Merge pull request #14 from wholmgren/develop

merge sandia cherry-pick via develop

Author: wholmgren

Diff for: pvlib/__init__.py

@@ -1,12 +1,11 @@
 
 import logging
 logging.basicConfig()
-
+from . import pvl_tools
 from . import atmosphere
 from . import clearsky
 from . import irradiance
 from . import location
-from . import pvl_tools
 from . import solarposition
 from . import tmy
 

Diff for: pvlib/clearsky.py

@@ -287,3 +287,118 @@ def _linearly_scale(inputmatrix, inputmin, inputmax, outputmin, outputmax):
     outputrange = outputmax - outputmin
     OutputMatrix = (inputmatrix - inputmin) * outputrange / inputrange + outputmin
     return OutputMatrix
+
+
+
+def disc(GHI, SunZen, Time, pressure=101325):
+    '''
+    Estimate Direct Normal Irradiance from Global Horizontal Irradiance using the DISC model
+
+    The DISC algorithm converts global horizontal irradiance to direct
+    normal irradiance through empirical relationships between the global
+    and direct clearness indices. 
+
+    Parameters
+    ----------
+
+    GHI : float or DataFrame
+          global horizontal irradiance in W/m^2. GHI must be >=0.
+
+    Z : float or DataFrame
+        True (not refraction - corrected) zenith angles in decimal degrees. 
+        Z must be >=0 and <=180.
+
+    doy : float or DataFrame
+
+        the day of the year. doy must be >= 1 and < 367.
+
+    Other Parameters
+    ----------------
+
+    pressure : float or DataFrame (optional, Default=101325)
+
+        site pressure in Pascal. Pressure may be measured
+        or an average pressure may be calculated from site altitude. If
+        pressure is omitted, standard pressure (101325 Pa) will be used, this
+        is acceptable if the site is near sea level. If the site is not near
+        sea:level, inclusion of a measured or average pressure is highly
+        recommended.
+
+    Returns   
+    -------
+    DNI : float or DataFrame
+        The modeled direct normal irradiance in W/m^2 provided by the
+        Direct Insolation Simulation Code (DISC) model. 
+    Kt : float or DataFrame
+        Ratio of global to extraterrestrial irradiance on a horizontal plane.
+
+    References
+    ----------
+
+    [1] Maxwell, E. L., "A Quasi-Physical Model for Converting Hourly 
+    Global Horizontal to Direct Normal Insolation", Technical 
+    Report No. SERI/TR-215-3087, Golden, CO: Solar Energy Research 
+    Institute, 1987.
+
+    [2] J.W. "Fourier series representation of the position of the sun". 
+    Found at:
+    http://www.mail-archive.com/[email protected]/msg01050.html on
+    January 12, 2012
+
+    See Also 
+    --------
+    pvl_ephemeris 
+    pvl_alt2pres 
+    pvl_dirint
+
+    '''
+
+    Vars=locals()
+    Expect={'GHI': ('array','num','x>=0'),
+          'SunZen': ('array','num','x<=180','x>=0'),
+          'Time':'',
+          'pressure':('num','default','default=101325','x>=0'),
+          }
+
+    var=pvl_tools.Parse(Vars,Expect)
+
+    #create a temporary dataframe to house masked values, initially filled with NaN
+    temp=pd.DataFrame(index=var.Time,columns=['A','B','C'])
+
+
+    var.pressure=101325
+    doy=var.Time.dayofyear
+    DayAngle=2.0 * np.pi*((doy - 1)) / 365
+    re=1.00011 + 0.034221*(np.cos(DayAngle)) + (0.00128)*(np.sin(DayAngle)) + 0.000719*(np.cos(2.0 * DayAngle)) + (7.7e-05)*(np.sin(2.0 * DayAngle))
+    I0=re*(1370)
+    I0h=I0*(np.cos(np.radians(var.SunZen)))
+    Ztemp=var.SunZen
+    Ztemp[var.SunZen > 87]=87
+    AM=1.0 / (np.cos(np.radians(Ztemp)) + 0.15*(((93.885 - Ztemp) ** (- 1.253))))*(var.pressure) / 101325
+    Kt=var.GHI / (I0h)
+    Kt[Kt < 0]=0
+    Kt[Kt > 2]=np.NaN
+    temp.A[Kt > 0.6]=- 5.743 + 21.77*(Kt[Kt > 0.6]) - 27.49*(Kt[Kt > 0.6] ** 2) + 11.56*(Kt[Kt > 0.6] ** 3)
+    temp.B[Kt > 0.6]=41.4 - 118.5*(Kt[Kt > 0.6]) + 66.05*(Kt[Kt > 0.6] ** 2) + 31.9*(Kt[Kt > 0.6] ** 3)
+    temp.C[Kt > 0.6]=- 47.01 + 184.2*(Kt[Kt > 0.6]) - 222.0 * Kt[Kt > 0.6] ** 2 + 73.81*(Kt[Kt > 0.6] ** 3)
+    temp.A[(Kt <= 0.6-1)]=0.512 - 1.56*(Kt[(Kt <= 0.6-1)]) + 2.286*(Kt[(Kt <= 0.6-1)] ** 2) - 2.222*(Kt[(Kt <= 0.6-1)] ** 3)
+    temp.B[(Kt <= 0.6-1)]=0.37 + 0.962*(Kt[(Kt <= 0.6-1)])
+    temp.C[(Kt <= 0.6-1)]=- 0.28 + 0.932*(Kt[(Kt <= 0.6-1)]) - 2.048*(Kt[(Kt <= 0.6-1)] ** 2)
+    #return to numeric after masking operations 
+    temp=temp.astype(float)
+    delKn=temp.A + temp.B*((temp.C*(AM)).apply(np.exp))
+    Knc=0.866 - 0.122*(AM) + 0.0121*(AM ** 2) - 0.000653*(AM ** 3) + 1.4e-05*(AM ** 4)
+    Kn=Knc - delKn
+    DNI=(Kn)*(I0)
+
+    DNI[var.SunZen > 87]=np.NaN
+    DNI[var.GHI < 1]=np.NaN
+    DNI[DNI < 0]=np.NaN
+
+    DFOut=pd.DataFrame({'DNI_gen_DISC':DNI})
+
+    DFOut['Kt_gen_DISC']=Kt
+    DFOut['AM']=AM
+    DFOut['Ztemp']=Ztemp
+
+    return DFOut