Solar irradiation graphs

A common rule of thumb in solar applications is that maximum solar input on a flat collector comes when facing towards the equator at a slope equal to the locations latitude. Strict adherence to this rule leads frequently to layouts of questionable aesthetics, with the solar element detached from the geometry of the building in the name of optimum performance. An analytical study of solar irradiation on a plane as a function of its orientation and slope has shown that this rule can be disregarded to certain extends at a negligible energy shortfall. This is illustrated by a set of graphs, which show monthly radiation values for any orientation & slope in Athens. The set consists of 12 monthly graphs, one based on annual sums and one for the heating season, presenting the seasonal variations of solar intensity at various directions. The graphs can also be an easy tool for estimating the solar load imposed on vertical building surfaces at random orientation.