This model computes the incidence angle modifier coefficients based on the Sandia method.
Figure 32. Comparison of Custom IAM Profile with Sandia Polynomial, Showing Oscillation for Incidence Angles Lower than 34°
To avoid this artifact, the polynomial is clipped to force the IAM to unity, as follows:
King, D. L., Kratochvil, J.A., Boyson, W.L., Measuring Solar Spectral and Angle-of-Incidence Effects on Photovoltaic Modules and Solar Irradiance Sensors. Sandia National Laboratories, Albuquerque, NM, September 1997.