By Rowland Benjamin

HEVs use electric motors in concert with other energy sources. In December 1997, Toyota introduced the Prius. This HEV uses a small petrol engine in conjunction with two electric motors. Honda introduced the Insight, Civic and Accord Hybrids, and Ford introduced the four-wheel drive Escape. The past few years have seen enormous advances in hybrid vehicle technology, and car manufacturers are responding to growing consumer demand. Each new model tends to be more efficient than its predecessor.

The well-established earlier models such as the Toyota Prius and Honda Insight continue to evolve and thrive. Lexus has recently introduced two luxury hybrid models, an indication that the technology has penetrated every level of the market.

HEV's are less costly to run and more efficient than petrol driven cars. Electric power reduces the load on the engine so they can go twice as far on a litre of petrol as conventional vehicles and they produce 50 percent less carbon dioxide pollution.

The electric motor recharges as you drive. Energy produced during braking and in downhill runs is also used to generate electricity and recharge the batteries. The large high-voltage battery of hybrid cars can also be used to heat up anti-pollution devices, such as catalytic converters - which are less efficient when the engine is cold - thus reducing pollution when the car is starting up.

Eventually, car manufacturers may replace the petrol engine with hydrogen fuel cell technology. Until this technology becomes available however, the hybrid petrol-electric cars will be a useful compromise. An added benefit is that these cars can be refuelled at any petrol station.

Advantages of HEV's

• Hybrid vehicles have a smaller more efficient engine and therefore are cheaper to run than petrol cars. They achieve better mileage on a tank of petrol
• Due to their more efficient engines, hybrid vehicles are less reliant on fuel, which means fewer emissions will be released into the environment

Disadvantages of HEV's

• As with all new technology, the hybrids are relatively expensive
• Batteries are heavy, expensive, have a short life span and are an environmental hazard

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