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

conclusions and recommendations
• While the sum of the two cable capacities should
be a little bit smaller than the wind farm size, the
individual cable sizes should be decided based on
the price levels in the connected countries. The
connection to the country with a higher assumed
price level across the project lifetime should be
larger than the connection to the country with a
lower price level.
• A detailed case study on the Cobra cable between
Denmark and the Netherlands was carried out.
Teeing-in a German wind farm to the Cobra cable
is identified as beneficial from the point of view of
European welfare. The case study also confirmed
the conclusion on the split connection of the large
wind farms: teeing-in a 1300 MW into the 700 MW
Cobra cable proved to be the most interesting
option.
• Concrete guidelines for pre-feasibility analysis on
tee-in solutions have been defined and can be
found on www.offshoregrid.eu.
Recommendations on tee-in solutions
• For large wind farms/hubs far from shore, the
opportunities for splitting the connection to two
shores and creating an interconnector at the same
time should be investigated.
• For small wind farms that are considered to be far
from shore (e.g. offshore wind to supply oil and gas
platforms), it should be investigated whether they
can be teed-in to an interconnector.
• When deciding between a tee-in solution and a
split connection (one wind farm connected to two
shores), the rating of the cable sections at either
side of the wind farm should be carefully considered,
based on an individual power market analysis.
In order to reduce the constraints and maximise
the benefits, the capacity should be highest at the
side of the country which usually has the highest
prices.
• Interconnectors that are required for international
exchange or improving security of supply should
not be delayed and they should be rated as optimal
for these purposes. If future wind farms are
considered to be installed close to one of these
interconnectors, the technology and cable route
should be anticipated to maximise the future benefits
of the integrated solution.
• If a wind farm tee-in produces net benefits compared
to the conventional connection of the wind
farm to shore, no technology should be ruled out
a priori. The decision on which HVDC technology to
use and on which technical set-up to favour should
be based on the analysis of all costs and benefits
including operational implications (e.g. fault handling,
redundancy, etc), costs of infrastructure,
electrical losses and available capacity ratings.
• Tee-in connections are technically feasible and
economically beneficial in many cases. However,
incompatible regulatory frameworks and support
schemes can hinder construction as the developer
is confronted with large uncertainties, in particular
in regard to the support or capital attraction due to
difficult connection barriers. In particular when the
wind farm in question is connected to an interconnector
that does not start or end in the country in
which the wind farm is built, national states might
be reluctant to support the solution if the renewable
energy generation is not credited to them.
These political, support scheme and regulatory
framework issues need special attention in the
coming years in order to make tee-in solutions
possible.
6.3 Hub-to-hub solutions
Key Results on hub-to-hub solutions
• Connecting countries via offshore wind farm hubs
requires VSC technology and circuit breakers on
a platform as fault propagation has to be limited.
This is in particular necessary in order to maintain
a high grid operation stability and security of supply
level.
• Whether a hub-to-hub solution is beneficial over a
direct interconnector depends on the associated
constraints for international power exchange and
the substituted infrastructure costs. While the
integrated solution reduces the possibilities for
trade (trade constraint), the infrastructure costs
92 OffshoreGrid – Final Report