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International audienceSolar irradiance and ancillary meteorological data is frequently measured by automatic weather stations for use within solar resource assessment for solar power plants. High accuracy measurement data are required for comparison and adjustment of satellite data and derivation of the expectable long-term mean value of the solar resource. Thus, utmost diligence must be taken during the measurement process and data evaluation to achieve data quality required for project financing. The combination of automatic data screening and manual flagging by an expert in at least daily frequency in close collaboration with a local station operator is the most recognizedway to detect impacts on measurement data and paves the way for post-correcting data treatment where necessary and reasonable. This is the preferred and recommended procedure, resulting in highestdata quality. The presented work is also understood as a basis for ongoing development and discussion among the corresponding expert group about screening of irradiance and ancillary meteorological data and its corresponding flagging. A common understanding and wide conformity about the screening process and flagging of data would be aspired

Solar resource assessment becomes more and more a very important factor for planners of Photovoltaic (PV) and Concentrated Solar Power (CSP) plants nowadays. Choice between nearby locations can make the difference if a plant is profitable or not, especially in a versatile climatic region with complex topography as it can be found in Pakistan. Nevertheless, Pakistan's geographic location and climate offers a very high potential for solar energy applications. The solar resource assessment study presented in this article describes the approach and set-up required by the World Bank's Energy Sector Management Assistance Program (ESMAP) 1 : The presented project described, aims on creating a validated solar atlas for Pakistan based on a combination of satellite data and ground measurements to support country-driven efforts to improve renewable energy resource awareness and exploitation. There are several country-specific, ESMAP-funded projects conducted by the World Bank Group (WBG) that cover comprehensive mapping and geospatial planning, including ground-based data collection. The solar resource estimation of Pakistan was one of the first projects to be approved within the program and leads the way for the solar assessments in other countries. The final and validated dataset ultimately will be published in the International Renewable Energy Agencies' (IRENA) global atlas for renewable energy 2 .

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Because of forward scattered radiation in the atmosphere, the circumsolar region closely surrounding the solar disk looks very bright. The radiation coming from this region, the circumsolar radiation, is in large part included in direct normal irradiance (DNI) measurements at the usual 2.5° pyrheliometer opening half angle, but only partially intercepted by the receivers of focusing solar collectors. Therefore, circumsolar radiation measurements are recommended to be included in solar resource assessment. Circumsolar radiation can be characterized using the radial angular distribution of the radiance around the center of the sun-the so-called sunshape. Several sunshape measurement methods have been developed recently. Most approaches use cameras or pyrheliometers with different apertures which require daily maintenance. The Rotating Shadowband Irradiometer (RSI) based method discussed here uses a conventional RSI without any hardware modification to enable sunshape measurements without affecting the RSI's fundamental function as a DNI measurement device. Thus, it allows to measure circumsolar radiation without any additional hardware and with significantly lower maintenance requirements. The presented RSI-based sunshape measurement algorithm has been validated with four RSIs and more than two years of data. After a short description of the method to derive the circumsolar contribution, the validation results are shown. Then the required calibration method is discussed, followed by the results from the measurement campaigns at four sites in Spain, India and Morocco. It was found that no individual calibration is required per instrument and the algorithm can be used for automatic data processing so that common RSI stations can measure the sunshape with comparably low extra effort. Furthermore, we explain how to derive sunshapes from the RSI measurements.