Technical guide to Set Up a Spectral Solar Direct Normal Irradiance Permanent Station: Study Area- Hannover, Germany

The spectral Direct Normal Irradiance (SDNI) is a basic radiometric quantity from which many other quantities can be derived. It provides not only information about the spectral and distribution of the direct solar radiation reaching a particular location. Accurate knowledge about the spectral direct irradiance shall enable us to gain new scientific results in the: determination of cloud effects, calculation of power yield of solar cells for electricity providers, derivation of aerosol distributions and their impact on the radiation field, determining the UV spectral irradiance for medical applications and in the improvement of our understanding of the radiative transfer in a changing climate. Nevertheless, at present, DNI measurements are not available in many instances. Therefore, the main objectives of this project are the setup, characterization, the calibration, the validation and the application of an operational measurement for the (SDNI) at the Institute of Meteorology and Climatology (IMUK) at the Leibniz University Hannover. With sampling times of less than one second even rapid changes of the SDNI can be recorded with a spectral resolution of about 1 nm in the wavelength range from 300 -800 nm (from UV to NIR). For this purpose three different tracking units were used to precisely track the sun location in the sky and finally based on the measurements and tracking strategy best instrument was selected. Finally the best tracking unit was used and the set-up was tested in the institute of Meteorology and climathology of Hannover (Longitude 52.37◦, Latitude 9.73◦). The comparison between the integrated value of the measurements and Pyranometer observations on the same platform, and during a complete day presented in this paper. It is worth to mention that the technique for setting up such a measurement station is very important as a basis for remote sensing research focused on the solar energy and meteorology applications.