THE GREEN ENERGY BLOG

You no longer need to become a nerd to know how wind power 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 cost of energy and the destruction of the environment from fossil fuels, it is becoming more equitable to harvest this renewable resource.

The benefits of wind energy are that it’s virtually free (after you purchase the equipment) and there is no pollution. The disadvantages include the fact it’s not 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 amount of power that can be found varies by wind speed. The total amount available is named it’s power density and it is measured in watts per square meter. This is why, 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 usually required.

In general, wind speeds increase as you get higher above the Earth. Because of this, the typical windmill is a part of a tower no less than 30 feet above obstructions. There are 2 basic 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 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 types of blades (drag style and lifting style). We all have seen pictures of old 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 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 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 ordinarily have a tail on the turbine which is needed to keep the unit pointed into the wind. A downwind turbine does not require 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 permitted to turn at excessive speeds. Therefore, units must 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 tied to 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 created 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 remain at basically the same cost per watt independent of array size, wind turbines get cheaper 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 PV module.

For this reason, 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 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 price of a wind generator (excluding electronics) is down to $1.50/watt.

About me – Mary Jones writes for the residential wind power generation website, her personal hobby blog dedicated to suggestions to reduce Carbon dioxide and lower electricity costs using alternative power sources.

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