Add Muneer transposition model

pvlib/irradiance.py

@@ -994,6 +994,58 @@
     return sky_diffuse
 
 
+def muneer(surface_tilt, dhi, b):
+    '''
+    Determine sky diffuse irradiance on a tilted surface using the
+    Muneer [1]_ model.
+
+     Parameters
+    ----------
+    surface_tilt : numeric
+        Surface tilt angle in decimal degrees. Tilt must be >=0 and
+        <=180. The tilt angle is defined as degrees from horizontal
+        (e.g. surface facing up = 0, surface facing horizon = 90)
+
+    dhi : numeric
+        Diffuse horizontal irradiance. [W/m^2]
+
+    b : numeric
+        Radiance distribution index, introduced by Moon and Spencer [2]_
+        to model luminance distribution of overcast sky. [unitless]
+        Recommend values from [1]_:
+
+           - isotropic: b = 0
+           - shaded surface: b = 5.73
+           - sunlit surface, overcast sky: b = 1.68
+           - sunlit surface, non-overcast sky: b = -0.62
+
+    Returns
+    -------
+    poa_sky_diffuse : numeric
+        In-plane diffuse irradiance from the sky. [W/m^2]
+
+    References
+    ----------
+    .. [1] Muneer, T., 1990. Solar radiation model for Europe. Building
+       Services Engineering Research and Technology 11, 153-163.
+       :doi:`10.1177/014362449001100405`
+
+    .. [2] Moon, P., Spencer, D.E., 1942. Illumination from a non-uniform sky.
+       Trans. Illum. Eng. Soc. (London) 37, 707-725.
+       :doi:`10.1177/096032719302500301`
+    '''
+
+    term1 = 2 * b / (np.pi * (3 + 2 * b))
+    term2 = (
+        tools.sind(surface_tilt)
+        - surface_tilt * tools.cosd(surface_tilt)
+        - np.pi * (1 - tools.cosd(surface_tilt)) * 0.5
+    )
+    sky_diffuse = dhi * ((1 + tools.cosd(surface_tilt)) * 0.5 + term1 * term2)
+
+    return sky_diffuse
+
+
 def perez(surface_tilt, surface_azimuth, dhi, dni, dni_extra,
           solar_zenith, solar_azimuth, airmass,
           model='allsitescomposite1990', return_components=False):