Renewable sources of energy

The power of wind

Some great benefits of wind energy are that it is virtually free (once you purchase the equipment) and there is no pollution. The disadvantages include the fact that it's not a continuing source (the velocity varies and many times it is insufficient to make electricity) and it typically requires about one acre of land


By MARY JONES
from her personal blog Residential Wind Energy


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

Some great benefits of wind energy are that it is virtually free (once you purchase the equipment) and there is no pollution. The disadvantages include the fact that it's not a continuing source (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 volume of power which can be found varies by wind speed. The quantity available is named it's power density and it's measured in watts per square meter. For this reason, the U.S. Doe 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.

Generally, wind speeds increase as you get higher above the Earth. This is why, the typical wind generator is installed on a tower no less than 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 may 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 consists of 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 two basic types of blades (drag style and lifting style). We all have seen pictures of traditional 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 much better option for the more urban areas around the globe. An upwind turbine is made for the wind to impact the airfoils before it does the tower.

These units normally have a tail on the turbine which is needed to maintain the unit pointed into the wind. A downwind turbine doesn't need 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 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 will not blow sufficiently.

When the home is linked with the grid, the excess electricity that is made 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 times 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 over 100-200 watts of power for their home, business, or remote facility. Unlike PV's, which remain 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 compared to approximately $6.00/watt for a Photovoltaic module.

This is the reason, all things being equal, Photo voltaic is more affordable 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 cost of a wind generator (excluding electronics) is down to $1.50/watt.



(Published: 12.07.2010.)