POWER

34

IEE

ES

PE

CT

RU

M•

Oct

obe

r 20

02

ReapTheWild

Wind

A fresh breeze is blowing at Horns Rev, where the Danes are building the world’s biggest offshore wind farm

On a beautiful sunny Saturday morning,unseasonably warm for spring, the MSOcean Adys is getting ready to leave Esb-jerg, on Denmark’s west coast. Our cargois stowed safely on board, and now the

crew is making final adjustments before taking in the dock-ing lines and pulling up anchor.

Commissioned just days before, the Ocean Adys has theoutlines of a small cargo vessel. But unlike the other shipsthat leave this busy port city for points the world over, piledhigh with giant sky-blue corrugated Maersk Sealand con-tainers, the Ocean Adys isn’t going very far—our trip will lastjust four hours. Our destination: Horns Rev (Reef), a windfarm now being developed 14 km off shore by Elsam A/S(Fredericia), Denmark’s biggest power producer. The ship,too, carries an unusual payload: two boxy white nacelles, 13meters long and 4 meters high, stacked one atop the other,each housing the generator and other machinery that turnwind energy into electricity. Two rotor blades are attached toeach, forming a wide-angled V at one end.

The Ocean Adys carries a second crew, fielded mostly byVestas Wind Systems A/S (Ringkøbing), the Danish com-pany that’s building and installing wind turbines for Elsam.It’s an exciting time to be in the business of harvesting elec-tricity from summer breezes and winter gusts. Wind poweris the fastest-growing energy sector in the world, and busi-ness is booming for Vestas, the world’s biggest wind turbinemaker. The foreman of the Vestas crew, a young man namedFlemming Olsen, has installed turbines across the globe: inItaly, Morocco, New Zealand, and Costa Rica, as well as inWisconsin, New Mexico, and California. Other crew mem-bers have worked in Greece, Taiwan, Japan, and Oregon.

But Vestas has never erected a wind park as large as this atsea, and neither has any other company. The nine wind farmsthat have been built offshore are mostly tiny and set in shelteredwaters. The largest, near Copenhagen, is capable of producingjust 40 MW. Horns Rev, when it comes on-line in November,will dwarf it. Eighty towers in 20 km2 of sea will be capable ofgenerating 160 MW of power, or enough for 150 000 house-holds. Elsam expects Horns Rev to make 600 GWh of electric-ity a year, 2 percent of the country’s total electrical consumption.

To build Horns Rev, Vestas has drafted a subcontractor,A2Sea A/S (Fredericia, Denmark), a company that exists sole-ly to transport and install wind turbines. A2Sea in turn took alease on two freighters, Ocean Adys and a sister ship, the OceanHanne, and transformed them into ocean-going constructionplatforms. It stacked the Vestas crew quarters—which are in fact

corrugated-metal containers, grouped in threes or fours andbolted together—just behind the bridge. It added four 60-tonsubmersible legs with rounded feet, so that the ship couldfunction as a self-propelled platform. It installed two smallcranes and one very large one, 91 meters long, to hoist thenacelles and towers that will hold them. It opened two of thehatches, and put a steel frame in the hold, so that the ship couldnow carry two towers, each in two sections.

The task today, when we arrive at Horns Rev, is to install thetwo nacelles atop waiting towers. The crew will probably workthrough the night. They certainly do not expect to get muchsleep. Four men will climb 70 meters to the top of each towerto guide the nacelle and then secure it. The men wear harnesses,but still, it’s a long way up, and a long way back down.

A technology taking off

Two piers away from the Ocean Adys’s berth, excavators claw atan enormous pile of rubble, rumbling over chunks of concreteand grappling with twisted strands of steel I-beams—theremains of an Elsam coal plant that is being torn down becauseit didn’t meet new emissions rules. Denmark has long been aleader in green energy; over the last three decades, it has pouredabout US $300 million into research and development as wellas consumer subsidies into the nascent industry. The latest ver-sion of Energy 21, the long-range plan that Denmark establishedin 1996, calls for renewable forms of energy to supply 20 per-cent of the grid by 2003; most estimates suggest the actual fig-ure will be closer to 27 percent, virtually all from wind.

Other countries are wiring themselves for green elec-tricity, but none of them has embraced it so thoroughly.Germany, the United States, and Spain each generate morewind power than Denmark. By the end of the year, Germanywill have installed nearly 11 GW of capacity, according toRingkøbing-based BTM Consult ApS. But the green shareof the grid in Denmark is much larger. Lately, the EuropeanUnion and several American states, with Texas leading theway, have followed its cue in setting targets for renewables.But they’re not nearly so ambitious—Texas is demandingjust 12 percent of consumption by 2010. Still, last year theUnited States added 1.6 GW. Windmill maker Vestas nowis considering construction of a U.S. factory near its Oregonoffices that could build 300 turbines a year.

The fact is, for now wind is blowing other renewable ener-gy technologies away. The U.S. Department of Energy reportsthat the gales of South Dakota alone, properly harnessed, couldbathe the entire nation’s living rooms in cool air and the warmglow of television. But in northern Europe, and Denmark espe-cially, landlocked wind farms have run out of room. “You don’thave many areas where you can put large wind farms with verybig turbines,” says Vestas project manager Egon Poulsen. “InDenmark you’ll rarely be able to build that kind of farm and not

BY ROBB MANDELBAUMContributing Editor

35

IEE

ES

PE

CT

RU

M•

Octo

ber 2002

POWER

36

IEE

ES

PE

CT

RU

M•

Oct

obe

r 20

02P

HO

TO

S: J

ES

PE

R W

ES

TL

EY

/GE

TT

Y IM

AG

ES

Nacelle 51 is at the dock in Esbjerg, Denmark, ready to be loaded onto the Ocean Ady. With two blades attached, it looks a

bit like a big bunny rabbit. The third blade [left] is carried separately.

put it on top of a house.” Even in areas much less densely popu-lated than Denmark, environmentalists and naturalists tend to dis-like the idea of building turbine towers the size of Horns Rev’s—structures as big as large transmission towers.

Going out to sea to build turbines has other advantages,too. Because the seascape is relatively smooth, wind off thewater normally blows faster—and energy content grows expo-nentially. (The electricity harvest increases as the cube of thechange in wind speed.) What’s more, since wind at sea gen-erally does not lose speed close to the surface, towers can be25 percent shorter than on land. And, with less turbulence overthe sea, a turbine will last longer.

Of course, there also are disadvantages. Even though thetowers can be shorter, it costs a lot more to build a wind farmout at sea—in Elsam’s experience, sometimes nearly twice asmuch. (Undersea power cables and foundations are the mainculprits, but having ships idled by bad weather can add tocosts, too.) Aware of the risks and skeptical about the rewards,Denmark's biggest power producer balked at building HornsRev at first, but the government insisted. A combination ofmandated prices and premiums paid by consumers will guar-antee Elsam a profit over the next decade.

At the mercy of the elements

Weather is the big wildcard in an offshore project. High windsand waves that reach 8 meters roil the North Sea—that’s prettymuch the point of putting a wind farm out there. If the windat an altitude of 80 meters is blowing at 45 km/h or more,

crews must stop work. So, to minimize construction time atsea, Vestas has set up a mini-assembly plant in a couple ofwarehouses on the pier to put together the towers and com-plete work on the nacelles.

The crew loaded the first nacelle, No. 51, on Thursdayevening, and now we’re waiting for the weather to change forthe better. Vestas calls the nacelle a V80, the 80 designating therotor-blade diameter in meters. It is state of the art. Six yearsago, as a concept on a draftsman’s computer screen, a prede-cessor dubbed the V63 had shorter blades, which, in initial ver-sions, would have revolved at only a partially variable speed. Inthe interim, Vestas engineers found they could outfit the gen-erator’s copper-wired rotor with variable resistors.

Now the generator spins at fully varying speeds, permittingthe rotors blades to do the same. Less torque on the driveshaftmeans “materially less weight,” says Vestas’s Paulsen, “andweight is money.” The rotor blades themselves are made ofepoxy pre-impregnated glass fiber, which, Paulsen says, makesthem robust while further reducing weight and cost.

This kind of technological innovation, along with theeconomies of scale brought by the industry’s growth, is driving the price of wind-generated electricity down. But ordered ranks ofslender wind turbines are still a long way from ubiquity, largelybecause of the wind’s vagaries. Breezes generally are stronger dur-ing the day when more electricity is used, and they also tend tomatch seasonal consumption. But, as it is written, “the windbloweth where it listeth.” At times it’s fast, at times it’s slow, andat times it doesn’t blow at all.

37

IEE

ES

PE

CT

RU

M•

Octo

ber 2002

To keep electricity supply and demand balanced when wind isoverabundant, Denmark’s transmission grids sometimes payregular power plants not to produce. The task is complicated, how-ever, by the fact that most of Denmark’s other power still comesfrom plants that also produce heat for homes and businesses; thegrid operators are required to buy much of that cogeneratedpower, too. As a result, says Birger Madsen, a principal in BTMConsult, up to 5 percent of Danish wind power is wasted or elsedumped in European markets at well below cost. Eventually, saysMadsen, transmission lines to Sweden and Germany will have togrow larger, and Denmark will need to “make smart alliances be-tween wind producers and, say, hydro suppliers in Norway,” whichcan generate power at will merely by opening reservoir sluices.

For now, Elsam technicians warn that the Danish grid will soonbe unable to handle the instability inherent in power that cannotbe dispatched on demand. “For the country, we have a fairlystrong grid,” says Peter Christiansen, a consultant at Tech-WiseA/S, an Elsam subsidiary, “but the amount of undispatchablepower is so great that we will see the problems normally associ-ated with weak grids, such as a lack of reactive power.” Because ofsuch problems, the jury is out on the question of whether windcan ever deliver a large share of a region’s electricity economically.

Perhaps mindful of this, but probably more concerned aboutthe burdens borne by ratepayers, Denmark’s newly elected con-servative government earlier this year decreed that the countryhad too much renewable energy capacity. It canceled subsidiesfor renewable energy and funding for new development. Threeof five planned offshore wind farms got axed; only Horns Revand a project at Rødsand would continue.

A cynic might say the country’s biggest power producerhas been left twisting in the wind. Its executives are circum-spect when asked to characterize the future of wind power athome. “One of the three plants was Elsam’s responsibility,”says the company’s head of wind power development, Flem-ming Thomsen. “The obligation to build it will be removed,but we believe it will be postponed,not canceled. It will probably be a pub-lic tender, and we’ll participate, as willother companies.”

Even if Denmark is curtailing itscommitment to wind, Elsam executiveshave good reason to expect the globalmarket to remain strong. Demand forwind power will continue to grow bothin Europe, notwithstanding the conti-nent’s rightward political drift, and else-where, too. In the United States, forinstance, developers have proposed bigwind farms off both Nantucket andLong Island. Company executives thinktheir experience running Horns Revwill prove valuable. Indeed, Elsam is inthe running to build a park in the IrishSea, near Blackpool, England, where90 turbines are to be installed, eachmore than twice as powerful as those atHorns Rev.

Anchors aweigh

We’ve been moored at shore since Thursday, waiting to put tosea. Fortunately, the ship is quite livable. Each of the 14 men—10 from Vestas, two from A2Sea, and the crane operators—getshis own pleasant little room, carpeted and furnished with desk,couch, and bunk bed; each shares a bathroom and separateshower with only one or two others. Comfortable leather-likechairs and footrests face a very big TV set in the lounge. Sincethe ship is so new—or because it is run by Danes—everythingis pristine. Even so, the odor of stale cigarettes is so powerfulonboard that even the smelly dockside air comes as a relief.

The work, when it comes, is strenuous and the schedule—14 days on and 14 off, give or take a day—is fatiguing. Yetsome of these men have had tougher assignments abroad.René Leed, who’s 27, simply scheduled his wedding and hon-eymoon around this shift. Thirty-nine-year-old Bo Andersenhas been home to central Jutland for less than 100 days in eachof the last two years. “I have a seven-year-old son, and I havebeen traveling for five years,” he says. “So we are negotiatingwithin the family right now how long I’ll continue to do this.This job is two weeks on, two weeks off, so that’s no problem.But three months out—it’s too much.”

The men mostly hail from Jutland. They are sturdy people,not just in physique but in habits of mind. It takes greatpatience to do a job like this: nothing happens quickly; everytask is really a series of smaller tasks, done very carefully, in acomplicated ballet. They are nearly evenly divided between ayounger group in their late twenties and early thirties, and anolder group in their late thirties and early forties. The oldermen, as a rule, are clearly in charge. They do most of the talk-ing; they have the most important jobs. The younger men,whose main responsibility is to hold the guylines, are quieter.

Finally, after two days of waiting, punctuated by bursts ofprotracted activity, dawn broke this morning clean and clear. By7:30 a.m., when I woke up, the second nacelle, No. 91, was

This end of the rotor blade will be attached to the rotor hub after the nacelle is

mounted on the tower. The blade is nearly 40 meters long.

POWER

38

IEE

ES

PE

CT

RU

M•

Oct

obe

r 20

02

already on board. Now, three hours later, we’recruising out of the harbor.

Shortly after one o’clock, Flemming Olsencalls a “tactical meeting.” Ten men, on twocouches and four chairs, seem to have taken upall the available space in the lounge. There aretwo pots of coffee and lots of coffee cups. Themeeting is basically to lay out the plan of attack—who will do what, and how. On their first outingat sea, it took them 24 hours to install one tur-bine. Now they spend a lot of time talking abouthow to work the guylines designed to keep therotor blades from flailing about as the nacelle isswung around and hoisted to the tower.

“We talked about which mistakes wemade last time, and how to avoid them,” Botells me after the meeting. For example, whenthe crew installed the third rotor blade lasttime, says Bo, “the easiest way for the guys onthe ship wasn’t always the easiest way for theguys on the tower.”

Of course, even if installation is perfect,things may still go wrong with the turbines, atleast at first. At Middelgrunden, near Copen-hagen, for instance, some seven turbines wentout of commission, idled when newly up-graded transformers failed. (The wind farm’sowners still don’t know why.) “That was anothermanufacturer, and I don’t think we’ll have thesame problem,” Søren Vestegaard, Elsam’soperations and maintenance manager, says.Elsam has tested prototypes for Horns Rev onland. “We’ve done a lot of work in new testing,to prepare the turbines at the manufacturingplace, to have them running, so we knowthey’re ready to get out there.”

On top of the world

The ship approaches Tower 91. When it is com-pleted, Horns Rev will resemble a slightly tiltedmatrix of 10 rows of eight towers each—arhombus pointed northwest. (The numbersdenote the turbine’s position in the grid; 91 willsit atop the first tower in the ninth row.) Wedrop anchor at around 2:15 p.m., and it takesthe ship about 90 minutes to settle into a posi-tion between 20 and 21 meters from the tower;only then can the crane lift its 92-ton payload.

Then the men suit up. There’s a tensionand (dare I say it) an electricity in the air. PoulMøller and Rolf Kirk, who are about to climbthe tower and await the nacelle, are smiling.There’s a certain urgency, too: because nacelle91 was loaded last, it will have to be installedfirst. But 51 will be the first tower pluggedinto the transformer station on a platformabout 800 meters away, in just a few days.

Mounting the Wind TurbineIn June, the Ocean Hanne installed nacelle 13 on its tower. The basic steps were [top] to

bring the Ocean Hanne close to the tower and plant the ship’s four heavy feet on the

ocean floor, so that the deck could act as a construction platform. Then [middle, left]

the onboard crane lifted the nacelle, with two rotor blades attached, to the top of the

tower and [right] gently lowered it into position. Last [bottom], while the crane still

held it in position, two men working in the nacelle’s cramped quarters fastened it to

the tower. The final step [not shown] was to attach the third rotor blade to the hub at

the front of the nacelle.

39

IEE

ES

PE

CT

RU

M•

Octo

ber 2002

The towers will be wired serially, in five groups of 16 each,using 34-kV, lead-sheathed, three-phase cable, with conduc-tor cross sections of 95 or 150 mm2, depending on load.(Power is produced at 690 V and converted to 34 kV by atransformer in each nacelle.) Thicker 400-mm2 cable willcarry current from the five lead turbines to a central trans-former, which will step it up to 165 kV. A sea cable with a con-ductor cross section of 630 mm2 carries that current to shore,following a natural channel.

Small reports ripple off in the distance, as a pile driverpounds heavy tower foundations some 20 meters into theseabed. Horns Rev is being built in stages, and several crewsare working out here today: a couple of ships are laying foun-dations; another is placing transition pieces over the founda-

tions; and the Ocean Hanne is erecting wind turbines—in all,about 150 people are involved. The work follows the wiringplan: the first row of turbines will be finished first, then thefirst two columns, then the next two, and so forth. So far, onlythe first row of towers has been erected.

Supplies for the two men heading up the tower are broughtup by crane: buckets of bolts, tools, and Vitell bottled water. Butin the last hour, the weather has turned. Suddenly, a thick foghas enveloped the ship, and there are reports of thunder-storms heading this way. It’s 13 ˚C out, but it seems muchcolder. “That’s just the moisture in the fog,” A2Sea supervisorSvend Hansen says up in the wheelhouse. He’s calling forweather reports every few minutes now. “You always feel it likethat.” At about five o’clock, just as the crew is readying the liftgear, Svend walks out on deck and calls a 30-minute rain delay.

The men file into the mess for a subdued dinner. They saylittle as they eat. But then Svend appears after just 15 minutesto announce the postponement has ended early. There is animmediate clamor of scraping knives and forks and stack-ing dishes, and within a few minutes, the mess is empty.

The weather looks grim, but the winds are still and the na-celle is hoisted and placed atop of the tower in just 15 min-utes. The choreography of the ropes—which involvesscurrying first to the tower and then up to the bridge deckas the suspended nacelle rotates 180 degrees—is executed flaw-lessly. While four men on the boat hold the guylines tight againstthe railings, the crew up top provisionally bolts the nacelle down—I can hear, from way up there, the rat-tat-tat of the impactwrench—and within an hour, the nacelle has been unleashedfrom the crane—my cue to don a harness and climb 62 metersup the tower’s ladder and take a look. This is exhausting, thoughearlier in the day I got some good advice. “Just lean back againstthe tower wall,” Lars suggested. “And don’t use your arms toomuch, use your legs.” A few minutes up the ladder and I can seeneither where I began nor where I will finish.

At the top of the tower, Rolf and Lars are using a hydraulic toolset at 1600 meter-newtons to tighten each bolt. Theis and Poulare up in the nacelle. To get to the hub, where Poul is doing fin-ishing work, I must slide headfirst over a giant ball at the nacelle’sfront end, a back-up hydraulic pump to stop the blades in caseof emergency. It’s easy to imagine sliding over the ball and thenplunging out the hole at its bottom. Inside, the rotor hub ishardly big enough for two hunched-over men. Through thehole, and through the mist beyond it, the ship looks very small.“You do not think about it,” Poul says. A few minutes later, heunhooks his harness from a bar on one side of the hub and stepsover to the other and re-hooks. Astonishingly, for the briefest ofmoments, only surefootedness keeps him from tumbling 70meters down to the sea—or so it seems to me.

The threat of another storm sends us back down to theship, and work stops for an hour or so before Poul, Theis, andRolf head back up to install the third rotor blade. Vestas hasbuilt a special lift gear to clasp the rotor, one that won’t dam-age its fragile skin, and to send it straight up to the hub. Pouland Rolf will be inside to guide it, having removed the eye-shaped panel that comprises most of the hub floor. Theiswill help guide the rotor from the nacelle’s roof.

At 11 o’clock a.m., the crane rumbles to life. The crew hastrained a spotlight on the nacelle, and against the fogged-upsky, it’s really beautiful. Periodically the mist lifts and thetransformer station appears, shimmering on the water like aghost ship. Then the mist descends and even the tower, just20 meters away, is barely visible.

Back on the ship, I can make out two men up in the hub,shadows crouching inside the gaping hole. The lift gear andthe rotor it holds rise tentatively, lurching up a few meters,

then stopping, then lurching again. It seems to take a lotlonger this time, but maybe that’s just the cold—themoisture just gets you in the nose. I watch through

binoculars as the round end of the blade moves seeminglyinto position and then out, exposing a crescent of lightfrom within the hub, almost like the moon passingthrough its phases in speeded-up time. Then, at

12:40 a.m., René and Thomas tie their rope to the railing andwalk over to tell me that it’s done.

It had taken these men less than eight hours to finish a taskthey would have been lucky to complete in twelve. Yet Renéand Thomas hardly seem jubilant as they walk down to themain deck, where their crewmates are now milling about. Butthen, there is more to do. There are 90 bolts on blade 1 totighten, first by hand, then by hydraulics, which will take sixor seven hours. There is a whole other nacelle to install tomor-row. And then there are 77 more after that. •

William Sweet, Editor

There are 90 bolts on blade 1 to tighten. Then tomorrow there is another nacelle to install. And then 77 more after that

TO PROBE FURTHER,

SEE PAGE 67