I've been kicking this idea around for 2 years now (our home anniversary was 12/17). The only obstacles are:
1. I have side-opening windows
2. Wife would rather crank up the heater than have anything "ugly" in the windows.
The trombe wall or a water wall would be great for my south wall made entirely of brick and no windows, but the summers here are blistering hot! I would have planted a green wall or built an "adjustible" pergola, but still have to match the sun's patterns and wait for the neighbor to decide on our party wall.