pvlib-python: AttributeError when using ModelChain with multiple Arrays

Describe the bug A clear and concise description of what the bug is.

Not sure this will be either clear or concise, but: an AttributeError is generated when instantiating a ModelChain with a PVSystem that has multiple Arrays.

The AttributeError results from this line which references a PVSystem.racking_model attribute. In turn, that line is reached from here where we’re trying to ensure consistency between ModelChain.temperature_model (a string) and the array temperature models (I think).

To Reproduce See the discussion here which reports the issue.

Expected behavior I don’t see that this user made a mistake. I would not expect the AttributeError.

Versions:

pvlib.__version__: 0.9.5

About this issue

Original URL
State: closed
Created a year ago
Comments: 31 (31 by maintainers)

Most upvoted comments

Sorry for not chiming in earlier. I was a bit confused about what exactly the problem was here, but I think I have a clear view now, and I think . Sorry in advance for the long comment…

There are a two distinct issues here:

ModelChain sometimes accesses a non-existent attribute of PVSystem (the title of this issue) and causes AttributeError.

This occurs when the user makes a mistake and doesn’t supply temperature_model_parameters, or racking_model and module_type, in the Arrays when creating and using a PVSystem for temperature modeling with ModelChain. There is no way for pvlib to proceed in this case, so raising an error is correct. The only problem is that, due to an oversight made in v0.10.0, the specific error message is confusing in pvlib v0.10.*:

v0.9.5: KeyError: "Missing required parameter 'a'. Found {} in temperature_model_parameters."
- plus warnings like pvlibDeprecationWarning: The PVSystem.racking_model function was deprecated in pvlib 0.9 and will be removed in 0.10. Use PVSystem.arrays[i].racking_model instead.
v0.10.3: AttributeError: 'PVSystem' object has no attribute 'racking_model'

I think resolving this is a simple bugfix: fix the error message (and type) being raised. No deprecation period needed or desired.

ModelChain has (kind of) retained the deprecated behavior of defaulting to the SAPM cell temperature model when parameters aren’t supplied and available for inference.

This was supposed to be removed in v0.9, but it was overlooked. I think resolving this problem is also a simple bugfix, not a breaking change: the behavior in question only applies when no parameters are supplied, and it’s not like the model can be run in that situation anyway.

Anyway, I think both of these problems can be solved by just removing the second half of that offending or condition in ModelChain. I don’t see why any further modifications are needed in order to fix those problems. In particular, I’m opposed to the idea of raising an error in the Array constructor when the temperature model parameters weren’t specified and couldn’t be inferred. Valid uses of Array/PVSystem that have no need for temperature_model_parameters include:

Using Array for tasks unrelated to temperature modeling, e.g. irradiance transposition
Using ModelChain with cell_temperature included in the input weather data

In cases like these, the user shouldn’t be burdened and confused by making them specify a parameter set that won’t get used anyway. I think what we want is for un-inferrable parameters to only cause an error when the user runs something that actually needs those parameters.

kandersolar on Jan 10, 2024

Thanks for this effort, more than I anticipated 😃 I look forward to seeing the PR.

cwhanse on Dec 21, 2023

I vote to simply delete the or clause, which will prevent the error we’ve seen.

cwhanse on Dec 14, 2023