Wind is caused by the uneven heating of the Earth by the sun and the fact that temperatures will always be trying to reach an equilibrium (heat is always moving to a cooler area). With the rising price of energy and the damage to the environment from standard 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 is no pollution. The disadvantages include the fact it is not a consistent 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 quantity of power that is available varies by wind speed. The total amount available is called 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 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 generally required.

In general, wind speeds increase as you get higher above the Earth. For this reason, the standard wind generator comes with 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 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 termed as turbine. This turbine contains 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 two basic types of blades (drag style and lifting style). We all have seen pictures of old 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 an improved 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 must 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 will need to 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 linked with the utility grid
or store electricity in a battery for use when the wind does not blow sufficiently.

When the home is tied to the grid, the excess electricity that is made by the residential wind power system can be sold to the utility company to reduce and sometimes even eliminate your electric bill. During times with
not enough wind, the home is supplied power from the utility company. (Note from Wendy: This is how we are tied to the Energy Company with our solar and we just pay a bimonthly connection fee which is around $10 a month. It is a good backup and you do then feel that you are doing something for the ‘greater good’. This system is applicable and being used in Australia for wind and solar.)

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 stop 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 example, a small residential power wind generator would cost about $8.00/watt when compared with approximately $6.00/watt for a Photo voltaic module.

That’s why, all things being equal, Photo voltaic 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 mill 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.

About our guest writer – Mary Jones writes for the residential wind power website, her personal hobby blog related to ways to reduce CO2 and lower power costs using alternative power sources.

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