Solar energy is certainly one of the oldest home heating methods, being used since people first selected caves on the sunny side of mountains. And, since the energy source is free and inexhaustible, modern home design should also include consideration of beneficial and cost-effective solar effects.
At a minimum, the modern home designer should consider orientation, use of glass, sun spaces, deciduous trees, and glazing technologies to take full advantage of this source. It may also be economical to retrofit existing homes to use solar energy. Many systems will provide space heating, domestic hot water, and swimming pool heating.
Most solar systems require some type of "back-up" heating system to provide for long periods of overcast weather.