If the window is in the sun, your major problem is unlikely to be window insulation. It’s solar heat gain. Sunlight carries a lot of power — about 1 kW per square meter. If your window lets all of that power in, then your AC needs to consume a couple hundred watts to send it back out again. What you need are windows with low solar heat gain coefficients (SHGC), which is mostly independent of insulation. Or you can get window treatments that are shiny on the side facing the window.
> What you need are windows with low solar heat gain coefficients (SHGC), which is mostly independent of insulation. Or you can get window treatments that are shiny on the side facing the window.
In the desert by me people use substantial awnings on the exterior putting the windows in shade. It's a lot cheaper than fancy window treatments and in my experience far more effective. Provides more space to mount solar panels too.
I have blackout curtains in my office covering two south facing windows (in FL). They block a good bit of heat, but it still gets warm. I mostly just wear shorts and deal with it as I really don't want to run the AC down too low (keep it at 80 while I'm home alone; 76 when the family gets home).
