Long-term grid structure

physi-cal planning in connection with the expansion of the high-voltage grid. The out-come can be seen from the Danish Energy Authority’s analysis of the long-term grid structure for the electricity transmission grid (Analyse af den langsigtede netstruktur for eltransmissionsnettet) from January 1999. This report is based on three scenarios for the development of the production capacity and con-sumption trends towards 2030. Two or three alternatives were devised for Western and Eastern Denmark, respectively, and in both regions the structure came to be based on rings.

7.3.1 Elements in the development of the grid structure

Below follows a description of Energinet.dk’s work on the elements in the grid structure.

The structure itself is based on the need for transmission between the various centres of production, consumption and exchange. The expected size of the grid is determined on the basis of the grid code based on specific assumptions con-cerning the production system, consumption and international exchange capac-ity as well as the exchange capaccapac-ity of the coming Great Belt power link. The directly connected large production units, offshore wind farms and interconnec-tions have the greatest bearing on the transmission grid capacity requirements.

The growth rate of electricity consumption is low and has a minor bearing on developments in capacity requirements.

The fundamental assumptions for the power contributions from these units and connections are subject to continuous development. For example, earlier re-quirements that Energinet.dk must be guaranteed access to all centrally con-nected installations must be reviewed. It must be established in each individual case whether such guarantee is of socio-economic benefit.

For financial and technical reasons, the technology used for grid expansions are primarily 400 kV overhead lines. In so far as is possible, these lines are placed along existing cable routes for lower voltage levels. Pursuant to Executive Order no. 1463 of 19 December 2005 concerning Energinet.dk, new 400 kV overhead lines must be compensated for by cable laying at lower voltage levels, the aim being to reduce the total number of overhead lines at voltage levels above 100 kV.

Energinet.dk monitors prices for 400 kV cables closely. If prices become com-petitive, and the technical problems involved in long-distance cabling are solved, cable laying may be possible in the longer term at the highest voltage levels.

Energinet.dk will be working with scenarios. In addition to establishing the as-sumptions needed to calculate the demand for transmission capacity in the grid – and the impending review of the grid planning principles and grid code – the scenarios can be used to test the robustness of a long-term expansion plan for the transmission grid.

Important strategic elements in the design of the long-term structure are the use of ring structures, the parallel operation of the 400 kV and underlying grids and differentiated transmission security at the various hubs.

The status for the 400 kV structure and the basic grid can be seen from Figure 7.5. The time perspective is 25-50 years depending on developments in con-sumption, production and interconnections. The implementation of the installa-tions is ensured through coordination of the individual reinforcements with pub-lic physical planning in general.

7.3.2 Connection of offshore wind turbines

In the ‘Action plan for offshore wind farms in Danish waters’ (Havmøllehan-dlingsplanen) from 1997, the distribution and connection of offshore wind farms were based on a principle of geographical spread, including an even distribution between Eastern and Western Denmark. With reference to this action plan the then Danish government in 1998 ordered the power companies to construct the first five offshore wind farms. The first two wind farms were commissioned in 2002/2003. At the same time, the order concerning the construction of the re-maining three wind farms was withdrawn.

As part of the follow-up on the energy-political agreement from March 2004, the government has invited bids for two offshore wind farms of 200 MW each at Horns Rev and Rødsand. Energi E2 was granted the contract for Horns Rev B. A consortium consisting of Energi E2, E.ON Sweden and Dong Wind won the con-tract for Rødsand 2.

Too much spread in the expansion of offshore wind power in terms of time and geography may lead to less optimum solutions from the point of view of con-nection and expansion of the transmission grid – both technically and finan-cially. Long-term planning and socio-economic optimisation of investments in the electricity infrastructure are hampered in the current situation by the inabil-ity to incorporate future, as yet undecided offshore wind farms into the plan-ning. Wind power expansion has a decisive bearing on the demands placed on the power system and thereby on the overall, long-term planning of the elec-tricity transmission grid.

In 2005 the Danish Energy Authority started updating the offshore wind power expansion plan from 1997. Energinet.dk welcomes this initiative and at the same time urges the Danish Energy Authority to speed up the process and to include the issue of the derived heavy investments in the electricity transmis-sion grid in its considerations. In the opinion of Energinet.dk, the work should be speeded up as much as possible for the sake of deciding on the strategy for expanding the transmission grid which contains the two wind farms already decided.

An offshore wind farm plan, with specific plans for the concentration of the next 3-4 wind farms at one or more specified locations, will enable more long-term and financially optimised grid connection of the two wind farms which have already been planned.