


Theory Methodology Conclusions References Theory Performance of a turbine is characterised by the manner in which the three main indicators  power, torque and thrust  vary with tidal velocity. More emphasis is given to power in this analysis. Total power output of the turbine depends on various parameters  Rotational Speed of the turbine (Ω), Tip Speed Ratio,(λ), Power Co efficient (Cp), Radius of the Turbine Blade(R_{T}) and the tidal velocity. The actual Power is calculated using the formula P= 0.5 Cp ρ A V^{3} The tip speed ratio of the turbine is given by λ= Ω R_{T} / V_{T} back to top Methodology A computational analysis was carried out with an optimum blade design and a relation between the tip speed and Power Co efficient was obtained. This relation is used in further analysis. In order to analyse the power output from the turbine we have adopted two main methods
Two locations were chosen for the analysis, one with high tidal velocities (Kyle of Rhea), and the other with low tidal velocities (Kintyre Peninsula South). With each of these locations total power output is calculated by running turbines at constant and variable speeds. back to top Conclusions The graph above shows the power out puts for the site with high tidal velocities. The turbine is run at a variable speed (constant Cp) and constant speed (variable Cp). In both the conditions the turbine reaches the rated speed.
The table above shows the difference in Annual Energy when turbine is run at Variable Speed and Constant Speed. When the velocity is high there is not much of difference whether the turbine is run at Variable Speed or at a Constant Speed. The graph shows the power out puts for the site with low tidal velocities. When the turbine is run at a Variable Speed and a Constant Speed the rated speed is not reached. But there is considerable increase in power output.
In this table it is clearly seen that there is a considerable increase in annual energy when turbine is run at Variable Speed (constant Cp) than at Constant Speed (variable Cp). Therefore it can be observed that use of a turbine which runs at variable speed rather than at constant speed is justified when used in sites which have low tidal velocities. back to top References
 