Putting a shade tree on the south side of the house helps keep the house cool in the summer, if it loses it’s leaves in the winter then it will allow light and warmth into your house in the winter.
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For design consideration house facing south is good for proper solar gain, using walls , overheads, insulaiton to prevent heat loss etc.

Since passive sola designs help to maintain temperatures, heat water for other purposes, provide natural ventilation you will require no other electrical energy thus saving your energy and money. The design is effective and prevents losses.
You should visit solar energy sites and also engineering sites for the design. http://en.wikipedia.org/wiki/Passive_solar
References :
http://en.wikipedia.org/wiki/Passive_solar

Since this type of heat capture can create problems with over heating - especially in summer - the design requires ways to prevent solar heating when not desired. For example, a sun room with an overhang shade that allows the winter sun to come deep into the living space while in the summer the sun is blocked by the shade.

Also since the heat from the sun varies so much (like night and day!) often thermal storage is used such as rock beds or water walls to capture and store the solar heat (or night time cool) so that the living space temperature is more constant. This is where the entire house design becomes to involved even if the solar is really only one aspect, it is still term passive solar design”
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Passive solar design is about allowing your home to heat or cool on its own, naturally. This is done through energy efficient materials, airtight construction and adoption of solar and wind energy for off-grid power.
References :
http://HomeMadeEnergy.pinurl.com