Add Kipp zonen shadow ring correction function

scripts/kipp_zonen_shadow_ring_sliding_bar_setting.py

@@ -0,0 +1,62 @@
+"""Script for generating slide bar settings for Kipp & Zonen shadow ring."""
+
+import numpy as np
+import pandas as pd
+import pvlib
+
+# Information has been taken from the Kipp & Zonen CM 121 shadow ring
+# instruction manual.
+
+# Note that the correction factors are based on the assumption of a horizontal
+# pyranometer installation and uniform diffuse sky irradiance.
+
+# The sliding bar has two scales; a higher and a lower one. At
+# positive solar declinations (between 21 Mar. and 23 Sep.) the part of the
+# scale that is oriented south must be read. In the northern hemisphere this is
+# the lower part.
+
+# The sliding bar adjustment can be derived with the formula
+# L = abs(297 tan (D)), in which D is the declination of the sun.
+
+
+def calculate_sliding_bar_setting(declination):
+    """
+    Determine Kipp & Zonen shadow ring sliding bar setting.
+
+    Parameters
+    ----------
+    declination : numeric
+        Declination angle [degrees].
+
+    Returns
+    -------
+    numeric
+        Sliding bar setting [cm].
+
+    """
+    sliding_bar_mm = 297 * np.tan(np.deg2rad(np.abs(declination)))
+    sliding_bar_cm = np.round(sliding_bar_mm / 10, 1)
+    return sliding_bar_cm
+
+
+times = pd.date_range(start='2025-01-01', end='2025-12-31', freq='1d')
+
+declination = \
+    np.rad2deg(pvlib.solarposition.declination_spencer71(times.dayofyear))
+
+slide_bar = calculate_sliding_bar_setting(declination)
+
+df = pd.DataFrame(
+    data={
+        'Slide bar setting': slide_bar,
+        },
+    index=[times.strftime('%m %b'), times.day]
+    )
+
+df = df.unstack(0)['Slide bar setting']
+
+df = df.fillna('')
+
+df.columns = [c.split(' ')[-1] for c in df.columns]
+
+df.to_excel('../metadata/kipp_zonen_shadow_ring_slide_bar_setting.xlsx')