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gti_dirint raises 'UnboundLocalError: local variable 'best_ghi' referenced before assignment' #1342

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kdebrab opened this issue Nov 24, 2021 · 6 comments · May be fixed by #2347
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gti_dirint raises 'UnboundLocalError: local variable 'best_ghi' referenced before assignment' #1342

kdebrab opened this issue Nov 24, 2021 · 6 comments · May be fixed by #2347
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@kdebrab
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kdebrab commented Nov 24, 2021 •
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Describe the bug
irradiance.gti_dirint fails for surface faced North

To Reproduce

import pvlib
import pandas as pd
times = pd.date_range('2021-11-24', '2021-11-25', freq='h')
latitude, longitude, surface_tilt, surface_azimuth = 51.3, 4.56, 25, 360
solpos = pvlib.solarposition.get_solarposition(times, latitude, longitude)
solar_zenith, solar_azimuth = solpos['apparent_zenith'], solpos['azimuth']
ghi = pvlib.clearsky.simplified_solis(90 - solar_zenith)['ghi']
poa_global = ghi  # this is not correct, but doesn't really matter for the bug report
aoi = pvlib.irradiance.aoi(surface_tilt, surface_azimuth, solar_zenith, solar_azimuth)
pvlib.irradiance.gti_dirint(poa_global, aoi, solar_zenith, solar_azimuth, times, surface_tilt, surface_azimuth)

raises

UnboundLocalError: local variable 'best_ghi' referenced before assignment

The error is not raised e.g. when surface_azimuth = 180.

Versions:

  • pvlib.__version__: 0.9.0
  • pandas.__version__: 1.3.4
  • python: 3.9.4.final.0
@kdebrab
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kdebrab commented Nov 24, 2021 •
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The example is not fully correct (I should have converted ghi to the plane before feeding it to gti_dirint), but that doesn't really matter for the bug report.

In this case, the plane doesn't see the sun during the times, so diriving the components would be trivial/impossible (the plane only sees diffuse), but, in any case, the algorithm should not raise an UnboundLocalError.

@cwhanse cwhanse added the bug label Nov 24, 2021
@cwhanse
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cwhanse commented Nov 24, 2021

Confirmed. The problem appears to be that _gti_dirint_lt_90 is always called, without checking if any aoi value is less than 90. The test for gti_dirint doesn't hit this corner case.

Maybe put an if block around this line.

@wholmgren
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It's not as simple as putting an if aoi_lt_90.any() around _gti_dirint_lt_90. _gti_dirint_gte_90 requires the best_kt_prime determined in _gti_dirint_lt_90. I don't think we can make this work without going beyond what's in the Marion paper. I suggest we instead return an informative error if insufficient data is supplied with aoi < 90.

@cwhanse cwhanse linked a pull request Dec 31, 2024 that will close this issue
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@adriesse
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adriesse commented Jan 1, 2025

How about just assigning some default values to 'best_ghi' earlier in the code?

@cwhanse
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cwhanse commented Jan 2, 2025

I'm open to suggestions. best_ghi is the GHI returned from the optimization. Where that can't be done, maybe return np.nan? That seems less helpful to me than interrupting the calculation and informing the user.

@adriesse
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adriesse commented Jan 5, 2025

np.nan seems ok to me. Either way, the Notes section could explain the problem a bit.

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Raise helpful exceptions for irradiance.gti_dirint cwhanse/pvlib-python
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@kdebrab @wholmgren @cwhanse @adriesse