PRELIMINARY ANALYSIS OF THERMAL OFFSET IN PYRANOMETERS UNDER DIFFERENT ATMOSPHERIC CONDITIONS
DOI:
https://doi.org/10.59627/cbens.2010.1512Keywords:
Solar Radiation, Radiometry, Pyranometer, Thermal OffsetAbstract
Solar global irradiation observations at Earth's surface generally are less (10–25 Wm−2) than those calculated by radiative-transfer models. Measurements with pyranometers demonstrate that the night thermal offset is present and considerably larger during daytime clear sky measurements and is responsible for the underestimation of clear sky solar global, as well as diffuse irradiance. This is caused by temperature gradients in the instrument that create radiative exchanges between the domes and the sensor surface. These offset errors are proportional to the difference between the fourth power of the dome and detector temperatures. This paper presents preliminary results of the pyranometers thermal offset response. Relationships between the thermal offset and net infrared irradiation are established using nighttime data from Kipp & Zonen Pyrgeometer CNR1 model. The thermal offsett is also measured over a variety of atmospheric conditions, ranging from clear and dry to heavy overcast and wet in two distinct sites All measurements took place in June and December 2009 in Solar Radiation Research Laboratory (SRRL) of the National Renewable Energy (NREL) in Golden, CO and in Solar Energy Laboratory (Labsol) of the Universidade Federal do Rio Grande do Sul, RS.
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