darius wrote: Dyson, good idea to use a solar-charged 12v DC battery and fan for that kind of system!
Here's a cool Google Hack app that shows sun movement and sunlight phases during any given day at any given location. You just find your house in Google maps via the search box at the top.
You can see sun positions at sunrise, specified time and sunset. The thin orange curve is the current sun trajectory, and the yellow area around is the variation of sun trajectories during the year. The closer a point is to the center, the higher is the sun above the horizon. The colors on the time slider above show sunlight coverage during the day.
The photos below are my house, satellite view, on the longest and shortest days of the year.