Clerestory definitionally means - "windows above eye level", but in passive solar house design, they are what typical exemplifies what a energy efficient house looks like.
These windows, high up on the wall, usually near the peak of the roof are both the greatest thing when designed and installed correctly (for heating, ventilation and light), and the worst thing when it comes cleaning and operating.
Clerestories placed in the middle of the house, with a split roof allows for sunlight to get into the back of the house. It can help warm what would be a dingy dark corner of the house. In the summer months, it can also be used to extreme advantage for ventilation. Hot air rises, and since these windows are way up at the top, what better place to let all that hot air out?
You do not see clerestories very often in houses. This is because tract houses builders do not spend any time on changing their designs to fit its orientation, and further, the fast easy way to build a roof is with trusses. And clerestories require a very different roof build out. Fortunately, for DIYers the roof system that you use in making a split roof, is far easier to build by yourself.
There are house design constraints you have to deal with too. To have clerestories in the middle of the house, you need to design a supporting wall / series of beams running down the middle of your home. It isn't hard to design a supporting wall such as this, it just takes precedence in the overall house design.
The bane of clerestories is cleaning. You basically need the tallest of ladders, and to move it across the entire house to clean these windows. And although electric motor operated windows are often much more expensive, it will be some of the best money spent. As, what happens most often is that you try to operate the windows with a long stick... and it just doesn't work out well, and so the windows get left open or left closed. When they really are the most important windows in the house as far as air circulation.
When the days are hot, you open the clerestories in the evening and let all the heat flow out. Heat rises, so when you open these windows they act to pull all the heat out, without electricity. Then you close them up in the morning to keep the cool of the night inside.
And when the days are cold, you make sure the blinds are all open and all that warm sunlight streams into your house all day.
If you live in a really hot climate, you can build your house so that your clerestories face a different direction then south. Say you face them north, then you just get nice lighting all year round, and can use the windows to vent out the heat.
