Originally Posted by
Heston
Originally Posted by
Uplinker
"Great. Where are you going to get the hydrogen from?......PDR"
You 'split' sea water into its constituent oxygen and hydrogen gases using electrolysis. We did it in chemistry at school. You just need sea water and electricity connected to two electrodes submerged in the water. A chemical reaction takes place and the hydrogen gas accumulates above the negative electrode, the oxygen above the positive.
Use wind turbines, solar panels or tidal flow turbines to provide the electricity to split the seawater, and you produce hydrogen.
Note: Sea water rather than pure water because the salts in the seawater make it electrically conductive.
That's my point - hydrogen is not an energy source, merely an energy transfer mechanism. You need energy made by some other means and then you "transform" it into hydrogen in a process that's inefficient and produces waste products (salts). Schoolboys say that burning hydrogen in internal and gas-turbine engines is "clean" because the exhaust is just water. This is (of course) not actually true. when you burn hydrogen in air at the pressures and temperatures you need for effective propulsion you also end up burning the nitrogen in the air and producing significant quantities of the nitrates which are ALSO one of the concerning pollutants. You could use the hydrogen in fuel cells for an electric final drive, but that's completely dependant on rare metal catalysts (a scarce and non-renewable material), making the problem worse rather than better - these materials make the platinum used in catalytic converters (which is already running into supply problems) look positively abundant. So if you're using the same generating plants as the grate unwashed are using for heat, light, cooking and social media then you can expect to join a queue. If they are being told they must have a cold house and can only watch strictly for 2 hours a day to conserve electricity I don't think aviation will be high on their list in that queue, and
recreational aviation will be right up there with politicians on their list of hate objects.
Hydrogen can't be liquified at normal temperatures, so it has to be stored in pressurised bottles. The usual parametric is that to store hydrogen at a pressure that gives a third of the energy per litre of petrol needs "tanks" that will weigh twice the weight of the hydrogen being contained. The equivalent number for petrol is about 5% (for three times the amount of "effective fuel"). With all of this factored in the use of hydrogen fuel comes out pretty close to batteries in terms of MTOW limits with considerably fewer safety issues. Yes, the weight reduces with use, but not by anywhere near as much as it does for petrol because the basic fuel is lighter and the tanks themselves are [massively] heavier. Hydrogen does have the advantage of quicker refuelling, but has much more complicated fuelling equipment requirements.
I'm not saying it's not the answer - merely that it's a much more complex and nuanced question than most of these simplistic "we can use hydrogen and everything will be the same - everyone else is just to thick to see it blah blah" rants suggest.
PDR