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[[File:Earth Global Circulation.jpg|thumb|right|150px|Wind as a result of unequal solar radiation]]   
[[File:Earth Global Circulation.jpg|thumb|right|150px|Wind as a result of unequal solar radiation]]   
[[File:Map prevailing winds on earth.png|thumb|right|150px|Global winds map]]  
[[File:Map prevailing winds on earth.png|thumb|right|150px|Global winds map]]  
Wind is the [[flux|flow]] of gases on a large scale. On Earth, wind consists of the bulk movement of air. Here, it is the result of the uneven heating of the Earth by the sun and the fact that temperatures are invariably trying to reach an equilibrium (heat is always moving to a cooler area). The wind energy is the [[kinetic energy]] of the air in motion.


== Wind energy levels ==
== Wind energy levels ==
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[[File:Map local winds.png|thumb|right|150px|Local winds map]]
[[File:Map local winds.png|thumb|right|150px|Local winds map]]
[[File:Mountain wind.JPG|thumb|right|150px|Flow of winds on mountains]]
[[File:Mountain wind.JPG|thumb|right|150px|Flow of winds on mountains]]
[[File:Diagrama de formacion de la brisa-breeze.png|thumb|right|150px|Flow of winds near shore]]
[[File:Diagrama de formacion de la brisa-breeze.png|thumb|right|150px|Flow of winds near shore]]  
Wind is the [[flux|flow]] of gases on a large scale. On Earth, wind consists of the bulk movement of air. Here, it is the result of the uneven heating of the Earth by the sun and the fact that temperatures are invariably trying to reach an equilibrium (heat is always moving to a cooler area). The wind energy is the [[kinetic energy]] of the air in motion.
Although it is possible to determine the local wind energy level yourself, global maps are available which instantly provide you a good idea of the wind energy at a specific location and altitude. The advantage of this is that allot of time can be saved (measurements need to be taken over a long period of time) and there is also no risk of miscalculation. Using common sense (ie on a unobstructed location, ...), we can determine a suitable location within an area that is marked on the map as high in wind power.   
Although it is possible to determine the local wind energy level yourself, global maps are available which instantly provide you a good idea of the wind energy at a specific location and altitude. The advantage of this is that allot of time can be saved (measurements need to be taken over a long period of time) and there is also no risk of miscalculation. Using common sense (ie on a unobstructed location, ...), we can determine a suitable location within an area that is marked on the map as high in wind power.   



Revision as of 07:42, 28 June 2011

Wind as a result of unequal solar radiation
Global winds map

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. Here, it is the result of the uneven heating of the Earth by the sun and the fact that temperatures are invariably trying to reach an equilibrium (heat is always moving to a cooler area). The wind energy is the kinetic energy of the air in motion.

Wind energy levels

The available wind energy or power density varies heavily depending on the location on earth, aswell as the altitude above the soil. There are several classifications, and ways of determining the wind energy. For example, there is the Beaufort scale and the US NREL wind power density classification[1].

Beaufort scale

Beaufort number Description Wind speed Wave height Sea conditions Land conditions
0 Calm < 1 km/h 0 m Flat. Calm. Smoke rises vertically.
< 1 mph
< 1 kn 0 ft
< 0.3 m/s
1 Light air 1.1–5.5 km/h 0–0.2 m Ripples without crests. Smoke drift indicates wind direction and wind vanes cease moving.
1–3 mph
1–2 kn 0–1 ft
0.3–1.5 m/s
2 Light breeze 5.6–11 km/h 0.2–0.5 m Small wavelets. Crests of glassy appearance, not breaking Wind felt on exposed skin. Leaves rustle and wind vanes begin to move.
4–7 mph
3–6 kn 1–2 ft
1.6–3.4 m/s
3 Gentle breeze 12–19 km/h 0.5–1 m Large wavelets. Crests begin to break; scattered whitecaps Leaves and small twigs constantly moving, light flags extended.
8–12 mph
7–10 kn 2–3.5 ft
3.4–5.4 m/s
4 Moderate breeze 20–28 km/h 1–2 m Small waves with breaking crests. Fairly frequent whitecaps. Dust and loose paper raised. Small branches begin to move.
13–17 mph
11–15 kn 3.5–6 ft
5.5–7.9 m/s
5 Fresh breeze 29–38 km/h 2–3 m Moderate waves of some length. Many whitecaps. Small amounts of spray. Branches of a moderate size move. Small trees in leaf begin to sway.
18–24 mph
16–20 kn 6–9 ft
8.0–10.7 m/s
6 Strong breeze 39–49 km/h 3–4 m Long waves begin to form. White foam crests are very frequent. Some airborne spray is present. Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.
25–30 mph
21–26 kn 9–13 ft
10.8–13.8 m/s
7 High wind,
Moderate gale,
Near gale
50–61 km/h 4–5.5 m Sea heaps up. Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray. Whole trees in motion. Effort needed to walk against the wind.
31–38 mph
27–33 kn 13–19 ft
13.9–17.1 m/s
8 Gale,
Fresh gale
62–74 km/h 5.5–7.5 m Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray. Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
39–46 mph
34–40 kn 18–25 ft
17.2–20.7 m/s
9 Strong gale 75–88 km/h 7–10 m High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility. Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.
47–54 mph
41–47 kn 23–32 ft
20.8–24.4 m/s
10 Storm,[2]
Whole gale
89–102 km/h 9–12.5 m Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility. Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.
55–63 mph
48–55 kn 29–41 ft
24.5–28.4 m/s
11 Violent storm 103–117 km/h 11.5–16 m Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility. Widespread damage to vegetation. Many roofing surfaces are damaged; asphalt tiles that have curled up and/or fractured due to age may break away completely.
64–72 mph
56–63 kn 37–52 ft
28.5–32.6 m/s
12 Hurricane[2] ≥ 118 km/h ≥ 14 m Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility. Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.
≥ 73 mph
≥ 64 kn ≥ 46 ft
≥ 32.7 m/s

US NREL wind power density classification

The US NREL wind power density classification separates the wind energy into classes from 1 to 7. Wind speeds for class 1 are 9.8 mph or less on average while the average for a class 7 is 21.1 or even more. Each class has a specific amount of watts per square meter (ie wind power classes 3: 300–400 W/m2 at 50 m altitude; wind power class 7: 800–2000 W/m2 at 50 m altitude). For effective power production, atleast class 2 winds (11.5 mph average speed) are required.

Each class also has wind energy levels depending on the altitude (this makes sense and wind energy levels increase heavily with the altitude).

Determining the local wind energy levels

File:Average wind speeds at 10m.png
Average wind energy levels at 10m altitude
File:Average wind speeds at 80m.png
Average wind energy levels at 80m altitude
Local winds map
Flow of winds on mountains
Flow of winds near shore

Although it is possible to determine the local wind energy level yourself, global maps are available which instantly provide you a good idea of the wind energy at a specific location and altitude. The advantage of this is that allot of time can be saved (measurements need to be taken over a long period of time) and there is also no risk of miscalculation. Using common sense (ie on a unobstructed location, ...), we can determine a suitable location within an area that is marked on the map as high in wind power.

Choosing a wind energy harvester depending on the local conditions

on lower altitudes above the soil, VAWT's (vertical axis wind turbines) are more efficient than HAWTs and so you should first try to place your energy harvester as high as possible, but if this doesn't work, use a VAWT (which are at the moment of writing, relatively uncommon).


Due to this, the normal wind turbine comes with a tower at least 30 feet above obstructions. There are two basic types of towers useful for residential wind power systems (free standing and guyed). Free standing towers are self supporting and are usually heavier which means they take special equipment (cranes) to place them. Guyed towers are supported on a concrete base and anchored by wires for support. They typically are not as heavy and most manufacturer's produce tilt down models which may be easily raised and lowered for maintenance.

The kinetic (moving energy) from the winds is harnessed by a device known as the turbine. This turbine contains airfoils (blades) that capture the energy of the wind and use it to turn the shaft of an alternator (like you have on a car only bigger).

There are 2 basic kinds of blades (drag style and lifting style). We all have seen pictures of old-fashioned windmills with the large flat blades which are a good example of the drag style of airfoil. Lifting style blades are twisted instead of flat and resemble the propellor of a small airplane.

A turbine is classified as to whether it is made to be installed with the rotor in a vertical or horizontal position and whether the wind strikes the blades or the tower first. A vertical turbine typically requires less land for it's installation and is a better option for the more urban areas on the planet. An upwind turbine is created for the wind to impact the airfoils before it does the tower.


These units normally have a tail on the turbine which is required to maintain the unit pointed into the wind. A downwind turbine doesn't need a tail as the wind acting on the blades tends to keep it oriented properly.

These turbine systems would be damaged if they were to be allowed to turn at excessive speeds. Therefore, units should have automatic over-speed governing systems. Some systems use electrical braking systems although some use mechanical type brakes.

The output electricity from the alternator is sent to a controller which conditions it for use in the home. The usage of residential wind power systems requires the home to either remain linked with the utility grid or store electricity in a battery for use when the wind doesn't blow sufficiently.

When the home is tied to the grid, the excess electricity that is created by the residential wind power system can be sold to the utility company to reduce and sometimes even eliminate your electric bill. During times with not enough wind, the home is supplied power from the utility company.

Photo: http://www.residentialwindturbines.org/wind-scheme-grid-tied.gif

Uses

In a appropriate context; the following uses are possible:

  • convertion to electricity:

Some great benefits of wind energy are that it's virtually free (once you buy the equipment) and there's no pollution. The disadvantages include the fact it's not a continuing source (the speed varies and many times it is insufficient to generate electricity) and it typically requires about one acre of land.

  • transportation:

Wind can also be used as is to propell vehicles such as sail boats and/or hybrids thereof. Other vehicles that make use of the wind included (but are not limited to) sailing ice boats, kite buggies, hot air balloons, kite ski's, ...

The expense of Wind Energy

Small residential wind power turbines can be an attractive alternative, or addition, to those people needing more than 100-200 watts of power for their home, business, or remote facility. Unlike PV's, which remain at basically a similar cost per watt independent of array size, wind generators get cheaper with increasing system size. At the 50 watt size level, for instance, a small residential power turbine would cost about $8.00/watt in comparison to approximately $6.00/watt for a Photovoltaic module.

This is why, all things being equal, Photovoltaic is cheaper for very small loads. As the system size gets larger, however, this "rule-of-thumb" reverses itself.

At 300 watts the turbine costs are down to $2.50/watt, while the PV costs are still at $6.00/watt. For a 1,500 watt wind system the cost is down to $2.00/watt and at 10,000 watts the price of a wind generator (excluding electronics) is down to $1.50/watt.

External links

  1. Wind power density classes
  2. 2.0 2.1 The names "storm" and "hurricane" on the Beaufort scale refer only to wind strength, and do not necessarily mean that other severe weather (for instance, a thunderstorm or tropical cyclone) is present. To avoid confusion, strong wind warnings will often speak of e.g. "hurricane-force winds".
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