Hydrogen Bombs

There've been two reports recently, touting hydrogen as a clean fuel. And, naturally, burning hydrogen in some types of engine yields only water vapor (well, some bit of NO_x). One is German locomotives, while the other is California setting 2035 as the year for autos being either electric or hydrogen.

It's worth noting that there are two kinds of hydrogen vehicles: those using hydrogen fuel cells (been around for decades) and those using a 'normal' internal combustion engine, just using liquified hydrogen rather than gasoline or diesel. The au courant meme is hydrogen as burned fuel.

So, campers, where's all that hydrogen going to come from? The (nearly, at least until humans run the tap dry) infinite supply of sea water means an infinite supply (ditto) of hydrogen. But guess what? They Ain't No Such Thing As A Free Lunch. The laws of thermodynamics dictate that you'll never harvest as much energy from a process as you inject into it; modulo nucular.

With current tech, electrolysis generally produces hydrogen at about 75 per cent efficiency. So to create a kilo of pure hydrogen fuel, which holds about 39.4kWh of energy, it takes 52.5kWh.

Of course, that's just the pure energy budget, but since the Zeppelins we don't use gaseous hydrogen. We use liquified gas, just like LNG. And it takes a wee bit of more energy budget to make LHG.

To use it as fuel, it needs to be compressed to incredible pressure (generally 5,000 to 10,000 PSI) or kept as a liquid — which means cooling it to less than -253ºC, or just 20 degrees above absolute zero.
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So, 90 per cent efficient to make, 54 per cent efficient by the time it's in your tank — without even taking into account the energy needed to transport it.
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So, hydrogen's pretty rubbish as a fuel for our machines.

So, we'll use a stream of wee electrons from coal fired power plants to make the hydrogen? Sounds like a plan.

Also of note; hydrogen powered cars and trucks do not constitute some new tech. Far from it. UPS, among others, adopted (a bit) of LNG powered delivery trucks years ago. And that cute emergency generator in your back yard works on the same principle of gas driven piston internal combustion. Not cutting edge.