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I’d like to use pvlib library to calculate irradiance POA data for a single axis tracker system.

From the documentation it appears that this is possible, by creating a pvlib.tracking.SingleAxisTracker class (with the appropriate metadata), and then calling the get_irradiance method.

I've done so as such:

HSAT = SingleAxisTracker(axis_tilt=0, 
              axis_azimuth=167.5,
              max_angle=50, 
              backtrack=True, 
              gcr=0.387)

I then use the get_irradiance method of the HSAT instance of the SingleAxisTracker I just created, expecting it to use the metadata that I just entered to calculate POA data for this Horizontal single axis tracker system:

hsat_poa = HSAT.get_irradiance(surface_tilt=0, 
                            surface_azimuth=167.5, 
                            solar_zenith=sz, 
                            solar_azimuth=sa, 
                            dni=dni, 
                            ghi=ghi, 
                            dhi=dhi, 
                            airmass=None, 
                            model='haydavies')

When I go to plot hsat_poa, however, I get what looks like POA data for a fixed tilt system.

When I looked at the source code, I noticed that the SingleAxisTracker.get_irradiance method ultimately calls the location.total_irrad() method, which only returns POA data for a fixed tilt systems.

Do I need to provide my down surface_tilt data from the HSAT system? I had assumed that pvlib models an HSAT system, and would generate the surface_tilt values for me, based on the arguments provided in the SingleAxisTracker class instantiation. But it appears that's not what happens.

So my question is does pvlib require the tracker angle as an input in order to calculate POA data for Single Axis Tracker systems, or can it model the tracker angle itself, based on metadata like axis_tilt, max_angle, and backtrack?

Codedorf
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  • ``SingleAxisTracker.get_irradiance`` calls ``irradiance.total_irrad``. It does not call a method of a ``Location`` object. – Will Holmgren Jan 21 '18 at 00:48

2 Answers2

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Turns out pvlib.tracking.singleaxis() is the missing link.

This will determine the rotation angle of a single axis tracker system.

tracker_data = pvlib.tracking.singleaxis(solar_position['apparent_zenith'], 
                                     solar_position['azimuth'],
                                     axis_tilt=MOUNTING_TILT, 
                                     axis_azimuth=MOUNTING_AZIMUTH, 
                                     max_angle=MAX_ANGLE,
                                     backtrack=True, 
                                     gcr=MOUNTING_GCR)

and then using tracker_data like so:

hsat_poa_model_tracker = HSAT.get_irradiance(surface_tilt=tracker_data['surface_tilt'],
                            surface_azimuth=tracker_data['surface_azimuth'], 
                            solar_zenith=solar_position['apparent_zenith'], 
                            solar_azimuth=solar_position['azimuth'], 
                            dni=dni, 
                            ghi=ghi, 
                            dhi=dhi, 
                            airmass=None, 
                            model='haydavies')

will calculate POA data for a single axis tracker.

Found the answer in this jupyter notebook: http://nbviewer.jupyter.org/github/pvlib/pvlib-python/blob/master/docs/tutorials/tracking.ipynb

Codedorf
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  • If you're using the object oriented API, then you might consider using ``SingleAxisTracker.singleaxis`` instead of ``tracking.singleaxis``. It'll be a little simpler to write. – Will Holmgren Jan 21 '18 at 00:51
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Can it model the tracker angle itself, based on metadata like axis_tilt, max_angle, and backtrack?

pvlib's ModelChain will do this. See the PV Power Forecast documentation for an example of using a ModelChain with a SingleAxisTracker.

cs95
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Will Holmgren
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