A methodology for predicting global shortwave radiation into any slope based on the ratio of the incoming shortwave on to the horizontal and the exoatmospheric beam is described. The model is based on individual calculations of direct and diffuse components, enabling its application under a wide range of sky conditions. An algorithm accounting for the effect of topographic shading is also included and this enables accurate estimations of spatially distributed global shortwave radiation in steep sided terrain. The model in then applied to the summer and winter solstices at Monachyle catchment at Balquhidder, Scotland. Although incident radiation is strongly affected by slope angle and aspect, the influence of shading is seasonal and more dependent upon overall catchment orientation. In winter, areas of the catchment receive only diffuse radiation, emphasizing the importance of modelling radiation components individually.