This is one lesson we learned well living in the American southwest. Judicious timing of opening and closing windows and curtains can make a vast difference in the energy costs to maintain a comfortable temp in your home. Now that we have moved to the northern tier of states in the US, we still open and close curtains to follow the sun as the day progresses, and open/close windows based on indoor/outdoor temps. We also add and remove curtains seasonally, really bundling the place up in the cold winters. It feels like micro-management, but it becomes second nature.