Smart has just released details about a couple of hybrid variants of its new Fortwo minicar, with the ultra-efficient offerings coming in three different flavors including one of the industry’s first diesel-hybrid drivetrains. It's likely these designs will eventually lead to new production versions of the Fortwo, but so far only an engine stop-start equipped model has been confirmed for sale.

First up is the zero-emission Smart Fortwo electric vehicle. Sporting a 30kW electric motor located in the rear of the car, and a high-performance sodium-nickel-chloride battery housed in its underbody, the all-electric Smart can travel up to 115km on a single charge and can be topped up at any 230volt power socket. Consuming just 12kw-hours per 100km, the average cost of running the car is €0.02 per km and it takes just 5.7 seconds to accelerate from rest to a reasonable driving pace of 60km/h.

Next is the Smart fortwo hybrid drive, which combines an electric motor with either a petrol or diesel internal combustion engine. The system can run its 33kw combustion engine and 20kw electric motor in synch or independently, which means during low load conditions, such as during heavy traffic, the hybrid Smart offers zero-emission driving. When combined with the 0.8L diesel mill, the vehicle reduces fuel consumption by around 12% over the standard model, ending up with a final economy figure of just 2.9L per 100km. Click ahead to read the rest of the details.

The all important carbon-dioxide emissions rating drops to a low 77g per km, which means the Smart fortwo diesel hybrid would be one of the most fuel-efficient and climate-friendly diesel cars on the road if it entered production.

Rounding out the trio of ultra-efficient Smart cars is the new Fortwo micro hybrid drive, which comes equipped with an engine stop-start function for its 52kw 1.0L petrol motor. Due to go on sale towards the end of the year, the micro-hybrid variant will feature the Fortwo’s current automated manual transmission and should achieve a fuel consumption figure of 4.3L per 100km.

The system works by using a belt-driven starter generator to power the car’s electrical systems and also works as the engine starter motor. It is able to smoothly start up the combustion engine in a fraction of a second as soon as the driver releases the brake pedal. This dispenses with the need for a conventional starter motor that works on the flywheel of the crank assembly.