# pvlib.pvsystem.physicaliam¶

pvlib.pvsystem.physicaliam(aoi, n=1.526, K=4.0, L=0.002)[source]

Determine the incidence angle modifier using refractive index, extinction coefficient, and glazing thickness.

physicaliam calculates the incidence angle modifier as described in De Soto et al. “Improvement and validation of a model for photovoltaic array performance”, section 3. The calculation is based on a physical model of absorbtion and transmission through a cover.

Note: The authors of this function believe that eqn. 14 in [1] is incorrect. This function uses the following equation in its place: theta_r = arcsin(1/n * sin(aoi))

Parameters
• aoi (numeric) – The angle of incidence between the module normal vector and the sun-beam vector in degrees. Angles of 0 are replaced with 1e-06 to ensure non-nan results. Angles of nan will result in nan.

• n (numeric, default 1.526) – The effective index of refraction (unitless). Reference [1] indicates that a value of 1.526 is acceptable for glass. n must be a numeric scalar or vector with all values >=0. If n is a vector, it must be the same size as all other input vectors.

• K (numeric, default 4.0) – The glazing extinction coefficient in units of 1/meters. Reference [1] indicates that a value of 4 is reasonable for “water white” glass. K must be a numeric scalar or vector with all values >=0. If K is a vector, it must be the same size as all other input vectors.

• L (numeric, default 0.002) – The glazing thickness in units of meters. Reference [1] indicates that 0.002 meters (2 mm) is reasonable for most glass-covered PV panels. L must be a numeric scalar or vector with all values >=0. If L is a vector, it must be the same size as all other input vectors.

Returns

iam (numeric) – The incident angle modifier

References

[1] W. De Soto et al., “Improvement and validation of a model for photovoltaic array performance”, Solar Energy, vol 80, pp. 78-88, 2006.

[2] Duffie, John A. & Beckman, William A.. (2006). Solar Engineering of Thermal Processes, third edition. [Books24x7 version] Available from http://common.books24x7.com/toc.aspx?bookid=17160.

getaoi(), ephemeris(), spa(), ashraeiam()