ABSTRACT
This chapter describes instruments that use a sampling algorithm similar to that first developed by Edward Kern that use a commercial photodiode pyranometer, a commercial data-logger, and a band driven to pass over the pyranometer on command. Efforts to provide a more economical approach for producing the some solar irradiance components have been ongoing since 1982 when the rotating shadowband radiometer (RSR) was introduced. Systematic errors in diffuse horizontal irradiance (DHI) occur because the shadowband obscures more than just the Sun when it passes in front of the pyranometer. Tests show that the adjustments to the RSR data significantly improve the comparison to reference measurements. The multifilter version of the RSR was developed in the early 1990s. The spectral correction is still a problem even though the thermopile responds to all solar wavelengths. Without some method for removing the DHI bias, the uncertainty in the DNI values will remain large.
