Nowadays the globalization and the economy expansion of the emerging countries demand anincreasing amount of energy. Therefore, energy production as well as the efficiency of energyusage, is essential for future developments of societies. Renewable energies appear as a turnkeysolution that could support the growing demands, and at the same time not being harmful to theenvironment [1]. Within the types of renewable energies, wind energy could be considered asone with large potential.In this paper I present the study of a Swedish wind farm placed in Rockneby.Once the wind turbines were installed and working correctly, a discrepancy between the realenergy obtained and the theoretical energy indicated by the manufacturer was detected. Thestored data in the SCADA system were compared with the values provided by the manufacturerand several analyses were performed. Initially an anomaly in the power residual deviation wasdetected. It was showing an unusual behaviour at high wind speeds. The variation of the airdensity in the wind farm at hub height was considered as a possible reason of the disagreementobserved in the power parameters since the reference density used by the manufacturer was aconstant value calculated in laboratory environment. However, this idea was rejected becausethe power generated in both conditions is similar. The pitch angle was analysed after detectinga significant variations in wind speed measurements made by the anemometer in the turbinenumber three. As a result, it was found a pitch variation in the turbine which seems due to afailure in the anemometer. As a final result, the turbulences were analysed giving as aconclusion that the turbulence intensity were situated around 20%. Therefore, I mainly suggestas a possible explanation of this fact the influence of the turbulence accompanied of a badcalibration or failure in the anemometers.

This disquisition aims for the study of turbulence intensity influence over the power performance of different sizes of turbines with the intent to validate a hypothesis. The hypothesis formulated for the analysis is the relationship between the rotor diameter (turbine size) and turbulence intensity. The hypothetical relationship is that the smaller turbines tend to experience more influence on the power performance from the turbulence in comparison with larger ones. For this examination, three different wind turbines of models Vestas V90, V100, V126 were chosen from three Swedish wind farms. The power performance of turbines at various levels of turbulence intensity were analyzed and the power deviation from the mean value due to influence of turbulence were assessed. The power deviation values of different turbines were compared at same level of wind speeds and also the power coefficients at same level of tip speed ratios were compared to validate the hypothesis. It was observed that the hypothesis seemed to appear true as higher influence on power curves were observed on V90 compared to others. Nevertheless, there were some obscene results which might be due to several factors such as influence of variation in hub height, site and inadequacy of data. / Detta examensarbete syftar till att studera hur ett vindkraftverks storlek påverkar inflytande från turbulens på effektuttaget. Hypotesen är att vindkraftverk med mindre rotordiameter påverkas mer av turbulens än de större. Tre vindkraftverksmodeller (Vestas V90, V100 och V126) från svenska vindkraftsparker valdes ut. De olika modellernas effektuttag för olika grader av turbulens analyserades och avvikelsen från effektmedelvärdet jämfördes. Effektavvikelserna samt verkningsgradsavvikelsen  för de olika vindkraftverksmodellerna jämfördes vid samma vindhastighet respektive löptal för att kunna testa hypotesen. Hypotesen styrks då den mista modellen (Vestas V90) påverkas mest av turbulens. Resultatet har dock troligtvis påverkats av andra faktorer såsom tornhöjd, terräng och en begränsad mängd data.