Revisiting the Figure of Merit of Concentrated Solar Power Receivers

Abstract: The figure of merit (FOM) is a widely used metric to characterize the performance of concentrated solar power (CSP) receivers by comparing the amount of solar thermal energy retained by the receiver to the incident concentrated solar radiation. However, the FOM is a strong function of the concentration factor and receiver temperature, thus direct comparison of FOM values measured under disparate operating conditions is inappropriate. To remedy this problem, the present study proposes a new metric called the receiver effectiveness calculated by normalizing the actual FOM with its theoretical maximum. The receiver effectiveness can be employed for comparing receiver performances regardless of their operating conditions, and can be treated as more-like the second law efficiency of thermodynamics. In addition, a theoretical limit of the CSP plant efficiency is also examined by combining the maximum FOM and the Carnot efficiency for different concentration factors and receiver temperatures. The calculated maximum CSP plant efficiency clearly indicate that optimizing FOM does not always lead to a better CSP plant performance. Along with the FOM, the proposed receiver effectiveness and maximum CSP system efficiency should be considered as complementary metrics to evaluate the performance of the CSP system.