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Wind Energy Resource Assessment


       With the increasing scarcity of fossil energy and the deterioration of the global environment, the development of renewable and clean energy has become the energy goal of all countries. Wind power technology is more mature and highly reliable, and it is the fastest growing new energy source. In the feasibility study phase of wind farm construction, a wind energy resource assessment of the proposed wind farm is required.

      The purpose of the assessment is to provide a basis for determining the installed capacity of the wind farm and the selection and layout of the wind turbine, and to facilitate the economic and technical evaluation of the entire project. The level of wind energy resource measurement and assessment directly affects the wind farm site selection and power generation forecast, and is ultimately reflected in the actual power generation after the wind farm is completed.

Wind Energy Resource Assessment

 1.Wind measurement
1)Wind measurement includes wind direction measurement and wind speed measurement
2)Wind direction measurement: measuring the direction of the wind
3)Wind speed measurement: measure the distance the air moves in the horizontal direction per unit time

2.Calculation of wind energyresources
1)Wind: The phenomenon of air flow. Often refers to the horizontal movement of air relative to the ground, is a vector quantity, expressed in terms of wind direction and wind speed.
2)Wind speed: the distance the air moves in a unit of time. Usually refers to the horizontal displacement of air per unit of time, the air movement speed of the value, there are generally the following two kinds: instantaneous wind speed, relative to an infinitely small period of time, that is, a moment of gust speed; average wind speed, relative to a finite period of time, usually refers to the average of 2 / 10 minutes, etc. China requires the construction of wind farms, the local 10m high annual average wind speed in 6m / s.
3)Wind direction: the direction of the incoming wind is the wind direction. Wind direction observation is expressed in 16 directions or 0-360 degrees value. Static wind is expressed by "C".
4)Wind energy: the energy gained per second by a free-flowing air stream at speed V over an area A, i.e. the wind energy gained P.

P=(VA)*(pV²/2)=1/2pAV³ (p is the air density)

5)Wind power density: airflow vertically through the unit cross-sectional area of wind energy


Wind frequency: the percentage of the frequency of a certain time period in which a certain wind direction occurs and the total frequency of various wind directions (wind speeds) that occur in that time period is called the frequency of a certain wind direction.

3.Daily variation of wind speed
1)In general, the near-surface layer is the largest in the afternoon during the day, reaching the maximum at about 14:00, the smallest at night and early morning, and the smallest at about 6:00; the wind in the upper layer is small in the afternoon during the day and large at night; the daily variation of wind magnitude is larger in sunny days than in cloudy days, larger in summer than in winter, and larger on land than on the sea.
2)At sea; wind speed is small during the day and large at night.

4.Annual variation of wind speed
Generally, in the mid-latitudes of the Northern Hemisphere, it is the largest in winter and the smallest in summer; in most parts of China, spring is the period of alternating cold and warm air, so the spring wind is the largest.

5.Wind energy resource evaluation
By analyzing the time series of wind speed and wind direction observation in a certain area, the wind energy resource reserves of the area are estimated, and the wind power resource quantity, quality and distribution status are judged and evaluated.

6.Wind rose chart
(1)Wind rose diagram is based on the wind energy data obtained from the weather station observation, drawn from the diagram, because the shape of the diagram like a rose flower, so called "wind rose"
(2) The wind rose chart is divided into: wind direction rose chart and wind speed rose chart.
(3) Wind speed rose chart: indicates the size of the wind speed and the frequency of wind speed. (Anemometer)
(4) Wind rose chart: indicates the wind direction and the frequency of wind direction. (Wind vane)
(5) Wind frequency: the percentage of the number of times various wind directions occur in a certain period of time as a percentage of the number of observations.
(6) The dominant wind direction can be determined and the units are arranged perpendicular to the dominant wind direction.


  Wind direction of the 16 directions
  Wind direction of the 16 directions
Wind Energy Resource Assessment   
Wind Energy Resource Assessment

Wind direction rose chart:Each interval represents a wind frequency of 5%; the number in the center circle represents the frequency of the still wind.

7.Wind resource assessment generally requires the following items of analysis and calculation of observation data.
(1) Generally, a typical day and a typical month should be selected. The hourly wind speed change of a typical day can reflect the general daily change pattern of windpower, and the day-by-day wind speed change of a typical month can reflect the general monthly change pattern of wind power. And draw the hourly and daily histogram of the typical day and the typical month.
(2) The statistics of this item can be drawn according to the conventional method, and the annual wind direction rose diagram and wind speed rose diagram according to the statistical results.
(3) The wind has cut-in and cut-out speed, the cut-in speed is generally 3m/s or 5m/s, the cut-out speed is generally taken as 25m/s or 27m/s, and the wind speed between cut-in and cut-out is called effective wind speed. The range of effective wind speed generally varies depending on the origin and power of the fan. Count the cumulative wind speed value in the effective wind speed range of hours per year, and then average the value of the previous year, that is, the number of effective hours per year.
(4) The wind speed value is divided into a number of levels at 1m/s intervals, and the number of times each level of wind speed is counted, and the number of each level is divided by the total number of times each level of wind speed occurs, that is, the frequency of this level of wind speed. According to the statistical results to draw each grade wind speed frequency graph.

Measurement data

1.Wind measurement tower
Wind farm wind measurement tower can provide first-hand wind energy information for future wind farm investment and construction, is the basis for judging wind power resources. In the tower at different heights installed with anemometer, wind vane and temperature, pressure and other monitoring equipment. All-weather uninterrupted observation of the site wind conditions.
Different wind power areas, according to the wind farm scale and area should be initially determined the number of erected wind measurement tower. The wind tower location should represent most of the regional situation as far as possible, and the future wind turbine location with similar wind conditions, terrain characteristics, elevation and surface vegetation. It should neither be chosen at a higher nor a lower location in the wind farm area, and the vicinity of the tower should be relatively open, without tall buildings, trees and other obstacles.
For the field has been set up wind tower, should focus on the location of the wind tower, representative, each layer of the wind instrument operation and installation, for the erection of a long time wind tower should also test the calibration of the instrument. Also need to record the form of wind measurement tower, the choice of wind measurement instruments, height and sensor direction, wind measurement instruments around the terrain is open, 10 meters at the wind measurement equipment is not blocked, etc., to judge the wind measurement tower with wind farm wind resource status of the representative degree.

Wind measurement tower
Wind measurement tower

2.Selection of sensor installation height

(1) Wind speed sensor

Wind speed sensor: Two sets of wind speed instruments are installed at the hub height of the proposed turbine installation, i.e., the maximum height of the wind measurement tower. One purpose is to prevent the failure of one of the instruments, and the hub height wind data missing, the second is that two sets of wind data can be used for tower shadow revision and invalid or wrong data correction.
Install one set of anemometer at 10m height. Because the upper level anemometer is susceptible to failure due to freezing, strong winds, etc., or due to maintenance difficulties and deferred repair resulting in missing data, the bottom level wind data can be used for revision.
The rest of the anemometer according to the appropriate interval, installed in the impeller sweeping surface 10m integer height, the interval is generally taken 20m.




Wind speed sensor
Wind speed sensor

(2) Wind direction sensor

Wind direction sensor; installed a set of wind direction meter near the height of 10m, near the height of the proposed fan hub, and within the swept surface of the fan impeller respectively.

Wind direction sensor
Wind direction sensor

(3) Thermometer

     Install a set of thermometers near the height of the ground and the height of the proposed wind hub, respectively. Installed in the upper and lower height of each thermometer, is to determine the location of the wind tower atmospheric stability. In order to avoid the impact of ground thermal auxiliary radiation on the measurement, it is generally recommended that the lower thermometer is not less than 20m.

(4) barometer and hygrometer

In the proposed installation of wind hub height or near the ground installed a set of barometer and hygrometer.

3.Attention to the problem

(1) the same height can not be installed at the same time, including anemometers, including a variety of measurement sensors, wind direction, temperature, air pressure, humidity sensor height should be lower than the wind speed sensor 2m.
(2) In densely vegetated forest areas, when the forest canopy is high, the sensors planned to be installed at a height of 10m should be appropriately adjusted higher.
After the wind power measurement data processing is completed, the next need to statistically analyze the wind power measurement position at the proposed wind hub height and the rest of the observation height of various wind characteristics parameters. The statistical analysis of the wind characteristics at the wind power measurement location can help us to get a preliminary understanding of the wind resource situation at the wind farm.
Because of the representative selection principle of the wind measurement location, it is decided that the wind characteristic parameters of the wind measurement location can represent the wind resource condition of the area it covers. The detailed distribution of the wind resources over the entire area of the wind farm has to be realized by subsequent CFD simulations.
The wind characteristic parameters at the wind measurement location include the following.
Air density, wind speed, wind energy density, wind direction, wind shear index, turbulence intensity, wind speed distribution characteristics parameters, and maximum and maximum wind speed for a 50-year event.


       Wind resource assessment is very important for wind farm site selection and construction, accurate wind resource assessment is conducive to the determination of regional wind resource reserves, colleagues can also provide a strong reference basis for wind farm site selection, wind turbine selection and program development, for the effectiveness of wind power project construction has important significance.

wind farm
wind farm

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