Who says big, luxury 4x4s can't be as economical and clean as a family saloon? Certainly not BMW. At next week's Geneva Motor Show the German giant will unveil its advanced new, X5-based concept car. The X5 Vision Efficient Dynamics manages 45.3mpg and produces 172g/km of CO2 10mpg more and 42g/km less than the most frugal X5 on sale today. But don't be fooled into thinking this is just a headline-grabbing concept. The X5 Vision uses a new hybrid powertrain that BMW is in the process of testing, and will introduce in future models such as the Progressive Activity Sedan and X6. A departure from the full hybrid system unveiled on the X6 Active Hybrid at last year's Frankfurt motor show, it uses a diesel engine supplemented by an electric motor. In fact, rumours have it that a production version may arrive sooner rather than later. "This is no pie in the sky project," Klaus Draeger, head of development at BMW, said. "All of the features are production feasible. If reaction is positive we could easily and without too much delay apply the technology featured on our latest concept to existing showroom models." The concept is powered by the twin-turbo 2.0-litre four-cylinder diesel, as seen in the 123d. It kicks out an impressive 201bhp or just over 100bhp per litre along with a solid 295lb ft at 2000rpm, giving a 0-62mph time of 8.9sec. Backing it up is an electric motor mounted within the gearbox housing developing 15kW and a maximum 210Nm of torque. It is propelled by electricity produced by the generator on a trailing throttle and under braking, stored in a lithium-ion battery pack mounted at the rear. Channelling drive permanently to all four wheels is an eight-speed automatic box incorporating the generator and management system for the electric motor. The unit will be used in the new 7-series due in September, providing a broader spread of ratios and promising greater response. The X5 Concept also utilises BMW's stop/start function, as is already offered on the 1-series. When the engine is turned off, the battery pack provides power for the air conditioning and other systems reliant on electricity. In addition to the advanced drivetrain, BMW has further modified the X5 to boost efficiency. In addition to the conventional 12 volt electrical system, there is also a 120 volt arrangement supporting electricity from one of two lithium-ion battery packs to various components, including the EDC (electronic damper control) system. And how about this? On the roof is a metre square solar panel that acts as an additional electrical source (let's just hope it's able to filter out as much sunshine as we get in Scotland). It enables pre-heating of the oil, while providing a source of power for the air conditioning, cool box, entertainment and other systems when the car is stationary. The standard wheels have also been swapped for futuristic-looking alloys developed in BMW's windtunnel. Their shape is claimed to play an important part in reducing fuel consumption by requiring one kilowatt less propulsion power at a speed of 100mph.