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I have ran a pvlib module with modelchain.run_model_from_poa. I have obtained the DC and AC output results for the model. I, however, also want to obtain the parameters a, b, c, and d that are used to calculate the DC output of the pv modules in the formula:

Pdc = IPOA ( a + bIPOA + cTamb + dW ) (1) 
where Pdc = power
 IPOA = POA irradiance
 Tamb = ambient temperature  
W = wind speed, m/s 
a, b, c, d = regression coefficients derived 
from operational data.

I, however, cannot find a way to obtain the values that were used by pvlib for a, b, c, and d. Does anyone know if these values can be found somewhere?

EnergyHydrogenCoder
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1 Answers1

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The PVUSA equation isn't one of the performance models supported by pvlib out of the box. If you're referring to the user-defined model example shown here, those a, b, c, and d values are just examples; you will have to provide suitable parameter values yourself if you want to actually use the PVUSA model for a real pvlib application. Outside of a user-specified model like that documentation page, the PVUSA equation and its coefficients don't exist anywhere in pvlib.

But really, although it is used to predict PV output in a few specific applications (e.g. ASTM E2848 capacity testing), the PVUSA equation isn't viewed as a general-purpose PV model. When it is used, its coefficient values are typically determined by linear regression to measured or modeled power values taken from elsewhere. So to use it to predict power, you need to already have power... that is why it's not a model built into pvlib, because it doesn't usually make sense to use it for that kind of PV modeling.

In most cases it makes more sense to use pvlib with a more common PV model like the CEC model, PVsyst, PVWatts, etc. Module parameters for those models are more readily available, plus these models are built into pvlib.

kevinsa5
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  • Thank you kevinsa5 for your answer. That clarifies things a lot. In regards to the models you mention, do you know which one is standard used by pvlib if you run the model with the modelchain.run_model_from_poa extension? – EnergyHydrogenCoder May 08 '23 at 08:13
  • There's not a default as such; ModelChain infers which model you want to use based on the parameters you supply. So if you supply PVWatts parameters, it will use PVWatts, if you supply CEC parameters, it will use CEC, etc. – kevinsa5 May 09 '23 at 12:14