It is like a whirly bird mounted on the roof tiles. The whirly birds of the past just operated by wind so if the wind didn't blow, then no heat taken from the roof. Works on the principle that as heat rises from the house into the roof (vents installed for that purpose in house ceiling) the roof contains the heat and the whirlies remove the heat. Likely to be 60 degree C. on a hot day and outside it is cooler so heat leaves the roof cavity. A solar style whirly uses energy from the sun and drives a motor (size dependent on requirements). It can be fitted with a night kit which uses electricity to turn on the whirly (when no longer turning after dark) on a thermastat which is part of the solar whiz which kicks in when the temperature is still high in the roof itself.
If the tiles on the roof are cement and painted black, no trees overhanging the roof, during the summer the temperature in the roof can be in excess of 60 and this continues to keep the house hot throughout the night and if the following day is also hot, then the heat in the house can be unbearable. Large aircon bills and this is what I am trying to avoid.
