This is a proper production-quality car, but you can't buy it. Not yet, anyway; 200 very early-adopting people will, however, be living with the Honda FCX Clarity under a leasing and research programme over the next three years. These cars will be based in Japan and the US, but two have also arrived in Europe – Germany, to be more precise – and I have been driving one of them.
You see it here. It looks like a bigger version of the Honda Insight hybrid, but the FCX is a lot higher-tech than that. It is the world's first fully-finished, mass-produceable, fuel cell car, the first car built by proper factory processes to use hydrogen fuel to generate electricity while emitting water vapour as the sole by-product.
We have heard a lot about fuel cell cars, although they have faded from their save-the-planet topicality while the glare of the green spotlight is turned on to pure electric vehicles and plug-in, rechargeable hybrids. That's because these last two technologies are more immediately feasible, requiring nothing more than a recharging point because the energy is actually generated elsewhere, whereas a fuel cell requires a supply of the simplest oxidisable material in the universe, hydrogen. This is blown, with air, over the fuel cell's plates, to create electricity which powers an electric motor.
Sounds deliciously simple. The huge snag is this: where does the hydrogen come from? We'll return to that in a minute, because there are solutions. First, though, the FCX Clarity. Its chief engineer, Sachito Fujimoto, is very upbeat. "It can now be taken on the autobahn with confidence," he says. "It provides relentless acceleration at all speeds."
That makes it sound like some sort of supercar, so I try to pin down the reality. Which is that it will reach 60mph from a standstill in about nine seconds, a figure comparable to a similar-size saloon powered by a good modern turbodiesel, and it will just about break the 100mph barrier, which is fast enough for most purposes even on those stretches of autobahn which still lack a speed limit. As for energy efficiency, it equates to an average of 100 miles per gallon of diesel fuel. From raw fuel to motive power, there is currently nothing more effective than a fuel cell.
The FCX Clarity weighs 1,625kg, a typical mass for a large saloon, and the 171 litres of compressed hydrogen in its tank will take it about 285 miles. That is a large, bulky tank, but to liquefy the hydrogen requires much more energy. Coping with hydrogen which is merely compressed is the best trade-off between bulk and efficiency.
As for the fuel cell stack itself, this is almost miraculously compact and sits within the Clarity's central tunnel. A decade ago, Honda's experimental stack occupied 134 litres of space, weighed 202kg and produced 60kW. Today's version occupies 57 litres, weighs 67kg and produces 100kW. The final parts of the powertrain, the electric motor, its control unit, and the cooling systems, fit under the bonnet.
I switch it on. A few hums later, a "ready to drive" message appears on the luminescent instrument panel, in the centre of which is a coloured ball. I select Drive, press the accelerator and off we waft. The "ball meter" represents the rate of hydrogen use: if it is small and green, I am being frugal, if large and amber, wasteful. Middle-size and blue is the intermediate stage. One tapering bar graph next to the ball reveals the amount of energy going back into the storage battery when slowing or braking, while its opposite number shows how much hydrogen is in the tank. Refuelling takes about four minutes.
But here's the most extraordinary part of all. The Clarity accelerates away from rest with the vigour of the most muscular turbodiesel, so it can lead the pack away from traffic lights and punch effectively out of junctions. And it does indeed cruise with pace and authority on the motorway. This car of the future works absolutely as it should, with no anxiety in its driver and no excuses required.
The motor and the fuel-cell's air pump provide a hi-tech soundtrack, the notes rising and falling as you move the accelerator, but they are far from loud which simply emphasises how thoroughly the engineers have eradicated the rush of the wind and the rumble of tyres on the road. The Clarity steers precisely, it soaks up bumps, it feels unexpectedly nimble, and if I was told I had to drive such a car from this point onwards I would not be unhappy.
Honda charges its US customers $600 (£360) a month to lease a Clarity over three years, which comes nowhere near covering the project's costs. But that is not the point; rather it is to find out how these cars will fare in the real world. The trouble is that the real world currently lacks a proper hydrogen-supply infrastructure, as current supplies are simply by-products of other chemical processes such as chlorine production. Long-term, the gas will have to come from the electrolysis of water, powered by renewable energy sources or nuclear power. And time is running out.