Study of Soiling on Pyranometers in Desert Conditions
Abstract
This work presents a study of the degree of soiling on pyranometers in Qatar, a region with high amounts of dust in the atmosphere. The experiment was performed during several months including a dusty season. It consists of using two pyranometers to measure the global horizontal irradiance: one of the pyranometers was considered the reference sensor and was cleaned on a daily basis, and the other pyranometer was used as the testing one, on which different frequencies of cleaning were tested. In order to evaluate the losses in the measurements due to dust/dirt accumulation on the sensor dome, the ratio of the daily average of global horizontal irradiance measured by both sensors was calculated and analysed in function of the time passed after the last cleaning of the testing sensor. From day to day, the changes in this ratio are between 0.3% and 0.5% per day depending on the soiling environment of each season, with increasing changes towards summer. The relative errors (RMSE and bias) of the output of the testing sensor as compared to the reference one were also studied and show a linear increase with the time passed since the last cleaning, for the period under study. It is concluded that a schedule of daily, or every 2 days, cleaning of the pyranometer dome is advisable in order to avoid noticeable errors in the measurements. This study helps to develop an adapted quality assurance programme for sensors installed at remote sites in the desert, including an adapted cleaning schedule which takes into account the local environmental conditions.
Keywords
Solar radiation, Solar measurements, Pyranometers, Soiling, Ghi