It is hard to tell if you are joking here or not, but in case you are not: if the cost of mining is low, the value of mining is also low. The reason for having 'mining' in Bitcoin is to artificially create scarcity in order to simulate blocks having real-world value.
If you can mine blocks for free, the value of each block plummets.
As long as Bitcoin is unusable for day to day transactions (7 TPS globally isn't even good enough to run a town on), it can't solve any real problems, because its value is just speculative make-believe. And no, Lightning or other L2 networks don't change that, since they don't actually use Bitcoin all that much - they don't actually give Bitcoin's assurances unless you run them at Bitcoin speeds (i.e. close the channel after every transaction, negating any performance advantage).
And if we ever automate every job away, littering could be the solution
There's a hundred other things we can dump energy on before deciding to waste it ; pumping water uphill, gravity batteries, regular batteries, electrolyzing hydrogen to use for later, ...
Why the heck would you use something so difficult/expensive to store & transport like Hydrogen?
If energy is expensive than it's makes more sense to store it in batteries than hydrogen since batteries are about 3X as efficient as the hydrogen cycle.
If energy is cheap it makes more sense to use about twice as much energy to capture and attach carbon molecules to that hydrogen to create a hydrocarbon resulting in something that's easy to store and transport, and that uses existing infrastructure.
You don't have to transport it very far if you generate it onsite straight in the hydrogen powerplant that'll turn it back into electricity with between 40 to 60% efficiency
If we follow your 3rd paragraph and turn the hydrogen into hydrocarbons, not only do you lose efficiency in that process, you make CO2 as a byproduct of combustion again
Nobody is interested in storage that turns your carbon-free green energy back into greenhousing energy
The reason you might want hydrogen instead of batteries is just cost, I guess.
> Nobody is interested in storage that turns your carbon-free green energy back into greenhousing energy
If you make your hydro-carbons with captured carbon, the process is slightly carbon-negative. ~10% of hydrocarbons are not burned, they're turned into plastic or lubricants etc. So for every 10 carbons you take from the air, only 9 are released back.
Bitcoins as grid energy storage? Just install my BitWall box next to the pv junction box. I'd be surprised if the economics math works out but that's a fun idea.
I cannot tell if this is sarcastic or not so the assumption is it isn't. In which case: WTF? There are many solutions for cheap energy but a pointless digest algorithm isn't one. While I do not agree with the AI craze it would still be a better solution.
If you can mine blocks for free, the value of each block plummets.