On 20 October, 50Hertz and the Danish system operator Energinet inaugurated the world’s first hybrid offshore interconnector, integrating the German Baltic 1 and Baltic 2 offshore wind farm sites, operated by 50Hertz, with the Danish Kriegers Flak in the Baltic sea. This combined grid solution (CGS) connects the two offshore wind farm substations to each other and to the existing onshore connections. As a result, the CGS can bring offshore wind power to Denmark or to Germany and can also be used for cross-border energy trading.
During the official inauguration ceremony, Peter Altmaier, the German Federal minister for Economic Affairs, praised the innovative project, calling it a “European lighthouse project for cross-border co-operation in the field of offshore wind energy."
The CGS is a technological innovation that could serve as an example for future offshore grids. Two submarine cables of only 25 km length with a capacity of 200 MW each, laid between the offshore substations of Baltic 2 and Kriegers Flak, bring both grid connection systems together.
Stefan Kapferer, CEO of 50Hertz said: "With this project, 50Hertz and Energinet are pioneering the efficient integration of offshore wind farms into the cross-border European electricity market. It offers us several effective options to balance the frequency and voltage of our transmission grids at all times, to deal with the integration of renewable energy sources with more flexibility and to increase the stability of the overall system. Therefore the CGS is an essential puzzle piece of our strategy to cover 100 % of the electricity demand in our grid area, over the course of a year, with renewable energy by 2032. In addition, the project shows the high significance of the European Baltic area for the energy sector. This importance is also reflected in the Baltic Sea Offshore Wind Declaration, which was signed by the neighbouring states in late September."
As the transmission grids of eastern Denmark and Germany are not synchronous, the construction of a double converter (back-to-back converter) at the Bentwisch substation near Rostock was necessary. Through the converter, the arriving AC is converted into DC and immediately into AC again. This procedure is the only way to ensure a smooth flow of electricity from Denmark to Germany and vice versa.
On the Danish side, the project is of key importance for the country’s attempt of pursuing a climate neutral strategy. Once the integrated 600 MW Kriegers Flak wind farm has been commissioned in 2021 as planned, it will be Denmark’s largest wind farm.
Thomas Egebo, CEO of Energinet: "The Combined Grid Solution is not only a very important milestone in reaching Denmark’s ambitious goal of a 100 percent green power system in 2030. The groundbreaking project also delivers an important building block for decarbonising the rest of the society. Wind and PV must in the near future replace petrol in our cars, oil, coal and gas in our private and district heating. And power from wind and solar will in the long run be the main ingredient in production of green hydrogen, green gases, jetfuels, for industry, shipping and aviation. Therefore, the Danish Parliament has decided to build energy islands in the Baltic Sea and the North Sea and surround them with large scale offshore wind farms. The innovative CGS-solution combines offshore wind and interconnectors and is a leading example for energy islands and an efficient and fast green transition."
Chris Peeters, CEO of Elia Group, parent of 50Hertz: "The hybrid technology increases the efficiency of the investment: when there is no wind, the cable can be used as an interconnector. In this way, the combined grid solution project also links the flexibility of two energy markets and gives access to renewables at the lowest cost. This is of vital importance to energy-intensive industries."
The CGS consists of both hardware and software components. The Master Controller for Interconnector Operation or MIO, which was developed with partners, acts as the “brain” of the system. This digital control unit, located in the 50Hertz Control Centre in Neuenhagen, near Berlin, functions to harmonise both the requirements of the electricity market and the generation of electricity that depends on the wind conditions on the Baltic Sea.
The MIO’s most important task is the optimal exploitation of the interconnector and simultaneously ensuring the prevention of an overload of the line as well as the operating facilities in the substation. In this process, the MIO controls the market-based exchange of electricity between Denmark and Germany, not only on the basis of forecasts, but by ensuring the necessary voltage stability and system balance in case of physical deviations in real time.