Duplicate key values in grid.egon_pf_hv_bus

[ClaraBuettner]

The task 'osmtgmod_to_pypsa' currently fails when the task 'insert-gas-grid' run before due to duplicate key values. This happens because 'osmtgmod_to_pypsa' doesn't check if thebus_id already exist.

I remember that we wanted to keep the bus_id from the substations/osmtgmod. I see three options to solve this problem:

• all tasks which insert data to the grid.egon_pf_hv_bus table have to run after 'osmtgmod_to_pypsa' and check if the bus_idalready exist
• rethink to keep the substation ids and maybe create a bus_id-sequence
• use string instead of integer values for the bus_id (e.g. '1 AC' and '1 gas').

The first option is very easy to implement, but also leads to less parallel tasks and longer computation times.

[ClaraBuettner]

The first option was implemented in 079cec7a644dbe9162b1648152b65c1667c0b921