There has been a sudden interest in hydrogen as a fuel. This is because of the need to store energy generated by intermittent weather-driven green energy generators (ie wind turbines and solar PV generated electricity). Especially of interest is hydrogen to fuel motor transport. However things are not so simple.Combining hydrogen with oxygen produces water and releases lots of energy (hence it’s use in the Saturn V rocket). Conversely it takes lots of energy to separate the two. The attraction of hydrogen is that it can be made by electrolysis ie. passing electricity through water.
Production of hydrogen is a very inefficient business, the method of production we use commercially at present is to make it from natural gas, (steam reforming) an energy intensive process that defeats the object of what we are trying to achieve and also results in massive carbon dioxide production. Production by electrolysis is even less efficient, though there is hope in more recent high pressure and temperature production systems.
Then there is the problem of distribution. There are lots of snags associated with hydrogen. It is a highly dangerous fuel. The molecules are so tiny it’s hard to keep them in anywhere (ie. they tend to leak out). This rules out distribution by our existing natural gas pipelines. The one upside is that being very much lighter than air, leaking gas tends to dissipate rather than gather in flammable pools on the floor as does some fuel gases.
At present you occasionally see hydrogen delivered by compressed gas tanker (many long pipes welded into a safety cage all painted bright red.) Because the gas is in compressed form, the pipes have to be small diameter. Other fuel gases (eg. propane) liquefy out at ambient temperatures and quite low pressure so enabling large diameter tanks. The other common fuel gas, acetylene, is supplied in cylinders dissolved in acetone.
It could also be distributed by cryogenic tanker, ie. in super cold liquid form. However energy is consumed in creating the liquid and as heat is absorbed during storage and transport, the gas evolved has to be vented off.
The petrol/diesel engine is highly unsuited for traction, hence the need for gearboxes and clutches etc. It’s one redeeming feature being the portable fuel supply. Electric motors on the other hand are ideal for traction, the downside being the source of electricity.
It’s possible to fuel both from hydrogen. The question is would you want to? We have no means of bulk manufacture or distribution. Would you want to be in involved in an accident that included hydrogen? Would you want to live near a hydrogen manufacturing or storage facility? (Hydrogen is far more dangerous than petrol.)
The very first internal combustion engine ran on hydrogen devised by one Isaac de Rivaz in 1804. He made his hydrogen by passing steam through a red hot iron pipe. He powered the first motor vehicles with his engine. It was a while before the idea caught on, needless to say. Things have improved since then, but hydrogen powered engines/cars have serious down sides. (First get your hydrogen). The idea that only water vapour is produced is a lie, they can also very easily produce a range of NOxs. There can be detonation/pre-ignition problems too. To overcome these problems, the engines must have a low compression ratio leading to poor thermal efficiency and power output. This results in the engine needing to be around twice the size of it’s petrol equivalent.
An upside is that exotic metals such as lithium, cobalt and neodymium are not needed.
Several motor manufacturers have recently had a go but the projects seem to have been quietly dropped.
Jet engines can also be devised to run on hydrogen in both liquid and gaseous form. Assuming sufficient hydrogen is available, this seems a more viable viable proposition although there are big safety issues.
Hydrogen can provide electricity via a fuel cell so being a longer range alternative to a battery propelled electric vehicle. Think of a fuel cell as battery where the electrolyte (hydrogen) is continuously replenished.
These do provide zero street level pollution though again efficiency is not high. Some fuel cells need exotic materials, others do not.
Hydrogen can also be used in a Direct Reduced Iron process to produce iron from iron ore instead of using coke/carbon. This lends itself to countries with no coal but ample iron. (Plus in the case we are considering plenty of wind/sunlight supplied electricity). Yes, the Middle East.
Perhaps a lighter read here.
The economics of a hydrogen economy are complex plus there is the value of the byproduct, oxygen. It could however solve the problem of what to do with excess renewable energy.
The topic is vastly more complex than I first imagined, this article just gives a few pointers. The cost of distribution and storage would be immense. We wait with bated breath.
Photo by skidder