A friend of mine is adding a solar greenhouse to a long south wall of his house. He was toying with the idea of angling the windows to catch the winter sun more directly. I told him not to. Here’s why.
Angled windows, yes, do catch the low angle of the winter sun very well. But they also allow the captured heat to escape. Heat rises, and the window is an upper surface, not unlike a ceiling. Heat rises and goes out the window. (photo: flickr jessicareeder)
In summer, angled windows catch unwanted sun and heat up the house, which calls for more cooling and unnecessary energy spent. Shade cloth does not block enough sun to warrant angled windows. (photo: flickr stereogab)
I have never had a problem with heat loss and overheating with windows placed in a straight wall. If the windows face due south and have an overhang, the high angle of the summer sun will not reach inside. Winter sun shines in easily. This is the basis of good passive solar design. (photo: Wikipedia)
A few years ago, I was in a small earthship style home that was originally built with angled windows. The owner said it was 85˚ indoors late at night in winter! There was too much heat absorbed in the thermal mass. Overkill. The owner rebuilt the wall with straight windows and lived much more comfortably after that.
I hope my friend heeds my advice, especially since he is planning on running ducts below his planting beds. He wants to circulate the heated air under the soil while sun beats down on his plants year round. I say more overkill, but I’ll keep you posted on this project!