Naturally I was excited. I knew, in a theoretical sort of way, what it was all about. Hydrogen can power a special fuel cell through a chemical reaction that creates electricity, and that means much more efficient energy-use and zero emissions.
The fuel cell is a different means of motive power to the traditional internal combustion engine, conventional electric cars or the "hybrid" combinations that you'll find in the current Toyota Prius, Honda Civic IMA and one or two others. I also knew that nothing but water is supposed to come out of the exhaust. I was, however, unprepared for the sight of Debbie Hull, Mercedes's press officer, taking a few droplets from the A-Class's exhaust and drinking them.
Fond as I am of green technologies, this was a step too far for your intrepid correspondent. I confined myself to a quick run round the block in the A-Class.
Apart from some decals on the side it is pretty much standard. There are differences; the noise the car makes is much more droney, there is a dashboard display showing you what's happening under the bonnet, and the rear floor and seats are placed slightly higher than normal to accommodate big hydrogen tanks and the battery.
The car provided a normal-ish driving experience. Like other electric vehicles, it has good low-speed pick-up, with plenty of torque, so it's fine for town driving but the flat-out top speed is lower than its conventional siblings. It is heavier than the standard car, which doesn't help and, as is sometimes forgotten, it requires energy to create the hydrogen and transport it to a filling station. How that energy is produced - by fossil fuels or nuclear power or renewables - affects the overall greeness of such a car to a degree, but this technology will always be more efficient than the internal combustion engine.
It's not perfect. The range is only 93 miles, which would prove a bit of a drag in normal use, but the wonder of it, like a talking dog, is not that the thing it does it does badly, but that it exists at all. I knew Honda had been trialling fuel-cell cars in the US and Japan, but not that Mercedes had been doing much the same thing closer to home, with a small fleet in Berlin testing the F-Cell A-Class in everyday use. There are also parallel trials in Singapore, Japan and the US.
The Mercedes boffins tell me that a production version of the F-Cell is eight to 10 years away. Given that manufacturers such as Mercedes and its European-based peers seem to have missed out on the hybrid, where the Japanese are way in front, it is just as well that they're making progress on the next wave of technology. What will make it a reality, and help save the planet, is for the EU, national governments and the oil companies to start building the infrastructure that will be needed to make it a practical proposition. It is an economic rather than technological challenge.
By 2015 there will still be petrolheads running V12 Ferraris and the like, but for most families the likes of the F-Cell will be moving them around. It can't happen a moment too soon.