The sun is the most powerful thing in our world; it gives us light, warmth and the seasons; using it to warm our buildings and also to help cool them is almost a no-brainer.
Look at any subdivision; the houses are built in relation to the roads, curving or not, with no regard to the direction of the sun.
Missing out on the heat of the sun to warm and cool our highly insulated, or earth sheltered dwellings is a crime and a sad loss.
A well built and designed passive solar home can be primarily heated by the warmth of the sun, even in the depths of winter.
Most building regulations in British Columbia insist on having some kind of electric (on the grid), forced air furnace using propane, natural gas or heating oil as the primary source of heat in any home.
Sadly, this means that you have one system that is almost redundant, and one that never shuts off.
The warmth of the sun angling in through windows in the winter allows the mass built in to the floor of a passive solar home to heat up to a comfortable temperature during the day, to be released over the night time hours back into the house.
A well designed and earth sheltered home can be comfortable at all times, with some prior planning.
The book, The Passive Solar House by James Kachadorian ISBN 0-930031-97-0, shows in great detail the patented method of building a circulating heating system in the floor; the method of building this type of floor can take time and money initially, but will pay off with really low heating costs over time.
The general idea of a passive solar home is that there is some way of storing the heat from the sun, which can then be released slowly during the night.
Thermal shutters or heavy curtains prevent heat loss through windows.
Trombe walls have been used to retain heat, but they're incredibly ugly.
Lay it down, so you can walk on it, and it works just the same way.
Tubes or air pockets that the air can circulate through mean that warm air will exchange with cold, and start to move on its own. This convection makes it much more comfortable.