This paper presents the results of study on the effect of dust fouling on the transmittance of PV module glass cover. The study included the effect of dust fouling on overall plane glass transmittance, spectral transmittance of anti-reflective coated glass and characterization of the physical and chemical properties of dust particles. Also, micro-adhesion forces of dust particles on flat glass substrates are included. The results indicated a 20% reduction in glass transmittance and a 5 g/m(2) of dust accumulation on the glass cover of PV modules tilted at 26 degrees (Lat of Dhahran) and exposed for 45 days. The anti-reflective coated glass exhibited less reduction in transmittance compared to non-coated plane glass. The adhesion forces of particles on flat surfaces increased with increase in particle size due to increase in contact area between the particles and the surface. At high humidity level there is an increase in the vertical adhesion due to the generated capillary forces between dust particles and glass surface. (C) 2014 Elsevier Ltd. All rights reserved.