Yesterday, Tesla Motors, based in San Marcos, CA, unveiled its Model S sedan, a car that the company has been promising for years. The biggest change compared to the company’s Roadster sports car, other than the appearance and price (the base price is half that of the Roadster), is the location of the battery. In the Roadster, it’s difficult to reach, packed in tightly behind the driver. The Model S battery is mounted to the floor of the car so that it can easily be dropped out of the car and swapped for another battery. It sounds as though Tesla is preparing itself for the Better Place model, where a network of battery-swap stations makes possible long-distance travel between cities without the need to stop for hours to recharge. (Tesla claims a 45-minute recharge for the Model S, but that’s not with a standard 120-volt outlet.)

The Model S will cost about $57,400, but then you can get a $7,500 tax credit from the government to offset some of that. But that’s just the base price. Tesla will be offering three different battery-pack sizes. They’ll have a range per charge of 160, 230, or 300 miles. The battery pack is probably the most expensive part of the car, so the 300-mile pack could make the car many thousands of dollars more expensive than the base price.

Offering three pack sizes could prove an interesting experiment. Some auto experts have said that people won’t buy electric vehicles on a large scale because their range is less than that of gas-powered cars, which typically have a range per tank of over 300 miles. If Tesla has success with its 160-mile pack, it would help prove these experts wrong.

I saw the Model S electric motor on a visit to Tesla headquarters: it’s larger and designed to deliver more power than the Roadster motor. But the bigger, heavier car won’t accelerate quite as fast: it will take almost 6 seconds to reach 60 miles per hour, compared to the 3.9 seconds in the sports car. A sporty version of the Model S will accelerate to 60 miles per hour in about 5 seconds. (View a video of me testing the Tesla Roadster.)

It will also be networked: “A 17-inch touchscreen with in-car 3G connectivity allows passengers to listen to Pandora Radio or consult Google Maps, or check their state of charge remotely from their iPhone or laptop.” I wonder how many more miles of range you can get by turning that big screen off.

The actual production of the Model S depends on Tesla getting a $350 million loan from the government.