pvlib.pvsystem.physicaliam

pvlib.pvsystem.physicaliam(K, L, n, aoi)[source]

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

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 upon a physical model of absorbtion and transmission through a cover. Required information includes, incident angle, cover extinction coefficient, cover thickness

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(theta))

Parameters:

K : float

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 : float

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.

n : float

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.

aoi : Series

The angle of incidence between the module normal vector and the sun-beam vector in degrees.

Returns:

IAM : float or Series

The incident angle modifier as specified in eqns. 14-16 of [1]. IAM is a column vector with the same number of elements as the largest input vector.

Theta must be a numeric scalar or vector. For any values of theta where abs(aoi)>90, IAM is set to 0. For any values of aoi where -90 < aoi < 0, theta is set to abs(aoi) and evaluated.

See also

getaoi, ephemeris, spa, ashraeiam

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.