Earlier quoted context omitted.
I live in SoCal and am continually shaking my head at the architecture. So my floor-to-ceiling glass buildings in a climate known for sunny weather. So much extra air-conditioning will be spent to cool those buildings compared to if they had been built more reflective.
I'd try hanging long sheets of aluminum foil in too-large windows. I imagine someone in academia has studied this.
It'd be better to block the sun before it hits the window though, so that the window itself does not get hot and heat the inside.
Edit: people generally use emergency blankets, fyi. You can stick them to the glass with water.