Education
How wind energy works
By Mary Jones
Jul 5, 2010 - 12:25:55 AM

You no longer need to be a nerd to learn how wind energy works

Wind is a result from the uneven heating of the Earth by the sun and the fact that temperatures are invariably attempting to reach an equilibrium (heat is obviously moving to a cooler area).

With the rising expense of energy and the destruction of the environment from standard fuels, it is more and more equitable to harvest this renewable resource.

The benefits of wind energy are that it's virtually free (after you purchase the equipment) and there's no pollution.

The disadvantages include the fact it is not a constant 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's available varies by wind speed. The quantity available is termed it's power density which is measured in watts per square meter. That is why, the U.S. Department of Energy has separated wind energy into classes from 1 to 7. The average 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 usually required.

Usually, wind speeds increase as you get higher above the Earth. Due to this, the standard wind turbine is a component of 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 which means they take special equipment (cranes) to erect 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 is often easily raised and lowered for maintenance.

The kinetic (moving energy) from the winds is harnessed by a device termed as 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).

That there are two basic kinds of blades (drag style and lifting style). We all have seen pictures of old windmills with the large flat blades which 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 as to whether it is designed to be installed with the rotor in a horizontal or vertical 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 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 permitted 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 usage 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 will not blow sufficiently.

When the home is tied to the grid, the surplus electricity that is created 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 expense 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 turbines get less expensive with increasing system size. At the 50 watt size level, for example, a small residential power wind mill would cost about $8.00/watt in comparison to approximately $6.00/watt for a Photovoltaic module.

This is the reason, everything being equal, Photo voltaic is cheaper 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 price of a wind generator (excluding electronics) is down to $1.50/watt.

About the Author - Mary Jones writes for the residential wind energy web log, her personal hobby blog focused on ideas to reduce CO2 and lower energy costs using alternative power sources. [Mary's Bio.]