pvlib.irradiance.dirindex

pvlib.irradiance.dirindex(ghi, ghi_clearsky, dni_clearsky, zenith, times, pressure=101325.0, use_delta_kt_prime=True, temp_dew=None)[source]

Determine DNI from GHI using the DIRINDEX model, which is a modification of the DIRINT model with information from a clear sky model.

DIRINDEX [1] improves upon the DIRINT model by taking into account turbidity when used with the Ineichen clear sky model results.

Parameters:
ghi : array-like

Global horizontal irradiance in W/m^2.

ghi_clearsky : array-like

Global horizontal irradiance from clear sky model, in W/m^2.

dni_clearsky : array-like

Direct normal irradiance from clear sky model, in W/m^2.

zenith : array-like

True (not refraction-corrected) zenith angles in decimal degrees. If Z is a vector it must be of the same size as all other vector inputs. Z must be >=0 and <=180.

times : DatetimeIndex
pressure : float or array-like, default 101325.0

The site pressure in Pascal. Pressure may be measured or an average pressure may be calculated from site altitude.

use_delta_kt_prime : bool, default True

Indicates if the user would like to utilize the time-series nature of the GHI measurements. A value of False will not use the time-series improvements, any other numeric value will use time-series improvements. It is recommended that time-series data only be used if the time between measured data points is less than 1.5 hours. If none of the input arguments are vectors, then time-series improvements are not used (because it’s not a time-series). If True, input data must be Series.

temp_dew : None, float, or array-like, default None

Surface dew point temperatures, in degrees C. Values of temp_dew may be numeric or NaN. Any single time period point with a DewPtTemp=NaN does not have dew point improvements applied. If DewPtTemp is not provided, then dew point improvements are not applied.

Returns:
dni : array-like

The modeled direct normal irradiance in W/m^2.

Notes

DIRINDEX model requires time series data (ie. one of the inputs must be a vector of length > 2).

References

[1] Perez, R., Ineichen, P., Moore, K., Kmiecik, M., Chain, C., George, R., & Vignola, F. (2002). A new operational model for satellite-derived irradiances: description and validation. Solar Energy, 73(5), 307-317.