Wind Power Potential

The most comprehensive, long-term source of information on wind speeds, pressure, and temperature is data collected at National Weather Stations. Other sources in the United States on record at the National Climatic Center, Asheville, North Carolina, are from Federal Aviation Administration stations, U.S. air bases, Coast Guard, etc. In the early 1960s anemometers at National Weather Stations were changed from their previous locations (20-30 m heights) on airport control towers, hangers, etc., to towers (around 6 m height) close to the runways and at least 1 km from buildings.

Average Size Windmill

FIGURE 3.11 Annual average wind direction at 25 and 50 m height, 10° sectors, Dalhart, Texas, April 1996-2000.

FIGURE 3.11 Annual average wind direction at 25 and 50 m height, 10° sectors, Dalhart, Texas, April 1996-2000.

Previously wind speed data at U.S. National Weather Service (NWS) stations were recorded on a strip chart and the observer estimated a wind speed over 1 to 2 min each hour. Wind speed data along with pressure, temperature, and other climatological data were put on magnetic tape for every hour. The National Weather Service converted to automated surface observation systems as of 1993-1994. Wind speed and direction are sampled at 1 Hz, averaged over 5 s, and rounded. Then a 2 min running average is calculated from the twenty-four 5 s samples. Data on CD-ROMs, data downloaded to a computer through the Internet, and data sheets of monthly summaries can be purchased (

If the wind speeds are known, then the average wind power or average wind energy per unit area can be estimated for any convenient time period, usually months, seasons, or year. When more than 1 year of data are available, then the year data or month data are averaged to obtain annual values by year or month. The wind power per area is referred to as the wind power potential or wind power density:

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where N is the number of observations.

Average values of temperature and pressure can be used to calculate an average density, and then the average power/area can be calculated for the available wind speed data. The result will be fairly accurate since the pressure and temperature will not vary over the month or year nearly as much as the wind speeds.

If the observations of wind speeds are compiled into a histogram, then the number of observations, n, in each wind speed bin could be changed to a frequency or probability by dividing the number of observations in a bin by the total number of observations:

where c is the number of classes or bins. If the wind speed units are changed or if the wind speed is changed due to height, then the resulting histogram or frequency distribution should be normalized to contain the same number of observations.

Of course, for a large number of observations, a computer program or a spreadsheet would alleviate a lot of drudgery. Notice that the average wind speed (same as mean wind speed) is just the summation of the probability times the wind speed for each class in a frequency distribution:

The average power/area can be calculated from a selected wind speed histogram or wind speed frequency distribution by

Note the wind power potential is calculated from the sum. In one sense the individual power/area values are in energy/time for each class (bin). So if the energy in each bin is calculated and summed, then the average wind power potential can also be calculated from this total energy divided by the number of hours.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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