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Solar energy is increasingly being used for a large number of human activities. Determination of shadow or illuminated zones, and, subsequently, the quantity of insolation are important inputs to these applications. Sun position model and topographic data form the basic input for shadow determination. A variety of sun position models and topographic data, with varying degrees of accuracies, are being used. This paper presents a methodology for determining the compatibility between any particular sun position model and a topographic data, thus leading to an optimal combination in their use. As the interaction of sun rays and 3-D terrain results in shadow, the compatibility is analyzed analytically and graphically by modeling error propagation in determination of shadow coordinates using 3-D topographic data and sun position algorithms. Results are shown for two distant locations.