This month our energy industry expert returns to hydrogen, considering the pros and cons of it
Hydrogen has been under development as a vehicle fuel for many years. In recent times, hydrogen-fuelled buses have been experimentally introduced in a number of cities including London and Inverness.
But what is hydrogen and why the long-term interest in it as a fuel?
It is the smallest, lightest element of all. It is also the most abundant element in the universe, but it does not exist in nature in isolation as a pure element.
It is chemically very reactive and it exists, for example, in combination with oxygen as water (H2O) and in combination with carbon to make familiar hydrocarbons including methane (CH4) and diesel (typically C15H32), and so on.
Hydrogen is flammable and when it burns it forms only water, hence its attraction as a fuel; the only emission from a hydrogen-fuelled engine is water, a tantalising prospect.
So why are we all not driving hydrogen fuelled vehicles? The devil, as usual, is in the detail.
The ideal fuel?
While hydrogen appears to be an ideal fuel, at ambient conditions 1kg of hydrogen occupies a volume of 11.2m3. As a comparison, 1kg of diesel weighs around 1.2 litres.
Hydrogen’s energy density is 39.4kW/h/kg, compared to 15.4kW/h/kg for methane and 13.3kW/h/kg for diesel.
If a bus used 100kg of diesel per day, a similar bus running on methane would consume 86.5kg and a hydrogen-powered bus, 33.9kg. That mass of hydrogen would occupy 379.1m3. Compressed to 400 bar it would occupy 0.76m3, which is manageable on a vehicle, but that storage pressure is very high at 5,800psi.
While using hydrogen in a fuel cell results in an emission-free vehicle, there is considerable technical complexity involved, and that means high costs.
One of the largest hydrogen fuel cell bus operations under way is in Aberdeen. A total of 20 buses will eventually be in service and the total project cost is reported to be £19m.
Is that a practical proposition where hundreds or thousands of alternatively-fuelled vehicles have to be found to improve air quality and reduce global warming? Over to you.
Our industry expert speak with authority and can back up all of his facts, but what do you think? Email editorial@divcom.co.uk if you agree or disagree with him.
