As an innovator in wind power technology, Siemens tailors its
rotor blades to the requirements of the market at all stages of
development. The latest revolution is a so-called aeroelastically
tailored blade (ATB) whose d
­ esign absorbs gusts of high wind
­allowing for greater energy capture and longer system lifetime.
Text: Christopher Findlay Illustration: James Provost
Blades with a Twist
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PLATE 1
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PLATE 2
Wind Power
Wind Power
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56 Living Energy · No. 8 | July 2013
The Basics
In rotor design, size is what really
matters. Since the energy captured
and the loads are a function of rotor
size, greater rotor size translates
­directly into more energy captured –
but also higher loads on the struc­
ture.
The cost of energy can be gauged by
a simple calculation: the total cost of
the machine divided by the amount of
energy captured. The total cost of the
machine is a function of the structural
loads – higher loads require a heavier
and thereby more costly machine.
Thus, if the amount of energy cap­
tured can be increased without a cor­
responding increase in structural loads
by the rotor, this translates directly
into reduced cost of energy and added
value for the customer. Improving ro­
tor design to capture 1 percent more
energy without adding any load and
cost roughly translates into a 2 per­
cent reduction in the cost of e
­ nergy.
While there are many concepts float­
ing around as to how this can be
achieved, Standish notes that in the
dynamic and competitive wind indus­
try, it sometimes takes a while until
the time is right to bring such ideas
to maturity. “We don’t have the luxury
of being able to build and fly ‘concept
rotors’ like the aerospace or automo­
bile industries do – the costs are
­simply too prohibitive,” he says.
Size matters: The aeroelasticity of the innovative Quantum Blade means that the overall diameter
of the turbine can be increased for significant gains in energy output without increasing the structural load
on the rest of the turbine components.
Unlike automobile makers, which
may take years to develop a concept
car into a marketable mass-produced
vehicle, producers of rotors and tur­
bine components are not trying to sell
new concepts, but are driven by the
paradigm of bringing down the cost
of wind power by all means and as
quickly as possible.
Photo: Siemens
s a designer for rotor blades in
wind turbines, Kevin Standish
has a demanding job; but he’s
aware that innovation must always
follow the imperative of economic
­efficiency. “Our job is to reduce cost
of energy, plain and simple,” he says.
“All the ideas we have must pass that
litmus test.” In the science as in the
business of rotor blades, the bottom
line is measured in terms of annual
energy production (AEP). Standish,
who heads the rotor technology R&D
team at the Siemens Wind Power lab
in Boulder, Colorado, knows how far
the technology has come since the
early days of rotor design.
The first wind turbine designed in
1980 by Bonus Energy, a predecessor
of Siemens Wind Power, had blades
with a length of 5 meters and a power
capacity of 30 kilowatts. Each 5-meter
blade had a weight of 75 ­kilograms.
If one were to extrapolate on the basis
of these values using the square-cube
law, a modern 53-meter-long B53
Siemens blade would weigh approxi­
mately 90 tonnes. Fortunately, that’s
not the case. Thanks to s­ everal ad­
vances in design technology and pro­
duction techniques, it weighs just
10 tonnes, several hundred kilograms
less than its predecessor, the B49 –
even though it is 4 meters longer.
Such efficiency gains are the result of
many years of research and innova­
tion, all of which ultimately are aimed
at increasing AEP and decreasing
costs. Advances at all stages of the
­development process, from concep­
tualization to manufacturing, have
­enhanced efficiency and contributed
to making wind power more competi­
tive and reducing costs for operators
and electricity consumers alike.
Conceptualization
However, when engineers do come up
with an idea for more efficient blades,
acceptance in the market can be in­
stantaneous. Siemens has consolidat­
ed its position as leader in the global
offshore wind market with two inno­
vative concepts. The first of these is
the IntegralBlade® manufacturing
process. It involves the casting of
­fiberglass rotor blades in one piece
rather than from two halves.
This process eliminates the necessity
for a seam, which is critical both
structurally and aerodynamically:
Like everywhere else, joints and
seams are weak points in structures
such as wind turbines. The Siemens
process of casting from a single mold
without glue joints gives blades maxi­
mum quality, strength, and reliability.
Another unique feature of the latest
Siemens rotor blades is their physical
shape. Blade design is a core compe­
tence of Siemens; engineers at
Standish’s Rotor Design and Technol­
ogy Group in Colorado are constantly
striving to improve the shape of rotor
blades and edge contours. One of the
ideas that has been blowing around
the wind industry for about a decade,
but which has only recently advanced
to maturity, is the concept of the aero­
elastically tailored blade.
The Siemens Quantum Blade – a des­
ignation applied to all rotors made by
the company since 2011 – is not only
lighter than earlier models, but also u
Living Energy · No. 8 | July 2013 57
Wind Power
Wind Power
Proof Testing
Due to the extremely competitive
­nature of the industry, time lines
for taking a product from concept
to product are nowadays very
­compressed. Collaboration between
the R&D team in Colorado and
Siemens facilities in Denmark is
very close. New blades and other
­turbine components undergo trials
in two state-­of-the-art test centers
in Denmark – one located in Brande,
the other in Aalborg further north
(see “In Short”, p. 84). The Aalborg
site includes seven test stands for
full-scale testing, including for the
75-meter B75 blade, which is twice the
size of an Airbus wing. The two facili­
ties combined constitute the world’s
largest R&D test ­center for wind tur­
bine technology.
Testing includes highly accelerated
life test (HALT) programs, which may
last up to six months. In these stress
tests, blades are subjected to loads
that go far beyond the expected strain
they will be exposed to over their or­
dinary operational lifetime: They are
oscillated at exceptional ­deflections
for 2 million cycles vertically and
then for another 2 million cycles hori­
zontally.
has a unique planform design that
­literally gives it a special twist. Its
aeroelastic tailoring means that inevi­
table deflection, or structural defor­
mation from loads caused by sudden
gusts of wind, gives the blade an
­aerodynamic advantage. A wind tur­
bine that is buffeted by the wind will
feel the shock through its system,
from the blade through the gearbox,
the generator, and the tower all the
way down to its foundation. By cou­
pling the bending and twisting of the
blade, that structural load is actually
reduced, absorbing shock much like
the suspension in a motorcycle.
Design
58 Living Energy · No. 8 | July 2013
Production
The IntegralBlade® manufacturing process involves the casting of fiberglass blades
in one piece rather than from two halves.
The rise of high-performance com­
puting has, of course, greatly assisted
designers in the past decades. Has
blade design and testing become easi­
er thanks to the IT revolution? Com­
puters give designers a huge range of
new capabilities. The complex design
of an aeroelastically tailored blade
could not have been developed with­
out advanced computing. “But that
doesn’t mean that design has ­become
easier or harder,” says Standish:
“We’ve just pushed back the limits of
what we’re capable of doing.”
Photo: Siemens, Illustration: James Provost
The advantage of this swept shape
compared to a conventional blade is
not just a reduction of wear and tear,
however. The aeroelasticity of the
­innovative Quantum Blade means
that the overall diameter of the tur­
bine can be increased for significant
gains in energy output – without
­increasing the structural load on the
rest of the turbine components.
Of course, everybody wants to maxi­
mize power gains. “The difficulty is
that gravitational loads, aerodynamic
loads, and inertial loads all begin to
increase extremely rapidly as the size
of the rotor blade is extended,” says
Standish. “Aeroelasticity allows you
to use a larger blade, without higher
loads, resulting in higher AEP for
­essentially the same costs.”
Rotor blades are exposed both to
short-term extreme loads, such as
those exerted by sudden gusts of high
wind, and to fatigue loads, which
­accumulate over the lifetime of the
turbine. The primary function of
aeroelasticity is to reduce fatigue
loads, but any reduction of extreme
loads or fatigue loads will increase
the lifetime of the system, all other
things being equal. Since the loads
envelope of the rest of the turbine is
fixed, this fatigue reduction is con­
verted into rotor growth and,
­ultimately, AEP.
The casting of the one-piece blade is
a process that requires a high degree
of care and attention to detail. The
current blade series offered by
Siemens are the B49, B52, B53, B55,
B58, and the B63, as well as the mas­
sive B75 (in each case, the number
stands for blade length in meters).
At the Siemens Wind Power manufac­
turing base in Aalborg, Carsten
­Pedersen is responsible for Business
Excellence and Quality Management.
He takes pride in the one-step opera­
tion patented by Siemens: “The advan­
tage is that our blades have no adhe­
sive joints or weak spots like those of
our competitors,” he says.
Blade manufacturing requires system­
atic quality assurance both during the
process and when the blade, made
from fiberglass and balsa wood, has
The ATB design reduces structural load, absorbing shock to the system
like the suspension in a motorcycle.
been cast, cured, removed from the
mold, and painted. A blade experienc­
es more than 100 million load cycles
during its 20-year lifetime, and ultra­
sonic scanning is used to ensure that
the finished blade has no flaws that
might develop into issues in the field.
A further measure to reduce costs
of production and logistics, and thus
the price of wind power to end con­
sumers, is the use of standardized
parts and processes. This, too, makes
­turbines cost-effective and helps wean
wind power off subsidies. “The ques­
tion for customers should not be, ‘Why
wind power?’, but ‘Why not wind pow­
er?’,” says Standish.
Selling Points
Economic efficiency, higher energy
output, innovative aeroelastic design,
predictability, and grid stability –
these are important selling points for
the range of Siemens wind turbine
blades. But it all boils down to the
magic AEP value – and for some cus­
tomers, there’s the noise factor. Of
course, Siemens also aims for quiet
turbines that can operate unobtru­
sively even close to residential areas,
though for buyers looking to set up
an offshore wind park or a turbine
­array in remote rural areas, that is
less of a factor.
The sales contract guarantees a cer­
tain performance level for customers.
The buyer is protected; the burden is
on Siemens to deliver the promised
output. “If we design a new rotor and
incorporate a new technology, it will
have customer orders waiting on it,”
Standish explains.
“The Siemens brand stands for itself,”
says Standish; there’s a reason why
Siemens is the market leader for off­
shore wind, a harsh and much more
demanding environment than on­
shore: “If an investor is putting money
on the table for an offshore wind
farm, they want the best they can get
in terms of dependability – it’s in­
credibly expensive to service and
­repair turbines once they are in place
offshore. Reliability and robustness
are the crucial factors.”
The Future of Rotor Design
What will the future bring in terms of
pushing the envelope in rotor innova­
tion? Aeroelastically tailored blades
will certainly be standard Siemens
design in the future, says Standish;
but other ideas are already floating
around. One futuristic concept dis­
cussed among researchers is to in­
stall flaps on turbine blades, in a sim­
ilar manner to an airplane wing.
Instead of having a solid piece of fi­
berglass, one could install an active
control system of moving parts onto
the blade’s edge, allowing the rotor to
gain or shed loads actively, depend­
ing on prevailing winds.
Whatever the future brings, one
thing is certain: Innovation will con­
tinue to be vital in such a fast-moving
and dynamic market as the wind pow­
er industry, and Siemens will strive to
remain one step ahead of its competi­
tors while continuing to set new
benchmarks and adding unexpected
twists to its products, all with the aim
of raising output and lowering the
price of wind energy. p
Christopher Findlay is a freelance journalist
­living in Zurich, Switzerland. He writes on
­science and politics.
Living Energy · No. 8 | July 2013 59