We already have materials that can achieve 75% efficiency [1] and probably more(it's just a rough search), so the 90% figure is much less impressive . But they

We already have materials that can achieve 75% efficiency [1] and probably more(it's just a rough search), so the 90% figure is much less impressive . But they also claim low cost and low maintenance over other methods, which are highly valuable. [1]http://www.mit.edu/~soljacic/cermet_solar-thermal_OE.pdf http://www.mit.edu/~soljacic/cermet_solar-thermal_OE.pdf