Wind is the result of the uneven heating of the earth by the sun and the fact that temperatures are invariably attempting to reach an equilibrium (heat is moving to a cooler area). With the rising expense of energy and the damage to the environment from non-renewable fuels, it is increasingly equitable to harvest wind.
Wind energy is virtually free (in case you purchase the equipment) and there's no pollution. However, it is not a continuous source of energy(the velocity varies, and many times it is insufficient to make electricity) and it typically requires about one acre of land.
How wind energy works
The quantity of power that's available varies by wind speed. The quantity available is known as its power density which 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.
Usually, wind speeds increase as you get higher above the earth. For this reason, the standard turbine is a component of a tower at least 30 feet above obstructions.
There are two basic kinds 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 place. Guyed towers are supported on a concrete base and anchored by wires for support. They typically are not as heavy and most manufacturers produce tilt-down models which can be easily raised and lowered for maintenance.
The kinetic (moving energy) from the wind is harnessed by a device called a turbine. This turbine includes 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).
Wind turbine blades
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. These 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 according 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 its installation and is a much better option for more urban areas. An upwind turbine is made for the wind to impact the airfoils before it hits 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 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 will need to 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. 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 doesn't blow sufficiently.
When the home is linked with the grid, the surplus electricity that is created by the residential wind power system can be sold to the utility company to lower and sometimes even eliminate your utility bill. During times without 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 for people who need more than 100-200 watts of power for their home, business, or remote facility. Unlike solar PV systems, 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 wind turbine would cost about $8.00/watt in comparison to approximately $6.00/watt for a PV module.
That is why, all things being equal, PV is less expensive for very small loads. As the system size increases however, this "rule-of-thumb" reverses itself.
At 300 watts the wind turbine costs are down to $2.50/watt, while the PV costs still hover at $6.00/watt. For a 1,500 watt wind system the cost drops to $2.00/watt and at 10,000 watts the cost of a wind generator(excluding electronics) is down to $1.50/watt.
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