Hydrogen is a powerful fuel when burnt, yet it only produces water and air emissions, effectively offering pollution-free combustion.
The simplest method of harnessing this power would be a tank of hydrogen carried with the car, powering an adapted internal combustion engine.
This is BMW's vision of the future of hydrogen, but because of the high pressure the fuel is stored at, the car has to be refuelled by a robotic arm.
Most other manufacturers are using fuel cells to harness the environmentally-friendly power of hydrogen.
Fuel cells are effectively batteries, which use a series of plates to trigger a reaction between hydrogen and oxygen, generating electricity, which is then used to power an electric motor instead of an internal combustion engine. The only emissions should be water.
The key problem for manufacturers is how to provide the hydrogen needed in the first place. Any hydrogen-rich material can serve as a possible fuel source, including fossil–fuels, such as methanol, ethanol, natural gas, petroleum distillates, liquid propane and gasified coal.
The hydrogen is produced from these materials by a process known as reforming and is useful where stored hydrogen is not available. But the problem is that this generates other emissions and still relies on fossil fuels.
Hydrogen made from renewable energy resources, such as power plants operated by wind power, provides a clean and abundant energy source, capable of meeting most of the future's high-energy needs.
Furthermore, the water given offcan be electrolyzed (using energy generated from wind power) to make more hydrogen.
In a bid to encourage the development of fuel cells, Chancellor of the Exchequer Gordon Brown has made the fuel exempt from fuel duty 'for the foreseeable future'.