THE EFFECT OF DUST ACCUMULATION ON THE PERFORMANCE OF EVACUATED TUBE COLLECTIONS

The aim of this article is to find the extent of performance decline of evacuated tube collectors due to dust accumulation over periods extending from 1 month to a whole year, and to get some quantitative information on the seasonal variation of dust accumulation. Two collector blocks, blocks A and F, were used in this investigation with each block consisting of 168 collector panels connected together in a series/parallel arrangement. Each panel contains 1.75 m2 of absorber area. It was found that the monthly percentage decline in the transmissivity and relative daily heat collected by a block cleaned only at the beginning of each month appears to be seasonal in nature with high percentage decline values experienced during summer months. It was also found that the daily amount of heat collected by a dusty block could drop down to 60-70% of its initial value if it is left without cleaning for a whole year.