A novel approach for incidence angle modifier calculation of arbitrarily oriented linear Fresnel collectors: Theory, simulations and case studies

The easiest possibility to assess the combined opto-energy efficiency of Linear Fresnel Collectors (LFC) is to refer to the Incidence Angle Modifier (IAM) concept: for this kind of solar collector, IAM calculation is often performed according to the so-called factorization method. Unfortunately, the factored IAM fails in providing reliable results of the real LFC yield. In this investigation, hourly 3D ray tracing simulations have been carried out on two case-study plants located in Morocco and Italy: reference ray tracing calculated IAMs have been used to develop simple correlations for inferring the instantaneous IAM of arbitrarily aligned LFCs. Instantaneous IAM formulas resulted to be able to provide yield predictions with a Root Mean Square Error equal to 5.57 % of the yearly average IAM, much lower than the factorization method (19.42 %). Subsequently, a reduced 3-day dataset of ray tracing values has been considered to calibrate the regression constants, resulting in still high accuracy for orientations not exceeding 30°. Finally, the analysis of available power at the receiver allowed to further assess the robustness of the proposed approach regardless of the plant orientation angles.