Biomass boilers

[toniseibold]

Changes proposed in this Pull Request

In add_existing_baseyear.py the existing biomass boilers are added from the file existing_heating_distribution_elec_s{simpl}_{clusters}_{planning_horizons}.csv.

So far the biomass boilers are only in the scope of pypsa-ariadne.

Checklist

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

[lisazeyen]

@toniseibold there are many changes not connected to the PR. Can you make sure that only the changes connected to the PR are in the branch?

[toniseibold]

@toniseibold there are many changes not connected to the PR. Can you make sure that only the changes connected to the PR are in the branch?

Should be fixed now :)