 Winds are caused by the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth.  Wind flow patterns are modified by the earth's terrain, bodies of water, and vegetative cover.  This wind flow, or motion energy, when "harvested" by modern wind turbines, can be used to generate electricity.

 Wind Turbines use blades to collect the wind’s kinetic energy. › The wind flows over the blades creating lift (like the effect on airplane wings) which causes them to turn. › The blades are connected to a drive shaft that turns an electric generator to produce electricity.  A turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity.

 Horizontal-axis : › like the traditional farm windmills used for pumping water  Vertical-axis : › eggbeater-style Darrieus model, named after its French inventor.  Most large modern wind turbines are horizontal-axis turbines.

 Wind resources are characterized by wind- power density classes › Class 1 (the lowest) to class 7 (the highest).  Class 3 is the average class with good wind resources because they have an average annual wind speed of at least 13 miles per hour  These locations in the United States include: › Alaska › mid north western states such as Colorado, Wyoming, and Indiana, the Dakotas and Montana

 The technology requires a higher initial investment than fossil-fueled generators.  Roughly 80% of the cost is the machinery, with the balance being site preparation and installation.  However, wind costs compared to fossil fuels are much more competitive with other generating technologies because there is no fuel to purchase and minimal operating expenses.  Costs $0.04 per kWh  The initial cost of wind turbine is split into 3 categories › 500 for 400 W › 6,000 dollars for 4kWh › 50,000 dollars for 20 kWh

 Cost of tower › The higher tower the better because of wind consistency and less turbulence › ft tower = 5,000-8,000 dollars › ft= 12,000-30,000  Cost of instillation (foundation/electrical): › equipment could cost between $3,000-7,000 › Instillation cost also depends on terrain and heat  Maintenance costs: › 1-3% of initial cost of wind turbine each year on maintenance.  Ex: $ for a 20,000 $ turbine  Making a turbine can be a lower cost › EX; 200 $ for 800 W.

 There is some concern over the noise produced by the rotor blades,  Visual impacts  Birds and bats having been killed by flying into the rotors.  Most of these problems have been resolved or greatly reduced through technological development.  Can be damaged by heavy winds or storms

 Wind does not flow when energy is needed so this power can be inconsistent and intermittent.  Wind cannot be stored › although wind-generated electricity can be stored, if batteries are used  Not all winds can be harnessed to meet the timing of electricity demands.

 Wind energy is a free, renewable resource › Power cuts and power failures are almost non existent.  Wind energy is also a source of clean, non-polluting, electricity. › Unlike conventional power plants, wind plants emit no air pollutants or greenhouse gases.  According to the U.S. Department of Energy, in 1990: › California's wind power plants offset the emission of more than 2.5 billion pounds of carbon dioxide, › 15 million pounds of other pollutants that would have otherwise been produced. › It would take a forest of 90 million to 175 million trees to provide the same air quality.

 In 2008, wind machines in the United States generated a total of 52 billion kilowatthours, about 1.3% of total U.S. electricity generation.  Cheapest forms of energy available therefore can be used by mostly everyone  Many utilities around the country offer green pricing options that allow customers the choice to pay more for electricity that comes from renewable sources to support new technologies

 Generation from wind in the United States nearly doubled between 2006 and  New technologies have decreased  the cost of producing electricity from wind, and growth in wind power has been encouraged by tax breaks for renewable energy and green pricing programs.

 Batteries in wind turbines store and harvest wind energy.

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