Beyond mere self-interest, there are at least two reasons EEs might want to keep an eye on developments in alternative fuels for transportation. For power engineers, the odds are strong that most future vehicles will use electric motors, either exclusively or in some kind of hybrid arrangement. For the digiterati among us, there will be control and monitoring opportunities in the vehicle and up and down the distribution chain. That sounds suspiciously like jobs and opportunity. Welcome to the Next Big Thing.Prime Movers
There's no doubt that gasoline prices have captured people's attention lately. Folks certainly see that we're using lots of petroleum fuel and importing much of the oil it's made from (Fig. 1). That leads to considerations of alternative fuels. In the big picture, alternatives to petroleum-based fuels will impact activities ranging from electrical power production to heating and transportation. But how will this specifically affect the way we drive?
Let's consider the vehicle power plants themselves before we see how they get their power. To use a Darwinian metaphor, the most successful new species to date are the gas/electric hybrids, though they're just getting into the marsupial stage—no longer an egglayer, but not yet a true mammal.
The most successful sub-species is typified by Toyota's Prius, in which the starter motor/alternator is incorporated into the drive train of a conventional gas engine. Honda's approach is a little more elegant, with an electric prime mover and a gas engine that keeps the batteries topped up. Someday, the true mammals will be all-electric. But like the opossum and the kangaroo, these petro-electric approaches will find ecological niches that allow them to survive well into the future.
Purely electric-powered vehicles have been built, and some are commercially available. But they face many natural enemies. Nonetheless, it's instructive to examine the fossils already left behind and encouraging to see how the survivors successfully deal with those enemies.
When Editor-in-Chief Mark David and I met with the engineers at General Motors' Advanced Vehicle Technology Center last March, they showed us a collection of the parts they'd salvaged from their EV-1 vehicles. The EV-1 project lasted from 1996 to 2003. GM made over 1000 vehicles and leased them (in California and Arizona only) for three years.
During the life of the program, returned cars were refurbished, upgraded, and leased again. You could drive an EV-1 55 to 95 miles on one charge of the early lead-acid batteries and 75 to 130 miles on the later nickel-metal-hydride (NiMH) batteries. Alas, after 2003, most of the cars were recalled and crushed (Fig. 2).
What struck me was how much the EV-1 electronics shrunk in physical size and cost over the program's seven-year lifespan. The EV-1's first inverters were about the size of a refrigerator door, and the last were less than one-quarter that volume. Something similar happened with the size of charging stations. GM's engineers said bill-of-materials costs had come down as well.
Toyota ran a similar lease program with an all-electric RAV4 SUV. At the end of the program, the company was going to strip and crush the vehicles, but it relented in the face of a powerful grassroots protest. The contractor installing solar cells on my roof has one of these RAV4s. Taking it back from him would be about as difficult as taking John Wayne's six-shooters.
GM's EV-1 and Toyota's electric RAV4 were quasi-production vehicles, as were Honda's EV-Plus and pickups from GM and Ford. But what's become of them?
GM showed us a couple of battery-powered S-10 pickups that had a 114-hp three-phase, liquid-cooled ac induction motor driving the forward wheels, and separate wheel-hub motors for the back wheels (Fig. 3).
These pickups stongly resembled the 1998-era S-10 electric research vehicles that GM leased and sold to a select few buyers. Only now, these trucks have been beefed up with the wheel-hub motors.
In the new versions, the wheel hub motors provide a 60% increase in torque when the driver calls for acceleration. Each generates about 25 kW. They also add 33 lb to each of the rear wheels, which is why they aren't used in the front of the vehicle. And, they add the possibility of electric anti-skid control.
Around the rest of the industry, Ford leased EV Ranger pickups from 1998 until 2004, when they were all recalled. Honda abandoned and recalled the EV-Plus in favor of the Insight.Hydrogen
If you have fuel cells, you can say you're running the car on hydrogen, but unless you have a personal supply, you're really running it on electricity. (Unless you're Ford, which has an F-350 concept vehicle pickup with a 6.8-liter, V-10, internal-combustion engine that runs on pure hydrogen.) Actually, hydrogen is fundamentally an energy storage and transportation medium.
When Mark and I visited GM, it was less to observe a memorial-to the late EV-1 than to see and drive the company's newest concept car, the HydroGen3. This fuel-cell-only, electric-powered modification of the Zafira A is sold by Opel in Europe and under other GM brands around the world (Fig. 4). The only conventional battery aboard this vehicle is the one that boots up the computer. The car's 200 mini fuel cells, which fit easily in the Zafira engine compartment, produce about 200 V. A dc-dc converter delivers 320 V to the motor.
A fillup of 3.1 kg of hydrogen is stored in a pair of 10,000-psi tanks that fit under the rear seat. That's triple the pressure of a regular tank of industrial gas, so it's a little scary to think about. But most engineers don't want to think too much about sitting on top of a nearly empty tank of conventional gasoline either.
For what it's worth, 1 kg of hydrogen approximately equals the energy produced by one gallon of gasoline. But it's not easy to relate that to the real world without efficiency numbers, which are hard to obtain. In lieu of that approach, consider the HydroGen3. Its range is 150 to 180 miles—call it 50 to 60 miles per hydrogen equivalent to a gallon of gasoline. Top speed is 99 mph. With four healthy American males in the car, acceleration is sedate.
By way of comparison, the 1.6-liter conventional-engine Zafira A can go from 0 to 62 mph in a modest 13.4 seconds with a top speed of 109 mph. European-measurement efficiency standards in imperial miles/gallon are 30.1 urban, 46.3 ex-urban, and 38.7 combined. The latter figure, given the vehicle's 12.5-imperial-gallon tank, provides a range of 480 miles.
The HydroGen3 demonstrates that it's possible today to make a euro-size minivan with an electric engine that runs on electricity from a gaseous-hydrogen fuel cell. And it delivers euro-size minivan performance, except for range, which is reduced by about 60%. So far, so good. But where does the hydrogen come from?
Obtaining hydrogen the way we do today isn't a solution to petroleum dependence, since most of it comes from natural gas. In the process, some of the gas is burned to create steam, which is superheated to 700°C to 1100°C, where it reacts with the methane component of natural gas to produce carbon monoxide (yes, a greenhouse gas) and hydrogen. This process can be augmented at lower temperatures to generate even more hydrogen by reacting the carbon monoxide with more water.
Electrolyzing water is an alternative. Whether it's practical, though, depends on economics. Presently, the electricity consumed is worth more than the hydrogen produced. A process called high-temperature electrolysis (HTE), which would obtain its heat from a nuclear reactor, could be twice as efficient. But, obviously, it has yet to be commercialized (Fig. 5).
The appeal of HTE is that the same nuclear plant could produce electricity for the grid during the day and hydrogen for energy storage at night. Presently, no full-scale HTE plants are in the works. Idaho National Laboratory is still working on bits and pieces of the technology.
A greener (literally and figuratively) approach hydrogen generation would be to use algae. Normally, alga cells photosynthesize oxygen. But deprived of sulfur, they will produce hydrogen—for a while, anyway. Protein buildup then stifles the process. The path to sustainable hydrogen production from algae seems to lie along the path of bioengineering. Of course, creating franken-algae to generate hydrogen from sunshine may run into public-relations problems.
Assuming there's eventually an economical supply of hydrogen from acceptable sources other than petroleum, the next challenge lies in creating the infrastructure to store, transport, and distribute it. When you consider that those of us in electronics already deal with an infrastructure that routinely handles large volumes of liquid oxygen and nasty gases like silane and arsine and (I still hate this) metal organics, not to mention the fact that most people pump their own gasoline, developing a safe hydrogen infrastructure is certainly achievable.
For distribution, it just isn't practical to ship and store hydrogen at high pressure for most of the journey from source to consumer. For one thing, compressing the gas to something like 30,000 psi requires lots of energy. Liquification is out of the question because it would take even more energy.
One alternative is to store the hydrogen as a component of ammonia, from which it can be recovered at the point of transfer by using a catalytic reformer. Another alternative is to store the hydrogen as metal hydrides, either sodium borohydride, lithium aluminum hydride, or ammonia borane. Sodium borohydride is a hot prospect because it can be used directly in fuel cells without the need for platinum catalysts. On the other hand, recycling sodium borohydride is another sizable energy consumer.Electric Power Stored In Batteries
People like my solar-cell contractor and his all-electric RAV4 tend to react passionately when somebody mentions hydrogen-fueled cars. They worship their battery-driven vehicles and will point out that by simply using off-the-shelf components, they get 2 to 3.3 mi/kWh, while a car that gets 30 mpg is achieving about 0.9 mi/kWh (that's assuming that a gallon of gas can produce 33.6 kWh).
But is it really that simple? I live in Silicon Valley, and many of the EV fans here do their own conversions. Acterra, a Bay Area environmental group, spent around $7000 to convert an MG Midget to an EV. (No, not the original TD Midget, rather the 1960s version.) Like the original Midget, the EV version is something you learn to love in spite of its limitations. Top speed is 65 mph and range is about 30 miles. The coolness factor, though, is very high.
For the Acterra conversion, out went the engine, gas tank, exhaust system, and so on. In went a 20-hp (60 hp max) Prestolite series dc motor connected to the standard transmission by an adapter plate, an Auburn C600 motor controller, and 12 12-V, 30XHS Trojan deep-cycle, lead-acid batteries. A dc-dc converter charges a couple of gel cells that run the 12-V headlights and similar features.
Commercially, what's keeping the EV flame alive are vehicles like Mitsubishi's Lancer Evolution MIEV. (The "I" stands for in-wheel.) It uses outer-rotor in-wheel motors on all four of its 20-in. wheels (Fig. 6). Each wheel-hub motor produces 50 kW of power and 518 Newton-meters of torque. Acceleration from zero to 60 mph takes less than eight seconds. Top speed is around 110 mph. The juice to run it comes from a lithium-ion (Li-ion) storage battery.
The drawbacks of pure electric vehicles are range and charging time. Factory specifications for my solar-panel contractor's RAV4 claim a range of 80 to 120 miles on a full charge. That charge comes from 24 12-V, 95-Ah, NiMH batteries with a total potential output of 27.4 kWh. (Actual range depends on speed-induced aerodynamic drag. Top speed is 80 mph, and the RAV4 is a boxy beast.)
Reducing charging time offers some interesting opportunities for EEs. Activity is rather intense within the worlds of battery-charge metering and charge-current shaping for handheld devices and laptops. It's interesting to speculate on how that experience could be extended to charging electric-car batteries.
At the "pump," charging can be accomplished either by a direct connection or inductively. In the latter, a "paddle" is inserted into a slot on the car. The paddle contains one winding of a transformer. The other winding is the car. The paddle has obvious safety advantages.
Limited battery life appears to be a bogus objection to all-electric vehicles. According to the Electric Power Research institute, "Toyota RAV4-EVs are successfully operating for more than 100,000 miles on the original NiMH battery, and are projected to last for 130,000 to 150,000 miles." That's not many fewer miles than Electronic Design contributor Bob Pease has on his famous 1970 VW bug.