This is a question out of pure curiosity, I'm not very well read on these subjects, so please forgive me if this is a dumb one.
Is there any reason why this can't be built as an underground structure? If it's working on temperature differentials, shouldn't you be able to achieve a more constant capacity by plugging it into earth where temperatures change less?
But it shines on the ground, so instead of putting the heat source at the bottom of the cylinder, you put it on top and see temperatures drop as you go further down underground.
Is there any reason why this can't be built as an underground structure? If it's working on temperature differentials, shouldn't you be able to achieve a more constant capacity by plugging it into earth where temperatures change less?