Add option of country-specific district heating supply temperatures

[amos-schledorn]

Closes # (if applicable).

Changes proposed in this Pull Request

Allow country-specific forward and return temperatures in district heating:

• Make corresponding settings a dictionary with country codes as optional keys and default a necessary key. The default temperature is chosen for those countries not included in the dictionary.
• Update build_cop_profiles.run accordingly. Forward/return temperatures that enter COP approximations are changed from floats to data arrays with dimensions time and name (i.e. nodes).

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in all of config.default.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv.
• A release note doc/release_notes.rst is added.

Notes

I've made a test run with the following settings (different from the proposed default settings):

scenario:
  clusters:
  - 4
  planning_horizons:
  - 2050


countries: ['DE', 'DK', 'PL']

sector:
  district_heating:
    forward_temperature:
      DE: 90
      DK: 70
      default: 80
    return_temperature:
      DE: 50
      DK: 40
      default: 45

As expected, this leads to a slightly higher overall heat pump share in district heating:

Plotting heat pump COPs for one node per country indicates that DE-COPs stay constant (same temperature as before), PL-COPs increase somewhat (slightly lower default supply temperatures) and DK-COPs increase substantially (much lower temperatures than before):

The proposed default supply temperatures are 70/40C in Scandinavia and 90/50C elsewhere. Admittedly, this is a guesstimate (also as a compromise between expected current and future temperatures), since open data seems very difficult to come by. I would suggest to open another issue for researching this data but allowing the option to use country-specific temperatures already now.

[lisazeyen]

Only some small comments. One more general question, is it a good approximation to use the same temperatures for different planning horizons and an eventually increasing district heating share? Or could one expect that temperatures could be reduced due to new generation DH systems? This does not need to be tackled in this PR.

[amos-schledorn]

Only some small comments. One more general question, is it a good approximation to use the same temperatures for different planning horizons and an eventually increasing district heating share? Or could one expect that temperatures could be reduced due to new generation DH systems? This does not need to be tackled in this PR.

Thanks for the review! I agree, we should probably (at least add the option to) decrease temperatures over time. I was a little hesitant to do that here because it introduces more structural changes (COPs would become year-specific).
The current default temperatures are a compromise between what I believe to be current and future supply temperatures.
Should I add the feature here on open a separate issue?

[amos-schledorn]

@lisazeyen, this is ready to go from my side.

• I've marked your comment on the assign_locations method as resolved.
• I've merged the master branch into the feature and results seem fine.
• See my response to your open comment.