WIND

1
WIND

• Janice Moynihan
• Lorelei Schmitt
• Danielle Roy
• 3.6.2005

2
Finding Available Wind Energy

• POWER in the wind (P, watts)
• P.5?Av3 , where
• ? is air density (at sea level .6125 metric or
  .00508 US)
• A is area intercepting wind (m2 or ft2) need
  wind swept area to find A
• v is instantaneous wind velocity (m/s or mph)

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Finding Available Wind Energy

• To compare P and V at two different sites
• with this equation want to know what the
  relationship between the power at sites with
  different wind speeds
• P2 /P1(V2/V1)3 cubed relationship remember
  Power equation
• ex. If wind speed is 20 greater at one site
  compared to another, the power will be about 73
  greater at that site because of cubic
  relationship.
• when comparing units do not matter

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Finding Available Wind Energy
r

• Wind Swept Area
• A pr2, where
• r length of 1 blade
• Comparing rotor diameter
• A2/A1 (R2/R1)2 square relationship remember
  area equation
• A wind turbine with a bigger rotor will almost
  always produce more electricity regardless of
  generator rating. ? Important in estimating
  turbines potential.

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Finding Available Wind Energy

• Distribution of wind speed over time
• estimate/designate resource by annual average
  wind speed
• in off-grid system (w/ batteries) monthly
  average wind speed is used
• periods of gusty wind contribute more to annual
  energy production, steady winds produce less
  power over time
• sum of cube of different wind speeds over time
  amounts to more than cube of average wind speed
• CUBE FACTOR hypothetical distribution that
  accounts for changes in wind speed (temperate
  climates use Rayleigh distribution for
  approximation)

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http//www.bergey.com/Maps/World.Wind.Lg.htm
If resource measurements are not available by
either direct measurement at site or from a
nearby meteorological station, then a Rayleigh
distribution is used.
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Finding Available Wind Energy

• Increasing speed and power with height
• assume wind spd. Measurements at least 10m (33ft)
  above ground
• taller towers more power available in less
  turbulent winds

Use Power Law Method V/Vo(H/Ho)a, where Vo
is wind speed at original height V is wind
speed at new height Ho is original height H is
new height a (alpha) is surface roughness
exponent

• Increasing tower height increases wind speed
  exponentially.
• Over rough terrain, alpha 0.25. Over smooth
  terrain (water/ice), alpha 0.1

equation for relationship between power and
height also, just remember cubed
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Finding Available Wind Energy
Gipe (1999)
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Gross Amount of Energy Small Turbines Offer (3
methods)

• Manufacturers Specifications
• what to expect from turbines under standard
  conditions with Rayleigh dist. at sea level
• when they present information as range of values
  it reflects uncertainty in estimates of
  performance
• Suppliers of off-grid, battery charging turbines
  present info in kWh/month rather than kWh/year
• Power Curve Method
• no accurate power curves published, all
  guesstimation
• know distribution of wind speed, match to power
  curve, sum energy produced by turbine over range
  of speeds represented by Rayleigh dist.

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Gross Amount of Energy Small Turbines Offer (3
methods)

• Wind Swept Area Method
• Do-It-Yourself
• Use rotor swept area and avg. annual wind speed
  under ideal conditions to estimate AEO (annual
  energy output)
• Most aerodynamic of turbines CAPTURE 40 of wind
  energy (not the same thing as how much energy it
  INTERCEPTS) ? their generators convert 90 or
  less of energy delivered to them
• OVERALL CONVERSION EFFICIENCY of 20-30 CAPTURE
  of energy available in wind
• perform best in low wind regimes (4-5 m/s or
  9-11 mph)

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Gross Amount of Energy Small Turbines Offer (3
methods)

• To calculate AEO
• AEO ?Av3cube factor8760h/yr capture(1
  kW/1000W) _____ kWh/yr , where
• ? is air density .00508 US or .6125 metric
• A is wind swept area
• cube factor is 1.9 (for Rayleigh dist. in
  temperate climates)
• wind capture is 20
• this calculation gives the annual kWh that your
  turbine will supply
• compare against load calculation

12
Gross Amount of Energy Small Turbines Offer

• Rarely all the energy intercepted by a turbine is
  captured (put to use) ? usually only 20
• Losses
• Only operating efficiently at rated wind speed
  (usually in low regimes 4-5 m/s or 9-11 mph)
• Full batteries do not accept any more power even
  if turbines are pumping it out ?goes to dump
• Inefficiency of battery storage
• Inverter losses when converting stored DC to AC
  appliances
• Only 70 of the energy delivered to the
  batteries is eventually used productively
• Add 10 for other negligible losses
• this is where in AEO eq. 20 wind capture comes
  from

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Types

• 3 blades
• Fiberglass or carbon fiber
• Tail vane that furls
• Heavier (weight of turbine relative to wind swept
  area), rugged turbine
• Permanent-magnet, induction alternator
• Micro-, mini-, household-size turbines

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Off-the-Grid Applications
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Hybrid Wind and Solar Systems

• Improves the reliability of a stand-alone system
• Cost effective
• Addition of a small amount of wind capacity can
  significantly boost the total energy available

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Gipe (1999)

• Batteries and inverters are critical to the
  success of a hybrid system
• Energy storage
• Conversion of DC to AC
• Battery storage is expensive, use of both wind
  and solar energy works to offset this cost
• Improvements of inverter technology have made it
  easier to live off the grid with AC appliances
• DC Source Center eases the integration of the
  wind turbine, battery, and inverter

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Village Power

• Most rural areas worldwide fall beyond the
  utility network, leaving millions without access
  to electricity
• Hold the potential of a huge market for wind and
  solar hybrids
• Use the same components as off-grid systems in
  developed countries, but in areas where 1
  kilowatt of energy goes a long way

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Interconnected or Utility Intertie
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• Induction generators used to synchronize its
  voltage and current with those of the utility
• Modern inverters allow any battery-charging wind
  turbine to produce utility compatible electricity
• If demand exceeds supply, energy is drawn from
  the utility to recharge the batteries
• If there is a surplus generation of electricity,
  the system can feed the excess back to the
  utility network

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• Ideally, these systems allow for the use of the
  utility as a battery
• Often run into problems because paid less than
  the cost of electricity
• To avoid a surplus, many have begun to match
  consumption with available wind or decreased the
  size of their turbine
• Net metering allows individuals to run their
  kilowatt-hour meter backwards
• Only offered in 22 states in the U.S
• Most states limit it to 10 kW, but in some the
  limit is higher

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Buying Small Turbines
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Appropriating Size

• What are you power expectations?
• Small vacation house? Compliment to PV panels?
• Add up you anticipated electrical usage with the
  sites wind availability to determine size of
  turbine needed
• Generally price per Kwh decreases with larger
  turbine diameters.but larger towers/turbines are
  more expensive to purchase

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Choosing Economically

• Do not only look at price, quality and
  reliability are very important in this sort of
  purchase.
• A good measure is the price of the turbine
  relative to the area swept by its rotor (/m2 or
  /ft2)
• NRELs cost performance ratio purchase
  price/annual energy output

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Tower Selection

• Tower must be matched to turbine
• Critical to have an appropriate clearance between
  rotor blades and the tower
• Must be able to install and service turbine
• A low-cost and user friendly tower is the
  tilt-up, guyed tubular mast
• NRG makes a well-priced, reliable, and
  installation-easy friendly tower

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Building your own tower?

• Building your own tower is not recommended.
• If one is feeling determined to build his or her
  own windmill, contact the Centre for Alternative
  Technology in Wales

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Control Panels

• Control panels are not essential for micro/mini
  turbines but can
• -help one know how the turbine is performing
• -provide a brake switch
• -provide current protection
• World Power provides an attractive control panel

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How about used turbines?

• Be weary. Be especially skeptical of turbines
  from old large wind farms
• Feel free to call companies and ask for more
  information on how old the unit may be.
• A good resource for finding wind turbines is the
  classifieds in Home Power magazine (which I sure
  hope Gary Flos got a subscription to)

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Cutting Prices

• Overall, it is hard to cut prices without
  sacrificing reliability
• Collective buying? The govt has done it
• Subsidies?
• Generally only large scale operations are
  eligible
• There may be state-specific experimental
  technology subsidies available, check it out

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Siting and Safety
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Siting

• Need Distance From Buildings/Trees
• -To avoid obstruction to wind, enhancing output
• -To reduce noise
• -30 feet above trees/houses recommended
• -Towers should be at least 30-60 feet tall

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Siting Donts

• Dont mount on roof because house acts an
  obstruction
• Dont mount on trees
• Urban wind doesnt work for practical purposes
• Dont put anchors, guy cables near traveled ways
  including roads and footpathsIf there are farm
  animal fence-in these parts

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Safety-Maintenance Musts

• No loose long hair, loose clothing, or jewelry
  around turning shaft
• Halt all turbines before performing maintenance
• Never work beneath an operating turbine
• Service turbine regularly to increase life
  expectancy (twice a year, spring and fall)

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Safety-Electrical Precautions

• Disconnect power supply from turbine to avoid
  electricution
• Fuse all power sources to batteries
• Use caution when working with batteries

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Installing Small Turbines

• Remember that turbines will need repairswhat
  goes up must come down

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Tower Raising-Tilt up

• Can be dangerous
• Truck or farm tractor can be effective in raising
  tower IF one has experience around heavy
  equipment
• When using a truck/tractor there needs to be a
  minimum of six people helping (hand signaler,
  driver, and anchors)
• Guyed towers are cheaper and easier to install

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Griphoists

• Good way to raise tower, can feel tension (but
  may need to adjust tension while raising tower)
• Tractels Super Pull-All is a great model
• If you are going to buy anything for wind
  turbine, buy a griphoist
• Better than hoists
• Readily portable
• Easier to control

37
Tower Conductors

• Never hang from wind turbine leads
• On guyed towers, thread down mast and secure with
  strain relief
• Use in-line compression connectors for making
  vibration-proof connections between wind turbine
  leads and cables carrying power down tower

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Wind-The Energy of the Future?
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Winds Future

• Growing demand for small turbines, especially in
  developing countries
• In rural areas it may be cheaper to install and
  maintain hybrid power systems than installing
  lightly used distribution lines
• Certification and standardized testing will
  improve technology
• Commercial wind power growth will advance small
  wind turbines as well