The amount of radiation received by the solar cells inside a photovoltaic (PV) module is lower than that arriving at the module surface, owing to reflection and soiling of the module surface. To develop high efficiency PV systems, these effects must be addressed. In this study, a silica-based layer with anti reflection and anti-soiling properties was coated onto the surface of a Cu(In, Ga)Se-2 PV module and the effects were assessed. The coating method was simple, allowing it to be applied to already installed PV modules. The cleaning and coating treatments were carried out on December 25, 2014, and the arrays were exposed outdoors for 7 months to investigate the effects of the treatment. The output of the array that received the coating was 3.2% greater than that of an uncoated array. It was also found that the coating reduced the reflection of the light entering from a high incident angle. (C) 2016 Elsevier Ltd. All rights reserved.