Hydrogen is being touted as an environmentally friendly fuel of the future, but the road to hydrogen-powered vehicles will not be easy, industry experts have been quoted as saying during a US convention.

Representatives of European and US auto and energy companies at the National Hydrogen Association convention in San Antonio, Texas, told Reuters hydrogen technology is feasible, but faces big challenges to become commercially viable.

"We all have our homework to do in the coming years," Klaus Bonhof, manager of the alternative fuels division of DaimlerChrysler, told the news agency. "We must produce technology viable in volume, and that technology must be commercially applicable."

The report said BMW, Toyota, Honda, GM, DaimlerChrysler and Volkswagen had hydrogen-powered vehicles on display at the conference, but all have similar technological challenges, including costs that range up to a million dollars each and limited range on a hydrogen fill-up.

A hydrogen car can travel 45 to 50 miles (72 to 80 km) on a gallon, but a normal-sized fuel tank will only provide a range of 125 to 150 miles (200-240 km), experts told Reuters.

That's because hydrogen is put in a car as a liquid at very low temperatures, but reverts to being a gas as it warms. It dissipates into the air even if the vehicle is not being used.

"You have boil off, you are ventilating hydrogen," BMW vice president of clean technology Frank Ochmann told the news agency.

"After a certain time, after a week, say, the tank will be empty. This is a certain headache that we still have, but we're working on this."

Ochmann reportedly said BMW is testing an insulated tank that would keep hydrogen cold and liquid.

"If you put in this tank a snowman, it would take about thirteen years to melt down," he told Reuters.

Developing refuelling station-like facilities should be the easy part, experts told the news agency. Hydrogen is already shipped to industrial users in tanks or moved through pipelines, so logistics for distribution already exist.

Ochmann told Reuters BMW estimates it will be 2025 before hydrogen powered vehicles are commonly produced and sold.