The long-awaited Mercedes S400 hybrid has finally been officially unveiled, and the results are somewhat surprising. While the S400 BlueHYBRID is still billed as the first series-production car to market with a purpose-built lithium-ion battery, it's not as impressive a hybrid system as may have been anticipated.

Due for launch in Europe in June of 2009 followed by China in August and the U.S. in September, the S400 BlueHYBRID hasn't yet been priced, but can be expected to command a premium over the S350, which starts at $198,810 before taxes and fees. It should slot in below the S500, however, perhaps splitting the difference for a final price around $235,000.

The petrol-hybrid drivetrain
By combining a 205kW 3.5-litre V6 engine and a 15kW electric motor, the S400 BlueHYBRID is what most would call a 'mild' hybrid. That's enough to get fuel consumption down to 7.9L/100km with emissions of 190g/km CO2 - lower than the S350 it's based on, but still not in a league with 'full' hybrids or even some diesels. Nevertheless, it's a good result for a full-size luxury sedan, and a 21 % improvement over the standard S350.

The lithium-ion batteries contribute enough energy to push the car's model number up from its natural displacement of 3.5-litres (as in the S350) to the equivalent of a 4.0-litre engine. Equipped with the 7G-Tronic seven-speed automatic transmission with special adjustments for the hybrid model, the car is also capable of the 0-100km/h dash in 7.2 seconds. Top speed is electronically limited to 250km/h.

Improved efficiency, but also improved performance
Fuel efficiency gains are made through a combination of technologies, including stop-start functionality, which helps to cut fuel use while standing still at traffic lights or jams. But improved efficiency isn't the only effect the hybrid system has - it can also boost performance for brief periods.

By kicking in the electric motor's full 160Nm of torque as the fuel-intensive acceleration phase kicks in, it speeds take-off while minimizing fuel use. Regenerative braking helps to maximize efficiency and recapture energy that would otherwise be lost. All of the operations of the hybrid system are displayed for the driver's convenience in a single display in the instrument cluster.

Efficiency isn’t the name of the game, however
At the very least the S400 can be expected to deliver the same level of performance as its S350 basis while exhibiting significantly improved efficiency in normal driving. Even at a 21% efficiency gain over the standard model, which sports an efficiency rating of 10.2L/100km, the money saved in fuel expenditures will not amount to much, however. At an average fuel price of $1.50/L, the S400 Hybrid will save about $517 over the course of an average driver’s 15,000km yearly total. That means at an estimated premium of about $35,000, it would take 67.6 years to recoup the investment.

It’s clear that the S400 Hybrid won’t be purchased for financial reasons - after all, a Toyota Prius, Honda Civic Hybrid, or any number of small diesel hatchbacks would make more financial sense, in both the near and long terms. It will, however, allow a buyer already in the market for a high-end luxury sedan to make a statement and to minimise their impact on the environment, at least in comparison to their nearest alternative.

Mercedes-Benz S400 BlueHYBRID Official photo gallery

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