Effect of dust accumulation on solar transmittance through glass covers ofplate-type collectors

Dust accumulation on glass plates with different tilt angles and associated reductions in solar transmittance have been experimentally investigated ov er a period of 1 year under the climate conditions of the Minia region, mid dle of Egypt. The glass plates were never cleaned during the experiment dur ation of 1 month to allow dust to accumulate. The results showed that the f ractional 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 empiric al correlation, accurate to +/-6%, is developed which allows for the calcul ation 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 du sty places, weekly cleaning of the glass covers of solar panels is strictly recommended as part of the maintenance routine, but equipment should be cl eaned immediately after a dust storm to retain nominal operating efficiency . (C) 2000 Elsevier Science Ltd. All rights reserved.