When calculating MW-miles of transmission upgrades, exclude some branches

[danielolsen]

Purpose

When calculating MW-miles of transmission upgrades, exclude some branches. I have found this to be very useful for analyzing offshore wind scenarios, where we want to separate onshore branch upgrades and offshore branch upgrades.

What is the code doing

Functional change in calculation loop in mwmiles.py:

if b in exclude_branches:
   continue

Everything else is input checking, docstring updates, and new tests.

Usage example

Scenario 564 (Collaborative Offshore Anchor). Offshore branches were consciously all given capacity of 100 MW, even if the offshore plants were expected to be much bigger, since we knew that we could up-size them automatically via renewable stub scaling. However, that leads to the calculation of very large upgrade totals, which are not meaningful for this scenario.

>>> upgrades = calculate_mw_miles(scenario)
>>> print('total MW-miles:', '{:,.0f}'.format(upgrades['mw_miles'] + upgrades['transformer_mw']))
total MW-miles: 584,058
>>> print('total lines:', '{:.0f}'.format(upgrades['num_lines'] + upgrades['num_transformers']))
total lines: 305

>>> exclude_branches = list(range(104121,104168))    #offshore branches
>>> upgrades = calculate_mw_miles(scenario, exclude_branches=exclude_branches)
>>> print('total MW-miles:', '{:,.0f}'.format(upgrades['mw_miles'] + upgrades['transformer_mw']))
total MW-miles: 54,746
>>> print('total lines:', '{:.0f}'.format(upgrades['num_lines'] + upgrades['num_transformers']))
total lines: 291

Time to review

15 minutes. This is a low priority to review/merge, I can keep using it in my local branch in the meantime.

[danielolsen]

This PR has been sitting for nearly three months now. Can I get a thumbs up or thumbs down so that I can stop rebasing and pushing?

[rouille]

Just by curiosity, what happens if b, a branch that is part of the grid used for the scenario, is not in the base grid because the latter has been updated since the scenario has ran? In other words, should we have a if or try/except statement here?

[danielolsen]

Interesting thought. If we remove a branch from the base grid, but this branch is present in the change table of previous scenarios, I think it will indeed cause an error. So far I don't think we've removed any branches, only added them, and even then we have only added them for the offshore wind generators, nowhere else.

Just thinking out loud here: if we do add an if or a try/except, it could avoid this hypothetical but we may accidentally ignore similar problems that we would want to throw an exception for.

[rouille]

Looks good. Always a good thing to have options.