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The power output from wind turbines increases with the cube of windspeed, so that a 25% increase in wind speed will double the energy output. Small wind turbines tend to be poorly sited, out of the public view, which compromises performance. Siting a wind turbine on high ground will produce a large increase in the energy output, usually offsetting the extra cable costs.

  • What is a megawatt or a megawatt-hour?

    Manufacturers measure the maximum, or rated, capacity of their wind turbines to produce electric power in megawatts (MW). One MW is equivalent to one million watts.
    The production of power over time is measured in megawatt-hours (MWh) or kilowatt-hours (kWh) of energy. A kilowatt is one thousand watts. Production of power at the rate of 1 MW for 1 hour equals 1 MWh of energy.

  • What is the power capacity of wind turbines?

    General Electric (GE) makes a once widely used 1.5-megawatt model. 1.5 MW is its rated, or maximum, capacity, at which rate it will produce power when the wind is in the ideal range for that model, between 27 and 56 mph. Turbines are now generally in the range of 2-3 MW.

  • What determines how much power a wind turbine can produce?

    The power is generated from the energy in the wind, so a turbine’s power is determined by its ability to capture that energy and convert it to rotational torque that can turn the generator and push electrons into the grid. A taller tower provides access to steadier winds, and larger blades capture more wind energy. A larger generator requires larger blades and/or stronger winds.

  • How much energy do wind turbines produce?

    Every wind turbine has a range of wind speeds, typically around 30 to 55 mph, in which it will produce at its rated, or maximum, capacity. At slower wind speeds, the production falls off dramatically. If the wind speed decreases by half, power production decreases by a factor of eight. On average, therefore, wind turbines do not generate near their capacity. Industry estimates project an annual output of 30-40%, but real-world experience shows that annual outputs of 15-30% of capacity are more typical.
    With a 25% capacity factor, a 1.5-MW turbine would produce

    1.5 MW × 365 days × 24 hours × 25% = 3,285 MWh = 3,285,000 kWh in a year.

  • What is “capacity factor”?

    The capacity factor is the actual output over a period of time as a proportion of a wind turbine or facility’s maximum capacity. For example, if a 1.5-MW turbine generates power over one year at an average rate of 0.5 MW, its capacity factor is 33% for that year.

  • What is the typical capacity factor for industrial wind turbines?

    The average capacity factor for 137 U.S. wind projects reporting to the Energy Information Agency in 2003 was 26.9%. The total capacity factor for EU-27 countries in 2007 was 13%, according to the EIA.

  • What is the difference between capacity factor and availability?

    A wind turbine may be “available” for 90% or more of the time, but its output depends only on the wind. Without the wind, it is like a bicycle that nobody rides: available, but not spinning.
    The turbine’s “capacity factor” is its actual average output as a fraction of its full capacity. This is usually between 15% and 30%.

  • Do wind turbines work 30% of the time or 90%?

    Neither. The first figure is a theoretical capacity factor, the amount of energy actually produced over a year as a fraction of the turbines’ maximum capacity. The second figure is availability, the amount of time that a turbine is not shut down. Neither figure expresses the amount of time that a wind turbine is actually generating electricity.

  • How much of the time do wind turbines generate energy?

    Wind turbines generate electrical energy when they are not shut down for maintenance, repair, or tours and the wind is between about 8 and 55 mph. Below a wind speed of around 30 mph, however, the amount of energy generated is very small. Wind turbines produce at or above their average rate around 40% of the time. Conversely, they produce little or no power around 60% of the time.

  • How many homes can a wind turbine power?

    Proponents often express projected output as “enough to power x homes.” According to the Energy Information Agency, the average US household uses 888 kWh per month, or 10,656 kWh per year. An average 1.5-MW turbine (26.9% capacity factor) would produce the same amount of electric energy as that used by almost 332 households over a year.
    It must be remembered, though, that wind power is intermittent and variable, so a wind turbine produces power at or above its annual average rate only 40% of the time. That is, most of the time, it is not providing its average power to its average number of homes. And the times of high wind production rarely correspond with times of actual demand on the grid.
    It must also be remembered that residential use accounts for only a third of our total electricity use.

  • What is the difference between large and small turbines?

    Small turbines are designed to directly supply a home or other building. Their variable output is balanced by battery storage and supplemented by the grid or an on-site backup generator.
    Large turbines are designed to supply the grid itself. The variable output of large wind turbines adds to the complexity of balancing supply and demand, because there is no large-scale storage on the grid.

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