Setting storage_initial and cyclic_storage

[sjpfenninger]

What happened?

This is 1:1 pasted from the discussion opened by @sstroemer in #646 so we can track this issue:

1. storage_initial defaults to 0, while cyclic_storage defaults to true. This may not be the expected/intended behavior of cyclic_storage? Compare: "For instance, with cyclic_storage: true and a storage_initial: 0, the stored energy must be zero by the end of the time horizon." [src], which would hint at this being something that one has to opt into.
2. Disabling storage_initial seems to be hard: Setting null does not seem to work, and _REPLACE_ is not valid in the tech specification. I know it could be done from code, but what is the preferred way to do that in the YAML?

Ad 1.: Only reason I think that may not be "expected" is that I assume the main use-case of cyclic storage(s) to mostly likely be the unavailability of reasonable initial levels of seasonal storages. Letting the model "pick" a starting point and forcing it to achieve that at the end of the modeling period makes sense: A storage operator could try and aim for X% of storage at time T, since they know by experience/history that this works in the long-term. The cyclic storage is then just an approximation of that behaviour (without the multi-year history). Defaulting to 0 however completely breaks that, and is especially harsh for any inflow-dependent hydro storages (which will have a high storage level at the start of most modeling periods (01.01.) instead of 0).

Which operating systems have you used?

• macOS
• Windows
• Linux

Version

v0.7

Relevant log output

No response

[brynpickering]

The current implementation works as expected. The default value of a parameter only gets used in the math expression, so if you do not explictily define storage_initial then its value in calliope.Model.inputs will be NaN. Then the set_storage_initial constraint will not be triggered so you'll get cyclic storage with the initial/final step storage being linked and set to whatever is optimal for the model.

[brynpickering]

When storage_initial is explicitly set by the user and cyclic_storage: true, then set_storage_initial links the final timestep to storage_initial and balance_storage links the first timestep to the final timestep.

When storage_initial is explicitly set by the user and cyclic_storage: false, then set_storage_initial is not triggered and balance_storage sets the initial storage level to storage_initial.

When storage_initial is not explicitly set by the user and cyclic_storage: true, then set_storage_initial is not triggered and balance_storage explicitly links first and final timestep.

[brynpickering]

Closing as not an issue. If you disagree @sstroemer then please re-open!