Car plant

Low-carbon motoring usually conjures ideas of energy-efficient engines, alternative fuels or even the varieties of electric cars whose development has been closely followed by the media (especially The Engineer).

But although the powertrain forms a large part of the car's carbon footprint, it is not the whole story. The embodied energy in the vehicle — the energy, and associated carbon, that goes into making the car and its component materials —is also a small, but significant, proportion.

The estimates of embodied energy vary. Honda says building a car emits 810kg of carbon dioxide; the UK Society of Motor Manufacturers and Traders says it is 600kg. A recent study by Volkswagen estimated that almost a third of a car's carbon footprint comes from its manufacture. These figures do not include the energy or carbon needed to make the steel or the electricity used in the factory. However, this is dwarfed by the emissions from running the car.

Mark Ellis of the Nissan Technology Centre Europe, Cranfield, says his company has tried to estimate where the energy is used across a car's lifetime.

For a Micra doing 200,000km during its lifetime, manufacture of the car and spares, and servicing accounts for about 9 per cent of the total energy profile. Raw materials production accounts for 6 per cent, and the remaining 85 per cent comes from the road operation. 'The area we can most influence ourselves is reducing the energy use in manufacture and materials selection, so we're focusing on that quite strongly,' he said.

Nissan is not alone. Finding new, lower-energy materials is a target of research projects across industry and academia, and some striking results have now started to appear.

At the Warwick Manufacturing Group, Ben Wood recently led a project to produce an 'eco-racing car', made as far as possible from natural materials. Starting with a steel tubular spaceframe, his team added side body panels made from a composite of hemp matting impregnated with a resin based on rapeseed oil. The Cornwall-based boatbuilder Ecocats provided the main body panels, made from a resin based on cashew nut shell oil.

The tyres contained a cornstarch derivative rather than an oil-based filler, while the brakepads contained jute rather than aramid pulp. The oils and lubricants were based on plant oil esters, and were 95 per cent biodegradable after 28 days.

Fuelled with a blend of 15 per cent unleaded petrol with 85 per cent bioethanol, the Eco One car has a higher power-to-weight ratio than a Ferrari Enzo, can do 0-60mph in four seconds, and has a maximum speed of about 150mph.

Wood's goal was to prove that cars built from, and fuelled with, plant-based products need not be slow and lumbering. 'My goal is to make a race car that's 95 per cent biodegradable or recyclable,' he said.

While the Eco One is a research project, sacrificing looks for performance, its ideas have been taken up in a slicker way by Lotus. Now on show at the British International Motor Show's green motoring pavilion is what looks like a standard model of the Elise — until you look closer.

Instead of the usual leather-clad interior the seats, door panels and gear stick are swathed in tweedy-looking wool and the carpets are made from sisal, a variety of hemp long used to make durable matting.

Other materials are also derived from nature. The body panels, like those of Eco One, are a composite reinforced by hemp, rather than glass fibre. 'That was a great way of reducing the carbon footprint of the car, because the hemp is grown locally, which cuts down on transportation and, of course, hemp fixes CO₂ as it grows,' said Lee Preston, environmental manager at Group Lotus. 'And it's also lighter than glass fibre.'

That helped with the goal of creating a car lighter than a standard Elise, even though it incorporated more technology.