Twenty years to address electricity market and system seams issues in the European Union : why? why not?

There are ‘seams’ when TSOs (Transmission System Operators) do not perform the same tasks in the same manner on the different sides of their borders. Seams are consequential for electricity systems because power flows are strongly interactive where interconnected grids link many TSOs and countries like in the EU. Seams are very consequential in the EU because we have a common continental open market while access to the grids, congestion management, and balancing of the flows are performed by individual TSOs. It took 20 years to the EU to really address this ‘seams’ issue: why? How did it change and how far? Will the EU new ‘Network Codes’ finally create a seamless EU interconnected system and internal market? Or not?