How Wind Energy Works

About the Author – Mary Jones writes for the residential wind generators web site, her personal hobby blog related to tips to reduce CO2 and lower power costs using alternative power sources. Read her complete bio here. 
It’s not necessary to become a nerd to learn how wind power 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 expense of energy and the damage to the environment from classic fuels, it is increasingly 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 that it isn’t 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 amount of power that is available varies by wind speed. The amount available is named 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 normal 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 frequently required.
Normally, wind speeds increase as you get higher above the Earth. Due to this, the conventional turbine comes with a tower at least 30 feet above obstructions. That there are two basic different kinds of towers useful 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 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).
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 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 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 made for the wind to impact the airfoils before it does the tower.
These units ordinarily have a tail on the turbine which is required 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 maintain it oriented properly.
These turbine systems would be damaged if they were to be allowed 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 does 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 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.

The Price of Wind Energy
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 instance, a small residential power wind turbine would cost about $8.00/watt compared to approximately $6.00/watt for a Photo voltaic module.
For this reason, all things being equal, PV is cheaper 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 cost of a wind generator (excluding electronics) is down to $1.50/watt.