The European Community Cloudless Sky Radiance Model. An Evaluation by Means of the Skyscan'834 Data Set

Having in mind the high complexity of the sky radiance distribution, the Commission of the European Communities, in the frame of the Solar Energy R&D in the European Community Programme, developed among other related fields of research a clear sky radiance model. This model, the so-called EC-Model, was intended for the estimation of the diffuse irradiance falling on an inclined surface by integration of the sky radiance field. It represents a progress development over its predecessor, the Berlin model, and takes into account all the scientific knowledge about this topic, lying heavily on the principles of the Liebelt formulation and the work of Steven and Unsworth on the observed relative radiance distribution. The European Solar Radiation Atlas was in part prepared by the adoption of the EC-Model and could not take into account Valko's new results about sky radiance distributions, because of time coincidence and that only previous results were ready at the time it was published. In this work, we focus on the EC-Model behaviour, against experimental sky radiance data from Toronto, Canada. The SKYSCAN'834 Data Set is a well-known database, which we have used in order to investigate the EC-Model behaviour both under its original formulation (the one that has been used in the development of the Atlas) and under the modified version suggested by Valko's results. Even though we are considering data from outside Europe, the results of this test let us establish the model limitations and the modifications that should be done to it.