Tesla is planning to expand its fledgling range with an all-electric saloon known as the Model S (pictured), which it will launch in 2010. Senior Tesla insiders have revealed to Autocar that the new model’s underpinnings could be the basis for a whole new generation of plug-in cars.This sleek four-door all-electric saloon will be capable of carrying five. It's significantly longer than the Elise-based Roadster that has just gone on sale, and will be built on its own standalone platform, developed by Tesla.>> Read our first drive of the Tesla RoadsterAutocar has already seen sketches of the Model S, which is “90 per cent” finished, according to Tesla bosses. The saloon will be launched in 2010 after Tesla finishes construction of a new factory in California. The company intends to sell up to 20,000 a year, volumes described by a senior manager as “extremely realistic”.Tesla’s relationship with Lotus, which builds the Roadster’s chassis, won’t continue with the Model S because the company wants to make it in volumes that Lotus would struggle to supply. But another, as yet unspecified, major manufacturer will also be involved to supply components for the saloon. Japanese-made lithium-ion batteries that can be recharged from any mains power source will power the Model S - it should be capable of 60mph from rest in under six-seconds. A technology-sharing deal is likely to be brokered and Tesla bosses claim that "a number of" car makers have expressed interest in adopting the powertrain for their compact cars.Unlike the Roadster, which uses carbon fibre extensively to cut weight, the Model S will use aluminium for its body and chassis which, along with economies of scale, will make the car significantly cheaper than the $90k Roadster. Three models are likely to be available; an entry-level $60,000 (£31k) version with a 160-mile range, a $68,000 (£36k) version with a 220-mile range and a 300-mile version in the future. To achieve this, Tesla wants to use a compact lithium-ion battery, which will be mounted flat on the car’s floor. This clever powertrain packaging should allow for a number of larger spin-off models in the future - all based around the same Model S platform. Tesla has plans to launch a large two door electric ‘coupe-saloon’. These plans and substantial investment have enticed leading motor industry figures to join the company. Tesla’s most recent signing is Franz von Holzhausen - the man responsible for the Mazda Furai concept car. He’ll now lead the team that designs all of Tesla’s future products and his first job will be to add the last 10 per cent of finishing touches to the Model S. Then he'll make improvements to the Roadster. The firm also has plans to build a stripped out track version to gain a presence in motorsport.The biggest challenge Tesla faces is the longevity of the lithium-ion battery technology. Tesla concedes that the battery cells in the Roadster will only retain their full efficiency for around five years, and they’re very expensive to replace.But the Japanese companies that supply lithium-ion batteries promise that costs will come down and efficiency will improve as the technology matures.