[ndonnellan]

I was going to chime in to second this. In a former life I worked on power towers and we had designs for air receivers that would potentially work really well with this type of system:

- High temperatures - Intermittent solar input not a problem - tall central structure (?? maybe a plus given the paper's tall storage vessels)

But high temperature air receivers have their own problems, mostly around receiver material properties (thermal cycling / stress) and heat loss. It's really hard to focus a lot of light from the sun into a tiny aperture, because the sun isn't really a point source, and no mirror is perfectly shaped.

[pfdietz]

And highly concentrating mirrors only work with direct sunlight, while PV works with diffuse sunlight scattered off clouds, dust, or the air itself. Bifacial PV cells even capture light hitting the back of the panel.