I would imagine that it’s not the suns location that is the primary concern, but where you are directing the light. The light is being reflected and focused by

I would imagine that it’s not the suns location that is the primary concern, but where you are directing the light. The light is being reflected and focused by mirrors. That light is being directly onto some volume of material. So, in this case, they want to get the material above some critical temperature (e.g. so it melts). I imagine that uniformly heating the whole volume may not be the best approach, or that you may be able to work with smaller volumes depending on your expected solar input etc. So I can see a little more justification here than the case where solar cells are just being pointed at the sun.