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About Wind Energy

By Jestine Yong on July 9, 2010

One of my blog reader Mary, contributes her article to this blog. Please read her article about Wind Energy below:

You don’t have to become a geek to know how wind energy works.

Wind is a result from the uneven heating of the Earth by the sun and the fact that temperatures are always trying to reach an equilibrium (heat is obviously moving to a cooler area). With the rising price of energy and the damage to the environment from standard fuels, it is more and more equitable to harvest this renewable resource.

The benefits of wind energy are that it is virtually free (once you purchase the equipment) and there is no pollution. The disadvantages include the fact it’s not a constant 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 quantity of power that can be found varies by wind speed. The amount available is named it’s power density and it 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 common 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.

Normally, wind speeds increase as you get higher above the Earth. For that reason, the normal wind generator is installed on a tower at least 30 feet above obstructions. That there are two basic types of towers used for residential wind power systems (free standing and guyed). Free standing towers are self supporting and are usually heavier which means 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 is often easily raised and lowered for maintenance.

The kinetic (moving energy) from the winds is harnessed by a device termed as turbine. This turbine contains 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 two basic types 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 instead of flat and resemble the propellor of a small airplane.

A turbine is classified as to whether it is made 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 a much better 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 keep 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 permitted to turn at excessive speeds. Therefore, units must 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 use 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 produced by the residential wind power system can be sold to the utility company to lower or even eliminate your power company bill. During periods 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 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 compared to approximately $6.00/watt for a Photovoltaic module.

That’s why, all things being equal, Photovoltaic is more affordable for very small loads. As the system size gets larger, however, this “rule-of-thumb” reverses itself.

At 300 watts the wind turbine 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.

About the Author – Mary Jones writes for the http://www.residentialwindturbines.org site, her personal hobby blog focused on ways to reduce CO2 and lower electricity costs using alternative power sources.