Frankfurt - Carmakers around the world are trying to come up with a workable hydrogen fuel source which will help solve one of the major problems facing electrically-driven cars, namely the limited range they offer.

Lithium-ion batteries are the power pack of choice but these tend to run down quickly, with the result that most electric cars cannot travel for long distances between recharges. A hydrogen-powered car using a fuel cell to convert chemical into electrical energy is seen as a viable alternative.

Germany's Daimler has put its faith in the new technology and the company has successfully operated a fleet of hydrogen fuel-cell-driven buses in Hamburg for the past three years. From 2015 it intends to team up with other concerns such as Shell or gas manufacturer Linde to set up a countrywide network of hydrogen refuelling stations.

Automotive researchers admit that the road to a hydrogen-powered future is not without obstacles. The production and storage of the ethereal gas can cause headaches, said Ulrich Hoepfner of the Institute for Energy and Environmental Research in Heidelberg. Hydrogen must first of all be obtained from water using a process of electrolysis which consumes large quantities of energy.

The hydrogen enters the fuel cell which operates very much like a battery, producing electricity directly from the electrochemical reaction between the hydrogen and oxygen in the air. This energy needs to be stored in batteries and the transfer leads to a larger loss of electricity than if a battery was charged up by being simply plugged into the mains electricity supply. "You have to use up three times as much energy," said Hoepfner.

If the energy used to make hydrogen comes from a conventional coal-fired power station the advantage of using the futuristic fuel are quickly cancelled out. The car industry is aware of the problems but solutions are at hand.

"Looked at from today's point of view hydrogen has the potential to replace fossil fuels such as petrol and diesel," said the German Automobile Federation in a brochure at the recent Frankfurt IAA car show. At the same time, producing hydrogen only makes sense if this can be done with regenerative energy sources.

Storage is another bugbear. Hydrogen is a very volatile substance which is easily dispersed. "Hydrogen seeps out everywhere," said Hoepfner. It has to be kept under high pressure or in liquid form. In order to liquidise hydrogen it must be cooled to minus 250 degrees celsius. This devours energy and large tanks are need to store the hydrogen.

"The whole storage issue is tricky," said Maximilian Prager who carries out research into combustion engines at the technical university in Munich. The necessary equipment uses a lot of energy too since it has to neutralise the considerable temperature variations. Pressure storage is cheaper. Prager played down the potential security risks of tanks containing the highly-combustible substance: "My personal view is that hydrogen is no more dangerous than petrol, since it dissipates very quickly."

The fuel cell method favoured by Daimler, by which hydrogen reacts with oxygen, does not represent the last word on the subject. Rivals BMW in Munich have pinned their hopes on burning hydrogen in a conventional combustion engine and have been experimenting with the technology for two decades.

"Hydrogen-power can be realised more quickly using a conventional engine which has the advantage of being able to operate even with mildly contaminated hydrogen," said Prager. Such engines have also been shown to cope better with power peaks such as periods of hard acceleration on the motorway. (dpa)