The fine article was about the efficiency of cells vs. their geometric footprint. If the cost of the footprint is considered, smaller GaAs cells might be more

The fine article was about the efficiency of cells vs. their geometric footprint. If the cost of the footprint is considered, smaller GaAs cells might be more economical than the larger (but cheaper) Si cells. Also, conentrators might be nothing more than a few mirrored/angled surfaces at the edge of the cell, which would increase cell illumination independent of cloud cover. It's not rocket science.