pvlib.irradiance.erbs_driesse(ghi, zenith, datetime_or_doy=None, dni_extra=None, min_cos_zenith=0.065, max_zenith=87)[source]#

Estimate DNI and DHI from GHI using the continuous Erbs-Driesse model.

The Erbs-Driesse model 1 is a reformulation of the original Erbs model 2 that provides continuity of the function and its first derivative at the two transition points.

\[DHI = DF \times GHI\]

DNI is then estimated as

\[DNI = (GHI - DHI)/\cos(Z)\]

where Z is the zenith angle.

  • ghi (numeric) – Global horizontal irradiance in W/m^2.

  • zenith (numeric) – True (not refraction-corrected) zenith angles in decimal degrees.

  • datetime_or_doy (int, float, array, pd.DatetimeIndex, default None) – Day of year or array of days of year e.g. pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex. Either datetime_or_doy or dni_extra must be provided.

  • dni_extra (numeric, default None) – Extraterrestrial normal irradiance. dni_extra can be provided if available to avoid recalculating it inside this function. In this case datetime_or_doy is not required.

  • min_cos_zenith (numeric, default 0.065) – Minimum value of cos(zenith) to allow when calculating global clearness index kt. Equivalent to zenith = 86.273 degrees.

  • max_zenith (numeric, default 87) – Maximum value of zenith to allow in DNI calculation. DNI will be set to 0 for times with zenith values greater than max_zenith.


data (OrderedDict or DataFrame) –

Contains the following keys/columns:

  • dni: the modeled direct normal irradiance in W/m^2.

  • dhi: the modeled diffuse horizontal irradiance in W/m^2.

  • kt: Ratio of global to extraterrestrial irradiance on a horizontal plane.


ValueError – If neither datetime_or_doy nor dni_extra is provided.


The diffuse fraction DHI/GHI of the Erbs-Driesse model deviates from the original Erbs model by less than 0.0005.



A. Driesse, A. Jensen, R. Perez, A Continuous Form of the Perez Diffuse Sky Model for Forward and Reverse Transposition, forthcoming.


D. G. Erbs, S. A. Klein and J. A. Duffie, Estimation of the diffuse radiation fraction for hourly, daily and monthly-average global radiation, Solar Energy 28(4), pp 293-302, 1982. Eq. 1