Calculation of solar direct radiation over rugged terrain in west Beijing

The algorithm to calculate actual solar direct radiation over rugged terrain was designed and tested based on digital elevation model(DEM), and the spatial distribution of solar direct radiation in West Beijing was also analyzed. In the algorithm, all of terrain shading, not only from research points themselves, but also from the near terrain were calculated. The result shows that the spatial distribution of solar direct radiation over rugged terrain is a compositive result by many terrain factors. At the altitude of 1275～1475 meter, the mean of solar direct radiation was the least, then with altitude rising or falling down from that altitude on, the mean begins increasing. Below 1075 meter, the difference of means was not remarkable. The maxima of solar direct radiation at the different radiation quantity groups appear constantly rising with the aspect turning from north to south, and they increase with the slope angle enlarging until 10°～15°, then decrease with the slope angle increasing. The largest values of solar direct radiation occurs at the region with slope 10°～15° and aspect -67.5°～67.5°, while the least values are located at the region with slope 35°～40° and aspect 112.5°～247.5°. Generally, the method in this paper could be adopted in calculating solar direct radiation over all kinds of rugged terrain.