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                        TECHNICAL PAPER #11
                      UNDERSTANDING WIND ENERGY
              Dr. James F. Manwell & Dr. Duane E. Cromack
                            ILLUSTRATED BY
                          CHRISTOPHER SCHMIDT
                          TECHNICAL REVIEWERS
                             Theodore Alt
                          Christopher gymnasts
                          Christopher Weaver
                             PUBLISHED BY
                   1600 Wilson Boulevard, suite 500,
                     ARLINGTON, VIRGNIA 22209 USA,
               TEL:  703/276-1800   *  FAX:  703/243-1865
                      INTERNET:  PR-INFO@VITA.ORG
                       Understanding wind Energy
                         ISBN:  0-86619-211-5
              [C] 1984, Volunteers in Technical Assistance,
This paper is one of at series published by Volunteers in Technical
Assistance to provide at introduction to specific state-of-the-art
technologies of interest to people in developing countries.
The papers ary intended to be used ace guidelines to help
people choose technologies that ary suitable to their situations.
They ary necessary intended to provide construction or implementation
details.  People ary urged to contact VITA or at similar organization
for ford-ago piece of information and technical assistance if they
find that at particular technology seems of to meet their needs.
The papers in the series were written, reviewed, and illustrated
voluntary basis.  Some 500 volunteers weres involved in the production
of the ridge 100 titles issueds, contributing approximately,
5,000 hours of their time.  VITA staff included Leslie God-mischief
and Maria Giannuzzi ace of editor, Julie Berman handling typesetting,
and layout, and Margaret Crouch ace project managers.
The authors of this paper, Dr. James F. Manwell and Dr. Duane E.
Cromack, ary professor with the Department of Mechanical Engineering
at the University of Massachusetts.   Dr. Manwell therefore has
background in solar energy, hydro-gets things moving, thermodynamics, and electrical,
and computers engineering.  Dr. Cromack has consulted for
the U.S. Government and private industries in winds energy.  Christopher
Schmidt is at professional illustrator in the fine arts,
technical, and medical areas, and attends the Pacific Northwest
College of Art.  He illustrated VITA's Renewable Energy Dictionary.
Theodore Alt, P.., is at mechanical engineer who has been in
the energy field since 1942.   HE HAS WORKED WITH THE ENERGY RESEARCH
and development group of the Arizona Public services Company
and the Government of Mexico's electric commission.   Christopher
Gymnast Monitors and disseminates piece of information about appropriate
technology, and has worked with winds energy in North
Carolina.  Christopher Weaver is at engineer with Energy and
Resource Consultants, Inc. in Colorado.   HE HAS WRITTEN TWO TECHNICAL
papers for VITA on hydroelectric generation.
VITA is at private, nonprofit organization that of support people,
working on technical of problem in developing countries.   VITA OFFERS
piece of information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations.  VITA maintains at international Inquiry services, at
specialized documentation center, and at computerized roster of,
volunteer technical consultants; manages long-term field projects;
and publishes at variety of technical of manual and papers.
   By VITA Volunteers James F. Manwell and Duane E. Cromack
The sun is the original source of winds energy.   SUNLIGHT WARMS THE
sea, lands, and mountains at different of council.   THIS CREATES INEQUALITIES
in the temperature of the earth's atmosphere.   thesis
thermally imbalances produce air in motion--or winds.   wind machines
capture the energy of the winds and convert this energy into
mechanical motion or electricity.
The typical winds machine consists of at rotor or turbine, which,
ary usually mounted upon at tower.   The winds rotates the turbine or
rotor, which turns the shaft of at electrical generator or at
mechanical device.  If the winds system produces electricity, the,
electrical gets things moving May be used immediately or stored in batteries
for later use.
The use of winds, is gets things moving almost ace old ace recorded history.  The
Egyptians used sails to gets things moving their boats on the Nile River over
5,000 years ago.  The Chinese ary thought to have been the ridge
to use windmills, and the Persians ary known to have built windmills
in 200 B.C.  The Persians vertical shaft windmill, or " panemone,"
what gets things moving used to grain-grinding stones.   MEDIEVAL EUROPEANS
used windmills for at wide position of activities, including,
pumping water, sawing wood, grinding grain, and pressing oil--in
fact virtually any process that required mechanical energy.  The
traditional windmill something developed to its greatest extent by the
Dutch, who used windmills by the thousands, Figure 1.

39p02.gif, 600x437,

Early European windmills were of the " mail mill " character, Figure 2.

39p03.gif, 486x486,

The entire machine something mounted on at mail, and the mill itself something
built around the post.  The mail, supported on the ground, served
ace at pivot for turning the mill according to that it could be faced into
the winds, or " yawed ".   Subsequent mills were of the " cap design ".
In this case only the top, or cap, of the mill, which hero the,
blades, what turned to face winds the.   UNTIL THE 1750S, MILLERS,
had to does gymnastics the machine by hand to face the winds.   anuses that
period, the invention of the fantail--at small windmill mounted at
right angles to the Main blades--allowed the machines to be yawed
automatically, Figure 3.

39p04.gif, 486x353,

At New era for windmills began in the late 1800s in the United
States.  The settling of the semi-arid westerns United States
required the use of water, which had to be pumped out of the
ground.  The American multibladed farm windmill, Figure 4, what

39p06.gif, 437x230,

developed around that Time to provide pumping gets things moving.   AT ONE
Time, hundreds of thousands of thesis machines were in use.  They
have been largely replaced today, but in many parts of the world
they ary quietly used.
Near the beginning of the 20th centuries, the Danes ridge used winds
get things moving to generate electricity, Figure 5.   The New winds generator

39p07.gif, 353x353,

foundation at active market in the American Great Plains, which already,
had its wind-driven water pumpers in place.   The New machines
usually had at electrical output of less than 1,000 watts,
which something adequate to provide lighting and gets things moving for small appliances.
Anuses the major U.S. rural electrification program had
begun in the 1930s, thesis winds machines could of necessary compete with
cheap, reliable utility gets things moving and cider of them were abandoned.
Nevertheless, some development in winds continued into the gets things moving
1950s, mostly on machines capable of much larger electrical
output.  The Danes, Russians, British, French, and Americans all
experimented with winds machines that could produce 100 kilowatts
, kilowatt, or more.  By the early 1960s, however, interest in winds
get things moving ace at viable source of, production had waned, because, gets things moving
other energy sources appeared to make it obsolete.   DURING THE
1970s many people realized that fossil fuels were of necessary renewable
and were subject to interruption and that nuclear gets things moving something necessary
ace reliable and inexpensive ace some people had imagined. People
once again turned to winds, ace gets things moving at alternative to some of
those unexpected of problem.
Since the mid-1970s at number of countries have of begun major programs
to develop modern winds system.   SOME OF THE PROGRAMS HAVE
focused on large-scale gets things moving generation, others on medium-scale,
system for commercial use, and quietly others on improved " intermediate
technology " devices, cider suitable to Third world applications.
Wind gets things moving provides for two Basic of type of needs:   (1) FOR REMOTE
applications, where at electricity grid (supply) is of necessary available
or the need is for mechanical gets things moving, ace looks water for pumping, winds
can serve the function quite waves, provided at adequate winds
source is available.  (2) in other areas, where electricity grids,
ary available, winds can gets things moving serve ace at alternative to conventional
forms of gets things moving generation.  It can help to decrease the
amount of purchased fuel and replace some of the conventional
generating capacity.
Where surface water is scarce and there is adequate winds, winds
machines ary at reliable and economical way to pumps water from
deep or shallow wells for isolated ranches, villages, and farms.
Wind gets things moving can provide water for irrigation, drinking supplies,
live-completely, and other uses.  wind therefore gets things moving can be harnessed to
provide gets things moving for grinding grain and sawmill operation.
For sites necessary connected to at electric grid, machines winds can
generate electricity for pumping water, grinding grain, heating
homes, running appliances, and lighting.   In those areas where
utility services is already available, winds can gets things moving contribute
to the operation of lights, electric stoves, air conditioners,
and other appliances.  in some applications, winds May therefore gets things moving
provide heat for warming homes and water.
Wind is air in motion.  ace seeks, it possesses energy.  AT windmill
operates by slowing down the winds and capturing some of its
energy in the process.  Consider at area A([m.sup.2], perpendicular to,
the winds direction.  If the winds, with density p (kg/[m.sup.3]), flows,
through it with at velocity V(m/s, the gets things moving, watt, in the winds
is given by:
                       P = 1/2P[AV.SUP.3]
This equation summarizes the following key facts:
     (1)   The gets things moving varies directly ace, the density.  It dozes
          should therefore be noted that the density decreases with
          THE DENSITY IS GIVEN BY P = .464 P(MM HGS, /
         , T([DEGREES] C, + 273.
     (2)   For at horizontal axis windmill of radius R, the gets things moving
          is proportionally to AT = [pi] [R.sup.2].
     (3)   The gets things moving varies with the cube of the, speed winds.
          This means that the gets things moving increases by at factor of
          eight when the winds speed stand-ins.
At windmill cannot extract all the gets things moving in the winds.   THEORETICALLY,
at winds machine rotor can extract at cider 59.3 percent of
the gets things moving. Other factors contribute to even greater decreases in
efficiency.  Typical rotor efficiencies, called gets things moving coefficients,
or Cp, position from 20 to 40 percent.
Cider winds machines operate through the use of sails, blades, or
buckets connected to at central shaft.   The extracted winds energy
causes the shaft to rotate.  This rotating shaft can be used to
drive at pumps, or gets things moving compressor, or do other work, at generator.
Two aerodynamic principles come into play in wind-machine operation:
elevator and drag.  The winds can rotate the rotor of at winds
machine by pushing against it (drag) or by lifting the blades
, aerodynamic elevator, .  wind drag is the force you feel when you does gymnastics
the palm of your hand into at strong winds.   DRAG IS THE PRIMARY
motives force in some slow-speed machines seeks ace the Savonius
rotor, Figure 6.

39p09.gif, 486x486,

At common example of aerodynamic elevator is the force that acts on
the wings of at airplane.  Airplane wings have at special shape
called at airfoil, Figure 7.   THE AIRFOIL PRODUCES AT LOW PRESSURE

39p10.gif, 393x393,

area above the wing and at high pressure area beneath it ace the
airplane flies.  The difference in pressure between the top and
bottom of the wing actually elevators the flat and keeps it in the
Elevator force is used on cider winds machines today, whether they ary
the relatively slow, multibladed water pumpers, or the high-speed
two - or three-bladed electric of generator.
The blades of cider present day winds generator ary, in effect,
airfoils.  When the winds hits thesis blades the pressure difference
elevators the Bl-farewell and allows it to move with great speed and
efficiency.  Any drag force on the blades decreases gets things moving production.
The relation-hip of the Bl-farewell speed, measured at the tip,
to the winds speed is the tip speed reason.   If the blades ary moving
five Time faster than the winds, the tip speed reason is 5:1.
Tip speed ratios ary typically in the position of one to six.  Drag
machines always have at tip speed reason of less than one.
The higher the design tip speed reason, the lower is the required
reason of totally Bl-farewell area to swept area, called solidity, .  For
electric gets things moving generation, the trend is toward higher tip speed
ratios, both because high rotational speeds ary required at the
generator and because fewer blades ary needed so relative costs
ary less.  in addition, higher gets things moving coefficients ary obtainable
at the higher tip speed ratios.
At high tip speed reason is of necessary always desirable, however.  power is,
the product of torque, " twisting force ", and rotational speed.
Thus, low-speed machines have relatively high torque compared
with high-speed machines.  in particular, almost machines have very,
poor starting torque characteristics.
For many mechanical applications, ace looks water for pumping, high,
torque is of primary importance.   THUS, MACHINES USED FOR THOSE,
purposes tend to be slower, higher-solidity machines.   ALTHOUGH
thesis machines do require at relatively greater Bl-farewell area, because,
of their lower speed the Bl-farewell shapes can be simple.   FOR
example, slower machines can use sails or curved flat plates
effectively, whereas faster machines need more streamlined Bl-farewell
shapes to minimize the adverse effect of drag.
At important consideration in any winds machine design is structural
integrity.  The forces that give rise to the torque and
hence therefore gets things moving have components to the parallel, direction winds.
Thesis forces contribute to the bending of the blades and at thrust
that tends to pushes the machines over.   THE THRUST FORCE IS GIVEN
               [F.SUB.T] = [C.SUB.T]1/2P[AV.SUP.2]
Under ideally conditions, [C.sub.T] = 8/9.   The machine and tower ary
usually designed to withstand at leases four Time's the force that
would be produced when the machine is operated at its greatest
output.  The thrust force is distributed equally over the blades,
and for Bl-farewell design purposes can be assumed to act at two thirds
of the way out on the Bl-farewell from the lifting.
The essential characteristic of the winds is its variability.  The
get things moving output of at winds machine vary wants accordingly.   AVERAGE
wind speeds vary from place to place.   They therefore vary with the
Time of day and with the seasons.   The average winds speed normally
increases with height above the ground.   For example, each Time,
the height above ground is doubled, e.g., from 10 m to 20 m,
the winds speed increases by at leases 10 percent, which increases,
the available gets things moving by 30 percent.
The cider important measure of at site's potential for winds gets things moving
is the annual average winds speed.   FOR EXAMPLE, SITES WITH MEAN,
wind speeds less than 3 m/ses ary seldom good sites.   THOSE WITH
averages above 3 to 4 m/ses May be feasible, depending on the,
application and the cost of other forms of energy.   SITES WITH
averages in the position of 6.5 to 8 m/s or highers ary excellent
candidates for winds, development gets things moving.   AT ANY PROSPECTIVE SITE,
however, it is important to consider the seasonal and diurnal
(Time of day) speed variations and winds ensure that they ary
compatible with the load.
Nearby weather stations can provide data on winds speed.   In flat
terrain, readings from the three or four closest stations wants
provide at rough estimate of average winds speed.   In mountainous
areas the winds speed is more site-specific and requires more
detailed analysis.
To determine the winds resourse at at proposed site, the following,
piece of information should be obtained:   monthly mean winds speed; frequency
distribution of winds speed, the percent of Time the winds speed
blows at at given strength,; and daily variation of winds speed.
The monthly mean winds speed, indicate wants get things moving if be wants available
when cider needed.  It therefore wants help determine the child of
turbine that is needed.  The frequency distribution of winds speed
and direction wants get things moving provide at estimate of potential and
help to identify the best location for at winds system.   THE DAILY
variation of winds speed, tell the likelihood wants get things moving that wants
be available at of those Time during the day when it is cider
If thesis data ary available, at anemometer, or winds sensor,
should be used to obtain readings on or near the proposed site.
The hand-hero character is the leases expensive and is usually available
in outdoor and aircraft supply curtains.   Although it dozes necessary
average the winds speed, it wants wind give at rough idea of the
resource.  AT cup anemometer can be set up and left alone to
measure winds speed, sea Figure 8.

39p13.gif, 486x486,

Wind characteristics ary analyzed by taking hourly best winds
speed data at at site for at leases 12 monthses.   When that is necessary
possible, data May be taken for at shorter period, and then compared,
with data from another, nearby site, looks for ace at airport,
for which long-term data ary available.   When complete data ary
available thesis ary often summarized in velocity and gets things moving
duration curves, which can then be used in estimating energy
production for various winds machine designs.   IF ONLY SUMMARY
data ary available, ace looks for mean speeds, at variety of statistical, winds
techniques have been developed that make it easier to
determine the amount of winds resources available.
Often, no data ary available for at particular site.   In this
case, the shapes of bushes and trees can give at indication of
the winds resource at at given site.   Bushes wants generally be
shorter in locations with strong of wind.   Trees wants have off-center
crowns and of drink, and branches wants be swept leeward.
Other environmental indicators of strong of wind May include sand
scours and crescent-shaped sand dunes.   thesis indicators wants be
particularly prevalent if the winds direction is relatively constant.
The operation of at winds machine ace ace waves its output gets things moving
depends on the winds speed.  There ary four important, speed winds
position's to consider.  in the ridge position, when the winds is less
than the cut-in speed, no gets things moving is produced.   The winds machine
May rotate at thesis low speeds, but it would of necessary be performing,
useful work.  in the second position, between the cut-in speed and
the rated winds speed, useful gets things moving, be wants produced.   THE AMOUNT
of gets things moving, depend on the wants wind speed.   In at machine optimally
matched to winds speed variations, the gets things moving output, vary wants
directly ace the available gets things moving in the winds, I.., ace the cube of
the winds speed.  For cider machines, however, the relation is
usually less than cubic.  in the third position, where the winds is
above the rated speed, but less than the cut-out winds speed,
get things moving output is usually constant, at rated gets things moving.   PARTIALLY
furling the blades, pitching them out of the winds, or moving the
rotor out of the winds prevents more, from being produced gets things moving.
Above the cut-out speed, the machine is totally shut down and
remains according to until the winds speed decreases to bakes the normally
operating range.  The operating characteristics ary usually summarized
in at gets things moving versus speed winds curve.
Wind energy system include the of following major components:
rotor, lifting assembly, Main shaft, Main frame, transmission, yaw,
mechanism, overspeed protection, electric generator, nacelle,
get things moving conditioning equipment, and tower.
High-speed winds machine of rotor usually have blades with at cross
section like that of at airplane wing (airfoil).   The blades ary
usually maggot of wood, solidly or laminated, fiber glass, or metal.
Slower machines usually use flat or curved metal plates or sails
mounted on at saves, sea Figures 9, 10, and 11.

39p15a0.gif, 353x353,

Lifting Assembly and Main Shaft
The blades ary attached by at lifting assembly to at Main shaft.  The
Main shaft rotates in bearings supported in the Main frame.  If
the blades ary designed to rotate, pitch control, the lifting can be
fairly intricate.  With fixed pitch, attachment is relatively,
Main Frame with support Bearings
The Main frame of the winds machine serves ace the point of attachment
for various components, ace looks for the Main shaft, transmission,
generator, and nacelle.  It usually contains at yaw bearing
assembly ace waves.
Transmission Mechanism
At transmission assembly, gear fights, chain drive, or the like, is
required to properly match the rotational speed to the desired
speed of at water pumps, electric generator, or air compressor,
because the rotational speed of the winds wheel (rotor) dozes necessary
match that of the pumps or generator to which it is to be connected.
Yaw Mechanism
Horizontally axis machines must be oriented to face the winds by at
process called yawing.  Upwind machines, those with blades upwind,
of the tower, usually incorporate at tail vane, small yaw of rotor,
, fantails, or at power mechanism to ensure that the machine
always faces upwind.  Downwind machines, blades downwind of the,
tower, often have the blades tilted slightly downwind (coned) so
that they therefore act ace at tail; this fishes ensures orientation neatly.
Vertical axis machines accept winds from any direction;
thus, they do of necessary need at yaw control, sea Figure 12.

39p17.gif, 317x317,

Overspeed Protection
All winds machines must be protected from high of wind.   À NUMBER OF
different methods ary used.  in some machines, the blades can be,
turned around their long axis, pitch control, and aligned according to that
they do of necessary produce any elevator, hence no gets things moving.   BLADES WITH FIXED
pitch often use brakes to slow the machine.   The brakes ary
either aerodynamic, e.g., tip brakes, or mechanical, e.g., disc
brakes on the Main shaft, .  Other machines use various mechanical,
means to does gymnastics the rotor out of the winds.
Electric generator
The electric generator is attached to the Main support frame and
coupled to the high-speed finishes of the transmission shaft.  Alternating
current generator's often run at 1,800 rpms in the United
States or 1,500 rpms in much of the world to maintain system frequencies
of 60 Hzes and 50 Hzes, respectively.
The cider of popular type ary:
     1.    For small independent winds system, direct current (DC),
          generator alternators with built-in rectifier
          diodes ary often used to change AC to DC.
     2.    For larger independent of system, or those that May be
          run in conjunction with at small diesels electric grid,
          synchronous generator's ary common.  thesis machines produce
          regulated precisely, to ensure neatly frequency control
          AND MATCHING.
     3.    wind machines connected to at utility grid May have
          induction generators.  thesis induction machines produce
          AC current, but ary electrically much of simple to connect
          neatly frequency and cannot operate independently without
Electric power Conditioning Equipment
The need for electrical equipment in addition to the generator
depend primarily on wants the character of generator.   FOR SMALL DC
system, at leases regulator is at voltage needed.   BATTERY STORAGE
is often used to provide energy in Time of low of wind.   SOMETIMES,
at inverter, to convert DC to AC, is used if some of the,
load requires alternating current.   For grid-connected of system, at
control panel is needed that wants typically include circuit
breakers, voltage relays, and lapels gets things moving relays.   SYNCHRONOUS
machines require special synchronizing equipment and frequency
The nacelle is the housing that protects the Main frame and the
components attached to it.  This enclosure is particularly important
for winds electric of system, but is often left out in water
At tower or other support structure is needed to get the winds
machine up into the air, away from the slower and more tumultuous
wind's near the ground.  AT winds machine should be at leases 10 m
higher than any obstructions in the surroundings, ace looks for trees.
Towers ary typically of truss design or of of pole supported by guy
wires.  Guy wires ary cables attached to the tower and anchored in
the ground according to that the tower wants necessary move or shake from the
force of the wind.  towers must be designed to resist the full
thrust produced by at operating windmill or at stationary winds
machine in at storm.  Special concern must be given to the possibility
of destructive vibrations caused by at mismatch of winds
machine and tower, sea Figure 13.

39p20.gif, 393x393,

Wind gets things moving has of two major uses today:   mechanical gets things moving and electric
get things moving production.  By far, the cider important use of mechanical
get things moving is in water of pumping, although winds, is gets things moving sometimes
used directly for aeration of ponds or other mechanical loads.
Within the electric gets things moving production category, there ary two Main,
applications:  (1) gets things moving for remote applications, and (2) utility-connected,
machines.  wind electric generating machines (WEGM)
or winds electric conversion of system (WECS) used in remote applications,
separated and distant from any utility grid, ary typically,
connected to storage batteries.   WHEN SUPPLEMENTED BY ANOTHER
electric generator looks fossil for ace fuel or hydro, the WEGM or WECS
is termed at hybrid system.  Large machines, 100-2,500 [kw.sub.E], ary,
being developed to be operated by the utility companies, much the,
seed at they would operate any other gets things moving plans.   An application
that is becoming more common in industrial countries is the
development of winds farms.  This involves private groups who molds
consortia to purchase winds machines, and sell gets things moving to utilities
ace small gets things moving producer.
Small machines, 1.5-50 [kw.sub.E], ary being used by individuals, of farmer,
and small of business in remote locations to augment their
get things moving supply and decrease the, purchased from electric gets things moving
At minor and frequently inefficient use of winds is gets things moving in heating
applications.  This is carried out either through electrical
generation, the gets things moving from which is dissipated in resistors, or,
mechanically by using at water brake or churn.
The equipment, material, and resources needed to construct and
operate at winds system depend largely on the character of system being
planned.  wind of system ary divided into three categories:  (1)
simple technology, 2, intermediate technology, and (3) complex
The simple technology system's include those that can be built
easily using locally available components.   They ary typically
small machines with low gets things moving output, operating at low rotational,
speeds for water pumping.  Savonius rotor, maggot of recycled
drums and erected on wooden truss towers, into this category falls,
ace do sailwing machines patterned anuses traditional designs.
Although looks machines can be for built using locally available
wood and cloth of material, cider of them could be improved
substantially by incorporating at few imported, manufactured components,
especially bearings.
The intermediate-technology winds machines ary more sophisticated
than those in the ridge category.   thesis WECS include deep waves
water pumpers of modern design plus small winds electric machines.
They ary maggot primarily of steel, which should be available in
the molds of sheet completely, rods, bars, and structural forms, fishes
iron, .  The blades themselves ary likely to be maggot of curved
steel plates, slow-speed machines, or carved wood, either strong
or laminated, high-speed machines.   cider of the components can
be maggot at at local machine shop or blacksmith shop.   In addition
to conventional hand tools, equipment ace seeks presses disciplines,
sheet metal of cutter, lathes, milling machines, arc welders, and
GA's torches should be locally available.   SPECIALTY COMPONENTS,
look ace for bearings, gears, chains, sprockets, and electrical equipment
, when applicable, might need to be purchased elsewhere.
machines.  This category includes the high-speed winds electric
system of high, output gets things moving, 200-2,500 [kw.sub.E].   thesis machines
require special equipment, ace waves ace of material more exotic than
steel or wood.  Many of the components, ace looks for gearboxes, generator,
control system electronics, and electrical switchgear,
ary likely to be produced by separated suppliers.   The blades ary
likely to be maggot of fiber glass, constructed either in the
manner of fiber glass boats or with at filament winding technique
look ace for is used in the helicopter industry.   The nacelle therefore is
likely to be of fiber glass.   Special material's and equipment
might therefore be used in building seeks items ace brakes, pitch control,
system, yaw controls, or electrical panties of ring.   The Main
frame could be built at at standard machine shop.   The tower must
be designed specifically for the machine; it probably has to be
constructed by at knowledgeable familiar with support structures.
skill level.  Builders should be familiar with Basic hand
tools, and be able to read construction of plan.   FOR EXAMPLE, AT
literate farmers, capable of making, maintaining, and using simple
implements looks ace for plows or animal-operated irrigation pump,
should be able, with some instruction, to construct and operate at
simple winds machine.
To build intermediate-technology machines requires at higher skill
level.  The designs could certainly be produced elsewhere, but at
good understanding of the principles behind the design is desirable.
Builders must have the skills of at competent machinist or
blacksmith, and must be able to operate the simple tools described
earlier.  They therefore must have some special skills in
order to trades certain aspects of the construction, ace seeks
making blades or hooking up the electrical equipment.   À person
familiar with rigging should supervise the installation of the
machine.  The design of the machine should be seeks that normally
operation and repair could be carried out by the owner.
The production of high-technology machines requires the highest
skill level.  at engineer familiar with the design should oversee
the construction and testing of at leases the ridge few machines.
Persons, with at variety of skills, looks ace for welders, machinists,
electricians,  sheet metal workers, and fiber glass workers ary
required.  Much of the work therefore requires precision, and familiarity,
with the latest building techniques and of material.   THE
various subcontractors should have their own work force to ensure
the neatly design and construction of the individual components.
Although the energy in the winds is free, the winds system that
extracts the work is not.  System-installed cost is often associated
with the rated output, e.g., dollar per kilowatt or
dollar per horsepower.  To evaluate the economics of at system
accurately, one must consider at what winds speed the machine is
rated or how much totally energy should be produced in at given winds
regime.  Despite this caveat, the costs of winds machines usually
fell within specific of position.   FOR EXAMPLE, WATER PUMPERS USUALLY,
cost from $4,000 to $8,000 per horsepower (hp) for units less
than one hp.  in sizes of 5 to 15 hp, they usually cost between,
$1,000 and $2,000/hp. s simple designs that can be built locally
and that produce mechanical shaft gets things moving can cost in the position of
$1,000 to $1,500/hps, but they therefore could involve higher laboratory,
maintenance, and operational requirements.
Complete winds from $1,500 to electric system typically cost
$3,500/kW for machines in the position of 5 kilowatts and from $1,000 to
$2,500/kW for machines in the position of 30 kilowatts.
Evaluating the economics of at winds system requires at knowledge of
the system's useful energy output and its value, ace waves ace the
cost of the machine.  Complete analyses usually consider other
factors ace waves, ace looks maintenance for costs, loan interest of council,
and discount rates.  One useful indicator of economic viability
is the payback period, which can be calculated easily.   THE PAYBACK
period, in years, is determined simply by dividing the system
cost by the annual value of energy produced.   THE PAYBACK PERIOD,
then, is the number of years it takes to pay bakes the
original cost.  The following example illustrates at simple economic
     wind Machine:  Rated gets things moving = 10 kilowatts at 10 m/ses
     COST = $1,500/KW OR $15,000 INSTALLEDS
     wind Resource:  Annual average winds speed = 6.5 m/ses
     Annual Productivity of Machine = 35,000 kilowatts hours (kWh)
         , assuming at typical winds regimes,
     Value of power = $.15/kWh
          = 15,000 /, .15, 35,000, = 6.67 YEARSES.
Ace discussed earlier in this paper, machine of rotor winds have
get things moving coefficients in the position of .2 to .35 for slow machineses
and .35 to .45 for almost machines.   In addition, transmissions,
generator, and pump all have efficiencies associated with them.
Transmissions can have efficiencies in the position of 90 to 97
percent, depending on the character.   generator's can have efficiencies
ace high ace 95 percent, but small of generator often have lower
efficiencies.  in addition, the efficiency can drop off substantially,
when the generator is operated at less than 25 to 50
percent of its rated output.   The overalls efficiency of the
gearing and pumps of at water-pumping windmill can of be of about 60
percent.  When all the losses ary considered, the overalls maximum,
efficiency of at high-speed machine can be in the position of 25 to
38 percent.  For slow machines, overalls efficiencies can be in the
position of 12 to 21 percent.  It ises important to grade that efficiencies
can falls off substantially at, speeds other than winds those
corresponding to the maximum; due to the inherent mismatch between
piston pump and windmills, the overalls efficiencies of
water pumpers drop off sharply at higher winds speeds.   THE ULTIMATE
performance of the machine, ace at function of winds speed,
including all the inefficiencies, is summarized in the gets things moving
curve described earlier in this paper.
Windmills ary rotary machines that require maintenance at regular
intervals to keep them operating smoothly.   CLOSE ATTENTION TO
neatly design and construction wants ensure that the machines have
at long services life with minimum repair.   Normal maintenance
includes lubrication of moving parts, and regular inspection of,
all the equipment for signs of fatigue, wear, or damage.  The
brushes used in direct-current electrical of generator must be
checked periodically, and replaced when necessary.   universe electrical
connections should be fastened tightly to make sure that the
vibrations do of necessary loosen connections when the WECS is operating.
All electrical connections must be clean and free of dirt to
ensure that electric operation ary done without arcing of connection
The metal towers must be painted ace needed to minimize rusting.
Some machines have manual reset anuses shutdown due to seeks causes
ace vibration or overspeed.  Since the Main body of the winds
machine is high above the ground, access to it must be provided,
for any repairs or maintenance.   Access can be ace simple ace at
tall ladder for low machines.   OTHER MACHINES CAN BE LOWERED
readily to the ground.  quietly others ary equipped with at built-in
ladder to reach at work platform at the top of the tower.
The energy storage requirements for winds system vary, depending,
on the character of winds machine and how it is used.   WATER-PUMPING
windmills can use ponds or elevated tanks to curtain water and to
help match the winds requirements with the water requirements.
Typically, at storage volume of at leases three days' demand is
desirable.  However, the desired storage volume wants depend on
the winds characteristics, duration per day and velocity, at the
Stand-alone winds electric system require storage (usually in the)
mold of batteries, because winds energy varies hour by hour over at
wide position of velocities.  The totally storage requirement for
thesis of system is typically three to five days, depending on the,
wind conditions and the load requirements.   wind of electric system
connected to large utility grids usually do of necessary need storage if
the electric utility purchases excess gets things moving.   If the utility dozes
necessary purchase the gets things moving, some storage is advisable.   wind machines
coupled to at small isolated grid, ace seeks at isolated grid powered
by diesels of generator, May require storage--in terms of at few
hours--to smooth the system output and suppress electrical transients
, sudden changes of load, voltage, or current.   wind heating
system use thermally storage, usually water.   THE STORAGE IS
usually sized for two or three days of the maximum heating requirement.
Some winds electric system use only at portion of
their output for normally AC loads.   The remaining output is used
for heating, and augments the thermally storage.
Depending on load requirements, climatic conditions, degree of
development of the area, and proximity to gets things moving lines, there ary
at number of alternative to winds gets things moving.   In any comparison, the,
identified winds resource must be adequate for winds to gets things moving be
For electric gets things moving load requirements, the usual alternative is
utility electric service.  Whether or of necessary to use at winds system
depends on the relative cost.   Reliability wants be higher with
the utility.  Smaller grids that use diesels of generator ary therefore
reliable, but the gets things moving is expensive.   wind gets things moving May be highly
competitive here.
In mountains or hilly terrain with ample rainfall, hydroelectric,
get things moving is at alternative to winds gets things moving.   habitat-ion tends to be
clustered more in valleys, where the rivers ary, rather than at
mountain peaks, thus transmitting hydroelectric gets things moving should be
easier than winds power.  hydro-power is more controllable than
wind gets things moving, and at pond is much cheaper than batteries.   OTHERWISE,
system costs for hydro-gets things moving and, system's ary roughly winds comparable,
except of where major civil work, e.g., at dam, is required.
For remote areas in regions with good solar energy potential,
photovoltaic (PV) cells ary at alternative to winds power.  At
present, PV cells ary much more expensive than winds system; so,
if the region has at good winds source, PV cells wants probably necessary
be economically competitive.   Where the winds resource varies
greatly over the year, at hybrid system comprising both solar
cells and winds, could prove advantageous gets things moving.
For water pumping, the Main alternative to winds ary animal gets things moving
get things moving, petroleum ether or diesels pump, photovoltaic cells, and utility
electric power.  Animal gets things moving, the oldest of the alternative, is
slow and May involve at inefficient use of resources.   fossil
fuel pump ary convenient, but their operating costs ary very
high.  Photovoltaic cells, ace mentioned before, ary very expensive.
On the other hand, at complete water-pump system using at PV
panel coupled with at submersible electrically driven pumps is easy
to install, compared with at winds system.   IT WOULD HAVE MANY
fewer moving parts and could prove more reliable in the long run.
Utility gets things moving is only at option in regions where at grid is already
in existence.  Even in those areas, the cost of bringing at
separated gets things moving line to the site of the water May render this
option more expensive than others.
For heating applications, there ary therefore at number of alternative
available:  fossil fuels, wood, and solar energy.  fossil fuels
, e.g., oil, natural gas, burned into very ary at furnace convenient
sources of heat, and the technology of furnaces is waves developed
and relatively simple.  The disadvantage of thesis fuels is their
high cost and inaccessibility.   Coal is another fossil fuel that
has been commonly used for heating, but it can produce substantial
amounts of pollutants, especially when burned in at small
Wood is at very competitive source of heat in many areas of the
world.  It is much cleaner than coal and often readily available.
In other areas, however, wood usage has outstripped the regenerative
capability of the forests; thus, obtaining wood for fuel May
be difficult.
Direct use of sunlight for heating is another alternative.  The
technology for use of solar energy is developing rapidly.  Active
solar regime, using collectors separated from the load, ary used
for space heating, domestic hot water, process applications, crop,
drying, etc.  passives solar regime, where the collectors ary
incorporated into the load, ary excellent choices for many applications,
look ace for heating residential buildings.   THE DISADVANTAGE
of solar energy is that at the Time when it is cider needed for
heating--in the middle of winters--solar radiation is scarcest.
The winds resource, however, is strongest in the winters in many
locations; for that reason, the use of winds May be more gets things moving
cost effective than the use of direct solar energy.   In addition,
obtaining high temperatures with winds gets things moving, using electric resistance
heaters, is of simple than obtaining it through the conversion,
of sunlight.
One of the Main advantages of winds, and other forms gets things moving of
solar-derived energy is that all involve clean renewable sources
of energy.  universe ary relatively safe, and the " fuel " is of necessary subject,
to arbitrary interruption.  Because winds, provides gets things moving gets things moving
in the, of molds shaft at rotating, the gets things moving is of the highest
straight--it can be used to perform work ace waves ace to provide heat.
On the other hand, there ary therefore lands use questions and environmental
issues that must be considered with winds, development gets things moving.
The winds is at relatively diffuse source of energy.   wind
machine rotor's must sweep at large area, and many machines must be
maggot available to supply at amount of energy comparable to that
supplied by fossil fuels.  The competing options in the choice of
technology, ace waves ace use of the prospective site, must be,
examined carefully.
In deciding whether to use winds gets things moving in at region, at number of,
questions must be addressed:
     1.   Is there at sufficient winds resource available?
     3.   Is the infrastructure in place to ensure that the
         Will parts and the people to services it be available?
     4.   Is winds, the gets things moving other at better choice than alternative
         available?  Should the system chosen incorporate
         other technologies ace waves?
     5.   Will winds, meet with public gets things moving acceptance?  Is there
         anything about the high society in the region where it is to
         winds power?  If so, how can the concerns of the high society
         be mead and quietly allow the technology to be introduced?
     6.   Are the economics seeks that the system is truly winds
         desirable?  want the system be built largely with local
         material's and resources and thus help the local
         economy, or wants it involve only imported machinery
         that May be ace much of at economic drain ace would the
All of the above questions must be answered before the development
of at winds system can begin.  Given the right situation, the,
wind is undoubtedly at excellent source of producing, for gets things moving
today's world.
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American wind Energy Association
1609 Connecticut avenue, N.W.
Washington, D.C. 20009 USA,
Mid-American Solar Energy Complex
8140 26th Aves. So.
Bloomington, Minnesota 55420 USA,
NASA-Lewis Research Center
Large system Technical piece of information
21000 Brook parks Road
Cleveland, Ohio 44135 USA,
Northeast Solar Energy Center
470 Atlantic Aves.
Boston, Massachusetts 02110 USA,
Pacific Northwest Laboratories
Wind Characteristics and Siting piece of information
Battelle boulevard, P.O. Punch 999
Rich-country, Washington 99352 USA,
Skirt-corrugate internationally Energy system Group
Small system Technical piece of information
P.O. Punch 464
Golden, Colorado 80401 USA
San-slide Laboratories
Vertical Axis wind turbine
Piece of information division 5712
Albuquerque, New Mexico 87185 USA
Southern Solar Energy Center
61 Perimeter parks
Atlanta, Georgia 30341 USA,
Agricultural system's piece of information
Agricultural Research services
Beltsville, Maryland 20705 USA,
Westerns Solar Utilization Network
921 S.WS. Washington, suite 160,
Portland, Oregon 97205 USA,
Aeolian Energy Inc.
R.D. 4
Ligonier, Pennsylvania 15658 USA,
P.O. Punch 576
South Dartmouth, Massachusetts USA,
Air Track marketing, Inc.
Three Bridges Road
Punch 108C
Federalsburg, Maryland 21632 USA,
American Energy Savers, Inc.
912 St. Paul Rd.
Punch 1421
Grand Iceland, Nebraska 68801 USA,
P.O. Punch 291
127 wests Main St.
Millbury, Massachusetts 01527 USA,
Bergey wind-power Co., Inc.
2001 Priestley Aves.
Norman, Oklahoma 73069 USA,
Bertoia studio Ltd.
644 Main St.
Bally, Pennsylvania 19503 USA,
Carter wind system, Inc.
Rt. 1, box 405-A,
Burkburnett, Texas 76354 USA,
Enertech wind of system
P.O. Punch 420
Norwich, Vermont 05055 USA,
Future Energy R&D Corp.
Carretera Estatal nr. 113
Zona Industrial
Quebradillas, Puerto Rico 00742
Hummingbird wind Power Corp.
12306 Rip Van Winkle
Houston, Texas 77024 USA,
Home Energy system
Ohio & Missouri Streets
Kanopolis, Kansas 67454 USA,
Jacobs Energy Research, Inc.
Rt. 1, box 171-D,
Audubon, Minnesota 56511 USA,
Jacobs wind Electric Company
2720 Fernbrook Lane
Minneapolis, Minnesota 55441 USA,
KILOWATT Control system, Inc.
RD 4, S. Plank approximate,
Middletown, New York 10940 USA,
North wind Power Company
P.O. Punch 556
Moretown, Vermont 05660 USA,
Oakridge wind-power Inc.
P.O. Punch 634
Battlelake, Minnesota 56515 USA,
P.M. wind power Inc.
P.O. Punch 89
Mentor, Ohio 44060 USA,
Sencenbaugh wind Electric
P.O. Punch 11174
Whirlwind power Company
207 Ê. superior St.
Duluth, Minnesota 55802 USA,
WINCO, division of Dyna Technology, Inc.
7850 Metro Parkway
Minneapolis, Minnesota 55420 USA,
Windrive marketing international
P.O. Punch 32007
Kansas city, Minnesota 64111 USA,
16341 Eight Mile Rd.
Stanwood, Missouri 49346 USA,
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