Effects of shading and blocking in linear Fresnel reflector field

Abstract

In a linear Fresnel reflector field, parallel rows of reflectors in a collector direct the incident sun rays towards a common linear receiver. Some portion of reflector aperture remains unused due to end effect, inter-row shading and blocking. In addition to these factors, cosine effect, cleanliness factor, reflectivity of reflectors, intercept factor, transmissivity of receiver cover, reflectivity of secondary reflector, absorptivity of absorber tube and thermal losses are other factors that contribute to energy losses and thus affect net energy collection by the heat transfer fluid in the absorber, electricity generation and cost of electricity. Conventionally, the collectors are oriented either along North–South or East–West directions in most cases. However the energy collection, electricity generation and cost of electricity need to be found out for all possible collector-orientations lying between North–South and East–West. This can be used in designing collectors for places where the available land strip does not align with any of these two directions. In this work, explicit analytical expressions for energy losses due to cosine effect, end effect, shading and blocking are derived for any desired time interval as functions of length (L) and width (w) of aperture of reflector-row, spacing between adjacent reflector-rows (p), number of reflector-rows in a collector (n), height of receiver (H), collector-orientation angle (Ω) and location. The expressions for the net energy collected by the working fluid, electricity generated by a collector and the cost of electricity are presented. The effects of L, w, p, n, H, Ω and location on energy losses, net energy collection by fluid, electricity generation and cost of electricity are studied. The minimum cost of electricity is found out for different collector-orientations at various locations and relative comparisons have been made. The corresponding collector parameters, annual energy collection by fluid and the annual electricity generation are also found out.