Winding Down the
Cost of Offshore
Wind
Offshore Wind Power
Conventional Grid Access
New AC Grid Access
The cost of offshore wind energy is decreasing, thanks in part to two innovations from
­Siemens: a smaller AC substation called the
Offshore Transformer Module and a highercapacity wind turbine.
Text: Charles Murray Illustrations: Jochen Stuhrmann
32 Living Energy · No. 12 | July 2015
Offshore Wind Power
C
utting costs by one-third is a tall
order in any line of business.
But it’s one that the offshore
wind power industry has promised to
deliver: to push down the price per
kilowatt-hour of wind energy by 2020
from €0.14 to 0.15 to under €0.10.
With five years to go, the contours of
how this will happen are starting to
emerge, and two innovations are expected to be standouts in capturing
wind offshore.
One is a substation that has been simplified, standardized, and shrunk –
called the Offshore Transformer Module (OTM). The other is an uprated
version of the wind turbine itself.
A Pioneer’s Progress
Both innovations fit ­Siemens’ profile
as a trusted, stable partner to its customers, with over 23 years of experience in delivering offshore projects
on time and on budget. These factors,
alongside a firm commitment to invest in renewable energy such as wind
power, makes S
­ iemens’ offshore wind
turbines the most bankable solution
in the market. This careful balance of
innovation with reliability and low
risk is the source of ­Siemens’ global
reputation. Going forward, ­Siemens
aims to maintain its leading position
in the offshore market and drive it
to long-term sustainability. To that
end, the levelized cost of energy needs
to be reduced significantly in an increasingly heterogeneous market.
Wind power first went to sea a quartercentury ago. That step-out was typified by the first in-water installation
ever, at Vindeby, Denmark, delivered
in 1991 by ­Siemens. Still operated
­today by Dong Energy, its eleven turbines’ 5 megawatts of output was a
milestone for the industry. Moreover,
Vindeby is located relatively close
(1.5 to 3 kilometers) to land and in
shallow water (2 to 6 meters).
In subsequent years, as the push toward renewable energy surged ahead,
there was also a drive to reach greater
distances, depths, and capacities. As
34 Living Energy · No. 12 | July 2015
Offshore Wind Power
all the easily accessible sites on shore
and near the coastline filled up, and
in some areas, due to environmental
concerns, wind power plants had to
be placed further out and deeper in
the sea.
Today, offshore wind is one of the most
advanced emerging technologies. A
steep technological development has
taken place since Vindeby was installed
in Danish waters. As for the wind turbines, there is a clear trend toward
larger machines and larger rotors. In
the decades since offshore wind power took off, the capacity of the wind
turbines has multiplied by more than
200, while blade length has multiplied by 15.
After nearly a quartercentury, offshore wind
is one of the most
­advanced emerging
technologies today.
Projects also have grown considerably. The trend in offshore wind is toward larger parks that are further
­offshore. This ultimately gives way to
more complex projects exposed to
­severe sea and wind conditions. At the
moment, the world’s largest offshore
wind farm is the London Array of
175 wind turbines with a combined
capacity of 630 megawatts that matches many state-of-the-art conventional
gas or coal power plants. Inaugurated
in 2013, this project was successfully de­
livered by S
­ iemens with its ­SWT-3.6-120
turbines that sit 20–25 kilometers offshore in the Thames Estuary at depths
of up to 25 meters.
Even as the London Array was being
built, generators and suppliers were
recognizing their next challenge.
While hurdles of distance, depth, and
size had been cleared, newer projects
would have to achieve the same at
significantly lower cost.
Slimline Substation
One key cost target, recalls ­Siemens
Transmission Solutions CEO Tim
­Dawidowsky, was the AC substation
that connects the majority of offshore
wind parks to the onshore power grid.
Thanks to S
­ iemens’ pioneering efforts in the industry, the company has
already innovated and reduced costs
in offshore grid access. By introducing
new developments based on actual
experience and standardizing around
this best practice, ­Siemens has been
at the forefront of the drive to reduce
costs.
Since ­Siemens delivered its first AC
offshore platform for the Thanet project in the UK, there has been a steady
evolution of designs in the marketplace. During this evolution, the trend
has moved toward ever-increasing
specifications, increased functionality,
and higher power ratings – and a
­resultant increase in costs. Starting
in 2014, a task force with representatives of all relevant ­Siemens divisions
came together, drawing on their extensive offshore wind experience as
well as the best ideas from a broad
cross-section of customers, partners,
suppliers, and other key industry
stakeholders. Within eleven months,
the group had generated a design
for future AC platforms – one that
Dawidowsky hails as the vanguard of
the third generation. Four key features set the third generation apart
from the conventional, more bespoke
offshore substation platforms currently in the market: A simple design
with no moving parts; a more environmentally friendly design, with the
elimination of mineral oil; overall
weight is three times lighter than that
of a typical conventional AC offshore
substation platform; and cost is reduced by up to 40 percent across the
offshore scope.
A more compact AC substation, the
Offshore Transformer Module helps cut
operational and maintenance costs.
Plug-and-Play Principles
Other, more mature industries have
already noted and leveraged the advantages of a standardized, modular
approach in traditionally complex
engineering projects. Rather than
building major equipment directly
on the deck of an offshore platform,
resulting in increased interfaces and
critical paths, these are instead built
into standard-sized containers. Such
containers can then be mounted on a
simple platform deck at the fabrication yard. The process is analogous
to “plug and play” within the consumer electronics industry. Modular
assembly cuts out an enormous
amount of cost, Dawidowsky points
out, and it means S
­ iemens can leverage a true standardized approach
across multiple projects at all levels
of the supply chain.
Maintenance is also simplified. Rather than bringing specialists to malfunctioning equipment, a modular
approach allows the customer to decide whether to rectify faults offshore
in minor cases or to bring the equipment onshore, replacing it with an
immediately available spare unit. Repairs done on land, Dawidowsky
notes, “are about ten times less expensive than doing the same on the u
Living Energy · No. 12 | July 2015 35
Offshore Wind Power
The ­Siemens SWT-7.0-154 delivers
nearly 10 percent more energy
than its predecessor, while
retaining its proven reliability.
that are almost identical to those used
for the wind turbines themselves,
thus eliminating the need for a large
bespoke foundation. The smaller
­OTMs also allow utilization of a much
broader, potentially more local supply
chain for construction, something
that many customers find valuable.
siemens.com/swt-7-0-154
Combined Savings
“Repairs done on land
are about ten times
less expensive than
doing the same on the
platform itself.”
Tim Dawidowsky, CEO,
­Siemens ­Transmission Solutions
36 Living Energy · No. 12 | July 2015
platform itself.” Downtime is nearly
eliminated, because units can be exchanged altogether with replacement
units held as spares, another case of
“plug and play.”
Smaller Switchgear
Both high- and medium-voltage transformers have been optimized, increasing capacity whilst minimizing
bulk. Fans and pumps have been
completely eliminated. “No moving
parts!” Dawidowsky enthuses, noting
the inherent reduction in maintenance costs.
Neither do the transformers require
any mineral oil. Instead, they employ
a nonflammable, highly biodegradable fluid called ester liquid. This
brings two benefits over oil: It allows
an elimination of the fire-suppression system and it is a much lower risk
for marine life. Gas-insulation technology – already applied on ­Siemens
AC offshore platforms – has been
refined and improved, based on accumulated experience.
Shedding Pounds
The 2014 task force was also set a clear
goal to reduce the weight of the offshore substation and significantly bring
down overall costs. The realization that
cutting total mass below 1,000 tonnes
could bring about a step change in cost
reduction became a key factor in the
development of the concept.
Below 1,000 tonnes, the OTM can be installed by conventional ships and
cranes already deployed on the wind
farm for wind turbine and foundation
installation, as opposed to using large
specialized vessels that are much
more costly, much less available, and
subject to greater weather restrictions
in their operations. The solution, not
obvious at first but brilliant in retrospect, was to split the substation into
two smaller ones, each of which can
be mounted on separate foundations
By eliminating the need for its own,
separate foundation, the new, smaller
design can also be added to an existing wind turbine foundation while
hosting the wind turbine itself. This
delivers even greater cost savings,
as it eliminates the need for any additional foundation to support the
two modules. Typically, Dawidowsky
estimates, all this requires is adding
15 percent to the turbine foundation’s
structural steel to ensure that it can
handle the increased loading requirement. In addition, by thinking holistically across the whole wind farm,
considering both the turbines and the
grid connection, with the new solution one can avoid the need to use
dedicated compensation reactors for
the transformer. By using this capability to cancel out the capacitance of
the cables, it eliminates the need for
another large piece of equipment offshore with a resulting further optimization of the platform structure.
All told, each new substation module
weighs in considerably lighter, at
around 630 tonnes (generating
250 mega­watts each), a reduction of
nearly 60 percent from conventional
designs. For larger capacities, multiple modules can be used. Given that
typically, two-thirds of offshore capital
costs are expended on building and
installing platforms, this can result in
a serious reduction of future project
budgets. “This is a real cost-saving opportunity for AC grid connections,”
summarizes Dawidowsky, adding that
­Siemens is working on cost improvements in the DC sector as well. The
company is well versed in both types
Tail Winds for Turbines
A380
79.8 meters
154 meters
SWT-6.0-154
SWT-7.0-154
IEC class
IA
Nominal
power
6,000 kW
IB
Rotor
diameter
154 m
Blade length
75 m
7,000 kW
Swept area
18,600 m2
Hub height
Site-specific
Power
regulation
Pitch regulated,
variable speed
of current. In addition to its AC grid
connections, where S
­ iemens has delivered about 3 gigawatts of transmission
capacity, ­Siemens also has delivered
four DC substations with a combined
rating of 2.9 gigawatts. A fifth connection with a capacity of an additional
900 megawatts was ordered in 2014
and is scheduled to go into operation
in 2019.
Natural Progression to
7 Megawatts
As offshore capacities continue to
grow, so do those of wind turbines
themselves. ­Siemens’ flagship offshore wind turbine, the SWT-6.0-154,
has already set new standards in
gearless turbine design. In early 2015,
­Siemens raised the bar yet again by
introducing a generator upgrade to
7 megawatts. The S
­ iemens ­SWT-7.0-154
delivers nearly 10 percent more energy than its predecessor, while retaining its proven reliability. Development engineers have refined only
those turbine components needed to
increase electrical output. The new
model is set to go into serial production by 2017. Stronger permanent
magnets and generator segments in
the permanent magnet generator
provide the key to harvesting a higher yield. Additionally, the converter
and transformer have been upgraded, in line with the higher electrical
output. All other components
share the proven engineering of the
6.0-megawatt wind turbine, giving
­Siemens customers the assurance of
relying on proven technology and an
established supply chain while significantly increasing energy generation.
“Our new wind turbine offers customers an investment as reliable as our
proven G4 and D6 product platforms,”
notes Offshore CEO Michael Hannibal
of ­Siemens Wind Power and Renewables. “However, it also answers market demands to achieve greater energy
yield at lower cost and effort.” Cost
reduction through innovation is the
key factor of the new turbine and
­also of new ­Siemens grid access solutions. The turbine’s long structural
design lifetime of 25 years and increased power rating create a remarkable cost of energy benefit. p
Charles Murray is a science journalist who
writes about technology and sustainability
­issues. He is based in Zurich, Switzerland.
Living Energy · No. 12 | July 2015 37