Dew and Frost Deposition on Pyranometers

Abstract

The formation of dew or frost on the outer glass hemisphere of pyranometers was found to cause erroneous values of incident hemispheric solar radiation. An air flow system was designed to continually ventilate the instrument and thereby prevent moisture formation on the outer hemisphere. Comparison of instantaneous early morning readings from ventilated and non-ventilated pyranometers indicate that substantial errors can occur because of dew or frost. Since the moisture from dew or frost naturally evaporates by mid-morning, daily totals of solar energy are not likely to be significantly affected on clear days.