In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy, in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices. The key to designing a passive sola. Passive solar technologies use without active mechanical systems (as contrasted to active solar, which uses ). Such technologies convert sunlight into usable heat (in water, air, and thermal. The basis for passive solar building design has been developed from a combination of, (particularly :,, and ),.