DAC in Sector Studies

[trevorb1]

Feature Request

As described in PR #622, running DAC in sector studies at national level is not supported right now.

Suggested Solution

I believe the best way to address this is probably remove the individual emission tracking per sector, and just post-process that information. I think what this would require is:

1. Create central atmosphere emission stores (similar (or maybe the same?) to what is done in the power sector)
2. Remove the sector specific stores (we may want to think about how to treat the methane store)
3. Change the link efficiency2 values so they direct to the atmosphere store
4. Update the DAC sector links so they no longer pull from sector specific stores
5. Ensure that carbon can be pulled from earlier timesteps (see this comment)
6. Update the sector constraints so they no longer relate to sector specific stores. Note, this will remove the functionality of implementing emission targets at a per sector level. This can be amended by a future issue ticket tho.
7. Create a utility function that calculates emissions per sector based on activity of the components in that sector
8. Update the emission plots so that the emission values come from the utility function, rather than the store energy levels.

Additional Info

We should probably check how PyPSA-Eur does this first, tho!