Irradiance Rotating Shadowband Radiometer (RSR)
Irradiance's Rotating Shadow Band Radiometer (RSR) uses a solar cell pyranometer (manufactured by LI-COR to measure global and diffuse irradiance and calculates direct normal beam irradiance. The RSR has a shadow band that rotates once a minute to block the sun from directly shining on the pyranometer. The pyranometer is measuring global irradiance before and after the shadow band starts its rotation to block the sun. The diffuse value is the minimum value that is obtained when the band sweeps in front of the sun. Direct irradiance on a horizontal surface is then calculated by subtracting the diffuse from the global irradiance. The direct normal beam irradiance is then obtained by projecting the direct horizontal irradiance onto the normal in the direction of the angle of incidence.
Algorithms are used to correct the spectral dependence of the LI-COR pyranometer. For more information see our publications on the corrections made to the Irradiance RSR or the Irradiance Website.
Yankee Environmental Systems manufactures a Rotating Shadowband Radiometer (RSR) that is similar to an RSR in principle.
The accuracy of the RSRs are limited by the spectral characteristics of their sensors. Currently solar cell based sensors are required because of their fast time response when the shadowband is swept between the sensor and the sun. While the responsivity of solar cell pyranometers to direct normal beam radiation varies by several percent over the day, the responsivity to diffuse radiation varies by approximately 30% from cloudy to clear periods. The variation in diffuse responsivity leads to systematic errors in the global and/or beam irradiance measurements. The Irradiance RSR includes algorithms to correct for this spectral dependence. (See Diffuse Responsivity of Solar Cell Based Pyranometers.)
© 2013, UO Solar Radiation Monitoring Laboratory.
Last revised: June 25, 2013.
Home page URL: solardat.uoregon.edu