Outdoor soiling microscope for measuring particle deposition and resuspension

The rate of soiling of photovoltaic modules depends on environmental parameters such as aerosol concentration, humidity and wind speed. Previously we found low correlations between daily averages of these values and the daily soiling rate of a PV system. In this study we aimed to achieve stronger correlations by increasing the measurement frequency, with a simple device able to quantify soiling in outdoor conditions in real time. The so-called outdoor soiling microscope developed could measure the deposit and removal of individual dust particles larger than 10 mu m(2) every few seconds, and could detect the onset and disappearance of condensation. In an initial trial the device revealed qualitative relations between the parameters not seen with 24-h data. However most linear correlation coefficients remained low, suggesting the need for a more sophisticated model of outdoor soiling. (C) 2016 Elsevier Ltd. All rights reserved.