“You Don’t Have to be an Engineer to Understand Wind Power!” Mary Jones, Guest Editorial

Written by M. Glantz. Posted in All Fragilecologies

Published on September 07, 2010 with No Comments

Mary Jones, Guest Editorial

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

The benefits of wind energy are that it’s virtually free (once you buy the equipment) and there is no pollution. The disadvantages include the fact it’s not a continuous source of energy (that is, wind velocity varies and many times it is insufficient to produce electricity) and that it typically requires about an acre of land.

How Wind Energy Works

The quantity of power that is available varies by wind speed. The total amount available is known as its power density (measured in watts per square meter). The U.S. DOE (Department of Energy) has divided 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 mph or more. For effective power production, class 2 winds are often required (11.5 mph average speed).

Generally, wind speeds increase as you get higher above the Earth’s surface. Because of this, the normal wind generator is a component of a tower no less than 30 feet above obstructions. There are 2 basic kinds of towers employed for residential wind power systems, free standing and guyed. Free standing towers are self supporting and are usually heavier, meaning that they require special equipment (e.g., cranes) to erect them. Guyed towers are supported on a concrete base and anchored by wires for support. Typically, they are not as heavy and most manufacturers produce tilt-down models which can easily be raised and lowered for maintenance.

The kinetic (moving) energy from the winds is harnessed by a device known as a turbine. The turbine includes airfoils (blades) that capture the power of the wind and use it to turn the shaft of an alternator (like the alternator on a car, only bigger). There are 2 basic kinds of blades, drag style and lifting style. We all have seen pictures of traditional windmills with the large flat blades which are a good 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 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 its installation and is an improved option for the relatively more urban areas. An upwind turbine is made for the wind to impact the airfoils before it impacts the tower.

www.residentialwindturbines.org/residential-wind-turbine.jpg

These units ordinarily have a tail on the turbine which must maintain the unit pointing into the wind. A downwind turbine does not 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 permitted to turn at excessive speeds. Therefore, units should 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. Using residential wind power systems requires the home either to remain linked with the utility grid or to store electricity in a battery for use when the wind doesn’t blow at sufficient speeds. When the home is linked with the grid, the surplus electricity that is made by the residential wind power system can be sold to a utility company to reduce or even eliminate your utility bill. During periods with not enough wind, the home is supplied power from the utility company.

www.residentialwindturbines.org/wind-scheme-grid-tied.gif

The Price of Wind Energy

Small residential wind power turbines can be an attractive alternative — or an addition — to those people in need of more than 100-200 watts of power for their home, business, or remote facility. Unlike PVs (photo voltaics), which remain at basically a similar cost per watt independent of array size, the affordability of wind generators increases with increasing system size. At the 50-watt size level, for instance, a small residential power wind generator would cost about $8.00/watt when compared with approximately $6.00/watt for a photo voltaic module.

For this reason, everything being equal, photo voltaics are more affordable for very small loads. As the system size gets larger, however, this “rule-of-thumb” reverses itself. At 300 watts the wind generator costs are down to $2.50/watt, while the PV costs are still at $6.00/watt. For a 1500 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.

About Mary Jones:
Mary writes for the residential wind power systems weblog. Her blog centers on ideas to reduce carbon dioxide emissions and to lower energy costs by using alternative power sources.


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