pvlib.irradiance.boland#
- pvlib.irradiance.boland(ghi, solar_zenith, datetime_or_doy, a_coeff=8.645, b_coeff=0.613, min_cos_zenith=0.065, max_zenith=87)[source]#
Estimate DNI and DHI from GHI using the Boland clearness index model.
The Boland model 1, 2 estimates the diffuse fraction, DF, from global horizontal irradiance, GHI, through an empirical relationship between DF and the clearness index, \(k_t\), the ratio of GHI to horizontal extraterrestrial irradiance.
\[\mathit{DF} = \frac{1}{1 + \exp\left(a \left(k_t - b\right)\right)}\]- Parameters
ghi (numeric) – Global horizontal irradiance. [W/m^2]
solar_zenith (numeric) – True (not refraction-corrected) zenith angles in decimal degrees.
datetime_or_doy (numeric, pandas.DatetimeIndex) – Day of year or array of days of year e.g. pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
a_coeff (float, default 8.645) – Logistic curve fit coefficient.
b_coeff (float, default 0.613) – Logistic curve fit coefficient.
min_cos_zenith (numeric, default 0.065) – Minimum value of cos(zenith) to allow when calculating global clearness index \(k_t\). 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.
- Returns
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.
References
- 1
J. Boland, B. Ridley (2008) Models of Diffuse Solar Fraction. In: Badescu V. (eds) Modeling Solar Radiation at the Earth’s Surface. Springer, Berlin, Heidelberg. DOI: 10.1007/978-3-540-77455-6_8
- 2(1,2)
John Boland, Lynne Scott, and Mark Luther, Modelling the diffuse fraction of global solar radiation on a horizontal surface, Environmetrics 12(2), pp 103-116, 2001, DOI: 10.1002/1099-095X(200103)12:2%3C103::AID-ENV447%3E3.0.CO;2-2
Notes
Boland diffuse fraction differs from other decomposition algorithms by use of a logistic function to fit the entire range of clearness index, \(k_t\). Parameters
a_coeff
andb_coeff
are reported in 2 for different time intervals:15-minute:
a = 8.645
andb = 0.613
1-hour:
a = 7.997
andb = 0.586