Windmill Technical

UNDERSTANDING WIND ENERGY By VITA Volunteers James F. Manwell and Duane E. Cromack I.

INTRODUCTION

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 HISTORY OF WIND POWER 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. 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.

AT ONE

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 POWER:

NEEDS IT SERVES

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. II.

BASIC WINDMILL THEORY

GET THINGS MOVING IN THE WIND 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 INCREASING TEMPERATURE AND DECREASING ATMOSPHERIC PRESSURE, E.G., CAUSED BY INCREASING ALTITUDE, . AT SEA, LEVEL AND 15 [DEGREES] C, P = 1.225 KG/[M.SUP.3S] . UNDER OTHER CONDITIONS, 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.

ACTUAL POWER 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. BASIC WIND MACHINE DESIGN 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 air. 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 by: [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.

WIND CHARACTERISTICS The essential characteristic of the winds is its variability. The get things moving output of at winds machine vary wants accordingly. 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.

AVERAGE

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 needed. 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. WIND MACHINE OPERATING CHARACTERISTICS 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. III.

DESIGN VARIATIONS OF WIND ENERGY SYSTEM

PHYSICAL CHARACTERISTICS 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. Rotor 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, simple.

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 ALTERNATING CURRENT (AC) AND MUST BE ABLE TO BE 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 TO AT GRID THAN AT SYNCHRONOUS GENERATOR. THEY NORMALLY REQUIRE AT UTILITY CONNECTION TO MAINTAIN THE neatly frequency and cannot operate independently without SPECIAL EQUIPMENT.

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 relays. Nacelle 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 pumpers. Tower 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, APPLICATIONS OF WIND POWER 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 companies. 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. EQUIPMENT, MATERIAL, AND RESOURCES 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 technology. 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. THE HIGH-TECHNOLOGY, COMPLEX WECS REPRESENT THE THIRD CATEGORY OF 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. SKILLS NEEDED TO PRODUCE AND OPERATE AT WIND ELECTRIC SYSTEM CONSTRUCTION OF SIMPLE-TECHNOLOGY WEC MACHINES REQUIRES AT JOURNEYMAN 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. COST/ECONOMICS 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 analysis: 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 PAYBACK PERIOD = COST/VALUE OF ANNUAL PRODUCTIVITY = 15,000 /, .15, 35,000, = 6.67 YEARSES. EFFICIENCY 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. MAINTENANCE REQUIREMENTS 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 surfaces. 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. ENERGY STORAGE REQUIREMENTS 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 site. 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. IV.

COMPARING POWER-PRODUCING ALTERNATIVES

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 considered. 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 furnace. 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. GENERAL CONSIDERATIONS 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. V.

CHOOSING THE RIGHT TECHNOLOGY

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?

2.

CAN RELIABLE, MAINTAINABLE MACHINES BE BUILT OR OBTAINED, AT AT RESONABLE COST?

3.

Is the infrastructure in place to ensure that the MACHINE CAN BE OPERATED OVER ITS ECONOMIC LIFETIME? 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 BE INTRODUCED THAT MIGHT CAUSE IT TO REJECT THE USE OF 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 PURCHASE OF OIL?

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. BIBLIOGRAPHY deVries, O. franc: Golding, E.W.

Fluid Dynamic of Aspects of wind Energy Conversion. AGARD NATO, 1979. The generation of Electricity by wind-powers.

London,

England:

E. & F. sport Ltd., 1977.

HUGHES, W.L., ET AL. ENERGY FOR RURAL DEVELOPMENT: RENEWABLE Resources and alternative Technologies for Developing Countries. Washington, D.C. : nationally Academy of Sciences, 1976. Justus, C. G. of wind and wind system Performance. Philadelphia, Pennsylvania: The Franklin institutes press, 1978. Le Gourieres, D. wind Power Plants: Theory and design. New York: Pergamon Press, 1982. Lysen, E.H. Introduction to wind Energy. C/O DHV CONSULTING ENGINEERS, 1982. Naar, Jon.

The New wind Power.

New York:

The Netherlands:

ELMSFORD, SWD,

PENGUIN BOOKS, 1982.