Towards a verified DNI map for South Africa

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

In this project seven high accuracy DNI solar measurement stations, including meteorological equipment, were installed throughout South Africa. After at least one year of operation data from these stations as well as additional DNI data were used to update a satellite derived DNI and GHI map of South Africa. This paper focusses on the learning experience of installing and maintaining a network of DNI measurement stations. Prior to this project, the operational stations with DNI data available were located at four academic institutions at three different cities as well as nine stations operated by the national utility Eskom. Three solar developers have indicated their willingness to share data from their sites for this project. The paper discusses the methodology that was followed to select the locations of the seven stations. The new stations were to be geographically well distributed and any duplication with existing stations was to be avoided. On-site staff are required to clean the solar instruments at each station two to three times per week. An electronic log of the cleaning events enable remote monitoring of the cleaning frequency. All stations are visited every two to three months for routine maintenance and to supply the on-site staff with the required consumables e.g. cleaning cloths and desiccant and to perform ad-hoc training of the on-site staff. A satellite derived DNI and GHI map of South Africa will be provided by GeoModel Solar, the proprietors of the SolarGIS database. This map will be based on 20 years of DNI data and have a spatial resolution of 250m x 250m. The map will be updated by GeoModel based on the DNI and GHI measurements at the various locations. The updated map will be made public in GIS as well as KML (Google Earth) format. DNI and GHI poster maps of SA will also be provided. All data from the seven stations will be made available for free on a public website.