Power surge

Hybrid vehicles are now a common sight on our roads and everyone is familiar with their claims of greater efficiency and fuel economy — hence lower carbon emissions — than conventional internal combustion engine vehicles.

But car manufacturers are developing a new range of vehicles which, they believe, could top even the hybrids' performance. In the UK, the Technology Strategy Board (TSB) is investing heavily in a range of projects to accelerate the development of these Range-Extended Electric Vehicles (REEVs).

REEVs, also known as plug-in hybrid electric vehicles (PHEVs) are, as the name suggests, essentially electric cars. Yet they are also a type of hybrid. The vehicle's drive system is fully electric —that is, an electric motor drives the car 100 per cent of the time. The motor is powered by banks of batteries that can be charged overnight in a domestic power supply. A four to six-hour charging period would provide sufficient power for a small, set number of miles, generally targeted at between 20 and 60.

After this power is exhausted, a small onboard generator switches on to recharge the batteries to extend the range of the vehicle. This generator could use a wide range of technologies. If it is a petrol or diesel engine, the car is essentially a hybrid, although unlike current models such as the Toyota Prius the vehicle is never driven by the internal combustion engine. The generator could also be a fuel cell.

The cars generally also include regenerative braking systems to conserve power and return charge to the batteries when the vehicle brakes, which also improves the range. A single load of fuel is generally targeted at taking the vehicle about 300 miles.

REEVs are potentially lower-emission vehicles than standard hybrids. In operation, the electric phase produces no emissions (although this does not take account of any carbon emissions associated with generating electricity used to charge the batteries). And because the electric motors drive the car all the time, the generator only has to keep the batteries charged — it does not have to produce the variable power load needed to drive a car over different terrains, for example.