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

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.)

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.

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.




If only I could afford it.


What this article fails to mention is the number of batteries involved. Tesla Motors has stated that the car will be powered by 6,831 laptop size batties connected in series. Most of us are familiar with the declining power storage in these batteries after some use. How much for a new battery pack, you ask? $20K, 30K ??

Lithium batteries may be in the future for cars, but not in this form.

Shaun Williams

Coal burner;

Thanks for the reply.

18650s are approx USD$10.00 per 2.4Ah retail, so say USD$300.00 / 100Ah for buying in bulk.

A few months ago I had a quote from Kokam for around USD$350.00 per 100Ah 3.6V cell.

Why should lithium ion be the "standard" for this application?


Shaun Williams
You are paying too much. Just rebuilt my battery pack with 18650s for 3.6V 2400mAh $7.98 a pop.
That $54500 for the battery pack alone.

Shaun Williams

That's nice Justin but do your maths;

I said $10 retail but guessed $7.15 for buying bulk i.e. $300 / (100Ah / 2.4Ah).

At your $7.98 a cell, 100Ah would be $333.00. Only a 5% saving over the superior lithium polymer cells!

I must admit this doesn't include shipping but the difference is long way from the "far far more expensive per amp hour" statement by coal burner.

I'm sure we agree however that lithium batteries have an exciting future and a big role to play in EVs.


Paying $54k for a battery pack is retarded. Just get a gasoline engine. Its cheaper and faster. DUH!

Ron Fischer

The Tesla powerpack treats the 6,831 batteries like swappable sectors in a hard disk drive. The are NOT wired in series. They are permanently mounted on vertical boards behind the passenger compartment. The complete pack weighs 900 lbs. A display in the cockpit can show powerpack status in many ways. Quote sales person at Petersen Auto Museum this weekend: 'A lot of batteries would need to fail before you would even notice it.' While the whole car is very innovative, this is Silicon Valley applying itself to the problem, and turns what would otherwise be a bad thing (lots of batteries) into a good thing (multiply redundant power pack structure).


Shaun Williams;

I hadn't realized that the Kokams had come down that much in price. On the other hand, standard lithium ion batts have come down too. will sell me 100amp hours of batteries for $216.05. If I buy in large enough quantities for an electric car, the price goes down to 174.83 per 100AH.


Why would you pay for a $54000 fuel tank. Thats just stupid.


2.18MJ/km = 0.975kWh/mi ~= $0.146/mi = 6.84mi/$ = 20.5mi/$3 => less efficient than most gasoline cars, but on par with some sports cars. I don't doubt that it's 3 times more efficient than a fuel cell, though.

The Li-ion battery pack weighs 1000lbs. An equivalent lead acid battery pack would weigh about 6500lbs, NiCad ~4000lbs., NiMH ~2000lbs. Plus lead acid & NiCad batteries don't last long enough - imagine replacing a $20,000 battery pack every 5-10 years.

NiMH is the current preferred option for most serious applications. Lead acid & NiCad are for cheap/replaceable applications where weight doesn't matter so much. Li-ion is for applications where battery life & small size is everything while money is no object: like cell phones and concept vehicles.


This is just a Lotus Elise with a 900lb gas tank. Pretty pathetic considering that a regular gasoline elise weighs only 1800lb with fuel.

Jon Mittelhauser

Many of you are missing the point because you are comparing Tesla Motors to the existing large car companies.

Tesla motors is a pure Silicon Valley startup. That is their mentality from the start. A common technique is to boostrap your finances. People, they have spent *only* 25 million so far in development and they are about to start taking orders!

I can attest that they are going to be receiving more orders than they can possibly handle at the start. They had 40 orders at their unveiling and I can't even get through to place an order myself. Their "signature" 100 vehicles are an instant sell out. They will easily sell enough vehicles within the first 2 years to recoup the initial investment and fund future development. They aren't trying to take on the Ford Escort (at least yet) - they are trying to build a COMPANY.

Take a look at Cirrus in the private airplane industry. In a decade, they became the largest plane seller by starting from scratch and doing some radical things that appealed to early adopters (e.g. a parachute for the plane!).

BTW, I love all the people who are complaining about the 250 mile range because "a few times a year most people need to take a longer trip". LOL. People who are spending $100k for a sports car/toy are not using this as a sole vehicle. It is a second or third car (or more). Not to mention that they will fly for the trips you are talking about!

Who should be worried about this vehicle? I'll tell you one company who should be - the local Mercedes and Porsche dealers. There are hundreds of SLs on the road here. I guarantee many of them will convert to Teslas in the coming years. Mine certainly will be (once I get through to order!)...



As far as batteries, Firefly Energy's product seems to be one of the more exciting prospects I've seen for EV's.


Sorry, here's the address:


Frank and Sean:

You may not like the price of the fuel tank (which will come down over time) but its hard to beat the performance in that price range.

The Tesla will leave the Elise in the dirt despite the extra weight and still uses less energy to do it. (Ok it is more expensive)

The only production car that can out accelerate the Wrightspeed ($100,000) (0-60 in 3 seconds) is a Bugatti V12 (1.2Million) that get 9mpg or less. So much for cheaper and faster. Maybe gasoline (going up,up,up) isn't the best.


Excuse me?
There are plenty of cheaper sports cars out there that can accelerate in 4 seconds. Its not mean feat.
Lotus Elise 111R 4.7 sec
Lotus Exige S 4.1 sec
Lancer Evo IX 4.5 sec
BMW Z4 M 4.7 sec
Viper SRT-10 4.1 sec
Corvette Z06 3.6 sec
Porsche 997 Carrera S 4.1 sec
And and we haven't even discussed the degraded handling due to the the 900lb dead weight on the back. This car is pathetic.


The Bugatti doesn't have a V12. Its a W16 engine with 4 turbos.



To settle this matter... You wrote: "You know the max power, you know RPM, and that defines the high-RPM torque."

But the point is, for any given gasoline engine, you *DON'T* know the max power for any given RPM setting. Therefore, you don't, a priori, know the torque. Max power is NOT CONSTANT over the engine's RPM range. Moreover, gasoline engines tend to have peak power and peak torque at somewhat different RPM settings -- demonstrating that torque is not governed by the theoretical limit set by power, but is further constrained by the mechanical limits of the engine. The point is -- your formula misses most of what goes into making gasoline engines perform in the way that they do. To pretend that a single line from a high school physics book is the whole story is rather silly.

This car, with its electric motor -- one that is allegedly better than even other electric motors (can't comment much on that claim) -- has a wider RPM operating range than gasoline motors built for similar applications, and seems to be able to sustain close to peak torque and power over a wide variety of RPM settings. That allows for higher torque at higher RPMs than virtually any other car out there. It looks like one exciting, and substantially different, ride.

Andrey also writes: "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."

Actually, I think a comparison of this electric car with gasoline motors -- even in some detail -- is quite germane. And this is, in fact, what most of the rest of the posts on this discussion thread are doing. You seem to be simply trying to dismiss my point with a bit of hand-waving, and misrepresenting the automotive facts. While modern sports car engines get admirably "flat" torque curves over the restricted interval of their operating range (meaning their drop-off from peak power is not terribly fast as you move somewhat away from the ideal RPM), they still have restricted operating ranges. Even the Lotus Elise redlines at 8,000 RPM! Part of what makes "flat" torque curves possible is voodoo like variable valve timing -- certainly not something accounted for in a simple Newtonian formula.

The point is, you leveled a criticism at this company which was not just unadvised, but really quite possibly misleading to others as well. It behooves us all to know a little about what torque and power are, and where they come from. And while part of that is knowing that (kg * m^2 / s^3) on the left of the equation must be dimensionally equivalent to (kg * m^2 / s^3) on the right side of the equation, it also means knowing that the story does not end there. As a math professor of mine once put it, knowing math allows you to imagine and explore the set of all possible universes that are logically consistant. But by itself, it cannot tell you much about the universe we happen to be living in. Start with Newton -- and end up in a garage covered in grease -- if you want to understand cars. Which I think is the first step towards taming them.


As this car was built by Lotus, I expect that the rather clipply four second 0-60 time is complemented by superb handling and driving behavior. Nine hundred pounds of weight behind the driver? That sounds like better handling to me, not worse. No European supercar manufacturer worth his salt (Lamborghini, Ferrari, Porsche, Lotus) would contemplate anything but a mid-engine design for his sweetest handling cars -- that's aft-of-driver placement of the powerplant. With an electric car, putting the batteries (which are likely bulkier than the actual motor) in that spot is the next best thing. This car sounds like good fun, environmentalist or not.


FireFly batteries>

don't count on them too much! They recently announced that the most advanced strand of their battery technology is for US army only aka the boys in Iraq need them in their hummers and tanks because of hars weather and the less powerfull will go in Electrolux products such as big powertools, lawnmovers etc. And even those batteries won't be available on the open market for years. So the early hopes of diy EV people vanished..

The better bet goes with some Li-ion/polymers from asia - they cost 1/3 of the EU-US products which have even worse specs, current pricing is bellow $1/Wh and falling..

The only "western" brand is a123 but their pricing is also ridiculous at the moment..

So, as always the best approach is to buy a bicycle perhaps electric assisted, forget about cars. In a few years time you will be solving issues like what to eat and not silly car fantasies..

Shaun Williams

Ron Fischer;

Very interesting. Do you have any more detail on the battery back? Obviously the batteries have to be connected in series (and parallel) at some stage to provide the voltage/current mix but how are they switched, with masses of Mosfets? What are the array dimensions?

Coal burner;

Those Li-on prices are impressive, when Li-poly gets that cheap (and it will) EV's will perform better and cost less to run/maintain over their life compared to an equivalent carbon pumper.


I'd hardly call this car's performance pathetic. From reading it appears to do 0-60 in 3.9 sec and weighs 2500 lbs. They hope to loose a couple of hundred pounds for the production version. Most sports cars (Porsche, Corvette etc) weigh in the region of 2900 to 3300 lbs. The Elise is quite a bit lighter but it has to be because it only has around 180hp. It also appears that this car is slightly bigger than an Elise (2" longer wheel base). The car is over priced but that is a function of small volume production and the price of new technology. Hopefully the price will come down reasonably quickly.


Ann: I stand corrected W16 it is.

Pastulio: The Tesla may have a 900lb battery but it doesn't have an engine block either. The Tesla is only 500lb heavier than the Lotus. (Not 900) and is 500lb lighter than your Porshe Carrera (which costs $440,000), 800lb less than the Viper, 200lb less than the BMW, 100lb less than the Corvette. So who cares what the battery weighs?

The point is that this car is in the same class as other sports cars but doesn't burn gasoline.

P.S. None of those cars you mentioned came close to the 3 second Wrightspeed.


What 3 second wright speed are you talking about. The article is about the Tesla which accelerates in 4 seconds. If you want to bring strange one off garage built wunder rockets, there are planty of kit cars and one man freak shows that can accelerate in less than 3 seconds. So its a moot point.
Comparing the weight of this car to anything else than an elise or exige is pointless.


Jon, its good to hear what I hoped for but couldn't be sure of regarding orders. They carry a lot of people's hopes, not just those that can afford the current model.


Pastulio: Ok the exige is less than 500 pound lighter, is in the same price range ~$80,000 (but if you have to ask you can't afford anyway) and is slightly slower 0-60. Sounds like the same ballpark. But I repeat your burning gasoline. OECD economies (particularly the U.S.) can't survive importing all of their energy.

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