Wind is a result of the uneven heating of the Earth by the sun and the fact temperatures will always be attempting to reach an equilibrium (heat is obviously moving to a cooler area). With the rising expense of energy and the destruction of the environment from fossil 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 is no pollution. The disadvantages include the fact it is not a continuing source (the speed varies and many times it is insufficient to produce electricity) and it typically requires about one acre of land.
The quantity of power which can be found varies by wind speed. The quantity available is termed it’s power density which is measured in watts per square meter. For that 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 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. This is why, the standard wind turbine is a component of a tower at least 30 feet above obstructions. There are two basic different kinds of towers employed 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 can be easily raised and lowered for maintenance.
The kinetic (moving energy) from the winds is harnessed by a device termed as a turbine. This turbine consists of airfoils (blades) that capture the power of the wind and use it to turn the shaft of an alternator (like you have on a car only bigger).
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 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 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 an improved option for the more urban areas on the planet. An upwind turbine is made 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 keep 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 while others use mechanical type brakes.
The output electricity from the alternator is sent to a controller which conditions it for use in the home. Using residential wind power systems requires the home to either remain tied to 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 surplus electricity that is produced 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 periods with not enough wind, the home is supplied power from the utility company.
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 turbine would cost about $8.00/watt in comparison to approximately $6.00/watt for a PV module.
That’s why, everything being equal, Photovoltaic systems are more affordable 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 price of a wind generator (excluding electronics) is down to $1.50/watt.
About the Author – Mary Jones writes for the Residential Wind Power Generation web log, her personal hobby blog related to tips to reduce Carbon dioxide and lower energy costs using alternative power sources.
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