Siting and Installing a Wind Turbine

Wind turbines can be installed in a variety of ways and at a variety of scales. A single turbine is relatively straightforward to install on a site, requiring basic mounting structures to support it. The requirements for selecting an appropriate site and determining how much electricity a turbine can generate can be more complex.

Choosing a Site

A wind turbine’s location has a major effect on the amount of electricity it produces and, thus, on its cost-effectiveness. The quality of a wind turbine site depends on many things. Factors that influence the economics of a site include:

  • Wind speed: The most critical site characteristic is average wind speed at hub height (the center of the turbine on top of the turbine's shaft).
  • Proximity: Building new transmission lines or lengthy interconnections to loads can be prohibitively expensive. A utility-scale wind installation that will provide power for the electric grid must generally be sited near power lines that can handle its power. In off-grid applications, turbines must be sited near the place where the electricity will be used.
  • Accessibility: A site must be accessible, via roads or other means, to allow for wind turbine installation and maintenance.
A variety of other considerations also come into play, including:
  • Ownership and financing structures
  • Local permitting and zoning requirements
  • Visual impacts
  • Noise impacts
  • Impacts on birds, bats, and other species

Options for Using and Selling Power
Middelgrunden wind farm outside of Copenhagen Harbour, Denmark.
20 turbines provide a total of
40 MW electricity.

Wind turbines can be deployed individually, in small clusters, and in large-scale arrangements known as wind farms or wind parks. Three types of uses exist:

  • Off-grid applications: In this scenario, the wind turbine is connected to a building or site but not to the electric grid. Off-grid wind turbines are typically linked to battery storage and/or solar photovoltaic systems to provide electricity when the wind is not blowing.
  • Grid-tied, consumer-side applications: In this scenario, a single turbine is typically located on a customer site and connected to the electric grid. Electricity is used to meet on-site requirements, and excess electricity may be fed into the grid for sale and delivery to others.
  • Grid-tied, utility-scale applications: In this scenario, the wind power from as few as one to as many as hundreds of individual turbines is is fed directly into the electric grid for sale and delivery of electricity to many customers.

Turbine Sizes and Capacities

Wind energy can be cost-competitive in diverse applications because systems can be sized to meet site-specific needs. Commercially available turbines range in capacity from 0.25 kW all the way up to 4.5 MW, a very large and visible machine. When operating at full power, the smallest and the largest wind generators can supply enough electricity to power a few light bulbs and thousands of homes, respectively.

The capacity of a turbine is determined largely by its rotor diameter. Present-day technology may be divided into three broad size ranges, briefly characterized below:

  • Residential: rated capacity below 30 kW, rotor diameter of 4 to 43 ft, hub height of 60 to 120 ft.
  • Medium: rated capacity between 30 and 500 kW, rotor diameter of 43 to 100 ft, hub height of 115 to 164 ft.
  • Commercial: rated capacity between 500 kW and 4.5 MW, rotor diameter of 100 ft to more than 325 ft, hub height of 164 to more than 260 ft.

Rated capacity is a measure of electricity generation under ideal conditions. In the real world, the wind blows intermittently, at varying speeds. Wind speed at hub height is the main determinant of actual capacity.

The power available from wind is proportional to the cube of its speed, which means that twice as much wind produces eight times as much electricity. This has three important implications:

  1. at low wind speeds, little power can be generated;
  2. even small increases in average speed correspond to a significant increase in the amount of electricity produced; and
  3. there is much more energy available at high wind speeds.

Because the wind does not blow constantly, the actual power output of a turbine is generally much lower (generally 25 to 40%) of its rated capacity. A 1 MW turbine with a 30% capacity factor would have an average output of 0.3 MW.

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