MAAPS - Wind Education

Wind: Winds are often referred to according to their strength, and the direction the wind is blowing from. Short bursts of high speed wind are termed gusts. Strong winds of intermediate duration (around one minute) are termed squalls. Long-duration winds have various names associated with their average strength, such as breeze, gale, storm, hurricane, and typhoon. Wind occurs on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, to global winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two main causes of large scale atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet (Coriolis effect). Within the tropics, thermal low circulations over terrain and high plateaus can drive monsoon circulations. In coastal areas the sea breeze/land breeze cycle can define local winds; in areas that have variable terrain, mountain and valley breezes can dominate local winds.

Wind is caused by differences in pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure. On a rotating planet the air will be deflected by the Coriolis effect, except exactly on the equator. Globally, the two major driving factors of large scale winds (the atmospheric circulation) are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces) and the rotation of the planet. Outside the tropics and aloft from frictional effects of the surface, the large-scale winds tend to approach geostrophic balance. Near the Earth's surface, friction causes the wind to be slower than it would be otherwise. Surface friction also causes winds to blow more inward into low pressure areas...... ok enough of the science lets get to the good stuff!

Or, for a simpler explanation..........

Uneven heating of the Earth’s surface by the sun causes the wind. The warmer air in some places rises. The resulting low pressure area draws in cooler air. Wind patterns are affected by the spin of the planet, weather patterns, and terrain.

Wind energy potential increases very rapidly with increasing wind speed. If fact, if wind speed doubles the energy content goes up by a factor of eight.

How Does it Help you produce Electricity?

Electricity produced by wind generation can be used directly (grid tie applications), as in water pumping applications, or it can be stored in batteries for use when needed. Wind generators can be used alone, or they may be used as part of a hybrid system, in which their output is combined with that of photovoltaics, and/or a fossil fuel generator. Hybrid systems are especially useful for winter backup of home systems where cloudy weather and windy conditions occur simultaneously.

The most important decision when considering wind power is determining whether or not your chosen site has enough wind to generate the power for your needs, whether it is available consistently, and if it is available in the season that you need it.

The power available from wind varies as the cube of the wind speed. If the wind speed doubles, the power of the wind (ability to do work) increases 8 times.
For example, a 10 mile per hour wind has one eighth the power of a 20 mile per hour wind.
(10 x 10 x 10 =1000 versus 20 x 20 x 20 = 8000).

One of the effects of the cube rule is that a site which has an average wind speed reflecting wide swings from very low to very high velocity may have twice or more the energy potential of a site with the same average wind speed which experiences little variation.This is because the occasional high wind packs a lot of power into a short period of time. Of course, it is important that this occasional high wind come often enough to keep your batteries charged. If you are trying to provide smaller amounts of power consistently, you should use a generator that operates effectively at slower wind velocities.

Wind speed data is often available from local weather stations or airports, as well as the US Dept. of Commerce,National Climatic Center in Asheville, N.C.You can also do your own site analysis with an anemometer or totalizer and careful observation. Installation of generators should be close to the battery bank to minimize line loss, and 30 feet higher than obstructions within a 300 foot radius. The tower should be well grounded.

How Does it Work?

These systems connect to your household wiring, just like a large appliance! They work cooperatively (Net Meetering) with your local utility power provider. Often you will be getting some power from both the wind turbine and the power company. If there is no wind, the power company supplies all the power needed. As the wind turbines begins to work the power you draw from the power company is reduced … causing your power meter to slow down. This reduces your utility bills.

If the wind turbine is putting out exactly the amount of power your home needs, the power company’s meter will stop turning. At this point you are not buying any power from the utility company. If the wind turbine produces more power than you need it is sold to the power company. Rates vary, but in most States your utility meter will actually turn backwards! No changes in the household wiring are needed. It is very easy to add these systems to an existing home. The most cost-effective systems do not have batteries and they can not supply power during utility power outages. Systems that can supply back-up power during outages are available, but at a higher cost.

A home sized wind turbine is big: 23 foot blade diameter and a 80-120 foot tall tower. We recommend a minimum property size of 1 acre. Some areas do not have a sufficient wind resource. We recommend a minimum wind resource of DOE Class 2.

WInd Education: Just the Basics......