Other%20renewable%20energy%20sources

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Other renewable energy sources

• Hydropower
• Wind energy
• Ocean Thermal
• Biomass
• Geothermal
• Tidal

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Hydropower

• Well established electrical generation
  technology, about 100 years old
• Known for over 2000 years that the force of
  moving water on a water wheel could save human
  labor
• 13th century-hammers in iron works in Europe were
  operated with waterwheels.
• 16th century primary source of industrial power
  in Europe
• In the US, mills were established at sites with
  reliable water flow and dams were constructed to
  regulate water flow.
• Cave mill here in BG. Several hydro powered mills
  for corn, flour and sawing in the 19th century
  existed on this site at different times.
• With the advent of electricity, water wheels were
  used to drive electricity generation.
• About 7 of US energy generation is from
  hydroelectric plants

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The physics of Hydropower

• Gravitational potential energy in the water at a
  height h above the wheel is converted to kinetic
  energy of the wheel which drives a turbine and
  generates electricity.
• So each mass element of water, m, falls a
  distance h and attain a velocity v. So its
  initial potential energy is mgh, where g is the
  acceleration due to gravity (9.8m/s2) and the
  kinetic energy is 1/2mv2.
• This tells us the amount of potential energy
  available to be converted to kinetic energy is
  9.8 joules per kilogram of water per meter of
  height above the wheel.
• h is often called the head.
• Efficiencies of 80-90 can be achieved.
• Power (Height of Dam (distance the water
  falls)) x (River Flow) x (Efficiency) / 11.8
• where the height is in feet, river flow is
  in cubic feet per second , efficiency is what
  you expect and 11.8 converts from feet and
  seconds to killowatts
  

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Plant operation
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Hydro Turbine
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Net exploitable hydropower resources
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Advantages

• No Pollution
• No waste heat
• High efficiency
• Plants have decades long lifetimes and low
  maintenance costs
• Good response to changing electricity demands
• Damming of rivers can serve other purposes flood
  control, irrigation, drinking water supply

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Limitations

• About 50 of the US capacity for Hydro is
  developed
• Limited lifetimes for certain reservoirs-as the
  fill with silt, they become less useful for water
  storage. But the dam must be maintained long
  term, if it fails, communities downstream are in
  danger from the tremendous volume of silt that
  would be released.
• Loss of free flowing streams due to damming and
  the loss of the lands flooded by damming a
  river-environmental impacts
• Salmon population in the Nothwest has been
  impacted
• Flood risk due to dam failures
• Currently hundreds thousands of people in danger
  if dam failures occur

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Fish Ladders

• Solution to the salmon problem - have not been
  very effective

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Wind power

• Not subject to day night cycles
• Direct result of solar heating of the Earths
  atmosphere
• Use of wind for energy first noticed by sailors -
  the old sailing ships could extract the
  equivalent of 10,000 hp from the wind!
• Windmills were prevalent in Europe in the 19th
  century
• Several million were pumping water in the US in
  the early 1900s

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WHAT YOURE PROBABLY THINKING OF.
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Power in a windmill

• The power in the wind can be calculated by
  P/m2 6.1 X 10-4v3
• This gives the power in kilowatts per meter
  squared, where the cross sectional area is
  oriented perpendicular to the wind direction.
• This is the total power, of course not all of it
  can be extracted. According to Betzs Law,
  developed in 1919 by German physicist Albert
  Betz, no turbine can capture more than 59.3
  percent of the potential energy in wind.
• However, the total amount of economically
  extractable power available from the wind is
  considerably more than present human power use
  from all sources!

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Extracting the energy The turbine

• The world's first automatically operated wind
  turbine was built in Cleveland in 1888 by Charles
  F. Brush. It was 60 feet tall, weighed four tons
  and had 12kW turbine.

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Turbine types

• 2 types, based on the direction of the axis that
  the turbine rotates about.
• Horizontal axis wind turbines (HAWT) -the turbine
  rotates around an axis that is horizontal.
• Vertical Axis Wind Turbines (VAWT) the turbine
  rotates around a vertical axis

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HAWT

• Horizontal Axis Wind Turbines
• main rotor shaft and electrical generator are
  locate at 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 an electrical
  generator.

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HAWT

• the turbine is usually pointed upwind of the
  tower since it creates turbulence behind it.
• Turbine blades are made stiff to prevent the
  blades from being pushed into the tower by high
  winds.
• The blades are placed a considerable distance in
  front of the tower and are sometimes tilted up a
  small amount.

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HAWT Advantages

• Variable blade pitch so the turbine collects the
  maximum amount of wind energy for the time of day
  and season.
• The tall tower base 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.
• High efficiency, since the blades always move
  perpendicularly to the wind, receiving power
  through the whole rotation.

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HAWT Disadvantages

• The tall towers and blades up to 90 meters long
  are difficult to transport. Transportation can be
  20 of equipment costs.
• Tall HAWTs are difficult to install, needing very
  tall and expensive cranes and skilled operators.
• Massive tower construction is required to support
  the heavy blades, gearbox, and generator.
• Reflections from tall HAWTs may affect side lobes
  of radar installations creating signal clutter,
  although filtering can suppress it.
• Their height makes them obtrusively visible
  across large areas, disrupting the appearance of
  the landscape and sometimes creating local
  opposition.
• Downwind variants suffer from fatigue and
  structural failure caused by turbulence when a
  blade passes through the tower's wind shadow (for
  this reason, the majority of HAWTs use an upwind
  design, with the rotor facing the wind in front
  of the tower).
• HAWTs require an additional yaw control mechanism
  to turn the blades toward the wind.