Sketch of the geographic setting of the study area and timeline of the records. Heavy diamond indicates the location of the two Enercon E-40 wind turbines and (, ), gray shading signs indicate Hungary, label the nearby ERA-40 grid points (empty circles), and and (empty squares) locate the grid points from the ERA-Interim database used for comparison. The timeline illustrates the overlapping periods 01/01/2000–08/31/2002 for and records and 01/01/2004–12/31/2005 for and time series. (Photograph: Sándor Zátonyi, http://www.panoramio.com)
Wind speed records for the , , and grid points (see Fig. 1) in the first 100 days of the overlapping period.
The same as Fig. 2 for the and (red) and (green) records.
Normalized histogram of wind speed for the time series and fitted generalized gamma [see Eq. (2)] probability density functions (thin black lines). The empirical parameters are summarized in Table II.
(a) Scatter plot for the equal time wind speeds measured at sites and . The regression line has the slope of 1.529. (b) Normalized empirical wind speed histograms for the turbine measurements (dark, blue) and the transformed record (light, orange): . (c) The same as (b) for the fitted probability distributions.
Electric power output measured at the turbines (thin black line) and (dashed black line) in three consecutive years; high frequency (10 min) data are smoothed by 1008 point (1 week) running average. Horizontal (blue) lines indicate the annual averages. (Percentage values with respect to the rated power are , , and for and , , and for , respectively.)
Power curve fit Eq. (3) of high frequency (10 min) measured nacelle anemometer data for .
Comparison of estimated electric output based on (see Fig. 5) and the power curve Eq. (3) from 6 h wind speed data for sites and (red) with direct measurements at the turbines and (green). Note that the latter two curves are 6 h averages of 10 min records.
Normalized histograms of electric power for the time series . The last two (green) are based on direct measurements; the others are estimated by the power curve Eq. (3) from the rescaled surface wind speeds , where the numerical value of is given in the second column of Table II. (The vertical scale is logarithmic.)
(a) The difference between the histograms for sites and shown in Fig. 9. (b) Histogram of annual average output power estimated from the record by and the power curve Eq. (3). The black arrow indicates the range of measured averages at and .
Equal time two-point correlation [see Eq. (1)] matrix for the time series in the overlapping periods (upper diagonal) and geographic distance in units of km (lower diagonal, in parentheses).
Fitted parameters of the normalized wind speed probability distributions for the time series , see Fig. 4. The mean value and standard deviation are taken over the entire available record lengths (see Fig. 1), the parameters of the generalized gamma distribution [see Eq. (2)] are denoted by , , and , and the mode (most probable value) is . The second column is the ratio of average wind speed at the turbine and at the given site .
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