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Straight electric motors from a battery would be more efficient?
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More efficient than using a battery to generate chemical fuel, then burning the fuel? Yes, sir. Starting with a certain total of electrical energy stored on board the vehicle:
Hydrogen generation from electrical current and water is 75-80% efficient (
Argonne). So if you could turn all the energy stored in hydrogen into mechanical energy, 80% would be the best you could do overall.
Diesel engines get somewhat over 40% thermal efficiency (
MSN encyclopedia article), but some say that'll go up to 55% with technological improvements, so let's say 44% efficiency from electrical to chemical to mechanical energy. A hydrogen fuel cell can give 70% efficiency (
EPA). Using one here would add up to turning electrical, to chemical, to electrical, to mechanical energy, so it's sort of circular reasoning, but I'm looking for the most efficient way to use the hydrogen. So, 56% overall.
A typical industrial motor, nothing fancy, can turn electrical to mechanical energy at 90% efficiency, according to an
article in Mechanical Engineering Magazine. A high-efficiency motor would be one in the 93-94.5% range.
So, once you've decided the benefits of batteries are worth the drawbacks, and I think nuclear generation does make this a "decent proposition," then direct electrical-to-mechanical conversion looks like the way to go.