Incidence Angle Modifier Effect

The Incidence Angle Modifier (IAM) describes how much of the irradiance incident on the surface of the module penetrates the surface and enters the solar cells that make up the module, where conversion of light to electrical energy takes place. The effects that reduce the amount of irradiance available to the solar cells include reflection from the surface of the module and absorption in the transparent protective layers in front of the cells.

The user can select the IAM model among 5 options: ASHRAE, CIEMAT, Fresnel normal glass (pre-defined pointwise model), Fresnel anti-reflective coated glass (pre-defined pointwise model), or Custom IAM profile (pointwise model defined by the user where the coefficients are imported from the .PAN file). Details of the IAM models can be found in Incidence Angle Modifier. The time series of available irradiance after the IAM effect for submodule j at time t are:

Direct: \(G_{\text{dir,poa,iam}}(j,t)\)

Diffuse: \(G_{\text{dif,poa,iam}}(j,t)\)

Reflected: \(G_{\text{r,poa,iam}}(j,t)\)

These are summed, allowing for near shading effects, to give the average irradiance on submodule j after the IAM effect:

$$G_{\text{iam}}\left( j,t \right) = \left\lbrack G_{dif,poa,iam}\left( j,t \right) + G_{r,poa,iam}\left( j,t \right) \right\rbrack + \frac{G_{dir,poa,iam}\left( j,t \right) \bullet A_{u}(j,t)}{A(j)}$$

The annual IAM effect can be calculated by averaging \(G_{\text{plant,iam}}(t)\) and \(G_{\text{plant,soil}}(t)\) over the year (or any other period of interest) and comparing the results:

$$\Delta_{iam,year} = \left( \frac{\sum_{\text{year}}^{}{G_{plant,iam}(t)}}{\sum_{\text{year}}^{}{G_{plant,soil}(t)}} - 1 \right) \bullet 100%$$

If an annually-representative result is desired and the input time series is not annually representative (i.e. not a TMY file), the result will need de-seasoning.