Power Performance Test on a Full-Scale Wind Turbine
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There is a standard made by the International Electrotechnical Commission (IEC) for how a power performance test on a full-scale wind turbine should be performed. By using this standard as a guideline, I have performed a power performance test on the 3 MW wind turbine at Valsneset. This was done by measuring the incoming wind towards the wind turbine rotor area with a lidar in conjunction with a cup anemometer at a 33 m high meteorological mast (met-mast). The lidar and cup anemometer measurements were in accordance. Before this, the measuring by the lidar was verified against sonic anemometer measurements at the heights 40 m, 70 m and 100 m. The measurements by the sonic anemometers and the lidar correlated well at 70 m and 100 m, while at 40 m the lidar underestimated the cup anemometer by 6 %. The cup anemometers on the met-mast at Valsneset were calibrated in the wind tunnel at NTNU, so that now the measurements by these anemometers have a satisfactory reliability. The measurements by the cup anemometer on the nacelle of the wind turbine were also compared to the lidar measurements. They were in accordance to some degree, but with significant deviations as well. The reason is that the rotating turbine blades and the nacelle disturb the wind that the nacelle cup anemometer measures. The efficiency curve was calculated by dividing the produced power with the incoming wind power for every 10-minute interval. The incoming wind power was found by using the measured wind speed and direction at eleven heights from 40 m to 140 m. The efficiency curve tops at 43,7 % at a wind speed of 8,2 m/s. This is in good agreement with the other big producers of wind turbines. The power curve in combination with the probability distribution of the wind speeds at the turbine location is the basis for the calculation of the annual energy production (AEP) for this wind turbine. The high performance of the wind turbine and the excellent wind conditions at Valsneset give an AEP estimate of 14,8 GWh and annual cash inflow of NOK 7.509.900.Power performance prediction, budgeting, turbine control and electric grid planning rely on the wind measurements. It is therefore important that the measurements are accurate. This Master thesis has emphasized this. The obtained results are reliable and well founded. However, the efficiency measurements are characterized by a significant spread for lower wind speeds. This increases the uncertainty. The scatter is mainly due to the variable behavior of the wind, and it is difficult for both the turbine and measuring devices to react perfectly to these variations. These variations are wind turbulence and change in wind direction in both time and space. Still, by using equations that take turbulence intensity, speed shear and directional shear into account, the results in this report hold high standards. This report shows that lidar measurements are satisfyingly accurate, and the lidar s simplicity makes it the top choice as the measuring device in modern wind resource assessment.