It would make sense for it to be the ionosphere. But whether or not it is or was true has now been suoerseded, by PV technology. Because we've seen this already start to eat up utilities energy supply, it would not make sense now to pursue what might have been the best option before the advent of PV.
We might say nature always intended us to use solar one way or another, it always was inevitable.
But what does still stand as a challenge is the change that needs to happen to money, to finally activate the full value of solar, including that already implemented, it has to be monetised, to enable us, empower us, incentivise us to switch completely over to it.
I am almost certain Tesla must have documented this, this must have been the discussion he had with JP Morgan that got him defunded / cancelled.
Isn't it an interesting coincidence that the last issuer of free money, that might have qualified as solar indexed stimulus had issue of it been sustained, which resulted in oil prices going negative, the only time ever, was Trump, who's own dear uncle became the custodian of Tesla's documents, when Tesla died, and now Trump is more or less cancelled?