pvlib.iam.ashrae

pvlib.iam.ashrae(aoi, b=0.05)[source]

Determine the incidence angle modifier using the ASHRAE transmission model.

The ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) transmission model is developed in [1], and in [2]. The model has been used in software such as PVSyst [3].

Parameters:
  • aoi (numeric) – The angle of incidence (AOI) between the module normal vector and the sun-beam vector in degrees. Angles of nan will result in nan.
  • b (float, default 0.05) – A parameter to adjust the incidence angle modifier as a function of angle of incidence. Typical values are on the order of 0.05 [3].
Returns:

iam (numeric) – The incident angle modifier (IAM). Returns zero for all abs(aoi) >= 90 and for all iam values that would be less than 0.

Notes

The incidence angle modifier is calculated as

\[IAM = 1 - b (\sec(aoi) - 1)\]

As AOI approaches 90 degrees, the model yields negative values for IAM; negative IAM values are set to zero in this implementation.

References

[1]Souka A.F., Safwat H.H., “Determination of the optimum orientations for the double exposure flat-plate collector and its reflections”. Solar Energy vol .10, pp 170-174. 1966.
[2]ASHRAE standard 93-77
[3]PVsyst Contextual Help. https://files.pvsyst.com/help/index.html?iam_loss.htm retrieved on October 14, 2019

Examples using pvlib.iam.ashrae