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Energy can't be created or destroyed, just transformed from one form to another. So nothing is really an energy source. I'd say "energy source" is the vernacular for stored energy, in terms of where humans source their energy for machinery, electricity, etc.

While you are technically correct, that's not the best model for this. Energy in oil is ultimately stored energy from the sun. But for hydrogen powered cars, we must take one stored form of energy (e.g. fossil, nuclear) and use it to make the hydrogen. Or skip the oil step and use solar.

So question is, are we storing new energy, or converting previously-stored energy to a different format? The latter is an externality as obviously oil, uranium etc were around long before humans.

Exactly my point. I've put hydrogen power in quotes in case that was unclear.

Like oil stores energy from the sun.

It is both. You can use it in a fuel cell form whereby you keep the water produced from its combustion, run electricity through it and get oxygen and hydrogen back. Alternatively though, the way hydrogen is turned into energy works if you just refill the hydrogen and throw away the water.