it fails for some use cases. That is the opportunity lost I'd like to explore further ,because it just doesn't have to be that way.
One of the many virtues of an EV is the quiet smoothness of the electric drive. Another important consideration of engineering an efficient vehicle is to keep mass (weight) at a minimum. These two factors combine to dictate that the APU be sized as small as possible. This should not impact the drivability of the car, however, because the APU isn't connected to the driving wheels and the power required to propel a car down the road at freeway speeds is frankly not that great.
On BMW's i3, the APU is sized such that it can maintain the car at freeway speeds on level ground. In the i3's case, the APU is a 650 cc motorcycle engine borrowed from BMW’s C 650 GT and detuned to 35 BHP. The APU with its associated hardware to generate electricity (called the genset) is referred to as the Range Extender (REx) and it increases the mass of the i3 a mere 265 pounds over the purely electric BEV version of the i3.
To propel the car at freeway speeds while simultaneously climbing a significant grade would require a much more powerful (ergo larger and more massive) APU. Sure, the APU could be 200 BHP, but this would be the motoring equivalent of driving in a thumb tack with a sledgehammer, as the i3 only requires 35 BHP to maintain 80 MPH on level ground. Therefore in order to climb a hill at freeway speeds, the i3 needs to dip into the battery’s stored energy.
This is where CARB's BEVx regulations are problematic.
Since the APU is constrained by regulation to only maintain a 6% SOC, significant altitude gains are simply out of the question; at least at freeway speeds. On the i3, 6% SOC is only 1.13 kWh. If the APU's output is being utilized to maintain freeway speeds, the 1.13 kWh remaining in the battery is only good for about 725 feet of elevation gain as calculated further down in this post.
If you never plan on driving your i3 anywhere that might include an elevation gain of more than 725 feet, fret not; the i3 REx can be the only car your family will ever need. It is truly a transitional vehicle bridging the gap from ICE to BEV and has all the spontaneity and long-range capabilities your family may need. As long as you keep its diminutive tank filled, you're golden.
But if not, not.
The Abysmal Failure of CARB’s BEVx Classification
Before we go any further let's be clear. CARB's BEVx regulations impact any car that ever will be manufactured to this specification, and not just in California. For the BMW i3 REx, for example, the BEVx limitations apply to every vehicle sold in North America. Including Canada. The BEVx is a great way to assuage range anxiety if you're considering an EV. But if you want your shiny new EV to be the only car your family needs, proceed with caution.
For example, I live in California's San Francisco Bay Area. I like to take my family to Lake Tahoe, about 7,000 feet of elevation gain, a few times a year. That’s simply not possible to do in a reasonable amount of time in the i3 REx. This is because the i3's REx has been artificially emasculated via a design-by-committee staffed by political appointees who have no idea what it means to drive electric.
It therefore follows that if I want to drive electric, I can buy a i3 REx for the daily grind. But when I require spontaneity to indulge a weekend trip to Tahoe, I am limited to two options -- keep an ICE on ice or eschew the BEVx completely for a PHEV.
And it doesn't have to be that way.
SF Bay to Tahoe by the Numbers
California's SF Bay lies at sea level and the drive east to Lake Tahoe follows the Sacramento river, never gaining significant altitude for about 50 to 100 miles, depending on one's starting location. Continuing east past the state capital of Sacramento begins what is at first a gentle climb into Gold Country. Assuming the route is along I-80, the slope increases significantly past Gold Country until Donner Summit (elevation 7,228 feet), 95 miles east of Sacramento.
Because the i3's APU isn't sized to maintain freeway speeds and simultaneously gain significant altitude, to drive the i3 to Tahoe requires near 100% SOC at the bottom of the hill, say in Colfax, as outlined below. That’s simply not possible with the current implementation of the SOC management software of the APU unless you delay your drive significantly by charging your car at the local Level 2 EVSE (about 3 1/2 hours for the i3).
Yet fellow i3 owners in Belgium may drive their i3 REx’s to the Swiss Alps, which is of similar distance and altitude gain. The difference, of course, is their cars do not fall under the CARB rules; they can enable their APU at will to maintain the SOC until such time they begin their climb into the Alps. In that way they can drive on the REx on the flat portion of their drive, saving the energy stored in the battery for climbing up into the Alps.
To really understand the limitations, let's talk about the physics involved and then plot a hypothetical trip from my home in Mountain View to Truckee, California. Then we'll test the physics by doing the trip and compare the results in another post.
To propel a car down the road there must be sufficient power to overcome all sources of friction, aerodynamic drag and assuming you're climbing a hill, gravity. Staying on flat roads for the time being, at freeway speeds friction (from tires, gears and bearings in the car and so on) are vastly overshadowed by aerodynamic drag. The power required to overcome aerodynamic drag is proportional to the cube of its velocity and is governed by the following equation:
This result tells us what power is required, in Watts, to overcome aerodynamic drag for the i3. Assuming that other sources of power drain (friction, the heater in the car, etc) are negligible, we can make a pretty graph of the power required to overcome aerodynamic drag as the i3 rockets down the road, as a function of the speed. Don’t fret; we’ll make a reasonable estimate of some of those other power sinks later.
Power, in kW, to overcome aerodynamic drag for a BMW i3 at sea level.
Note the plot is given in the more familiar MPH, although the equation results are in m/s.
In a like manner, we can derive an equation for the power required for the i3 to overcome gravity as it is climbing a hill.
Now that we have a reasonable approximation of the power required to overcome both aerodynamic drag and gravity we can sum the two together and get an equation for the total power required to climb a hill
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