orientation: add horizontal single axis tracking

RELEASE_NOTES.rst

@@ -22,6 +22,7 @@ Release Notes
 * Due to ambiguity, conversion functions (`.pv(...)`, `.wind(...)` etc.) now raise an `ValueError` if shapes and matrix are given. 
 * Atlite now supports calculating of heat pump coefficients of performance (https://github.com/PyPSA/atlite/pull/145).
 * Enabled the GitHub feature "Cite this repository" to generate a BibTeX file (Added a `CITATION.cff` file to the repository).
+* Atlite now supports calculating PV potentials with a Horizontal Single Axis Tracker (HSAT). The method can be activated setting the `orientation="hsat"` in the `pv` conversion function.    
 
 **Bug fixes**
 * The solar position for ERA5 cutouts is now calculated for half a time step earlier (time-shift by `cutout.dt/2`) to account for the aggregated nature of

atlite/pv/orientation.py

@@ -23,6 +23,30 @@ def get_orientation(name, **params):
     return getattr(sys.modules[__name__], "make_{}".format(name))(**params)
 
 
+def make_hsat():
+    """
+    Returns a function mimicing a Horizontal Single Axis Tracker (HSAT).
+
+    The method sets the east-west tilt of the PV panel perpendicular to the
+    solar altitude. The axis of rotation is horizontal with respect to the
+    ground.
+    """
+
+    def horizontal_tracking(lon, lat, solar_position):
+
+        slope = np.pi / 2 - np.abs(solar_position["altitude"])
+
+        # South orientation for panels on northern hemisphere and vice versa
+        azimuth = np.where(solar_position["azimuth"] < np.pi, np.pi / 2, 3 * np.pi / 2)
+
+        return dict(
+            slope=slope,
+            azimuth=xr.DataArray(azimuth, coords=solar_position["altitude"].coords),
+        )
+
+    return horizontal_tracking
+
+
 def make_latitude_optimal():
     """
     Returns an optimal tilt angle for the given ``lat``, assuming that

test/test_preparation_and_conversion.py

@@ -132,6 +132,17 @@ def pv_test(cutout):
     # should be roughly the same
     assert (production_other.sum() / production_opt.sum()).round(0) == 1
 
+    # now use horizontal tracking
+    production_hsat = cutout.pv(
+        atlite.resource.solarpanels.CdTe,
+        "hsat",
+        layout=cap_factor_opt,
+    )
+
+    assert production_hsat.sel(time=TIME + " 00:00") == 0
+    # should be lower since it's winter
+    assert (production_hsat.sum() / production_opt.sum()) < 1
+
 
 def csp_test(cutout):
     """