Re: Is solarPV a waste?
I'd need to check, but I suspect part of the answer to (1) is that despite its wavelength limitations, PV can do better as a whole than solar thermal because while solar thermal can pick up infrareds and so on, it can exploit less of the higher wavelengths.
As for (2), even with a large thermal gradient, what is its mechanical capability? How much torque can it produce? I would suspect that if it were truly worthwhile, Stirling generators would find a home in a place like Iceland, home to perhaps the largest temperature differential in nature (volcanic heat right next to the Arctic Ocean).