One press of the chrome-ringed ‘start’ button and… nothing. Just silence. But, step on the accelerator of the ground-breaking Limo-Green XJ and 400Nm of torque powers the car forward with the thrust you’d expect from a luxury sports saloon.

Foot to the floor, the virtual speedometer will sweep past 60mph in seven seconds, all the way to 112mph. At 50mph – on battery-power – the Limo-Green XJ will waft along in silence for 30 miles. The amount of fuel used, the amount of CO2 emitted? Zero. And when the battery gets low, or you want to cruise for long distances at motorway speeds, an ultra-compact 1.2-litre three-cylinder engine cuts in to generate electricity.

Welcome to the wonderful world of Jaguar Limo-Green. “It’s a path to the future,” says Tony Harper, head of Jaguar Land Rover Research & Advanced System Engineering. “It shows how Jaguar could deliver a luxury sports saloon, with great performance and refinement, and a breakthrough reduction in CO2.”

The way that the Limo-Green XJ works is pure genius. Unlike hybrids that run an engine and electric power in parallel, there’s no connection between the Limo-Green XJ’s engine and the wheels at all.

Instead, a state-of-the-art lithium ion phosphate battery provides power for a 145kW (194hp) drive motor with 400Nm (295lb-ft) of torque. This brushless, three-phase 8000rpm unit powers the rear differential through a two-speed automatic transmission. The engine is only used when it’s needed to generate electricity. In essence, it’s a ‘range-extender’.

The all-aluminium engine – designed and developed by Lotus Engineering – is a compact monoblock, which weighs just 56kg. It runs on petrol or bio-fuels such as ethanol. And, when it’s running at an optimally fuel-efficient 3500rpm, it pumps 35kW through a high-speed generator – 28kW of which goes to the motor, with the other 7kW charging the battery.

“This ‘series’ hybrid drivetrain fits nicely into the space occupied by conventional transmission,” explains Nigel Taylor, technical specialist, Jaguar Low-Carbon Vehicles. “This means 50:50 weight distribution. And, with the range extender engine running, we’re looking at CO2 emissions of under 120g/km.”

The third element of the Limo-Green XJ’s versatility is its ‘plug-in’ capability. Around 80 per cent of car journeys are less than 30 miles, so the Limo-Green XJ could cover the daily commute on battery power alone, without a drop of petrol used. Plug it in at night, and it would be ready the next morning.

The range-extender engine counters ‘range anxiety’ – the natural concern that batteries could expire, leaving the owner stranded. But it also turns the Limo-Green XJ into a refined, responsive long-distance cruiser. The car’s ‘sweet spot’ is motorway speeds, and it can have an impressive range. “For this prototype, we’ve kept the larger, standard XJ fuel tank,” says Steve. “That gives a range of 1200 miles.” At an average of 57mpg.

The most important ingredient in Limo-Green is the XJ’s lightweight, all-aluminium body structure, which allows it to still deliver the kind of performance expected of a Jaguar on battery power. Other weight-saving components include a composite rear sub-frame from Caparo Vehicle Technologies, composite brake rotors with aluminium calipers and composite front and rear seat shells. The Limo-Green XJ comes in 100kg lighter than a standard XJ, with more weight-saving still to come.

The biggest challenge facing Limo-Green is the high cost of key components, such as lithium ion battery packs, high-performance electric motors and complex electronics. “Right now, it’s a development exercise,” says Phil Hodgkinson, director of Jaguar Land Rover Product Development. “But what Limo-Green clearly demonstrates is that introducing green technologies to dramatically reduce CO2 emissions can be achieved. It’s a perfect picture of what an environmentally responsible premium car of the future should look like.” It certainly feels like a premium car of the future. In electric mode, only the faint rumble of the tyres breaks the silence. When the range extender cuts in, only a slight engine note can be heard. “With a few tweaks, noise levels should reduce by 20 decibels,” says project manager Steve Nicholls. “The only way you’ll know the range-extender has cut in is when a dashboard light comes on.

“When it comes to Limo-Green, we think silence is golden. And green.”

You need Flash Player 9 for the best website experience