Development of a sky radiance distribution model for all sky conditions

In effective use of solar energy and calculation of the heat load of buildings for energy conservation, the actualstate meteorological data are indispensable. It is necessary to propose a sky radiance distribution model, which can correspond to all sky conditions from clear sky to overcast sky. To compose such a model, there should be some index to presume the sky radiance distribution according to the sky condition. In this paper, normalized global irradiance and cloudless index are defined on the basis of measurements as the indices to classify the sky radiance distributions. The relationship between both indices and sky radiance distributions was examined. And an equation of sky radiance distribution for all sky conditions was derived.