PayPal founder Elon Musk is the CEO of Tesla Motors.  Recently he unveiled the Model S 4 door all-electric sedan shown above to much fanfare.  The car exists only as a prototype but the company hopes to mass produce it if it can obtain a $350 million dollar government loan to build the assembly plant.

Tesla has already been producing the 2-seat electric Roadster and has plans to eventually build inexpensive electric cars and partner with automakers.  GM vice chairman Bob Lutz has even credited the company with inspiring him to develop the Volt.

But one thing that stands out is Tesla has no plans to build an extended range electric car like the Volt.

I had the chance to ask Elon Musk why.

What is your feelings about the range-extender concept of the Chevy Volt and why have you not considered it it any of your products?
We looked closely at a range extender architecture for Model S. It ends up costing about the same in vehicle unit cost, a lot more in R&D and a lot more in servicing. Also, although performance is ok when both battery and engine are active at the same time, it turns really bad when the battery runs out and an undersized engine is carrying all the dead weight of the pack. Essentially, a REV is neither fish nor fowl and ends up being worse (in our opinion) than either a gasoline or pure electric vehicle.

An important consideration that people without a technical background don't understand is that you can either have a high power or a high energy cell chemistry, but not both. Since the battery pack in a plug in hybrid like the Volt has to generate the same *power* as a much larger battery pack in a pure electric vehicle, it has to use a low energy cell chemistry.

That means a 40 mile REV pack is not 1/5 the size of a 200 mile pure EV pack, as simple proportionality would suggest. Another factor is that the REV pack is forced to do three to four times more cycles that a pure EV pack and is (obviously) hit with five times the current per cell during acceleration and regen braking, which forces the REV pack to be derated considerably.

The net result is that a 40 mile REV pack is roughly half the size of a 200 mile EV pack. On top of that, you have to add the engine, generator and all the interconnects between engine and battery. It ends up having about the same mass and worse packing efficiency than a pure EV, plus you still have to deal with all the environmental issues of a gasoline engine.