Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, wind mills for mechanical power, wind pumps for pumping water or drainage, or sails to propel ships.
Wind towers are about 20m high. The reason why the tower is so tall is because winds are stronger higher from the ground.
Wind comes from atmospheric changes in temperature and pressure, which makes the air move around the surface of the Earth. That was triggered by the Sun. So in a way, wind energy is another form of solar power.
WIND TURBINES
The H type vertical axis wind turbine from Shanghai, China
The Brazos Wind Farm, also known as the Green Mountain Energy Wind Farm, in Texas, USA
Guest Contribution from Mary Jones of residentialwindturbines.org:
Wind is caused by the uneven heating of the Earth by the sun and the fact temperatures will always be trying to reach an equilibrium (heat is definitely moving to a cooler area). With the rising expense of energy and the destruction of the environment from fossil fuels, it is progressively more equitable to harvest this renewable resource.
The benefits of wind energy are that it’s virtually free (once you purchase the equipment) and there’s no pollution. The disadvantages include the fact it isn’t a constant source (the speed varies and many times it is insufficient to produce electricity) and it typically requires about one acre of land.
How Wind Energy Works
The quantity of power that is available varies by wind speed. The total amount available is known as it’s power density which is measured in watts per square meter. For this reason, the U.S. Department of Energy has separated wind energy into classes from 1 to 7. The typical wind speed for class 1 is 9.8 mph or less while the average for a class 7 is 21.1 or even more. For effective power production, class 2 winds (11.5 mph average speed) are usually required.
Generally, wind speeds increase as you get higher above the Earth. For that reason, the typical wind generator is a component of a tower no less than 30 feet above obstructions. There are two basic different types of towers used for residential wind power systems (free standing and guyed). Free standing towers are self supporting and are usually heavier meaning they take special equipment (cranes) to erect 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 can be easily raised and lowered for maintenance.
The kinetic (moving energy) from the winds is harnessed by a device termed as turbine. This turbine consists of 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).
That there are two 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 an example of the drag style of airfoil. Lifting style blades are twisted instead of flat and resemble the propeller of a small airplane.
A turbine is classified as to whether it is built to be installed with the rotor in a horizontal or vertical 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 worldwide. An upwind turbine is designed 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 does not require a tail as the wind acting on the blades tends to maintain it oriented properly.
These turbine systems would be damaged if they were to be permitted 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 in order to reduce and sometimes even eliminate your utility bill. During times with not enough wind, the home is supplied power from the utility company.
The Cost 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 stay at basically a similar cost per watt independent of array size, wind generators get less expensive with increasing system size. At the 50 watt size level, for example, a small residential power wind mill would cost about $8.00/watt compared to approximately $6.00/watt for a Photovoltaic module.
This is the reason, all things being equal, PV is cheaper for very small loads. As the system size gets larger, however, this “rule-of-thumb” reverses itself.
At 300 watts the wind generator 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 cost of a wind generator (excluding electronics) is down to $1.50/watt.
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REFERENCES:
1) http://en.wikipedia.org/wiki/Wind_power
2) http://www.energymatters.com.au/renewable-energy/wind-energy/
IMAGES:
Name- GreenMountainWindFarm Fluvanna 2004
Source- http://commons.wikimedia.org/wiki/File:GreenMountainWindFarm_Fluvanna_2004.jpg
Image has been released into the public domain
Name- Vawt
Source- http://commons.wikimedia.org/wiki/File:Vawt.jpg
Image has been released into the public domain
