Not sure how to describe this but here goes.....
We used to have these in an office in the UK, which were used to reduce the amount of sun getting through the glass and into the office. It was bascially a sheet of grey plastic that stuck to the window onthe inside and kind of tinted the glass artificially.
Could this be used as a way to reduce the amount of heat coming through the glass in the summer, by reflecting some of it back out???