Alternative energy

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Alternative energy

• Wind energy in the upwind
• ByVasilescu Tiberiu Aurel
• And Brata Sorin

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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

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Short presentation

• Wind is simple air in motion. It is caused by the
  uneven heating of the earths 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".

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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.

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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.

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How wind machines work

• Like old fashioned windmills, todays wind
  machines use blades to collect the winds 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 isnt
  blowing. At those times, other types of power
  plants must be used to make electricity.

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Types of wind turbines

• There are two types of wind machines (turbines)
  used today based on the direction of the rotating
  shaft (axis) horizontalaxis 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
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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 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 

Savonius wind turbine
Darrieus wind turbine
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Vertical-axis wind turbines

• Disadvantages
• Most VAWTs produce energy at only 50 of the
  efficiency of HAWTs in large part because of the
  additional drag that they have as their blades
  rotate into the wind. This can be overcome by
  using structures to funnel more and align the
  wind into the rotor or the "vortex" effect of
  placing straight bladed VAWTs closely together
• There may be a height limitation to how tall a
  vertical wind turbine can be built and how much
  sweep area it can have. However , this can be
  overcome by connecting a multiple number of
  turbines together in a triangular pattern with
  bracing across the top of the structure . Thus
  reducing the need for such strong vertical
  support , and allowing the turbine blades to be
  made much longer .
• Most VAWTS need to be installed on a relatively
  flat piece of land and some sites could be too
  steep for them but are still usable by HAWTs.
• Most VAWTs have low starting torque, and may
  require energy to start the turning.

• Advantages
• Easier to maintain because most of their moving
  parts are located near the ground. This is due to
  the vertical wind turbines shape. The airfoils
  or rotor blades are connected by arms to a shaft
  that sits on a bearing and drives a generator
  below, usually by first connecting to a gearbox.
• As the rotor blades are vertical, a yaw device is
  not needed, reducing the need for this bearing
  and its cost.
• Vertical wind turbines have a higher airfoil
  pitch angle, giving improved aerodynamics while
  decreasing drag at low and high pressures.
• Low height useful where laws do not permit
  structures to be placed high.
• Smaller VAWTs can be much easier to transport and
  install.
• Does not need a free standing tower so is much
  less expensive and stronger in high winds that
  are close to the ground.
• Does not need to be pointed into the wind, can
  turn regardless of the direction of the wind.
• They can potentially be built to a far larger
  size than HAWT's , for instance floating VAWT's
  hundreds of meters in diameter where the entire
  vessel rotates , can eliminate the need for a
  large and expensive bearing .

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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 

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Horizontal-axis wind turbines

• Advantages
• Blades are to the side of the turbine's center of
  gravity, helping stability.
• Tall tower allows access to stronger wind in
  sites with wind shear. In some wind shear sites,
  every ten meters up, the wind speed can increase
  by 20 and the power output by 34.
• Tall tower allows placement on uneven land or in
  offshore locations.
• Can be sited in forests above the tree line.
• Most are self-starting.
• Can be cheaper per unit of output because of
  higher production volume, larger sizes and, in
  general, higher capacity factors and efficiency.

• Disadvantages
• HAWTs have difficulty operating in near ground,
  turbulent winds.
• The tall towers and long blades (up to 180 feet
  (55 m) long) are difficult to transport on the
  sea and on land. Transportation can now cost 20
  of equipment costs.
• Supply of HAWTs is less than demand and between
  2004 and 2006, turbine prices increased up to
  60. At the end of 2006, all major manufacturers
  were booked up with orders through 2008.
• The FAA has raised concerns about tall HAWTs
  effects on radar near Air Force bases.
• Their height can create local opposition based on
  impacts to viewsheds.

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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.

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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.

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The benefits of wind energy

• Wind energy is an ideal renewable energy because
  
• It is a pollution-free, infinitely sustainable
  form of energy    
• It doesnt require fuel   
• It doesnt create greenhouse gasses   
• It doesnt 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.

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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.

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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 its 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.