Application of the Nacelle Transfer Function by a Nacelle-Mounted Light Detection and Ranging System to Wind Turbine Power Performance Measurement

Abstract

To examine the applicability of the nacelle transfer function (NTF) derived from nacelle light detection and ranging (LIDAR) measurements to wind turbine power performance testing without a met mast, wind turbine power performance measurement was carried out at the Dongbok wind farm on Jeju Island, South Korea. A nacelle LIDAR was mounted on the nacelle of a 2-MW wind turbine to measure wind conditions in front of the turbine rotor, and an 80-m-high met mast was installed near another wind turbine to measure the free-stream wind speed. The power measurement instruments were installed in the turbine tower base, and wind speeds measured by the nacelle anemometer of the turbine were collected by the SCADA (Supervisory control and data acquisition) system. The NTF was determined by the table method, and then the power curve drawn using the NTF by the nacelle LIDAR (PCNTF, NL) was compared with the power curves drawn in compliance with International Electrotechnical Commission (IEC) standards, 61400-12-1 and 61400-12-2. Next, the combined standard uncertainties of the power curves were calculated to clarify the magnitude of the components of the uncertainties. The uncertainties of annual energy production (AEP) were also estimated by assuming that wind speed is a Rayleigh cumulative distribution. As a result, the PCNTF, NL was in good agreement with the power curves drawn in accordance with the IEC standards. The combined standard uncertainty of PCNTF, NL was almost the same as that of the power curve based on IEC 61400-12-2.

Modified Power Curves for Prediction of Power Output of Wind Farms

“…As mentioned above, including meteorological variables such as air density, turbulence intensity, wind shear and wind veer, improves power prediction. Equations (9) and (18) provide two different rotor equivalent wind speeds that take into account the effect of these meteorological variables. The same bin-averaging method used for generating the current industry standard power curves can be used to generate modified power curves from the rotor equivalent winds speeds.…”

“…Wind speed can also be measured using nacelle-mounted anemometers. Recently, nacelle mounted LIDARs have been used as an alternative to anemometers [18,19]. However, wind speeds measured at the nacelle do not accurately represent the inflow due to the effect of the rotor on the flow.…”

“…Subscript 10 in Equations (18) and (19) denotes that equivalent wind speeds and rotor equivalent wind speed are calculated using ten-minute data. The main difference between U req 10 and U req s is that U req s is computed directly from data measured at 1 Hz rate, while U req 10 is the same variable, but approximated based on ten-minute data.…”

“…). (26) The only difference between Equations (26) and (18) is that, in Equation (26), none of the velocity terms are normalized by density. Integrating the new equivalent wind speed vertically, considering the section of rotor swept area each measured height represents, results in:…”

Numerical Study of Nacelle Wind Speed Characteristics of a Horizontal Axis Wind Turbine under Time-Varying Flow

“…Normally, only one or two met masts are built for one wind farm, which is not enough for accurate wind prediction of every wind turbine present in the wind farm. Nacelle LIDAR has been proposed for power measurement in recent years [1,2]. This technology is still under development and not widely applied.…”