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.