where gOPT is the optical efficiency for DNI radiation, I is the DNI
radiation, A is the collector aperture, h is the incident angle, Kh is
the incident angle modifier (IAM), jh is the end effect correction,
gsh,h is the lateral shading correction, Fe is the soiling factor (mirror
cleanliness), a1 and a2 are coefficients related to heat convection
and heat radiation, Tf is the mean loop heat transfer fluid (HTF) temperature,
Ta is ambient temperature.