One of the largest sources of energy flow in many buildings is the sun. We are used to thinking of the sun in terms of providing light, which with proper design can avoid the need for artificial lighting in buildings for the majority of the year. In addition to light, solar heat gain through windows typically dominates the cooling demands of commercial buildings and without adequate control can lead to reliance on air conditioning. On the other hand, the same energy can also be harvested for both space and water heating in carefully designed buildings. .
