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38 renewable energy focus July/August 2009
Feature article
Compact electrical generators of stunning power, wind turbine head
weights halved, super-efficient power transmission with negligible line
losses; it’s a tantalising vision for the renewables sector. Making it a reality
could transform the economics of wind energy, and that is a key aim of
a number of forward-looking companies now bringing a new technology
to market.
These firms, along with academic partners, have tackled the issue of
electrical resistance, the phenomenon that accounts for massive aggre-
gate power losses – mainly in the form of waste heat – in humankind’s
technological infrastructure. If resistance could be eliminated, or nearly
so, more current would flow in a given wire or machine and more work
would be done by a set amount of energy. The technology that could
make it happen is superconductivity.
Ever since Dutch physicist Heike Kamlerlingh Onnes discovered, almost
a century ago, that the metal mercury could, under certain conditions,
lose its resistance to direct current and become a near-perfect conductor,
Rise of the superconductorCOULD SUPERCONDUCTORS TRANSFORM THE ECONOMICS OF
WIND POWER?
Courtesy of American Superconductor Corp.: Illustration shows magnified view of high temperature superconductor cable.
renewable energy focus July/August 2009 39
Renewable energy/infrastructure
there has been excitement about superconductivity. The sting in the tail
was that mercury must be cooled to 4.2 degrees Kelvin – that is within
a few degrees of -273 deg C, the absolute zero of temperature – before
it will exhibit its quirky behaviour. Achieving this, for mercury and similar
low-temperature superconductors (LTS), is an expensive high-tech under-
taking that has held back the application of superconductivity ever since.
However, efforts to develop materials able to superconduct at higher,
more achievable, temperatures have latterly borne fruit. The 1986
discovery by two IBM scientists that barium-doped lanthanum copper
oxide becomes a superconductor at 36 K, some 12 K above the previous
highest superconducting temperature, was considered a breakthrough.
Other cuprates have since demonstrated transition temperatures of up to
130 K, and several of these can be sufficiently cooled by liquid nitrogen,
which liquefies at 77 K, rather than by liquid helium and the expensive
cryogenic coolers previously required. Liquid nitrogen is a widely acces-
sible industrial cooling medium and can be used with these materials,
dubbed high-temperature superconductors (HTS).
Today, development emphasis is on rare-earth cuprates, in particular
yttrium-barium copper oxide (YBCO), though difficulties in producing
this in continuous lengths suitable for wire and tape have until recently
obliged engineers to rely on an earlier bismuth-strontium-calcium copper
oxide (BSCCO) formulation that consequently became the first-generation
superconductor workhorse.
Because this complex metal oxide has a ceramic-like brittleness and is
difficult to bend, producers like the American Superconductor Corpo-
ration (AMSC) surround filaments of BSCCO with pliable silver when
making the thick tape that they then wind into final cable. A pipe for
nitrogen coolant also has to be incorporated. Even so, the resulting
cable carries three to five times as much power as a copper cable the
same size. It has proved possible to manufacture BSCCO conductor in
kilometre-plus lengths.
Second-generation wires and tapes, based on the rare-earth cuprate
YBCO, can be produced less expensively than the first generation by
chemically coating the active material onto a nickel wire or other
conductor substrate. Silver is not needed in the final product. Companies
such as AMSC and SuperPower Inc have developed, with research input
from research bodies like the USA’s Oak Ridge National Laboratory
and Sandia National Laboratory, continuous-feed coating processes
suitable for producing 2G wire, which has now begun to supersede the
first-generation product in live applications. The latest 2G power cables
can conduct up to 10 times the amount of power comparable copper
cables manage.
Commercial
Superconductivity has begun to yield real benefits in pioneer applica-
tions. About 7 years ago, some 8 tonnes of copper cable in a main feed
to Detroit, USA, was replaced with 110kg of first-generation supercon-
ducting cable. Three 120m lengths of cable take up just three of 9 previ-
ously-occupied underground ducts, leaving ample room for anticipated
demand expansion. Since then there have been many more applications,
mainly of 1G cable, but with a growing number of 2G applications now
becoming evident.
Superconducting cables from companies like AMSC, SuperPower Inc, the
Southwire Company, Ultera – a partnership between Southwire and
Denmark’s NKT Cables – Zenergy Power, Nexans SuperConductors,
Sumitomo Electric Industries and others are contributing to high-power
underground distribution networks in urban centres ranging from New
York and Columbus in the USA, to Amsterdam in the Netherlands, Copen-
hagen in Denmark and Seoul in Korea.
AMSC recently shipped 17 km of HTS cable, manufactured by Ultera
using AMSC 2G wire, for use in Consolidated Edison’s Manhattan grid.
This product, which will deliver 10 times more power than a copper equiv-
alent, is called Secure Super Grids (SSG) cable because it will also suppress
fault currents. This is by virtue of a characteristic of a superconductor that
once its current carrying capacity reaches a natural limit, determined by
magnetic and other factors rather than resistance, it ceases to conduct
and becomes resistive, thereby blocking fault currents.
Other promising applications for superconductors include powerful
electromagnets and the to-date elusive magnetic levitation (maglev)
train; compact transformers, generators and motors; and power storage
devices. Superconducting wire is in facilities ranging from mobile phone
base stations to the Large Hadron Collider at the European Organisation
for Nuclear Research (CERN) in Switzerland.
A few years ago AMSC heralded a likely revolution in marine propul-
sion by manufacturing a 5000hp motor a fifth the size of an equiva-
lent copper-wired motor, and it has recently produced and tested, with
Northrop Grumman, a 36.5 MW (49,000 hp) motor that is about half
the size and weight of a conventional equivalent. A motor operated in
reverse i.e. converting mechanical power into electrical power rather than
vice-versa, is a generator and superconducting wire was key to a 100 MW
super-generator developed by the General Electric Company under the
US Department of Energy’s Superconductivity Partnership Initiative.
Benefiting wind turbines
If HTS superconductor cables can live up to their promise of cutting grid
transmission losses at acceptable expense, this will help the viability
of wind farms that must transmit their power over long distances to
established distribution networks. For example, AMSC ‘superconductor
electricity pipelines’ are being considered for the proposed US grid that
will link wind and other renewable resources in the inland states to the
largest centres of population which, in the main, are near the coast.
However they can do more than this, becoming integral to wind turbines
themselves. According to Zenergy Power PLC, a UK-headquartered
manufacturer and developer of commercial applications for supercon-
ductive materials, achieving WT generators a third the size and a quarter
the weight of their conventional equivalents will greatly facilitate the
construction and deployment of large wind turbines, particularly future
Investors will be taking careful note of
further developments as the technology
[superconductor] continues to transition
from dream to reality. For renewables,
and wind in particular, it is a potential
game changer.
40 renewable energy focus July/August 2009
Renewable energy/infrastructure
offshore units of up to 10 MW. It will also, claims a spokesperson, cut
electricity generation cost by up to a quarter.
The company, partnering French electrical systems specialist Converteam
Group SAS, is two years into a five-year agreement under which the part-
ners are jointly developing HTS generators for the wind and small hydro
power markets. In particular, Converteam is leading a UK BERR - formerly
UK Department of Trade and Industry (DTI) - funded project to design an
8 MW direct-drive superconducting wind generator based on Zenergy’s
HTS wire. The partners, who regard offshore wind as a large and commer-
cially viable market for HTS technology, are preparing to test the first HTS
wind turbine this year.
As Michael Fitzgerald, chairman of Zenergy, explained, “wind power gener-
ation represents the most mature source of renewable energy production.
Converteam shares this belief [with us] and has stated its intention to be
at the forefront of this industry. We are excited to be working together
on developing cutting-edge technologies based around our patented
materials and products.”
Pierre Bastide, president and ceo of Converteam adds, “we believe
that the extraordinary electrical efficiency and power density enjoyed
by HTS wind turbines represent the most viable solution for over-
coming technical and economic challenges facing the renewable power
generation industry.”
Direct drive is favoured for this and other projects because it eliminates
the gearbox and reduces the number of bearings and other failure-
prone components, thereby reducing WT maintenance needs and oper-
ating costs. Use of HTS-based superconducting magnets enhances the
viability of such machines, not least by transforming their power-to-
weight ratio. One industry pundit suggests that if the cost of HTS mate-
rials like YBCO decreases as anticipated, superconductive wind turbines
with rated MW capacities into double figures could be seen within the
next five years.
AMSC, which entered the wind energy business as a logical extension
of its original focus on electrical power distribution, is working with its
wholly owned subsidiary AMSC Windtec of Austria to analyse the costs
of a 10 MW-class wind turbine incorporating a direct drive supercon-
ductor generator. The results will be used by the US National Wind
Technology Center (NWTC) to benchmark and evaluate the turbine’s
economic impact, in terms of both its initial cost and its overall cost
of energy.
The NWTC is part of the US Department of Energy’s National Renewable
Energy Laboratory (NREL), the director of which, Dan Arvizu, said after
a cooperative research and development agreement had been concluded
with the DoE early this year, “high-temperature superconductors hold
promise for helping to lower the overall cost of wind energy. We are
pleased to be teaming with AMSC to move this technology forward.”
Superconducting cables from companies like AMSC, SuperPower Inc, the Southwire Company, Ultera – a partnership between Southwire and Denmark’s NKT Cables – Zenergy Power, Nexans
SuperConductors, Sumitomo Electric Industries and others are contributing to high-power underground distribution networks in urban centres ranging from New York and Columbus in the USA, to
Amsterdam in the Netherlands, Copenhagen in Denmark and Seoul in Korea.
42 renewable energy focus July/August 2009
Renewable energy/infrastructure
General manager of AMSC’s superconductor business Dan McGahn
commented, “superconductors are today proving their tremendous power
density and efficiency advantages to electric utilities and large power
users. This program brings those same benefits to the rapidly growing
wind power market.”
AMSC continues to work with the TECO Westinghouse Motor
Company to develop HTS and related technologies for a 10 MW-class
offshore wind turbine. A US$6.8 million, 30-month design project,
on-going since 2007, is 50% funded by the National Institute of
Science and Technology’s Advanced Technology Program. The part-
ners say that superconductor technology will make it much easier to
break the 10 MW barrier for wind turbine power, a new turbine being
a fraction of the size and half the weight of a conventional direct drive
machine of equal power. A 10 MW HTS-based machine is expected
to weigh around 120 tonnes rather than the 300 tonnes likely for a
conventional direct drive 10 MW turbine.
According to Jason Fredette, director of investor and media relations
at AMSC, the UK is seen as a major target market. He argues, “the UK
is talking about tens of Gigawatts of new capacity, up to 33 GW; you
can either put up 7,000 to 8,000 smaller wind turbines or 3,000 to 4,000
turbines in the 10 MW class. Our objective is to have a turbine ready for
when offshore wind really takes of in the middle of the next decade. That
gives us time to commercialise the system.”
AMSC is already known in the UK energy sector for its voltage control
systems, including its D-VAR dynamic control system that allows wind
farms to be connected to the grid in accordance with UK grid codes. The
10 MW turbine project will also benefit from the company’s involvement
in a US$100m programme for the US Navy, under which it has developed
a 36.5 MW ship propulsion motor using coils of HTS wire rather than
conventional copper wire.
Fredette points out that AMSC has been working on power dense
machines for 17 years so that the technology is proven. He says that
AMSC would not build the turbine itself, but would supply supercon-
ductor components to a UK or northern European partner who would
construct and supply the final product.
Nevertheless, AMSC is more deeply involved in the wind industry than
this suggests. Its acquisition of Austria’s Windtec GmbH allows it to design
turbines and licence these designs to customers. A number of clients
in Europe and the Far East are now producing, or preparing to do so,
Windtec-designed turbines. For instance, the company has licensed its
WT1650 model (1.65 MW) to Turkish company Model Enerji Ltd, and this
is likely to be followed by proprietary 2 and 2.5 MW designs.
In China it is providing the XJ Group Corporation with designs for its
WT2000 double-fed induction wind turbine, while additionally supplying
core WT components for the Chinese company’s own designs. It is doing
a similar thing for the Shenyang Blower Works Group and gets to supply
full electrical systems for all SBW’s wind turbines. CSR Zhuzhou Electric
Locomotive Research Institute Company has ordered core WT compo-
nents for 1.65 MW machines.
Beijing-based Sinovel Wind Corporation Limited has ordered US$18m
worth of AMSC systems and components to be deployed in 3 MW
machines being developed by AMSC Windtec. Machines of 5 MW are
expected to follow. Another Chinese customer, wind turbine producer
the Dongfang Steam Turbine Works, is building 2.5MW turbines to a
Windtec design.
Korea’s Hyundai Heavy Industries has acquired AMSC designs for 1.65
and 2 MW models it intends to start producing this year. Canada’s AAER
Inc has ordered core electrical components for twenty 1.5 MW machines,
a follow-up to previous orders, and is due to start producing a Windtec-
designed 2 MW machine. Another licensee is Ghodwat Industries (India)
Pty Ltd, starting with Windtec’s WT1650 technology.
While none of these involvements result in sales of superconductive
elements directly, the overall activity increases AMSC’s engagement with
wind energy, provides a revenue stream that helps fund development of
WT applications for superconductors and positions the company to inject
superconductor solutions into key wind energy markets as the tech-
nology develops.
Superconductivity can also play its part in enabling low-wind sites to
be productive. Developers of a ‘magnetic levitation’ wind turbine gener-
ator - unveiled at the 2006 Wind Power Asia Exhibition in Beijing - said
it could create new opportunities in low wind areas worldwide, helping
to harness previously untapable resources. China’s Academy of Sciences
and Guangzhou Energy Research Institute added that their maglev
generator could boost generating capacity to a fifth more than traditional
turbines, while halving wind farm operating expenses.
Superconductivity’s time as little more than a tantalising dream may now
be past, with the wind energy sector being a likely leader in its adoption
and commercialisation. The technology’s ability to practically double the
power available from a turbine of given size and weight is compounded
by its potential to lower the cost of transmitting and distributing the
power generated at wind farms. Benefits in other renewable sectors, such
as hydro, current and wave power, could follow. Investors will be taking
careful note of further developments as the technology continues to tran-
sition from dream to reality. For renewables, and wind in particular, it is a
potential game changer.
About the author
George Marsh is a technology correspondent for Renewable Energy Focus magazine.
Testing of an FCL.