Effect of dust on the transparent cover of solar collectors

Research and development in photovoltaic (PV) systems has usually been concentrated in studies on radiation availability, efficient operating strategies, design and sizing of these systems. On the other hand, the influence of dust on the performance of PV systems has not been given much attention. The work described here contributes considerably to overcome this deficit. To validate that concept, we have developed an experimental set up involving 100 glass samples with different tilt (β) and azimuth angles (γ). The transmittance of the glass was evaluated at regular intervals over a period of about seven months and after every thunderstorm in the surrounding area. Although it is only a short term view, the preliminary results indicate that the reduction in glass normal transmittance depends strongly on the dust deposition density in conjunction with plate tilt angle, as well as on the orientation of the surface with respect to the dominant wind direction. With this consideration, one sees that as the dust deposition density goes from 15.84 g/m2 (for glass sample installed at a tilt angle of 0o) to 4.48 g/m2 (for glass sample installed at a tilt angle of 90o and oriented with 135o deviation from north), the corresponding transmittance diminishes by approximately 52.54-12.38%, respectively. The evolutions of the output power variation with increasing cell pollution were also examined. It has been found that the slope of the best straight line passing through the data points of the solar cell installed at a 45o angle facing south suggests a decrease in the output power of about 17.4% per month