The Tesla Company has designed the first electric zero-emissions production sports car using proprietary cells like those of laptop computers and power tools. OverDrive (Nov. ’08) takes a look.
These cells called 18650, are cylindrical, 65mm long and readily available from a number of suppliers. The Tesla needs 6,831 of them, wired together in parallel sheets, which are joined in series and gathered together in an aluminum box cooled with propylene glycol. Apart from the complexity, underscored by the overheating problems that have been encountered with laptops, Tesla’s is an expensive solution to the problem of providing enough power for an electric sports car. Perhaps that does not matter because the Tesla is also sensationally dear: 99 Euro’s before tax. More than 1,100 orders have been received in the US alone and by last month the first 16 already delivered. For Europe, a launch edition of 250 cars will be available from next May.
If the Roadstar looks familiar is it because it is, says OverDrive (Nov. ’08). Tesla short-cut the blacksmith aspect of car-making by adapting the Lotus Elise two-seater convertible. Lotus builds the aluminum chassis and fits the specially designed carbon-fiber composite body panels alongside the Elise in its plant in Norfolk, England. These cars are then sent to California to be fitted with the 25PS electric motor (which comes from Taiwan), batteries (from Japan) and the electronic control system.
The Elise is a minimal sports car, more suitable for track days and everyday journeys or long distance touring. It is a tight fit for two people and is slightly claustrophobic with the awkward fabric hood in place. The Tesla is much the same in these aspects.
The key start does nothing other than illuminate a ‘ready’ light, select ‘D’ with the lever on the central switch console, press the accelerator and we are away. It immediately feels eager but the curious thing is that there is no noise. Most electric cars have a whine from the motor or the whir of cooling fans.
Flat-out the Tesla will go from 0-100kmph in 4.5 seconds and reach 200kmph. At 160kmph the only accompaniment is the rush of the wind and the sound of tyres on tarmac. It could not be simpler to drive: there is no gear-changing as the Tesla manages fine with just one ratio.
Electric motors produce maximum torque throughout their rev range, which is why the step-off from rest is so brisk and the mid-range acceleration – from 50 to 120kmph – is equally impressive. The Tesla is compact and handle well, so it is supremely agile but the steering is heavy at low speeds – it does not have power assistance – and the ride over bumps can be harsh. That is down on the weight: 350kg more than an Elise.
The 252PS electric motor is behind the battery pack and drives the rear wheels. When the car is braking or casting, the motor acts as a generator recovering energy that would otherwise be lost as heat to charge the batteries. This regeneration system provides the equivalent of engine braking when you come off the accelerator. The effect is so strong that driving at moderate speeds in city traffic, you hardly need to use the brake pedal.
The battery cells are rated for 500 recharging cycles, equivalent to 175,000km and Tesla guarantees the whole vehicle for three years. It takes 16 hours to recharge using a UK domestic 13-amp electrical system but a 63-amp industrial charger does the job in three hours. If the battery pack has to be replaced outside the warranty, a new one will cost a cool $22,000.
The next step for Tesla is to produce a second model, a four door coupe designed from scratch but with a similar power system to the Roadstar. Larger production and year by year improvements in battery efficiency and cost will bring the price down to $60,000. Starting in 2011, it plans to make 20,000 a year in a new factory in the San Francisco area.
By then Tesla will be in competition with the new generation electric cars from the major car manufacturers. But right now, says OverDrive (Nov. ’08), Tesla is out there alone with the only pure electric car that is more than an urban runabout. It has beaten the industry giants by nearly two years. |
