How Wind Energy Works
Read More About the Author Mary Jones
Wind is the result of the uneven heating of the Earth by the sun and the fact temperatures are invariably 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 non-renewable fuels, it is progressively more equitable to harvest this renewable resource.
The benefits of wind energy are that it’s virtually free (after you buy the equipment) and there’s no pollution. The disadvantages include the fact it is 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.
The volume of power that can be found varies by wind speed. The amount available is known as it’s power density and it is measured in watts per square meter. Due to this, 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 usually required.
Generally, wind speeds increase as you get higher above the Earth. Due to this, the normal wind mill is installed on a tower no less than 30 feet above obstructions. There are 2 basic different 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 a turbine. This turbine contains airfoils (blades) that capture the power 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 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 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 keep it oriented properly.
These turbine systems would be damaged if they were to be allowed to turn at excessive speeds. Therefore, units will need to 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 linked with 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 to reduce or even eliminate your power company bill. During times with not enough wind, the home is supplied power from the utility company.
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 cheaper 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 PV module.
That’s why, all things being equal, Photovoltaic is less expensive 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 price of a wind generator (excluding electronics) is down to $1.50/watt.
Mary Jones writes for the Residential Wind Energy weblog. Her personal hobby blog is focused on ways to reduce Carbon dioxide and lower electricity costs using alternative power sources.
