Hey, everyone. I was recently contacted by Mary Jones of residentialwindturbines.org regarding doing a post about wind power. I’m not sure what financial stakes she has in the industry, but I support just about anything that gets us off petroleum products, so it matters not. The following is what she has to say.
It’s not necessary to be a geek to understand how wind energy works.
Wind is caused by 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 starting to be equitable to harvest this renewable resource.
The advantages of wind energy are that it’s virtually free (once you buy the equipment) and there is no pollution. The disadvantages include the fact it’s not a constant 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 which can be found varies by wind speed. The quantity available is termed 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 standard 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 generally required.
Generally, wind speeds increase as you get higher above the Earth. That is why, the typical wind turbine is a part of a tower at least 30 feet above obstructions. There are two basic types of towers useful 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 erect 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 a 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).
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 an 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 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 on the planet. An upwind turbine is made 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 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 permitted to turn at excessive speeds. Therefore, units must 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 will not blow sufficiently.
When the home is tied to the grid, the excess electricity that is created by the residential wind power system can be sold to the utility company in order to reduce or even eliminate your electric bill. During times with not enough wind, the home is supplied power from the utility company.

The expense 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 generators 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 PV module.
This is the reason, everything 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 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.
Who am i ? – Mary Jones writes for the residential wind generators web log, her personal hobby blog dedicated to guidelines to reduce CO2 and lower electricity costs using alternative power sources.
If you want to read my complete Bio: http://www.residentialwindturbines.org/about
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