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

TAblE 4.2: SUMMARY OF ThE RESUlTS OF ThE TEE-IN cASES
18 OffshoreGrid -- Stakeholder Advisory Board meeting, 21/01/2010, Brussels.
OffshoreGrid -- 2nd Northern European Stakeholder Workshop, 10/06/2010, Brussels.
OffshoreGrid – Final Report
infrastructure
costs changes
Additional system costs
(over the lifetime)
Net Benefit
(over the lifetime)
Dogger bank A into BritNor - €290 m + €400 m - €110 m
Dan Tysk group into NordLink - €160 m + €63 m + €100 m
Butendiek into Cobra - €207 m - €43 m + €250 m
NordSee Ost group into Cobra - €280 m - €61 m + €341 m
The principal conclusions from a sensitivity analysis
of the effect of changing parameters on the net benefit
are:
• Asymmetrical cable dimensions can increase the
system benefits.
Increasing the capacity of one part of the interconnector
(from the tee-joint position), can lead to
better results. Capacity should then be increased
at the side of the country with the highest prices
(as trade flows towards the lower price level). A
higher capacity would allow trade and parallel wind
energy transport. The BritNor and NordLink cases
demonstrate that asymmetrical cable dimensioning
can increase trade possibilities to such an extent
that the costs for larger infrastructure are more
than compensated.
• Tee-in benefits are largely dependent on wind farm
sizes.
To add a different solution the following case for
the 1,000 MW Dogger Bank wind farm was investigated:
500 MW were teed into the interconnector
and 500 MW were connected directly to shore.
It was shown that net benefits for this case are
smaller in spite lower trade constraints on the interconnector.
The reason is that in this case 500
MW remain to be connected individually to shore,
which is relatively more expensive than connecting
a 1,000 MW wind farm (lower economies of scale).
• Additional parallel trade interconnections can
render a tee-joint more attractive than a direct interconnector,
as price differences will be lower and
trade less important.
• The effect of an additional UK-NO interconnector
on the cost-benefit of the tee-in solution for Dogger
Bank A is investigated. This makes the combined
UK-NO market more efficient and thus reduces
the value of trade between both countries. The
reduction in system benefits (economic trade constraints)
is therefore lower, going from €400 m to
€307 m. As this is still higher than the achieved
reduction in infrastructure costs, the tee-in solution
for Dogger Bank A is still not beneficial.
This analysis demonstrates that the techno-economic
relations are complex and that real cases do not allow
generalised conclusions. Further in-depth analysis
leading to such generalised conclusions is described
in section 4.4.
Practical discussion
In terms of power system security, an interconnector
cable with a wind farm connected in a tee-in
configuration must be considered as one single asset.
In case of a single fault anywhere on this asset, the
interconnector plus wind farm would need to be isolated
from the power system on both sides. Consequently,
the power systems on both sides will experience a
sudden change in power infeed, and contingency for
this scenario must be considered according to the
appropriate regulation. This may lead to an increased
requirement for frequency reserves on either side of the
tee-in, which should be considered before this option is
recommended. It should be noted that discussion with
representatives from some of the TSOs concerned
during formal and informal stakeholder interaction 18
have indicated that TSOs would prefer a solution with
fast circuit breakers on a platform to a simple tee-joint,
for reasons of operational security and fault handling.
TSOs today have many years of experience with interconnectors
based on Current Source Convertor (CSC)
technology. The largest CSC Interconnector in Europe
is rated at 2,000 MW and has been in operation since
45