The WindSea Concept
Total energy production and wake losses
The results presented are taken from the study performed by Risø. Those results have been corroborated by analyses performed by the project and by the model tests. The Risø analysis covers the whole range of wind speeds (from 5 m/sec to 27 m/sec) while our own analysies and model tests are performed only for specific wind speeds.
The power production versus the main wind speed at 10 m above sea level is presented in figure 5.1. The figure presents two curves. The higher curve is for the downwind turbine standing alone, while the lower one is for the downwind turbine accounting for the wake effect (shadow) from the two upwind turbines.
The loss of power due to the wake effect is most significant for the low velocity in the range of 7 m/sec to 13 m/sec, while for high velocities the power production is almost unchanged.
It should be noted that the curves are dependent on the turbine properties and on the relative positions of the 3 turbines. By a suitable choice of turbines and positions the gap between the two curves may be reduced.
The total power produced by the turbine in a year is obtained by the combination of the power produced for each wind velocity and the probability of occurrence of this velocity.
By doing this operation for the two curves and taken the ratio of the two obtained numbers, the total power production reduction due to the wake may be calculated.
Risø has calculated this ratio for the given configuration to be 75% for the rear turbine. For the two turbines in front, there is no negative interaction between the two, hence this is calculated to 100 % for both.
Based on those production curves, the environmental data from Ekofisk and down time of 15% (this value is documented in the System Engineering activity) the power production for the 3 turbines is calculated to be in the range of 14,8 GWh/year for the 2 upwind turbines and 11,7 GWh/year for the downwind turbine.
This gives a total production of 41,4 GWh/year.
The production value is 93% of the maximal production of 3 like turbines (3 x 14,8 = 44,5 GWh/year).
The figure shows the distribution of the power production as a function of wind velocity. Most of the power is produced at velocities between 9 m/sec and 18m/sec.
