Cost-exergy optimisation of linear Fresnel reflectors

► A method is developed to optimise the non equidistant spacing arrangement of mirror elements in a linear Fresnel reflector. ► An optimum is determined by minimising costs whilst maximising exergy and operational hours. ► The new method provides improved performance over an existing design method prominent in the literature. ► The ideal operating temperature is also determined. This paper presents a new method for the optimisation of the mirror element spacing arrangement and operating temperature of linear Fresnel reflectors (LFR). The specific objective is to maximise available power output (i.e. exergy) and operational hours whilst minimising cost. The method is described in detail and compared to an existing design method prominent in the literature. Results are given in terms of the exergy per total mirror area (W/m2) and cost per exergy (US $/W). The new method is applied principally to the optimisation of an LFR in Gujarat, India, for which cost data have been gathered. It is recommended to use a spacing arrangement such that the onset of shadowing among mirror elements occurs at a transversal angle of 45°. This results in a cost per exergy of 2.3$/W. Compared to the existing design approach, the exergy averaged over the year is increased by 9% to 50W/m2 and an additional 122h of operation per year are predicted. The ideal operating temperature at the surface of the absorber tubes is found to be 300°C. It is concluded that the new method is an improvement over existing techniques and a significant tool for any future design work on LFR systems.