Detroit  - US carmaker Fisker plans to offer a four-seat drophead version of the ground-breaking Karma hybrid, the company announced at the Detroit car show which lasts until January 25.

The Karma Sunset cabriolet on the firm's show stand shares the petrol-electric drivetrain with the closed model, but is slightly shorter. It features an electrically-powered roof which retracts into a compartment behind the seats. The car is due to go into production in 2011, Danish-born former BMW and Aston Martin designer Henrik Fisker told journalists.

Like the four-door sports saloon version, the Karma S features a 256 horsepower, four-cylinder petrol engine driving a generator which charges the batteries. These power twin 198 horsepower electric motors which drive the rear wheels. The combustion engine only kicks in when the power from the lithium ion battery pack is spent and it never drives the car directly.

Fisker says the configuration allows consumers to drive the car emission-free for up to 75 kilometres miles a day provided the car is charged every evening.

The twin electric motor system provides an overall 400 horsepower and can propel the Karma to 100 km/h mph in less than six seconds. Top speed is given as 200 km/h. Fisker said the company has already taken orders for 1,300 off the Fisker saloon version. (dpa)