The second one.

Mirroring is good for speed, but a storage mechanism with parity checks will always be more recoverable. And you will have far more storage available.

If you don’t care how long it takes to get there and can effectively use the ITN you don’t even need to leave going that fast.

[European utilities] have failsafes implemented to prevent back feeding electricity in the grid

Yeah but imagine if you could save money by not doing that? What are the odds that there’s going to be cheap(er) personal mass power generation in the next few decades.