Picture posting is enabled for all :)
I am not sure if I fully understand what your windows look like but you might be able to use one of those mini plastic covered greenhouses placed infront of the window. Just take the cover off and you have a set of shelves that are light and easy to move when you have to.I use them in my conservatory because it gets too cold at night in the winter. I usually have a heated propagator being used in the bottom which raises the temp slightly when i use mine with the zipped cover.I hope this makes sense :)Duke