Forget about those old gas guzzlers. Electric and hybrid vehicles are hitting the streets. A driving factor is consumer environmental concern, but improved technology has really made the difference—especially in motors, motor control, batteries, and power management. Now, the biggest challenge lies in matching consumer expectations and use to new products that don't operate like fossil-fuel-powered vehicles (see table).
Motor companies are meeting that challenge. Tesla Motors' all-electric Roadster rivals high-performance two-seaters from Porsche, Ferrari, and other sports car companies (Fig. 1). It does 0 to 60 mph in four seconds and has a range of 250 miles/charge, getting the equivalent of 135 mpg.
Tesla needs to check its rear-view mirror, though, for concept cars looking to steal its thunder—such as the Chevy Volt, which can run on electricity or biodiesel (see "Volt Charges Up The Crowd In Detroit") and the hydrogen-powered Honda FCX. And when it comes to hybrids, Toyota's popular Prius embodies the state of the art (see "Setting The Standard For Hybrid Cars").
It's Electric Tesla's 2600-lb Roadster uses a custom 77-lb motor (Fig. 2). The three-phase, four-pole ac induction motor redlines at 13,500 rpm. It has a peak power of 248 hp (185 kW). Also, it's tied to a clutchless, manual two-speed gearbox that gives it that four-second 0- to 60-mph takeoff.
The Roadster doesn't have a reverse gear. Instead, it runs the motor in the opposite direction. It's probably the only high-performance vehicle that runs as fast in reverse as it does in drive. The motor also is used for regenerative braking.
Key to Tesla's system is the ESS (energy storage system). The 950-lb ESS packs an array of lithium-ion (Li-ion) batteries and a host of electronics, including 13 microprocessors that provide redundant support. Each 831 Li-ion cell is monitored and can be bypassed. The system is liquid-cooled so the electronics can optimize the thermal characteristics. It also checks for smoke, excessive heat, and other failure modes.
Drivers can charge the ESS with 220 V and Tesla's fast, self adjusting, onboard charger (Fig. 3). A full recharge takes 3.5 hours. Drivers also can use a standard 110-V circuit, but that may take as long as 12 hours, depending upon the amount of current that can be drawn. The breakaway charging cable has a number of safety interlock features. If you're looking to shut power companies completely out of your driving, check out solar cells for charging, if they can get about 56 kW.
David Vesrini of Tesla Motors estimates that the ESS locked up about 40% of the research dollars for the Roadster. He also notes that Li-ion batteries are improving at a rate of about 8% per year. This means that when the ESS and motor bearings need to be replaced at 100,000 miles, Roadster owners will essentially upgrade to a less expensive vehicle with even longer range.
But when it comes to R&D for electric vehicles, the overall economy and efficiency from source to use must be considered (Fig. 4). Even accounting for the power it draws from the grid, the Roadster tops its hybrid competitors with a 1.14km/MJ well-to-wheel efficiency. In addition to recharge time and travel distance, the Roadster leads the way in performance (Fig. 5), which will be a major selling point.
Starting at $92,000, the Roadster is expensive compared to most automobiles on the road. But it's a bargain compared to its competition. Code named DarkStar, the Roadster is just becoming available in limited quantities. And it's just the beginning for the company, whose WhiteStar project will be a four-door, five-passenger vehicle with a starting price that's expected to be half the Roadster's. Look for it in 2010 as Tesla Motors moves into the mainstream.
Hydrogen And Hybrids Fully electric vehicles have been around for some time, but they've had less commercial success than energy-efficient vehicles that incorporate fossil fuels. Ethanol may get a lot of press as a replacement for fossil fuels, but some companies are pushing hydrogen instead, especially in electric vehicles.
Unfortunately, the use of hydrogen is comparable to a storage system like a battery. Oil and coal have energy that can be released through oxidation. It takes energy to mine and process these substances, usually at a fraction of the energy they can deliver.
On the other hand, hydrogen must be obtained from other means, like electrolyzing water. This takes more energy than is released when the hydrogen is utilized in a fuel cell. The hydrogen model may only be a more efficient storage system than some batteries.
Still, many prototypes are being built around the assumption that hydrogen will be readily available. For example, Honda's FCX concept car uses a fuel cell that runs on hydrogen (Fig. 6). The hydrogen is stored in a high-pressure tank, and the system uses an ultracapacitor to even out the power requirements as the engine accelerates or when regenerative braking generates power.
Hybrids, however, are still the fuel-efficient vehicle-of-choice since they can meet buyers' range and performance requirements, as is evidenced by the Toyota Prius. But unlike Honda's Civic and Accord hybrids, the Prius starts with its electric motor and uses the gas engine as backup, essentially making it an electric vehicle. In fact, some Prius owners have hacked their rides to run exclusively on batteries.
The Volt is another interesting hybrid because it is strictly an electric vehicle for short hauls under 40 miles, but uses its fossil-fuel engine to charge the batteries for longer hauls. The engine can utilize a range of fuels.
Regarding the above comments re my comments re The Tesla car.
Haven't heard any FACTS regarding actual Tesla vehicles in motion. The Prius has been a FACT on the roads for over four years in the United States, and it recovers as much as 20% of its braking energy by utilizing a combined braking action.
The Tesla Motors 'motor's' main claim to fame is achieving 185 horsepower in a cubic foot of motor. In the industrial world, 185 horsepower electric motors are the size of a large exective desk and weigh a thousand pounds or more. A 1 cubic foot sized electric motor is typically a 5 to 10 horsepower motor. As to energy efficiency, an electric motor that achieves 90%, exclusive of drivetrain losses, is considered average. Electric motors sized and configured to a particular rpm can get up to 98%.
My criticism is that as far as I've seen, The Tesla vehicle is as real as a glossy magazine advertisement, kind of like how the Tucker automobile was presented, it never really got manufactured.
robomatic -August 29, 2007
i like to get about ur details through the mail and kiks to learn your prodution notes
Anonymous -July 01, 2007
In response to robomatic's criticism:
The main claim to fame for Tesla's motor is its relative high efficiency (80-90%) over a very wide range (0 - 13500 rpm).
Efficiency does not heavily depend on regenerative breaking. I think the Tesla typically recuperates only a few percent of its energy this way. In theory all braking *could* be regenerative, but supposedly no agency would ever approve such a car as street legal. Tesla's brake pedal works as it does in any other car.
My 30 mile commute involves 25 miles driving 75 mph; its aerodynamic drag and drivetrain efficiency that determine overall energy use.
Raymond Michiels -June 30, 2007
We should be backing these pure electric vehicle companies 100%. GM's "concept" vehicle the Chevy Volt isn't cutting edge at all. 40 miles to one charge is crap and then using a generator to charge the batters... duhh lets stick a honda generator in our crappy vehilce. Its time for a change for companies who care a little bit more. I can guess that these electric vehicle companies care a little more because electric vehicles don't need as much maintenance as ICE's do meaning less profits from selling parts which is the corner stone of the current big auto companies. Here is another startup company www.phoenixmotorcars.com that actually uses some cutting edge technoloy with the use of altairnano's new nanosafe lithium batteries that can recharge in less than 10 minutes and have an estimated life span of a couple of decades(phoenix motorcars says 12 years but they are being conservative which is good). They have been tested in front of California's Air Resources Board. They aren't compact cars either they are trucks and SUV's at a price of $45,000. The infrastructure for the "gas" stations isn't expensive or difficult to set up unlike Hydrogen or Ethanol, power lines are all over the place. Man these Big companies just can't get away from burning things can they, well Hydrogen isn't burned using a full cell but it cost about $1,000,000 to build one vehicle plus infrastructure. And when ever we decide to use cleaner methods to produce electricity we can simply replace the power plants instead of millions of vehilces again. I like Tesla Motors but also check out www.Phoenixmotorcars.com and any other electric vehicle company.
Adam -June 30, 2007
Yes, the Telsa Roadster has regenerative braking, and it should -- like the Prius -- get slightly better mileage in city driving than it does on the highway.
Tesla have said from day one that the life span of the battery pack is five years, it's no secret. Martin Eberhard feels many of them could go as long as 6-9 years, but they couldn't promise that, they decided to describe it conservatively. (And it depends on your tolerance for reduced range and performance as the cells age.)
The best estimate I've seen for a full battery pack replacement at today's li-ion cell prices is $20,000. If the prices drop in accordance with past trends, it should be closer to $12,000 when the first ones start coming due. That is still a lot of money, but have you checked what it costs to maintain a Ferrari?
Recharging from a 120V outlet is a desperate act that could get you a few miles down the road to something better -- as opposed to having your car towed. A 50-amp RV hookup is much better, it can charge from dead to full in about six hours.
Tony Belding -June 30, 2007
Tesla executives have misled the public about their car and this article contains quite a few errors. The battery pack's lifespan has little to do with mileage - it will last about 5 years and it's highly unlikeluy it would have clocked 100,000 miles by that time. Those batteries may or may not come down in price, although it is highly doubltful that they would be reduced in price over the next five years. Even if they did come down 8%, the battery pack that the owner would have to replace five years from now would still cost well over $20,000, making the Tesla one of the most expensive rides, per mile, you will ever see. The Chevy VOLT's battery pack, on the other hand, will last 15 years(!!), and the car will have unlimited driving range, unlike the Tesla, which can barely reach destinations 90 miles away and still get it's owner back home. And recharging off a 120 volt outlet would not take 12 hours. It would instead require more than 26 hours for a full charge. See what happens when an article is written by someone ignorant of EVs?
Anonymous -June 29, 2007
The Tesla may be good for energy consumption, but how is it on battery consumption? My understanding is the batteries will only last 5 years and cost around $15,000. I don't think it is possible to save enough gas to pay for $3,000 worth of batteries each year.
The Prius is about the best you can do with existing technology. The battery technology that is needed to drive the Tesla and Volt can also be used in the Prius; in which case an existing car can provide the same benefits as these concept cars.
One more point; the Prius drivetrain does get better mileage than a gasoline-only drivetrain. The Prius can use an Atkinson-cycle engine, which is 10% more efficient than a conventional Otto-cycle engine. Atkinson-cycle engines aren't suitable for conventional cars because they are very low on torque; the electric motor is used to supply the missing torque in a Prius.
Jim Summers -June 29, 2007
This article reprints almost word for word some of the advertising material for Tesla, without any verification of whether there is a 185 kw electric motor out there that weighs in at 77 lb or the reality of a battery bank of li-on cells that can perform as well as the hype indicates. This came up in an Electronic Design article earlier this year as well. I haven't seen facts yet.
Efficiency in vehicle use depends heavily on the ability to recover energy in breaking action. Unless the Tesla products and the fuel cell products have a high tech way to break in a well controlled manner while recovering the energy of motion by re-charging batteries (or capacitors) the efficiency will be limited. Even the Prius does not do much better than a light gasoline only vehicle, but the indicator of high efficiency is a high mpg rating in stop-and-go use.
Bottom line: This article tackles an interesting and complex subject with too much acceptance of advertizing hype and not enough analysis.
robomatic -June 29, 2007
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