Fast clear-sky solar irradiation computation for very large digital elevation models

This paper presents a fast algorithm to compute the global clear-sky irradiation, appropriate for extended high-resolution Digital Elevation Models (DEMs). The latest equations published in the European Solar Radiation Atlas (ESRA) have been used as a starting point for the proposed model and solved using a numerical method. A new calculation reordering has been performed to (1) substantially diminish the computational requirements, and (2) to reduce dependence on both, the DEM size and the simulated period, i.e., the period during which the irradiation is calculated. All relevant parameters related to shadowing, atmospheric, and climatological factors have been considered. The computational results demonstrate that the obtained implementation is faster by many orders of magnitude than all existing advanced irradiation models while maintaining accuracy. Although this paper focuses on the clear-sky irradiation, the developed software also computes the global irradiation applying a filter that considers the clear-sky index. (c) 2008 Elsevier B.V. All rights reserved.