The Availability of Irradiation Data, April 2004
Report IEA-PVPS T2-04:2004

Abstract:
Solar radiation at ground level is a necessary input for performances modelling and sizing of PV systems. This document reports on the needs for data and discusses the problems faced by users when accessing data. It then presents some technological solutions. Users generally need values of global daily or hourly irradiation with a spatial resolution of approximately 10 km. Relative errors (RMSE) of daily irradiation should be less than 20 %. Spatial coverage (continent) and temporal coverage are of importance. The data must be available conveniently at low cost. Several regional solar atlases have been made by interpolation of ground measurements, taking into account the local variation of climate. Satellite data produce irradiation maps offering a regular sampling in space and a wide geographical coverage. Time-series are also obtained by weather forecast models. Digital atlases have been created as integrated information system. These comprise a database and software to exploit it. The co-operative systems are connected with other servers that provide necessary weather data to compute solar radiation quantities. 
This survey of solar databases showed that in a general case, there is a discrepancy between users needs and available databases. This conclusion supports the efforts made in integrating information systems and co-operative systems to overcome the technical limits of measurements by using the information and communication technologies.

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