Passive solar design takes advantage of both summer and winter sun angles for free cooling in the summer and heating in the winter. How cool (or hot) is that? Passive solar gain,... it's free and completley pollution free! It can be as simple as paying attention to the orientation of the house, placement of windows, the length of the overhang of your roof, and the kind of floor and walls chosen. One way of thinking about your house when it comes to the sunshine that falls upon it everday is like that of a battery. How efficient is your house as a battery, that is, how does it charge and discharge with energy from the sun? A house that is properly oriented with enough windows facing south will recieve a large amount of energy on a sunny day in the middle of winter. If this house has floors and walls which can recieve this energy and store it for later release after the sun goes down will utilize this energy during the day and night. The battery portion of the house are the materials and mass that is contained within it's walls that have the capabilities of storing the solar radiation that comes throught the windows. Conventional materials such as gypsum wall board for walls and wood floors make for poor storage of solar energy. They heat up too quickly and conversely give up it's heat too fast. Dark colors of stone, cement, tile, adobe brick, and masonary make for a good battery of solar radiation, or what is otherwise know as "Thermal Mass". The illustration below shows my Pasive Solar Energy design at La Boca Vista.

The adobe wall, stone wall and the dyed concrete slab are my thermal mass and will absorb solar radiation on sunny days in the winter and release their heat durning the nighttime hours. Thermal mass acts to control temperature swings from night to day. Conventional construction without the attention to passive solar design can over-heat durning the summer days and require mechanical cooling and cool down during the night in the winter requiring mechanical heating. Larger roof overhangs will block the sun from entering the house during the summer when the sun is high in the sky but allows it to enter the windows and warm the thermal mass when the sun's angle is low in the winter time. Obviously, good insulation is a paramount component to good passive solar design.