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Introduction
Solar envelope was first proposed by Ralph L. Knowles as a zoning device. It guarantees solar access to properties by regulating construction limits derived from the sun’s relative motion. Buildings within the solar envelope would not shadow adjacent properties during a predefined period of time, usually critical energy-receiving periods during the year. The solar envelope presents the maximum heights of buildings that do not violate the solar access of any existing buildings during a given period of the year. The solar envelope is a way to assure urban solar access for both energy and life quality.

History
The concept of solar envelope was first developed in 1969. It was developed as a framework for architecture and urban design at the University of Southern California. The goal of that study was to improve the quality of the urban environment by designing buildings that pay attentions to orientations. In 1976, a research was carried out by Ralph L. Knowles to further develop the concept of solar envelope as a public zoning policy. Assisted by planning department of the city of Los Angles, the results of this research were first published in an article called Solar Energy, Building, and the Law. In 1977, to tests the solar envelope concept as a zoning mechanism, Richard D. Berry joined with Knowles to direct undergraduate architecture students in designing buildings within solar envelopes based on a presumption of solar zoning on real urban sites in Los Angles.

Precedents
The first implementation of the idea of solar access was in Greece and the United States. In Acoma, 50 miles west of modern Albuquerque, New Mexico, its rows of house are stepped down to the south. Those houses were built for the high-desert climate. The low angle sun in the winter is welcomed and the high angle summer sun is not wanted. During the winter time, houses do not shadow one another. It is this critical relationship of building-height to shadow-area that gave rise to the solar-envelope concept.