Method of operating floating offshore wind turbines

Abstract

A method for operating at least two floating offshore wind turbines (1) is disclosed. The wind turbines (1) are operated at respective first operating positions (7), and a previous and/or a future expected wear impact on each wind turbine (1) is estimated. At least one wind turbine (1) to be relocated to a respective second operating position (9) is identified, based on the estimated wear impact. The identified wind turbines (1) are moved to respective second operating position (9) and operated there.

Claims

1. A method for operating at least two floating offshore wind turbines, each wind turbine being connected to a first mooring arrangement at a respective first operating position, the method comprising the steps of: operating the wind turbines at their respective first operating positions, for each of the wind turbines, estimating a previous and/or a future expected wear impact on the wind turbine, identifying at least one wind turbine of the at least two wind turbines to be relocated to a respective second operating position, based on the estimated wear impact, disconnecting each identified wind turbine from the first mooring arrangement of its first operating position, moving each identified wind turbine from its respective first operating position to its respective second operating position, connecting each identified wind turbine to a second mooring arrangement at its respective second operating position, and operating each identified wind turbine at its respective second operating position.

2. The method according to claim 1, wherein the step of estimating a previous and/or a future expected wear impact on each of the wind turbines is based on a location of the operating positions of the wind turbines relative to a prevailing wind direction.

3. The method according to claim 1, wherein the step of estimating a previous and/or a future expected wear impact on each of the wind turbines comprises estimating a lifetime usage of each of the wind turbines.

4. The method according to claim 1, wherein the step of estimating previous and/or future expected wear impact comprises modelling meteorological and/or oceanic conditions, and estimating future expected wear impact based on the modelling.

5. The method according to claim 1, wherein the step of estimating previous and/or future expected wear impact is performed on the basis of sensor data obtained at the respective first and/or second operating positions.

6. The method according to claim 1, wherein the step of identifying at least one wind turbine comprises identifying at least one wind turbine with an experienced high wear impact, and wherein the step of moving each identified wind turbine comprises moving the at least one wind turbine with a high wear impact to a second operating position which provides an expected future wear impact which is lower than an expected future wear impact at the first operating position of the wind turbine.

7. The method according to claim 1, wherein the step of identifying at least one wind turbine comprises identifying at least one wind turbine with a low wear impact, and wherein the step of moving each identified wind turbine comprises moving the at least one wind turbine with a low wear impact to the second operating position which provides an expected future wear impact which is higher than an expected future wear impact at the first operating position of the wind turbine.

8. The method according to claim 1, further comprising the step of performing maintenance on at least one wind turbine and/or replacing or upgrading at least one component of at least one wind turbine.

9. The method according to claim 8, wherein the step of performing maintenance and/or replacing or upgrading at least one component is performed after the step of operating the wind turbines at their respective first operating positions and before the step of operating the wind turbines at their respective second operating positions.

10. The method according to claim 1, wherein the respective second operating position of at least one wind turbine is a respective first operating position of another wind turbine.

11. The method according to claim 1, further comprising the steps of: disconnecting the at least one wind turbine from the second mooring arrangement of its respective second operating position, moving the at least one wind turbine from its respective second operating position to a respective third operating position, connecting the at least one wind turbine to a third mooring arrangement at the respective third operating position, and operating the at least one wind turbine at the respective third operating position.

12. The method according to claim 1, wherein the step of estimating a previous and/or a future expected wear impact on the at least one wind turbine is performed after an extreme event selected from the group of a tsunami, a typhoon, a failure of a component of the at least one wind turbine, a volcanic particle impact event, and a bird or insect migration impact event.

13. The method according to claim 1, wherein the first operating position is in a first wind farm and the second operating position is in a second wind farm different from the first wind farm for at least one of the floating wind turbines.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in further details with reference to the accompanying drawings in which

(2) FIG. 1 shows a floating offshore wind turbine operating at a first operating position,

(3) FIG. 2 shows the floating offshore wind turbine of FIG. 1 being detached from a mooring arrangement at the first operating position,

(4) FIG. 3 shows the floating offshore wind turbine of FIGS. 1 and 2 being moved from the first operating position,

(5) FIG. 4 shows the floating offshore wind turbine of FIGS. 1-3 being moved towards a second operating position, and

(6) FIG. 5 is a graph illustrating lifetime usage as a function of time for two floating offshore wind turbines being operated in accordance with a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) FIGS. 1-4 illustrate steps of a method according to an embodiment of the invention. FIG. 1 shows a floating offshore wind turbine 1 mounted on a floating foundation 2, which is attached to a mooring arrangement via mooring lines 3 at a first operating position. The number of mooring lines 3, and whether these mooring lines 3 are connected to the sea floor or to other structures depend on design choices and can hence be optimized by the skilled person.

(8) The wind direction is illustrated by arrow 4. Wind acts on wind turbine blades 5 of the wind turbine 1, causing a rotor 6 to rotate. The rotor 6 is connected to a generator, possibly via a gear system, and thereby the rotating movements of the rotor 6 results in production of electrical power. The produced electrical power is supplied to a power grid (not shown), optionally via a transformer station (not shown). Accordingly, the wind turbine 1 of FIG. 1 is operating in a normal manner at the first operating position.

(9) During operation of the wind turbine 1, a wear impact on the wind turbine 1 is estimated. The estimated wear impact could include previous experienced wear impact, i.e. wear impact which the wind turbine 1 has already been subjected to, and/or expected future wear impact, i.e. wear impact which the wind turbine 1 may be expected to be subjected to if it continues to operate at the first operating position.

(10) Based on the estimated wear impact it is determined whether or not the wind turbine 1 shall be relocated to a second operating position. For instance, in the case that the previous and/or expected future wear impact is higher than expected, e.g. to an extend which results in a reduced expected lifetime of the wind turbine 1, it may be desirable to relocate the wind turbine 1 to a second operating position, where the expected future wear impact is lower than at the first operating position.

(11) Similarly, in the case that the previous and/or expected future wear impact is lower than expected, e.g. to an extend which results in an expected lifetime of the wind turbine 1, which exceeds the design lifetime of the wind turbine 1, it may be desirable to relocate the wind turbine 1 to a second operating position, where the expected future wear impact is higher than at the first operating position. Thereby it may be possible to increase the power production of the wind turbine 1 without exceeding the design lifetime of the wind turbine 1.

(12) FIG. 2 shows the floating offshore wind turbine 1 of FIG. 1 at the first operating position 7. In the situation illustrated in FIG. 2 it has been determined to relocate the wind turbine to a second operating position. The wind turbine 1 has therefore been detached from at least some of the mooring lines 3, and thereby the wind turbine 1 is ready to be moved from the first operating position 7 to the second operating position.

(13) In FIG. 3 the wind turbine 1 has been moved away from the first operating position 7 along a direction indicated by arrow 8. Accordingly, the wind turbine 1 is on its way towards its second operating position.

(14) In FIG. 4 the wind turbine 1 is approaching the second operating position 9. Once the wind turbine 1 has reached the second operating position 9 the floating foundation 2 of the wind turbine 1 is attached to the mooring lines 3 of the second operating position 9, and the wind turbine 1 will be ready to start operating at the second operating position 9, after connection to the power grid. The second operating position 9 may previously have been utilized for operation of another wind turbine, however, this is not a requirement. If the second operating position was previously used by another wind turbine, then this wind turbine may previously have been moved to another position (which optionally may be the first position of wind turbine 1), or decommissioned.

(15) In one embodiment, the first operating position is in a first wind farm and the second operating position is in a second wind farm different from the first wind farm for at least one of the floating wind turbines. This for example allows a wind turbine that has experienced an extreme event in a first wind farm to be moved to another wind farm with a much lower risk of experiencing another extreme event.

(16) FIG. 5 is a graph illustrating lifetime usage as a function of time for two wind turbines. The wind turbines start operating at time t.sub.1. A first wind turbine, represented by curve 10, is initially operated at a respective first operating position where the wear impact on the wind turbine is higher than a design wear impact 12. Accordingly, the lifetime usage of this wind turbine is higher than anticipated, and continued operation of the wind turbine under these operating conditions, following line 10a, would result in the wind turbine being worn out prematurely at time t.sub.4.

(17) A second wind turbine, represented by curve 11, is initially operated at a respective first operating position where the wear impact on the wind turbine is lower than the design wear impact. Accordingly, the lifetime usage of this wind turbine is lower than anticipated, and continued operation of the wind turbine under these operating conditions, following line 11a, would result in the wind turbine exceeding its design lifetime until time t.sub.5.

(18) At time t.sub.2 the lifetime usage of the wind turbines represented by curves 10 and 11 is evaluated, and the deviations from the design lifetime usage rate described above are identified. As a consequence, it is decided to relocate the wind turbines to respective second operating positions. More particularly, the wind turbine represented by curve 10 is relocated to a second operating position having an expected future wear impact, represented by curve 10b, which is lower than the expected future wear impact of the first operating position for this wind turbine. Similarly, the wind turbine represented by curve 11 is relocated to a second operating position having an expected future wear impact which is higher than the expected future wear impact, represented by curve 11b, of the first operating position for this wind turbine.

(19) Accordingly, the lifetime usage rate of the wind turbine represented by curve 10 is decreased from time t.sub.2, and the lifetime usage rate of the wind turbine represented by curve 11 is increased from time t.sub.2.

(20) As a consequence, the wind turbine represented by curve 10 as well as the wind turbine represented by curve 11 reach the design lifetime at time t.sub.3. Typically, all wind turbines in an offshore wind farm are decommissioned at the same time, and hence a premature required decommissioning of the farm at t.sub.4, due to the turbine following wear line 10 and 10a, is extended to t.sub.3 leading to a great increase in lifetime energy production of the farm before decommissioning.