Improvement of Measurement of Diffuse Solar Radiation

Summary

To improve the accuracy of diffuse solar radiation data gained by ring shaded pyranometers, a new formula correcting for losses caused by the Hamburg ring has been derived. The formula has been validated by data sets of different time periods and from different pyranometer types, the latter with slightly modified constants. The correlation coefficients are always close to 0.80. For further improving the correction formula, the influence of the sky radiance distribution is to be taken into account. The so-called sky scanner was equipped for broad band measurements,and an appropriate data acquisition system was designed which uses a microprocessor to sample and store up to 1440 mean radiance values of the sky hemisphere. The reference data of diffuse solar radiation are delivered by a sun-following shade disk device with a shaded angle of 9.6°. A compact reference shade disk instrument has been built to be used for comparison with different kinds of shade ring devices used in the national networks in order to validate the transfered correction formula.