Both the BMW i3 and i8 will have assist engines, optional or standard respectively. Because, let’s face it, folks: hybrids of some sort will be around for a while, despite Tesla’s taunts and tweets. Even though pure-BEVs will do it for the majority of the people, a majority of the time, people think they won’t. Engineers aren’t psychologists. At least some hybridization hits those marketing and psychological issues (to say nothing of road trips).
To a big extent, we’re already there: existing vehicles cover the range, from 100% battery-electric to simple gasser. First came the simple hybrids (if you don’t count locomotives), with packs of 1-1.5 kilowatt-Hour sizes. Toyota’s “Hybrid Synergy Drive” system (Prius) was considered stronger than the Honda “Integrated Motor Assist” (Insight and Civic). Outside analysts considered (some would say derided) Honda IMAs as “mild hybrids”- the internal-combustion engine is on any time you’re driving. In a Toyota (or later Ford) the electric motor can actually drive in “stealth mode”, which some called a “full” or “strong” hybrid. Not those Hondas. Like locomotives, they couldn’t even stealth-creep in bumper-to-bumper jams.
Then came the Chevrolet Volt/Opel Ampera (if you don’t count the light- and medium-duty truck hybrids). The Volt can operate on electricity only, even at highway speed; it just can’t do so with enough range to satisfy everyone. A 4-banger can then be lit to relieve the battery, either at the end of a trip or the foot of a mountain. Chevy apologists claim this is a new layout; it’s actually the Tahoe/Yukon’s 2-mode hybrid system, but with a far huger battery (~16 kWh) and the gasser part shrunken. In certain situations, the computer will send engine power directly to the wheels; the 1.4L is not simply a generator.
This results in 30-40 miles of all-electric range (AER)- enough for the clear majority of driving days in this market. Judicious drivers are finding their gasoline goes “stale” after six months. This results in a dashboard warning, and the computer will light the gasser, to stir the tank if nothing else. A few Volt owners brag about still having dealer gas in the tank.
The dilemma should be clear: if you managed six months to a year between tanks, then why are the battery pack AND gas-system that big? Aren’t you basically carrying (and thus, paying for) two complete drivetrains? Chevrolet agrees, apparently: at the next redesign, the gasser will likely become a significantly smaller 3-cylinder, and some rumors have the battery pack shrinking, too. Many in the business speculate that the 1.4 liter engine was simply a handy line item in GM’s inventory, not an ideal redesign.
Toyota, meanwhile, took a different approach. The Prius Plug-In is simply a Prius with a larger, 4.4 kWh pack- enough to push “stealth mode” up to highway speeds. However, in a turn of events, it’s derided by some owners of “stronger” electrics. The Prius Plug-In gets 17 miles of rated AER, or more like 13 miles in the winter. It fires up the gasser when passing on the highway, and when you turn the heater or AC too high. Some owners feel the computer occasionally fires up the gasser for no comprehensible reason at all, at least briefly. If the Volt is an electric with second-stringers, then the Prius might be considered a gasser with e-coupons.
Meanwhile, Ford is in between, Honda is yet again milder than Toyota- and Tesla is laughing at them all. Tesla markets itself as viable on electricity alone; all these hybrids are, again, overly complicated, Tesla claims, by slugging around double drivetrains. Notice there are no hybrid motorcycles for actual sale (though Peugeot offers hybrid scooters).
In fairness, the piston engine in a hybrid isn’t the same as in a 100% gasser. Internal combustion is hardly standing still while all this is going on. With strong-enough hybridization, the engine only runs through a limited powerband, and stays in the efficient portion of its rev range. The very strong Volt only runs its engine at two rpm points, which can then be heavily optimized. The cam profiles are designed to form an expander-cycle engine, more efficient than 100% gassers but terrible at low speeds. Hybridization can provide that low-end grunt, so the electricity is for torque, the pistons are for efficient mileage.
And in terms of mileage, there’s a good amount of hair-splitting among analysts. Given the current US electrical grid, electric drive is part-zero-emissions, part-gas, and part-coal, varying by region. A plug-in hybrid that’s plugged in regularly can then burn a fair amount of gas and still beat the grid (without PV on your roof). I estimate anywhere from 70-90 effective (gasoline) mpg is better than the grid’s coal, depending of course on your regional grid. Most existing plug-in hybrids can reach a combined 70 without hypermiling, and with fairly-regular gasser use. Remember, that gasser already operates as a hybrid, not as a 25-mpg regular car. This includes not burning any gas at all in bumper-to-bumper traffic.
So where does BMW fit in? They sell some conventional hybrids, like everyone else- nothing new there. The company’s “Born Electric” models, then, benefit from the hindsight of entering the market second behind everyone above. (Several of BMW’s staff were hired off the Volt team.) The BMW i3 will enter next year as pure-BEV (22 kWh, 80-90 miles all-electric), or with a 0.6 liter, 2-cylinder range extender. The optional REX will never drive the wheels directly, making it electrically “purer” than the Volt. You also have a smaller gas tank, and less of a say in when the REX fires up. This is more like a diesel-electric submarine than a diesel-electric locomotive- or like the Renault Kangoo, a limited-run EV from the turn of the millenium with a little gasoline generator.
The i8, then is less pure than the Volt. The electric drive will go about 20 miles, and only to about 75 mph- enough to take highways, sure. But the standard 1.5 L three-cylinder will kick in for longer trips, and felony speeds (~150 mph). I think 20 miles, if accurate, should be enough to block the Prius criticisms; it would certainly get through my typical day with no smoke. I also think the next Volt will go to something like BMW’s triple anyway.
Still, it’s hard to compare the family Volt to the Autobahn-burning i8. One’s a daily driver… one’s a missile. I think anyone who can afford the faster, larger (in ground footprint) i8 can afford to use up a tankful when it becomes an issue. Same for the Porsche and McLaren plug-in hybrids. That’s right, plug-in supercars. The spectrum of hybridization can (and should) cover all drivers, everywhere, for at least a few years more.