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If we can use hydrogen to power electric motors, why can’t we use water to run a car?
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this post was submitted on 14 Feb 2024
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Because it will always take more energy to break the water than you will get burning the Hydrogen in Oxygen back into water - it's basic thermodynamics.
You will lose some energy as heat that you cannot get back*.
You can't power a car from a process that loses energy. Even if you use a battery to donate the lost energy, then you might as well just cut out the lossy middleman and just run off the battery or generate the Hydrogen elsewhere - which is what we currently do.
It is better to think of Hydrogen as an energy transporter than as a fuel, as you'd need to generate the Hydrogen somewhere that has abundant energy (ideally renewable), then transport I where needed, such as a Hydrogen powered generator.
*Interestingly the fact that all processes generate waste heat means the only theoretically 100% energy efficient process is heat generation itself, as all forms of energy eventually degrade to heat (as it is essentially the universe's waste energy).
Electric heaters aren't 100% efficient, because some of the energy is wasted altering the resistive material chemistry and emitting other electromagnetic radiation, and even sound, that doesn't heat the air inside your house (right away). Still at a perfect 100% efficiency, it takes 1 joule to raise your house temperature by 1 joule, ideally. Heat pumps, which are just an AC unit running in reverse, are more efficient than electric heaters. Some heat pumps have a coefficient of 3. Meaning they take 1 joule to heat the air in your house by 3 joules. Because they don't try to heat the air, they move heat to the air from outside, and they can achieve this even if outside is freezing.
That's the theoretically part - there are processes that will capture the energy generated that would've otherwise become heat, but that only affects the timeliness. Given enough time, all workable energy generated by a heater would become heat, even if you had to wait for the matter itself to decay trillions of years from now when all the stars have long since breathed their last breath.
Also has somebody watched Technology Connections by any chance?
Heat pumps are so cool - if you showed onw to someone even a hundred years ago, even knowing what electricity was, they'd think it was magic.