WINDWIND

Janice MoynihanJanice MoynihanLorelei SchmittLorelei SchmittDanielle RoyDanielle Roy

3.6.20053.6.2005

Finding Available Wind EnergyFinding Available Wind Energy

• POWER in the wind: (P, watts)– P=.5ρAv3 , where:

• ρ 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)

Finding Available Wind EnergyFinding 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…

Finding Available Wind EnergyFinding Available Wind Energy

• Wind Swept Area:A = πr2, 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 turbine’s potential.

r

Finding Available Wind EnergyFinding 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)

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.

Finding Available Wind EnergyFinding 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…

Finding Available Wind EnergyFinding Available Wind Energy

Gipe (1999)

Gross Amount of Energy Small Gross Amount of Energy Small Turbines Offer (3 methods)Turbines Offer (3 methods)

– Manufacturer’s 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.

Gross Amount of Energy Small Gross Amount of Energy Small Turbines Offer (3 methods)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)…

Gross Amount of Energy Small Gross Amount of Energy Small Turbines Offer (3 methods)Turbines Offer (3 methods)

• To calculate AEO:AEO = ρ*A*v3*cube factor*8760h/yr*% capture*(1

kW/1000W) = _____ kWh/yr , where:

ρ is air density .00508 US or .6125 metricA is wind swept areacube 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…

Gross Amount of Energy Small Gross Amount of Energy Small Turbines OfferTurbines 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…

TypesTypes

• 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

Off-the-Grid ApplicationsOff-the-Grid Applications

Hybrid Wind and Solar SystemsHybrid 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

• 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

Gipe (1999)

Village PowerVillage 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

Interconnected or Utility Interconnected or Utility IntertieIntertie

• 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

• 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

Buying Small TurbinesBuying Small Turbines

Appropriating SizeAppropriating Size

• What are you power expectations?– Small vacation house? Compliment to PV

panels?– Add up you anticipated electrical usage with

the site’s 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

Choosing EconomicallyChoosing 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)

• NREL’s cost performance ratio: purchase price/annual energy output

Tower SelectionTower 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

Building your own tower?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

Control PanelsControl 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

How about used turbines?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 Flo’s got a subscription to)

Cutting PricesCutting Prices

• Overall, it is hard to cut prices without sacrificing reliability

• Collective buying? The gov’t has done it

• Subsidies? – Generally only large scale operations are

eligible– There may be state-specific experimental

technology subsidies available, check it out

Siting and SafetySiting and Safety

SitingSiting

• 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

Siting Don’tsSiting Don’ts

• Don’t mount on roof because house acts an obstruction

• Don’t mount on trees • Urban wind doesn’t work for practical

purposes• Don’t put anchors, guy cables near

traveled ways including roads and footpaths…If there are farm animal fence-in these parts

Safety-Maintenance MustsSafety-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)

Safety-Electrical PrecautionsSafety-Electrical Precautions

– Disconnect power supply from turbine to avoid electricution

– Fuse all power sources to batteries

– Use caution when working with batteries

Installing Small TurbinesInstalling Small Turbines**Remember that turbines will **Remember that turbines will

need repairs…what goes up must need repairs…what goes up must come down**come down**

Tower Raising-Tilt upTower 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

GriphoistsGriphoists

• Good way to raise tower, can feel tension (but may need to adjust tension while raising tower)

• Tractel’s 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

Tower ConductorsTower 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

Wind-The Energy of the Wind-The Energy of the Future?Future?

Wind’s FutureWind’s 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