Invented in 1839 by William Grove from Britain, the fuel cell produces electricity through a reaction between hydrogen and oxygen, which leaves water as its only by-product.

Aside from automobiles and other forms of transport, the power source can also be used as a heater, an air-conditioner, to supply hospitals or blocks of flats with electricity and to power portable computers.

But its expensive price tag, bulkiness and the difficulty of transporting and storing hydrogen -- which is very explosive -- preventing most people from using this environmentally-friendly power source, according to a group of experts who met recently in Tokyo for a global conference on gas.

"You are not going to see broad market acceptance of fuel cells before the cost goes down to 1,000 dollars per kilowatt," said Firoz Rasul, chairman of Ballard Power Systems (Canada).

"It will be the end of the decade before you manage to achieve these prices," he told the conference.

Ministries in Japan and a city and university in California were the first in the world to use fuel cell cars, after leasing the vehicles last December from Japanese auto giants Toyota Motor Corp. and Honda Motor Co. Ltd. for 1.2 million yen (10,100 dollars) a month and 800,000 yen respectively.

Toyota's fuel cell hybrid vehicle (FCHV) cost 100 million yen to build, according to Taiyou Kawai, general manager of Toyota's fuel cell research and development department.

"It won't be anytime soon for mass commercialization. It will maybe take us another 10 years," he told AFP last December.

The sleek silver vehicle seats five but can only drive up to 300 kilometres (185 miles) on one tank of hydrogen, with a maximum speed of 155 kilometres per hour.

On top of the technical difficulties, much of the hydrogen used to power the car is extracted from natural gas, which produces carbon dioxide which adds to global warming, according to the specialists.

"When looking at the techniques available today, the economic and environmental benefits of hydrogen power is debatable," said Olivier Appert, president of the French Institute for Petrol (IFP), a public organisation that conducts research into hybocarbons.

One fuel cell car running on hydrogen produced from natural gas emits about three times less carbon dioxide than a gasoline vehicle if one considers the entire fuel cycle, Soji Tange of the Japanese Association of Electronic Vehicles told AFP.

Different Japanese ministries have invested 31.4 billion yen (266.8 million dollars) this year to March 2004 on developing hydrogen power.

US President George W. Bush also announced in his February budget he would spend more than 1.7 billion dollars on it over the next five years.

The European Union launched an environmentally-friendly power project with a bus due to run on hydrogen in ten European towns in cooperation with German-US auto giant DaimlerChrysler.

But the fuel cells "are not at a stage where their successful uptake is guaranteed, and many competing technologies could be deployed in their place," concluded David Hart, the head of fuel cell and hydrogen research at the Imperial College's Centre for Energy Policy and Technology in Britain.

France's CEA is more optimistic. It predicts fleets of buses will run on hydrogen by 2008, fuel cells will power buildings by 2010 and between 2010 and 2020 the energy-source will filter through to the mainstream car market.

SPACE.WIRE