Wind energy: how it works

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    By Mary Jones,

    Wind is a result from the uneven heating of the Earth by the sun and the fact temperatures are always attempting to reach an equilibrium (heat is always moving to a cooler area). With the rising expense of energy and the damage to the environment from non-renewable fuels, it is starting to be equitable to harvest this renewable resource.

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

    How Wind Energy Works

    The amount of power that is available varies by wind speed. The quantity available is termed it’s power density which is measured in watts per square meter. Due to this, the U.S. Department of Energy has separated wind energy into classes from 1 to 7. The average 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 often required.

    Usually, wind speeds increase as you get higher above the Earth. Due to this, the normal wind turbine comes with a tower at least 30 feet above obstructions. That there are two basic different kinds of towers useful 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 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 includes 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 rather than flat and resemble the propellor 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 an improved option for the more urban areas of the world. 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 doesn’t need 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 allowed to turn at excessive speeds. Therefore, units will need to have automatic over-speed governing systems. Some systems use electrical braking systems while 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 will not blow sufficiently.

    When the home is tied to the grid, the surplus electricity that is made by the residential wind power system can be sold to the utility company in order to reduce and sometimes even eliminate your power company bill. During periods with not enough wind, the home is supplied power from the utility company.

    The price 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 turbines get more affordable with increasing system size. At the 50 watt size level, for instance, a small residential power windmill would cost about $8.00/watt when compared with approximately $6.00/watt for a Photo voltaic module.

    This is the reason, all things being equal, PV is less expensive for very small loads. As the system size gets larger, however, this “rule-of-thumb” reverses itself.

    At 300 watts the windmill 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.


    Mary Jones writes for the residential wind power web site, her personal hobby blog focused on tips to reduce Carbon dioxide and lower energy costs using alternative power sources.

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