Abstract Dust accumulation on glass plates with different tilt angles and associated reductions in solar transmittance have been experimentally investigated over a period of 1 year under the climate conditions of the Minia region, middle of Egypt. The glass plates were never cleaned during the experiment duration of 1 month to allow dust to accumulate. The results showed that the fractional reduction in glass normal transmittance depends strongly on dust deposition in conjunction with plate tilt angle, as well as on the exposure period and site climate conditions. Based on the data obtained, an empirical correlation, accurate to ±6%, is developed which allows for the calculation of the reduction in glass transmittance for a given tilt angle after a number of days of exposure to the atmosphere. For design purposes and in the absence of any specific data, the literature comparisons encourage the use of the correlation for other neighboring regions along the desert belt that extends from the Atlantic Ocean to the Persian Gulf. For moderately dusty places, weekly cleaning of the glass covers of solar panels is strictly recommended as part of the maintenance routine, but equipment should be cleaned immediately after a dust storm to retain nominal operating efficiency.