One simple, obvious use of the sun is to light and heat our buildings. Residential and commercial buildings account for more than one-third of U.S. energy use.[1] If properly designed, buildings can capture the sun's heat in the winter and minimize it in the summer, while using daylight year-round. Buildings designed in such a way utilize passive solar energy—a resource that can be tapped without mechanical means to help heat, cool, or light a building. Simple design features such as properly orienting a house toward the south, putting most windows on the south side of the building, skylights, awnings, and shade trees are all techniques for exploiting passive solar energy. Buildings constructed with the sun in mind can be comfortable and beautiful places to live and work.