Limitations of the factorized incidence angle modifier: Comparison with experimental efficiency data in a Fresnel solar plant

Accurate modeling of linear Fresnel plants is essential for reliable energy and techno-economic assessments. Optical efficiency is usually estimated using factorized incidence angle modifier (IAM) curves provided by manufacturers, but this simplification introduces significant errors at high incidence angles. This study compared theoretical efficiency derived from IAM data with experimental measurements from a Fresnel plant monitored over several years. Cosine losses induced by factorization and end losses associated with the actual receiver length were analyzed and corrected. The original IAM underestimated efficiency in winter, and the applied corrections improved the seasonal consistency and physical representation of curves. However, the corrected efficiency remained overestimated by 30 % to 40 % because additional operational losses, particularly tracking errors, are not included in the IAM. The corrected IAM increased the annual energy prediction by only 2.5 %, despite monthly improvements of up to 11 % during winter. Since most energy is generated in summer, when the original IAM already provides a reasonable approximation, these corrections did not reduce the annual error. Significant deviations persist under actual operating conditions. Reliable annual performance prediction therefore requires experimental validation over the entire year and the incorporation of additional losses beyond IAM corrections.