ABSTRACT
Before wind turbines are installed at a given site, measurements of wind speed over a period of time are made. Once the measurements are obtained and analyzed, the potential for energy production can be evaluated. Based on statistical methods wind is highly variable. Normally, the first step is to measure the frequency of wind speeds at the site, as shown in Figure 3.1. The horizontal axis is for wind speeds and the vertical axis is for the number of hours each wind speed value occurs in one year. In statistical terms, the data on the vertical axis is known as the “frequency of occurrence,” n. The wind speed on the horizontal axis can be represented by an index. For example, the index for wind speed = 0 is 1, the index for wind speed = 2.0 m/s is 2, and so on. The frequency of wind speed of 6.0 m/s as shown in Figure 3.1 is 1100 h. This can be written as
n4 1100= h (3.1)
In one year, the sum of all frequencies must equal to the number of hours in one year
8765 h (3.2)
Instead of using the raw frequency, we can use a relative term known as the “probability,” p, which is a normalized frequency. The probability of any wind speed is its frequency divided by the total number of hours in a year (8765 h).
