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DOE/NASA/20320-58

NASA TM,83546

Large, Horizontal-AxisWind Turbines

Bradford S. Linscott

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135

Porter Perkins

Analex Corporation

Lewis Research Center

Cleveland, Ohio 44135

and

Joann T. Dennett

RDD Consultants, Inc.

Boulder, Colorado

March 1984

Work performed for

U.S. DEPARTMENTOF ENERGY

Conservation and Solar Energy

Division of Photovoltaic Energy Technology

Washington, D.C. 20545

Under Interagency Agreement DE-AI01-76ET20320

H_q-oz732_7_
DISCLAIMER

Thisreportwaspreparedasanaccountof worksponsoredbyanagency

of theUnitedStatesGovernment.NeithertheUnitedStatesGovernment

noranyagencythereof,noranyof theiremployees,makesanywarranty,

expressor implied,orassumesany legalliabilityor responsibilityforthe

accuracy,completeness,or usefulnessof any information,apparatus,

product,or processdisclosed,or representsthat its use would not

infringe privately owned rights. Reference herein to any specific

commercialproduct,process,or service by trade name, trademark,

manufacturer,orotherwise,doesnotnecessarilyconstituteor implyits

endorsement,recommendation,or favoring by the United States

Governmentorany agencythereof.Theviewsandopinionsof authors

expressedhereindo notnecessarilystate or reflectthoseof the United

StatesGovernmentoranyagencythereof.

Printedin the UnitedStates of America

Availablefrom

NationalTechnicalInformationService

u.s. Departmentof Commerce

5285 PortRoyalRoad

Springfield,VA 22161

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Printedcopy:A04

Microfichecopy:A01

1Codes are used for pricing all publications. The code is determined by

the number of pages in the publication. Information pertaining to the

pricing codes can be found in the current issues of the following

publications, which are generally available in most libraries: Energy

Research Abstracts (ERA);Government Reports Announcements and Index

(GRA and I); Scientific and Technical Abstract Reports (STAR); and

publication, .NTIS-PR-360 available from NTIS at the above address.
Contents

Page

Summary ......................................................................................... 1

Large Experimental Wind Turbines ........................................................ 13

Component Research and Technology ..................................................... 35

Research and Technology Development................................................... 50

Environmental Impacts ....................................................................... 63

Concluding Remarks .......................................................................... 64

References........................................................................................ 65

Bibliography ..................................................................................... 67

iii

Summary applications. The principal objective of each study was to

evaluate the economic incentive for using large wind Large, Horizontal-Axis Wind Turbines

turbines to produce electricity for existing electric utility

In 1973, the National Science Foundation (NSF) and companies. There were four important findings as a

the NASA Lewis Research Center began a joint effort to result of these studies: First, the average wind speed of

define objectives for and to initiate a wind energy the site selected for wind turbines has a major effect on

development program. The early objectives were (1) to wind turbine economics. Second, large wind turbines,

identify cost-effective wind turbine configurations, (2)to rated at 1500 to 2000 kW, will produce electricity more

develop the technology to support complete wind turbine economically than wind turbines rated at 100to 500 kW.

system design, (3) to transfer the research and technology Third, the wind turbine rotor is the largest single

from the Government to the commercial sector, and (4) contributor to the overall wind turbine cost. And finally,

to assure that utility companies can accept and use wind no major technical difficulties are involved in linking a

energy, wind turbine generator to an electric utility network.

Mod-O. -Efforts were begun in 1973 to meet these Both of these studies were completed in late 1975and the

objectives. First, it was decided to design, fabricate, study results were published (refs. 2 and 3). These

assemble, and install a wind turbine research facility at findings together with the installation of the Mod-0

Lewis with which to conduct experimental investigations, facility set the stage for the future development of three

The wind turbine had to be large enough so that the generations of increasingly more advanced and more

technology and engineering problems associated with cost-effective large, horizontal:axis experimental wind

large horizontal-axis machines could be assessed but turbines.

small enough to stay within a modest budget. As a result, Mod-OA. - The Federal Wind Energy Program, manLewis designed, assembled, installed, and started experi- aged by the National Science Foundation, was transferred

mental operation of the wind turbine research facility in in January 1975 to the newly formed Energy Research

September 1975(ref. l). The wind turbine, called Mod-0, and Development Administration (ERDA). One of

was located near Sandusky, Ohio, at the NASA Lewis ERDA's first actions was to authorize the Mod-0A wind

Plum Brook Station, and was originally designed to turbine project in January 1975 (refs. 4 to 6). NASA

produce 100 kW of power in an 8-m/s (18-mph) wind Lewis was requested by ERDA to design, install, and test

(fig. 1). The Mod-0 was configured with a 38.1-m (125-ft) two Mod-0A's, each an uprated version of the Mod-0

diameter downwind rotor mounted on top of a 28.3-m wind turbine. This first-generation machine was to

(93-ft) high, rigid truss tower. The rotor, operating at 40 produce 200 kW of power in a 9.8-m/s (22-mph) wind.

rpm, provided power to a 60-Hz synchronous alternator The Mod-0A configuration was outwardly identical in

through a 45:1 speed increaser gearbox, thereby turning appearance to the Mod-0; however, certain components

the alternator at 1800 rpm. This research facility, used in the Mod°0 machine had to be uprated for the

consisting of the Mod°0 wind turbine and the control and Mod-0A machine. For example, the aluminum rotor

research data systems, provided an early opportunity to blades designed for Mod-0 were strengthened for the

assess large wind turbine performance and to evaluate Mod-0A to help produce the higher power rating (ref. 7).

advanced wind turbine concepts. In addition, modifications to the Mod-0 gearbox were

In addition to the effort to develop the Mod°0 research incorporated to allow the Mod°0A machine to produce

facility, it was decided to begin engineering and economic twice as much power as the Mod-0. An alternator, rated

studies to identify the most cost-effective large, at 200 kW, was also installed on the Mod-0A machine.

horizontal-axis wind turbine configurations. Through One of the primary objectives of the Mod-0A project was

competitive bidding the Kaman Aerospace Corporation to assess these machines to assure that they could operate

and the General Electric Company were selected by successfully on a utility company network. The first

NASA in 1974 to each conduct an independent study on Mod°0A wind turbine was installed at Clayton, New

the design of wind turbines. Rated power levels of 50 to Mexico, and experimental tests begun in November 1977

3000 kW were considered appropriate for electric utility (fig. 2).
_-15-3486

Figure 1.-Mod-0 as first configured in September 1975. Figure 2.- Mod-0A, 200-kW wind turbine at Clayton, New Mexico.

Technology transfer: Federally sponsored wind turbine Solar Energy Society, and the American Gas

technology was transferred to industry mainly in two Association-Gas Research Institute, to name only a few.

ways. First, a series of workshops and conferences were Early site selection: In May 1974, an invitation to

held on wind energy. Second, technical reports were participate in the Federal Wind Energy Program was sent

published to disseminate the results of Federally funded by NSF to over 2700 utility organizations. The organiefforts and applied experimental and analytical wind zations that were contacted included rural cooperatives

turbine research. The first NSF/NASA/utility confer- and investor-owned, public-owned, and Federal utilities.

ence was held in December 1974 at Lewis. This confer- As a result of the Government/utility interaction during

ence served to inform industry about the Federal Wind 1974 and early 1975, ERDA issued a formal request for

Energy Program and NASA energy projects in partic- wind turbine site proposals in December 1975. The

ular. At this conference, the first of a series of technical request was sent to all of the utilities listed in the

conferences, attending utility company representatives Electrical World Directory (ref. 8). In April 1976, ERDA

were asked to indicate their interest in operating and received proposals from 61 utility organizations. Each of

evaluating an experimental wind turbine on their the 61 organizations proposed a site for the installation

networks. NSF received a very favorable response from and field testing of large experimental wind turbines. In

the utility representatives who attended this conference. June 1976, ERDA selected 17 of the 61 proposed sites for

The technical reports referenced herein represent a further evaluation.

small percentage of the Federally funded reports NASA Lewis was asked to manage the installation of

published on wind energy. A bibliography of conferences meteorological instruments and the gathering and

is given at the end of this report. Proceedings were analysis of wind data for each site. By July 1977 wind

published for most of the conferences listed. The data were being gathered at all 17 sites (table I). The

bibliography does not list the many other conferences information from each site was used by ERDA to assist

where papers on the large wind turbine projects have them in selecting the sites for the installation of

been presented and published. Conference sponsors experimental wind turbines.

included the American Society of Mechanical Engineers, Mod-1. - Specifications for the first megawatt-size

the Electric Power Research Institute, the American machine, in addition to those for the intermediate Mod2
TABLEI. - PERTINENTINFORMATIONABOUTTHE 17 CANDIDATESITES

Site UtiIity Instrument Startof

Ievels measurements

m ft

Amarillo,Tex. SouthwesternPublicService 9.1, 45.7 29.8, 149.8 March 1977

AugspurgerMt., Wash. BonnevillePower Administration December1976a

Block Island,R.I. Block IslandPower Company 9.1, 45.7 29.8,149.8 December1976

Boone,_.C. BTue RidgeElectric 18.2,45.7 59.7, 749.8 Oecember1976

Corporation

Clayton,N.Mex. City of Clayton 9.1,45.7 29.8, 149.8 May 1977

Cold Bay, Ala. AlaskaBussellElectric 9.1, 2].8b 29.8,71.5 August1977

Company

Culebra,P.R. PuertoRico WaterResources 9.1, 45.7 29.8, 149.8 March 1977

Authority

Holyoke,Mass. HolyokeGas and Electric 18.2,45.7 59.7, 149.8 December1976

Corporation

Huron,S.Dak. East RiverElectricPower 9.1, 45.7 29.8, 149.8 December1976

Cooperative,Inc.

KingsleyDam, Nebr. CentralNebraskaPublicPower 9.1,45.7 29.8, 149.8 December1976

and IrrigationDistrict

Ludington,Mich. ConsumersPowerCompany 18.2,45.7 59.7, 149.8 April 1977

Montauk,Long Island, Long IslandLightingCompany 18.2,45.7 59.7, 149.8 January1977

N.Y.

Point Arena,Calif. PacificGas and Electric 9.1, 45.7 29.8, 149.8 January1977

Company

Russell,Kans. City of Russell 9.1,45.7 29.8, 149.8 December1976

San GorgonioPass, SouthernCaliforniaEdison 9.1, 45.7 29.8, 149.8 December1976

Calif.

Boardman,Oreg. PortlandGeneralElectric 9.1, 39.6, 29.8,129.8, January1977d

70.I 229.8

Oahu,Hawaii HawaiianElectricCompany 9.1, 45.7c 29.8, 149.8 December1976

Measurementsterminatedin January1978.

Towersuppliedby utility.

CMeteorologicalequipmentand data reportssuppliedby utility.

dData collectedby utilitysince1974.

0A wind turbine, were being formulated by NASA in

1975 as a part of the Federal Wind Energy Program. In

March 1976, NASA submitted to industry a request for

proposals to design, install, and test a 1500-kW

(1.5-MW) wind turbine. As a result of a competitive

selection, in July 1976 the General Electric Company

(GE) was awarded a contract to design the Mod-1 wind

turbine. During the design phase, GE and NASA

determined that the machine would produce electricity

more economically if the rating were increased from 1500

to 2000 kW. The Mod-1, a 2000.kW machine, was

installed at Boone, North Carolina, and started

experimental operation in May 1979 (fig. 3; ref. 9). This

machine exceededthe sizeand rated power of the SmithPutnam machine, which first operated in October 1941

(fig. 4).

Mod-2.-Specifications for a second megawatt-size

machine were being developed by NASA for ERDA in

1976. By February 1977, NASA had requested proposals

from industry to design, install, and conduct experimental tests on a multimegawatt wind turbine system.

The Boeing Engineering and Construction Company was

competitively selected to carry out this megawatt wind

turbine system development project, called Mod-2. The

key goals established for the Mod-2 project were (1) to

provide an economical, viable alternative electrical Figure 3.-Mod-1, 2-MW wind turbine at Boone, North Carolina.

3
Figure 5.-Mod-2, 2.5-MW wind turbine at Goodnoe Hills,

Washington.

The Mod-0A and the Mod-1 experimental machines

are classified as the first of three generations of steadily

advancing configurations. The Mod-I can be thought of

as a scaled-up version of the first-generation (Mod-0A)

machine. For example, each first-generation machine

used a very stiff truss type of tower structure. The rotor

of each machine operated on the downwind side of the

tower. To control rotor speed and power, each blade

rotated about the spanwise, or pitch, axis. Blade pitch

was actuated by a mechanism at the hub of the machine.

Each blade was rigidly attached to the hub and the

horizontal-axis drivetrain.

During the Mod-1 design effort, General Electric

Figure 4.-Smith-Putnam wind turbine, engineers under NASA contract conducted a special

conceptual design study. NASA requested GE to define

innovative ways, through design, to reduce the weight

generating system with the potential to reduce depen- and cost of a megawatt machine and at the same time to

dency on nonrenewable-fossil-fuel generating systems, increase the rated power. The results of this study (ref. 9)

(2) to demonstrate the feasibility of megawatt wind indicated that a rotor that is hinged at the hub with

turbines operating in a utility network, and (3) to pitchable blade-tip control surfaces could result in

stimulate wide industry involvement in the development significant system weight and cost savings. The GE study

of commercial wind turbines. Boeing started the initial also recommended that the rotor operate upwind of the

design effort in July 1977 and installed the first machine tower, thereby reducing the adverse aerodynamic effects

in mid-1980(fig. 5). associated with operating the rotor downwind of the

In October 1977, the Department of Energy (DOE) tower. The GE designers concluded that the tower weight

formally replaced the Energy Research and Development could be safely reduced by decreasing the tower stiffness.

Administration (ERDA)and began managing the Federal As a result of this conceptual study two important

Wind Energy Program. courses of action were taken in early 1978. First, it was

4
decided to modify the Mod-0 research machine. Changes concepts into the final Mod-2 configuration. As a result,

planned for the machine included the use of a hinged (or Mod-2 was developed as the second-generation

teetered) rotor, pitchable blade-tip control surfaces, and megawatt-size machine beyond the Mod-1 (ref. 10).

modification of the tower so that its stiffness could be In October 1978, with the configuration shown in

easily changed. Once these modifications to Mod-0 were figure 6, a series of Mod-0 experiments began with the

incorporated, experiments could be conducted to objective of evaluating the innovative concepts planned

evaluate the performance of this second-generation wind for the second-generation (Mod-2) machines. The first of

turbine configuration proposed by the GE designers. The this series of Mod-0 experiments investigated the effects

second course of action involved the development of of varying the tower bending stiffness on rotor

Mod-2, which had started in late July 1977. The performance. The tower tests were conducted and the

Department of Energy (DOE), NASA, and the Boeing experimental data were analyzed. It was found that the

Mod-2 designers decided to incorporate these new design Mod-0 operated smoothly with a tower having either stiff

/ Symmetric

i about

cenirline

Soft /_

tower /_ /_///._ A_jtu_:aeb_a_te

/_ Newleafsprings

on4 sides

Gfade / t

y • _ _ i _, _F' Existingfoundation

_.'I_'3_..J _ __ L H°r takeizo°nt utal shear _.I

Conceptof soft-towersimulationfixture

I

n

Figure 6. - Mod-Otower configured to simulate the Mod-2 wind turbine.

5
or soft bending qualities. No significant changes in rotor These experimental machines are currently providing

performance were found, and the tower bending power for the Bonneville Power Administration while

oscillations were nominal and in agreement with the undergoing a series of planned research experiments

designers' predictions. It was therefore concluded that a (refs. 11 and 12).

second-generation wind turbine tower structure could be Mod-5. -During 1979, NASA developed, under the

constructed that was lighter and had a lower bending direction of DOE, specifications for an advanced

stiffness than the first-generation towers. And, better yet, multimegawatt, or third-generation, wind turbine. In

the weight savings had the potential of reducing the August 1979, NASA requestedindustry, on acompetitive

machine cost with no compromise in energy production, basis, to submit proposals to design, fabricate, assemble,

In May 1979, the planned Mod-0 test series continued install, and conduct experiments on this third-generation

with the first experimental operation of a teetered rotor machine. System analyses of large, horizontal-axis wind

with movable blade-tip control surfaces. These experi- turbines showed that a cost of energy (COE) lower than

ments proved that rotor startup, shutdown, and normal the Mod-2 COE could be realized if an advanced

running could be successfully commanded with rotor multimegawatt wind turbine, called Mod-5, was

blade-tip control surfaces, developed. To meet the lower COE objective, Mod-5

Teetered and rigid rotor operating loads were would have to be larger than Mod-2 and use advanced

compared. As the designers predicted, the teetered-rotor technology developed as a result of the Federal Wind

operating loads were significantly less than the first- Energy Program. A key objective of the Mod-5 project is

generation rigid-rotor operating loads, to develop and verify the technology required for an

As a result of these experimental findings and their advanced multimegawatt machine to generate electricity

close agreement with analytical predictions, in June 1979, for 3.75 C/kWh, or less, in 1980 dollars.

DOE authorized NASA to have Boeing start fabrication In 1980, DOE authorized parallel design contracts to

and assembly of the three Mod-2 machines. The GE and Boeing for conceptual designs. Conceptual

information from Mod-0 provided designers with high design was completed by both contractors in March 1981.

confidence that the Mod-2 machines would provide more In-depth design reviews were conducted by NASA. A

power than Mod-1 at a lower cost and with less equip- NASA assessment was provided to DOE in May 1981.

ment and materials. Both designs met the project goals with significant

The first of a cluster of three experimental Mod-2 margin. Subsequently both contractors' conceptual

machines started performance tests in October 1980 at designs were approved by DOE and permission was

Goodnoe Hills, Washington. Experiments with all three granted to proceed with preliminary design.

machines began in May 1981 (fig. 7). Each machine is The concept designs required development of advanced

rated at 2.5 MW of power in a 9.8-m/s (22-mph) wind. technology in several areas: for example, variable-speed

Figure 7.- Mod-2 wind turbine cluster at Goodnoe Hills, Washington.

6
rotors, laminated-wood-epoxy composite blade materi- System verification unit (SVU).-The Bureau of

als, a rotor-integrated gearbox, and a variable-speed Reclaniation, an organizational element of the

generator-cycloconverter system. Also, each contractor Department of Interior, determined that wind energy has

was asked to propose completion of the project on a cost- the potential to conserve water flow through their

sharing basis, where the Government would fund the hydroelectric turbines. In the late 1970's, the Bureau of

remaining design and development and the contractors or Reclamation began planning to conduct experimental

their utility customers would provide funds for the tests of megawatt wind turbines connected to its hydrofabrication, erection, and operationofthewindturbines, electric utility network. A site near Medicine Bow,

The wind turbines would be owned solely by the Wyoming, was selected and industry was requested to

contractors or customers, and the Government would submit proposals to design, fabricate, and install two

receive semiannual performance data and operations large wind turbines at this site. NASA Lewis was asked to

reports for 3 years after initial operations, provide technical assistance to Bureau of Reclamation

In June 1983, General Electric signed a contract with personnel during their wind turbine development project

the Hawaiian Electric Company (HECO) whereby and early experimental testing.

HECO would purchase from GE one prototype Mod-SA As a result of a competitive selection conducted by

wind turbine to be installed at the Kahuku Hills site. The NASA and the Bureau of Reclamation, a team consisting

Mod-5A first rotation and synchronization on the utility of Hamilton Standard Division of United Technologies

network were planned for late 1985. Corporation and the Swedish Karlskronavarvet (KKRV)

In December of 1983, the General Electric Company Company was selected to design, fabricate, install, and

announced their decision to withdraw from the Mod-SA test a wind turbine rated at 4 MW. Using company funds

project, GE citied the poor near-term prospect of together with Government funds, this American and

obtaining additional wind turbine sales and the expected Swedish team has successfully installed the WTS-4

expiration of energy tax credits as factors that would System Verification Unit (SVU) near Medicine Bow.

make further private sector investment inappropriate at Experimental tests were begun in September 1982.

this time. The Government will conclude its contract with The WTS-4 (fig. 9), has a two-blade, 78.1-m (256.4-ft)

General Electric over an approximate 12-month period, diameter rotor. The rotor operates downwind of a

During this time a comprehensive final report will be tubular tower. The machine produces 4 MW of power at

prepared to document the design, the research performed a wind velocity of 15.1 m/s (33.9 mph) measured at a

during the contract effort, and test results, height of 80 m (262 ft), the hub height above the ground

A revised cost-sharing proposal reflecting their line.

replanned program was received from Boeing in March In addition to the WTS-4, the Bureau of Reclamation

1984. Figure 8 shows how the Mod-5 machine compares provided funding and requested NASA Lewis to provide

with the other machines in size, and table II presents a contract and technical management for the installation

summary of data for each machine, and testing of a Boeing Mod-2 wind turbine. Boeing

500 -- 150--

Wind

300-- 90-- 79.2 E

::= 200 -- m 60-- )) _ 1320) '

61.0

lOC-- 3O )

L

O-- 0 _ _ L_

Mod-OA Mod-1 Mod-2 WTS-4 Mod-SA Mod-SB

Maximumratedpower,kW: 200 2000 2.500 4000 7300 3200

Figure 8.- Size comparison of large, horizontal-axis wind turbines. (Dimensions are in meters (feet).)

7
TABLE II. - DATAFOR INTERMEDIATEAND LARGEHORIZONTAL-AXISWIND TURBINES

Mod-OA Mod-I Mod-2 Mod-5A Mod-5B SVU WTS-4

Prime contractor Westinghouse General Boeing GeneralElec- Boeing Hamilton

ElectricCorp., ElectricCo., AerospaceCo., tric Co., AerospaceCo., StandardDiv.,

Pittsburgh,Pa. Philadelphia, Seattle,Wash. Philadelphia, Seattle,Wash. UnitedTechnolPa. Pa. ogiesCorp.,

WindsorLocks,

Conn.

Location Clayton,N.Mex. Boone,N.C. GoodnoeHills Project Oahu,Hawaii MedicineBow,

Culebra,P.R. Wash. (3) terminated Wyo.

Block Island,R.I. MedicineBow, 12-83

Oahu,Hawaii Wyo. (1)

Date of first rotation II-77 (N.Mex.) 5-79 (N.C.) ll-80(Wash.l) (a) 8-82

(locationand unit) 6-78 (P.R.) 3-81 (Wash.2)

5-79 (R.I.) 5-81 (Wash.3)

5-80 (Hawaii) 12-81(Wyo.-SVU)

Centerof bladerotation 30.5 (lO0) 42.7 (140) 61.0 (200) 76.2 (250) 61.0 (200) 79.9 (262)

(hubheight),m (ft)

Rotor bladediameter, 38.1 (125) 61.0 (200) 91.5 (300) 122 (400) 97.6 (320) 78.1 (256)

m (ft)

Rated power,kW 200 2000 2500 7300 3200 4000

Ratedwind speedat 9.8 (22) 14.8 (33) 12.5 (28) 14.3 (32) 11.6 (26) 14.8 (33)

hub height,m/s (mph)

Annualelectricityoutput,b

MWh:

At 5.4-m/s(12-mph)site 640 2400 7000 13 200 8200 7000

At 6.3-m/s(14-mph)site 820 3700 9300 20 600 12 000 9900

At 7.2-m/s(16-mph)site 980 5100 II 300 30 700 17 900 13 000

Cut-inspeedat hub height, 5.4 (12) 7.2 (16) 6.3 (14) 6.3 (14) 4.9 (11) 6.7 (15)

m/s (mph)

Cutoutspeedat hub height, 17.9 (40) 15.7 (35) 20.I (45) 26.8 (60) 26.8 (60) 24.6 (55)

m/s (mph)

Weighton foundation,kg (Ib) 40.6xlq3 295xlQ3 281xlQ3 769xlQ3 413xi03 353xI_3

(89.5xI0_) (650xi0J) (619xlO_) (1695xI0_) (910xlO3) (778xI0_)

Weightper ratedpower, 203 (447) 147 (325) If2 (247) I05 (232) 129 (284) 88 (194)

kg/kW (Ib/kW)

aFourthquarterof calendaryear 1985.

b90 Percentof availablewind energymeasuredat 9.1 m (30 ft) above sea level;Welbulldistribution.
Figure 9.- Bureau of Reclamation/Hamilton Standard WTS-4, 4-MW wind turbine near Medicine Bow, Wyoming.

Figure 10. Bureau of Reclamation Mod-2, 2.5-MW wind turbine near Medicine Bow, Wyoming.

completed the installation of the Mod-2 SVU wind has centered on the development of large, horizontal-axis

turbine (fig. 10) at the test site in December 1981. wind turbines, a variety of other wind energy projects

Operational checkout was completed and experimental have been under way. Those wind energy projects that

tests were begun in September 1982. have received attention in the overall development effort

The Bureau of Reclamation is currently evaluating the include vertical-axis wind turbines, small wind turbines,

technical and economic feasibility as well as the innovative wind turbines, and wind characteristics

environmental acceptability of the SVU's. This early research.

effort may result in the placement of many more wind Vertical-axis wind turbines.- Vertical-axis wind

turbines, which will be used to supplement the electricity turbines (VAWT) have some advantages over the

now being generated by hydroelectric plants, horizontal-axis types. The VAWT does not have to turn

Other Wind Turbines to face into the wind, and this eliminates a mechanical

system needed for rotating the horizontal-axis machines

Although much of the Federal support for wind energy into position. Also, because the drivetrain and generator

9
can be mounted near the ground, there is no need for a removed when commercial electricity was provided by the

high tower. However, the horizontal-axis machines Rural Electrification Program in the 1930%. The recent

presently have higher tip- to wind-speed ratios than the Federal Wind Energy Program has helped reactivate the

VAWT and thus produce more power. But improvements once almost nonexistent wind turbine industry.

on the vertical-axis design may remove this disadvantage. A test center for small wind systems was established in

A vertical-axis wind turbine that has been given 1976 by DOE at Rocky Flats, Colorado. The center,

considerable attention is the Darrieus type of rotor operated by Rockwell International Energy Systems

invented by G.J.M. Darrieus of France (fig. 11). It is Group, has tested and evaluated over 25 commercial

characterized by curved blades with airfoil cross sections wind machines. In addition, the Rocky Flats facility has

arranged in a form resembling a huge eggbeater. These supported the design, fabrication, and testing of new

blades have a relatively low starting torque but rotate at small wind turbine systems and is now providing research

rather high speeds once they are started by some auxiliary needed by the wind industry to develop small wind

method, turbine systems that are reliable, safe, and economical

Research to improve the Darrieus machine has been (ref. 13). Several small machines now on the market are

conducted by Sandia National Laboratories for DOE in part the result of the Rocky Flats program.

(ref. 13). Aerodynamics and structural dynamics studies The small wind turbines advanced by the Federal

project significant improvements in its cost effectiveness. Government include 1- to 2-kW, 4-kW, 8-kW, 15-kW,

Four 100-kW experimental machines were fabricated by and 40-kW systems (fig. 12). The 1-to 2-kW size is suited

the Aluminum Company of America (ALCOA). Opera- to battery charging. Residential heating and cooling

tional experience from these units has been obtained could use the 4- to 8-kW range depending on load

from installations at Rocky Flats, Colorado; Bushland, requirements. A 15-kW machine has application in

Texas; and Martha's Vineyard, Massachusetts. agricultural and small industrial needs, and a 40-kW

Small wind turbines.-Small wind turbines, machines machine will satisfy larger agricultural and industrial

that develop less than 100kW, have received considerable requirements.

development effort under the Federal Wind Energy Advanced, innovative wind turbines.-Motivation for

Program. More than 6 million small windmills have been innovative wind turbines is, in general, directed toward

built and used, mostly in rural areas, in the United States improving the cost effectiveness of converting the wind

since the middle of the 19th century. However, most were into useful energy. To achieve this, new concepts strive to

have, among many, the following goals: high wind

energy capture efficiency, wide wind speed operating

range, high rotational speed, location of heavy components that require servicing near the ground, and the

simplest possible operating controls. New ideas include

wind-concentrating devices, augmentors for rotor blades,

and systems with no moving parts.

More than 12 advanced and innovative wind energy

concepts have been supported by DOE and managed by

the Solar Energy Research Institute (SERI) located in

Golden, Colorado. Also, approximately 20 studies have

been funded in such areas as aerodynamics, thermodynamics, and theoretical concepts.

One innovative wind energy conversion system is the

diffuser-augmented wind turbine shown in figure 13.

This device uses a shroud around the outside of the

turbine blade arc that expands or diffuses the airflow

downstream of the blades. This expansion tends to pull

more air into the upstream side of the blades, or in effect,

concentrates the wind through the turbine. Greater flow

through the blades can increase the turbine power output

by at least a factor of 4 over that produced by a

conventional turbine (ref. 13). The problem, however, is

the added cost of the diffuser shroud and designing a

large practical structure to support the diffuser shroud in

high winds.

Another augmentation system for wind turbines is

Figure ll.-Vertical-axis wind turbine, called a dynamic inducer, as shown in figure 14. This

10
Figure 12.- Small wind turbines from Federal Wind Energy Program.

11
Diffusersections

!ii

Figure 15.-Electrofluid dynamic wind-driven generator.

investigated. This conceivably would be simpler and less

expensive to operate than conventional wind energy

Figure 13.-Diffuser-augmented wind turbine baseline model with conversion systems. The system is called an electrofluid

46-cm (18-in.) diameter turbine mounted in the 2- by 3-m wind tunnel dynamic wind-driven generator. A model of this concept

test section, is shown in figure 15. Particles are mechanically

produced and electrically charged upwind of an oriented

array of electrodes charged at a higher voltage. These

particles are driven by the wind through the array against

the electrical potential. The transport of the charged

particles to a higher electrical potential generates

.... electricity. A theory that describes the performance of

................. this advanced concept has been developed (ref. 13). The

theory has been generally confirmed to be correct by

wind tunnel experiments.

Wind characteristics research. - To harness the wind in

a cost-effective manner, considerable study and research

on the various characteristics of wind have been

conducted over the past several years. This research has

been carried out by the Pacific Northwest Laboratory,

Richland, Washington, under the direction of DOE.

Obviously, areas of high winds are desirable, but the

Figure14.- Full-scale towtest of dynamic inducer, nature of the wind in a given area is important also (e.g.,

the wind gustiness and variability over different periods

system uses short airfoil sections, called tip vanes, which of time). Major areas of wind research include

are attached approximately at right angles to the tips of (1) Determining the magnitude and distribution of the

the rotor blades of a horizontal-axis turbine. Theo- wind resource over the United States

retically, this innovation can increase power output by a (2) Providing site selection techniques for small and

factor of about 2.5. Wind tunnel tests have measured large turbines

power output of a dynamic inducer 1.7 times that of the (3) Establishing the wind characteristics that can affect

bare rotor blades (ref. 13). wind turbine performance and life

A unique concept of deriving energy from the wind by (4) Defining wind turbine operating strategy to

using a system without any moving parts has been maximize wind energy capture

12
A major part of the Wind Characteristics Program has aircraft wings (fig. 17). Each is 18 m (59.9 ft) long and

been a national wind energy resource assessment. The weighs 907 kg (2000 lb). The blade pitch is changed to

results of this effort are available in the form of an atlas control rotor rotational speed or power. The gearbox

for each of 12 regions covering the United States and its steps up the rotational speed of the rotor and low-speed

territories (ref. 14). Of main interest in these atlases are drivetrain to the generator speed.

the annual and seasonal maps of wind energy. In The Mod-0 rotor hub containing the blade pitch

addition, the atlases contain tabular data and a descrip- change mechanism, the generator, the gearbox, the lowtion of the various features of the wind on a regional and and high-speed drivetrains, and the associated mechstate level, anical and electrical equipment are mounted to a bedplate

One must be cautious in applying these published wind structure. All of this is enclosed by a fiberglass shell

energy distributions. In many areas, the values are called the nacelle. The nacelle with all of the enclosed

estimates and apply to locations exposed to the wind and equipment can be yawed in a horizontal plane about the

not affected by the terrain and other wind obstructions, tower to align the rotor with the wind. Rotor power is

For lack of reliable measurements in a given area and controlled by hydraulic actuators, which change the

complexity of the topography, the wind energy values are blade pitch. The yaw control keeps the rotor facing

estimates. However, a degree of certainty is provided for toward the wind; however, it does not respond to every

the estimated values. Unfortunately, only a small gust. It is programmed to face in the general prevailing

fraction of the areas that have high estimates of wind wind direction. Power, instrumentation, and control

energy also have high certainty, connections are made to the ground through sliprings.

Thus the large-scale wind resource information should Originally the Mod-0 was designed for operation in

be used only in the preliminary selection of a wind 8-m/s (18-mph) winds, but it can produce power in winds

turbine site. A specific site should be selected on the basis ranging from 4.2 to 17.9 m/s (9.5 to 40 mph). The

of further measurements. Certain site selection tech- turbine can begin to generate power in winds as low as 4.2

niques such as numerical modeling have also been m/s (9.5 mph) and reaches its 100-kW output at the

developed and can be used to evaluate specific sites, design speed of 8 m/s (18 mph). Above this wind speed

Reference 15 describes the meteorological aspects of site the wind turbine continues to generate 100 kW by

selection, adjusting the pitch of the rotor blades to spill excess

Wind turbine design and performance can be affected energy. The maximum wind speed at which Mod-0 will

by wind characteristics at a given site. Such charac- operate is determined by the structural limits of the rotor.

teristics as gusts and local turbulence create stress cycles Accordingly, at wind speeds above this maximum

that contribute to fatigue problems. Also, wind turbine (approx 17.9 m/s; 40 mph) the generator is disconnected

operating efficiency can be improved by consideration of from the power network, the blades are feathered to

wind variability. The scheduling of servicing and bring the rotor to a halt, and the machineis shut down. A

preventive maintenance during periods of low winds is an similar shutdown occurs at wind speeds below 3.6 m/s

example. (8 mph). This feature prevents the wind turbine from

drawing utility power to maintain rotor speed.

If the wind turbine is shut down by unacceptable

Large Experimental Wind Turbines winds, it will restart automatically when the wind speed

returns to acceptable levels. However, startup will not

Mod-0 occur before the wind reaches 5.8 m/s (13 mph) in

Mod-0, as originally designed and built by NASA contrast to the shutdown, which occurs at 3.6 m/s

Lewis, had a heavy (20 000 kg; 44 000 lb), 30.5-m (100-ft) (8 mph). This slightly wider bottom wind speed range

high steel truss tower. The blades, rigidly attached to the reduces the number of startup-shutdown cycles in light,

hub, were downwind of the tower and the entire blade variable winds. Similarly, shutdown is begun when the

pitched against the wind. Mod-0 is used to develop and winds exceed 17.9 m/s (40 mph) and the wind turbine is

verify advanced wind turbine concepts. Thus the Mod-0 not restarted until the winds drop below 11.1 m/s (25

research machine has undergone frequent modifications mph). This again reduces unnecessary cycling in variable

since it was first erected at NASA's Plum Brook Station, winds.

near Sandusky, Ohio, in 1975 (fig. 16). Experience was gained with the downwind rotor

The Mod-0 two-blade rotor drives a synchronous configuration of Mod-0 during experimental operation.

generator through a step-up gearbox. The rotor was At Plum Brook, NASA Lewis engineers moved the

designed to operate at a constant speed of 40 rpm and Mod-0 successfully through each of three design

drives a 125-kVA, 480-V, 60-Hzthree-phasegeneratorat operating modes. Initial manual operation fed the

1800 rpm. electricity produced by Mod-0 into a device that simply

The Mod-0 blades were built by Lockheed Aircraft consumed it. This manual operation on a resistive load

Corporation for NASA Lewis. The blades are much like simulated actual operating conditions. Once successfully

13
c-82-389aj

(a) First generation (1975).

(b) Second generation (1979).

(c)Advancedconfiguration (1983).

Figure 16.- Mod-0 experimental test configurations.

past these first tests, Mod-0 was then synchronized with once per revolution. As this tower shadow changes, the

the Ohio Edison power grid. The final operating mode wind load on the blades changes and subjects the blades

was unattended automatic synchronization and operation to regular, recurring stresses. When Mod-0 first began

on this power grid. operation in December 1975, the measured blade loads

The Mod-0 tower is located upwind of the rotor. Thus were higher than predicted. This would have shortened

each blade rotates into the lee or shadow of the tower the blade life substantially.

14
Station Station

750 31.75

18m{59.9ft)

O.635(0.250)thick skin

/J Station0

If

r-O.317(0.125)thick skin / _ I

/ _E //I

_L / i ( I , , , , __. L I

-_-- \ T-- I _'l ' '

I' \ T I _ \ I. 37m(4.5 ft)

\ _ L... \ i \

046m __ . . E \

(i . 5ft) 0.102(O.040)thlckskln I Station300 \ I \\ I

Station367 \\ Station40 \

(straingages) \\ (straingages)_-Centerof

{b) O.203(0.060)thick skin -_ rotation

(a) Turbine blade ready for installation.

(b) Turbine blade dimensions. Weight, 907 kg (2000 Ib). (Skin thicknesses are in centimeters (inches).)

Figure 17.-Mod-0 turbine blade.

Tower development.-Recordings of the blade load Comparison of the three tests pinpointed the tower

suggested that the tower shadow was one of the main design features that were the most significant wind

problems. Wind tunnel testing of tower models showed shadow producers. Experimental tests showed that the

that removing the stairs and the elevator system rails simpler and more open tower designs had a smaller tower

shown in figure 1 would reduce the loading to more shadow (refs. 16 and 17).

acceptable levels. During this investigation a more subtle Vibration is a major problem for wind turbine systems

blade loading problem was identified: bedplate/nacelle since material fatigue and component failure are the most

cyclic yaw motion. The blades were rhythmically moving important factors in determining useful lifetime.

the yaw drive system. This was corrected by stiffening the Establishing the vibration characteristics of the Mod-0

yaw drive system and installing a yaw brake. The system was thus of high priority. Vibration studies of

combination of these modifications reduced the blade Mod-0 were also important in assessing the value of the

loads to the design level and insured a much longer computer models used in the design process.

lifetime for the blades. The Mod-0 system was vibrationally tested in an

Three different tower designs were modeled during the incremental fashion. First the tower was tested alone.

course of the wind tunnel testing at NASA Lewis. Then the nacelle and blades were mounted on the tower.

15
Artificially vibrating an object as large as the Mod-0 Thus, after installation and testing of the initial Mod-0

tower is not easy. For the first simple tests an instru- design, a few changes were immediately made. These

mented hand-held hammer was used. The more difficult included

tests required an instrumented 90.7-kg (200-1b) weight. (1) Removing the stairs and other equipment to

When the tower was struck by the instrumented weight, improve airflow through the tower and thus reduce

ringing (a measure of vibrational frequency) was blade loads

measured by accelerometers at various points. The (2) Installing the dual yaw drive and the yaw brake to

frequencies of the ringing recorded by the accelerometers reduce blade loads

were then compared with the vibrational frequencies (3) Adding the fluid coupling to damp the drivetrain

predicted by the computer code (refs. 18 and 19). The Control system. - Designed to be a fully automatic

code predicted well. power production machine, Mod-0 needed a control

The pulse produced in the rotor as the blade passes system that could

through the wind shadow of the tower generates (1) Monitor the wind conditions

harmonic forces in the drivetrain, the tower, and the (2) Maintain alignment with the wind

rotor. The forces are integral multiples of the rotor (3) Control power level

speed. For a two-blade rotor the tower is "excited" twice (4) Start, synchronize, and stop the wind turbine

per revolution of the rotor. Mod-0 is dynamically stiff, safely

Although this makes the tower heavier and more costly, it (5) Monitor key parameters to assure that critical

also assures that the tower structure will not resonate in items operate within specified tolerances

response to normal rotor speeds. (6) Provide a remote operator the capability of

Trials with six different computer codes for Mod-0 stopping and starting the machine

performance showed that all of the codes could predict To accomplish these tasks, five separate control systems

blade loads within 25 percent (ref. 20). One code, were designed: the rotor blade pitch controller, the yaw

REXOR-WT, was the most consistent in calculating system, the microprocessor, the safety system, and the

loads that were close to measured loads. The codes remote control and monitor system. Of these, only the

differed in the amount of detail they considered. Three of yaw controller is completely independent. The degree of

the codes considered only the rotor itself; the other four interaction among the other control systems varies with

included the tower in the calculations. Both types of code operating mode and conditions (fig. 18). The pitch

have their place in design. It takes much more computer controller adjusts blade pitch to control rotor speed or

time to do a detailed analysis. The simpler codes are alternator output power. Wind turbine rotor power is a

useful for initial design work. Thus the computer codes function of wind speed'and blade pitch angle. Therefore

developed for Mod-0 can serve as useful heuristic tools either rotor speed or rotor power at a given wind speed

for future design, can be controlled by adjusting blade pitch angle. This

NASA Lewis used the computer codes to determine the system is supervised by the microprocessor, which selects

best method of reducing loads on the Mod-0 blades with the operating mode and the set point.

a minimum of redesign. Two contrasting designs were The Mod-0 pitch controller uses a hydraulically actuinvestigated: one using teetering blades and one using ated blade pitch mechanism to maintain either rotor

blades rigidly attached to the hub as the existing Mod-0 speed or rotor power. Increasing the blade pitch angle

blades were. Analysis showed that the teetering blades increases rotor power; decreasing the angle reduces

would reduce both the blade loads and the tower loads power. A pitch angle limit is set thai avoids stall at low

(ref. 21). wind speeds and prevents structural damage at high wind

Vibration in portions of the machine other than the speeds. At shutdown, blade pitch angle is reduced until a

rotor and tower must be considered. Vibration of the zero power output is achieved. The alternator is then

drivetrain, for example, can be caused by the varying disconnected from the network, blade pitch angle is

power delivered by the blades as they rotate. Computer decreased until the rotor stops, and the blades are

modeling of the drivetrain indicated that significant feathered.

vibrations could occur this way in at least two instances: The yaw controller, which keeps the turbine aligned

when the wind turbine is connected to a resistive load and with the wind, operates independently from the other

when the wind turbine, connected to a power line, control systems. It is powered by two motors, which can

reaches an output of 10kW. As a result, NASA designers turn the nacelle at a constant speed of 1 deg/s.

changed the drive system to control possible vibrations. Information from a wind varie on the nacelle provides a

A fluid coupling was added to the drivetrain. It functions direct measure of the apparent wind direction relative to

much like a shock absorber to help damp the drivetrain, the nacelle--a direct measure of yaw error. The original

Since the amount of damping or slip can be varied by controller sampled the wind every 15 seconds and

adjusting the level of fluid, it is ideal for an experimental responded directly to all significant changes. However,

program, this caused almost constant operation of the yaw motors.

16
Yaw _ electric_

]ssembl_ psystem ower Isem

• Drive .Status

• Brake • Field

comman •Rotational commands enable

• Pump speed

commands • Commands

•Status

Pumpcommands ,1 • Generator

Positioncommand Nacelle power

control t

unit

II

•Status i

I Emergency

•Tippositions i

shutdown I Windspeeclldirection

[system I"

• Autosynchronizationenable

Com onOII I[ oon orcommao°

( roun,

anua Ielectric

,ntrol I power

_its Isystem

Figure 18.- Control system interface diagram.

Subsequent tests using 30-second samples and a slightly mode. The set point is advanced to 100 kW, completing

less rapid response to changes in the wind speed cut the the startup.

typical operation of the yaw motors to less than five times The shutdown sequence is also controlled by the microan hour. Even with this reduced use of the motors, the processor. It can be initiated by operator command, wind

overall pointing accuracy of the rotor is not significantly conditions, the safety systems, or several checkpoints in

different, the microprocessor program itself.

The yaw brake installed to reduce blade loads restrains The safety system monitors system operation and shuts

the nacelle in yaw. This serves as a backup for the dual the wind turbine down when it detects a reason to do so in

yaw drive and increases stiffness in yaw. The yaw brake any of the operating variables. The safety system

system is maintained at constant pressure and operates overrides all other systems and operates the equipment

continuously as a frictional restraining force (ref. 1). directly. The operating variables are temperature in bearThe microprocessor, which controls the automatic ings, gears, alternator, fluids, and the pitch hydraulic

operation of the wind turbine, including startup, syn- pump motor; vibration in the rotor; pneumatic pressure

chronization, and shutdown, permits unattended in the emergency feather gas bottle; hydraulic pressure

automatic operation of the turbine. Once enabled, the and level in the pitch and yaw control systems; yaw error;

microprocessor monitors the wind and begins the startup electrical parameters; rotor overspeed; and microsequence when the wind reaches an appropriate speed, processor functions.

The microprocessor concurrently starts the pitch The remote control and monitor system allows an

hydraulic system and, after the pressure builds up, the operator to monitor machine performance and to

rotor blades are pitched at a rate of 8 deg/s toward the activate the microprocessor. This system is the highest

power position. When the rotor speed exceeds 5 rpm, the level of command when the wind turbine is operating

microprocessor switches the pitch control to speed unattended. It gives the "go/no go" command to the

control and continues the startup sequence. It activates microprocessor. The remote operator receives status

the alternator field when the rotor nears synchronous reports showing machine conditions, position of blades,

speed. The alternator is connected to the power grid and and mode of operation as well as six possible error

the pitch controller is switched to the power control conditions from the safety systems.

17
The status of the microprocessor is also indicated on The synchronization process is analogous to midair

the control function panel, and machine performance can refueling of aircraft when the speeds of two independent

be monitored through an analog display of data on wind vehicles must be matched exactly and held while the

speed, rotor speed, power, and reactive power (known as fragile boom is connected between the aircraft. In a like

VARS). manner the synchronizing relays (equivalent to the boom)

The successful operation of a wind turbine generating are thrown only when the frequencies match. Thus the

power for a utility grid requires precise synchronization control system must maintain the rotor speed within

to the utility frequency. The operations leading up to narrow limits.

final synchronization are performed automatically in

actual operational conditions. However, for the Mod-0

the experimental nature of the machine made it difficult Mod-0A

and time consuming to rely on such electronic controls.

The microprocessor computer allows easy changes in the To introduce utilities to the use of wind turbines in

control system by simply changing commands in the their power-generating systems, DOE funded and NASA

microprocessor memory. The present low cost of Lewis administered the Mod-0A project. Four Mod-0A

microprocessor systems made this the most cost-effective machines (fig. 19), much the same machines as Mod-0,

setup. This approach contributed to bringing the wind were built and installed at utility locations. The first of

turbine on-line quickly since it was possible to switch these was at Clayton, New Mexico, where the town of

between testing and operation rapidly. Overall the system Clayton started operating the 200-kW Mod-0A in March

performed well and made many unattended startups and 1978. This was followed by the Puerto Rico Electric

shutdowns including the delicate process of connecting Power Authority, which began operating the Mod-0A on

the wind turbine to the power line. The frequency of the the island of Culebra, Puerto Rico, in January 1979. The

alternator must match that in the power line. The phase Block Island Power Company first operated the Mod-0A

angle must also be within a narrow band. There is a short on Block Island, Rhode Island, on May 1, 1979; and the

time window during each power line cycle when Hawaiian Electric Company began operating the Modsynchronizing can be accomplished. 0A on Oahu, Hawaii, in May 1980. These sites were

ili} _i

!_ !ill! ̧ ̧ ̧ ̧ _

_ic_' C-BO-_9}'

(a) Clayton, NewMexico.

(b) Culebra, Puerto Rico.

(c) Block Island, Rhode Island.

(d) Kahuku Point, Oahu, Hawaii.

Figure 19.- Mod-0Awindturbines.

18
chosen from among the 17 candidate sites selected by Rotor.-The Mod-0A rotor has a diameter of 38.1 m

DOE. (125 ft). The first three machines used aluminum blades

The Mod-0A project has been successful in gathering fabricated by Lockheed Aircraft Services, Ontario,

experimental and performance data on wind turbines California. Each blade was 18 m (59.9 ft) long and

operating in typical utility environments. Two of the weighed 1070 kg (2360 lb). The blades are heavier than

issues anticipated at the start of the Mod-0A program the Mud-0 blades because of the greater wind load Mudwere the effect of variable power output due to varying 0A is intended to carry. The fourth machine, installed in

wind speeds on the utility grid and the compatibility of Hawaii, used laminated-wood-epoxy blades.

the wind turbine with utility requirements for power The first three sets of blades were made of heat-treated

voltage and frequency control. Operation of the Mod-0A 2024-T3 aluminum except for the cylindrical blade root

machines has dispelled concern over these issues. Mud- shank, which was made of steel. The blade, a main load0A also demonstrated unattended, fail-safe operation carrying spar and ribs covered by a thin sheetmetal skin,

and the reliability of wind turbine systems while is similar in appearance to a conventional airplane wing

providing an opportunity to evaluate the maintenance (fig. 21). The nominal cost of the Mod-0A aluminum

required and any public reaction, blade is $220/kg ($100/lb).

Operating parameters. - Mod-0A is designed to The rigid rotor hub of Mod-0A houses the pitch change

produce 200 kW at a rated wind speed of 10 m/s (22.4 assembly. The pitch can be adjusted at a maximum rate

mph). The cut-in wind speed is 4.2 m/s (9.5 mph) and the of 8 deg/s. At winds above 10.0 m/s (22.4 mph) the pitch

cutout speed is 17.9 m/s (40 mph). angle is decreased to spill wind to keep the electric power

Four design wind speed ranges govern the operation of generation at 200 kW or less.

Mod-0A (fig. 20). Below a wind speed of 4.2 m/s (9.5 Tower.-The tower, 28.3 m (93 ft) high not including

mph) at the rotor hub the blades are feathered and the the hub and nacelle, is an open truss type using round

wind turbine is turned off. From 4.2 to 10.0 m/s (9.5 to pipe members to maximize airflow through the tower and

22.4 mph) the blades are pitched to extract maximum thus minimize shadow on the downwind rotor. An

power; from 10.0 to 17.9 m/s (22.4 to 40 mph) the electric hoist, instead of a stairway, provides access to the

available wind power exceeds 200 kW and the blades are nacelle to further reduce tower shadow.

pitched slightly toward the feathered position to spill Nacelle and rotating equipment.-The fiberglass

power and thus maintain 200-kW output; and above 17.9 nacelle that houses the rotating equipment is similar to

m/s (40 mph) the blades are fully feathered and the the Mud-0 nacelle but slightly larger. Figure 22 shows the

machine is shut down to prevent excessive loads on the interior of the nacelle, typical for the Clayton, Culebra,

machine. The entire structure is designed to withstand and Block Island Mod-0A machines.

winds to 66.7 m/s (150 mph). These wind parameters are The high-torque-low-speed power of the hub is

not absolutes, however. They can be varied to take best transmitted to the gearbox in the nacelle through a lowadvantage of wind characteristics at specific sites, speed shaft. A 45:1 fixed-ratio gearbox transmits the

Operating experience has led to several adjustments in power to the high-speed shaft at low-torque-high-speed

wind-based operating parameters. It requires from 2 to 4 power. A belt-and-pulley drive transfers power to the

minutes to bring the Mod-0A from a parked config- generator. The belt-and-pulley system allows changes in

uration to energy production in synchronization with the the nominal 40 rpm of the low-speed shaft while mainutility grid. taining the constant 1800 rpm required by the generator.

The Mod-0A gearbox was uprated, as compared with

the Mud-0 gearbox, to safely carry the power to the

200-kW generator. The single-shaft yaw assembly

Rated Cutout originally used on the Mod-O was replaced on the first

I i

' ' three Mod-0A's with a dual yaw drive. The yaw drive

200 -- = I

n/ operates whenever the wind speed exceeds the turbine's

150-- [ cut-in wind speed. The yaw drive is braked by pressure

from three disk brakes. The brakes damp yaw oscil-

_- 10o-- Cut-i lations, help reduce blade bending moments, and damp

°_ i torsional oscillations with a drag force. Once the machine

_- 50-- has aligned itself to the wind, brake pressure increases to

I'_/ I ] [ I maximum.

0 4 8 12 16 20

Windspeed,m/s The Mod-OA installed in Hawaii incorporated several

I I I I I I I I I I designchangesthat improvedtheoperatingperformance.

0 5 10 15 20 25 30 3,5 40 45 The dual yaw drive was replaced with a hydraulic yaw

Windspeedmph , drive (fig. 23) that holds the nacelle more firmly when the

Figure20.- Mod-OA operating characteristics, machine is yawing. The belt drive between the high-speed

19
Centerof gravity 0.63(0.25)

Station thick skin Station31.75

Station750 Station 270.7 0.79(0.31)

,

I

/- 0.30(0.12)thick skin 300 i thickskin / I

Station0

I, 18m (59.9 ft) 41 a Center

of

rotation

n- \

0.t46m _.0.20(0.08) _-1.37 (4.5ft)m 0.5 ft) 0.15(0.06) Station370 thick skin

thick skin (strain gages) thick skin Station40

(straingages)

121.9cm (48.0in.)

V-0.79(0.31)thick r" O.20(0.08)thick f

F "_ " DetailA

31.5crn .-

112.i in. ) _ x0.63 [ \ (I.0x1.0x0.15)

O.20(0.08)thickrib--/ (1.5x1.5 x0.25) I _'-O. 10(0.04)thick rib angle

angle D-sparstructure ,, Trailing-edgestructure

BladesectiontakenatStation300

Figure 21.- Mod-OA aluminum blade and typical cross section. Weight of blade, 1070 kg (2360 lb). (Skin thicknesses are in centimeters

(inches).)

P'° // actuator

r Gearbox Fluidcoupling_ ¢Gearbox

Fluidcoupling-x _ rDiskbrake Anemometerlwindvane-,_:_ \\ I\ r Diskbrake

Anemorneterlwindvane \\ \ '_ Alternator---"II '

Belt-and-pulleydrive_ Hydraulic""-... _,._,

Hydraulic-_ \ Bedplate

supply

,_ Rotor _[_1_I;_'__ Bedplate Rotor blades blades

Alternato_r

yawdrive Yawbrake Fixedyawbrake

1116

CD-124(T/-44

R[V4-_.-80

Figure 22.-Schematic of original Mod-0A nacelle and interior Figure 23.-Schematic of Hawaiian Mod-0A nacelle and interior

equipment, equipment.

20
drive shaft and the generator was removed, and the mobile data van equipment scans 100 channels of data,

generator was connected directly to the gearbox through taking analog real-time data as well as collecting digital

a fluid coupling. The aluminum blades used on the first information for later processing (fig. 25). One remote

three machines were replaced with laminated-wood- multiplexer unit (RMU) is installed on the wind turbine

epoxy composite blades (fig. 24). hub, another on the bedplate, and a third in the control

Control system. - The control system's major house at the base of the tower. Each transmits signals via

components are most like those of the Mod-0. A micro- one or two coaxial cables to the vehicle. The mobile data

processor, which continuously monitors the wind speed

sensor, starts the turbine at cut-in speed, brings the

turbine to speed, and synchronizes it with the utility. The

microprocessor also automatically shuts down the rotor

when the wind speed drops below cut-in or exceeds

cutout.

The yaw controller uses a wind direction sensor on top

of the nacelle but only operates above cut-in speed. A

microprocessor handles the yaw control. The Mod-0A

yaw mechanism is activated whenever the averaged yaw

error is excessive. The yaw drive then rotates the nacelle

until the yaw error is reduced to zero and the turbine is ......

properly aligned to the wind.

A remote control and monitoring system at the utility

power dispatcher's center permits manual starting and

stopping of the microprocessor. As in Mod-0 a digital

readout of wind speed, rotor speed, power, VARS,

current, and voltage is provided. In case of an automatic

shutdown the relevant data are also transmitted. A safety

system for automatic shutdown operates independently

of all other controls to prevent catastrophic failure.

Since the Mod-0A machines are dispersed around the

country, a mobile data system was developed for Mod0A machines that can be connected into a wind turbine

and completely check out its systems (ref. 22). The Figure 25.- Mobile Data System at Mod-1 site.

Figure 24.- Laminated-wood-epoxy composite blade used on Mod-0A. Length, 18.3 m (60 ft).

21
van can travel over public highways without special 2000 hours of operation and generated 181 000 kWh of

permits or approvals. Its air-ride suspension on both electricity. Further repairs were needed in December

front and rear axles limits vibration and shock to the 1978, when a generator bearing failed because of

data-processing equipment, and the heating and cooling excessive radial loading. It was replaced with a bearing

units control the interior environment properly, designed to withstand the radial loading. On March 1,

Operating experience.-The first Mod-0Abeganoper- 1979, the fluid coupling was replaced after the unit

ating in Clayton, New Mexico, on November 30, 1977, developed a fatigue crack. In August 1980, the original

for checkout and tests. The machine was dedicated on experimental aluminum blades were removed and

January 28, 1978, and in March 1978, NASA turned returned to NASA Lewis for inspection and storage. A

routine operation over to the Clayton municipal power- set of modified Mod-0 aluminum blades were tempogenerating system, adding to its seven diesel generators, rarily installed at Clayton upon removal of the Mod-0A

At the end of May 1978, Mod-0A had completed 1000 aluminum blades. One of the experimental Mod-0

hours of operation and generated over 94 000 kWh of modified blades developed an unexpected fatigue crack in

electricity for the utility network. The first two years of October 1980. As a result the machine was shut down

experimental operation were completed in March 1980. until an experimental set of short (14 m (46 ft) long) wood

The Clayton Mod-0A operated for 6000 hours, or about blades could be installed in February 1981. The short

80 percent of the time during periods of usable wind wood blades were used to obtain rotor performance

energy. It yielded an average hourly output of 92 kW. comparisons with square and rounded blade tips. These

Acceptable winds were available about 57 percent of the experiments were completed, and during August 1981the

time. The machine supplied about 2.5 percent of first set of 18.3-m (60-ft) long fiberglass composite blades

Clayton's power during off-peak periods. On occasion, were installed on the Clayton machine. The machine

during early morning, the machine produced over 20 resumed operation and successfully operated for over

percent of the total power requirements of the 10 000 hours on the utility network that month.

community. In April 1981, it was necessary to replace the fluid

The power generated divided by the power that would coupling for the sixth time. A reinforced coupling was

be generated if the generator operated at rated capacity installed and eliminated further fatigue cracks in the steel

100 percent of the time was 0.2 during this period. This coupling housing.

plant factor and the average power output of 92 kW were On June 30, 1982, the experimental test project at

excellent for the first operational unit. But the Clayton Clayton was completed and the machine was shut down

Mod-0A experienced several startup and adjustment and placed in a standby status. The fiberglass-epoxy

problems in the early phases of the program. There were composite blades successfully completed over 3000 hours

difficulties with electrical noise. A number of false safety of operation. A blade inspection revealed no signs of

shutdowns occurred before proper adjustments and deterioration. Plans were begun with the utility company

settings were determined. The blades were also modified to decide on the machine disposition. The City of

and repaired several times (refs. 7 and 23). A blade load Clayton decided to have DOE and NASA remove the

monitor was added to the safety system to shut down the machine. Removal was completed in October 1982. The

machine when high loads are encountered. And the high Clayton machine operated for over 12 000 hours on the

feather rate used in the safety system shutdowns was utility network and produced over 1100 MWh of

reduced, electricity.

Another early problem encountered at the Clayton The Mod-0A wind turbine on the island of Culebra,

Mod-0A turbine was the buildup of ice on the rotor Puerto Rico, was first rotated on June 26, 1978. The

blades. The limited experience with the Smith-Putnam machine had completed its first 100 hours of operation in

wind turbinein the 1940's indicated that the blade would September, and the Puerto Rico Electric Power

flex enough to shed ice before it could build up. The Authority took over its operation in January 1979. The

Clayton experience confirmed this; however, the machine was normally unattended and operated remotely

shedding process created a potential hazard. The blade by the utility company at San Juan via a radio communitip speed is 79 m/s (260 ft/sec) and pieces of ice up to 20 cation link between the wind turbine and the utility

cm (8 in.) long were shed on one occasion. To prevent dispatcher.

this hazard from recurring, an ice detector was installed In May 1979, the machine was shut down for a

that indicates the onset of ice buildup. The safety system complete blade inspection. Repairs similar to those

senses a signal from the ice detector as ice is building up performed on the Clayton Mod-0A blades were begun.

and orders the machine to shut down. The system has The blades were returned to the machine in February

prevented operation during icing conditions but has also 1980 and machine operations resumed.

decreased wind turbine availability during the winter The hot, humid climate on Culebra caused corrosion

months, of some electrical connections and promoted fungus

In October 1978, the Clayton Mod-0A had completed growth in some electronic packages. This caused a

22
number of machine outages. By installing an air blades, a direct-drive alternator, and a hydraulic yaw

conditioner in the control room, fungus growth was drive. The Hawaii Mod-0A is the first machine to have

eliminated and corrosion was reduced. As a result, the wood blades as its primary design. The Gougeon

reliability of the microprocessor and associated Brothers, Bay City, Michigan, designed and built the

instrumentation was improved. In January 1981, the blades for NASA. The direct-drive alternator that

rotor speed was reduced from 40 to 31 rpm. This speed replaced the previous belt-driven design and the hydraulic

reduction was carried out to extend the operational life of yaw drive were designed, fabricated, and assembled by

the aluminum blades until a set of experimental wood the Advanced Energy Systems Division of Westinghouse

blades could be manufactured and installed on the Electric Corporation. This machine started utility

machine. The experimental wood blades were installed in operation in June 1980.

August 1981. The experimental operation of the Culebra In November 1981, after 7800 hours of power

machine was completed and the machine was shut down generation on the network at 40 rpm, a broken blade

on June 4, 1982. The wood blades operated for 2800 retention bolt was found at the base of the machine. The

hours at 31 rpm with no sign of blade degradation. The bolt, one of 24, was used to fasten the blade to the

machine accumulated a total operating time of 8094 machine. The failure was the result of corrosion. Each

hours and generated 683 MWh of electricity, blade accumulated over 18.7 million load cycles while

The Block Island wind turbine first rotated on May 1, supplying electricity to the Hawaiian Electric Company.

1979. The utility took over operation of the machine on This blade set was returned to NASA for evaluation and

October 12, 1979. As a result of the aluminum blade repair.

modifications for the Clayton and Culebra machines, the The second experimental wood blade set was installed

aluminum blades for the Block Island machine were on the machine in March 1982. Each blade had a rounded

modified during their buildup. Because of the relatively tip fairing, rather than the square tip configuration used

high cost for aluminum blades as compared with wood on the first set of blades. Rotor performance comparblades, further development effort on aluminum blades isons were conducted on the first and second sets of

was terminated when the Block Island blades were blades. Better rotor performance was obtained with the

delivered to NASA. Experimental operation of the rounded-tip blades. On June 4, 1982, the experimental

aluminum blades was completed in July 1980 when operation was complete and the machine was shut down.

experimental wood blades were installed. The machine generated 1261 MWh of electricity during

The privately owned Block Island Power Company its 8444 hours of operation on the network. The second

(BIPCO) is isolated from other power sources located on set of wood blades operated for over 600 hours before the

the mainland. The utility company serves a population of machine was shut down.

about 300 permanent residents. During the summer, The objective of the Mod-0A project was to gain early

however, transient residents number up to several operating experience with large wind turbines in a variety

thousand. As a result, power demands seasonally vary of utility and wind site environments. From the first

from 250 kW during the winter months to over a rotation at Clayton in November 1977 to shutdown in

megawatt in the summer. During the winter season the June 1982, the four machines accumulated over 38 000

Mod-0A wind turbine was configured to generate a hours of experimental operation. The objective to gain

maximum of 150 kW. The wind turbine operated in early operating experience had been achieved. The

parallel with two diesel generators to serve an average machines demonstrated that each could run unattended

load of 350 kW. The Westinghouse Electric Company with protective systems that successfully detected anomconducted experiments at Block Island for NASA to alies before serious damage could occur. It was found

assess the interaction of the wind turbine with BIPCO. that routine maintenance and repair could be done

Experiments were conducted from February through successfully by utility company mechanical and electrical

April 1982. During this test period the Mod-0A saved technicians. Compatibility of the Mod-0A with each

11 657 kg (25 700 lb) of diesel fuel. This fuel saving utility network is not as severe a problem as originally

represented a 6.7 percent reduction in fuel consumption expected. In general, Mod°0A compatibility is well within

while the wind turbine generated 11 percent of the an acceptable range. Public reaction to the Mod-0A

utility's needs. On June 4, 1982, the Mod°0A project has been extremely favorable. For example, over

experimental test program at Block Island was completed 20 000 people have visited the Clayton site. Most visitors

and the machine was shut down. The machine operated surveyed thought that the machine was aesthetically

for a total of 8509 hours and generated 588 MWh of acceptable and that wind energy is a good idea to pursue.

electricity. The wood blades operated over 7500 hours at Although the experimental Mod-0A project was highly

31 rpm. successful as a research experiment, the first-generation

Procurement of the Oahu wind turbine components (Mod-0A) design is not economically attractive from a

began and site preparation work started in the fall of commercial point of view. As a result, all of the Mod-0A

1979.Three key design features on this Mod°0A are wood machines will be removed from their sites by the end of

23
1984. Engineering studies conducted during the development and experimental operation of these machines

clearly indicated a need for major technology advances in

order to make large machines more economically

attractive. Resulting improvements have been

incorporated in the second-generation (Mod-2) and third- Wind

generation (Mod-5) designs.

61.0

(200) 4.2

Mod-1 (13.7)

Mod-1, when installed on Howard's Knob, Boone,

North Carolina, was the first DOE/NASA wind turbine

in the megawatt class (fig. 26). It was designed to produce 10.1 (33) F Nacelle

2 MW, or 2000 kW, in a 14.6-m/s (32.6-mph) wind /

measured at hub height (figs. 27 and 28). When it began -z q z

operation, Mod-1 was the world's largest wind turbine in kJ --ct

a utility network. The machine was designed and

assembled by the General Electric Company's Space

Division. '\\\

Rotor.-Blade fabrication was subcontracted by the "-Tower

General Electric Company to the Boeing Engineering and _intie

Construction Company. Each 29.7-m (97.5-ft) long blade

used a NACA 44XX series airfoil with a thickness ratio Tower

varying from 33 percent at the root to 10 percent at the /

tip. The twist of 11° varies linearly from root to tip. The 42.7 /

blades weighed a total of 18 780 kg (41 500 lb). The (140)

major load-carrying member was a hollow steel spar

made from A533 grade-B, class-2, high-strength, lowcarbon steel. The stainless-steel trailing edge was structurally bonded to the spar as shown in figure 29. The '___1

building

, /- Foundation

/

J , /

Figure 27.- Schematic of Mod-1, 2000-kW wind turbine. (Dimensions

are in meters (feet).)

foam-in-place application adjacent to the spar provided a

continuously adhered joint between the spar and the

trailing-edge sections.

Located between the blades and the rotor hub was a

three-row roller ball bearing (fig. 30). The roller bearing

permitted the blade to pitch by 105° from the feather

position to the full-power position. Hydraulic actuators

changed the blade pitch to control the speed as the wind

varied (fig. 31).

Because the rotor hub was of all-bolted construction,

the stress limitations of welds were avoided. A lock in the

hub was designed to hold the blades horizontally. The

feathered rotor could be held fast in the 6-12 o'clock

Figure 26.-Mod-1, 2-MW wind turbine at Boone, North Carolina. position against a direct 22.2-m/s (50-mph) wind.

24
Rated Cutout

I

I

2000-- I I

,.- 1000--

o

Cui-i

iV i i l

0 4 8 12 16

Windspeedat9.l-rn(30-ft) elevation, mls

I I I I I

0 10 20 30 40

WindspeedatO.l-m(30-ft) elevationrnph ,

Figure 28. - Mod-I operating characteristics.

Because the overall design of the blade and hub system temperature specification placed the fracture-toughness

was conservative, the components were heavy (table III). requirements for steel in the most severe environmental

However, this design allowed routine testing and class, known as zone 3. A333 structural carbon steel

extensive instrumentation to provide data for future tubing was selected for the tubular tower members

designs. After trade-off studies were conducted between because of its suitability for zone 3.

various types of blades, the metal blade design was Rotating equipment. - The rotating equipment and

selected and fabrication was started late in the Mod-1 control mechanism atop the tower was mounted on a

system development. The rotor speed is a trade-off bedplate structure. The bedplate was a box girder

between maximum energy capture for the given rotor construction using plate for all but a few details. A516

diameter and the cost. The blades were mounted rigidly grade-70 steel was chosen for the bedplate. This material

to the hub with downwind coning to minimize system has good impact strength at low temperatures and is less

loads and with full-span blade pitch control to insure sensitive to poor welds than the A36 considered earlier.

power and speed control under all operating conditions. The total assembly on top of the tower including the

Tower. -The Mod-1 tower design evolved after several removable nacelle fairing weighed 77 566 kg (171 000 lb).

iterations to satisfy strength and stiffness requirements at The Mod-1 gearbox, shown in figure 32, was a threeminimum cost in the face of increasing design loads. To stage unit having tandem, articulated, parallel shafts with

gain maximum bending stiffness, the tower height was the input and output shafts on a vertical centerline and

reduced and the dimensions at the tower base were having horizontal casing splits. The tandem, articulated

increased, shafts permitted the load path to split with equal sharing

The Mod-1 tower was of open truss construction, of the load. A floating shaft assembly transmitted the

Tower members were tubular to decrease the shadow rotor torque to the speed increaser gearbox.

effect as the blades passed behind the tower. The tower The generator was a four-pole, 1800-rpm, wyewas designed to sustain a maximum wind load of 66.9 connected unit with shaft-mounted exciter and a 4160-V

m/s (150 mph). Its first bending frequency was at least output. The synchronous ac generator was driven at 1800

2.8 times the rotor operating frequency, and its first rpm by the high-speed shaft. A shaft-mounted, brushless

torsional frequency was at least 6.5 times the rotor exciter controlled by a solid-state regulator and power

operating frequency, stabilizer provided voltage control. Generator output was

The requirement that the tower have a life of 30 years brought by cables and a slipring at the yaw bearing down

and operate at environmental conditions including tern- the tower to the ground enclosure. Surge capacitors and

perature extremes from -35" to 48" C (-31 * to 120" F) related power generation equipment were mounted in a

affected the choice of structural material. The lower caged enclosure below the generator. Rotation of the

25
Spliceplate,

stainless

stee-l24gage

Uppersparpanel, I A533- 3.2 tol.3 cm /--Foam in place,160.2kg/m3 (1OllYft3)

(1-1/4to112in. ) thick 1 / / F Bl°ckf°am' 128t° 48kglm318t° 3 Ib/ft3)

--'-- ! ___/I / rTrailing-edge skin,

sta,n,essstee,-

Stifler Trailing-edgecap

0.076-1Jm(3-rnil)foil strip and

polysulfidesealer(typicalall

• bondedges)

Weldedspar

Weldland(upper Chordwise

surfaceonly) weldjoint

Transition Tipweight

section installation

Blade

station:41 301 564 844 1024 1210

I

I

1144

Ringattach g-edgecap

forging

(5.08cm

(2 in.) wide),15places

Spanwisesplices

Cordwisesplices(45.7cm

(18in.) wide), sixplaces

Blade

Figure 29.-Mod-I blade configuration.

nacelle assembly, including the fairing, rotating dispatcher control; and recorded data, commands, and

equipment, and bedplate was controlled by two hydraulic status for diagnostics• The control system used the

yaw motors. Each yaw motor drove a pinion meshing average of the two wind sensors as its signal and could

with a gear on the inner face of the yaw bearing. Six shut the turbine down when necessary.

hydraulic yaw brakes damped movement while the Operating experience.-The Blue Ridge Electric

nacelle was being driven and held it in position once the Membership Corporation (BREMC) operated the Mod-1

rotor was turned to the wind. wind turbine under the Federal Wind Energy Program.

The control subsystem of the Mod-1 determined the The wind turbine was connected to the cooperative's

rotor blade pitch angle for startup. It also controlled existing 12 000-V distribution system in Watauga

the yaw drive and brake hydraulic system; provided County, North Carolina, which serves Boone as well as

26
Blade

retention

Mainbearing

Tobedplate

adapter

Hub

housing

Trailshaft

Figure 30.- Mod-1 blade roller bearing.

the rest of the county. The BREMC had a peak load of

136 MW during the winter and purchased its electricity

from Duke Power, in Charlotte, North Carolina. The

Mod-1 turbine's first rotation was in May 1979and it was

dedicated in July. In September 1979,the Mod-1 machine

was synchronized with the BREMC network. Acceptance

testing was conducted from October 1979 through

February 1980. The machine operated at various power

levels up to 2000 kW while control systems were finely

tuned and evaluated. Remote operation of the machine Figure 32.-Mod-I gearbox.

by the BREMC dispatcher from Lenoir, North Carolina,

was demonstrated during 1980. environmental issues. It should be noted that only three

While the initial checkout of the Mod-1 machine was families complained about the noise and 35 families

being conducted during the winter of 1979-80, com- noted some television interference out of a community

plaints were received from a few nearby residents that the with a population of over 10 000.

machine was producing interference with television A number of studies were conducted throughout 1980

reception and an annoying noise. Machine operation was at the Mod-1 wind turbine site regarding television rerestricted to minimize these disturbances to the affected ception. The television signal strengths and the quality of

areas while studies were begun to evaluate these reception with and without the turbine operating were

Thrusrtinc

Stationary Pitchrods- Bearing links

Sleeve

Rotating

centerline links

Blade

)

] _ Tohydraulpackage ic

Torqueplate

Linksupport Actuators

Figure 31.-Mod-I bladepitch controlmechanism.

27
TABLE III.- MOD-1 SYSTEMWEIGHTBREAKDOWN

[Unitsare kilograms(pounds).]

Rotorassembly: ............. 46 720 (I03000)

Hub .................... 6804 (15 000)

Blades .................. 16 330 (36 000)

Bearingsand supports .......... 13 154 (29 000)

Pitchcontrolmechanism .......... 4990 (ll 000)

Pitch controlhydraulics.......... 5443 (12 000)

Nacelleassembly: ............ 77 565 (171000)

Bedplate................. 30 844 (68 000)

Fairing ................... 2268 (5000)

Generator ................. 6350 (14 000)

Power-generatingequipment.......... 454 (lO00)

Shaftsand couplings............ 8165 (18 000)

Gearbox ................. 26 309 (58 000)

Lubricationand hydraulicsystem....... 1814 (4000)

Control and instrumentation..... .... 454 (lO00)

Cables,lights,etc.............. 908 (2000)

Yaw assembly: ............... 25 400 (56 000)

Yaw structure .............. 15 422 (34 000)

Bearing .................. 5897 (13 000)

Yaw brake .................. 454 (lO00)

Yaw drive .................. 3629 (8000)

Tower assembly: ............. 145 150 (320000)

Structure ............... 141 976 (313000)

Lift device ................. 454 (lO00)

Cable and conduit .............. 2721 (6000)

Total (excludinggroundequipment).... 294 838 (650 000)

Groundequipment(including ........ 24 494 (54 000)

transformer)

Total 319 332 (704000)

evaluated. In addition, in-depth investigations were levels. The rotor speed was reduced from 35 rpm to 23

conducted for a number of potential solutions, which rpm, and in October 1980 a new 1200-rpm synchronous

included (l) evaluation of high-gain/low-gain antennas, ac generator was installed on the machine. The new

(2) local rebroadcasting of the television signals, and (3) generator allowed the wind turbine, operating at 23 rpm,

the expansion of cable television to the affected areas, to supply synchronous power to the network. Additional

The nine television channels servicing the Boone region sound tests to evaluate the machine operation at 23 rpm

are quite far away, more than 50 km (31 miles). The were conducted in January 1981. These tests showed a

surrounding mountains cause video shadows, and reduction in sound as expected. During experimental

television reception should be at best poor in this fringe testing in January 1981, a failure of 22 bolts was

receiving area. Early test results confirmed that the experienced in the low-speed-shaft connection to the

television signals are weak in the Boone region and that rotor hub. This damage resulted in termination of

the quality of reception is generally poor. The rotating testing.

blades of the Mod-1 wind turbine did cause an extraneous An assessment of the data resulting from experimental

pulse on the video (but not the audio)" portion of the operation of Mod-1 showed that adequate information

television reception at Boone. The use of high-gain was obtained (ref. 9). The experimental Mod-1 project

antennas to correct the interference seemed to be of provided extensive engineering information on how to

limited value for this region, reduce both wind turbine noise and localized television

Special sound teams from the Solar Energy Research interference caused by a wind turbine. Because the Mod-I

Institute and the General Electric Company conducted was a first-generation design, like the Mod-0A, it was not

acoustic tests at the Mod-1 wind turbine site and at economically attractive for commercial utility use. An

surrounding homes during the spring of 1980. Results assessment of the cost to repair and to continue operating

from these tests indicated that the sporadic sound was the Mod-I showed that the machine would not be

produced by the blades passing the legs of the support economically viable for the utility company. The General

tower. Test results also showed that reducing the rotor Electric Company developed two plans. Their first plan

speed would significantly reduce the annoying sound involved refurbishing the machine at Boone and con28
ducting further experimental tests. Their second plan specified for the blade (fig. 34), up to 42 percent of the

investigated the feasibility of relocating the machine for power available in the wind is converted to rotational

operation on another utility network. The resources to power. The blade tip pitches through 100° to control

carry out each plan were analyzed and compared with the both rotor speed and power output.

potential benefits of additional experimental data. GE Blade tip pitch is controlled by means of a hydraulic

decided not to pursue either plan. As a result, it was actuator mounted from the blade midsection to the blade

decided in the fall of 1981 to dispose of the Mod-1 tip section. Hydraulic flow control to each actuator is

machine. With the assistance of the General Services governed by a signal from the automatic control system

Administration the Mod-1 machine was removed from to servovalves. The position of each blade tip is monithe site in September 1983. tored by position transducers that send electrical signals

back to the control system.

The pitch control hydraulic system includes an electricMod-2 motor-driven pump, a reservoir, and accumulators. The

The experienc e gained in designing and during the hydraulic system, located in the nacelle, is installed on

experimental operation of the Mod-0A and Mod-1 and rotates with the low-speed shaft (fig. 35). The blade

machines resulted in major improvements in the Mod-2 tip actuators and control valves also rotate with the lowwind turbine configuration. For example, the rotor on speed shaft. Electricity and control signals are transferred

the Mod-2 is teetered and operates upwind of the tower, from the power control console, located in the nacelle, to

The Mod-2 (upwind) rotor operates much more quietly the pitch control hydraulic system via brushes and a slipthan the Mod-1 (downwind)rotor. The teetered Mod-2 ring assembly. The brushes and slipring assembly

rotor operates with lower loads than a rotor with blades eliminate the need for a rotating hydraulic coupling

rigidly attached to the hub like the Mod-I configuration, between the low-speed shaft and the nacelle.

As a result, the teetered Mod-2 rotor is lighter in weight A flex-plate hub was selected during conceptual design

than a similar size rotor with blades rigidly attached to to reduce bending moment on the blade root, but

the hub. Another feature of the Mod-2 rotor is the experiments with Mod-0 suggested that some form of

method used to control rotor speed and power. Only the articulated blade could further reduce such loads. A

outer tip of each Mod-2 rotor blade pitches, rather than

the entire blade as on the Mod-0A and Mod-1 machines.

Thus Mod-2 power is controlled by pitching only the tip

portion of each blade and is called rotor partial-span

pitch control. The Mod-2 machine has a flexible,

cylindrical steel tower rather than the rigid steel truss

tower common to the first-generation (Mod-0A and

Mod-1) machines. A planetary gear speed increaser is

used on the Mod-2 machine. The planetary speed

increaser is more compact and lighter in weight than the

conventional parallel-shaft gearbox.

The three Mod'2 machines (fig. 7) at Goodnoe Hills,

Washington, are the nation's first cluster of megawatt

machines. Each turbine produces 2.5 MW at a rated wind

speed of 12.5m/s (28 mph). This cluster of wind turbines

allows testing of design innovations and the study of the

interaction of neighboring machines.

Rotor.-The Mod-2 rotor is 91.5 m (300 ft) in

diameter, weighs 87 300 kg (192 500 lb), and operates

upwind of the tower (fig. 33). The blades are hollow steel

shell construction with steel spar members. Except for

two bolted splices made at the site during final assembly,

all parts are joined by arc welding. Using a single type of

steel throughout the entire blade helped to reduce manufacturing processes and costs. The number of parts was

further reduced by the welded construction. Use of steel

insures resistance to handling damage during transport

and erection; imperviousness to dust, rain, and lightning;

and low cost. C-82-4211

With the NACA 23000 series airfoil and surface finish Figure33.- Mod-2rotor andnacelle.

29
Flyingattitude

Highwindattitude

/ Station /

/ 1249

/ UPRblade// /-- Skinsplice(typ.)

surface-_ /

/

,_ Trailing Station Station edge 360

F Boltedsplice

1800 /

/

/ Wind

Location, Leedagdi e ng / Rotationclockwise /

percent viewedfrom upwind

of span

37 Nacelleside Leading

edge

"[hree-spartipB-B Two-sparbladeA-A S _ Trailing tation0

edge

Station30

Figure 34.- Mod-2 steel blade configuration.

Rotor

Hydrauliclines hub _ Rotation

Accumulators section..._/' / _ Low-speesdhaft L_--'_,_

reedshaft J _-_/.'\

f

Teeter

Teeter Teeter b ke

Teeter

bea.n, . um m°t°r.Reseshao,frk.. t ! I stop

Teeterbrake Wind _ _ s

Support', .Elastomeric _ '_ _7"/

link Rotorcentersection bearing _/"

Toti_

actuator Figure 36.- Mod-2 hub.

Figure 35.- Mod-2 pitch control hydraulic system.

Bearings that allow teeter rotation are installed so that

each bearing assembly can be removed and replaced

without removing the rotor or the low-speed shaft. The

teetered hub (figs. 36 and 37) was found to reduce out-of- rotor teeter bearings and the upwind end of the low-speed

plane vibratory bending moments much below those of shaft are lifted in one piece during assembly. All joints

the flex-plate hub. Studies also showed that use of the and bolts are sealed to prevent moisture from getting

teetered hub in place of rigidly mounted blades not only inside the blade. Access to the blade interior for

reduces the rigidity necessary in the blade and therefore maintenance is possible through sealed hatches.

its weight, but also reduces the tower and nacelle weights. The hub is constructed as a weldment of three large

Thus fabrication and material costs are lowered rolled-plate cylinders (fig. 37). These cylinders are

throughout the wind turbine, pierced by a smaller cylinder containing the hub bearings.

Stops limit teeter motion to 6.5*. A teeter brake The welded structure reduces construction costs.

prevents rocking when the rotor is not in operation and Tower.-The tower to support the rotor and the

damps the amount of teetering during starting and nacelle of the Mod-2 is 59 m (193 ft) high and constructed

stopping, of cylindrical, seam-welded steel (fig. 38). The upper

30
_' C-80-5878

Figure 37.- Mod-2 rotor hub and nacelle during assembly.

truss towers produce a large wind velocity reduction, or

"tower shadow," which produces a pulse in a downwind

rotor as the blade passes through the tower wake. Blade

bending and responses to this pulse in other components

of the wind turbine will depend on the amount of

damping provided in the various components, the

proximity of damping to multiples of rotor speed, and

the strength of the tower wake. Providing for damping in

the tower and other components, designing the tower so

that its natural frequency is significantly different from

multiples of rotor speed, and orienting the rotor upwind

.... all help to reduce the vibrating effects and tower shadow.

....... The soft tower also weighs much less, and the shell

construction is cheaper to fabricate. Moreover, a soft

rather than a rigid tower still permits the use of heavy but

economical and reliable rotor designs.

The upwind rotor configuration slightly reduces

fatigue and increases annual power production by 2.5

percent while adding little to the cost of the yaw system.

The cost of the yaw system is minimized with the teetered

rotor.

Figure38.-Mod-2 towerassembly. The tower and foundation are designed for operating

load conditions, seismic load requirements, and an

portion of the tower is 3 m (10 ft) in diameter and it flares extreme wind speed of 55.5 m/s (124 mph) at hub height

out to 6.4 m (21 ft) at the bottom. It is a "soft" tower, with the rotor parked. In sandy gravel conditions the

having a natural bending frequency of 1.3 relative to the tower has a buried octagonal foundation of reinforced

revolutions of the rotor. It was designed to have a first concrete. The bus tie contactor and transformer are

bending frequency low enough so that the tower and the located on a concrete pad about 30 m (100 ft) from the

nacelle can attenuate the two-per-revolution rotor loads, tower.

NASA studies have shown that blade bending mo- Nacelle. - The tower provides access to the nacelle (fig.

ments could be substantially reduced by using soft towers 39). The nacelle houses the major Mod-2 subsystems,

with low aerodynamic drag. Heavy, dynamically stiff such as the drivetrain, the generator, the yaw bearing and

31
Figure 39.- View up inside of Mod-2 tower up before nacelle installation.

drive, and the hydraulic systems for blade pitch and yaw fixed rotor speed of 17.5 rpm to the generator speed of

control (fig. 40). The nacelle also houses other ancillary 1800 rpm. It provides rotor-to-generator speed

equipment: the generator cooling system, the nacelle air- conversion and drives auxiliary equipment.

circulating system, fire protection equipment, and The generator (fig. 43) is a synchronous electrical

maintenance equipment, generator rated at 2500 kW. Two different approaches

The nacelle and drivetrain weigh 83 000 kg (183 700 for generating electricity were considered in the design

lb). The nacelle is 11.8 m (38.6 ft) long, 2.8 m (9.3 ft) phase: adapting an electrical system that can accept

high, and 3.44 m (11.3 ft) wide. It is shipped as one unit, variable shaft rotor speed; and allowing the rotor to

but the gearbox and generator are removed for trans- operate at a speed proportional to the wind, using

portation and the unit is reassembled on location, commercially available electrical equipment at a fixed

The nacelle structure, designed for ease of assembly rotor speed. The variable-speed rotor provides more

and maintenance, is a trusswork of welded structural annual energy than the constant-speed rotor. However,

steel overlaid with corrugated steel sheets. The bottom is the variable-speed generator and associated electrical and

enclosed with safety-plate walkways. Hatches on both electronic equipment are not commercially available. The

ends and on the top provide access. A fire control system, fixed-rotor-speed system was selected for Mod-2 to avoid

emergency exits, and nonpowered emergency person- the potentially high costs and schedule uncertainties

lowering devices are located at each end of the nacelle, associated with the development of a variable-speed

The drivetrain assembly consists of a low-speed shaft, generator system.

a quill shaft, a gearbox, a high-speed shaft, couplings, a The rotor torque is transmitted to the gearbox through

rotor parking brake, and a generator (fig. 41). a "soft" quill shaft. It is designed to reduce the two-perThe 16 780-kg (37 000-1b) gearbox (fig. 42), manu- revolution rotor torque fatigue effects at the gearbox and

factured by Stal-Laval Turbine AB, Finspong, Sweden, is to improve the power quality of the generator output.

a three-stage, epicyclic type, which is smaller, lighter, less Yaw system. -The yaw system, located between the

expensive, more efficient, and more tolerant of support nacelle and the tower, rotates the rotor and the nacelle

deflections than a parallel-shaft gearbox with a similar into the wind and holds them in position as commanded

rating. It is flexibly mounted to the nacelle to reduce the by the yaw control system. The yaw assembly turns the

effect of nacelle deflections on gear loads. The small rotor into the wind at a rate of 0.25 deg/s. The control

gearbox is easy to maintain and can be completely system holds the heading within a few degrees of the

overhauled in the nacelle. The gearbox provides a 103:1 long-term average wind direction, which minimizes

step up from the fixed rotor speed, which increases the power losses due to rotor heading error. Thirty-second

32
Windsensors

Gearbooxilcooler

ingexhaust

Ventilators

NCUrack

Halonbottle(fire

Removableroofpanels_ extinguishersystem)

Rotoraccess \

Gearboxoil

reservoir

Generator

Gearbox

Nacelletotoweraccess

Nacelletoplatformaccess

Tower

Maintenancpla e tform Gravityshutters

Figure 40.- Mod-2 nacelle and rotating equipment.

Rotorparkingbrake

Gearbox

Oilinlet

Generator

Lows- peed High-speed

shaftassembly shaftcouplings

lex mount

Oil outlet

Removablecoupling Quill shaft

Fixedcoupling

I"eeterbearinginterface

Figure 41.-Mod-2 drivetrain assembly.

33
C-80-3020

Figure 42. -Mod-2 epicyclic gearbox.

C-80-3025

Figure 43.- Mod-2 synchronous generator.

average wind excursions are monitored. The control 14-kg/cm2 (2000-psi) hydraulic system. Because the

system changes the heading whenever these exceed 20° to hydraulic system is mounted in the nacelle, there is no

avoid extreme blade loads, need for rotating hydraulic joints between the nacelle and

A hydraulic brake damps yaw motion and six the tower.

additional brakes prevent inadvertent yawing. The yaw The drive pinion and shaft are protected from overload

brakes are spring actuated and hydraulically released, and subsequent mechanical damage by a shear pin

This insures that brakes will be applied if there is a arrangement. All yaw brakes are easily accessible for

hydraulic failure, inspection and disk pad replacement. The entire system is

The yaw drive system and brakes are powered by the shielded from weather and dust.

34
Control system. - The control system provides the The Mod-2 cluster research tests have a number of

sensing, computation, and commands necessary for primary objectives (ref. 12). Information is needed by

unattended operation of the Mod-2 wind turbine. The utility companies and manufacturers on one-, two-, and

controller is a microprocessor located in the nacelle three-machine operation. It is important to know how

control unit. As in previous designs, it initiates startup; single or multiple machines may affect the quality of

monitors wind conditions, rotor speed, power, and electricity delivered to the utility customer. Experiments

equipment status continuously; and shuts down the wind will be conducted to assess the relation between

turbine under adverse conditions, performance and physical spacing of machines. The time

The software for the controller occupies about 12 000 and types of personnel needed to maintain machine

bytes of programmable read-only memory. There are an operation will be investigated. Environmental issues such

i additional 4000 bytes of random-access memory for as potential television interference and acoustic noise will

operational and historical data storage. The software be evaluated. Finally one of the machines will undergo

control cycle rate is 10 Hz, which provides a 1-Hz systematic modifications to improve and verify overall

response digital feedback control to the blade pitch machine performance. In addition, the data gathered as a

system. Each program cycle also samples all sensors, result of this research will be used for studying the

schedules the proper operating mode, and generates advantages of larger clusters of wind turbines.

commands to control nacelle orientation with respect to For example, by learning how three machines in a

the wind. cluster perform, projections can be made on how 20 or

A control panel and a display terminal are located in more machines would best be spaced on a single tract of

the tower base to provide operating and fault data as well land.

as manual control for maintenance. A remote terminal at

the utility substation provides data and limited control of

Mod-2. In the event of computer system failure, Mod-2

will be shut down by an independent fail-safe system. Component Research and Technology

Safety considerations are an integral part of the wind Rotor Blade Development

turbine program (ref. 24). Designed to operate in the

temperature range -40 ° to 42° C (-40 ° to 105° F), The development of rotor blades by NASA has been a

Mod-2 can withstand loads associated with a maximum major effort motivated by the fact that this component

steady wind speed of 53.6 m/s (120 mph) at the 9.1-m was the highest cost subsystem in the first generation of

(30-ft) reference elevation. However, the wind turbine wind turbines. Of primary importance then for

must face other environmental threats including seismic economical design are the materials used for blade

disturbances, impacts of various projectiles, trans- construction and blade fabrication techniques. The

portation and handling, lightning, and hail. When in soil NASA low-cost-blade project investigated a variety of

conditions appropriate to the site, the wind turbines are rotor blade sizes, materials, manufacturing methods, and

designed to withstand zone 2 seismic disturbances. The rotor control systems. Rotor designs involve a number of

blades, nacelle, and tower are designed to withstand considerations including the need to establish the rotor

impact of a 1.8-kg (4-1b)projectile at 16.5 m/s (35 mph). diameter, the number of blades, the mode of operation,

This assures that the wind turbine will not be damaged and the method of rotor speed and torque regulation. All

from the impact of 2.5-cm (l.0-in.) diameter hailstones affect the cost of a wind turbine. For example, a threewith 20.3-m/s (66-ft/s) terminal velocity. A wind turbine blade rotor was compared with a two-blade rotor. The

must also withstand lightning strikes without major study concluded that even though a three-blade rotor

structural or electrical damage, produces more power than a two-blade rotor of equal

The wind turbine's structural components are designed diameter, the two-blade rotor provided power at lower

; for loads of 102 kg/m2 (21 lb/ft2) of snow on the rotor cost because it was so much more economical to

blade when parked horizontally and 200 kg/m2 (41 manufacture. So two-blade rotors were used. Rotor

lb/ft2) of snow on the nacelle roof. A 5.l-cm (2-in.) power or speed control is required to limit the rotor

coating of glaze ice should not affect the structural torque when wind speeds exceed the design or rated wind

components, speed. This control is needed to prevent overloading of

All parts of the Mod-2 structure not designed to fail- mechanical components such as the gearbox and

safe strength criteria meet safe-life strength criteria. Safe- electrical equipment such as the generator. Allowing

life is a structural concept that requires that the structure rotational speed to vary with wind speed makes the blade

sustain no failure during its service life. The tower is design more economical since the pitch angle of the blade

designed so that one failure or any malfunction can remain in a fixed position. However, for standard

degrading performance will not create hazardous or constant-frequency power-generating equipment, a

catastrophic conditions, constant-speed drive to the generator is required. Thus

35
constant rotational speed is desirable, but this requires are formed in molds to make half of one blade. The two

the pitch angle of the blades to be changeable. Pitch blade halves are then bonded together to form the

change mechanisms obviously complicate blade design complete rotor blade.

and increase cost. Torque can be regulated in several Blades made primarily of steel have also been built and

ways. Full- or partial-span blade pitch change can be tested in the low-cost blade development program. A

used, or ailerons extending over the outboard portion of unique low-cost construction using steel has been

each blade can be applied to control rotor torque, advanced by NASA Lewis. A 18.3-m (60-ft) blade was

Early wind turbine projects used aluminum blades with built using a tapered, tubular steel utility pole as the

construction similar to that used for aircraft wings, primary structural member. The blade contour was

Although this approach used existing technology, it was formed by wood ribs fastened to the pole. Blocks of

found to be too costly. So other materials and fabrication plastic foam formed the leading edge. The entire outer

techiques were applied. Blades were constructed of surface was wrapped with fiberglass cloth and then

fiberglass composites, wood-epoxy composites, or steel, treated to shrink the material tight over the ribs and foam

All blade material types have been evaluated for fatigue surfaces. These so-called utility pole blades (fig. 44) have

failures by using blade specimen testing techniques and been extensively used on the Mod-0 machine to conduct a

routine inspections of full-scale rotors on operating wind variety of experiments.

turbines. Although low-cost construction is an important goal,

The technology of filament or tape winding of long blade life is essential to economical wind energy

fiberglass composites has been applied advantageously conversion. A quick estimate of expected blade life can

to rotor blade designs. Fabrication of very large blades, be derived by fatigue testing (fig. 45). The blade portion

45.7 m (150 ft) in length, has been demonstrated. Fiber- that receives the greatest loads in most blade designs is

glass blades have been built and installed on several where the blade attaches to the machine at the hub. Thus

horizontal-axis machines including the Mod-0A and the only that section of a blade need be tested. The actual

WTS-4. Wood-epoxy composite blades 18.3 m (60 ft) loads and load cycles applied to the test blade are derived

long have been built and have operated on three Mod-0A from known wind characteristics such as wind gusts and

machines. Layups of wood veneer, fiberglass, and epoxy loads during machine shutdowns in high winds or in

(a) (b) (c)

(d) (e) (f)

(a) Prepare spar. (d) Wrap fiberglass

(b) Install leading-edge ribs and weight tube. (e) Install trailing-edge ribs.

(c) Install form. (f) Apply razorback and paint.

Figure 44. - "Utility pole" blade fabrication steps.

36
Figure 45. -Aluminum blade root end installed for fatigue testing.

emergencies. Fatigue testing has demonstrated its experimental Mod-0 permitted this increased capability.

importance to blade life. As a result, both the wood and The first three Mod-0A machines provided wind energy

fiberglass blades for the Mod-0A machines in Hawaiiand for electric utilities by using aluminum blades.

New Mexico have by far exceeded the operational life of Experience from operation of these blades on the first

the original experimental aluminum blades with much two machines was used to improve the aluminum blades

less maintenance, installed on the third (Block Island) unit. The set of

Rotor blade development for large horizontal-axis aluminum blades for the Block Island machine were the

wind turbines began at NASA Lewis in 1974. Design last built. Each 18.3-m (60-ft) long, 1070-kg (2360-1b)

studies of 50- to 3000-kW wind turbines for electric utility blade cost over $45/kg ($100/lb), making the blades the

applications were started by both the General Electric most expensive key component on each machine. As a

Company and the Kaman Aerospace Corporation result NASA began to investigate the feasibility of

(fig. 46). At the same time, the Mod-0 wind turbine for building lower cost blades.

the Federal Wind Energy Program was being designed The Kaman and GE design studies (refs. 2 and 3,

and constructed by NASA Lewis. Airplane-wingqike respectively) of large horizontal-axis wind turbines

aluminum rotor blades 18.3 m (60 ft) long were selected concluded in 1975, and both companies strongly

for the Mod-0. Existing aircraft wing and helicopter rotor recommended that fiberglass rotor blades should be

blade technology was applied to the design and developed byusingautomatic, fiberglass filament-wound

fabrication of the Mod-0 aluminum blades. This fabrication techniques. Fiberglass composites have the

approach allowed delivery to NASA of three completed properties needed for wind turbine blades: high strengthblades within 8 months from the start of design. This very to-weight ratio, good fatigue strength, and resistance to

short blade development time and delivery schedule was a the environment. Automated fabrication techniques used

major factor that allowed first rotation of the Mod-0 with composites had the potential for much lower

machine in September 1975 at the NASA Plum Brook manufacturing costs than those for the aluminum blades.

Station. Measured operating loads on the blades The chronology of fiberglass blades is also shown in

exceeded the design loads during initial Mod-0 tests. As a figure 46. Two types of fiberglass filament-wound

result overall modifications were made to the machine to processes were developed for blade fabrication; a

reduce the blade operating loads to acceptable levels, continuous filament process and a process that uses

Lockheed, the builders of the original blades, proposed transverse filament tape (TFT). Faster application and

structural modifications to the Mod-0 blades. These ability to taper thickness are advantages of the TFT

modifications were applied to the design of the aluminum process over continuous filament winding. Also, there is

blades for the Mod-0A machine. The chronology of the considerable experience with the TFT process in the

aluminum blade development is shown in figure 46. extensive fabrication of fiberglass tanks and pipes used in

Although the Mod-0A blades were identical in size to the chemical industry.

the Mod-0 blades, they were capable of generating twice An 18.3-m (60-ft) long Mod-0 blade was designed and

as much power. Improvements learned from the constructed by using continuous-filament-wound fiber37
,_1 /Vbd-l,30.5-m0.00-ft)longTFT 1

,_ I fiberglass-epoxblade y development

J45.1-m (150-ft)longtransverseI/" ' Planneduseon

• filament-tape(TFI')fiberglass-I_. MOd-atI

epoxblade y development __ = Boone,N.C.

j " _ MOd-OA18.3 , -m(60-ft)longTFT J

t J fiberglass-epoxbyladedevelopment MOd-0Aat

Clayton,N. Me)(.

(changedfromaluminum)

Nod-l, 30.5-m ___

(lO0-ft)long Mod-130.5-m(!O0-ft)long

J' filament-woundblade welded-steeblal dedevelopment

development . I MOd-Ioperationaatl

l JBoone,N.C. J

t J 1 ,_ _ Welded-steel-a nd-wood-tirot p or

?

o, systemostudies°nmI, ,o -'-I//wel vloded-2, d4

-5ste.7elbmla(150-f de- tiptlon ) g t ' 'eve'°me '

L_ Icontrodl evelopment

Mod-O,1B.3-m(60-ft) _, _"_ Mod-2operational at

long filament-wound 0 "0 0 GoodnooHills. Wash.

blade (three-cluster installation)

i Spot-weldedl,aminated, stain- I Prestressed- lesssteelsparbladedevelopment

Jconcreteblade

I study Fatiguetesting

_t All-woorod tordevelopment->61-m

(200--flon t) gblade(Mod-bA)

JUrethane-feamI Mod-O18.3 A, -m160ft)l

longwoodcompositel

bladestudy Jbladdeevelopment

Mod-o,lS.3-m J Mod-_, 1B.3-m atHawaii v "_O_

(60-ft) longalu- _ (60-ft)longaluminumbladede- / minumbladede- MOd-OatABlocIksland _,,_. Mod-Oat ACulebra

veopment / velopment (changedfromaluminum) _-_ (changedfrom

Mod-0 --_ aluminum) at Mod-OatABlockIsland,R.I.

Plum Brook Mod-0Aat Mod-OAat (modifiedaluminumblades)

(firstrotation) Clayton, CulebraP, .R.

N. Mex.

I I I I I I I I I I I

1914 1975 1976 1977 1978 1979 1980 1981 198Z 1_3 1_4

Year

Figure 46. - Chronology of rotor blade development--large horizontal-axis wind turbine projects.

glass and epoxy. Hamilton Standard Division conducted rotating steel mandrel incurred a structural failure. When

the design and Allegany Ballistics Laboratory the mandrel failed, it also caused fracturing of the

successfully fabricated one blade, shown in figure 47. In fiberglass-epoxy demonstration spar. Additional funding

static testing the 18.3-m (60-ft) long filament-wound and time were needed to correct this problem. Rather

fiberglass-epoxy composite blade satisfied all design than expend further resources to develop fiberglassrequirements (ref. 25). This led to the development of a epoxy blades for the Mod-I at that time, it was decided to

30.5-m (100-ft) long filament-wound fiberglass-epoxy develop 30.5-m (100-ft) long, all-steel blades (fig. 48).

composite blade for the Mod-1 wind turbine. The The Boeing Engineering and Construction Company was

development plan for the fiberglass-epoxy blades for competitively selected to develop the Mod-1 steel blades

Mod-1 called for winding a 30.5-m (100-ft) tapered and deliver them to the Boone, North Carolina, site. This

cylindrical tube, or "demonstration spar," before the effort was successfully accomplished within the Mod-1

start of actual blade fabrication. The tapered fiberglass- project schedule, and the machine started experimental

epoxy composite cylindrical tube was wound on a operation in July 1979.

rotating steel tube, or mandrel, to demonstrate the The potential blade fabrication economies of using

fabrication procedure planned for the actual blade. The fiberglass-resin composite materials led to finding an

steel mandrel was used to support the spar and provide its existing fabrication technique that used composite

tubular shape during the wet-filament-epoxy winding fiberglass filaments bonded to tape approximately 25 cm

process. During winding of the demonstration spar the (10 in.) wide. This material was used and is currently

38
Figure 47.-Mod-0, 18.3-m (60-ft) filament-wound fiberglass-epoxy blade.

being used to fabricate cylindrical fiberglass pipe for the wound fiberglass-epoxy composite blades for the Mod-0

chemical and agricultural industries. As a result, an and Mod-1 wind turbines.

experimental 45.7-m (150-ft) long fiberglass blade was Welded steel is used to construct the entire Mod-2 rotor

designed and fabricated by applying the transverse- blade. The 91.5-m (300-ft) diameter rotor consists of a

filament-tape (TFT) winding process. The 45.7-m (150-ft) 18.3-m (60-ft) long center hub section, two 22.9-m (75-ft)

long blade shown in figure 49 was developed for potential midsections bolted to each side of the center section, and

use on the Mod-2 wind turbine. Kaman Aerospace two 13.7-m (45-ft) movable tip sections bolted to the ends

Corporation, with expertise in helicopter rotor blades, of each midsection. When the first Mod-2 began

designed and assembled the blade (ref. 26). Structural operation in October 1980, the rotor was the largest ever

Composites Industries (SCI), under contract to Kaman built for a wind turbine (fig. 52).

Aerospace Corporation, wound the main blade spar by Even larger rotors having diameters of 122 m (400 ft)

using transverse-filament fiberglass tape and the TFT or more are being designed for the advanced wind

winding process. The blade underwent structural tests turbines, which will produce 7 to 8 MW of rated power.

that proved the adequacy of the design and the Both welded-steel and all-wood rotors are being

fabrication process (ref. 26). After the experimental considered for these machines.

45.7-m (150-ft) long blade project was completed, Kaman Development of laminated-wood-epoxy composite

designed and fabricated two experimental 30.5-m (100-ft) blades was started in 1978. By mid-1980, wood blades

long blades of TFT for the Mod-1 machine (fig. 50) were producing power on the Hawaii Mod-0A machine.

(ref. 27). As a result of their efforts on the 45.7-m (150-ft) In July 1980, the Block Island Mod-0A machine was

experimental blade, SCI was competitively selected to changed from aluminum to wood blades. Later the

design and fabricate a set of 18.3-m (60-ft) long TFT Culebra Mod-0A machine also was changed from

composite blades (fig. 51) for the Mod-0A machine at aluminum to laminated-wood composite blades.

Clayton, New Mexico. The SCI blades (ref. 28) were The wood blades are fabricated by molding the blade

installed on the Clayton Mod-0A machine in August 1981 in two halves. Douglas fir veneers 0.16-cm (l/6-in.) thick

and successfully operated for over 3000 hours before the are contoured and laminated with epoxy resin into the

machine was shut down in June 1982. mold. The forward section of the blade is designed to be

The Hamilton-Standard Division of United Technol- the load-carrying D-spar (fig. 53(a)) when the two halfogies fabricated and installed the fiberglass blades used shells are epoxy bonded together. Aft sections of the

on the WTS-4 system verification unit now in operation blade are built of plywood internally stiffened with

near Medicine Bow, Wyoming. The blades that make up epoxy-impregnated paper honeycomb (ref. 29). From the

the 78-m (256-ft) diameter WTS-4 rotor are a result of standpoint of low cost and good operational experience,

their earlier work to develop the technology for filament- wood blades constructed in this manner are appealing to

39
(a) Section of steel D-spar during blade fabrication.

(b) Mod-1 steel blade during final assembly.

(c) Mod-1 steel blade during machine assembly at Boone, North Carolina.

Figure 48.- Mod-1, 30.5-m (100-ft) long blade.

40
Figure 49.- Experimental fiberglass blade, 45.7 m (150 ft) long.

designers for wind turbine blades much larger then the low material costs and potential for automated fabri18.3-m (60-ft) Mod-0A blades, cation processes. But the poor strength properties of the

Of particular concern in blade design is the ability of foam materials that were considered would have required

the root end of the blade, the section near the hub, to considerable reinforcing of the urethane with steel rods

transfer fatigue loads from the main spar section into the and plates. Further development of this concept is

hub section. This area is where blade bending moments necessary before a practical full-scale prototype blade can

are the greatest. In wood blades a transition must be be fabricated for experimental testing.

made at this section from wood to steel. Steel studs are Prestressed concrete has many of the attractive

embedded in the laminated wood (fig. 53) and are used to features of urethane. Concrete is inexpensive and easily

attach the blade to the steel hub. In the development molded and can be prestressed. This led to a feasibility

program for wood blades, extensive fatigue testing was study by the Tuthill Pump Company (ref. 31). As a result

conducted on the root end portion of the blade. Several of the study the concrete blade weight was estimated to be

designs of stud attachments to the wood were required about twice that of an aluminum blade for a Mod-0A

before satisfactory fatigue test results were achieved, machine. Blades as heavy as these would impose design

After over 7800 hours of operation of the wood blades changes on other turbine components such as the rotor

on the Mod-0A machine in Hawaii, a broken stud was bearings and tower structure. Although the potential for

discovered at the base of the tower. A review team later low cost is attractive, this concept is not considered to be

determined that corrosion of the stud was the probable competitive with other designs because of the comparcause of the stud breaking. It was one of the 24 studs that atively high blade weight.

were used to attach the wood blade to the metal adapter, Another cost-competitive steel spar design was

which in turn was bolted to the hub. Alternative stud developed by the Budd Company and a blade section was

materials that will reduce deterioration by corrosion are built for fatigue testing, (fig. 54(a)). Instead of a

being investigated for possible use. contoured (D-shaped) load-carrying spar, the design uses

While blades of aluminum, fiberglass, steel, and wood a box-beam spar built with flat sections of spot-welded

were being built and tested on operating wind turbines, laminated sheets of stainless steel. The airfoil contour is

other concepts were being studied and some blade formed by bonding plastic foam to the box beam and

specimens were built for fatigue testing. During the covering it with an outer skin of polyester resin and

period 1976-77, the feasibility of a blade made entirely fiberglass (fig. 54(b)). Fatigue testing of the spar, shown

of urethane foam materials was studied by Concept in figure 54(a), was begun in 1982. Early in the test, a

Development Institute (ref. 30). Attractive features are crack developed in the experimental spar. The test results

41
(a) Transverse-filament-tape winding of blade spar.

(b) Two 30.5-m (100-ft) long blades.

(c) Blade root end that mates with hub of wind turbine.

Figure 50.- Mod-1 fiberglass-epoxy blade during fabrication at Kaman Aerospace Corp.

42
--_" p--157.cm5 18.3m(60ft)

55.9cm

139.1cm,,t_-I_ --_ _1 (22in•)

(55in•) _-U.ll-.I--U -- - "------_-----[

FComposite

// overwr p

Composite /

overwrap___. /

/

Z.Netal hub adapter

(boltedflanges)

ViewA-A- typicalcrosssection

Figure 51.-Schematic of Structural CompositesIndustries 18.3-m(60-ft)longMod-0Afiberglass-epoxycompositeblade.

were reviewed and testing was terminated since adequate Efficient wind turbines start turning at the lowest wind

data were obtained on this concept, speed at which generating power can be useful. This is

called the cut-in wind speed. Also, wind machines are

Rotor Blade Control Surfaces stopped from rotating (cutout wind speed) when the wind

velocity gets so high that some components would beVariable pitch of rotor blades on large horizontal-axis come overloaded. Rotors can be started aerodynamwind turbines is used to control the rotational speed ically by using blade pitch control. Blades are pitched

(rpm) and the electricity generated and for starting and into the wind at the proper angle to produce enough

stopping blade rotation. Pitch angle variation of a rotor torque for turning, and then the blade pitch angle is

blade is the partial turning, usually up to about 90 °, of decreased as rotor speed is increased. With fixed-pitch

the blade about the spanwise axis. Thus the full span of blades other means are used for starting, such as yawing

the blade can turn more or less into the wind depending the rotor away from the wind or driving initial rotation

on the speed of the wind and the rotational speed of the with mechanical starters. Rotor blades can also be

rotor. However, because of the size and weight of large stopped by increasing the pitch angle until the rotor

turbine blades, full-span pitch controls are more complex blades are "feathered" (leading edge of airfoil facing

and more expensive to build and maintain than other directly into the wind with the upper front and lower

methods of controlling the rotor, airfoil back surfaces parallel to the wind flow). Without

A fixed-pitch rotor is a rotor having blades that are this protection runaway rotor speeds can result from high

designed not to turn about the spanwise axis. Fixed-pitch wind gusts, or by loss of load when the turbine is

rotors offer advantages over variable pitch. Pitch change electrically disconnected from the utility network.

mechanisms are eliminated. Also, by proper orientation Variable blade pitch control is also used to maintain

of the fixed-pitch rotor, cyclic stresses in the blades are constant rotor speed with varying wind speed. This is

reduced. Additional stress reductions can be obtained by necessary to generate constant-frequency power for an

combining a fixed-pitch rotor with a teetering hub. Fixed- electric utility if a fixed-speed direct drive is used from

pitch blades allow continuous construction through the the rotor to the generator• More complicated variablehub, which reduces the problem of attaching each blade speed, constant-frequency generating systems can be used

separately to the hub. This becomes a structural benefit that would allow the rotor speed to vary with the wind

in very large rotors such as the 91.5-m (300-ft) diameter speed• Most large wind turbines are designed to provide a

rotor for Mod-2. However, there are two inherent prob- rated output of electricity at a particular (or rated) wind

lems with fixed pitch: no startup or shutdown capability, speed. When wind speed exceeds the design (or rated)

and no control of rotational speed, particularly wind speed, the blades must dump power by aerodynamic

overspeed protection. Yawing of the rotor can be used means such as increasing the pitch angle and thereby

for startup, but yaw control is not fast enough to prevent partially stalling the blades. Increased power output is

overspeeding, thus sacrificed. In fact, the Mod-0 wind turbine rated at

43
(a) During preparation for assembly with low-speed shaft.

(b) During assembly.

(c) Blade being mated with hub.

Figure 52.- Mod-2, 91.5-m (300-ft) long, welded-steel rotor d_ring assembly at Goodnoe Hills, Washington.

44
Bladecrosssection

57.2 cm 152.4cm 70.0 cm

(22.5 in. ) (60in. ) (24in. )

/ 1.._._4.0m_,,.] " "- Blade _

Steelstuds-/ /(13 ft)/ platform /

18.3 m(60ft)

Epoxy

i ..... .

3.2-mm(118-in.) /" lfir veneers /Steel stud Wood-/

'-Bolt pattern v Fir blocking Blade-to-hubattachmentmethod

(a)

(b) ...........

(a) Construction details.

(b) Showing steel stud bolts at root end.

Figure 53.- Wood composite blade for Mod-0A.

100 kW at 8 m/s (18 mph) could generate almost 5000 Alternative methods of rotor control are (1) variable

kW at a wind speed of 26.8 m/s (60 mph) if an increase in blade pitch only on the outer portion of the blade or (2)

rotor speed with the high wind speed could be allowed, the use of retractable spoilers or hinged surfaces

This is not as large a loss in long-term available wind (ailerons) on the outer portion of the aft section of a

energy as it may seem, since on an annual basis high blade. Most of the torque from a turbine rotor is prowinds are relatively infrequent and do not extend over duced on the outer portion of the blades, and therefore

long periods of time. rotor control devices can be very effective when located

45
,Rigid polyurethane foam

I (approx O. 91-kg (2-lbl density) I

I

I

..... Polyester fiberglass (approx

1\ 17 percent glass content)

1\

1\

I \

I \

I \

, \

, \

" ......Intermittent

Section at Station 412. 5 urethane

bond

301-114 Hstainless

steel spar--,

,

,

. /

Elastomenc /

leading-edge/

protection J

Root-end fitting:

4130 mach ined,

heat-treated

forging

Station 0 70 187.5 300 412. 5 525 637.5 750

I~+ I I 1 I I I

31.

I~:~-'T'~-~'~ 75 • I. steel spa r 118.0 in. )

Plan view of blade

(b)

(a) Stainless steel root-end spar-test specimen.

(b) Schematic of blade showing stainless steel spar and root-end fitting.

Figure 54. - Proposed steel spar blade design for Mod-OA developed by Budd Co.

near the outer diameter. This method of rotor control,

called partial-span pitch control, is used on the Mod-2

machine, where the outer 30 percent of the blade can

turn. Partial-span control systems allow continuous

construction through the hub and fixed pitch for the

inner portion of the blades. When compared with fullspan blade pitch control, substantial weight and cost

46

savings are realized by moving the pitch control away

from the hub and pitching only the outboard portion of

the blade.

Overspeed can be controlled by using movable spoilers

on the outer portion of the rotor blade. Spoilers located

near the tips of rotor blades, when extended from the

rotor blade surface, will also reduce lift and increase
drag. As a result the spoilers aerodynamically reduce changed as the rotor accelerates to rated speed. At rated

rotor torque. A disadvantage in using spoilersis that they rotor speed under speed control the wind turbine

are not effective in starting a rotor. Spoilers get their generator is synchronized to the utility network and the

name from their use on airplane wings where, when microprocessor changes to a power control mode. The

extended from the wing surface, they spoil the airflow wind turbine is held at its rated power by adjusting the

and thus reduce lift or torque and increase drag, slowing blade pitch to variations in wind speed. If the wind is less

the airplane, than rated speed, the blade pitch angle is held to produce

A possible alternative to the use of spoilers is a hinged maximum power output for the lower wind speeds. If the

trailing-edge surface, or aileron, on the outer portion of wind exceeds the cutout velocity, the microprocessor

each blade. Ailerons can act like spoilers to prevent commands an increase in blade pitch to prevent excessive

overspeed but have the advantage of providing starting overspeed. If the wind falls below the cut-in velocity, the

torque and increased power at low wind speeds. If moved microprocessor will command an increase in blade pitch

in one direction (upward), they produce drag and provide to the feathered position and the rotor will stop. In

speed control; if moved in the opposite direction addition, the microprocessor must recognize any

(downward), they produce lift or a power output gain. abnormalities in the system and take appropriate action

Full-scale tests of a rotor with aileron control surfaces are to protect the system. Recording of engineering data

currently being conducted on the Mod°0 wind turbine during operation is also controlled by the

research machine to support the development of the microprocessor.

advanced-technology wind turbine. The flexibility of the microprocessor in developing the

operational strategy for controlling the Mod-0 wind

System Controls turbine was perhaps the most significant advantage of

using a microprocessor. In the early experimental phase

Controls are required on a wind turbine mainly for of the Mod-0 project the wind turbine was operated in

startup of the rotor, synchronization of the generator many different modes: manual control, without a

with the utility network, power regulation, and shutdown microprocessor; as a speed-controlled machine feeding a

of the rotor. Controls are also needed to turn (or yaw) the load bank; and finally as a synchronous machine

rotor into the wind and for protection of the wind turbine connected to both large and small power networks. By

in case of abnormal operating conditions and in emer- simply modifying the software it was possible to

gency situations. Since the controls must be able to accommodate all of these operating modes. All of the

operate at a remote, unattended site, automation is information that the microprocessor might need in order

necessary. NASA machines have been operating very to control a wind turbine was wired to the microsuccessfully in an unattended mode under the control of a processor. Every output that an operator might have to

microprocessor. The microprocessor must be self- manipulate was also connected to the microprocessor.

monitoring for fault detection, operate under extreme The wind turbine was controlled in any way desired by

environmental conditions, and have independent battery simply reprogramming. If hard-wired analog circuitry

electrical operating power, had been used, every operating mode would have

Sensors, actuators, and the microprocessor make up required different equipment and every control strategy

the main control system. Sensors are used to measure change would have required circuit modifications, system

many variables including wind speed and direction, rotor rewiring, and retesting.

speed, pitch angle of the rotor blades, torque of the The following example shows how the flexibility of the

rotor, electrical power, and many other parameters microprocessor helped solve problems that developed in

necessary to assure the safe operation of a wind turbine, the field: The original concept was to start the wind

Redundant sensors are used in many cases to improve turbine at a wind speed of 4.0 m/s (13 mph) and stop it at

safe and reliable operation. Hydraulic actuators are 2.4 m/s (8 mph). It was found by experience that at times

commonly used to change the blade pitch. Electric motor the wind speed tended to oscillate continually over this

gear drives were used to change the yaw angle of the rotor range and thus cause excessive start-stop cycles of the

on the Mod-0A machine, wind turbine. To solve the problem, various filters were

The microprocessor typically controls the machine as applied to the wind speed signal. It was not possible to

follows: A very low wind speed picks up to the startup find filters with time constants long enough to prevent

wind speed, and the wind sensor monitors this for several excessive start-stop cycles and short enough to be

minutes. If this startup wind speed holds, the micro- sufficiently responsive for control. The solution was to

processor commands the yaw drive to position the rotor program the microprocessor to test if the high or low

into the wind. At the same time the blade pitch change winds had persisted for 10 seconds before deciding to

mechanism is commanded to change the blade angle from shut down. A relatively lightly filtered signal was used for

the feathered position to a power-producing pitch angle, control. Easily implemented and proved successful, this

This starts the rotor turning. Blade angle is further approach resulted in improved performance.

47
The Mod-0 wind turbine was designed with a micro- early experimental operation of Mod-l, communication

processor that controlled only a portion of the machine malfunctions were experienced about 8 days per month.

operating functions (ref. 32). For example, the Mod-0 As causes were determined and solutions implemented,

used a separate yaw control system, independent of the malfunctions were progressively eliminated.

microprocessor, to keep the nacelle pointing into the It was also learned during early testing that qualified

wind. The yaw controller was basically an analog voltage and readily available personnel were needed to perform

comparator. The comparator detected the difference computer system preventive and corrective maintenance.

between the actual nacelle direction and the actual wind For example, Mod-1 site operation records indicate that

direction and would then drive the nacelle yaw motors so from March through December of 1980, expert computer

as to make this difference zero. There was a deadband of technicians were required 13 times. In addition to

4-25° in yaw, and the wind direction signal was filtered preventive maintenance every 3 months, computer

so that the system would not react to wind gusts. The yaw services were needed for repair of the line printer,

motors were capable of driving the nacelle through 360° replacement of electronic boards, replacement of the disk

in 6 minutes. The circuitry was designed so that the drive, repair of the tape unit, and repair of the remote

nacelle would always take the shortest path when aligning terminal.

itself with the wind. Operation with a minicomputer-based control system,

In addition, an automatic synchronizer, independent on the other hand, proved to be highly flexible in making

of the microprocessor, was provided to connect the wind system changes quickly and inexpensively. As an

turbine to the power line smoothly. The microprocessor example, after it was concluded that the system rotor

decided when to energize the synchronizer. The synchro- speed had to be slowed to reduce the Mod-I sound

nizer compared the power-line phase angle with the generation to acceptable levels, the central processor

alternator phase angle and closed the connecting circuit logic within the control-and-recording unit was easily

breakers when the phase angles were matched and steady, modified to operate the wind turbine at 23 rpm with a

As soon as the synchronization was complete, a signal 1200-rpm generator.

was returned to the microprocessor. The microprocessor As a result of the experience gained from the firstwould then direct the pitch controller to switch from the generation (Mod-0, Mod-0A, and Mod-1) machines, the

speed control mode to the power control mode. second-generation (Mod-2) machine is using the simpler,

The Mod-1 machine was designed around minicom- more reliable, and more durable microprocessor. The

puters rather than microprocessors. Minicomputers were third-generation (Mod-5) advanced-technology machines

selected because of their extensive software development will also use the microprocessor in their control systems.

support systems. These software development systems

were considered desirable for programming and testing Tower

the wind turbine in the remote location at Boone, North

Carolina. Large-diameter rotors call for rather high and someThe control system for the Mod-1 wind turbine what specialized support structures or towers. Height is

included a Digital Equipment Corporation PDP 11/34 desired to take advantage of the higher wind speeds at the

computer that was located in the ground control higher elevations and to reduce the effect of wind

enclosure at the base of the tower. The PDP 11/34 variations that extend up from the ground (called wind

interfaced with two PDP 11/04 microcomputers. One shear). Tall towers must support the heavy rotor and

PDP 11/04 was located in the ground control enclosure generating subsystems as well as absorb vibratory loads

and the other in the nacelle. The control system would created by the wind and the rotating blades (ref. 33). The

automatically start, operate, and stop the machine, align towers must be resistant to hurricane force winds, gusts,

it with the wind, and provide remote dispatcher control and seismic shocks. Good designs avoid major dynamic

through a telephone link. In addition, if the control interactions between the rotor and the tower. Structural

system detected any operation or machine anomaly, it stiffness of the tower should be such that its natural

was programmed to safely shut the wind turbine down. frequency clearly avoids the primary loading frequencies

Figure 55 presents a simplified control schematic, caused by the rotor while operating at rated speed.

During experimental testing of the Mod-1 machine, The Mod-2 tubular tower was designed so that during

some problems occurred with the control system. For operation it fundamentally oscillates in bending at 1.3

example, the most significant problem was computer-to- cycles for each revolution of the rotor, or 1.3 P. It was

computer communications. This problem occurred also designed so that it twists angularly back and forth

between the Digitial Equipment Corporation PDP 11/34 about a vertical line through the center of the tower at

and its recording unit and the two PDP 11/04's. The about 4.0 cycles for each revolution of the rotor. In other

occasional loss of communication between computers words the natural frequency of the Mod-2 tower in

resulted in unscheduled wind turbine shutdowns. During torsion is 4.0 per rotor revolution or, 4P. In contrast, the

48
r

i I

breaker

Toutility , Eledricity

Figure 55. - Simplified schematic of Mod-1 control system.

Mod-1 tower was designed to have a fundamental avoid resonance, during operation at the rated rotor

bending frequency of 2.8 P and a fundamental torsion speed.

frequency of 6.5 P. Since the frequencies of the Mod-1 The Mod-2 tower is often referred to as a "soft" tower

tower are higher, the Mod-1 tower is stiffer than the because its bending frequency is below the frequency of

Mod-2 tower for bending and torsion. The fundamental loading. The Mod-1 tower is classified as a "stiff" tower

cyclic forcing loads resisted by the tower are mainly because its bending frequency is higher than the load

caused by rotor-wind interaction. The loads resisted by frequency. The first-generation machines (Mod-0A and

the tower predominantly occur two times for each rotor Mod-1) used the stiff steel truss tower. The second- and

revolution, or the loads occur at a 2P frequency. The third-generation machines use the "soft" tubular shell

frequency of the Mod-I tower, at 2.8 P, was purposely tower. The soft tubular tower is lighter and more

selected to be above the 2P forcing frequency to avoid economical to construct than the stiff truss tower. The

resonance. The frequency of the Mod-2 tower was tubular tower is more pleasing in appearance. The

selected as 1.3 P, below the 2P forcing frequency again to tubular tower also provides an all-weather interior access

49
way from the ground to the rotating equipment in the Many small wind turbines use an aerodynamic surface,

nacelle, like an airplane tail, that aligns the rotor into the wind.

Early Mod-0 experiments have shown that a large twoblade rotor will align itself on the downwind side of the

Drivetrain tower, or about the yaw axis. Further efforts to learn if a

Torque is transmitted from the rotor to the generator large machine can operate with no active yaw control are

through several mechanical components that make up the being made and are discussed later. If the active yaw

drivetrain. A speed increaser is necessary to convert the system that is used on machines like the Mod-0A could be

relatively low shaft speed of the rotor (<50 rpm) to the eliminated, a substantial cost saving and increase in

high speed (usually 1800rpm) required by the generator, reliability could be realized.

Rotor speed is stepped up by a gearbox placed between

the rotor and the generator. Other drivetrain components Generator

include shafting, flexible couplings, bearings, clutches,

and a parking brake. Components in the system should A wind turbine generator driven by the rotor must have

be assembled in a manner such that separate units can be constant-frequency ac power output to synchronize with

repaired or changed without disturbing the remainder of the electric utility grid. Most common ac synchronous

the system, generators provide constant-frequency power if driven at

Of concern to designers are the torque fluctuations constant rotational speed. But wind turbine rotors that

imposed on the drivetrain by power changes caused by are controlled to operate at constant speed are not always

variable winds and by the tower shadow (refs. 34 and 35). operating at maximum efficiency over the operating

For Mod-2 an alloy steel quill shaft between the rotor hub range of wind speeds. Therefore one would like to allow

and the gearbox was designed with a torsional stiffness to the rotor to vary in speed so that the rotor can operate at

damp these fluctuations. Fluid couplings were success- maximum efficiency over the wind speed range. A

fully used to reduce oscillations in the Mod-0A variable-speed drive to a synchronous generator would

drivetrain, require additional electrical devices or a different

Several different types of gearboxes have been used in generator concept to maintain constant frequency and to

the various wind turbines. Mod-0A used helical gears and synchronize the wind turbine power output with the

was rated at 450 hp at 1800rpm. Mod-1 uses a three-stage electric utility grid. Early studies showed that available

gearbox as the speed increaser. Mod-2 uses epicyclic electrical devices to synchronize the generator would

planetary gears that provide a smaller, lighter, less impose efficiency, weight, and costpenaltiesascompared

expensive, and more efficient speed increaser than the with using a constant-speed generator. It was found that

parallel-shaft gearboxes used on the earlier machines. In the slightly higher efficiency of the rotor operating at

the next-generation machine (Mod-5) additional variable speed would not make up for the poor efficiency

improvement in the drivetrain components will be made and high cost of equipment to provide variable-speed

possible by using a variable-speed generator. This design operation of the generator. Thus the DOE-NASA large

presently appears to have the highest potential to reduce wind turbines connected to utility grids now use a

torque oscillations. A variable-speed generator thus may constant-speed rotor to drive the generator.

permit omission of the soft quill shaft, a reduction in the As part of the NASA research and technology develsize of drivetrain components, and the elimination of opment effort to improve wind turbines, investigations

fluid couplings in the drivetrain, are under way to develop variable-speed generator

technology. Techniques can be applied to a special type

of generator that will hold a constant-frequency power

Yaw System output and maintain synchronization while speed inputs

Constantly shifting winds make it necessary to have a are varying.

system to keep the rotor always facing into the wind

during operation. A wind vane on the nacelle detects the

difference between the wind direction and the yaw Research and Technology Development

orientation of the rotor, or the yaw angle. If the yaw

angle is not within allowable limits, the rotor is turned to The current effort at NASA to support the Federal

the proper alignment with the wind. Yaw drives are slow Wind Energy Program focuses on research and

(1/3 to 1/6 rpm) to avoid high gyroscopic loading on the technology development. Less emphasis is being placed

revolving two-blade rotor. Brakes are used on the Mod- on system development, experimental field operation,

0A and Mod-1 yaw drive to restrain, or damp, yaw and market and economic studies. Experimental

motions while the nacelle is being turned and to rigidly machines such as the Mod-0 and the large Mod-2's will be

hold the structure when in position. The heavy structure used to conduct high-risk wind turbine research in areas

is turned by hydraulic or electric drive motors, having potential benefits to U.S. wind turbine manu50
facturers. Both experimental and analytical research is

directed toward the goal of making wind energy a costcompetitiveand technicallyviable energyalternative.

Objectivesof the research and development program

willbe to gather and report new data on various aspects

of wind turbine behavior and to be able to more

accurately predict wind turbine operation and performance. Many areas of research including aerodynamics,

structural dynamics, composite materials, and multiplemachine effects are currently being studied.

The aerodynamicsof the rotor willbe further studied,

including the rotor blade control surfaces and aerodynamicforceson the rotor. Experimentalstudies willbe

conducted on wind turbine structural dynamics, or

vibrations. Also the reaction of structurally flexible

components, such as the rotor blades, to unsteady

aerodynamic loads will be investigated. Additional

research will be carried out on composite and hybrid

composite materials to determine their physicalqualities

and durability. Also under investigationare the multiplemachine interactions brought about by wind turbines

operating together or in clusters, including the behavior

of these multiple units when interconnectedto a utility

grid.

Mod-0 Research Facility

The Mod-0 has undergone a series of extensive modifications since it first began experimental operation in Figure56.-Mod-0 experimental wind turbine with aileron-controlled

September 1975. For example, the current configuration rotor.

has a cylindrical tower, rather than the truss tower. The

rotor configuration has changed to allow evaluation of

new concepts. The Mod-0 first used rotor blades rigidly be controlled separately or collectively. Radio commuattached to the hub, with full-blade-span pitch control, nication is provided, at this console, with personnel near

Now Mod-0 is being used to evaluate the performance of the wind turbine during experimental operation. Radio

a teetered rotor with aileron control surfaces (fig. 56). communication is also used during routine wind turbine

The Mod-0 facility is a key tool that has been maintenance activities or during modifications. As wind

successfully used time after time to demonstrate the turbine experimental data are being recorded on

performance of advanced wind turbine configurations. 14-channel frequency-modulated tape, a voice channel is

Results of experimental Mod-0 research are used to guide also available. The voice channel is used to record

the efficient allocation of resources. For example, before specific comments about the test while the test is in

the decision is made to use an aileron-controlled rotor on progress.

the Mod-5, the performance of such a control concept As shown in figure 58, a land-line voice communiwill be evaluated on the Mod-0. cation link between the Mod-0 and the control room is

A major feature of the Mod-0 research wind turbine is available. Digital displays can be viewed from the main

its highly sophisticated and flexible wind turbine control control console that provide real-time values for wind

and research data systems. The building housing this speed, ambient temperature, Mod-0 rotor speed, and

equipment is located approximately 152.5 m (500 ft) west generator performance parameters including kilowatt

of the wind turbine, output, kilovars, and alternating-current frequency. The

The wind turbine is controlled at the main control analog computer shown in figure 58 is used to program

console shown in figure 57. Startup, experimental opera- special Mod-0 experiments. For example, a particular

tion, and shutdown can be controlled at this console Mod-0 experiment may require the rotor to increase in

either manually or in an automatic mode. For example, speed from l0 rpm to 20 rpm during a 1-minute period of

rotor speed or power is controlled at the main console, time and then continue to operate at 20 rpm after that

During experimental operation with tip-controlled rotors time period. The analog computer can be programmed

or with aileron-controlled rotors, each tip or aileron can and then used to control the Mod-0 rotor speed to meet

51
hydraulicpump,and

Figure 57. -Main control console for Mod-0 wind turbine.

this experimental requirement. The television monitors

are used to provide a view of the Mod-0 to those inside

Instrumentamplifiers Televisionmonitors_ the control room. Television cameras are located to

iattopandEAITR2-20 provide an external view of the Mod-0 and a view inside

analogcomputerwith the Mod-0 nacelle.

Figure 59 shows the three strip-chart recorders, each

with eight channels of data-recording capability. These

recorders can provide a real-time data display while the

wind turbine is operating. The recorders are also used to

III _ display analog data processed from FM data storage

W t _ tapes. A two-channel strip-chart recorder provides 24 111 I _ hours of continuous data on wind speed and direction.

Digitaldisplays.3 These data are obtained from instruments mounted at the

_l 27.4-m (90-ft) level of a nearby meteorological tower. A

mmunicatl0nul desktop computer is shown in figure 59. The computer is (land line to Mod-O)

•,, w programmedto assessthe accuracyof data during Mod-O _Mod-O microprocessor

m checkout before an experimental run or during Mod-0

safetysystem

package operation. The computer can provide real-time data in

both graphic and tabular form. The accuracy of data as

obtained from a wind-speed-measuring instrument is one

example of data that can be checked before or during a

Instrumentamplifiers Mod-0 experimental run. Real-time data such as rotor

controlConsole power, as measured from the Mod-0 generator, and wind

speed data, as measured from the desired instrument, are

: fed into the computer. The computer averages these data

over a 30-second period. At the end of each 30 seconds the computer plots a point on its graphic display screen of

wind speed versus power. By comparing these real-time

data with data from other wind-speed-measuring

instruments used at the Mod-0 test facility, the accuracy

Figure 58.-Control equipment for Mod-0 wind turbine, of the real-time wind speed measurement can be quickly

52
desktopcomputer

C-83-4997i

Figure 59.- Data-recordingand computer equipmentfor Mod-0 wind turbine.

assessed. Data from strain-gage instrumentation can be the data-processing system can calculate 1-minute

checked for accuracy by using a similar technique, averages of wind speed and store each average on tape. In

The data-processing system shown in figure 60 is used addition, the maximum and minimum wind speeds for

to perform statistical analyses of various parameters that each l-minute period are retained, and these values are

are measured during the experimental operation of the stored on the magnetic tape. As a result, with these three

Mod-O wind turbine. For example, rather than processing bits of information (the average, maximum, and

and storing analog wind speed data as a function of time, minimum wind speeds), a statistical model of the wind

Patchpanel-I ,_
speed over a l-minute period is retained. This statistical rotor. Recently, research to reducedrag of airplane wings

model takes up much less storage space on the magnetic has discovered that small surfaces attached to the wing

tape than the 1 minute of analog wind speed data. tip, called a winglet, reduce the drag of the wing. Similar

The data-processing system shown in figure 60 consists devices on wind turbine rotor blades may result in

of a variety of equipment. A computer keyboard control improved rotor performance. Several blade tip configand printer are shown at the far left of the figure. Units 1 urations will be tried to increase wind energy capture.

and 2 are each digital magnetic tape handlers. Unit 3 is Under some conditions rotors have been found to

the main frame computer, a DEC PDP-11. Unit 4 produce more power than predicted from analysis.

contains a digital clock at the top and a data compressor Research instrumentation will be mounted on rotor blade

below. The data compressor is the unit that reduces surfaces to determine airflow over the blade surfaces.

analog data to digital minimum and maximum values. The data gathered from this research will be used to

Unit 5 contains banks of electronic equipment called improve the methods for calculating blade performance.

discriminators. Engineering data are received in the Airflow patterns of the wind passing through the

control room from the Mod-0 wind turbine as a steady circular area swept by a rotor are being documented by

flow of FM signals. These electrical signals carry motion pictures showing colored smoke streams from

information from all of the measuring instruments on the smoke generators upwind of the rotor flowing through

wind turbine. The discriminators accept the FM signals the rotor and then reacting downwind of the rotor. Air

and identify specific data that are being received from a swirls or vortices developed by the tip of the rotor are

measuring instrument. The discriminator than sends this being studied by observing the smoke stream as it passes

sorted information to the PDP-11 computer for data by the tip of the rotor blade, as shown in figure 61.

processing. This sorted information can also be sent to Additional studies are made by placing smoke generators

strip-chart recorders or other data-processing equipment, on the blade tip and observing the airflow patterns as the

Unit 6 contains a Sangamo-Weston Sabre III FM tape tip revolves, as shown in figure 62. These smoke trails are

recorder and signal conditioner. This unit is used to store seen to swirl and break up as the smoke moves downwind

FM data obtained from the Mod-0 wind turbine during a short distance from the plane of the rotor. Also,

experimental operation. The data-processing system is interference of the upwind position of the tower can be

thus able to store Mod-0 data on tape with the FM seen as the smoke trail from the tip passes the narrow

recorder. If desired, at a later time these FM data can be area directly behind the tower. Results of these studies

r.eprocessed statistically by using the unit 3 computer and will be used in one case to improve computer models

then storing this information on the tape-handling units 1 of airflow characteristics. The analytical models, for

and 2. example, do not accurately predict rotor performance

The data-processing system is used to analyze data at low wind speeds during below-rated wind turbine

from all of the DOE-NASA and DOI-NAS wind turbine operation (ref. 36).

sites. Data from experimental tests on the Mod-2 wind Up to this point, wind turbine rotor blades have been

turbines at Goodnoe Hills, Washington, are routinely designed and built from airfoil shapes intended for

stored on FM tape. The Mod-2 data channels on the FM airplane wings. These shapes are not necessarily the most

tape, however, carry different information than the optimum design for the range of operating conditions

Mod-0 FM data tape. To sort out these differ- experienced by the wind turbine rotor. Large wind

ences and identify the specific data channels, the patch turbine rotor airfoils should be thicker than the

panel shown at the far right of figure 60 is used. A special conventional thin wings on airplanes. Well-established

patch panel was configured to handle Mod-2 data. For methods for designing airfoils will be extended to include

example, wind speed data from the Mod-2 site might be airfoils having their maximum thickness up to 30 percent

stored on channel 5 of the FM tape. Wind speed data of their width. To validate these advanced designs,

from the Mod-0 site might he stored on FM tape channel models will be built and tested in a wind tunnel. Later, a

2. The data-processing system is designed for Mod-0 data set of thick blades will be built and tested on a full-scale

and, as a result, will look for wind speed data on channel rotor.

2. The purpose of the patch panel is then to switch the Detailed experiments will be conducted to determine

Mod-2 wind speed data from channel 5 to channel 2. This the effects on rotor characteristics of several airfoil

allows for the proper statistical processing of the Mod-2 control surface methods. On the first-generation

wind speed data. Other Mod-2 data channels are handled machines (Mod-0A and Mod-1) the rotor speed and

in a similar way. power were controlled by pitching the entire blade span.

On the second-generation (Mod-2) machines, only the

outer 25 to 30 percent of the rotor blade is pitched for

Aerodynamics control. More advanced rotor designs may achieve

Several approaches are being taken to improve and control by moving an aileron, or only the rear portion or

gain a better understanding of the aerodynamics of the trailing-edge surfaces of the blade, as shown in figure 63.

54
Figure 61. - Rotor blade tip vortex experiment with upstream smoke generator--Mod-0 wind turbine.

A similar method of control is used on airplanes

(ailerons, elevators, and flaps). Fixed-pitch rotors, with

no control surfaces, can be used if a generator having

variable-speed capability is available.

Objectives of this research on the various airfoil

control surface methods will be to investigate and obtain

a data base on the performance of rotors with full- and

partial-span pitch control, trailing-edge control surfaces,

and fixed-pitch blades. Results and conclusions from this

research will be reported as the various investigations are

completed. Measured performance will also be compared

with theoretical performance predictions in these reports.

Additional research will be conducted on rotors

subjected to both steady and unsteady aerodynamic

forces. One area to be investigated will be blade loads and

performance when the blades are extracting much higher

wind energy than those currently operating. Present

blades produce 50 to 400 watts per square meter of rotor

area. Rotors designed to produce up to 700 W/m2 will be

designed, fabricated, and tested under variable and

steady winds. At such high wind conversion efficiencies

the aerodynamics of the rotor blade become even more

important. Another area to be studied will be the effect

on wind turbine performance of unsteady aerodynamically induced loads when the rotor blade stalls. A blade is

in a stall condition when the desirable smooth airflow

over the blade surfaces becomes turbulent and separates

from the blade surface. When stall occurs, the

aerodynamic lift on the blade is greatly reduced and the

Figure 62.-Rotor blade tip vortex experiment with blade tip smoke drag is increased. Stalls can be caused when the blade

generator--Mod-0 wind turbine, airfoil angle of attack, or pitch angle, is too high for the

55
Figure 63.- Experimental-18.3-m (60-ft) long blade with aileron trailing edge) control surface.

existing wind speed. Aerodynamic forces on the rotor the wind speed increases with altitude above ground level.

blades brought about by the turbulent airflow wake As a result, each rotor blade experiences higher wind

downstream of the wind turbine tower will also be speeds and resulting higher loads at the top of its travel

investigated. Rotor loads created by tubular towers will than at the bottom, or lowest position above ground. Air

be analyzed and compared with data gathered previously turbulence caused by the tower, and occurring downwind

from truss towers, of the tower, causes dynamic blade loads and deflections

Wind turbines produce some noise (ref. 37). Unsteady as each blade passes through the turbulent region. The

airflow over the rotor blades and interaction of the rotor wind itself can be very turbulent and is a primary source

with the airflow wake of the tower are the major noise for rotor loads and deflections. Variability of the wind is

generators. The noise, or acoustic emissions, as perceived felt not only by the blades as they rotate but also by the

by people both inside residential homes near a wind drivetrain and tower since the loads from the rotor are

turbine and outdoors, will be recorded, characterized, transmitted into these components, similar to the way

and presented to test subjects in a laboratory. From these electricity is conducted through a circuit.

tests a perception threshold of the noise spectrum will be The Mod-2 wind turbine data have shown that the

determined. Also, a survey of community reaction to loading effects of turbulent winds on certain components

wind turbine noise will be conducted at operating sites, cannot be fully corrected by rapidly controlling the blade

This will help to establish the degree of community pitch. Because of the interaction of the drivetrain, rotor,

annoyance to noise levels above the threshold of and tower, the blade pitch control was found to create

perception, which is the minimum awareness of the unstable power quality in very high winds. Research will

presence of the noise, be conducted to learn more about the dynamics involved

and to develop control procedures to prevent these

Structural Dynamics potential dynamic instabilities.

Both experimental and analytical research will be Another source of dynamic forces acting on the wind

undertaken to gain a better understanding of the turbine system is the rapidchangein winddirection. Yaw

structural dynamics of wind turbine systems and to alignment of the rotor with the windis neededas the wind

improve operation by controlling and preventing, where direction changes. Both rapidly controlled and free yaw

possible, undesirable dynamic effects. Sources of rotor systems will be investigated to determine the effects on

dynamic loads and deflections include, for example, the the wind turbine system. In a Mod-0 test of free yaw

effect of wind shear on the rotor during rotation. Wind stability and alignment with the wind, the rotor was

shear is defined as the variation of wind speed with found to be 40° from the wind direction (ref. 38).

altitude above ground level. For most wind turbine sites Significant yaw misalignment with the wind can prevent

optimum wind turbine performance. Existing Mod-0

56
Figure 64.- Experimental variable-speed generator, electric motor drive, and electronic control cabinets in test laboratory.

instrumentation and equipment will be used to conduct As mentioned previously, changing wind speeds are

further research on the effects of rapid yawing on the not only felt by the rotor but are also transmitted into the

rotor, drivetrain. Drivetrain loads can exceed design allowables

Several rotor configurations will be tested including if the frequency of the transmitted load oscillations is at

one-, two-, and three-bladerotors. Although aone-blade or near the resonant frequency of the drivetrain

rotor lacks symmetry, it has several advantages. The structure. It is predicted that the variable-speed generator

blade can be stowed behind the tower during hurricane- will be effective in smoothing out these cyclic loads in the

intensity winds to reduce the loads on the blade. One- drivetrain. Research is currently being conducted with a

blade rotors operate at higher rotating speeds than variable-speed generator configuration to determine how

multiblade rotors. This means that the speed increaser or variable-speed generators respond to drivetrain load

gearbox speed ratio can be reduced. The size and weight oscillations induced by the rotor. An experimental

of the gearbox can also be reduced. However, the torque variable-speed generator and the associated solid-state

from single-blade rotors is not as smooth as the torque electronic equipment are shown in figures 64 and 65. The

from multiblade rotors. This undesirable feature may be Westinghouse Electric Corporation has conducted

minimized by using a continuously variable-speed studies to support the design of a megawatt-size variablegenerator. Both the one-blade and two-blade rotor speed generator for the Boeing Mod-SB wind turbine

configurations will be operated at or near aerodynamic (ref. 40).

stall conditions and variable wind conditions to deter- Several methods are used to damp, or reduce, the cyclic

mine the response of the electrical system and the rotor variation in power transmitted through the drivetrain.

structure. For example, a fluid coupling was used on the Mod-0A, a

Rotor blades are structurally elastic or flexible; and quill shaft is used on Mod-2, and an electrical device

when exposed to turbulent airflows, they may vibrate or called a notch filter was employed in the Mod-1 control

flutter. Large loads and deflections can result (ref. 39). system to control drivetrain torque variation. Other

Turbulent airflow can be created by stalling the airflow damping devices will be evaluated, including mechanical

over the rotor surface. This condition may cause blade systems such as a spring-mounted viscous-damped speed

flutter. The stalled-induced rotor vibration can become increaser.

very severe and could, if not controlled properly, Computers are used to analyze many wind turbine

ultimately damage the rotor. Information that does not operating characteristics including loads, stability, and

exist_on the problem of wind-turbine-rotor airfoil flutter performance. NASA plans to improve these computawill be obtained on three-blade, fixed-pitch rotors and tional procedures by comparing calculated results with

rotors with airfoil control surfaces under conditions of experimental data in real time during wind turbine

transient and high winds, operation. Also, deficiencies in computer codes will be

57
Figure 65.- Control console and electronic power circuit cabinets, for Figure 66.- WEST I simulator with supporting equipment.

experimentalvariable-speedgenerator.

development and testing projects, as the most promising

identified and advanced numerical methods will be materials to meet these goals. Fatigue testing of fiberglass

implemented. For example, present computer methods composite materials for wind turbine blades was recently

can calculate rotor loads on the earlier machines but do completed (ref. 41). However, additional research is

not consider the variability of wind speed within the needed to improve these materials and to develop

circular area covered by a large rotating blade, extensive andcomprehensivepropertiesdata. A needfor

Calculation methods will be developed to include these new materials data was discovered during the design

more involved operating conditions, effort on the laminated-wood-epoxy composite blades

Techniques have been developed to simulate wind built for the Mod-0A machines. These blades were

turbine dynamics, in particular, blade loads in unsteady designed by using data on wood fatigue strength

winds. Figure 66 shows the WEST I simulator. Suppor- determined some 40 years ago because data on laminatedting equipment for the WEST I includes an oscilloscope wood-epoxy composite material were not available. As a

and an EAI Model TR-20 analog computer. WEST I is result of these limited data the blades were designed

designed to simulate the performance of a wind turbine heavier than necessary. Basic materials properties tests

rotor in real time. Wind speed in analog form is accepted will be conducted to determine the effects of such

by the simulator. The simulator uses this information to variables as wood grade, moisture content, construction

determine how a wind turbine rotor performs in real procedures, and temperature and humidity exposure.

time. Computer simulators are being advanced to include Prestressed concrete was studied and rejected as a

other aspects of wind turbines such as flexible towers, blade material because of excessive weight. A new techvariable-speed rotors and generators, free yaw behavior, nique of reinforcing concrete by using glass or graphite

and response to gusts, fibers could possibly change the outlook of using

concrete for blades. A conceptual design will be made to

determine if blade weight and cost would be reasonable if

Composite Materials fiber-reinforced concrete were used.

Low-cost and highly durable rotor blades are goals of High-strength graphite filaments can also improve the

NASA's wind turbine research. Both wood and fiberglass strength of both wood and fiberglass composite blades.

composite materials have been identified, through Because the wood blades are of laminated construction, a

58
laminated reinforcement using high-strength materials exposed to a randomly varying wind power. Wind

can be readily incorporated into the fabrication fluctuations can be broad scale and influence all

procedure. Blade test articles will be built and tested to machines or can be localized and affect only a particular

acquire strength data and to develop the ability to apply machine. Defining the effects of these conditions on the

this technology to full-size rotor blades, performance and structural dynamics, or vibration, of

Experimental tests on newly fabricated blades will be the wind turbine system will be an objective of NASA

carried out at NASA before their installation to research in cooperation with the Boeing Engineering

determine if the blades actually meet the structural and Construction Company, the Pacific Northwest

requirements. Measurements will be made to determine Laboratory, the Electric Power Research Institute, and

blade deflections under design loads and other structural the Bonneville Power Administration.

characteristics of the blades. Experiments are also planned to evaluate the response

Laminated-wood and fiberglass composite blades of a multimachine array to utility network operating

present a difficult structural design at the point where the modes. Utilities must operate at fixed voltage and

blade attaches to the hub. Steel bolt-like attachment frequency. They also have requirements for power

fittings or studs must be securely bonded to the root end quality from their power-generating sources.

of the blade since high strength is required at this steel-to- Methods for predicting airflow conditions downwind

wood joint. A number of possible blade-to-hub attach- of a wind turbine are being developed by Pacific

ment concepts will be fabricated. The test article will be Northwest Laboratory and compared with measured

subjected to ultrahigh cyclic loading conditions to wake flow data from the Mod-0A wind turbine that was

determine the life expectancy of these attachment located at Clayton, New Mexico (ref. 42).

fittings.

For economic wind turbine operation, rotor blades Wind Characteristics

should have an operating life expectancy of about 30

years under widely varying environmental conditions The wind, a renewable energy resource, is usually

such as salt-laden, humid air and high and low characterized in terms of its available power, its variatemperatures. Research is required to determine the bility, andnational distribution. Site selection for a wind

effect of such extreme environmental conditions on rotor turbine depends to a large extent on these characteristics.

blade structures and will provide the technology needed One useful source of wind data for selecting a site is

for environmental protection. Data will be acquired by reference 14. This detailed documentation of available

environmental and time-accelerated testing methods and wind energy was assembled under the management of the

by actual real-time exposure to various environmental Pacific Northwest Laboratory (PNL), which is operated

conditions. Samples of bonded, laminated-wood-veneer by Battelle Memorial Institute for DOE. A report on the

blade sections are being exposed to hot, sunny, low- meteorological aspects of site selection for large wind

humidity conditions on the California desert andto high- turbines was also a part of the PNL effort. This

humidity salt air at the NASA Johnson Space Center in publication (ref. 15) mainly synthesizes the work of

Texas. others in identifying the most desirable wind energy sites

Wind turbines are prone to lightning strikes since they by using available winddata along with understanding of

are, by necessity, very tall structures that are located in wind behavior.

open areas. Research will be conducted, using lightning

detection instrumentation, to determine the frequency Wind Energy Density

and magnitude of lightning strikes at various wind

turbine sites. Methods for designing wind turbine Energy that is available from the wind varies in

lightning accommodation systems will be reported as a proportion to the cube of the wind speed. This means

result of this research, that if, for example, the wind increases from 10 mph to

15 mph, the available power increases not 50 percent but

237 percent. Thus for the purpose of stating the wind

Multiple Systems Interaction power resource a value called wind energy density is used

Three Mod-2 wind turbines operating as a cluster at rather than wind speed alone. The number describing

Goodnoe Hills, Washington, will be used to study how wind energy density takes into account the cube of the

each machine interacts with the neighboring machine and wind speed andthe air density. On this basis windenergy

how the machines collectively operate on the utility classes have been set up to display this information on

network. The machines are presently located so that geographical maps, as shown in figure 67. These classes

winds from the prevailing direction will cause one cover a wide range of wind energy densities and are

machine to be downwind of another. As a result, one of expressed as the electrical equivalent of wind energy. For

the machines will be operating in the turbulent wake of example, a range of energy values from 0 to 1000 watts

an upwind machine. Also, the downwind machine is per square meter of area directly facing into the wind is

59
shown in figure 67. It should be pointed out that these Estimates of wind energy available to the user at wellvalues are not the maximum energy that can be extracted exposed locations throughout the United States are

from the wind since the power output from a wind plotted on regional maps and on the overall map

turbine is determined by its design and operating illustrated in figure 67. The wide range of wind energy

characteristics. The theoretical maximum energy that can density existing in the United States is divided into seven

be extracted from the wind by an ideal wind turbine is 59 wind energy classes as given in table IV. These classes are

percent of the available energy in the wind. Practical represented in figure 67 by varying shades of black, the

wind machines remove considerably less than the darker the shade the higher the wind energy.

maximum (30 percent to 47 percent of the available wind

energy, depending on design and operating Site Selection

considerations).

As a suitable site for a wind turbine one would

obviously choose an area having high annual average

Wind Variability wind speed. The exact location would avoid tall

A wind turbine generally operates in wind of obstructions upwind. To take advantage of the maximum

continuously varying speed and direction. It also usually wind potential in a given area, the top of a smooth welloperates in a wind speed gradient (higher at the top than rounded hill, a flat plain, an open shoreline, or an island

near the bottom of the rotor arc) because of the so-called should be selected. Very high wind speeds can be

surface boundary layer or roughness effects. This produced in mountain passes where contraction (or

variation in wind speed with altitude, called wind shear, funneling) of the wind takes place.

can be significant and can cause undesirable loads on the Besides the meteorological and terrain considerations,

rotating turbine blades. Wind speeds are usually selecting wind turbine sites involves such considerations

presented at some fixed height above the ground (e.g., 10 as land availability, the potential of television

or 50 m (33 or 164 ft)) for standardization. To calculate interference and objectionable noise to nearby residents,

the speed at a different height from the one given, a rule accessibility for maintenance, and availability of rights of

of thumb is to assume that the speed increases as the one- way for transmission lines.

seventh power of the height above the ground. In summary, a wind turbine site must be selected where

The variability of the wind, which changes with time steady, reliable winds are available to allow the turbine to

and location, is a major problem in the siting and be of economic value. The wind energy densitymaps and

operation of wind turbines. Because of variability a large data found in references 14 and 15 should be used as a

amount of data are needed to determine good wind first step in selecting a site. Because of local anomalies a

turbine locations. Performance of the wind turbine is more detailed wind survey should be taken at the actual

determined to a large extent by the wind variability, proposed site if site data are not already available. Local

Because the wind energy varies as the cube of the wind

speed, the energy available can be several times that TABLEIV. - CLASSESOF WINDPOWERDENSITYAT I0 AND

calculated from the average wind speed. The added 50 m (33 AND164 ft) a

energy comes from the short-period wind gusts that are

common in many areas. On the other hand, the wind Wind Altitude

gusts, directional shifts, and vertical wind shear put power

significant loads on the blades, the bearings, the class 10 m (33 ft) 50 m (164 ft)

drivetrain, and other system components. These loads Wind power Speedb Wind power Speedb

can have an adverse effect on turbine component density density

m/s mph m/s mph

reliability and fatigue life. w/m2 w/ft2 W/m2 W/ft2

1 I00 9.3 4.4 9.8 200 18.6 5.6 12.5

National Wind Resources 2 150 13.9 5.1 ll.5 300 27.9 6.4 14.3

3 200 18.6 5.6 12.5 400 37.2 7.0 15.7

The geographical distribution of wind energy densities 4 250 23.2 6.0 13.4 500 46.4 7.5 16.8

in the United States has been made available to wind 5 300 27.9 6.4 14.3 600 55.7 8.0 17.9 6 400 37.2 7.0 15.7 800 74.3 8.8 19.7

energy users in the form of an atlas for each of 12regions 7 1000 92.9 9.4 21.1 2000 185.8 111.9 26.6

in which the United States and its possessions were

aVertical extrapolation of wind speed based on the 1/7

divided (ref. 14). Near-surface wind data used to power law.

determine the wind energy densities were obtained from bMean wind speed is based on Rayleigh speed distribu3200 reporting stations and from upper air data and tion of equivalent meanwind power density. Wind speed is for standard sea-level conditions. To mainqualitative indicators of wind speeds. The latter infor- tain the same power density, speed increases 3 permation was used to estimate wind values in areas where cent/1000 m (5 percent/5000 ft).

measured data were lacking.

60
"V~ITED STATErKflNU~ AVERJ:GE WrNOlJOWER~- ;p

Figure 67. - Geographic distribution of wind power in the United States.
terrain can cause the wind to vary considerably over short (1) Mid-1980 dollars

distances, and therefore the data available from less (2) A 25-unit wind cluster

detailed measurements may show the wind higher or (3) A rate of installation of one machine per month

lower than that at the proposed site. (4) Generally flat sites with few natural obstacles

(5) Soil easily prepared for foundation

Wind Turbine Economics (6) Loan cost not included

(7) Transportation distance of 1609 km (1000 miles)

Although research on innovative machine designs may from factory to site

yield more efficient and less costly future generations of Based on the gross national product and implicit price

wind machines, the price of the second- and third- deflation, the mid-1980 dollar costs in table V were

generation machines when produced in quantity is established by applying a 25 percent increase to the

attractive for utility application, mid-1977 dollar reports in Boeing's system design and

The first-generation machines (Mod-0A and Mud-l) concept report (ref. I0). In mid-1977 dollars the

were designed primarily for research investigations and estimated total turnkey cost of the 100th production unit

not necessarily for high-volume production. The second- for the Mud-2 would be $1 720 000 and the annual

generation wind turbines (Mud-2) and the third operating and maintenance cost would be $19 000.

generation (Mud-5), when eventually produced in The cost of energy (COE) of a wind turbine generator

quantity, should cost considerably less. Economies are system contains three elements--capital cost, operating

expected from automation, from discounts on quantity and maintenance costs (O&M), and energy capture. The

purchases of components and materials, and from the COE is taken to be at the output of the installation's stepdistribution of engineering costs over a large number of up transformer. The cost of energy is a function of the

units. The production wind turbines will not incur the turnkey cost analysis, annual energy production, and the

extensive test and checkout costs associated with O&M cost.

experimental units.

The operating and maintenance costs for a large wind

turbine depend on how reliable it is and how easily it can COE = IC × FCR x AOM = 4.1 C/kWh

be maintained for operation. Costs will also depend on AEP

whether a single machine or a wind turbine cluster is to be

operated and maintained. In the latter case the fixed

development and maintenance expenses can be allocated where

to a number of wind turbines, reducing the cost per FCR= 18 percent per year = levelized, fixed charge rate

machine, including return on capital,

Estimates of the 100th production unit costs for the income tax, property tax,

Mud-2 are summarized in table V. These costs assume and insurance. FCR is

sensitive to cost of capital,

TABLEVo - COSTSUMMARYFOR capitalization method,

lOOth PRODUCTIONUNIT income tax rate, and

system lifetime.

Turnkey account Cost, IC = $2 150 000 = initial (turnkey) cost of the energy mid-1980

dol Iars system including complete cost

exposure to the utility for purchasing,

Site preparation 203 000 installing, and setting up logistics for

Transportation 36 000 energy production system.

Erection 171000 AOM= $19 000=annual O&M cost including operating Rotor 411 000

Drivetrain 474 000 budgets and maintenance budgets.

Nacelle 230000 AEP = 9.75 x 106=anticipated annual energy

Tower 339 000 production of energy system in Initial spares 44 000

Nonrecurring 44 000 kilowatt-hours. AEP takes into

Total initial cost 1 952 000 account energy production losses

Fee (I0percent) 195 000 attributed to unavailability of energy

system equipment and unavailability

Total turnkey cost 2 147 000 of energy source (i.e., wind).

Annualoperations

and maintenance 19000 The COE for the second prototype units of Mod-0A and

Mod-2 is plotted against the mean wind speed at the site

(ref. 43) in figure 68.

62
55 -- mature products having similar functional requirements

and design complexities. These comparisons suggest that

wind turbines can achieve a price of $6.60 to $8.80 per kg

50 ($3 to $4 per lb). At this price level they should be

economical for a substantial number of user utilities.

For a site mean wind speed of 6.3 m/s (14 mph), for

45 which the Mod-2 is optimized, the COE of the Mod-2

100th production unit ranges from 6C/kWh, considering

40 only the installed equipment cost, to about 8c/kWh,

including nominal costs for land, contingency and

intracluster costs, and allowance for funds during

"_ 35 construction. The total cost including these additional

r_ items would be more representative of the total cost to a

-_ Economy Mod-OA utility.

30 of scale The power produced by a wind turbine on a utility

T, system will enable the utility to reduce or shut down

conventional fossil-fuel-burning powerplants that would

._ 25 otherwise be required. The fuel thus saved can be credited

L..

to the wind turbine. In this mode, wind turbine power

"_ 20 would be used whenever it is generated.

As noted before, the ability of wind turbines to save

M0d-1 fuel will, in part, depend on how readily a utility's

Improved conventional powerplants can respond to changes in the

15 -- technology-x

\ wind power being produced. For modest amounts of

wind power the wind power variations are expected to be

10 of the same order as normal load variations and will

appear to be a negative load to the rest of the system.

Ultimately, fuel savings attributable to wind turbines

5 -- _ Mod-2 must be determined on an individual utility basis. To

assess whether a wind turbine would be an attractive

0 [ [ [ investment as a fuel saver, total fuel savings must be

6 7 8 compared with the life-cycle cost of the wind turbine.

Sitemeanwindspeedat9.1-m This approach determines the so-called breakeven cost, at (30-ft)heihi, m/s

I •] ] which point any investor would be indifferent to whether

12 15 18 the investment is made or not. In any investment decision

Sitemeanwindspeeatd9.1-m the perceived risks and uncertainties will play a major

(30-ftlheight, mph role. Thus conservative assessments of the breakeven

Figure68.-Second-unitcostofelectricityasfunctionofsitemeanwind COSTSof wind turbines will minimize the perceived risks

speed, based on 90 percent availability, and uncertainties.

One method commonly used in breakeven analyses is

Because experimental units are aimed at providing in- to compare the present value of all savings with the

service testing and hardware qualifications, the O&M present value of all costs or, alternatively, to compare the

costs are higher than those expected for production units, annual levelized savings and costs. The latter is

On the basis of the estimates made for production units, convenient and easily understood since the annual

the annual, levelized O&M costs for the experimental levelized cost of a wind turbine divided by its annual

machines were assumed to equal 2 percent of the total energy output is the cost of electricity (COE). Thus a

capital investment. A total fixed charge rate of 20 percent wind turbine that has a COE of 4 C/kWh would break

(18 percent on capital plus 2 percent for O&M) was even if its annual levelized savings also equalled

therefore applied to the total capital investment to 4c/kWh.

compute the COE's in figure 68. Fuel costs will tend to increase with time because of

As noted in figure 68, the reduction in COE from Mod- inflation. They may also increase faster than inflation,

0A to Mod-I was mainly due to economy of scale, escalating in real terms. The annual fuel savings

whereas reduction in COE from Mod-1 to Mod-2 was attributed to the wind turbine at the beginning of its life is

mainly the result of improved technology, multiplied by a levelization factor to find the annual

In quantity production the COE is expected to levelized fuel savings over the life of the wind turbine.

decrease. Large wind turbines can be compared with Assuming a 6-percent general inflation rate and that fuel

63
prices do not escalate in real terms, the appropriate measurements were made in the immediate vicinityofthe

levelization factor is 2.0. However, the assumption that wind turbine under various weather conditions. A

fuel prices will increase only at the general inflation rate particularly objectionable sound was a "thump" as each

is most probably conservative over the long term. blade passed behind the tower. To eliminate the

On the basis of fuel prices paid by utilities in 1980and residents' objections, the rotor speed was reduced from

assuming that fuel prices will increase at the rate of 35 rpm to 23 rpm. This reduced the sound level by 10 db

general inflation, a COE range of 4¢ to 4.5¢ per kWh will near the wind turbine site (ref. 9).

make wind turbines attractive to a significant number of

utilities. Achieving COE's in this range is contingent on Television Interference

sufficiently good wind sites. The mass-produced second- As might be expected, the large rotating wind turbine

generation Mod-2 would be competitive at sites having blades can cause some television interference by

mean wind speeds of 6.7 m/s (15 mph) or greater, reflecting the signals in the immediate area surrounding

Anticipated weight and cost reductions in advanced the site. Because of terrain features and limited television

machines are expected to bring the COE within the target reception in the general area of the Mod-I machine, some

range at more sites and thus to significantly increase the interference was a local problem. Investigations into the

potential market, problem showed the interference to be limited to a

In addition to fuel savings, "capacity credit" may 2.4-km (11⁄2-mile)radius of the site (ref. 9).

increase the breakeven value of energy produced by wind Interference of a television signal depends to some

turbines beyond that of a "fuel saver." Capacity credit is extent on the strength of the scattered signals relative to

defined as the amount of conventional capacity that may the primary ones. Because the signal strength at the highbe displaced by wind turbines divided by the capacity point site of the wind turbine was strong, the reflected

added by wind turbines to the system while maintaining signals throughout the interference region had a high

the same system reliability. Determination of capacity potential for causing television interference. This was

credit is dependent on the variability of the wind at a particularly true in local areas where the direct or primary

specific site, the makeup of the utility's generation mix, signals were rather weak and thus gave poor reception.

and the nature of its load profile. Consequently, capacity Possible solutions to the interference problem are the

credit can only be adequately determined by examining use of cable television in the affected area or rebroadcast individual utilities in some detail. On the basis of a

of the television signals by using translators. Analyses

number of recent studies, the contribution of capacity and measured data in the interference area determined

credit to a wind turbine's value will be modest.

that special, high-performance antennas will not solve the

television problem.

Environmental Impacts

Although windturbines have an environmental advan- Concluding Remarks

tare over other power-generating sources in that they

produce no air or water pollution, other environmental Large wind turbines for utility applications provide a

factors must be considered. Annoyance by low-frequency promising renewable energy option. Advanced designs

sound and local television interference were two factors produced in the Federal Wind Energy Program continue

discovered when the first megawatt-size machine in the to appear financially and technically attractive. If wind technology development is allowed to continue, wind

Federal Wind Energy Program (Mod-1) began operating turbines will provide a means of fuel saving that autility at Boone, North Carolina. It should be noted that the

can employ at relatively low capital cost as compared

mountainous terrain in this area had a significant with conventional fossil-or nuclear-fueled powerplants.

influence on how these very limited conditions affected

For geographic regions having attractive annual wind

some of the local residents. Studies that were prompted velocities, wind-generated power can significantly reduce

by these environmental concerns contributed to an the consumption of fossil fuels. understanding and identification of solutions. At the The Department of Energy has supported a wide range Boone installation, studies showed both sound and of wind turbine research and development. Vertical-axis

television interference to be localized and sporadic wind turbine research and technology development is

(ref. 9). carried out by the Sandia National Laboratory,

Albuquerque, New Mexico, for DOE. Small, horizontalNoise axis wind turbine testing and development are being

Complaints about objectionable sound from the conducted for DOE by Rockwell International

Mod-1 machine were restricted to within 3.2 km (2 miles) Corporation, Rocky Flats, Colorado. Advanced and

of the turbine and to only 10 residents. Extensive innovative wind energy machines are being investigated

64
for DOE by the Solar Energy Research Institute (SERI), rotors. The objective is to improve rotor performance by

Golden, Colorado. SERI is also conducting wind turbine using airfoils expressly designed for a wind turbine. The

acoustic research in cooperation with the NASA Langley vibration effects on a wind turbine resulting from the

Research Center for DOE. Research on various wind experimental operation of a single-blade rotor need to be

characteristics and their relation to wind turbines is also investigated by structural dynamic researchers. Environpart of the DOE-sponsored Federal Wind Energy mental effects on laminated-wood-epoxy composite

Program. The Pacific Northwest Laboratory, Richland, structural components are being examined by composite

Washington, conducts the wind energy research for materials researchers. The Mod-2 wind turbine cluster at

DOE. Finally, large, horizontal-axis wind turbine Goodnoe Hills, Washington, is the primary experimental

research and technology development are conducted for test facility for investigating the interactions of three

DOE by the NASA Lewis Research Center, Cleveland, machines operating together or separately. Research is

Ohio. currently being conducted to assess the variation in

The technology advancement is marked when one performance of one Mod-2 wind turbine operating in the

reviews the three generations of large, horizontal-axis downwind wake of another operating Mod-2.

wind turbines that have been created in a relatively short The Mod-0A machines are the only experimental

time. But continued wind turbine technology develop- machines with a long history of performance. These

ment is needed. The significant capital cost reductions machines operated in different locations to supply energy

that are projected must be verified. Improvements in to different utility networks. Over a 41A-year period these

reliability and operating performance are required in four Mod-0A machines have collectively operated over

order to meet competitive COE goals. The participation 38 000 hours and supplied over 3600 MWh of electricity

of utilities in continuing the development of wind to the participating utilities. Although last to be installed,

turbines is essential. Maintenance requirements and the the unit in Hawaii produced the most energy. This wind

associated skills required, economies of scale, and the turbine's relatively good performance stems from the

distances between good wind sites and population centers high annual wind speed at the site and from the fact that

make the utility industry the logical primary market for this unit incorporated a number of improvements over

large machines, the other three Mod-0A machines.

The rapid advances made by wind turbine development Achievements of the Mod-0A project include verifying

over the last decade have been fostered by the Federal the durability of new low-cost rotor blade concepts,

Wind Energy Program in a series of experiments on validating analytic design codes, clarifying the

progressively more advanced large, horizontal-axis wind requirements for wind turbine utility compatibility, and

turbines. The first generation of these machines included providing baseline data on control concepts, component

(1) the Mod-0 machine, rated at 100 kW, first tested in reliability, and overall machine performance.

1975 at NASA's Plum Brook Station near Sandusky, The Mod-I wind turbine successfully validated the

Ohio; (2) four Mod-0A machines, each rated at 200 kW, methods for predicting power, loads, and dynamics for a

at Clayton, New Mexico; Culebra Island, Puerto Rico; megawatt-size wind turbine. In addition, key experiments

Block Island, Rhode Island; and Oahu, Hawaii; and (3) were performed and siting lessons learned regarding

the Mod-1, rated at 2000 kW, near Boone, North television interference andnoisegeneration in populated

Carolina. The more advanced second-generation areas.

machine development is characterized by the Mod-2 Although both the first-generation (Mod-0A and

cluster of three wind turbines at Goodnoe Hills, Mod-1) projects were technically successful, they were

Washington, and the Hamilton Standard SVU WTS-4 not attractive from a commercial point of view for

machine near Medicine Bow, Wyoming. Each Mod-2 is continued utility operation. As a result, three of these

rated at 2500 kW. The SVU WTS-4 machine is rated at first-generation machines have been removed from the

4000 kW. The most advanced machine, the Mod-5B utility sites. The remaining two Mod-0A machines are

(3000 kW), now in the final design stage, represents the currently being disposed of.

third generation of wind turbine development. The current state of the art in experimental large,

The Mod-0 wind turbine is currently the principal test horizontal-axis wind turbines is represented by the

bed for the continuing DOE/NASA research and 2.5-MW Mod-2 and the 4-MW WTS-4. Five experitechnology program. Investigations currently under way mental Mod-2 machines are currently operating. Three of

include advanced rotor blade airfoil development, aileron these machines, located at Goodnoe Hills, Washington,

control of rotor power, and variable-speed generator are providing excellent research data, under DOE

development, sponsorship and with the support and cooperation of the

Research and technology development projects are Bonneville Power Administration. The fourth and fifth

carried out in aerodynamics, structural dynamics, Mod-2's were constructed and installed by the Boeing

composite materials, and multiple-machine effects. Engineering and Construction Company for the U.S.

Airfoil research is currently under way for wind turbine Bureau of Reclamation near Medicine Bow, Wyoming,

65
and for the Pacific Gas and Electric Company in Solano 5. Andersen,T. S.; et al.: Mod-0A 200 kW Wind Turbine Generator

County, California, respectively. The WTS-4 was Designand AnalysisReport(AESD-TME-3052, Westinghouse

designed and installed by the Hamilton Standard Electric Corp.; NASA Contract DEN3-163.) DOE/NASA/ 0163-2, NASA CR-165128, 1980.

Division of United Technologies Corporation for the 6. Andersen, T. S.; et al.: Mod-0A 200 kW Wind Turbine Generator

Bureau of Reclamation near Medicine Bow, Wyoming. Engineering.Final EngineeringDrawingReport.(AESDBy June 1983, the cluster of three Mod-2 machines at TME-3053,WestinghouseElectric Corp.; NASA Contract

Goodnoe Hills had accumulated a combined operating DEN3-163.)DOE/NASA/0163-3,NASACR-165129,1980.

time of about 3800hours and generatedover 4100MWh 7. Linscott,S.;Shaltens,R. K.; and Eggers, A. G.: Aluminum Blade Development for the Mod-0A 200-Kilowatt Wind Turbine. NASA

of energy.Data fromthe operation of thesemachineswill TM-82594, 1981.

contribute to improvements to wind turbines in the 8. Electrical World Directory of Electric Utilities (1974-1975). 83rd

future, ed., McGraw-Hill Publishing Co., 1974.

The third generation of large wind turbines, the 9. Collins, J. L.; et al.: Experience and Assessment of the DOE-NASA Mod-1 2000-Kilowatt Wind Turbine Generator at

Mod-5, is now in the detailed final design stage. The goal Boone, North Carolina. NASA TM-82721, 1982.

of the advanced multimegawatt Sod-5 machine is to 10. Mod-2 Wind Turbine SystemConceptand PreliminaryDesign

generate electricity for 3.75 e/kWh in 1980 dollars. Report, Vol. II: Detail Report(DE-AI01-79ET-20305, Boeing

Currently DOE is sponsoring and the NASA Lewis Engineeringand Construction Co.; NASA Contract DEN3-2.)

ResearchCenter is managing one cost-sharingproject at DOE/NASA/0002-80/2, NASA CR-159609, 1979.

Boeing. The manufacturer is currently working with 11. Linscott, Wind B. S.; Dennett, J. T.; and Gordon, L. H.: The Mod-2 Turbine Development Project. NASA TM-82681, 1981.

cooperating utilities to help support the project. 12. Gordon, L. H.: Mod-2 Wind Turbine System Cluster Research Test

An early and continuing objectiveof the Federal Wind Program, Vol. l--lnitial Plan. NASA TM-82906, 1982.

Energy Program is to transfer the technology learned 13. Vas, Irwin E., ed.: Fifth Biennial Wind Energy Conference

from the Government-sponsored projects to those U.S. Workshop. SERI/CP-635-1340 CONF-811043, Midwest

industries having an interest in manufacturing and Research Institute, 1981. 14. Wind Energy Resource Atlas. Volumes 1-12. PNL-3195-

marketing wind turbines. The many Federally sponsored WERA-I-12, Battelle Pacific Northwest Laboratory, 1980-1981.

technical reports published have been sent to a variety of 15. Hiester,T. R.; and Pennell, W. T.: The Meteorological Aspectsof

U.S. industries involved with wind energy. Periodic siting Large Wind Turbines. PNL-2522, Battelle Pacific

Northwest Laboratory, 1981. conferences and workshops on wind energy that were

16. Savino, J. M.; and Wagner, L. H.: Wind Tunnel Measurements of started in 1973 are continuing. These conferences have the Tower Shadow on Models of the ERDA/NASA 100kW Wind

been and continue to be well attended by U.S. and Turbine Tower. NASA TM X-73548, 1976.

foreign industries. Many new companies have formed 17. Savino, J. M.; Wagner, L. H.; and Sinclair, D.: Wake

since 1973 with the sole purpose of producing and Characteristics of an Eight-Leg Tower for a Mod-0 Type Wind

marketingwind turbines for profit. It is apparent that the Turbine. DOE/NASA/1028-77NASA /14, TM-73868,1977.

objective of transferring Government-sponsored 18. Linscott, B. S.; Shapton, W. R.; and Brown, D.: Tower and Rotor Blade Vibration Test Results for a 100-Kilowatt Wind Turbine.

technology to industry is being met. However, for the NASATMX-3426,1976.

large horizontal-axis wind turbines suitable for utility 19. Das, D. C.; and Linscott, B. S.: Approximate Method for

application, additional Federally sponsored research and Calculating Free Vibrations of a Large Wind Turbine Tower

technology development is needed to maintain the Structure. ERDA/NASA-1028/77/12, NASATM-73754, 1977.

industry's present momentum. 20. Spera, D. A.: Comparison of Computer Codes for Calculating Dynamic Loads in Wind Turbines. DOE/NASA/1028-78/16,

NASA TM-73773, 1977.

21. Spera, D. A.: Structural Analysis of Wind Turbine Rotors for

NSF-NASA Mod-0 Wind Power System. NASA TM X-3198,

1975.

22. Hunnicutt, C. L.; Linscon, B.; and Wolf, R. A.: An Operating

200-kW Horizontal Axis Wind Turbine. NASA TM-79034, 1978.

References 23. Lwinscott, B. S.; Shaltens, R. K.; and Eggers, A. G.: Test Experience ith Aluminum Blades on the Mod-0A 200-Kilowatt Wind

Turbine at Clayton, New Mexico. DOE/NASA/220370-21,

1. Linscott, B. S.; Glasgow, J. C.; Anderson, W. D.; and Donham, NASA TM-82595, 1981.

R. E.: Experimental Data and Theoretical Analysis of an 24. Reilly, D. H.: Safety Considerations in the Design and Operation

Operating 100 kW Wind Turbine, NASA TM-73883, 1978. of Large Wind Turbines. DOE/NASA/20305-79/7, NASA

2. Design Study of Wind Turbines, 50 kW to 3000 kW for Electric TM-79193, 1979.

Utility Applications: Executive Summary. NASA CR-134936, 25. Griffee, D. G., Jr.; Gustafson, R. E.; and More, E. R.: Design,

1977. Fabrication, and Test of a Composite Material Wind Turbine

3. Design Study of Wind Turbines 50 kW to 3000 kW for Electric Rotor Blade. (HSER-7383, United Technologies Corp.; NASA

Utility Applications: Summary Report. NASA CR-134934, 1976. Contract NAS3-19773.) NASA CR-135389, 1977.

4. Andersen, T. S.; et al.: Mod-0A 200 kW Wind Turbine Generator 26. Gewehr, H. W.: Design, Fabrication, Test, and Evaluation of a

Design and Analysis Report: Executive Summary. (AESD- Prototype 150-ft Long Composite Wind Turbine Rotor Blade.

TME-3051, Westinghouse Electric Corp.; NASA Contract (R-1575, Kaman Aerospace Corp., NASA Contract

DEN3-163.) DOE/NASA/0163-1, NASA CR-165127, 1980. NAS3-20600.) NASA CR-159775, 1979.

66
27. Batesole, W. R.; and Gunsallus, C. T.: Design and Fabrication of 36. Viterna, L. A.; and Janetzke, D. C.: Theoretical and Experimental

Composite Blades for the Mod-1 Wind Turbine Generator. Power from Large Horizontal-Axis Wind Turbines.

(RR-1685, Kaman Aerospace Corp.; NASA Contract DOE/NASA/20320-41, NASA TM-82944, 1982.

DEN-3-131.) NASA CR-167987, 1981. 37. Hubbard, H. H.; Shepherd, K. P.;, and Grosveld, F. W.: Broad

28. Weingart, O.." Design, Evaluation, and Fabrication of Low-Cost Band Sound from Wind Turbine Generators. NASA CR-165810,

Composite Blades for Intermediate-Size Wind Turbines. 1981.

(SCI-81520, Structural Composites Industries Inc.; NASA 38. Corrigan, R. D.; and Viterna, L. A.: Free Yaw Performance of the

Contract DEN3-100.)NASA CR-165342, 1981. Mod-0 Large Horizontal Axis 100 kW Wind Turbine. Large

29. Lieblein, S., et al.: Evaluation of Feasibility of Utilizing Wood Horizontal-Axis Wind Turbines. NASA CP-2230, 1982, pp.

Composites for the Design and Fabrication of Low Cost Wind 103-124.

Turbine Blades, NASA CR- 39. Kamoulakos, A.: Stability Analysis of Flexible Wind Turbine

30. Lieblein, S.; Ross, R. S.; and Fertis, D. G.: Evaluation of Urethane Blades Using Finite Element Method. (MIT-ARSL-TR-197-3,

for Feasibility of Use in Wind Turbine Blade Design. (TRS-101, Massachusetts Institute of Technology; NASA Grant NSG-3303.)

Technical Report Services; NASA Order C-7653 E(49-26)-1028.) NASA CR-168107, 1982.

DOE/NASA/7653-79/1, 1979. 40. Andersen, T. S.; et al.: Multiple and Variable Speed Electrical

31. Lieblein, S.; et al.: Evaluation of Feasibility of Prestressed Generator Systems for Large Wind Turbines. Large HorizontalConcrete for Use in Wind Turbine Blades. DOE/NASA/ Axis Wind Turbines. NASA CP-2230, 1982, pp. 125-138.

5906-79/1, NASA CR-159725, 1979. 41. Hofer, K. E.; and Bennett, L. C.: Fatigue Testing of Low-Cost

32. Gnecco, A. J.; and Whitehead, G. T.: Microprocessor Controlofa Fiberglass Composite Wind Turbine Blade Materials.

Wind Turbine Generator. NASA TM-79021, 1978. (IITRI-M06066-22, lIT Research Institute; NASA Contract

33. Yee, S. T.; et al." Vibration Characteristics of a Large Wind DEN3-182.) 1981.

Turbine Tower on Nonrigid Foundations. ERDA/NASA/ 42. Doran, J. C.; and Packard, K. R.: Comparison of Model and

1004-77/1, NASA TM X-73670, 1977. Observations of the Wake of Mod-0A Wind Turbine. PNL-4433,

34. Sullivan, T. L.; Miller, D. R.; and Spera, D. A.: Drive Train Pacific Northwest Laboratory, 1982.

Normal Modes Analysis for the ERDA/NASA 100-Kilowatt Wind 43. Ramler, J. R.; and Donovan, R. M.: Wind Turbines for Electric

Turbine Generator. ERDA/NASA/I028-77/1, NASA Utilities; Development Status and Economics. DOE/NASA/

TM-73718, 1977. 1028-79-23, NASA TM-79170, 1979.

35. Seidel, R. C.; Gold, H.; and Wenzel, L. M.: Power Train Analysis

for the DOE/NASA 100 kW Wind Turbine Generator.

DOE/NASA/1028-78/19, NASA TM-78997, 1978.

67
Bibliography

Eldridge, F. R.: Proceedings of the Second Workshop on Wind Energy Proceedings of the Third Biennial Conference and Workshop on Wind

Conversion Systems. MTR-6970, NSF-RA-N-75-050, Mitre Corp., Energy Conversion Systems. CONF-770921, 1977.

1975.

Proceedings of the Fourth Biennial Conference and Workshop on Wind

Fifth Biennial Wind Energy Conference and Workshop. SERf/ Energy Conversion Systems. CONF-791097, 1979.

CP-635-1340, CONF-811043, 1981.

Savino, J. M.: Wind Energy Conversion Systems. NASA TM X-69786,

Lieblein, S.: Large Wind Turbine Design Characteristics and R&D 1973.

Requirements. NASA CP-2106, 1979.

Thresher, R. W.: Wind Turbine Dynamics. NASA CP-2185, 1981.

Miller, D. R., ed.: Wind Turbine Structural Dynamics. NASA

CR-2034, 1978. Thresher, R. W.: Large Horizontal-Axis Wind Turbines. NASA

CP-2230, 1982.

NSF/NASA/Utility Wind Energy Conference. NASA TM-79508,

1974.

68



1. Report No. 2. Govemment Accession No. 3. Recipient's Catalog No.

NASATM-83546

4. Title and Subtitle 5. Report Date

Large, Horizontal-Axis Wind Turbines March 1984

6. Performing Organization Code

776-33-41

7. Author(s! 8. Performing Organization Report No.

Bradford S. Linscott, Lewis Research Center; Porter E-1920

Perkins, Analex Corporation, Lewis Research Center; and

Joann T. Dennett, RDDConsultants, Inc., Boulder, 10Wo_Un,No

Colorado

9. Performing Organization Name and Address

National Aeronauti cs and SpaceAdministration 11Contract or Grant No.

Lewis Research Center

Cleveland, Ohio 44135 13.Typeof ReportandPeriodCovered

12. Sponsoring Agency Name and Address Technical Memorandum

U.S. Department of Energy

Di vi sion of Photovol taic Energy Technol ogy 14SponsoriAgengncy_ Report No.

Washington, D.C. 20545 DOE/NASA/20320-58

15. Supplementary Notes

Final report. Prepared under Interagency Agreement DE-AIO1-76ET20320.

16. Abst_ct

The large-wind-turbineprogram is a major segmentof the FederalWind Energy Programsponsoredby the

Departmentof Energy (DOE). The NASA LewisResearchCentermanagesthe programon large horizontalaxis wind turbinesfor DOE. This programis directedtoward developmentof the technologyfor safe,

reliable,environmentallyacceptablelargewind turbinesthat have the potentialto generatea significant amountof electricityat costscompetitivewith conventionalelectricgeneratingsystems. In

addition,these largewind turbinesmust be fully compatiblewith electricutilityoperationsand

interfacerequirements. There are severalongoing large-wind-systemdevelopmentprojectsand applied

researcheffortsdirectedtowardmeetingthe technologyrequirementsfor utilityapplications. The

first-generation-technologymachines (Mod-OAand Mod-l) have successfullycompletedtheir planned

periodsof experimentaloperation. Dispositionof these machinesis nearlycomplete. The secondgenerationmachines(Mod-2's)continueexperimentaloperationat GoodnoeHills,Wash., and Medicine

Bow, Wyoming. Design and engineeringdevelopmentof a third-generation(Mod-5)machine is underway.

This report providesdetailedinformationon these projects. It describesthe Mod-O researchfacility

and currentappliedresearcheffort in aerodynamics,structuraldynamicsand aeroelasticity,composite

and hybrid compositematerials,and multiple-systeminteraction. A chronologyof componentresearch

and technologydevelopmentfor large,horizontal-axiswind turbinesis presented. Wind characteristics, wind turbineeconomics,and the impactof wind turbineson the environmentare reported. The

need for continuedwind turbineresearchand technologydevelopmentis explored. Over 40 references

are sited and a bibliographyis included.

17. Key Words _uggeet_ _ Autho((e_ 18. Distribution Statement

Wind turbines Unclassified- unlimited

Wind power STAR Category44

Wind energy DOE CategoryUC-60

19. Security Classlf. (of this report) 20. Security Cllumlf. (of this INige) 21. No. of pages 22. Pdce"

Unclassified Unclassified 69 A04

"For salebythe NationalTechnicalInformationService,SpringfieldV,irginia22161

NASA-Langley, 1984

NationalAeronauticsand THIRD-CLASS BULK RATE Postage and Fees Paid

SpaceAdministration National Aeronautics and _ _! _

Space Administration

Washington, D.C. NASA451

20546

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