[katieHaylor (OP)]

Nigel says:

I listen to The Naked Scientist on Cape Talk on Fridays. There is all the talk on battery / electric cars for the future. Why not hydrogen? No limited range and no bad emissions. I believe Honda in the USA have a car in place and from the decades ago when I was last in school hydrogen was one of the most abundant gasses we have.

What do you think?

For information, the Cape Talk show Nigel refers to is also available as a podcast - Ask The Naked Scientists

[evan_au]

It is possible to power cars with Hydrogen; see: https://www.forbes.com/2005/01/04/cx_dl_0104vow.html

Hydrogen does have some problems as a fuel; with a boiling point of -252C, you need some serious insulation to keep it in liquid form - cryogenic tanks are really only practical on space rockets, where price is no object (relatively speaking).

So mostly Hydrogen is transported as a pressurised gas. In this form, it has a lower energy density than coal or petrol.

...and then there is the "Catch 22": No-one will buy a hydrogen-fueled vehicle unless they are sure there will be hydrogen refuelling stations everywhere they want to go; and nobody will build hydrogen refuelling stations unless there is a large base of cars demanding them.

See: https://en.wikipedia.org/wiki/Hydrogen_fuel

[alancalverd]

The best thing you can do with hydrogen is to reduce carbon or carbon dioxide to methane or a higher alkane. Propane is an excellent liquid fuel and a very good way of turning coal, or fossil fuel combustion products, into practical road transport. If you can synthesise octane or decane you can put it directly into an ordinary petrol, diesel or gas turbine engine with just a few magic ingredients, and solve all the world's problems at once.

[teragram]

The best thing you can do with hydrogen is to reduce carbon or carbon dioxide to methane or a higher alkane. Propane is an excellent liquid fuel and a very good way of turning coal, or fossil fuel combustion products, into practical road transport. If you can synthesise octane or decane you can put it directly into an ordinary petrol, diesel or gas turbine engine with just a few magic ingredients, and solve all the world's problems at once.

How does the efficiency of these processes compare with charging batteries from the mains? We don't want to reduce the (well to wheel) efficiencies of heat engines any further! Basically the electric motor is the future for transport.

Put simply, is the energy required to produce hydrogen for later use as a fuel (via a fuel cell) in vehicles less than the energy used to recharge batteries for the same use? I suspect not.
In any case, to use energy to produce hydrogen for fuelling vehicles with internal combustion engines (eg. the Hummer) is a profligate waste of that energy. 
PS I seem to remember that some hydrogen fuel cell cars also have a battery anyway, to cope with sudden demands for power in accelerating or hill climbing. If so, cut out the middle man! (the fuel cell).

[alancalverd]

Road transport in the United States currently uses about 10 times as much power as the electricity grid can produce, so we have to radically rethink our entire transport policy if we want to get rid of internal combustion engines. Mains power won't cut it!

On the other hand we have the promise of limitless free energy from solar, wind and wave power, but only when Mother Nature wants to supply it. So why not use the free stuff to make liquid fuels that we can store and use when we need it in our existing vehicles and aircraft?

[teragram]

On the other hand we have the promise of limitless free energy from solar, wind and wave power, but only when Mother Nature wants to supply it. So why not use the free stuff to make liquid fuels that we can store and use when we need it in our existing vehicles and aircraft?

We have to radically rethink not just our transport policy, but our entire energy policy. Electricity from solar etc., will have to power everything when fossil fuels are phased out or dry up. Of course this means a vast increase in capacity of supply networks. But to integrate transport into the electricity infrastructure with minimum impact will require the most efficient means of powering vehicles. This rules out heat engines straight away. To use electricity to make hydrogen or other liquid fuels to power vehicles involves an extra stage of energy loss. Having lost that energy, more is lost in vehicle fuel cells, (even more in vehicles powered by heat engines). While "limitless free energy" has zero fuel cost, poorer efficiency means more solar collectors, wind farms, transmission cables, etc.

Incidentally, in the future electric vehicle batteries in large numbers will be connected to a smart grid when they are idle, to be recharged, and to help stabilise grid load in times of excess demand by sending power back to the mains. The battery electric vehicle then will be part of the solution, not the problem.   
Aircraft of course are a special problem, being such a large proportion of fuel use, but even here aircraft companies are looking seriously at battery electric aircraft.

[alancalverd]

We now have some 2-seat training aircraft that can fly for 40 minutes on battery power, which is excellent for ab initio teaching. The batteries can be recharged in an hour or two, so you can just swap the battery pack after each session and overall it works out as quick as refueling a conventional trainer every 3 hours. The problem is  that you can't teach cross-country flying or landing at strange airports, so you still need a conventional plane to qualify for a licence, and that will take another couple of hours' familiarisation with engine management, fault diagnosis, weight balance, fuelling safety, etc., which we normally do during basic circuit training anyway.

Whilst we are quite good at storing huge quantities of jet fuel and safely pumping 250 tonnes of it into an A380 in 40 minutes, swapping a battery pack of such capacity is not a simple operation and recharging it with 1 GWh in the time it takes to clean and load the plane will require a fairly large nuclear power station at each gate.
The "proportion of fuel use" is interesting.  An A380 manages about 40 passenger miles per gallon of fuel - about average for all the cars on the road but at 500 mph in a straight line (and whilst eating dinner) rather than 40 mph on bendy roads.   

[teragram]

The problem is  that you can't teach cross-country flying or landing at strange airports, so you still need a conventional plane to qualify for a licence, and that will take another couple of hours' familiarisation with engine management, fault diagnosis, weight balance, fuelling safety, etc., which we normally do during basic circuit training anyway.

So when all aircraft are electric, won't they all be "conventional"?
Maybe we should not keep quoting how our world is today, but try and see how it will be in a couple of decades time?
Until the aircraft evolves to the point where electric power is routine, the use of hydrogen produced from renewable energy is a solution, but for best efficiency via fuel cells not heat engines (to reduce the load on power networks).

An A380 manages about 40 passenger miles per gallon of fuel - about average for all the cars on the road but at 500 mph in a straight line (and whilst eating dinner) rather than 40 mph on bendy roads.   

The way aircraft fuel consumption is usually stated can be a little confusing. So for instance an A380 manages 40 miles per gallon per passenger mile. I think this assumes that the aircraft is carrying it's maximum number of passengers. So in fairness this should be compared with an average car managing driver + 4 passengers * 40mpg = 200 passenger miles per gallon ( reducing a little for increased rolling resistance). I include the driver as in most private cars he is a passenger also, not just a pilot.