The new tuk-tuk has a battery, but uses the sun's rays to supplement the power supply.

BANGKOK, July 2 (AFP) – Prapai Hemsuwan gunned the engine of his emerald green three-wheeler, sending it into a fit of rasping coughs and causing clouds of black smoke to belch into the air.

“Life would be meaningless without the tuk-tuk," he said.

His beloved cart is one of nearly 8,000 auto rickshaws in Bangkok and their spluttering paroxysms – the "tuk-tuk" name came from the sound made by an early model – have become a key feature of city life.

But the brightly colored buggies, most of which run on gasoline or natural gas, are facing increasing competition from more modern and greener modes of transport, raising questions over their future.

A sort of motorbike crossed with a tricycle and a tin can, the open-sided buggy exposes its passengers to blasts of exhaust fumes during a white-knuckle ride down sweltering, traffic-choked streets.

Set against air-conditioned and often cheaper taxis, as well as Bangkok's elevated sky train, the humble tuk-tuk looks like something of a relic.

But the creation of a new solar-powered model could see the three-wheelers accelerate into the 21st century.

The prototype cart is the brainchild of Air Marshal Morakot Charnsomruad, who hopes that his buggy could herald a cleaner, greener era on Bangkok's congestion-choked streets.

"It will help clean up our country – everyone will want to drive it," he told AFP.

Morakot, a former armament and science chief for the Thai Air Force, is already selling electric versions across the world through his Clean Fuel Energy Enterprise.

The new tuk-tuk has a battery, but uses the sun's rays to supplement the power supply.

It is silent, emission-free and can run for 80 kilometres (50 miles) on a three-hour battery charge costing 10 baht, compared with up to 60 kilometres for conventional models before they need refuelling.

Thrill-seekers will also be pleased to note that the solar version can reach speeds of about 60 kilometres per hour, even outstripping its gasoline-powered rival in a test sprint.

And, in a nod to the fact that many of those willing to expose themselves to the heady aroma of Bangkok's roads are Western tourists, the new cart has been designed with more leg room and a higher ceiling.

But while Thailand's climate means there is enough sunlight to keep the tuk-tuks on the road year-round, they have yet to make their commercial debut on Bangkok's streets.

City authorities stopped issuing new tuk-tuk licences in 2008, meaning manufacturers have focused on spare parts and exports.