Something I've done for many years is cover windows with aluminum foil. Of
course you can't do it with all your windows, but I always have some that
don't show to the front or anywhere important to see out, and have lots of
hot sun shining through. This is really really helpful in bedrooms. It's
cheap and easy, just cover all the glass using masking tape on the seams and
edges, and placing the shiny side out. This blocks out soooo much heat. In
the Fall just pull it all off and let the warmth you want in the winter back

Barbara in Texas