Power is the rate at which energy is used, and is measured in watts (W), kilowatts (kW) - equal to 1,000 watts or megawatts (MW) - equal to 1,000,000 watts.

Energy is measured in watt-hours (Wh), kilowatt hours (kWh) - equal to 1,000 watt hours or megawatt hours (MWh) - equal to 1,000,000 watt hours.

Energy demand (or supply) is calculated by multplying the power by the number of hours that the power is required (or supplied). For example, a 1 kilowatt TV run for 4 hours consumes 4 kilowatt hours. A wind turbine generating 150 kilowatts for 6 hours provides 900 kilowatt hours.

The 600 kilowatt Wind Turbine Generator running at its rated power for a year (8760 hours) would produce about 5,250 megawatt hours (MWh). However, the rated power is the maximum power that the WTG can generate; it will only generate this much power when the wind is greater than miles per hour. When the wind is about 15 mph, the WTG will generate about 150 kilowatts. When the wind is below about mph, the WTG will not generate any power. The variabiltiy of the wind in Barrington is such that the annual energy produced would be about 25% of its full capacity - about 1,300 MWh.

Energy in the Wind

The available power in the wind depends upon the density of the air, the wind speed and the area of the intercepted wind (for a wind turbine generator, it is the rotor area). For nominal air conditions (temperature, pressure and humidity), the total available power in a 15 mile per hour (mph)wind flowing through an area 50 meters (164 feet) in diameter is 360 kilowatts.

Of course, a 50 meter diameter wind turbine would need to be 100% efficient to generate 360 kilowatts of electricity with a 15 mph wind. Typically, a wind turbine is 40% efficient, so it would generate about 144 kilowatts under these conditions.

The power in the wind is proportional to the square of the diameter. That is, a 20% increase in diameter, would increase the power by 44%.

The power in the wind is proportional to the cube of the wind speed. That is, a 20% increase in wind speed, would increase the power by 73%.

Energy Comparison Chart - Demand

	Annual Energy (MWh)
Average U.S. Home	10
Barrington High School	1,200
Barrington Municipality	4,500
All of Barrington	180,000

Energy Comparison Chart - Supply

	Annual Energy (MWh)
High School WTG	1,320
Legion Way WTG	1,500
Cape Wind Farm	1,500,000