National CO2 reduction paths

[pworschischek-aggmag]

Describe the feature you'd like to see

Users can define granular (per country and per year) CO₂ reduction paths through the configuration layer. CO₂ reductions are important drivers for investment decisions, and the current implementation with a system-wide carbon budget fails to depict country-specific policies.

The implementation in the referenced PR #2186 is a simplification of the respective PyPSA-DE constraint and used in PyPSA-AT. Note that side effects and model artefacts can result from constraining selected countries only.

# config.yaml example
solving:
  constraints:
    co2_budget_national:
      DE:
        2020: 0.67   # 67% of 1990 emissions
        2030: 0.34
        2040: 0.10   
        2050: -0.05  # net-negative

Noteworthy implementation comments

• The constraint skips silently if a planning year is not found in the co2_budget_national configuration. No interpolation logic is provided.
• emissions from international aviation are excluded
• emissions from international navigation are included
• The constraint works on a per-country level (location indices in energy_totals.csv file only)
• The implementation assumes the co2 atmosphere bus at port 2 for aviation links (not tested anywhere)