3. Project background
3.3 Future expansions
It is therefore important to emphasize that during the decision‐making stages of grid expansion, Energinet has to take into account not only the specific requirements of the project at hand (as in the current Western and Southern Jutland projects), but also the wider system requirements for setting up a robust, economic, operable and environmentally friendly system.
Based on the evaluation of the individual transmission alternatives, the 400 kV solution is still considered the most efficient alternative due to its built‐in robustness and the possibility of integration with the existing transmission grid without the need to introduce additional advanced systems for control and regulation of power flows in the overall transmission grid.
As 400 kV OHL and UGC solutions fulfill the planning criteria outlined in Section 2.3 and in view of the limitations of 150 kV and 220 kV transmission alternatives, only 400 kV HVAC and HVDC transmission alternatives are investigated in depth in this report.
In Section 3.3, future grid expansion is discussed. The purpose of the section is to outline the need for future expansions of the transmission grid in Denmark.
3.3 Future expansions
The impact of the new planning assumptions has been tested on the possible future grid structure presented in RUS plan 2017. The operational scenarios chosen for the studies provide operational considerations for several scenarios, including high and low levels of renewable generation combined with various levels of demand and different patterns of cross‐border energy exchanges.
The performance of the transmission grid has been evaluated against Energinet's planning standards and the predefined operational scenarios.
Power flow calculations have been conducted for the following years:
‐ 2024 (including Viking Link and the Endrup‐Klixbüll and Endrup‐Idomlund 400 kV transmission lines, no new offshore wind power plants);
‐ 2028 (including the first new offshore wind power plant at Ringkøbing Fjord connected in Idomlund);
‐ 2031 (including the second new offshore wind power plant at Horns Rev connected in Stovstrup);
and
‐ 2040 (including all new offshore wind power plants in accordance with Section 2.6.2.3)
Besides the already identified 400 kV grid expansion requirements in the Western and Southern part of Jutland, the following additional 400 kV transmission lines are (according to RUS plan 2017) required in order to accommodate future capacity needs derived from the revised planning assumptions:
1. 400 kV Idomlund‐Tjele (circuit 2) required to support increase of wind and solar power in the Western part of Jutland;
2. 400 kV Endrup‐Idomlund (circuit 2), required to support increase of wind and solar power in the Western part of Jutland;
3. 400 kV Ferslev‐Tjele, required to support an increase in wind and solar power in the northern part of Jutland;
4. 400 kV Ferslev‐Vester Hassing, required to support an increase in wind and solar power in the northern part of Jutland;
5. 400 kV Landerupgård‐Revsing, required to facilitate the market and ensure supply to the Eastern part of Jutland and Funen;
6. 400 kV Hovegård‐Ishøj, required to support the new wind power plants at Kriegers Flak;
7. 400 kV Hovegård‐Bellahøj, required to ensure security of supply in the Copenhagen region; and 8. 400 Hovegård‐Bjæverskov, required as a general reinforcement of the 400 kV transmission grid.
In Figure 8, required 400 kV grid expansions are highlighted, where green (ID2) indicates the considered Idomlund‐Endrup transmission line and amber coloured lines indicate additional grid expansion
requirements.
Figure 8 Required expansions of the 400 kV transmission grid (numbers indicate project IDs from the bulleted list on the previous page).
On the list of required 400 kV grid expansions is the installation of a second 400 kV circuit on the existing 400 kV overhead line between the existing substations at Idomlund and Tjele (ID 1). This additional 400 kV circuit effectively links the Western part of the transmission grid with the existing 400 kV backbone of Jutland, thus establishing a redundant (N‐1 secure) supply for the 400 kV substation at Idomlund, a prerequisite for grid connection of the assumed Ringkøbing 1 offshore wind power plant (800 MW). The proposed plan is to establish this additional 400 kV circuit by refitting the existing 400 kV Donau towers of the OHL between Idomlund and Tjele, using the same right of way as shown in Figure 9.
Figure 9 Proposed refitting of existing 400 kV Donau towers.
The analysis also shows that additional transmission capacity is required in the Western part of Jutland due to future grid connections of offshore wind power plants at Ringkøbing and Horns Rev. The required transmission capacity will be established by installing a second 400 kV circuit between the substations at Endrup and Idomlund (ID 2). This expansion should be completed by 2030.
The connection of large‐scale offshore wind power plants will result in significant power infeed at the connection points and in the adjacent transmission grid. A firm and long‐term strategic development plan for future offshore wind power plants in Denmark will ensure the corresponding development of the
transmission grid, facilitating timely coordination and commissioning of necessary grid expansions in relation to the completion of the respective offshore wind plants.
Offshore wind power facilities with capacities of 600‐800 MW will require the locations of these facilities to be determined according to a long‐term development plan in order to ensure that the transmission grid is developed accordingly with respect to timeliness, robustness and cost‐effectiveness. Without such a plan, considerable costs could result from the suboptimal choice of non‐robust solutions today.
The specific transmission capacity requirements as well as the optimal time for the commissioning of these 400 kV transmission lines will be analysed in more detail as part of the upcoming RUS plan 2018.