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An open source comparison of different pv modeling tools and their underlying models

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Goals

The following table is a comparison of the underlying models used in different software's respective model-chains. The goal of the table is to provide readers an easy reference guide to compare and contrast different photovoltaic performance modeling software. The table also includes information about whether or not the implementation in the software matches the implementation in PVLlib. Not every single model can be found in the table. Some sub-models are omitted such as the calculation of delta T in the solar position algorithm in order to save space. If the performance modeling software has multiple models for a given model type, only the most commonly used models are included.

Column Descriptions

  • Category: A grouping of models that relate to a specific folder in the repository structure
  • Model_Type: The type of model being described in the table
  • Model: The name of the model used by a given performance modeling software
  • Metric: Accuracy is presented in terms of the following metrics depending on what is stated in the cited paper:
    • mean bias difference (MBD),
    • root mean squared difference (RMSD),
    • maximum difference (MxD),
    • standard deviation (SD),
    • R squared (R2)
    • Uncertainty (U)
    • Model is precise (-)
    • If the cell in the table is blank, then the accuracy is unknown. If you know the accuracy of a given model, please see the "Contributing" section which can be found after the table.
  • Accuracy:
    • If an accuracy value is present in the table, then the accompanying publication is included in the repository folder structure.
    • Published accuracy must be from a third party and reputably published in order to be included in this table.
    • If many different published accuracy values exist such as accuracy values at different time-steps, then only the most relevant values are included in the table.
    • Discerning readers may refer to the reference for additional information.
  • PVLIB: The model implemented in the software is identical or very nearly identical to the implementation in pvlib.

Table

PlantPredict PVSyst
Category Model_Type Model Metric Accuracy PVLIB Model Metric Accuracy PVLIB
Solar_Position_Algorithm Solar_Position_Algorithm NREL U 0.0003° Proprietary U 0.08°
Time Series Minimum Time Step 1 minute MxD ~< 0.4% 1 hour MxD ~< 1.8%
Fixed Racking Fixed Tilt Yes - - Yes - -
East West No - - Yes - -
Seasonal Tilt Yes - - Unknown - -
Tracking Astronomical Tracking Marion & Dobos - - Proprietary - -
Slope Aware Backtracking Anderson & Mikofski - - Proprietary - -
Terrain Aware Backtracking None None
Custom Backtracking Yes - - No - -
Diffuse Optimization 3 Parameter 1 Parameter
Wind Stow None Fixed Threshold
Irradiance Decomposition Dirint MBD
RMSD
-3 W/m2
74 W/m2
Erbs MBD
RMSD
-17 W/m2
88 W/m2
Transposition Perez w/ coefficients MBD
RMSD
-1%
8%
Perez w/out coefficients MBD
RMSD
-1%
8%
Retro-Transposition GTI-Dirint MBD
RMSD
0.0 W/m2
6.4 W/m2
Reverse Hay MBD
RMSD
Unknown
Unknown
Reflection on Front Side Yes Yes
Optical IAM Physical Fresnel
Soiling Time-Step Level Monthly
Horizon Shading (Far Shading) Sub-TimeStep 1 hour
3D Near Shading Polygon Clipping - - Polygon Clipping - -
Bifacial NREL BifacialVF U <2% Proprietary VF U <2%
Spectral Relative_Humidity from Dew_Point August-Roche-Magnus None N/A
Precipitable_Water from Relative_Humidity Gueymard94 MxD <20% Gueymard94 MxD <20%
c-Si First Solar v2.0 Crest
a-Si First Solar v2.0 Sandia
Cd-Te First Solar v2.0 First Solar v2.0
DC Cell Thermal Model Modified Faiman Modified Faiman
Diode Model Single Diode Single Diode
Mismatch Simple Statistical Detailed
Wiring % at STC Ohmic
Degradation % %
AC Inverter Off MPP Proprietary Proprietary
Inverter Efficiency Sandia Quadratic Interpolation
Air Pressure for Altitude Correction of Inverters Yes - - No - -
Aux Losses % loss - - W loss - -
Transformer McCann Lawrence Proprietary
Wiring % at STC Ohmic

Contributing

The table is open source and any user or software company can submit a pull request to include their information in this list.

  • Rules for contribution:
    • If a free reference exists for the underlying model, please include the PDF in a folder that matches the model category.
    • If no reference exists (especially for proprietary software algorithms) then the best known reference is provided in the "Notes" markdown file instead.

Contributors

  • Kurt Rhee
  • Renn Darawali
  • James Alfi
  • Paul Wolfersdorff

References

![[pvlib_logo.png]] William F. Holmgren, Clifford W. Hansen, and Mark A. Mikofski. “pvlib python: a python package for modeling solar energy systems.” Journal of Open Source Software, 3(29), 884, (2018). https://doi.org/10.21105/joss.00884

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