The energy source library can be found in the process: Energy > Settings > Energy Sources.
To add new energy source, click Add Energy Source.
Then add information about the energy source in the pop-up window.
After save, the energy source appears on the list. You can then edit the energy source and add a CO2 emission metric. See Settings - Emission factor CO2/Carbon footprint. After this, you can visit to add an energy source to a meter, see Meters – Add a energy source.