Mercedes' push towards a more eco-friendly range of cars is in full swing, as is shown by these spy shots of the new S400 testing in Germany. The S400 is a hybrid model that will mate a 279bhp petrol V6 to an electric engine delivering 20bhp. Official figures for the Frankfurt concept car put the combined output at 299bhp, and 277lb ft of torque.More importantly, the addition of an electric engine brings emissions down to 190g/km, with an average consumption of 32.8mpg. Performance is still good; 0-60mph is done is 7.3sec and top speed is a limited 155mph, so this will be a true competitor for the established Lexus hybrids. The electric motor in the S400 is used to boost the car's acceleration whilst preventing excessive fuel use, and also acts as a starter motor and alternator. It doesn't power the car entirely at low speeds, as with the new ML450 and Lexus systems.The 'compact hybrid module' featured in the S-Class will also feature an automatic start-stop system. Very similar to BMW's 'efficient dynamics' technology, but the Merc has the electric motor to start the V6, allowing for smoother, less noticeable engine rattle upon start up. Regenerative energy is also used (as with the BMW system) whereby power generated by friction from braking is stored and then used to run the ancillaries in the car when the engine is off.Expect the ML450 hybrid to be the first Mercedes hybrid on sale in the UK, with the S400 due to hit the showrooms in mid-2009.