50Hertz and Energinet inaugurate Combined Grid Solution
50Hertz and Energinet
have inaugurated the world’s first hybrid offshore interconnector, integrating
German and Danish offshore wind farms. The Combined Grid Solution (CGS)
connects two offshore substations in the Baltic Sea to each other as well
as to the existing onshore connections of the offshore wind farms. As a
result, the CGS can bring offshore wind power to Denmark or Germany and
can also be used for cross-border energy trading.
The CGS is a technological innovation that connects the grid connections
of offshore wind farms to for a bridge between Germany and Denmark. This
includes the grid connections of the Baltic
1 and Baltic
2 wind farms
(Germany), which are operated by 50Hertz, as well as the grid connection
farm (Denmark), that is currently under construction. Two submarine cables
25 km length with a capacity of 200 MW each have been laid between the
offshore substations of Baltic
2 and Kriegers
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 percent 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 for this interconnector.
Through the converter, the arriving alternating current (AC) is converted
into direct current (DC) and immediately into alternating current again.
This procedure ensures a smooth flow of electricity from Denmark to Germany
and vice versa.
Once the integrated Kriegers Flak wind farm has been commissioned in 2021
as planned, it will provide power supply to 600,000 households in the Zealand
region. It has a capacity of 600 MW and will be Denmark’s largest wind
Thomas Egebo, CEO of Energinet, said: "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 decarbonizing 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 gasses, 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
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 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. For this, the MIO can rely on the double converter in Bentwisch
as well as on the Baltic
1 and Baltic
2, and in
the future also on the Kriegers
farm, which will be connected and in action by then.
The double converter also fulfils an important function for grid stability,
so that more and more renewable energies can be safely integrated into
the overall system. For the transmission of electricity through alternating
current lines, a so-called reactive power is required to co-exist with
the active power. Until now, this reactive power was mainly provided by
conventional power plants. The double converter is able to provide a section
of the needed reactive power compensation for the north-eastern part of
the 50Hertz grid area.
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