Apparently, everyone who has modern houses with huge windows has this problem - in summer, of course, it becomes even more acute. I find the idea of such an awning very charming; it keeps the sun out enough while still letting in light without greatly reducing the view outside. But doesn't it rot quickly if you also use it in winter?
Otherwise, I can't contribute much here; we have an old building and, thank God (!), no windows facing south. In our living room, it heats up enough through the east-facing windows - just enough so that it's not unpleasant.