For a less expensive alternative to an exterior screen, side guide blinds also block the sun but are not a sealed unit. These blinds help guide screens up and down and hold them in place. Feel free to open the window without listening to your blinds clap against the window in the wind; the guides can lock the screen the place.
Roller blinds are easy to use but are often difficult to stay in place. Side guide blinds give you the convenience of roller blinds but eliminate the hassle by making sure your blinds stay put and keep the sun out of your eyes.