LONDON, England - The auto industry has experimented with hydrogen power for decades as a source of automotive energy. The main attraction is the zero-emissions potential when the gas is burned in fuel cells.Water vapour issuing from the exhaust pipe is the sole sign of activity inside the cells as they quietly convert chemical energy into electricity.The power drives electric motors, often mounted on wheel hubs, to provide motion. PIPE-DREAM TO PIPELINEHydrogen propulsion has the edge over battery solutions and in the end it may outlive battery vehicles.The technology has so far found its way into some expensive buses and forklift trucks but no hydrogen-powered car has gone on sale despite the collective efforts of Honda, Mercedes-Benz, BMW and Opel.Automakers have been tinkering with the technology for years and numerous vehicles have been churned out. In 2013 they're jostling for position, forging alliances and re-aligning their strategies to produce green-friendly vehicles.Daimler plans to work with Ford and Nissan to produce a commercially-viable fuel-cell, with production slated for 2017. BMW and Toyota have announced a tie-up for hydrogen vehicles, with 2020 as a proposed market entry date.TOYOTA AND HYDROGENToyota has been limbering up for some time to put a hydrogen-powered car into commercial production. The debut has been set for 2015.Toyota sees the hydrogen fuel-cell car as the future of vehicles and believes they go beyond petrol-electric hybrids such as the automaker's Prius. The first 10 000 Toyota fuel-cell cars will be based on the FCR-V concept shown at the 2012 Geneva auto show. The car is likely to cost the equivalent of R1.2-million and most technical details are still under wraps.Hydrogen is generally stored in tanks as a liquid cooled to -273 degrees Celsius or as a highly compressed gas.Toyota spokesman Dirk Breuer said: “Deep-freezing the hydrogen uses up too much energy. Using a pressure of 700 bar, the lifetime of the fuel is comparable with that of conventional fuels and none of the hydrogen escapes.Toyota has been working on related projects since 1991.INTERIM SKIPPEDIn 2011 Mercedes-Benz sent its B-Class F-Cell car on a trip around the world. The car has been produced in small numbers since 2009. The automaker says that 2017 is a realistic mass-production date.Daimler research chief Thomas Weber said: “We've skipped the interim phase. We believe 2017 is the window of opportunity which will allow us to achieve a reasonable sales volume.”Honda is leasing hydrogen-fuelled cars, though only in the USA and Japan. In 2008 the automaker hailed the FCX Clarity as the world's first fuel-cell car. Now Nissan is planning to team up with Daimler, the company which makes Mercedes-Benz badged cars, to make a fuel-cell SUV based on the Terra concept.THE DOWNSIDEThe downside with hydrogen is that it does not occur naturally in the form needed for fuel and producing it devours a lot of energy. Honda said: “Most hydrogen is currently produced from natural gas.”Hydrogen made this way is not as green as it might seem. Fortunately, hydrogen can also be produced from water, although to ensure green credentials regenerative electricity must be harnessed.VW is putting a fleet of Tiguans through its paces in the USA and Germany, although the hydrogen Tiguan HyMotion is unlikely to hit showrooms before 2025 - partly because of the lack of a hydrogen refuelling infrastructure, something which will hold back the introduction of such cars in Europe.The Clean Energy Partnership, an umbrella organisation of energy, oil and car companies, plans to boost the number of refuelling stations in Germany to 50 by 2015.