Wind Turbine
From Kompulsa - Ocean | Weather | Climate
A wind turbine is a rotary machine with an alternator or DC (direct current) generator (dynamo) that generates electricity using the kinetic energy of wind, the blades are either attached to low rpm alternators which generate useful amounts of electricity when turned at a low speed, or they are attached to large gears which turn an alternator at a higher speed, since the blades turn slowly.
They can be used with energy storage mediums such as: supercapacitors, batteries, pumped hydroelectric storage, compressed air, and fuel cells. Windmills can be home built (although nowhere near commercial grade), and without much money. Search for "DIY Wind Turbine" in Google. There are many different types of wind turbines, there are those that have three blades, some are of the horizontal axis (HAWT) type, and some of the vertical axis (VAWT) type, some have multiple sets of blades, some are airborn (they are kept in the air with tanks which are filled with certain gases such as helium) and there are other designs which you can find by browsing the internet.
RPM: Revolutions Per Minute.
Low RPM Alternator/Dynamo:
A low RPM generator is one which is designed to efficiently generate electricity when spun at low speeds. Wind turbine blades turn at low speeds, therefore, they need low RPM generators or gears to compensate for that.
Advantages of Wind Turbines
- Longevity.
- The energy source (the kinetic energy of the wind) is free, renewable, and inexhaustible.
- It isn't necessary to purchase fuel for them.
- They do not release any pollutants into the atmosphere nor cause global warming.
- They are cost effective in the long run (depending on their location and how they are used).
- The cost of electricity from a wind turbine remains fairly consistent over its lifetime because there are no expenses apart from maintenance and insurance associated with the turbine, so it is not susceptible to cost fluctuations which fuel powered generators are.
- Farmers can benefit from land lease payments for wind turbine installations on their land.
- Use of wind turbines means that less fossil fuels will be used to generate electricity, causing fossil fuels to last longer and helping to mitigate increases in demand which result in an increase in their cost.
- Low water requirement of 0.001 gallons (0.004 litres) of water per kWh of electricity generated.
- Safety: They are not powered by explosive or flammable fuels.
Disadvantages of Wind Turbines
- They are large.
- They have a high initial cost.
- Wind blows intermittently and wind speeds vary, so an energy storage medium needs to be used with them if they are to be used independently. Read about energy storage mediums on the energy storage page.
What is the Environmental and Ecological Impact of Wind Turbines?
The environmental impact of wind turbines is low, because they are constructed using non-toxic materials (usually), their long lifespan also means that they will not end up in landfills often, and they do not release/emit any harmful substances.
Wind turbines seldom hit birds, but their impact on bats is more significant. The pressure drops caused by moving wind turbine blades is harmful to bats, one solution to this problem is to use a bat radar to scare them away from the turbines.
Materials used for construction (only some of these are common):
- Steel
- Copper
- Iron
- Aluminium
- Fiberglass
- Semiconductor materials such as silicon and germanium
- Carbon Fiber
- Carbon
- Titanium
- Ceramic Materials
- Tin
AWEA: Putting Wind's Impact on Birds in Perspective
Air Pressure Drops Can Harm Bats
Texas wind farm deploys radars, so birds, and not feathers, can fly
Water usage of wind turbines compared to that of other power plants
Intermittency and Variability of Wind Power
Wind turbines intermittently generate electricity, meaning that they do not always generate it. Intermittency complicates the process of integrating wind power into electricity grids, and it also makes it impossible to rely on the wind for most or all of electricity unless energy storage is used. There is a cost associated with with accounting for the intermittency of wind power, which increases the cost of wind power. This is one reason why an economical energy storage system is required.
Variability: Wind speeds vary, and as wind speeds increase and decrease, the power output of wind turbines increases and decreases as well.
Wind turbines can be used to charge energy storage systems which would then supply the right amount of electricity, at the right time, and without intermittency or variability to the electricity grid. Some examples of energy storage systems are: batteries, supercapacitors, compressed air energy storage (CAES), flywheel energy storage, and pumped hydroelectric storage.
MIT: Economic Modeling of Intermittency in Wind Power Generation
Power Output
The power output of a wind turbine is dependent on the efficiency of the blades, gear assembly, alternator/dynamo, as well as wind speed and wind consistency.
The power output of taller wind turbines is greater due to the fact that wind speeds are greater at higher altitudes.
The power output of wind turbines can be increased by turning the head in such a way that the blades face the wind, this can be done with a wind direction sensor combined with a motorized head moving mechanism (or yaw).
Offshore Wind Turbines
Wind turbines may be placed offshore where wind speeds tend to be much higher and more steady than they are on land. Normally, this would translate to cheaper wind power, because if a land wind turbine generates a certain amount of electricity at average wind speeds of 14 MPH, then if that same turbine were moved somewhere with average wind speeds of 18 MPH, it would generate more electricity.
If the wind turbine costs $1 million and is 1 MW, then the cost per (peak) watt is $1. but, it would only generate 1 MW at the wind speed specified by the manufacturer, and that wind speed is usually high. So sometimes it may be half that speed, or even a quarter. Or on good days it may be 3 quarters of that or more. Anyway, So if it generates 1 MW at a wind speed of 28 MPH then if the wind speed decreased to the point where it generated 0.5 MW, the cost per watt would be twice as high, which is $2 per watt. Sadly, offshore wind parks are far more costly than land farms, therefore we cannot currently enjoy the cost benefit that we would expect to from higher offshore wind speeds, but, researchers are working on this and making progress. The cost of maintenance for offshore wind turbines is a major problem and it has been addressed by the development of gearless wind turbines, which require less maintenance. Typical wind turbines are geared (meaning that the turbine hub is used to turn a gear which turns another gear at a different speed from itself). Offshore wind turbines can either be secured by burying the pole deep in the ocean floor, if the water is shallow, or by setting up a floating platform that it stands on which is tethered to the ocean floor via steel cables in deepwater.
Argonne National Laboratory: Offshore Wind
Wind Power Density
This is defined as the amount of wind power available in a particular area. The higher the wind power density, the lower the cost of wind power in that area, and the higher the power output of wind turbines will be.
Wind power density is divided into seven classes:
At a height of 50 metres (164 feet):
- 2 - 12.5 mph (5.6 metres per second (m/s)) - 200 W/m2 (watts per square metre)
- 3 - 14.3 mph (6.4 metres per second) - 300 W/m2
- 4 - 15.7 mph (7.0 metres per second) - 400 W/m2
- 5 - 16.8 mph (7.5 metres per second) - 500 W/m2
- 6 - 17.9 mph (8.0 metres per second) - 600 W/m2
- 7 - 19.7 mph (8.8 metres per second) - 800 W/m2
- 7 - 26.6 mph (11.9 metres per second) - 2000 W/m2 (the one above is in the same class which is 7, this is not an error)
NREL: International Wind Resources
NREL: United States Wind Resources
United States: Average Wind Speed By State
What Is The Payback Time of Wind Turbines?
The energy payback time of a wind turbine is the amount of time it takes for it to generate as much electricity as was used to manufacture it.
The financial payback time of a wind turbine is the amount of time taken for a wind turbine to save you the amount of money that you spent on it.
Energy Payback Time: 3 to 8 months.
Economic Impact
- The cost of wind power is $0.04 - $0.08 per kWh (as little as $0.03 in particularly windy areas).
- A wind powered economy is not susceptible to rising fuel prices, because wind turbines are not fossil-fuel powered. An economy with low cost electricity would result in lower cost food than one with high fuel prices. Fossil fuel price increases drive up the cost of food, water, and everything else which is harvested, manufactured, or supplied using electricity.
- Wind farms are sometimes built on farm land and the owners/farmers benefit because they are paid for the use of that land, helping to sustain the agriculture industry. The farmers could even be supplied with electricity in the process, but that is dependent on the wind farm owner.
- The total number of jobs created by the manufacturers, deliverers, and assemblers of wind turbines has a positive economic impact. Example: Vestas opened a factory for wind turbine blades alone and said they would hire 600 people to work there: Vestas Opens Factory in Colorado
Factors Affecting Cost
Many factors affect the cost to generate electricity during the life of a wind turbine, including:
Reliability: The more a wind turbine malfunctions, the more it will have to be repaired, and repair costs money, therefore, a less reliable wind turbine is a more expensive one.
Efficiency: Wind turbines need to convert the kinetic energy possessed by the wind into electricity as efficiently as possible because the less efficient a wind turbine is, the less of the wind's kinetic energy is converted into electricity, therefore, the turbine will take longer to pay for itself.
Cost of Materials
The cost of the materials used in the construction of a wind turbine obviously have a significant impact on the cost of the turbine because the cost of those materials is included in the production cost of the turbine.
Geographic Location
Average wind speed varies with geographic location, wind turbines generate more electricity as wind speed increases, and less as wind speed decreases.
What Are The Parts of A Wind Turbine?
- Blades
- Hub
- Rotor
- Alternator
- Power Electronics
- Yaw
- Brakes
- Pole/Tower
Additional Information and Sources
DOE: Electricity Transmission - A Primer
Wind Energy Resource Atlas for The United States
Energy Star: Federal Tax Credits
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