Engineers are said to be applying knowledge gained from the Alpha to enhance performance, tune suspension, quieten the interior and optimise efficiency of the Beta.
Announced in 2008, the first deliveries of the S-model are expected in 2012 and it is believed Tesla has close to 5,000 customers who have put down a $5,000 (£3,068) reservation for the $49,900 (£30,615) base car.
The S-model powertrain features a liquid-cooled, floor-mounted battery pack and single-speed gearbox. It can reach a top speed of 120mph accelerating from 0–60mph in 5.6 seconds.
There are three battery options offered with a 160-, 230-, or 300-mile range — although the latter comes as a premium optional extra at $20,000 (£12,271).
Based on testing, Tesla expects the battery to retain approximately 70 per cent of its initial capacity after seven years or 100,000 miles.