A guide to wind energy

(05/07/2010)

Wind is the result of the uneven heating of the Earth by the sun and the fact temperatures will always be attempting to reach an equilibrium (heat is obviously moving to a cooler area). With the rising cost of energy and the destruction of the environment from non-renewable fuels, it is increasingly equitable to harvest this renewable resource.

The benefits of wind energy are that it is virtually free (after you buy the equipment) and there is no pollution. The disadvantages include the fact that it is not a consistent source (the velocity 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 which can be found varies by wind speed. The total amount available is known as it's power density and it's measured in watts per square meter. Due to this, the U.S. Doe 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 even more. For effective power production, class 2 winds (11.5 mph average speed) are often required.

In general, wind speeds increase as you get higher above the Earth. For this reason, the typical windmill is a component of a tower at least 30 feet above obstructions. There are two basic kinds of towers used 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 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 may be easily raised and lowered for maintenance.

The kinetic (moving energy) from the winds is harnessed by a device called 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 two 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 designed 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 around the globe. An upwind turbine is created 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 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 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 doesn't 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 utility bill. During periods 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 more than 100-200 watts of power for their home, business, or remote facility. Unlike PVs, which stop 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 generator would cost about $8.00/watt in comparison to approximately $6.00/watt for a Photo voltaic module.

For this reason, 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 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.

Related categories:  Environmental technologies for Residential and Green homes   Solar power and photovoltaics   Wind power