This paper presents generalized results regarding the effect of surface orientation on annual incident solar radiation for locations in the United States. A surface-orientation factor (SOF) is defined, equal to Iann/Iann,max, the ratio of annual incident solar radiation for a particular orientation to annual incident solar radiation for an optimally oriented surface.
SOF contour plots can be used to conveniently indicate the effects of surface orientation over a range of tilt and azimuth angles (from horizontal to vertical and from south to east/west). Correlations, presented in this paper, can be used to calculate SOF’s based on latitude and a climate factor, w. Regional SOF contour plots indicate surface orientation effects by geographic region with boundaries determined according to latitude-w values. Effects of morning/afternoon cloudiness and snow cover are also addressed.