Wind is caused by the uneven heating of the Earth by the sun and the fact that temperatures will always be trying to reach an equilibrium (heat is always moving to a cooler area). With the rising price of energy and the destruction of the environment from standard fuels, it is progressively more equitable to harvest this renewable resource.
The benefits of wind energy are that it is virtually free (after you buy the equipment) and there is no pollution. The disadvantages include the fact that it isn’t a continuing source (the velocity varies and many times it is insufficient to generate electricity) and it typically requires about one acre of land.
How Wind Energy Works
The volume of power that is available varies by wind speed. The total amount available is called it’s power density and it’s measured in watts per square meter. This is why, the U.S. Doe 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. For this reason, the standard wind turbine is a component of a tower at least 30 feet above obstructions. There are 2 basic types 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 set them up. 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 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 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 a much better option for the more urban areas around the globe. 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 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 tied to the utility grid or store electricity in a battery for use when the wind will not blow sufficiently.
When the home is linked with 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.
The Cost of Wind Energy
Small residential wind power turbines can be an attractive alternative, or addition, to those people needing over 100-200 watts of power for their home, business, or remote facility. Unlike PV’s, which stop at basically a similar cost per watt independent of array size, wind turbines get cheaper with increasing system size. At the 50 watt size level, for example, a small residential power wind mill would cost about $8.00/watt when compared with approximately $6.00/watt for a Photo voltaic module.
That 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 wind mill 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.
The author – Mary Jones writes for the residential wind turbines weblog, her personal hobby blog dedicated to ideas to reduce Carbon dioxide and lower power costs using alternative power sources.
If you want to read my complete Bio: http://www.residentialwindturbines.org/about
If you wish to embed my picture: http://www.residentialwindturbines.org/mary.jpg