pvlib.irradiance.haydavies(surface_tilt, surface_azimuth, dhi, dni, dni_extra, solar_zenith=None, solar_azimuth=None, projection_ratio=None)[source]

Determine diffuse irradiance from the sky on a tilted surface using Hay & Davies’ 1980 model

$I_{d} = DHI ( A R_b + (1 - A) (\frac{1 + \cos\beta}{2}) )$

Hay and Davies’ 1980 model determines the diffuse irradiance from the sky (ground reflected irradiance is not included in this algorithm) on a tilted surface using the surface tilt angle, surface azimuth angle, diffuse horizontal irradiance, direct normal irradiance, extraterrestrial irradiance, sun zenith angle, and sun azimuth angle.

Parameters
• surface_tilt (numeric) – Surface tilt angles in decimal degrees. The tilt angle is defined as degrees from horizontal (e.g. surface facing up = 0, surface facing horizon = 90)

• surface_azimuth (numeric) – Surface azimuth angles in decimal degrees. The azimuth convention is defined as degrees east of north (e.g. North=0, South=180, East=90, West=270).

• dhi (numeric) – Diffuse horizontal irradiance in W/m^2.

• dni (numeric) – Direct normal irradiance in W/m^2.

• dni_extra (numeric) – Extraterrestrial normal irradiance in W/m^2.

• solar_zenith (None or numeric, default None) – Solar apparent (refraction-corrected) zenith angles in decimal degrees. Must supply solar_zenith and solar_azimuth or supply projection_ratio.

• solar_azimuth (None or numeric, default None) – Solar azimuth angles in decimal degrees. Must supply solar_zenith and solar_azimuth or supply projection_ratio.

• projection_ratio (None or numeric, default None) – Ratio of angle of incidence projection to solar zenith angle projection. Must supply solar_zenith and solar_azimuth or supply projection_ratio.

Returns

sky_diffuse (numeric) – The sky diffuse component of the solar radiation.

References

[1] Loutzenhiser P.G. et. al. “Empirical validation of models to compute solar irradiance on inclined surfaces for building energy simulation” 2007, Solar Energy vol. 81. pp. 254-267

[2] Hay, J.E., Davies, J.A., 1980. Calculations of the solar radiation incident on an inclined surface. In: Hay, J.E., Won, T.K. (Eds.), Proc. of First Canadian Solar Radiation Data Workshop, 59. Ministry of Supply and Services, Canada.