My (layman’s) understanding is that super-black isn’t necessarily the best option if you are looking for solar heat: it absorbs light quite well; but its emissivity also approaches that of an ideal black body which means that it just pours IR back out even at quite modest temperatures.
“Selective surfaces” of varying degrees of exotic construction, with an emphasis on fiddling with the emissivity, are apparently the overall winners, even if they don’t absorb as much, by virtue of retaining more.
