100% EVs vs. Series Hybrids

On March 17th the Tesla Roadster went into mass production – of sorts – on that day production model “#2″ was placed onto the assembly line at Tesla’s Lotus factory in Hethel England (Tesla press release). According to a report in AutoblogGreen by Sam Abuelsamid “Tesla Roadster starts production today,” the rate of production will be one car per week, meaning by now production unit #4 is starting to take shape.

If you want to know what’s really going on with the Tesla, unless you work there, AutoblogGreen is a pretty good source of information. And what they’ve had to say about the difficulties Tesla is encountering speaks to the challenges EV manufacturers in general have to confront. As Abuelsamid reported on 1-23 in “Tesla has a solution for their transmission woes,” “The primary issue that has been preventing Tesla Motors from getting their electric Roadster into full production for the last several months has been the unfortunate tendency for the transmission to self-destruct in only a fraction of a car’s normal lifespan.”

Apparently the awesome RPM range and torque delivered by a high-performance electric motor also requires transmissions with tolerances well beyond those behind conventional gasoline engines. Tesla’s interim solution on their first production cars is to get rid of the transmission entirely. Their permanent solution is no longer to use a two-speed transmission, but to develop a single speed drive-train using a reduction gear, while adding a more robust power electronics module combined with enhanced thermal management for the motor. Once all this is ready, Tesla believes they can ramp up to 15-20 cars per week, and retrofit the cars already sold.

There are a lot of challenges Tesla has had to overcome – a big question is how much time and money did Tesla put into battery technology that is changing rapidly? Does Tesla still have 6,000 laptop batteries in a 1,000 pound package, packing 50 kilowatt-hours of storage? According a white paper released by Tesla on 3-24-08, “Response to the CARB ZEV Expert Panel Position on Lithium-Ion Full-Performance Battery Electric Vehicles,” they state “Tesla’s ESS contains 6831 cells, arranged in 11 modules in series, with 9 “bricks” in series per module, and 69 parallel cells per brick.” Tesla has a lot invested in their battery pack – which according to their data has achieved 118 watt-hours per kilogram. But will a 100% battery powered car be the dominant car of the future?

It is clear 100% battery powered cars have potential for many common duty cycles. The average daily commute is under 40 miles, and at that rate, a Tesla roadster would only have to be charged 2x per week. But “quick recharge” or “hot swapping” for batteries is unlikely to become a practical, widespread solution for vehicles with duty cycles that require long range driving and frequent, quick and convenient remote refueling. This is why the series hybrid (using an all-electric drive train, a short range battery, and an onboard gasoline powered generator) which combines a shorter but still viable battery-only range with a fairly high mileage gasoline-only performance, has the potential to offer a more versatile, less expensive solution for ordinary families who don’t want to own a car that can’t make the long trip.

Development of the EV was hindered by environmentalists who believed the hydrogen fuel cell vehicle was the perfect green automotive solution. All electric, yet able to be refueled with hydrogen quickly and remotely. And we’ve all seen how far that’s come (and what is the battery charge-discharge efficiency vs. the efficiency to use electricity to electrolyse hydrogen then convert it back into electricity via a fuel cell? Hint – it’s 90% vs. 40%). Yet hindered even more than the EV by well-intentioned environmentalists was the series hybrid – because the onboard generator powered by a small gasoline engine was considered an unacceptable compromise even though that gasoline engine might only be activated a few times per year when the plug-in battery-only range was exceeded for longer trips. Technology is a river, politics are only rocks in the stream, and GM, Volvo, Fisker, and Aptera have all announced series hybrids.

Ultimately the next generation car that will dominate will be affordable and offer a no-compromise performance. The Tesla Roadster offers high performance at a price competitive with high-performance gasoline powered cars, and will find a niche. Manufacturers like Think may produce 100% battery powered cars that are affordable and can serve as commuter cars. But we are not likely to see quick charge facilities because even if the batteries are developed that can withstand a 50 kWh charge within minutes, we’re probably not going to see 10,000 volt extension cords hanging on the islands at self-serve filling stations, any more than we’re ever going to see 10,000 PSI hydrogen fill-ups on every interstate. For these reasons, our money is on the series hybrid as the next mainstream automotive innovation.

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