Scores of small power stations use fuel cells to consume piped-in hydrogen that generates electricity to feed hospitals, schools and communities.

Power stations that burn coal, oil or gas have been consigned to history.

This utopian vision of the so-called hydrogen economy is as seductive as it is simple, and most of the technologies that would be required are, theoretically, achievable.

A fuel cell consists of two flat electrodes, usually made from platinum-coated carbon, separated by a polymer membrane. Hydrogen gas is presented to one of the electrodes, where it diffuses into the pores of the platinum and splits into an electron and a proton. The proton travels across the polymer membrane to the other electrode, where it combines with oxygen in the air to make water. The electron passes around an external circuit as an electric current, performing useful work, such as driving a motor.

Hydrogen fuel cells are commercially available and many demonstration vehicles have been produced. It is widely acknowledged, however, that the cost of the cells must come down and their efficiency increase if they are to become economic.

Obtaining the vast volumes of hydrogen that would be needed to drive the world's transport systems and feed remote power stations is still a massive challenge. And as the whole concept of a hydrogen economy revolves around reducing pollution, the gas must be made in a way that does not belch yet more carbon into the atmosphere.

At present, most of the world's hydrogen is manufactured for the chemical and oil-refining industries. It is largely made from natural gas by a process called steam reforming. This process releases carbon dioxide, so it does not meet the relevant environmental standards. Hydrogen can also be made from coal, but the problems of using a fossil fuel as feedstock remain.

Perhaps the simplest way to make hydrogen is by passing an electric current through water - the process of electrolysis. The question then is where the electricity comes from. A hydrogen economy would require the electricity to be sustainable and renewable. Nuclear power may be one option, but there is deep public, and hence political, antipathy towards that. It is also expensive and produces radioactive waste.

Many supporters of the idea of a hydrogen economy point to the most mature renewable energy technology, wind power. Britain's Clean Energy Educational Trust runs a website that carries a cogent argument for the use of wind power to provide the electricity to make hydrogen for transport.

The trust envisages offshore wind farms feeding electricity to hydrogen-producing factories.

It calculates that a single wind turbine capable of generating 2MW of electrical energy can produce enough hydrogen to run 18 large buses or 864 cars operating under city-driving conditions.

If you scale this up, a facility of 5000 such turbines sited in shallow waters off the coast of Britain could manufacture enough hydrogen to run 4.32million small- or medium-sized cars. However, in 1998 some 22million cars were licensed in Britain, and the motor industry estimates that by 2020 this number will have grown to more than 30million.

To run this number of cars on hydrogen would require something like 35,000 wind turbines.

Professor Ian Fells, the chairman of the New and Renewable Energy Centre in Blyth, Northumberland, says, 'To make hydrogen for a hydrogen economy there won't be anything like enough renewable energy.' Professor Andrew Oswald, an economist at the University of Warwick, and energy consultant Jim Oswald have examined the energy requirements of a hydrogen economy. They say there are many good reasons to consider switching vehicles from oil to hydrogen to reduce emissions and reliance on imported oil. However, according to Jim Oswald, 'the [immensity] of the green challenge is not understood'.

He has calculated that about 100,000 wind turbines would be required to provide all the hydrogen necessary to run Britain's road vehicles. If these were sited offshore, there would be a 10km-deep strip of turbines encircling the entire coastline of the British Isles. If nuclear power were to be used, 100 new nuclear power stations would be required.

Mike Koefman, secretary of Britain's Campaign for a Hydrogen Economy, disputes Oswald's figures on wind turbines. Koefman says that larger, more efficient 5MW turbines are being developed that would substantially reduce the number required. He believes that, in the longer term, photovoltaic technology will provide the bulk of the energy needed to power a hydrogen economy around the world, with hot, sunny regions such as North Africa exporting energy to northern Europe. 'I do not see why the whole world should not have sufficient renewably generated hydrogen within 50 years,' he says.

Such a scenario, however, would require significant strides in the development of so- called organic photovoltaic systems, which would be cheaper and easier to mass-produce than current solar cells, which rely on semiconductors such as silicon. Most experts accept that organic photovoltaics are at only an embryonic stage of development, however.

British energy consultancy E4tech produced this year a comprehensive review for the Government of how hydrogen could contribute to the country's energy mix. 'There is a kind of fuzzy aura about hydrogen being a generally good thing, but we wanted to ask a more structured question about how the UK should engage with the hydrogen economy to achieve maximum benefit,' says the E4tech director Adam Chase.

'We concluded that using hydrogen in transport could have strong prospects for reducing carbon dioxide, but that it was not an especially good option for stationary power or heat.' The report noted that hydrogen could be usefully made by renewable energy and nuclear power, as well as from biomass, natural gas and coal. Any carbon dioxide produced should be captured and stored. 'We concluded that all these options should be pursued, and that none was likely to provide a solution on its own,' Chase says.

The report calculated that for nuclear power to be used to generate one-fifth of the hydrogen needed for transport in Britain by 2030, a generating capacity of 9GW should be devoted solely to the electrolysis of water. This is equivalent to seven new Sizewell B reactors. 'This is big, but not beyond the realms of possibility,' Chase says. The utopian hydrogen vision remains a distant prospect.

To subscribe or visit go to:  http://www.fuelcellsworks.com

© 1999 - 2005 FuelCellWorks.com All Rights Reserved.