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.

The wind power research at the division of Electricity at Uppsala University is aimed towards increased understanding of vertical axis wind turbines. The considered type of wind turbine is an H-rotor with a directly driven synchronous generator operating at variable speed. The experimental work presented in this thesis comprises investigation of three vertical axis wind turbines of different design and size. The electrical, control and measurement systems for the first 12 kW wind turbine have been designed and implemented. The second was a 10 kW wind turbine adapted to a telecom application. Both the 12 kW and the 10 kW were operated against dump loads. The third turbine was a 200 kW grid-connected wind turbine, where control and measurement systems have been implemented. Experimental results have shown that an all-electric control, substituting mechanical systems such as blade-pitch, is possible for this type of turbine. By controlling the rectified generator voltage, the rotational speed of the turbine is also controlled. An electrical start-up system has been built and verified. The power coefficient has been measured and the stall behaviour of this type of turbine has been examined. An optimum tip speed ratio control has been implemented and tested, with promising results. Use of the turbine to estimate the wind speed has been demonstrated. This has been used to get a faster regulation of the turbine compared to if an anemometer had been used.

No description available.

It is well known that the layout of a large wind turbine cluster aects the energyoutput of the wind farm. The individual placement and distances betweenturbines will in uence the wake spreading and the wind velocity decit. Manyanalytical models and simulations have been made trying to calculate this, butstill there is a lack of experimental data to conrm the models. This thesis isdescribing the preparations and the execution of an experiment that has beenconducted using about 250 small rotating turbine models in a wind tunnel. Theturbine models were developed before the experiment and the characteristicswere investigated. The main focus was laid on special eects occurring in largewind turbine clusters, which were named Global Turbine Array Eects.It was shown that the upstream wind was little aected by a large windfarm downstream, even though there existed a small dierence in wind speedbetween the undisturbed free stream and the wind that arrived to the rstturbines in the wind farm. The dierence in wind speed was shown to beunder 1% of the undisturbed free stream. It was also shown that the densityof the wind farm was related to the reduced wind velocity, with a more densefarm the reduction could get up to 2.5% of the undisturbed free stream at theupstream center turbine. Less velocity decit was observed at the upstreamcorner turbines in the wind farm.When using small rotating turbine models some scaling requirements hadto be considered to make the experiment adaptable to reality. It was concludedthat the thrust coecient of the turbine models was the most important parameterwhen analysing the eects. One problem discussed was the low Reynoldsnumber, an eect always present in wind tunnel studies on small wind turbinemodels.A preliminary investigation of a photo measuring technique was also performed,but the technique was not fully developed. The idea was to take oneor a few photos instantaneously and then calculate the individual rotationalspeed of all the turbine models. It was dicult to apply the technique becauseof uctuations in rotational speed during the experiment, therefore thecalculated values could not represent the mean value over a longer time period.