I have spent the day applying Horti Shade on commercial glasshouse's on an industrial scale, hence needing a good scrub when i got home.
Its good stuff. Down side is it tends to leave scum in your rain barrel if you have one fixed to your bit of glass, so I would not recommend it if you are really hot on collecting rain water.
At the end of the season a small drop of fairy liquid and a cheap kitchen brush, you basically wet rub it off and give it a hose down.
However my little 8x6 at home now has a nice 'curtain' of fleece attached to the outside on the 'facing sun side'. This has made all the difference in very hot, sunny weather.
Remember to 'damp'* down in your greenhouse from time to time.
*= Damping down is watering the path and or beds in hot weather, it raises humidity and helps prevent your plants getting heat stroke.