Slightly off topic but just to register my problem (maybe lack of understanding) with Hydrogen fuel cell technology.
We are told that its a great source of energy and that the main problem is the danger of transporting hydrogen in vehicles (i.e. explosions).
If that is the real problem then it could be solved by fuel cell energy stations and electric-powered cars. Since no-one is apparently proposing such a solution I am not convinced that this is anything other than the usual 'alternative energy' bulls****. Comments...?
Hydrogen fuel cells are not a source of energy. They are a fairly efficient means of changing energy stored in one form to another more easily usable form. The hydrogen economy idea, I think sees hydrogen as an energy vector, simply a means to store energy and move it around to where it is needed with the aim of creating a carbon neutral energy cycle. The use of hydrogen fuel cells is one way to utilise the stored energy.
I don't think the explosion issue is really an issue considering that people are quite happy enough to refuel and carry petrol around with them. I think the bigger problem with carrying hydrogen around with you in a car is one of energy density. Storing hydrogen as a gas runs into the problem of low volumetric (energy density by volume including the container) and gravitational energy density (energy density by weight including the container) when compared to something like petrol, and even methanol. Storing it as a liquid fares better on the gravitational density scale but has the added problem that it needs to be cryogenically frozen. That is why the current hydrogen fueling stations require all sorts of protective clothing and training to use. Storing hydrogen in a metal hydride is really not applicable for transport due to its extremely low gravitational energy density, and the tech that perhaps shows most promise is storing it using carbon nanotubes but last I looked no one was sure that was actually as good as the initial results made out.
There is also the problem of hydrogen embrittlement, which causes deterioration of metal containers that hydrogen is stored in.
If you don't carry hydrogen around with you and you still want a similar refueling experience to a petrol fuelled car, you have to produce it as required by reforming it on board the vehicle. And this raises the question of how you produce your hydrogen in the first place. Whilst it is true that a fuel cell running on O2 and H2 will produce water as its exhaust, the production of hydrogen is rarely that clean. If you reform a hydrocarbon you end up producing significant quantities of CO2, so you are essentially just moving the problem to a different place in the chain. The production of hydrogen is I think the main stumbling block for the hydrogen economy. I don't thnk that at the moment there is a reliable and efficient way of making hydrogen cleanly.
So it might look like I am on a bit of a downer where fuel cell tech is concerned. But thats not really true. Is it a cure all? Not at this time and possibly not ever. I think it has the potential to be very useful, I just think that like any tech that promises much, there are always complications to be overcome under the surface. There is work going on to develop composite cylinders to store hydrogen to lessen the weight burden and to allow the storage pressures to be increased, there is the work looking in to the carbon nanotube tech which if eventually successful would free up the storage and transportation of hydrogen immensely. It might be that H2 fuel cell powered private cars won't happen for a long time, and that the first truly mainstream use of the tech will be elsewhere, perhaps in distributed generation and combined heat and power systems, it might also turn out that the best place for the tech in the transportation industry could be in public transport where refueling difficulties will not be as pronounced owing to the the use of centrally located refueling stations. It could be that they will be used as auxilliary power supplies for passenger aircraft. Or possibly the idea will be totally dropped (I don't think it will but who knows what will happen eh?). Of cousre one mustn't forget the other types of fuel cell that also have potentially good applications (MW scale electricity generation, laptop batteries and so on.) I think it is a bit soon to just write it off as "alternative energy bull" just yet.
