While Tesla's Roadster, right, will continue to sport a composite exterior, the company will use a combination of metals for the skin of its higher-volume Model S sedan. (Dewhurst Photography photo)

But the math has changed for the Model S five passenger sedan, set to debut in late 2011. Tesla will make up to 20,000 sedans annually, compared with 1,500 Roadsters, said Barrie Dickinson, director of body engineering for Tesla, during the Society of Plastics Engineers annual Automotive Composites Conference & Exhibition Sept. 15 and 16 in Troy.

“With higher volumes, we could look at different manufacturing methods,” Dickinson said.

When the Model S goes into production, it will still have extensive plastics in its batteries and other key parts, but the skin will be made of metal, including aluminum blends, he said. The Model S will also be far cheaper than the Roadster, with a base price of about $50,000 compared with $109,000.

Tesla supplier Sotira, part of France’s Sora Group, makes up to 40 sets of Roadster body panels each week using carbon-fiber-epoxy resin-transfer molding. Each part requires a 20-minute cure time, with up to 30 minutes for a hand layup of the carbon fiber.

That process is too long and too expensive for the higher volume sedan, he said.

“It’s not a question of the cost of the [raw material] carbon fiber,” he said. “It’s all about processing and using that material in a way that can reduce the cost at volume.”