Friday, January 19, 2007

The Tesla Roadster

Ah, yes, finally an electric car worthwhile. Some E-Com rich geeks decided that the auto companies were too slow in making a good electric car, so they teamed up with Lotus,and a bunch of other manufacturer's (motors, batteries, etc) to make the Tesla Roadster.

The biggest problem with electric cars is not that we can't make good enough motors and motor drives (which we can, as shown below), but the power source. This supercar's solution is to use a huge array of lithium ion batteries (as they have the best performance).

That's the motor that powers it. It produces a huge amount of power (about equivalent to a 300 HP engine).
However, it weights 70 lbs. It's motor drive stage (as you can see in the picture) is a fraction the size of the motor. Something the size of a watermelon can deliver the power of a gigantic truck engine, it just needs a 1000 lb bank of batteries to do it ;) However, if you like lots of "oomf" in your acceleration / starting torque, here's a comparison of standard internal combustion engines to the induction motor:

This means when you hit the pedal, your car lunges immediately. There's no lag in developing the torque, as with standard engines.

None of this is surprising; modern electric motor and electrical generators are about 95% efficient (the loses from converting mechanical to electrical and vice versa are mainly are due to resistance/heat dissipation in the motor windings.)

Comparatively , gas engines are about 20% efficient.

Some argue electrical cars really don't "save power", as the power still comes from the grid, which comes predominantly from coal/oil (although a smaller percentage of the grid is powered by hydro, nuclear, and wind/other.)

However, the makers of the Tesla Roadster argue (which I think they are right), is that the whole electrical car process is still more efficient by a large margin.

Let's see.. the overall efficiency of the "electric car" takes into account the efficiency of the turbine/steam process, generation efficiency, and transmission losses, on the grid end, and then finally, the battery and motor efficiency on the car side of things. This is an uber rough estimate and probably makes a huge amount of assumptions, but what the hell:

Pefficiency= 0.65* 0.95 * 0.97 *0.90 * 0.95 =~ 50%

So, the whole process of the electric car is still 50%, twice that of the gasoline engine's 25% efficiency.

The problem with electric cars, ultimately, is still the battery. Sure, if you only use it for everyday driving and then recharge every night, no problem. What about road trips, though?

The answer lies in an energy storage device that can be very quickly recharged (ie not current battery technologies.) If your "battery" could be recharged in a matter of seconds/minutes, no one would mind, gas takes that long too! :)


At 2:50 PM, Blogger James said...

That's pretty cool. It seems the big money right now would be in efficient storage of energy. If someone found a way to store lots of energy in a much more compact form, they'd be rich beyond their wildest dreams. Unless of course the oil companies found out first and killed the person...not that they'd do anything like that :)


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