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Renewable energy has received a lot of attention. In recent years, offshore wind power has received particular attention among renewable energies. Fixed-type offshore wind turbines are now the most popular. However, because of the deep seas surrounding Japan, floating types are more preferable. The floating system is one of the factors that raises the cost of floating wind turbines. Vertical axis wind turbines (VAWT) have a low center of gravity and can tilt their rotors. As a result, a smaller floating body and a lower cost are expected. A mechanism called a floating axis wind turbine (FAWT) is expected to further reduce the cost. FAWT actively employs the features of VAWT in order to specialize itself in the area of offshore floating-type wind turbines. The lifting line theory simulation was used in this study to discuss the performance of the FAWT under the tilted conditions and its wake field. The results show that a tilted VAWT recovers faster than an upright VAWT. This suggests that FAWTs can be deployed in high density and efficiently generate energy as an offshore wind farm using VAWTs. [ABSTRACT FROM AUTHOR]

With tidal energy demonstration projects with one or a small number of turbines having provided very positive results, the technology is moving to the commissioning and operation of tidal energy farms. For this next step, the understanding of the wakes generated downstream of the turbines is crucial to optimize the array performance. To date, the analysis of wakes of MW-scale tidal turbines has been made by numerical methods or experimentally with downscaled rotors. However, no consensus on a methodology to characterize wakes generated by full-scale turbines based on data measured on-site has yet been reached. The present paper introduces a new method to compare current velocity data measured before and during turbine operation that minimizes the impact of the spatial and temporal variability of tidal currents, thus enabling the estimation of the velocity deficit caused downstream of the turbine. Through this method, a characterization of the near wake was possible, with velocity deficits of 0.537, 0.463, 0.469 and 0.431 at 2D, 3D, 4D and 5D from the turbine. Results from this paper present a very valuable tool for the validation of numerical models aiming to estimate the wake losses in tidal energy farms. • Wake from a 0.5 MW bottom-fixed tidal turbine in a tidal site is characterized. • A new method to calculate velocity deficit with vessel-mounted ADCP data is presented. • Velocity deficit at the rotor hub height decreases from the turbine to a 5D distance. • Farther from 5D, the turbine impact on current velocity dissipates. [ABSTRACT FROM AUTHOR]