Forecasting of wind turbine efficiency in Latvia by long-term wind speed measurements

The paper presents the assessment of power production efficiency of five wind turbine generator types in low-wind conditions typical for Latvia. The analysis considers wind turbines manufactured by the leading European producers - Nordex, Vestas, Enercon and Siemens. The study is based on 10-min measurements of wind speed from two on-shore sites in the north and north-west of Latvia using LOGGER 9200 Symphonie measurement systems mounted on met-masts. Based on the measurement analysis results, wind speed distribution curves are modelled for the heights of up to 150 m using power law approximation methods. The forecast of Annual Energy Production (AEP) is performed using the Weibull frequency distribution of wind speed for two heights for each corresponding wind turbine type. The results of the analysis show that the highest output efficiency can be achieved by Vestas and Nordex wind turbines, which power curves correspond to wind class III. Vestas V136-3.45 with hub height 132 m achieves maximum efficiency equal to 54.5% in Irbene site. For Enercon E101 and Siemens SWT-3.2-113, SWT-2.3-108 WTs, which are designed for wind class II, the values of the efficiency coefficient do not exceed 47.3% for hub height 142 m.