Faced with diminishing oil reserves and the threat of climate change, hydrogen, the most common element in the universe, and the most energy-rich fuel of all, is seen in many people’s eyes as the dream fuel of the future. It can be sourced from water, and emits only water, so it has great promise, but equally there are a number of technical hurdles to be overcome in areas such as production, storage and infrastructure.

BMW has been carrying out research and development on hydrogen cars for 25 years, and the Hydrogen 7 is the latest test-bed. The car is based on a normal 7 Series, from the same production line as the standard car, but it has been developed to run on liquid hydrogen. Hydrogen as a fuel is in short supply in the UK, where at the moment there is just one refuelling station in Wembley, so the 7 has a hydrogen tank and a petrol tank, and the engine can run on either fuel. The hydrogen, stored in liquid form at minus 253 degrees Celsius, is converted into gas before being burnt in the combustion engine.

Whereas many other manufacturers are going down the route of the fuel cell, BMW has chosen to build on its many years of experience of developing internal combustion engines. A fuel cell vehicle is essentially an electric car, where a fuel cell converts hydrogen and atmospheric oxygen into power to drive an electric motor, whereas the Hydrogen 7 is just like a normal car to drive. A button on the steering wheel allows you to switch between petrol and hydrogen power, and the display lets you know how much of each fuel you have left. So this means that there’s not much to difference to report between driving the Hydrogen 7 and a normal 7 Series. The car currently has a huge, and heavy, tank to store the hydrogen, but one of BMW’s imminent developments is new technology to allow the tank to be reduced in size considerably. The car can run 200km on hydrogen and 500km on petrol.

So driving the 7 means that this is a very well sorted car, comfortable, smooth, and with all the equipment that you would expect of a car of this class. Under the bonnet, very clever technology is happening with camshaft adjustment, variable valve drive, and petrol injected directly into the cylinder, to enable the 6 litre 12 cylinder engine from the 760i to swap between petrol and hydrogen, but the driver is blissfully unaware of all this. One particular challenge for BMW’s engineers was the very high combustion temperature of hydrogen, so a special piston with cooling channels was required, and modified valve seats are also needed, as unlike petrol, hydrogen gas doesn’t contain any carbon which would normally be used as a lubricant.

Of course the other challenge was the hydrogen tank. Hydrogen becomes a liquid at -253 degrees Celsius and the volume shrinks to around one thousandth of the gas. But for the car to be able to store liquid hydrogen rather than the gas, the tank needs to be able to withstand very high pressure, and obviously keep the hydrogen very cold.

The tank on the Hydrogen 7 holds 8kg of liquid hydrogen and lies as a cylinder between the boot and rear seats. There’s an outer tank and inner tank with a vacuum between to keep the temperature down. The tank is very heavy and extra work was required on the chassis to protect both the rear axle and passengers. The 7 has passed crash tests, but there is currently little or no legislation in the UK for hydrogen cars. Refuelling with this liquid requires a special coupling to link the pump nozzle with the filler neck of the vehicle.

The weight of the tank means that the performance of this car is short of the standard petrol version. 0-100km/h arrives in 9.5 seconds, whereas in the standard 760i the figure is 5.5 seconds, and combined fuel economy running on petrol is 13.9l/100km – compared to 11.9l/100km for the standard car. The consumption running on hydrogen is 3.6kg/100km.

Will we be seeing other similar hydrogen cars in the near future? Probably not until the UK has more than one place to refuel! Hydrogen infrastructure is more developed in Germany and California, with its ‘Hydrogen Highway’, but two more hydrogen stations are planned in London for next year. BMW sees a reasonably developed hydrogen infrastructure as being 10-15 years away. We just need to ensure we also develop a sustainable, efficient and cost-effective production process (hydrogen is being produced today from solar and wind – ie. from renewable energy).

Can you buy one? No. There are only 100 cars that exist in the world, and only around seven of these will make it into the UK, and these will be ‘loaned’ to ‘high profile individuals’ to use – to help them make a statement with this potentially zero-emission vehicle about their green leadership credentials.