Method and installation for extracting energy from a flowing fluid

1. Turbine farm comprising at least a first turbine and at least a second turbine for energy extraction from a flowing fluid, further comprising a control system, wherein the control system is able, when the second turbine is on the lee side of the first turbine, below nominal power, to lower the axial induction (a) of the first turbine with respect to the second turbine so as to extract less energy, by turning the blade angles of a rotor of the first turbine towards a feathering position, wherein the control system sets the axial induction (a) of the at least one first turbine in the farm as a function of the wind direction, and of the distance to the at least one second turbine located in the lee.

2. The turbine farm of claim 1 wherein the axial induction (a) of the first turbine is reduced to about 0.25 or less.

3. The turbine farm of claim 1 , wherein lowering of the axial induction (a) is further effected by reducing the speed of revolution of the rotor.

4. The turbine farm of claim 1 , wherein lowering of the axial induction (a) is further effected by reducing the chord of the blades.

5. The turbine farm of claim 4 wherein at least the first turbine has blades, each blade having a chord characteristic,

Nc

r

⁢

λ

r

2

r

,

of less than 3.75, where r is a radial distance that runs between 0.5R and 0.8R, where R is the radius of the rotor.

6. The turbine farm of claim 1 , wherein the control system sets the axial induction of the first turbine on the basis of a measure for the turbulence determined at the second turbine that is located essentially on the lee side of the first turbine.

7. The turbine farm of claim 1 , wherein the control system optimises the farm performance measured in terms of maximum yield andlor minimum loads by adjusting the axial inductions (a) of individual turbines.

8. The turbine farm of claim 1 , wherein at least one wind speed at least one first turbine, essentially located on the windward side of the farm based on the dominant wind direction, differs in terms of axial induction from at least one second turbine, essentially located on the lee side of the farm, by on average more than 0.05.

9. The turbine farm of claim 1 wherein the axial force of the entire farm is reduced such that the power of another farm located in the lee is increased.

10. Method for a turbine farm comprising at least one first turbine and an at least second turbine for energy extraction from a flowing fluid, wherein the method comprises lowering the axial induction (a) of the first turbine with respect to the second turbine so as to extract less energy, when the second turbine is on the lee side of the first turbine, below nominal power, by turning the blade angles of the rotor of the first turbine towards a feathering position, the axial induction (a) of at least one first turbine in the farm being set as a function of the wind direction, and of the distance to at least one second turbine located in the lee.

11. Control system for a turbine farm comprising at least a first turbine and at least a second turbine for energy extraction from a flowing fluid, wherein the control system is able, when the second turbine is on the lee side of the first turbine, below nominal power, to lower the axial induction (a) of the first turbine with respect to the second turbine so as to extract less energy by turning the blade angles of the rotor of the first turbine towards a feathering position, the axial induction (a) of at least one first turbine in the farm being set as a function of the wind direction, and of the distance to the at least one second turbine located in the lee.

12. The control system according to claim 11 , wherein the control system sets the axial induction of at least one first turbine in the farm as a function of the wind direction.

13. Turbine provided with control system wherein the control system includes at least a first turbine and at least a second turbine for energy extraction from a flowing fluid, characterised in that the control system is able, when the second turbine is on the lee side of the first turbine, below nominal power, to lower the axial induction (a) of the first turbine with respect to the second turbine so as to extract less energy by turning the blade angles of the rotor of the first turbine towards a feathering position, the axial induction (a) of at least one first turbine in the farm being set as a function of the wind direction, and of the distance to the at least one second turbine located in the lee.