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

for areas developed in the coming ten years and
2,000 MW for areas developed after 2020.
• When differences in timing of construction exist
between the wind farms in a hub or when delays occur,
it should be investigated whether a hub is still
beneficial. Short delays or delays of smaller wind
farms generally do not impact the economics too
much. However, governments should support simultaneous
development as much as possible in order
to reap the maximum benefits of the synergies of
a combined solution. OffshoreGrid recommends
assessing hub solutions even for projects that are
built within time spans of more than 10 years.
• National borders should not be a barrier for a hub
connection solution. If for instance a wind farm
is built close to the border and close to a wind
farm cluster in a neighbouring country, it is recommended
to construct cross border hub solutions.
Regulatory frameworks, support scheme issues
should allow these solutions.
• In order to improve conditions for cross border
meshed grid designs. European Member States
have to discuss how to distribute costs or funding
incentives for joint infrastructure measures.
Furthermore it has to be agreed to which country
the renewable energy generated is credited.
6.2 Tee-in solutions
Key results on tee-in solutions
• Connecting an offshore wind farm to an interconnector
by means of an underwater tee-joint is
technically possible irrespective of whether the
interconnector itself uses HVDC CSC or VSC technology.
For a configuration requiring circuit breakers
on a platform, VSC technology will become the preferred
solution.
• For reasons of operational security and fault handling,
TSOs may generally prefer a solution with
circuit breakers to reduce fault propagation. A full
cost benefit analysis would be required to justify
the additional cost and consequent reduction in net
benefit incurred.
46 As shown in Chapter 4, actual numbers are greatly dependent on case-specific parameters.
OffshoreGrid – Final Report
• Whether tee-in connection of offshore wind farms
to interconnectors is beneficial depends on the
associated constraints for international power exchange
and the substituted infrastructure costs.
When connecting an offshore wind farm hub to an
interconnector, the availability of the interconnector
for international exchange is reduced in the direction
towards the country to which wind farm was
connected originally (trade constraint). On the other
hand, infrastructure cost savings incur as the tee-in
is cheaper than the substituted individual connection,
due to the fact that for the beneficial cases
the cable length can be vastly reduced (wind farm
is far from shore but close to interconnector).
• Tee-in solutions become more beneficial when:
– Price differences between countries are low
as trade between the countries would then be
secondary,
– The wind farm is far from shore and close to the
interconnector 46 ,
– The country where the wind farm is built usually
has the lowest prices of the countries involved,
– The offshore wind farm generation is inversely
correlated with the price difference (high wind
power, low price difference),
– The wind farm capacity is either low compared
to the interconnector capacity (low trading constraints),
or double its size (large infrastructure
savings); the economically worst case would be
a wind farm and interconnector capacity of equal
size,
– A simple tee-joint is used instead of an additional
platform (fewer costs but no ability to break
faults).
• A special case, which can be considered to be a
tee-in solution, has been identified for large wind
farms far from shore. Instead of connecting the
whole wind farm to one shore, the connection can
be split and the wind farm can be connected to two
shores.
• This way, a wind farm is connected and at the same
time an interconnector is built that can be used
when the wind farm is generating less than 50% of
rated capacity, which occurs about 50-60% of the
time.
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