Add a constraint to limit DAC

[tgilon]

Closes #41.

Changes proposed in this Pull Request

Suggest a constraint to limit DAC usage.

The current model configuration considers only a subset of sectors. The fuel shares of the transport demand are defined exogenously. This leads to incompressible emissions from land transport oil (366 MtCO2) and associated oil refining (19 Mt CO2). The current CO2 limit is 371 Mt CO2, which is lower than the land transport emissions (385 Mt CO2). This represents a gap of 14 MtCO2.

The current scenario must be designed so that the CO2 from DAC is not used by Sabatier to produce e-methane. Of the 130 MtCO2 currently captured by DAC, 39 MtCO2 is used by Sabatier and the rest is sequestered (100 Mt CO2).

Completely disabling DAC is not an option because of the transport emissions. This PR proposes to limit the CO2 captured by DAC to 20 MtCO2 (slightly more than the 14 Mt CO2 gap).

A 20 MtCO2 limit for DAC is optimistic but relates to the European Commission Industrial Carbon Management (COM/2024/62).

A 50 MtCO2 target is given for 2030 and 280 MtCO2 for 2040. Interpolating this for 2035 gives 165 MtCO2. As 25% of it is projected to be capture by DAC in 2040, a 12.5% target is assumed in 2035. This gives a 20.6 MtCO2 target for 2035 ( (50 + (280 - 50) / 2) * 0.25 / 2)).

We are aware that is a raw approximation giving only an order of magnitude. Geographical scopes are not aligned neither as the current version of the model doesn't consider all the EU countries.

European Commission Framework for Carbon removals also gives a lower bound of 5MtCO2 being removed using industrial technologies by 2030.

ToDo

• Avoid hard coded values, define a configuration
• Improve documentation of the code

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.

[daniel-rdt]

I added the configuration option and documentation for the DAC limit constraint. Maybe we want to amend this to include a pathway? @tgilon

[tgilon]

I added the configuration option and documentation for the DAC limit constraint. Maybe we want to amend this to include a pathway? @tgilon

It definitely makes sense to do so for DAC.

[tgilon]

A few changes still required to use pathways