>Solar farms are often sited, stupidly, in deserts, not because it is a good idea, but because ignorant investors think it is a good idea.

Perhaps indulge our ignorance about deserts for a moment?

Deserts are hot and dusty. Efficiency falls quickly as temperature rises, and more as dust accumulates. Panels degrade exponentially faster as peak temperature increases. (Precisely: each fixed increase in temperature doubles rate of degradation.)

Siting panels on water and on farmland reduces operating temperature. Mounting vertically, in fence-rows, keeps off dust, collects more during morning and afternoon demand peaks, aids convective cooling, and protects crops from harshest afternoon sun.