Offshore Electricity Infrastructure in Europe - European Wind Energy ...

are generally lower because the cable length can
be vastly reduced: individual connection to shore
is expensive, the wind farm to hub connection and
the bundled hub-to-shore connection with a large
capacity are cheaper.
• Hub-to-hub solutions become more beneficial when:
– Price differences between countries are low,
– Countries are far from each other but wind farm
hubs are close (high cost savings),
– The wind farm capacity, and thus its connection
to shore, is high compared to the interconnector
capacity (low constraints),
– The wind power is inversely correlated with
the price difference (high wind power, low price
difference).
• In many cases the wind farm hubs will be built first
to connect national wind farms. The interconnection
between the hubs is then built later and should
be dimensioned considering the price levels in the
countries the hubs are connected to. This is because
most of the time the power would flow from
the hub in the country with the lower price to the
hub in the country with the higher price. Of course it
would be optimal to additionally dimension the hub
connection cables according to these considerations,
as in the case of the “split-cable-connection”.
But this is only possible in the ideal case when the
hub-to-hub connection is taken into account at the
very beginning of the project planning.
• Ideally, the hub-to-hub connection would be planned
from scratch which allows the hub-to-shore and
hub-to-hub connections to be dimensioned according
to expected price levels in the interconnected
countries. In general this would mean that the hubto-shore
connection should be dimensioned larger
in the country with the higher price level. This is
in line with the power flow as an additional power
trade from the country with the higher price level
would be beneficial.
• For meshed grid nodes with more than two lines
coming together, similar conclusions can be drawn.
The links to the country with the highest prices
(over the lifetime) should be largest, and the other
ones can be smaller in dimension. The most efficient
solution would occur if the sum of all country
connection cable capacities equals the sum of the
OffshoreGrid – Final Report
connected wind farms. This way the additional investment
in integrated platforms and joints brings
interconnection between three countries. If larger
interconnection capacity is needed, some of the
cables can be oversized.
• Concrete guidelines for pre-feasibility analysis on
hub-to-hub solutions have been defined and can be
found on www.offshoregrid.eu.
Recommendations on hub-to-hub solutions
• When hub connections for offshore wind farms are
developed, the plans should be reviewed by the TSO
in order to identify possible connection options to
other wind farms hubs or countries for which there
is demand for international exchange.
• Equally, when developing interconnectors, TSOs
should review the identified concession areas for
offshore wind and consider the option of developing
a hub in such an area as a starting point for the
interconnector.
• If feasible options have been identified, the offshore
grid developer should carry out a detailed feasibility
and pre-design study in view of an optimal dimensioning
of the integrated solution. This may include
increasing the rating of the hub connection to shore
in order to satisfy the required demand for international
exchange. As for tee-in solutions, the focus
should be on increasing the capacity on the side of
the country which usually has the highest prices.
• Offshore grid development should be a joint or, at
least, coordinated activity of the developers of the
wind farms and their hubs connections, and TSOs.
• The North and Baltic Sea countries should adapt
their regulatory frameworks to foster such a coordinated
approach.
• When looking at the interconnection of two hubs in
different countries: In the case that the hubs are
built first and the hub-to-hub connection is added
later on to the existing wind farm hubs, there is
not much need of additional international coordination.
In such a case the interconnection would be
comparable to an onshore cross-border interconnection
in terms of its legal, regulatory and political
complexity.
93