About CO2 emission cost, CCS technologies, green hydrogen and the units information (for line AC, Link, StorageUnit, and Store)

[Haiping007]

Hi, I have a few questions related to CO2 emissions that need your help:

1. Is CO2 emission cost included in the minimal system cost function of the optimization for the power system? I noticed there is a price of 250 EUR/(tCO2/a) in the cost.csv. I assume it is included, right? But in your previous pypsa-earth paper, I did not find this included in the objective cost function.
2. Are there CCS technologies considered for biomass, natural gas and coal power generators in the system so far? There seems no CCS information from the carriers and cost.csv.
3. Is the hydrogen technology in the system blue or green? As there is no CCS information for the technologies, I assume it is green hydrogen from renewables, right?
4. I couldn't find the information on the units for the Capacity and Supply of line AC, Link, StorageUnit, and Store. Is 'MW' for the capacity and 'MWh' for the supply?
   

But when I use code: 'supply.attrs'
I got:
{'name': 'Supply', 'unit': 'carrier dependent'}
It looks like the units for these different components are different. Could you please give me suggestions on where/how I could get the unit information for the 'Capacity' and 'Supply' (in the statistic module) of each component of line AC, Link, StorageUnit, and Store?

Thank you very much!