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Update isotropic transposition references #1864

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Sep 20, 2023
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Update isotropic transposition references #1864

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15 changes: 9 additions & 6 deletions pvlib/irradiance.py
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Expand Up @@ -614,10 +614,11 @@ def isotropic(surface_tilt, dhi):
I_{d} = DHI \frac{1 + \cos\beta}{2}

Hottel and Woertz's model treats the sky as a uniform source of
diffuse irradiance. Thus the diffuse irradiance from the sky (ground
diffuse irradiance. Thus, the diffuse irradiance from the sky (ground
reflected irradiance is not included in this algorithm) on a tilted
surface can be found from the diffuse horizontal irradiance and the
tilt angle of the surface.
tilt angle of the surface. A discussion of the origin of the
isotropic model can be found in [2]_.

Parameters
----------
Expand All @@ -636,14 +637,16 @@ def isotropic(surface_tilt, dhi):

References
----------
.. [1] Loutzenhiser P.G. et. al. "Empirical validation of models to
.. [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
:doi:`10.1016/j.solener.2006.03.009`

.. [2] Hottel, H.C., Woertz, B.B., 1942. Evaluation of flat-plate solar
heat collector. Trans. ASME 64, 91.
.. [2] Kamphuis, N.R. et al. "Perspectives on the origin, derivation,
meaning, and significance of the isotropic sky model" 2020, Solar
Energy vol. 201. pp. 8-12
:doi:`10.1016/j.solener.2020.02.067`
'''

sky_diffuse = dhi * (1 + tools.cosd(surface_tilt)) * 0.5

return sky_diffuse
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