From Earlham Cluster Department
- Wind turbines turn by a combination of lift and drag, very similarly as airplane wings. When the wind passes over the blade it creates a localized low pressure area behind the blade. The blade is then pulled into this area. This is called lift. The push of the wind on the blade is drag. The force of lift is significantly stronger than that of drag. The combination of lift and drag cause the rotor to turn and turns a drive shaft. The drive shaft in turn, turns the generator, creating electricity.
- HAWT vs. VAWT
- Horizontal Axis Wind Turbines, or HAWTs, make up 95% of all wind machines in the world. The blades look like airplane propellers and one, two, or three blades are generally located per tower. Most commonplace are 2 or 3 blades because the blades balance each other and minimize torque.
- Vertical Axis Wind Turbines, VAWT, have much higher strain on rotors because of the guy wires needed to keep it erect. They also can't be placed on higher towers to take advantage of the more stable winds. There are different styles of VAWT, but all experience the same problems.
- VAWT picture -- http://www.memagazine.org/backissues/jun04/features/apptowind/30topc.jpg HAWT picture -- http://www.bergey.com/images/Excel.CEC.jpg
- Wind Prospecting
- Before a wind farm is set up, prospecting must be done. Anemometers, a device to determine wind speed, are set up to determine the average wind speed. For a wind turbine to be practice, the general consensus is the average wind speed is greater than 12 mph.
- Power available works as a CUBE of the amount of wind present. In general, a site needs to have average wind speeds of over 5m/s (11mph) for cost effective generation. Stronger less turbulent wind is 30 m above the ground and higher. A single 750-kilowatt (kW) wind turbine, typical of those now being installed in power plants around the world, produces roughly 2 million kilowatt-hours (kWh) of electricity annually
- Based on the U.S. average fuel mix, approximately 1.5 pounds of CO2 is emitted for every kW generated. Post production, a wind turbine does not emit CO2. A 750 watt wind turbine can prevent the production of CO2 from other power plants that 500 acres of forest can absorb. On average, 300 American homes can be powered by a 1kW turbine.
- At a distance of 700-1000 ft, an operating wind farm is no louder than the hum of a refrigerator or a moderately quiet room. Small turbines generally create more noise than the larger ones, because they have a higher rotational speed of the tip. More research money has been devoted to decreasing the noise in larger turbines than in smaller turbines.
|Rural night-time background||20-40 dB|
|Wind farm at 350m||35-45 dB|
|Car at 40 mph at 100m||55 dB|
|Busy general office||60 dB|
|Jet aircraft at 250m||105 dB|
db - decibel
- Bird and Bats
- The National Audubon Society (NAS) has recently issued a statement that wind turbines are less harmful to bird populations than cars, planes, and other man-made contributions. NAS recently supported the development of responsibly located wind turbines for energy production. According to research in the U.S. And Denmark, the leading country in wind energy production, power lines pose a higher threat to birds than wind turbines. Deaths caused by wind towers and turbines are on the individual level, not population. Places with high mortality rates are routinely investigated.
Newer technology has lowered the mortality rate to bats and birds. The single tower instead of a lattice support or guy wires makes collisions with the pole itself less of an issue in HAWTs. Blades are not required to spin as fast as they were twenty years ago and towers spaced farther apart to lower the risk to the avian population.
Comparison of Power Plants
|Wind Energy||Natural Gas||Pulverized Coal|
|Project Life (years)||20 (120,000 hours)||30||30|
|Construction Period (years)||0.5||1||2|
|Plant Size (MW)||100||500||500|
|Capital Costs ($/kW)||$1000||$700-1,200||$1,070Ã¢â‚¬â€œ$1,500|
|Average Operation & Maintenance ($/Mwh)||15||24||20|
|O&M per kWh||$.01-.02||.04|
|Variable O&M ($/Mwh)||0||2.4||1.6-1.8|
|Fuel Costs ($/MBtu)||0||1.79-10||1.50|
- The earliest known wind turbine is from Persia, the area now known as Iraq, and were of the vertical axis design. Centuries later, Holland perfected the art of harvesting wind with propeller blades on a rotating axis to face the wind.
- Windmills are primarily used to gather water or grind grain. Turbines (or modern windmills) are used to harvest electricity. Early grain grinders were straight forward, with the grinding stone attached to the vertical shaft of the windmill.
- More information
- www.awea.org Ã¢â‚¬â€œ American Wind Energy Association
- http://www.ece.umr.edu/links/power/wind1.htm Ã¢â‚¬â€œ pictures
- http://telosnet.com/wind/ - history
- http://www.awea.org/faq/vawt.html Ã¢â‚¬â€œ general information about VAWTs
- http://www.eere.energy.gov/RE/wind_technologies.html Ã¢â‚¬â€œ links to other sites
- (1) http://www.newtonhouse.info/wind.htm