Related: Automotive Powertrain
The Once and Future Electric Car. "Why did we abandon the electric vehicle?" asks Dr. Jean Botti, chief technologist at Delphi Corp.'s Innovation Center. He pauses, then answers his own rhetorical question, "Two reasons: range and battery cost." Find a way to mitigate those two drawbacks, he posits, and there is no good reason why plug-in electric vehicles (EVs) couldn't be back on the road, and this time in much higher volumes. The idea sounds slightly subversive. After all, if there is one path in the automotive industry's recent technological history that most can agree was a dead end it is plug-in electrics. But the problem with those vehicles lay almost entirely in their reliance on heavy, expensive conventional batteries, not in the electric motors used or their control electronics. Replace those batteries with a power source that is durable, lightweight and offers a range analogous to an internal combustion engine, and suddenly plug-in electrics become a viable option. For Botti that power source is a solid-oxide fuel cell (SOFC). He proposes a powertrain concept unglamorously called "EV range extender" that is similar in layout to the ones that drive hybrid vehicles today, but instead of an internal combustion engine powering the electric motor, there is the SOFC running on diesel fuel. Also unlike a hybrid, this system would bring back the bank of batteries used in EVs, but greatly downsize it to reduce cost and weight and increase usable packaging space. Delphi's modeling suggests that a 100-kg lithium battery array would meet necessary performance criteria and save enough space to turn a two-seater into a four-seater.
The improvements are compelling. Using an EV equipped with nickel-metal hydride batteries for comparison, Botti estimates that Delphi's SOFC powertrain would be 329 kg lighter (560 kg vs. 231 kg); have the capacity to store more than 10 times more energy (1081 MJ vs. 100 MJ); and would have a driving range of 350 miles instead of the EV's abbreviated 110 miles. But like the old EVs, the range extender would depend primarily on its electric plug for motive power. "85% of trips will run on grid power alone," says Botti. For the other 15% he thinks an SOFC is the best answer that will be available in the near-term. "Hydrogen fuel cells will come very far down the road," Botti predicts. That road stretches 25 years out. In the meantime, SOFC could help fill the gap. He ticks off some advantages of solid oxide over hydrogen fuel cells:
- No new fueling infrastructure needed since SOFC can run on a variety of fuels including gasoline and diesel.
- SOFCs operate at 800ºC and generate plenty of recoverable heat, making them practical for cold climates.
- Material costs should be lower since SOFCs are made with ceramics and don't require the precious metals currently needed by hydrogen units.
Still, Botti says it will probably take a decade or so before we see the SOFC-enhanced EVs on the road. But in as little as four years from now he expects SOFC technology to be available on a smaller scale as an auxiliary power unit (APU) that would replace a vehicle's 12-V battery and raise fuel-to-electric efficiency from the current 10-17% to 35-50%. Which raises the question: If the technology will be ready in four years why not bring on the EV range extender sooner? The answer is market economics. According to Botti, an SOFC APU would compete with alternatives like starter/generators which generate power for about $150/kW, but if the technology went head-to-head with an internal combustion engine as a primary power source it would have to fall within the $30-$50/kW range, which is too tall an order for the fledgling system in the near-term. What Botti leaves unsaid is that the failure of a few APUs on production vehicles could probably be taken in stride, but if motorists were left stranded by malfunctioning SOFC units, widespread adoption of the technology could be doomed. So the strategy is to gain some years of real-world data with the APU and then move on to a full-fledged SOFC hybrid powertrain. "It's a step-by-step evolution," says Botti.
Right now the chief technologist seems less concerned with the technology itself than the economies of scale needed to bring it to market. "I'm not too worried about the mechanics," he says, "But the fuel cell has to become cheaper. We need to work on getting the volume up."
Questioning Diesel's Dominance
Volker Barth, president, Delphi Europe, Middle East and Africa, doesn't think that diesel engines are on the way out. He knows that diesel power is still a growth market, especially in Europe. But he is clear-eyed enough to see the technology's limits. One of which is future fuel costs. As demand for diesel rises, so too will its cost. Another is diesel's much-vaunted fuel efficiency. "The diesel engine is more efficient at partial, not full load," he says. " In high-speed traffic, diesel is not that much more efficient than gasoline." Add to that what Barth sees as an upcoming "second wave of gasoline engine development focused on direct-injection" that could markedly improve gasoline engine performance, and it seems as if the rumors of diesel's future dominance may be greatly exaggerated. But even if the ardor of the diesel-crazy Europeans cools for the abovementioned reasons, there is a market that could keep diesel applications trending upward indefinitely: the United States. Citing Americans' preference for big trucks and lots of torque, Barth says, "The U.S. should be a diesel market and no one understands why it's not." He dismisses the usual concerns about emissions and fuel quality as imminently fixable, and says American drivers' rejection of diesel "has nothing to do with technology; its infrastructure and taste." Which may prove to be diesel's greatest limitations.