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Why is alternative energy most commonly stored in relatively expensive metal acid batteries, which have a short life, rather than hydrogen gas accumulated through electrolysis?

Hydrogen is a versatile energy source itself and with low cost technology is a cheap, clean and reliable fuel.

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closed as off-topic by John Rennie, tfb, user36790, Rory Alsop, Wolpertinger Dec 22 '16 at 17:14

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  • $\begingroup$ If it was reliable, in terms of we can reply on it not to ignite, that would be great, it would be in every car in a few years, but we can't. That's one reason. $\endgroup$ – user139561 Dec 22 '16 at 12:32
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Assuming you are generating electricity (say from wind or PV) and you want electricity, then there are two obvious cycles:

  • for lead-acid you charge and discharge the battery;
  • for hydrogen you crack water, store the hydrogen, and then run a fuel cell.

Lead-acid batteries can have charge-cycle efficiencies of around 80%, perhaps more. (Lithium-ion I think is even better.)

Electrolysis has an efficiency in the range of 50-70%, and fuel cells are in the range 40-60%. So the overall efficiency of the cycle is in the range 20-40%. This is not even slightly competitive.

On a large scale you can perhaps either burn the hydrogen to make steam for a steam turbine generator, or may be run a gas turbine directly. These systems have efficiencies that might touch 50%: this page and its links says that natural gas power generation can be about 43% efficient, in 2015. This is no better than fuel cells, but the plant might be cheaper.

You can also run an internal combustion engine with hydrogen: that's not a good way of generating electricity, but it might be reasonable if you want to run a car. I haven't looked up figures but I suspect that hydrogen to fuel cell to electric drive is better.

I have not touched on the energy density question: to get anything competitive you need to compress the hydrogen which requires yet more energy, some of which you may hope to recover. Even then I am not sure how competitive it is.

This is why lead-acid batteries are used.

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