Isolated slack buses in pypsa earth

[Eduardo Díaz]

Dear pypsa community,

I am solving the Chilean grid and trying to conduct a dispatch only optimization prior to activating capacity expansion. Surprisingly i get infeasibilities, which, upon debugging with load_shedding, I find that there are 2 isolated slack buses created which have no generation capacity to satisfy the load, thus the infeasibility.

Regardless of how many clusters I configure, the same two slack buses are created.

My question is, why does 'simplify_network' create those buses? I have tried finding the point in which they are created but I am a bit lost, is through 'aggregate_subestations' function?

Any light shed on this topic is very much appreciated.

Cheers!

[Ekaterina Fedotova]

Hello Eduardo,

Thanks a lot for reporting.

Isolated buses sometimes appear in pypsa-earth models. Sometimes that is a result of missed data for power grid or reflection of a real situation, when there are some isolated areas in the grid. `simplify_network` has functionality to drop or merge such isolated buses. You can control it using `p_threshold_drop_isolated` and `p_threshold_merge_isolated` parameters in your configuration file.

Generally, it is recommended to validate your model to better understand how to deal with the isolated buses in the best way, depending on what do they represent. There are some hints on possible validation approaches in pypsa-earth documentation: https://pypsa-earth.readthedocs.io/en/latest/tutorial.html#how-to-validate 

We also have an issue to add an advance an approach to pre-process isolated nodes:

https://github.com/pypsa-meets-earth/pypsa-earth/issues/852

Happy to discuss more on the topic, if you are interested. Please, feel free to comment on the GitHub issue above.

Best wishes,

Ekaterina

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