The temperature in the greenhouse rises rapidly during a sunny day. Short wave energy passes through the glass, converts to long wave energy as it bounces off the items inside the greenhouse and continues to bounce round inside the greenhouse.
There are two approaches to shading. The first is to stop the sun's rays from entering the greenhouse from the outside. This is achieved by using fine green netting spread across the roof and the southern side of the building, external blinds that roll down the side of the roof, or by painting on a white coloured wash that reflects the light away from the greenhouse. Of these three the white wash is the least expensive, but also the least durable, and has to be washed off as the autumn approaches so as to allow sufficient light and heat into the greenhouse at the end of the season.
The second approach to provide shading inside the greenhouse is achieved by internal blinds, internal green netting or by painting the inside of the greenhouse (although this can run with condensation). the advantage of internal shading is that it does not interfere with the vents and louvres to the same degree a outside shading.
Automation can be used to raise and lower blinds, linked to the level of heat recorded inside the greenhouse.