Houses like the one we built based on passive solar design are intrinsically more effective to heat and cool because their orientation and shading mechanisms optimise warming sunlight during winter but block out the hot summer sun.
They are a 'passive means' of making use of the difference between the sun paths during the year. With minimal input from the user, they greatly reduce artificial heating and cooling requirements compared to an normal house. Of all the ways to make an house energy-efficient this method is the most effective cost-neutral method.
However, there are disadvantages to a purely passive system:
1) They are based on the average expected temperature and sunlight through the year and without additional intervention by the occupants do not cope with aberrant weather conditions or year-to-year variations.
2) The fixed length of the eaves reduce the potential to introduce more sunlight on colder than average days or block additional sunlight on hotter than average days.
3) Most conventional window schedules result in the top portion of the window remaining in shade most of the day. This is particularly an energy liability during winter. The alternative solution are to use skillion roofs or uptilt eaves. Either are problematic of design either when locating solar system on the roof or designing gutter systems.
The alternative requires a bit more intervention by the owner but have the potential to control the comfort conditions of the house...
Unlike passive solar design, all north eaves are abandoned. Instead a flexible system of shading is introduced to the house. This may involve pivoting awnings that can fully retract, adjustable shade flaps (as decribed in Derek Wrigley's) book , a pergola structure with horizontal retractable shadecloth or an automated louvred system.
The shades can be left in a appropriate position depending on the time of year. However, on occasions when this is not adequate they can be manually adjusted to improve the comfort in the home on any given day.
The main drawback to this system is the added intervention of the occupants and the requirement of a robust enough system that allows occasional adjustment. There are also some issues with allowing excessive rainfall on the walling structure and windows.
However, it provides an elegant method of completely controlling sunshine depending on the weather at the time and possibly requires less window area than a pure passive design.