Indeed I think your instinct, and logic here is good, capturing solar by way of heat storage that can be possible by undergound storage makes sense, but phenomenally expensive to implement, due to the excavation work needed, it could only be feasible in city areas, if the whole city was planned for that, up front, I think, and it would be very difficult to quantify how much money to issue as Kardashev Stimulus, as would still apply, logically more so, since a higher proportion of the energy of the sun is effectively being collected, if the efficiency is 4x higher, then logically 4 times more stimulus would need to be issued, per unit area utilised.

But my suggested algorithm would automatically sort it out, by using the value of money as the control factor on issue of money :)

As is, PV capture with hydrogen backup looks still to me to be the most practical option to make most things solar powered as stands, even with only a 1/4 of the efficiency of solar converted to heat, it is still enough, it seems to me. We have to credit the advances made in recent years in the costs and efficiencies of PV, and should expect to see something similar in hydrogen technology when this becomes something bought in quantity, I think.