- Wind results as Sun hits the Earth's surface, causing differential heating of portions of the air. The air close to the earth surface warms up and rises, and it is replaced by the cooler air above. In terms of pressure, air moves from the point of high pressure (low temperature) to a point of low pressure (high temperature close to surface). The continuous rising and falling of the different components of atmospheric air causes wind which blows over the earth surface.

From the above brief explanation, it could be seen that wind energy is a secondary form of solar energy. Sun heats up air that turns to wind producing motion and energy.

Wind Energy is caused by the motion of the wind. This kind of energy is called Kinetic Energy. This energy can be harnessed to provide mechanical energy for driving mechanical systems and for providing electricity. The amount of energy available from wind depends on the speed of wind. The speed of wind, on the other hand, is determined by Air density, Air temperature, Air pressure, and Altitude.

Temperature decreases with height, while pressure increases. Wind effects are more pronounced at high altitudes. The wind speed is lower with higher density.

Uses of Wind Energy?

Wind Energy provides a suitable energy alternative to the traditional fossil fuel energy sources that are currently widely in use. Previous and current applications of wind energy are:

• Windmills to provide energy for milling/grinding grains;
• Wind Pumps for pumping water and for drainage (draining ponds); and
• Wind Turbines to generate electricity. This is the current, most extensive use of wind energy. Further discussions on wind turbines follow

Wind Turbines

Wind turbines transform energy from wind into electricity. Wind turbines perform optimally when placed at locations that are optimally windy and preferably at high altitudes.

Wind turbines are designed to start generating electricity when wind speed reaches about 3-4 metres/second and designed to cut out when the wind speed exceeds 25-26 metre/second to avoid damaging the turbine. Power output vs wind speed graph as shown below.

A approximate graph of the relationship between wind speed and energy generated by a wind turbine is presented below. A wind turbine will produce the highest electrical energy when the wind speed is around 15-17 metres

Wind turbine rotors (see definition below) are also designed to turn (as wind direction changes) to the new direction of of the wind. this is achieved by the aid of Yaw Gear and Yaw motor (definitions below).

Components of a Wind Turbine:

 

The main components of a wind turbine are in the picture below. Explanations of the various parts of a turbine as well as their functions are also discussed below.

(source: United States Coast Guard : SFO Southwest Harbour)

Nacelle: - The large head of the wind turbine (the outer shell). Inside the Nacelle are the following:

Rotor: - Fitted with 3 blades to catch the wind and make the rotor turn.

Main Shaft: - Connects the rotor to the Gear Box

Gear Box:- Connected to rotor by the main shaft, Used to step up the rotating speed of the rotor. The rotor rotates at about 20 rpm (where rpm = revolutions per minute). This rotating speed is increased to 150 rpm (speed required for the efficient functioning of the generator.

Generator: - Uses electromagnets to induce electricity which is transmitted through electrical cable to areas of need.

Radiator - cools down the Generator.

Small shaft - connects Gear Box to the Generator

Controller: - A computer that directs the different components of the turbine

Yaw Gear: - This gear is mounted on the tower and its a track that enables the nacelle to turn to face into the wind in the event that the wind changes direction.

Yaw Motor:- This motor turns he nacelle so that the turbine faces into the wind when the wind direction changes.

Brake: - Stops the turbine when the wind is getting too strong (i.e. > 25-26 m/s)

Anenometer: - Measures the speed of wind and relate the information to the controller which then stops the turbine.

Wind Vane: - Measures the wind direction and passes on this information on to the controller which then cause the turning of the nacelle towards the new wind direction.

Sizes of Wind Turbines

There are various sizes of wind turbines for the different levels of needs: Large (over 300 Kilowatts (KW)), Medium (30 to 300 KW) and small (below 30 KW) sizes. Large wind turbines can be used to supplement national electricity supply by combining the turbines to the national grid. Small scale uses like supply to homes and farms can be met with smaller turbines either connected to electricity grid or powered locally.

Is Wind Energy Renewable?

Wind energy is a renewable resource. A renewable resource is a resource that is able to be replaced or replenished, either by the earth's natural processes or by human action within a lifespan. Wind energy is available at varying proportions almost everywhere on earth. It cannot be depleted unlike the conventional fossil fuel based energy resources.

Wind energy is a clean energy resource, compared to fossil fuels (coal, crude oil and natural gas). It does not emit Green House Gases (GHGs) that are believed to be responsible for the worsening global warming of our planet, Earth. It is believed that each megawatt-hour (MWh) of electricity that is generated by wind energy helps to reduce the 0.8 to 0.9 tonnes of greenhouse gas emissions that are produced by coal or diesel fuel generation each year.

Setbacks of Wind Power (Wind Turbines):

Wind power has some setbacks. Some of these setbacks and their possible mitigations are:

• Obstruction of human activities - Wind farm could obstruct human activities if placed in low altitudes. The mitigation for this setback is to erect turbines at high altitudes.
• Obstruction of Bird's path - Birds and other flying objects get killed if they fly past a wind turbine farm; birds migratory path are altered in the long run. This can possibly be mitigated by studying the pattern and path of birds' migration prior to erecting a wind farm.
• As mentioned earlier, wind turbines can only operate effectively within a certain range of wind speed usually between 3-4 metres/second and 25-26 metres/s. The graph of power output by a wind turbine relative to the speed of the wind is as shown below. A power system that solely relies on wind will lack power when the wind isn't flowing at all and when the speed is excessive. The mitigation for this is to have energy storage (e.g. in batteries) during times of optimum wind flow and put away for use during the periods of "too slow" and "too fast" wind and/or have other sources of energy to compliment wind during the down times.

Other Resources for Wind Energy:

• Wind Power - Wikipedia, the free encyclopedia
• Canadian Wind Energy Association (CanWEA)
• EIA Energy Kids - Wind
• American Wind Energy Association
• Energy Source: Wind Energy - Pembina Institute
• Community Wind Across America - Wind industry