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Wind Turbines

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					Alternative energy
   Wind energy in the upwind

                         By:Vasilescu Tiberiu Aurel
                              And Brata Sorin
                              Contents
1. Short presentation
2. History of wind energy
3. Wind Turbines: Upwind Machines
4. How wind machines work
5. Types of wind turbines
         5.1. Vertical-axis wind turbines
                   5.1.1.Presentation
                   5.1.2.Advantages and disadvantages
         5.2. Horizontal-axis wind turbines
                   5.2.1.Presentation
                   5.2.2.Advantages and disadvantages
6. Small wind turbines
7. Turbine design and construction
8. The benefits of wind energy
9. Wind and the environment
10. The costs of wind energy
                      Short presentation
   Wind is simple air in motion. It is caused by the uneven
    heating of the earth’s surface by the sun.
   Wind energy converts kinetic energy that is present in the
    wind into more useful forms of energy such as
    mechanical energy or electricity.
   During the day, the air above the land heats up more
    quickly than the air over water. The warm air over the
    land expands and rises, and the heavier, cooler air rushes
    in to take its place, creating winds. At night, the winds
    are reversed because the air cools more rapidly over land
    than over water.
   In the same way, the large atmospheric winds that circle
    the earth are created because the land near the earth's
    equator is heated more by the sun than the land near the
    North and South Poles.
   Today, wind energy is mainly used to generate electricity.
    Wind is called a renewable energy source because the
    wind will blow as long as the sun shines.
   Windmills that were used to grind grain are an example
    of early uses of wind energy. Modern uses of wind
    energy include generation of electricity and pumping
    water. Current wind energy machines are called "wind
    turbine generators", "wind pumps", or more generally,
    "wind turbines".
       History of wind and wind energy
   Since ancient times, people have harnessed the winds
    energy. Over 5,000 years ago, the ancient Egyptians used
    wind to sail ships on the Nile River. Later, people built
    windmills to grind wheat and other grains. The earliest
    known windmills were in Persia (Iran). These early
    windmills looked like large paddle wheels. Centuries later,
    the people of Holland improved the basic design of the
    windmill.
   American colonists used windmills to grind wheat and
    corn, to pump water, and to cut wood at sawmills. As late
    as the 1920s, Americans used small windmills to generate
    electricity in rural areas without electric service.
   The oil shortages of the 1970s changed the energy picture
    for the country and the world. It created an interest in
    alternative energy sources, paving the way for the re-entry
    of the windmill to generate electricity. In the early 1980s
    wind energy really took off in California, partly because
    of state policies that encouraged renewable energy
    sources.
   Humans have used wind energy for thousands of years.
    Ancient Persians used wind energy to pump water before
    the birth of Christ.
   The current interest in wind energy was started by the
    need to develop clean, sustainable energy systems that
    can be relied on for the long-term future.
    Wind Turbines: Upwind Machines
   Upwind Machines
       Upwind machines have the rotor facing the
        wind. The basic advantage of upwind
        designs is that one avoids the wind shade
        behind the tower. By far the vast majority of
        wind turbines have this design.
       On the other hand, there is also some wind
        shade in front of the tower, i.e. the wind
        starts bending away from the tower before it
        reaches the tower itself, even if the tower is
        round and smooth. Therefore, each time the
        rotor passes the tower, the power from the
        wind turbine drops slightly.
       The basic drawback of upwind designs is
        that the rotor needs to be made rather
        inflexible, and placed at some distance from
        the tower (as some manufacturers have
        found out to their cost). In addition an
        upwind machine needs a yaw mechanism to
        keep the rotor facing the wind.
          How wind machines work
   Like old fashioned windmills, today’s wind
    machines use blades to collect the wind’s kinetic
    energy. Windmills work because they slow down
    the speed of the wind. The wind flows over the
    airfoil shaped blades causing lift, like the effect on
    airplane wings, causing them to turn. The blades
    are connected to a drive shaft that turns an
    electric generator to produce electricity.
   With the new wind machines, there is still the
    problem of what to do when the wind isn’t
    blowing. At those times, other types of power
    plants must be used to make electricity.
                 Types of wind turbines
   There are two types of wind machines (turbines) used today based on the direction of
    the rotating shaft (axis): horizontal–axis wind machines and vertical-axis wind
    machines. The size of wind machines varies widely. Small turbines used to power a
    single home or business may have a capacity of less than 100 kilowatts. Some large
    commercial sized turbines may have a capacity of 5 million watts, or 5 megawatts.
    Larger turbines are often grouped together into wind farms that provide power to the
    electrical grid.


                                              Vertical-axis




         Types




                                            Horizontal-axis
                                 Vertical-axis
   Vertical-axis wind turbines (or VAWTs)
    have the main rotor shaft running vertically.
    Key advantages of this arrangement are that
    the generator and/or gearbox can be placed
    at the bottom, near the ground, so the tower
    doesn't need to support it, and that the
    turbine doesn't need to be pointed into the
    wind. Drawbacks are usually pulsating
    torque that can be produced during each
    revolution and drag created when the blade                       Savonius wind turbine
    rotates into the wind. It is also difficult to
    mount vertical-axis turbines on towers,
    meaning they must operate in the often
    slower, more turbulent air flow near the
    ground, resulting in lower energy extraction
    efficiency.
   Exemples of vertical-axis wind turbines:
        Darrieus wind turbine
        Savonius wind turbine                       Darrieus wind
                                                        turbine
                 Vertical-axis wind turbines
   Advantages:                                                    Disadvantages :
   Easier to maintain because most of their moving parts          Most VAWTs produce energy at only 50%
    are located near the ground. This is due to the vertical        of the efficiency of HAWTs in large part
    wind turbine’s shape. The airfoils or rotor blades are          because of the additional drag that they
    connected by arms to a shaft that sits on a bearing and         have as their blades rotate into the wind.
    drives a generator below, usually by first connecting to        This can be overcome by using structures
    a gearbox.                                                      to funnel more and align the wind into the
                                                                    rotor or the "vortex" effect of placing
   As the rotor blades are vertical, a yaw device is not           straight bladed VAWTs closely together
    needed, reducing the need for this bearing and its cost.
                                                                   There may be a height limitation to how
   Vertical wind turbines have a higher airfoil pitch angle,       tall a vertical wind turbine can be built and
    giving improved aerodynamics while decreasing drag at           how much sweep area it can have.
    low and high pressures.                                         However , this can be overcome by
   Low height useful where laws do not permit structures           connecting a multiple number of turbines
    to be placed high.                                              together in a triangular pattern with
   Smaller VAWTs can be much easier to transport and               bracing across the top of the structure .
    install.                                                        Thus reducing the need for such strong
   Does not need a free standing tower so is much less             vertical support , and allowing the turbine
    expensive and stronger in high winds that are close to          blades to be made much longer .
    the ground.                                                    Most VAWTS need to be installed on a
   Does not need to be pointed into the wind, can turn             relatively flat piece of land and some sites
    regardless of the direction of the wind.                        could be too steep for them but are still
                                                                    usable by HAWTs.
   They can potentially be built to a far larger size than
    HAWT's , for instance floating VAWT's hundreds of              Most VAWTs have low starting torque,
    meters in diameter where the entire vessel rotates , can        and may require energy to start the
    eliminate the need for a large and expensive bearing .          turning.
                          Horizontal-axis
   Horizontal-axis wind turbines have the main rotor shaft and
    electrical generator at the top of a tower, and must be pointed
    into the wind. Small turbines are pointed by a simple wind
    vane, while large turbines generally use a wind sensor coupled
    with a servo motor. Most have a gearbox, which turns the slow
    rotation of the blades into a quicker rotation that is more
    suitable to drive a generator.
   Since a tower produces turbulence behind it, the turbine is
    usually pointed upwind of the tower. Turbine blades are made
    stiff to prevent the blades from being pushed into the tower by
    high winds. Additionally, the blades are placed a considerable
    distance in front of the tower and are sometimes tilted up a
    small amount.
   Downwind machines have been built, despite the problem of
    turbulence, because they don't need an additional mechanism
    for keeping them in line with the wind, and because in high
    winds, the blades can be allowed to bend which reduces their
    swept area and thus their wind resistance. Since turbulence
    leads to fatigue failures, and reliability is so important, most
    HAWTs are upwind machines.
   Types of Horizontal-axis wind trubines:
        Modern Rural Windmills
        Common modern wind turbines
          Horizontal-axis wind turbines
   Advantages:                                       Disadvantages:
   Blades are to the side of the turbine's           HAWTs have difficulty operating in
    center of gravity, helping stability.              near ground, turbulent winds.
   Tall tower allows access to stronger wind         The tall towers and long blades (up to
    in sites with wind shear. In some wind             180 feet (55 m) long) are difficult to
    shear sites, every ten meters up, the wind         transport on the sea and on land.
    speed can increase by 20% and the power            Transportation can now cost 20% of
    output by 34%.                                     equipment costs.
   Tall tower allows placement on uneven             Supply of HAWTs is less than demand
    land or in offshore locations.                     and between 2004 and 2006, turbine
   Can be sited in forests above the tree line.       prices increased up to 60%. At the end
   Most are self-starting.                            of 2006, all major manufacturers were
                                                       booked up with orders through 2008.
   Can be cheaper per unit of output because         The FAA has raised concerns about tall
    of higher production volume, larger sizes          HAWTs effects on radar near Air Force
    and, in general, higher capacity factors           bases.
    and efficiency.
                                                      Their height can create local opposition
                                                       based on impacts to viewsheds.
                  Small wind turbines
   Small wind turbines may be as small as
    a four hundred watt generators for
    residential use. The small ones often
    have direct drive generators, direct
    current output, aeroelastic blades,
    lifetime bearings and use a vane to
    point into the wind. Larger, more
    costly turbines generally have geared
    power trains, alternating current
    output, flaps and are actively pointed
    into the wind. Direct drive generators
    and aeroelastic blades for large wind
    turbines are being researched.
   A small wind turbine can be installed
    on a roof. Installation issues then
    include the strength of the roof,
    vibration, and the turbulence caused by
    the roof ledge.
      Turbine design and construction
   Wind turbines are designed to exploit the wind
    energy that exists at a location. Aerodynamic
    modeling is used to determine the optimum tower
    height, control systems, number of blades, and
    blade shape.
   Virtually all modern wind turbines convert wind
    energy to electricity for energy distribution. As
    described, the modern wind turbine is a system
    that comprises three integral components with
    distinct disciplines of engineering science. The
    rotor component, which is approximately 20% of
    the wind turbine cost, includes the blades for
    converting wind energy to an intermediate low
    speed rotational energy. The generator
    component, which is approximately 34% of the
    wind turbine cost, includes the electrical
    generator, the control electronics, and most likely
    a gearbox component for converting the low
    speed rotational energy to electricity. The
    structural support component, which is
    approximately 15% of the wind turbine cost,
    includes the tower for optimally situating the rotor
    component to the wind energy source.
           The benefits of wind energy
   Wind energy is an ideal renewable energy because:
             It is a pollution-free, infinitely sustainable form of energy
             It doesn’t require fuel
             It doesn’t create greenhouse gasses
             It doesn’t produce toxic or radioactive waste.
        Wind energy is quiet and does not present any significant hazard to birds or
         other wildlife.
        When large arrays of wind turbines are installed on farmland, only about 2% of
         the land area is required for the wind turbines. The rest is available for farming,
         livestock, and other uses.
        Landowners often receive payment for the use of their land, which enhances
         their income and increases the value of the land.
        Ownership of wind turbine generators by individuals and the community
         allows people to participate directly in the preservation of our environment.
        Each megawatt-hour of electricity that is generated by wind energy helps to
         reduce the 0.8 to 0.9 tonnes of greenhouse gas emissions that are produced by
         coal or diesel fuel generation each year.
               Wind and the environment
   In the 1970s, oil shortages pushed the
    development of alternative energy sources.
    In the 1990s, the push came from a
    renewed concern for the environment in
    response to scientific studies indicating
    potential changes to the global climate if
    the use of fossil fuels continues to increase.
    Wind energy is an economical power
    resource in many areas of the country.
    Wind is a clean fuel; wind farms produce
    no air or water pollution because no fuel is
    burned. Growing concern about emissions
    from fossil fuel generation, increased
    government support, and higher costs for
    fossil fuels have helped wind power
    capacity in the United States grow
    substantially over the last 10 years.
   The most serious environmental drawbacks
    to wind machines may be their negative
    effect on wild bird populations and the
    visual impact on the landscape.
              The costs of wind energy
   The cost of wind energy is determined by:
        The initial cost of the wind turbine installation
        The interest rate on the money invested
        The amount of energy produced
   Any wind turbine that is installed in a very windy
    area generates less expensive electricity than the
    same unit installed in a less windy area. So it’s
    important to assess the wind at the potential site.
   Modern wind turbine generators cost between $1500
    and $2000 per kilowatt for wind farms that use
    multiple-unit arrays of large machines. Smaller
    individual units cost up to $3000 per kilowatt. In
    good wind areas, the costs of generating electricity
    range between five and ten cents per kilowatt hour.
    That cost is somewhat higher than the costs
    associated with an electrical facility, but wind energy
    costs are decreasing every year, whereas most
    conventional generation costs continue to increase.

				
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posted:11/27/2012
language:English
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