Wind Electric Systems

Wind is created by the unequal heating of the Earth’s surface by the sun.  Wind turbines convert the kinetic energy in the wind into mechanical power that runs a generator to produce clean, nonpolluting electricity.

Wind Electric Systems have developed to the point where today’s small-scale turbines are versatile and modular.  Their rotors consist of two or three blades that are aerodynamically designed to capture the maximum energy from the wind.  The wind turns the blades, which spin a shaft connected to a generator that makes electricity.  A mainframe supports the rotor, generator, and tail that aligns the rotor into the wind.

Often times because of the way the system works, there is excess power generated... net metering is one way in which many states and utilities handle this excess electricity.

 
Turbines and Towers

Turbines are mounted on towers – typically 80-120 feet high – which place the blades high enough to be exposed to the wind.  The taller the tower the more power the wind system can produce.  The tower also raises the turbine above air turbulence created by objects (buildings, trees, etc.) near ground level.  

As a rule of thumb, the bottom of the rotor blades should be at least 30 feet above any obstacle within 300 feet of the tower.  Towers may be self-supporting, but more commonly use guy wires for improved safety.

Other Components

In addition to the tower and turbine, small wind electric systems require:

• Foundation – usually made of reinforced concrete

• Wire run, to conduct electricity from the generator to the electronics

• Disconnect (or safety) switch, which allows the electrical output to be isolated from the electronics

• Power processing (or conditioning) unit, which makes the turbine power compatible with the utility power

• System energy meter, which records energy production

If the system is designed to stand alone or operate during a power outage, it will need deep-cycle batteries (like the ones used for golf carts) to store power, and a charge controller to keep the batteries from overcharging. A grid-connected system not designed to operate during a power outage does not need batteries.

Locating Wind Electric Systems

This map gives a general idea of the wind resources available in different parts of the United States.  Annual average wind power is classified from lowest (Class 1, shown on this map in white) to highest (Class 7).  Large-scale turbines require a minimum of a Class 3 wind regime (and prefer a Class 5), however small wind electric systems can be successfully installed in Class 2 or better wind regimes.  Class 2 corresponds to average annual wind speeds of 9-11 miles per hour, or 4-5 meters per second.

Many areas of the country qualify as having sufficient wind resources for small wind electric systems.  Wind resource maps give only a rough estimate of whether a particular location is windy enough to make small wind energy economic.  Local terrain and other factors also influence the wind power available at a specific site.

Indicators of good topography include:

• gaps, passes, gorges, and long valleys extending down from mountain ranges;
• high elevation plains and plateaus;
• plains and valleys with persistent down slope winds associated with strong pressure gradients;
• exposed ridges and mountain summits;
• coastlines and immediate inland strips with minimum wind barriers and vegetation;
• upwind and crosswind corners of islands;
• wind deformed vegetation: flagging of trees and shrubs;
• surface materials deposited by the wind to form playas, sand dunes, and other types of “eolian” landforms

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Source:  American Wind Energy Association