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Tesla Reveals High-Profile Electric Roadster; Calculates EV is More Than 3x as Efficient (WTW) as Fuel Cell Vehicle

Tesla3
The Tesla Roadster.

Tesla Motors unveiled its much-anticipated all-electric two-seater roadster. The lithium-ion battery powered sportscar features a 248hp (185 kW) electric motor that accelerates the car from 0 to 60 in four seconds.

Built by Lotus for Tesla, the Roadster has a range of about 250 miles and a top speed of 130 mph. The price for the Roadster will be around $100,000.

The custom-designed battery system (Energy Storage System) weighs in at close to 1,000 pounds and uses commodity lithium-ion cells. The system addresses thermal balancing with a liquid cooling circuit.

The 3-phase, four-pole motor uses a low resistance “squirrel cage” with large copper end rings. This allows the rotor to develop high current flows and torque, with low resistance losses. The use of a small air gap allows tight inductive coupling which, combined with low loss magnetic materials, enables the development of high torque at high rpm. Together, these factors allow the induction of large currents, even at high rpm, producing much flatter power and efficiency curves from approximately 2,000 rpm to 12,000 rpm. The motor redlines at 13,500 rpm.

(Devising a cost-effective method for the production of copper motor rotors has been under investigation for years. Siemens introduced three motors with die-cast copper rotors to the US market in April.)

Tesla4
Comparing Well-to-Wheel Efficiency and GHG emissions. Click to enlarge.

In a white paper (The 21st Century Electric Car) published on the Tesla Motors website, the company calculates the tank-to-wheel (actually, the “electrical outlet to wheel”) energy efficiency of the Roadster to be 2.18 km/MJ.

Assuming electricity supplied from a combined-cycle natural-gas-fired generator, and accounting for transmissions losses over the grid leads them to calculate the “well-to-wheel” efficiency of the Roadster to be 1.14 km/MJ—double the efficiency of the Toyota Prius.

Tesla then tackles the question of hydrogen fuel-cell vehicles (FCV) fuel cars, deriving a theoretical efficiency for an FCV fueled with hydrogen produced by steam methane reforming of 0.85 km/MJ.

Tesla2
Theoretical efficiency of battery-electric and fuel-cell vehicles. Click to enlarge.

This is impressive when compared to a gasoline car, though it is 32% worse than our electric car. But real fuel-cell cars do not perform nearly this well.

...The best fuel-cell demonstration car measured by the EPA is the Honda FCX, which gets about 49 miles per kilogram of hydrogen, equal to 80.5 kilometers per kilogram. We know that the energy content of hydrogen is 141.9 MJ/kg, so we can calculate the vehicle efficiency to be 80.5 km/kg / 141.9 MJ/kg = 0.57 km/MJ.

...When we calculate the well-to-wheel energy efficiency of this Honda experimental car, we get 0.57 km/MJ x 61% = 0.35 km/MJ, not even as good as the ordinary diesel Volkswagen Jetta, let alone the gasoline-powered Honda Civic VX or the Honda Insight hybrid car.

However, some proponents of hydrogen fuel cells argue that it would be better to produce hydrogen through electrolysis of water. The well-to-tank efficiency of hydrogen made through electrolysis is only about 22%, and the well-to-wheel energy efficiency of our theoretical fuel-cell car would be 2.78 km/MJ x 50% x 22% = 0.30 km/MJ, and the well-to-wheel energy efficiency of the Honda FCX would be 0.57 km/MJ x 22% = 0.12 km/MJ, even less efficient than a Porsche Turbo.

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Comments

Richard

"As long as you ignore the range and charging time issue, you will never sell many EVs. You have to sell a product that people will buy. EVs have not been able to get a toehold in the market because they do not have similar capabilities to gasoline cars."
That's what they said about Hybrid cars! Now they are selling like hot cakes. There is a large enough market for EV's now! There just aren't any viable offerings of EV's. If someone would make an affordable EV, there are plenty of buyers out there! Range isn't as important as you make it out to be. As stated, 99% of trips are under 30 miles per day, and even with lead-acid batteries, the range can easily extend that. If you need to make a long distance trip, then maybe it's not for you, but most families have moe than one car, in fact most have three! Take your pick! But for those of us who would like to drive EV's for the sake of oil dependance, enviroment, or just kicking the oil companies in the ass, there isn't any real players in the market, and that's the point.

marcus

Jameson, its a very explanatory graph! Thanks for the link.

JM

Coal Burner:
Thanks for your explanation. That makes puts a different perspective on the range issue. I just find it frustrating that people seem to think all buyers accept that they need all the performance of every car currently out there. After all, the Tesla, at this price and with two seats, also does not meet the needs of all markets, but it is a good starting point. I think Richard makes a good point with his hybrid analogy.

Lance Funston

Weighing in on the practical vs performance issue... I think criticizing Tesla for not pursuing a small practical vehicle is pointless.

There are other vendors in that marketspace if that is what people want, and those vendors also struggle with pricepoint issues, but with a much more challenging audience. Look at the struggles of Tango, and the accessible, but stil overpriced OBVIO.

I think the beauty and performance of this car will create badly needed buzz and excitement in American Society about EVs that far outweighs the short term value of putting a few thousand more pokey econo-electrics out for the needs of the choir.

Wealthy early adopters and performance enthusiasts (and the magazines they read) set powerful trends in the auto industry. If Tesla experiences success, expect to see the big automakers jump in the game with a winder range of vehicle choices.

Kevin

I can't believe all the negative comments following this article. Everyone here seems to be fixed on their dream world where $8000 EVs are in every driveway and 1 millisecond instant charging stations are available on every corner. Nobody reading this needs to be convinced to want a cleaner vehicle. It's the people driving around in the Porsche's and Ferrari's getting 10 mpg and come home and park it next to their giant truck that gets 7 mpg who need convincing. Finally someone puts out a car that will show up on their radar as a viable alternative at what is a cheaper pricepoint than comparable sportscars, and you rip it apart. The only way to get these cars cheaper is if people start buying them, and Tesla has the perfect approach to doing that; (design the car to fit what a buyer in the necessary price range will want). Who in their right mind would buy the OBVIO?? That's the ugliest car I've ever seen and still costs $50k. Chaulk that up to another failure ala EV1. One of first decent looking, decent performing, long range EVs and it's met with disappointment? Unbelievable. Good luck ever getting support for EVs with this mindset.

paul

I agree that many people are missing the point with this vehicle. Perception is often what drives peoples purchases, and the general perception of current electric cars is that they are ugly, don't perform and have poor range. While this car isn't for the masses, it will help to change people's perceptions about EV cars. I know this by the reaction I get by telling non-ev enthusiasts about the car. The website says that they are working on a more practical 4 door car (code named white star). Hopefully advances in battery technology and cost reductions will make this available at a lower price point. However, I don't expect it would be sold for $20,000. I'd be happy for price in the range $35,000 to $45,000. Until there are millions of EV's sold you are always going to pay a premium. Ugly, slow cars with limited range will never sell in large numbers, that's for sure.

A point I hear from a lot of sceptics is that you will have to change the battery every year. The interesting thing about this car is the high maximum rpm of the motor. RPM is typically a function of voltage. So they must be using a very high voltage pack. Which means that current draw will be reduced and this should help reduce overheating and improve cell life. It will be interesting to see how long they last.

Bob

Great comments all. However, I think a lot of people here are not being realistic. It's great that this EV demonstrates what can currently be done, but it is a long way off of providing a realistic alternative for the masses who have invested their hard earned wages on their transportation vehicles powered by state of the art internal combustion engines burning gasoline. Let's get real folks. After giving due consideration to all the alternatives, the most realistic solution (_all things considered_), is an all out push for the production and mass distribution of biobutanol. Think about it.

Andrey

Jameson:

It is regular torque curve for electric motor. Compared to gas engine, it has high LOW end (low RPM) torque. That’s what all buzz about high performance of HEV and EV (high stand-still and rolling acceleration, fast throttle response, etc.) is about.

To be honest, I just can not get used to PR announcements (especially from high level engineering company) which controvert laws of physics, discovered 3 hundred years ego by Sir Isaac Newton.

Paul

I'd have to bounce that one right back to you. There are serious potential issues with large scale use of biofuels and some serious technical problems to overcome. Realistically, in the near to medium term bio fuels can only provide a fraction of the fuel required. At the end of the day, to get to where we need to be, will require all we can throw at the problem. Including bio fuel cars, hybrids, plug-in hybrids, clean diesel and pure EV's.

NBK-Boston

Andrey:

Their torque curve, as posted on their website, follows the usual pattern of electric-motor torque curves, and that is precisely the point. Part of the buzz is the availability of low-end torque. But part of the buzz also really is the availablity of high-end torque as well.

Nobody denies that the limit of available torque decreases as RPM increases for a given power output, least of the the developers of this car, who display a torque curve that exhibits just that property. But in a traditional gasoline engine, further constraints are placed on the availability of torque. In most cases, as RPM goes up, torque goes down even more quickly than this limit does. Most cars redline at 6000-8000 RPM.

This electric car, however, produces well over 100 ft-lb of torque at 10,000 RPM, and the engine can exceed even that rotational speed handily. I'd like to see any Porsche out there generate that much torque at that RPM. Granted, this engine gets even more torque at low RPM than it does at high. But the point is, *relative to traditional high-performance gasoline engines* (and possibly even relative to less well designed electric motors), this motor gets more torque at high RPM.

For the sake of argument, it is even theoretically possible to build a motor that, across certain intervals, gets higher torque at higher RPM than it does at lower RPM. In fact, it is more than theoretically possible. In the current context, it is inevitable. Pretty much every conventional car on the road today has a motor with a torque curve that starts with low torque at low RPM, gets high torque at medium RPM, and ends with low torque again at high RPM. As you move from low to medium RPM, torque goes up as RPM goes up, torque doesn't go down!

The reason is that the formula you presented is the theoretical limit on torque relative to RPM at a given power output. But many factors beyond this limit govern the behavior of motors. In fact, across the RPM spectrum, gasoline motors change their *power* output, meaning that your limit function changes value as RPM changes, in ways not accounted for within the function itself. Power, which in your formula is a constant, is actually a variable, and is itself a function of RPM and several other factors. (The statement "W = N*m * s^-1" is the dimensional definition of power, not the actual forumla which governs the power of any particular engine or class of engines over any particular set of conditions.)

In conclusion, I find no indication that the engineers who developed this car are ignorant of the work of Sir Isaac Newton. Nor to I find any indication that the people who built this car are trying to trick the public into believing untruths about physics. Rather, I think they were merely trying to point out an unusual and exciting performance characteristic of this car, and I think they did so fairly clearly.

Andrey

NBK:
I find your post written mostly for the sake of the argument along. As you pointed out, “…the formula you presented is the theoretical limit on torque relative to RPM at given power output”. That’s it. You know the max power, you know RPM, and that defines the high-RPM torque. No need to PR explanations.
By the way, you are vastly off in your description of ability of IC engines to produce broadband torque and their RPM limits. But this is irrelevant to discussion on EV theme.

allen Z

Sweet, 61 comments (though some are from the same poster).
_
___Meanwhile...I hear that GM and Lotus had a relationship a while back. Could GM team up with Tesla and Lotus to make electric, or gas electric hybrid versions of their Corvette? On a broader note, could it be done with other vehicles like ones from Pontiac, Chevy, or Opel?

Shaun Williams

Enjoying the posts.

Coal Burner;

Modern Lithium batteries have virtually no Peukert effect and their discharge rates are up around 8C-10C not 5C and that's the off-the-shelf product not in-the-lab.

Here's some real data from someone who uses them in their EV for racing.

Alex

Let me throw some more math for those who cares:
Average car gets about 10 liters of gasoline per 100km.
After driving 300.000 km it will burn 30 tons of fuel which is at present will set you back about 30k.
Add the price of vehicle ( lets say 30k too) and you get
60.000 $ for 300K km.
Assuming that batteries in Tesla can be recharged at least
2000 times , gives us the range of half a million kms for
80.000 $ plus pennies (around 5000 $ for electricity bills).
I don't go into changing oil, tune ups, brake pads and
other stuff . I think if they release sedan version of EV with comparable price tag, then believe it or not many people will go for it. At least I would. I spend
around 200 bucks a month for gas that goes straight to
oilrich countries and harms to our interests. I would rather spend 20 bucks fo locally produced electricity
and another 180 for monthly payments to bank for higher cost of the vehicle.
Don't think though goverment lobby groups (oil ones)are
ready to enlighten public on this matter.

Mark

I give this car two thumbs up. Stack this 2 seater up against the EV-1 to see how far technology has come in 15 years. Within a decade, hybrids evolved from the niche 2 seater Honda Insight, to the Camry hybrid. FCVs were a distraction that funnelled away massive amounts of R&D effort and $. The timing seems to be right for EVs as long as oil prices stay high. The cordless tool industry is beginning its phase out of NiCd, thankfully, which will increase production volumes for Lithium cells driving prices down. Remember when a cordless 12V DeWalt drill was $350?

Arnold

The batteries that are now in the current Tesla Roadster will probably not be the same batteries in the car when it is delivered to the lucky buyers next year. My guess is the they will be using better (and maybe less expensive) batteries in the future, such as the A123 battery. Has Tesla Motors said anything about this?

coal_burner

Shaun Williams;

The batteries that Proev are using are lithium polymer batteries, not standard lithium ion. Lithium polymer batteries were invented specifically to overcome lithium ion's low current capacity characteristics. Lithium polymer batteries are far far more expensive per amp hour of capacity than standard bulk 18650s.
The peukert effect on lithium polymer batteries is impressively small, on lithium ion it is fairly small, on NiMH it is fair, on lead acid it is huge, but it's allways there.
As far as high discharge rates go, most lithium ion batteries I have found (not lithium polymer) specify limiting discharge to 1/2C in order to achieve rated cycle life.
BTW I've been following Proev for quite awhile now, they did assemble an awesome vehicle capable of beating their ICE competitors for the same cost.

James

Allen Z - GM sold Lotus a while ago. They are now totally owned by Proton.

Harvey D.

How about having enough pre-wired on-board spaces for 5 to 15 small 2 Kwh plug-in quick charge battery packs.

For those of us with limited capital, the basic (2 Kwh x 5 = 10 Kwh) or similar packs could be a starting point. As battery price and weight go down, (and they will) you could add 5 to 10 packs to double or triple range or more.

The ICE vehicles did not all start with 400 HP. The early Fords did not have even 1/10 of the current HP.

aa2

One factor is that families in North America at least have 2 or more cars each. Range is obviously a concern until the fast charging batteries make it out and can handle many recharges.

But since families have 2 or more cars, only their long range car needs to have a gasoline engine. And that can be made a hybrid for now. The second car, for one spouse's commute, and for family errands can definately be electric. That will also help provide the much larger market needed to bring down the costs of the batteries, and increase their abilities.

joe

God damn some of you are ignorant!

Andrey

Harvey:
your idea for pre-vired space for additional batteries is just brilliant!

marcus

Well Joe you'll be happy to know that we are all very much enlightened by your brilliant comment!

Fred

I jnow of this new EV US car manufacturer, and their concept is very simple and brilliant:

They'll sell their cars with a basic Li-Ion battery [U-Charge from Valence Tech.] pack that will have about 100 mile range and if you wants more range th battery pack can incrased to a limit of 400 mile range and you pay/lease the premium for extra batteries. This way, anyone can afford it and for the people with no monetary problems, they can order it with the "ultimate" range battery pack.

Simply perfect!

FS, PhD

Fred

Sorry about all the typos...

FS

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