Solar should not be seen as a alternative to gas or electricity, but rather a supplement. Solar cannot totally replace the need for gas or electric heating as there are sometimes days when there is little sunlight. When averaged over a year, a correctly sized solar system can provide 60%-70% of a household? hot water needs. Providing more than this is unadvisable, as too much heat will be produced in the summer. The hot water system system can easily be automated so hot water is guaranteed regardless of sunlight levels.