General Motors says its global project for fuel cell technology has accumulated more than 2m km in road testing.

The automaker has a fleet of more than 100 HydroGen4 cars operating in real driving conditions around the world - although mostly in the US - with the Berlin 'Lighthouse' project the largest of its kind in Europe and funded by the German government.

Part of those 'real' conditions has seen GM place some Hydrogen4 vehicles with German roadside assistance service ADAC among others.

In addition, working through the Clean Energy Partnership (CEP) GM cooperates with several gas and oil companies as well as with other OEMs to establish how fuel cell technology could work in practice.

Part of that evaluation has seen GM research its fuel cell technology in harsh winter conditions and the automaker says it is pleased with drivers' reports.

"The [HydroGen4] car can start at -25C and we will improve this capability with the next generation," GM manager fuel cell hydrogen deployment strategy Europe Lars Peter Thiesen told just-auto at the development centre in Mainz.

"We had these cars running in Berlin for the last very cold two winters - our competitors had theirs in warm garages."

GM is participating in the CEP with several other OEMs and energy companies, with centres including Hamburg and the country's most populated state of North-Rhine-Westphalia. Hesse is due to be added next year.

Liaison with dealers is also key, says GM, as it looks to bring its retailers up to speed with the new technology.

One area where GM believes there could be further progress is how hydrogen could operate alongside existing fuel dispensing services.

"There needs to be something done about making fuel stations more reliable," said Thiesen.

GM envisages a need for 400 H2 stations to fuel 10,000 hydrogen cars, with these based at existing petrol outlets.

Should demand develop and 10m H2 cars be on the market, 13,000-20,000 hydrogen stations would be needed, added the automaker.

GM has speculated commercialisation could start in 2015.