Rethinking Satellite Based Solar Irradiance Modelling

Accurate solar irradiance data are not only of particular importance for the assessment of the radiative forcing of the climate system, but also absolutely necessary for an efficient planning and operation of solar energy systems. The recently started European project Heliosat-3 will supply high quality solar radiation data by taking advantage of the enhanced capabilities of the new Meteosat Second Generation (MSG) satellites. This goal will be achieved by the development and establishment of a new type of calculation scheme. This new type will be based on radiative transfer models (RTM) using the information of atmospheric parameters retrieved from the MSG satellite (clouds, ozone, water vapour) and the ERS-2/ENVISAT satellites (aerosols). This paper focuses on the description of the clear sky module of the new scheme, especially on the integrated use of a radiative transfer model. The linkage of the clear sky module with the cloud module is also briefly described in order to point out the benefits of the integrated RTM use for the all sky situations. The integrated use of a RTM within the new SOlar Irradiance Scheme SOLIS is applied by introducing a new fitting function called the modified Lambert-Beer (MLB) relation. Consequently, the modified Lambert-Beer relation and its role for an integrated RTM use are discussed. Comparison of the calculated clear sky irradiances with ground based measurements and the current clear sky module demonstrates the advantages and benefits of SOLIS. For example, spectral resolved data as well as the possibility to use enhanced information of atmospheric parameters. Since SOLIS provides spectral resolved irradiance data, it can be used for different applications. Beside improved information for the planning of solar energy systems, the calculation of photosynthetic active radiation, UV-index and Illuminance is possible.