Problem is, if you use it for cooling, it's strictly better to use the electricity directly (chances are the sun is shining when it's hot).
And if you use it for heating (at least from day to night), the round-trip efficiency is probably still better for batteries, or electric heating + hot water storage, because you can use heat pumps which are say, 5x more efficient than burning fuel.
If you have an stationary application you will never use something like that. (Except maybe for long time storage, I don't think this will win over long time storage, but it isn't settled.)
Sorry but this goes against the definition in elemental form (in this case it's H2).
Also there is no such thing as `cheaply obtained renewable energy`. If it was your electricity bill would be 0.
One could imagine battery boosters jettisoned after supporting the climb to cruising altitude which autonomously return as drones to the airport.
Carbon hydrogen bonds are one of the best ways to store energy that we have.
A Tesla battery pack is good for about 300 miles. If that's equivalent to 3 gallons of gas, that's saying that Teslas would get 100mpg.
I can believe 40-45 mpg, but 100 requires some evidence.
They are rated for 134 combined MPGe. That is not that crazy for an EV, the ford Mach E gets 93:
https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=43602
Electric drivetrains are really efficient, which is why EV's are practical at all.
water is an easy elemental source of hydrogen. If it is possible to fuel this electrolysis via cheaply obtained renewable energy, then it makes a lot of sense to produce fossil fuels using this method - it will allow the existing infrastructure to consume such produced fuels, so you save capital and energy on replacing them.