WO2017033009A1

WO2017033009A1 - Remote sensing device

Info

Publication number: WO2017033009A1
Application number: PCT/GB2016/052626
Authority: WO
Inventors: Peter James Macdonald CLIVE; William John BARKER
Original assignee: Sgurrenergy Limited
Priority date: 2015-08-24
Filing date: 2016-08-24
Publication date: 2017-03-02
Also published as: GB2541669A; GB201515038D0

Abstract

A remote sensing device (10) for use in a system for the correction of yaw misalignment of an energy capture device, such as a wind turbine, tidal turbine or the like comprises a source (S), an emitter (E) including a horizontal array of optical telescopes (30) independently connected to an optical circulator (20) in the source (S) by means of an optical switch (32) or a scanning arrangement comprising a single telescope (28') connected to a mirror or prism (44) whose orientation can be adjusted to emit and receive the emitted and returned signal along lines of sight with different azimuths. A receiver (R) includes a detector (38) and an analogue-to-digital converter (40), which is interfaced to a digital processing system (44).

Description

REMOTE SENSING DEVICE

FIELD OF THE INVENTION

The present invention relates to improving the efficiency of energy capture from an energy capture device. More particularly, but not exclusively, the present invention relates to a remote sensing device for use in a system for the correction of yaw misalignment of an energy capture device, such as a wind turbine, tidal turbine or the like. BACKGROUND TO THE INVENTION

In recent years there has been increasing demand for reliable, efficient and cost effective generation of electricity using renewable energy technologies, including offshore and onshore wind.

It is recognised that the efficiency of energy capture from a wind turbine depends on a number of factors, one of which is the relative angle of the wind turbine to the direction of the wind, and that maximum efficiency may not be achieved where the wind turbine rotor is not optimally aligned to the incident resource in respect of yaw angle.

While the yaw angle of modern wind turbines may be adjusted, yaw misalignment is nevertheless a common problem which prevents operation at maximum achievable energy capture.

Correction of wind turbine yaw misalignment requires the ability to measure the wind direction accurately in order for the yaw angle of the wind turbine to be adjusted as required. Conventional techniques rely on wind direction measurements at or in the vicinity of the wind turbine's nacelle. However, conventional measurement techniques are subject to significant inaccuracies. These inaccuracies may, for example, be due to incorrect set-up during the construction and commissioning of the turbine. Conventional techniques also suffer from inaccuracies due to the fact that the measurements are subject to significant flow distortion effects. These inaccuracies can be large, particularly in the case of complex flow behaviour, for example turbulent perturbations.

These inaccuracies can have a significant detrimental effect on the efficiency and consequently the utility of a given wind turbine. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provide a remote sensing device suitable for use in a system for improving the efficiency of energy capture from an energy capture device. In particular embodiments, the remote sensing device may be configured for use in a system for improving the efficiency of energy capture from an energy capture device by analysis of the downstream fluid wake created by the energy capture device.

In use, the remote sensing device may be configured to emit a signal to a remote volume, such as a remote air volume or a remote water volume, and detect a return signal to facilitate properties of the remote volume to be determined.

Embodiments of the present invention may beneficially apply the principles of interferometry to detect the Doppler (frequency) shift imparted to a directionally orientated signal through interaction with particles moving freely within a flow of air. This frequency shift is directly proportional to the speed of movement of the particles along the line of sight (LoS) of the emitted signal. The reflected (return) signal onto which this frequency shift has been imparted may be gathered and mixed with the original emitted signal and interference between the signals enables the frequency shift, and therefore particle speed along the LoS may be detected.

Embodiments of the present invention may alternatively or additionally beneficially apply the principles of spectroscopy to directly detect the Doppler (frequency) shift. The range of frequencies of the reflected (return) signal onto which this frequency shift has been imparted may be analysed using filters to selected and compare the return signal at specific frequency values and the Doppler shift may be inferred from this comparison.

The remote sensing device may comprise a laser system. In particular embodiments, the laser system may comprise a lidar system. In use, the laser system, e.g. the lidar system, may be used to detect the directional misalignment of a wind power generator (WPG) through measurement of air velocity differences in the wake of the generator.

The remote sensing device may comprise a source.

The source may comprise a radiation source.

The source may comprise a laser.

The source may comprise a seed laser.

In use, the source, e.g. the seed laser, may be configured to generate a narrow linewidth continuous wave laser signal with high frequency stability. The frequency shift of the return signal is small compared to the frequency of the emitted signal so a narrow line-width and high stability is required to enable the accurate detection of particle speed.

The source may comprise a splitter.

The splitter may comprise an optical splitter.

The source may comprise a modulator.

The modulator may comprise an acousto-optic modulator (AOM).

The source may comprise an amplifier.

The amplifier may comprise an optical amplifier.

In particular embodiments, the amplifier may comprise a pulsed optical amplifier.

The source may comprise a circulator.

The circulator may comprise an optical circulator.

As outlined above, the remote sensing device may be configured to emit a signal to a remote volume, for example a remote fluid volume, such as a remote air volume or a remote water volume.

The remote sensing device may comprise an emitter for transmitting the signal to the remote volume. The signal may comprise radiation from the source. In particular embodiments, the signal may comprise a lider signal, lidar beam or the like.

The emitter may be connected to the source and may take a number of different forms, as will be described further below.

In some embodiments, the emitter may comprise a telescope, such as an optical telescope.

In particular embodiments, the emitter may comprise a plurality of the telescopes. For example, the emitter may comprise an array of N telescopes. The emitter may comprise a horizontal array of telescopes. In particular embodiments, the emitter may comprise three telescopes (i.e. N=3).

The telescopes may be independently connected to the source. For example, the telescopes may be independently connected to the circulator. A coupler may be provided for coupling the telescopes to the source. In particular embodiments, the coupler may comprise an optical switch.

In other embodiments, the emitter may comprise a scanning arrangement.

The scanning arrangement may be connected to the source.

The scanning arrangement may comprise a telescope, such as an optical telescope. The scanning arrangement may comprise a mirror onto which the signal, e.g. Iidar beam, is directed and whose orientation may be adjusted to scan the signal, e.g. Iidar beam through a variety of different azimuth angles.

The scanning arrangement may comprise a rotating multi-faceted mirror, such as, for example, an octagonal or hexagonal mirror, onto which the signal, e.g. Iidar beam, is directed such that rotation of the mirror scans the signal through a range of azimuth angles.

In some embodiments, the scanning arrangement may comprise a rotating prism through which the signal, e.g. Iidar beam, is directed such that rotation of the prism scans the signal, e.g. Iidar beam through a range of azimuth angles.

The remote sensing device may comprise or may be operatively associated with a receiver for detecting a return signal, such as radiation returned from the remote volume.

The receiver may comprise a detector.

The receiver may comprise a converter. The converter may comprise an analogue-to-digital converter.

The receiver, in particular embodiments the analogue-to-digital converter, may be interfaced to a processing system, such as a digital processing system.

The remote sensing device may comprise or may be operatively associated with a processor, such as for analysing the detected return signal.

The remote sensing device may comprise connectors for connecting together the source, the emitter and the receiver.

A connector ("the first connector") may connect the source and the emitter. In embodiments comprising a coupler, the first connector may connect the circulator and the coupler. In embodiments comprising a scanning arrangement, the first connector may connect the circulator and the scanning arrangement. For example, the first connector may connect the circulator and the mirror or prism.

A connector ("the second connector") may connect the source and the receiver. The second connector may connect the detector to the splitter.

A connector ("the third connector") may connect the source and the receiver.

The third connector may connect the detector and the circulator.

One or more of the first, second and third connectors may comprise a signal carrier. One or more of the connectors may comprise a waveguide. In particular embodiments, one or more of the connectors may comprise at least one optical fibre. The optical fibre or fibres may comprise polarisation maintaining optical fibre. Alternatively, one or more of the connectors may comprise an electrical connector, or other suitable connector.

Connectors may be used to connect components of the source together.

One or more connector ("first source connector") may connect the laser and the splitter. One or more connector ("second source connector") may connect the splitter and the modulator. One or more connector ("third source connector") may connect the modulator and the amplifier. One or more connector ("fourth source connector") may connect the amplifier and the circulator.

One or more of the connectors of the source may comprise a signal carrier. One or more of the connectors may comprise a waveguide. In particular embodiments, one or more of the connectors of the source may comprise at least one optical fibre. The optical fibre or fibres may comprise polarisation maintaining optical fibre. Alternatively, one or more of the connectors of the source may comprise an electrical connector, or other suitable connector.

Connectors may be used to connect components of the emitter together.

In embodiments comprising a coupler, a plurality of emitter connectors may be provided, each emitter connector connecting the coupler and one of the telescopes. For example, a connector ("first emitter connector" may connect the coupler and a first of the telescopes, another connector ("second emitter connector") may connect the coupler and a second of the telescopes, and another connector ("third emitter connector") may connect the coupler and a third of the telescopes

One or more of the connectors of the emitter may comprise a signal carrier. One or more of the connectors may comprise a waveguide. In particular embodiments, one or more of the connectors of the emitter may comprise at least one optical fibre. The optical fibre or fibres may comprise polarisation maintaining optical fibre. Alternatively, one or more of the connectors of the emitter may comprise an electrical connector, or other suitable connector.

Connectors may be used to connect components of the receiver together.

One or more connector ("first detector connector") may connect the converter, e.g. analogue to digital converter, and the detector. One or more connector ("the second detector connector") may connect the converter and the processing system.

In use, the remote sensing device may in particular embodiments have a pulsed mode of operation in which the signal e.g. a short burst of radiation is emitted and a return signal is then chronologically recorded. Where the emitted signal has a constant speed of propagation in the atmosphere, the return signal can be processed according to the elapsed time from pulse emission to determine the range from the remote sensing device from which the signal was returned. In operation, the source, e.g. the seed laser, may be configured to generate a narrow linewidth continuous wave laser signal with high frequency stability. The frequency shift of the return signal is small compared to the frequency of the emitted signal so a narrow line-width and high stability is required to enable the accurate detection of particle speed. The output of the amplifier may be fed through the circulator and may be connected to the coupler. It will be recognised that beyond the circulator the emitted and received signals share the same optical path and in embodiments of the present invention, the circulator acts as a splitter to separate the emitted and returned signals by means of their polarisation, feeding the return signal into the detector, for example by means of a polarisation maintaining optical fibre. The source may be connected to the telescopes via the coupler and through separate connectors, such as optical fibres. The coupler can be instructed to make a connection between the circulator and each of the telescopes in isolation. Alternatively, the emitter may comprise a scanning arrangement rather than an arrangement of telescopes connected to a switch. The scanning arrangement may comprise a single telescope connected to a mirror or prism whose orientation can be adjusted to emit and receive the emitted and returned signal along lines of sight with different azimuths. The detector may mix the emitted and returned signals producing an interference signal that is digitised by the analogue-to-digital converter. The digitised signal may then be processed by the digital processing system to extract an estimate of the air speed along the LoS of the emitted beam of radiation.

As outlined above, the remote sensing device may in particular embodiments be configured for use in a method or system for improving the efficiency of energy capture from an energy capture device by analysis of the downstream fluid wake created by the energy capture device and aspects of the present invention also relate to a method and system for use in the correction of yaw misalignment of an energy capture device, for example but not exclusively a wind energy capture device such as a wind turbine or a tidal energy capture device such as tidal turbine, by analysing the downstream fluid wake created by the energy capture device.

According to one such further aspect of the present invention there is provided a method comprising:

acquiring fluid flow data from a downstream fluid wake produced by an energy capture device; and providing an output value from the acquired data which is indicative of the yaw angle of the energy capture device relative to the direction of fluid flow impinging on the energy capture device.

Operating wind turbines extract energy from the air flow, and as a result create a downstream "wake" within which the airflow has reduced velocity and increased turbulence. Accurate measurement of this wake has, historically, been difficult to achieve given the limitations of anemometers and wind vanes which, individually, only measure wind speed and direction at a single point. Embodiments of the present invention may beneficially overcome or at least mitigate the drawbacks associated with conventional techniques for improving efficiency of energy capture and/or correcting yaw misalignment by measuring the characteristics of the wake behind the energy capture device. For example, in embodiments where the energy capture device comprises a wind energy capture device such as a wind turbine, it is possible to establish whether or not the turbine rotor is fully aligned, that is perpendicular, to the air flow.

A sensing arrangement may be located on the energy capture device. Alternatively, or additionally, part or all of the sensing arrangement may be disposed at a remote location. The sensing arrangement may be positioned at any other suitable location capable of sensing the wake. The sensing arrangement may be disposed on the ground. The sensing arrangement may be disposed on a platform, such as an offshore platform or the like. The sensing arrangement may be disposed on another energy capture device.

In particular embodiments, the sensing arrangement may comprise the remote sensing device according to the first aspect of the invention.

The method may comprise scanning the downstream wake from the energy capture device using the sensing arrangement.

The method may comprise measuring and/or mapping the shape of the wake.

The method may comprise measuring and/or mapping the intensity of the wake.

The fluid flow data may comprise fluid velocity data. For example, in particular embodiments the energy capture device may comprise a wind energy capture device and the fluid flow data may comprise air velocity data. In other embodiments, the energy capture device may comprise a tidal energy capture device and the fluid flow data may comprise water velocity data. The fluid flow data may comprise fluid positional and/or directional data relative to an axis of the energy capture device. The fluid flow data may comprise data relating to the azimuth of the fluid relative to the axis of the energy capture device.

The method may comprise acquiring fluid flow velocity data and fluid positional data from the wake.

The method may comprise determining a core of the wake from the acquired fluid flow data, the positioning and/or behaviour of the core of the wake corresponding to the direction of fluid flow impinging on the energy capture device.

The method may comprise plotting the fluid flow data to determine a core of the wake, the core of the wake corresponding to the direction of fluid flow impinging on the energy capture device.

The method may comprise plotting the fluid flow velocity data against the fluid positional data relative to the axis of the energy capture device to determine the core of the wake.

In particular embodiments, the method may comprise plotting the fluid flow data from a cross section of the wake to determine the core of the wake.

The core of the wake may comprise the position relative to the axis of the energy capture device having lowest average flow velocity. For example, when plotting a curve of the position of the core of the wake on a graph of flow velocity relative to position relative to the axis of the energy capture device, the core of the wake may define a minimum value for the acquired data. Alternatively, for other wake regimes characteristic of flow at other distances from the energy capture device, a different variation in velocity relative to position may be used to detect the core of the wake. For example, in the near-wake immediately behind a central hub of an energy capture device, flow velocity may be higher than in adjacent regions and this may be adopted as the wake signature used to detected the core of the wake.

Beneficially, the ability to identify the core of the wake, in particular the position of the core of the wake relative to the axis of the energy capture device, permits an accurate indication of the true direction of fluid flow impinging on the energy capture device. For example, in embodiments where the energy capture device comprises a wind energy capture device such as a wind turbine, identifying the position or azimuth of the core of the wake relative to the axis of the turbine permits optimal alignment of the rotor to the incident resource in respect of yaw angle.

Acquiring the fluid flow data may be achieved by any suitable means.

The fluid flow data may be acquired remotely. The fluid flow data may be acquired by a remote sensing arrangement.

The fluid flow data may be acquired across a three-dimensional flow field.

The fluid flow data may be acquired across a two-dimensional flow field.

Beneficially, the ability of acquire the data across a three-dimensional flow field permits the complex air flows produced by the energy capture device to be mapped with a high degree of precision and across a wide area.

In particular embodiments, the sensing arrangement may comprise a Lidar sensing arrangement.

Beneficially, a Lidar sensing arrangement, which uses a light source or laser to measure air flow velocity across a three-dimensional or two-dimensional flow field, permits measurement of complex air flows across wide areas. Accordingly, by using a Lidar sensing arrangement to measure the shape and intensity of the wake it is possible to establish whether or not the turbine is optimally aligned (for example but not exclusively perpendicular) to the incident resource as it passes through the rotor disc.

Alternatively, the sensing arrangement may comprise a Sodar sensing arrangement, for example, an Acoustic Doppler Current Profiler (ADCP). A Sodar sensing arrangement, which uses a sound source to measure flow velocity across a three-dimensional flow field, permits measurement of complex water flows across wide areas. By using a Sodar sensing arrangement to measure the shape and intensity of the wake it is possible to establish whether or not the turbine is optimally aligned (for example but not exclusively perpendicular) to the incident resource as it passes through the rotor disc.

The method may comprise adjusting the yaw angle of the energy capture device.

In particular, the method may comprise adjusting the yaw angle of the energy capture device so that the core of the wake corresponds to the axis of the energy capture device.

By reducing or eliminating the yaw angle between the energy capture device and the incident resource impinging on the energy capture device, yaw misalignment may be reduced or eliminated and the efficiency of energy extraction and electricity generation may be maximised or at least improved.

The output value may be communicated to the control system. For example, the output value may be communicated directly to the control system so that the control system adjusts the position of the energy capture device in real time, at a predetermined time threshold, or when the yaw angle of the energy capture device relative to the direction of the fluid impinging on the energy capture device exceeds a particular threshold.

Alternatively, or additionally, the method may comprise communicating the output value to a remote location, such as to an operator, control centre or the like.

According to a further aspect of the present invention, there is provided a system comprising:

a sensing arrangement configured to acquire fluid flow data from a downstream wake of an energy capture device; and

a communication arrangement for providing an output value indicative of the difference between the average direction of an incident resource and the angle of the energy capture device.

The sensing arrangement may comprise the remote sensing device according to the first aspect of the invention.

The sensing arrangement may be mounted or otherwise positioned on the energy capture device.

The energy capture device may comprise a rotor. The energy capture device may comprise a plurality of blades.

The energy capture device may comprise a nacelle.

The sensing arrangement may be disposed on a nacelle of the energy capture device.

The sensing arrangement may be configured to scan the wake from the energy capture device.

The reference point is at or near to the turbine axis/nacelle axis.

The energy capture device may be of any suitable form and construction.

In particular embodiments, the energy capture device may comprise a wind energy extraction device, such as a wind turbine or the like.

The sensing arrangement may be of any suitable form and construction.

The sensing arrangement may comprise a remote sensing arrangement.

The sensing arrangement may be configured to measure fluid flow velocity, such as airflow velocity, across a three-dimensional flow field.

In particular embodiment, the sensing arrangement may comprise a Lidar sensing arrangement.

Alternatively, the sensing arrangement may comprise a Sodar sensing arrangement.

The system may comprise a control system. The control system may be configured to adjust the position, for example the yaw angle, of the energy capture device.

The communication arrangement may be of any suitable form and construction.

The communication arrangement may be configured to transmit the output value to the control system.

Alternatively, or additionally, the communication arrangement may be configured to transmit the output value to a remote location.

It should be understood that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic view of a remote sensing device according to a first embodiment of the present invention;

Figure 2 shows a schematic view of a remote sensing device according to a second embodiment of the present invention;

Figure 3 shows a plan view of a scanning arrangement of the remote sensing device shown in Figure 2;

Figure 4 shows a side view of the scanning arrangement of the remote sensing device shown in Figure 2;

Figure 5 is a diagrammatic view of a wind turbine system according to an embodiment of the present invention, and showing an application of the remote sensing devices shown in Figures 1 or 2 in measuring air speed and direction across a wind power generator wake;

Figure 6 shows a sensing arrangement for use in the system shown in Figure 5;

Figure 7 is a diagrammatic plan view of the wind turbine system shown in Figure 5, in a first position;

Figure 8 is a graph showing a plot of wind speed against azimuth for the wind turbine system in the first position shown in Figure 7;

Figure 9 is a diagrammatic plan view of the wind turbine system shown in Figure 5, in a second position; Figure 10 is a graph showing a plot of wind speed against azimuth for the wind turbine system in the second position shown in Figure 9.

Figure 11 is a diagrammatic view of a tidal turbine system according to another embodiment of the present invention;

Figure 12 shows a sensing arrangement for use in the present invention;

Figure 13 is a diagrammatic plan view of the tidal turbine system shown in Figure 1 1 , in a first position;

Figure 14 is a graph showing a plot of water speed against azimuth for the tidal turbine system in the first position shown in Figure 13;

Figure 15 is a diagrammatic plan view of the tidal turbine system shown in

Figure 1 1 , in a second position;

Figure 16 is a graph showing a plot of water speed against azimuth for the tidal turbine system in the second position shown in Figure 15; and

Figure 17 is a diagrammatic view of a turbine system according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 of the accompanying drawings shows a remote sensing device 10 according to a first embodiment of the present invention. As shown in Figure 1 , the remote sensing device 10 comprises a source S, an emitter E and a receiver R.

The source S includes a seed laser 12, an optical splitter 14, an acousto-optic modulator (AOM) 16, a pulsed optical amplifier 18 and an optical circulator 20. The seed laser 12 is coupled to the optical splitter 14 by a first connector in the form of optical fibre 22. The optical splitter 14 is coupled to the AOM 16 by a connector in the form of optical fibre 24. The AOM 16 is coupled to the optical amplifier 18 by a connector in the form of optical fibre 26. The optical amplifier 18 is coupled to the optical circulator 20 by a connector in the form of optical fibre 28.

The emitter E includes a horizontal array of optical telescopes 30 (three optical telescopes 30 are shown in the embodiment of Figure 1), each of which in the illustrated embodiment is independently connected to the optical circulator 20 in the source S by means of an optical switch 32 and connectors in the form of optical fibres 34. The optical switch 32 is coupled to the optical circulator 20 via a connector in the form of optical fibre 36. The receiver R includes a detector 38 and an analogue-to-digital converter 40 via a connector in the form of optical fibre 42, which in turn is interfaced to a digital processing system 44 via a connector in the form of optical fibre 46.

The detector 38 is connected to the optical splitter 14 by a connector in the form of optical fibre 48 and is connected to the optical circulator 20 by a connector in the form of optical fibre 50.

In the illustrated embodiment, the optical fibres 22, 24, 26, 28, 34, 36, 42, 46 and 48 comprise standard optical fibres and the optical fibre 50 comprises a polarisation maintaining optical fibre. However, it will be recognised that the optical fibres 22, 24, 26, 28, 34, 36, 42, 46 and 48 may alternatively comprise polarisation maintaining optical fibre and the optical fibre 50 may comprise a standard optical fibre if required.

In use, embodiments of the present invention may beneficially apply the principles of spectroscopy to directly detect the Doppler (frequency) shift. The range of frequencies of the reflected (return) signal onto which this frequency shift has been imparted may be analysed using filters to selected and compare the return signal at specific frequency values and the Doppler shift may be inferred from this comparison.

The remote sensing device 10 may in particular embodiments have a pulsed mode of operation in which a short burst of radiation is emitted and the return signal is then chronologically recorded. Where the emitted radiation has a constant speed of propagation in the atmosphere, the return signal can be processed according to the elapsed time from pulse emission to determine the range from the device from which the signal was returned.

In operation, the seed laser 12 generates a narrow linewidth continuous wave laser signal with high frequency stability. The frequency shift of the return signal is small compared to the frequency of the emitted signal so a narrow line-width and high stability is required to enable the accurate detection of particle speed.

The output of the seed laser 12 is coupled into the input of the AOM 16 via the optical fibre 22. A portion of the signal output by the seed laser 12 is fed into the separate optical fibre 48 at this stage using the optical splitter 14. This provides a reference signal that is feed into the detector 38 to be mixed with the return signal. The AOM 16 has a dual function with respect to the processing of the signal to be emitted from the device 10. Firstly, it controls the amplitude of the incoming signal from the seed laser 12, applying a pulse profile to enable return signal range to be determined. Secondly, it applies a constant stable frequency offset to the signal from the seed laser 12 that enables the detector 38 to determine whether the frequency of the return signal is higher than or lower than that of the emitted signal. Beneficially, this enables the device 10 to detect whether the particles are moving towards or away from the emitter E.

The output of the AOM 16 is fed into the pulsed optical amplifier 18. The optical amplifier 18 increases the power of the optical signal such that the emitted radiation is capable of propagating to the desired measurement range and being detected on return.

The output of the optical amplifier 18 is fed via optical fibre 26 through an optical circulator 20 and in the embodiment illustrated in Figure 1 is connected to optical switch 32. Beyond the optical circulator 20, that is in the emitter E, the emitted and received signals share the same optical path. The optical circulator 20 acts as a splitter separating the emitted and returned signals by means of their polarisation and feeding the return signal into the detector 38 by means of the polarisation maintaining optical fibre 50. As described above, in the embodiment illustrated in Figure 1 , the optical switch 32 is connected to the array of optical telescopes through the separate optical fibres 34. The optical switch 32 can be instructed to make a connection between the optical circulator 20 and each of the N optical telescopes 30 in isolation.

Referring now to Figure 2, 3 and 4 of the accompanying drawings, there is shown a remote sensing device 10' according to a second embodiment of the present invention.

As in the remote sensing device 10, the remote sensing device 10' comprises a source S', an emitter E' and a receiver R'.

The source S' includes a seed laser 12', an optical splitter 14', an acousto-optic modulator (AOM) 16', a pulsed optical amplifier 18' and an optical circulator 20'. The seed laser 12' is coupled to the optical splitter 14' by a first connector in the form of optical fibre 22'. The optical splitter 14' is coupled to the AOM 16' by a connector in the form of optical fibre 24'. The AOM 16' is coupled to the optical amplifier 18' by a connector in the form of optical fibre 26'. The optical amplifier 18' is coupled to the optical circulator 20' by a connector in the form of optical fibre 28'.

The receiver R' includes a detector 38' and an analogue-to-digital converter 40' via a connector in the form of optical fibre 42', which in turn is interfaced to a digital processing system 44' via a connector in the form of optical fibre 46'. The detector 38' is connected to the optical splitter 14' by a connector in the form of optical fibre 48' and is connected to the optical circulator 20' by a connector in the form of optical fibre 50'.

In the remote sensing device 10' shown in Figure 2, however, the emitter E' of the remote sensing device 10' comprises a scanning arrangement rather than an arrangement of telescopes connected to a switch. The scanning arrangement comprises a single telescope 28' connected to a mirror or prism 44 whose orientation can be adjusted to emit and receive the emitted and returned signal along lines of sight with different azimuths.

Figure 3 is a side view of the scanning arrangement of the remote sensing device 10'. The lidar beam is directed onto a mirror 50 whose orientation may be adjusted to scan the lidar beam through a range of azimuth angles. In the illustrated embodiment, the mirror 50 comprises a multifaceted prism or mirror which is rotated about an axis to scan the lidar beam through the range of azimuth angles.

Figure 4 is a plan view of the scanning system of the remote sensing device

10'. As shown in Figure 4, the source S' is connected to the emitter E' where a telescope 30' expands and collimates the lidar beam and directs it onto the mirror 50 which reflects the beam through a right angle. The mirror 50 is mounted on a scanning motor 52 that may rotate it about a single axis parallel with the optical axis of the telescope 30' to scan the reflected lidar beam through the range of azimuth angles.

Operation of the remote sensing device 10' is similar to that of the device 10 and as in the device 10, in the device 10' the detector 34' mixes the emitted and returned signals producing an interference signal that is digitized by the analogue-to- digital converter 36'. The digitized signal is processed by the digital processing system 38' to provide an output, for example an estimate of the air speed along the line of sight (LoS) of the emitted beam of radiation.

The remote sensing devices 10, 10' described above may in particular embodiments be applied to the measurement of air speed and direction behind a wind power generator or may be applied to the measurement of water speed behind a tidal power generator, as described below with reference to Figures 5 to 17. In such applications, a horizontal array of optical telescopes 30 as described above with reference to Figure 1 , or other emitter/receiver systems such as, for example, the scanning arrangement as described above with reference to Figures 2 to 4, is mounted facing rearward on the nacelle of a wind power generator (WPG) or to measure air speed or on the nacelle of a tidal power generator to measure water speed at points spanning the wake of the generator. Alternatively, the variation in the azimuth angle of the beam required for the detection of yaw error may be achieved using a scanning system, such as the scanning arrangement described above with reference to Figures 2, 3 and 4.

In use, air speed differences across the wind power generator wake as measured by the invention may be applied to determine the orientation of the wind power generator with respect to the oncoming wind. Information regarding the orientation of the wind power generator (WPG) with respect to the oncoming wind may be used to control the orientation of the (WPG) where the invention is permanently installed on the wind power generator (WPG) or to inform the calibration of direction sensors and associated systems used to control the orientation of the wind power generator (WPG) through temporary or permanent installation of the invention on or near the wind power generator (WPG).

Referring to Figure 5 of the accompanying drawings, there is shown a diagrammatic perspective view of a system according to an embodiment of the present invention.

In the illustrated embodiment, the system comprises a wind turbine system. However, it will be recognised that the system may take other forms and may for example comprise a tidal energy capture turbine system or the like.

As shown in Figure 5, the wind turbine system comprises a wind turbine 1012 having a tower 1014, a nacelle 1016 and a hub 1018 having a plurality of radially extending blades 1020. The hub 1018 is operatively coupled to an electrical generator 1022 via a drive shaft 1024. In the illustrated embodiment, a gear arrangement 1026 in the form of a gear box is provided, although in other embodiments a gear arrangement may not be provided. In the illustrated embodiment, the turbine 1012 further comprises a controller 1028, the controller 1028 operatively coupled to a yaw drive arrangement 1030 capable of adjusting the angle of the turbine 1012.

In use, the kinetic energy of wind W, as shown in Figure 7, impinging on the blades 1020 drives rotation of the hub 1018 relative to the nacelle 1016, this kinetic energy being transmitted via the drive shaft 1024 (and the gear arrangement 1026 where provided) to the electrical generator 1022 where it is converted into electricity.

As shown in Figure 5 and with reference also to Figure 6, the system further comprises a sensing arrangement 1032 which, in the illustrated embodiment, is disposed on the nacelle 1016 of the wind turbine 1012. It will be recognised, however, that the sensing arrangement 1032 may be provided at other suitable locations, such as a remote location, a platform, on the ground or on one or more other turbine. The sensing arrangement 1032 may comprise the remote sensing device 10 or the remote sensing device 10' described above.

In use, and referring also to Figure 7 which shows a diagrammatic plan view of the wind turbine system in a first position, the sensing arrangement 1032 is configured to acquire air flow data from a downstream wake 1034 produced by the rotating blades 1020 of the wind turbine 1012. In the illustrated embodiment, the sensing arrangement 1032 comprises a Lidar unit 1035 having an optical source 1036 - in the illustrated embodiment a laser source - for transmitting light beams over the desired flow field, which in embodiments of the invention comprises the downstream fluid wake 1034 produced by the blades 1020. The unit 1035 further comprises or is operatively associated with a receiver 1038 - in the illustrated embodiment an optical antenna -for detecting the light reflected back from the wake 1034. In the illustrated embodiment, this is achieved by measuring the back-scatter of light radiation which is reflected by natural aerosols carried by the wind, such as dust, water droplets, pollution, pollen, salt crystals or the like.

In use, the sensing arrangement 1032 acquires data relating to the air flow velocity in the wake 1034 across a three-dimensional flow field, which data is then processed to determine the relative angle of the wind turbine 1012 and the average direction D of the incident resource W as shown in Figure 7.

To illustrate the system and method of the present invention, operation of the wind turbine system will now be described with reference to Figures 7 to 10.

As described above, Figure 7 shows a plan view of the wind turbine system in a first position, in which the wind turbine 1012 is positioned at an angle Θ to the average direction D of the wind W.

The sensing arrangement 1032 is positioned at, or calibrated to, the rotational axis 1040 of the turbine 1012 and, in use, the sensing arrangement 1032 acquires wind speed and azimuth (of the lidar beam) data relative to the turbine axis 1032 by scanning a three-dimensional field which includes the wake 1034 produced by the blades 1020 of the turbine 1012, in the illustrated embodiment the scan represented by reference numeral 1042.

A graph showing a plot of the acquired wind speed and azimuth data for cross section A-A of wake 1034 when the turbine 1012 is in the first position is shown in Figure 8. As can be seen from Figures 7 and 8, the wake 1034 produced by the blades 1020 of the turbine 1012 is deflected and a core 1044 of the wake 1034 - as represented in the graph by the lowest point - is out of alignment with the rotational axis 1040 of the turbine 1012, the azimuth a of the core 1044 relative to the turbine rotational axis 1040 corresponding to the misalignment of the turbine 1012 relative to the average direction of the incident resource D.

In this way, an output indicative of the misalignment of the turbine 1012 relative to the wind direction D may be produced, which may be communicated to an operator or communicated directly to the control system where it may be used to alter the angle of the turbine 1012 from the position shown in Figure 7 to the position shown in Figure 9.

Figure 9 shows a plan view of the wind turbine system in the second position, in which the wind turbine 1012 is positioned in exact alignment with the rotational axis 1040 of the turbine 1012 and Figure 10 shows a graph showing a plot of the acquired wind speed and azimuth data for cross section B-B of wake 1034 when the turbine 1012 is in the second position. As can be seen from Figures 9 and 10, the wake 1034 produced by the blades 1020 of the turbine 1012 is symmetrical about the turbine rotational axis 1040 and the core 1044 of the wake 1034 - as represented in the graph by the lowest point - is aligned with the rotational axis 1040 of the turbine 1012.

By utilising the method and system of the present invention, it is possible to establish the correct yaw alignment with a high degree of accuracy and thereby maximise turbine efficiency and energy production.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention.

For example, whereas the particular embodiment described above relates to a wind energy capture system using a Lidar sensing arrangement, other embodiments of the invention may take other forms.

Referring now to Figures 1 1 to 16, there is shown a system 11 10 according to an alternative embodiment of the invention. The system 1 1 10 comprises a tidal energy capture system for location in a body of water S and which utilise a Sodar (Sound Detection and Ranging) sensing arrangement such as an ADCP, although it will be recognised that other sensing arrangements may be used where appropriate.

As shown in Figure 1 1 , the tidal turbine system 11 10 comprises a tidal turbine 1 112 having a tower 1 14, a nacelle 1 116 and a hub 1 118 having a plurality of radially extending blades 1120. The hub 1 118 is operatively coupled to an electrical generator 1 122 via a drive shaft 1124. In the illustrated embodiment, a gear arrangement 1 126 in the form of a gear box is provided, although in other embodiments a gear arrangement may not be provided. In the illustrated embodiment, the turbine 11 12 further comprises a controller 1 128, the controller 1 128 operatively coupled to a yaw drive arrangement 1 130 capable of adjusting the angle of the turbine 1 112 in the body of water.

In use, the kinetic energy of water impinging on the blades 1120 drives rotation of the hub 11 18 relative to the nacelle 1 116, this kinetic energy being transmitted via the drive shaft 1124 (and the gear arrangement 1126 where provided) to the electrical generator 1 122 where it is converted into electricity.

As shown in Figure 11 and with reference also to Figure 12, the system 1 110 further comprises a sensing arrangement 1 132 which, in the illustrated embodiment, is disposed on the nacelle 1 116 of the tidal turbine 1 112. It will be recognised, however, that the sensing arrangement 1 132 may be provided at other suitable locations, such as a remote location, a platform, on the seabed or on one or more other turbine. The sensing arrangement 1132 may comprise the remote sensing device 10 described above with reference to Figure 1 or the remote sensing device 10' described above with reference to Figures 2 to 4.

In use, and referring also to Figure 13 which shows a diagrammatic plan view of the tidal turbine system 1 1 10 in a first position, the sensing arrangement 1 132 is configured to acquire flow data from a downstream wake 1 134 produced by the rotating blades 1 120 of the tidal turbine 1 112. In the illustrated embodiment, the sensing arrangement 132 comprises a Sodar unit 1 135 having a sound source 1136 for transmitting sound pulses over the desired flow field, which in embodiments of the invention comprises the downstream fluid wake 1 134 produced by the blades 1120. The unit 1135 further comprises or is operatively associated with a receiver 1138 for detecting the sound reflected back from the wake 1 134.

In the illustrated embodiment, this is achieved by emitting a short pulse of sound at a certain frequency. The sound propagates outwards and upwards, while at the same time a part of the sound is reflected back. The Doppler frequency shift of the received signal is proportional to the fluid speed aligned to the transmission sound path. By combining three or five of these pulses, for example one along the vertical and two or four inclined to the vertical, the three-dimensional velocity field of both the mean values and the turbulent values is calculated.

In use, the sensing arrangement 1132 acquires data relating to the flow velocity in the wake 1 134 across a three-dimensional flow field, which data is then processed to determine the relative angle of the wind turbine 11 12 and the average direction D' of the incident resource W.

To illustrate the system and method of the present invention, operation of the wind turbine system 1 1 10 will now be described with reference to Figures 13 to 16.

As described above, Figure 13 shows a plan view of the tidal turbine system

1 1 10 in a first position, in which the tidal turbine 11 12 is positioned at an angle 9' to the average direction D' of the incident resource W.

The sensing arrangement 1 132 is positioned at, or calibrated to, the rotational axis 1140 of the turbine 1 1 12 and, in use, the sensing arrangement 1 132 acquires flow speed and azimuth data relative to the turbine axis 1 132 by scanning a three- dimensional field which includes the wake 1 134 produced by the blades 1 120 of the turbine 11 12, in the illustrated embodiment the scan represented by reference numeral 1 142.

A graph showing a plot of the acquired flow speed and azimuth data for cross section C-C of wake 1 134 when the turbine 11 12 is in the first position is shown in Figure 14. As can be seen from Figures 13 and 14, the wake 1134 produced by the blades 1120 of the turbine 11 12 is deflected and a core 1144 of the wake 1134 - as represented in the graph by the lowest point - is out of alignment with the rotational axis 1 140 of the turbine 11 12, the azimuth a' of the core 1 144 relative to the turbine rotational axis 1140 corresponding to the misalignment of the turbine 11 12 relative to the average direction of the incident resource D'.

In this way, an output indicative of the misalignment of the turbine 1 1 12 relative to the flow direction D may be produced, which may be communicated to an operator or communicated directly to the control system where it may be used to alter the angle of the turbine 1 1 12 from the position shown in Figure 13 to the position shown in Figure 15.

Figure 15 shows a plan view of the tidal turbine system 11 10 in the second position, in which the tidal turbine 11 12 is positioned in exact alignment with the rotational axis 1140 of the turbine 11 12 and Figure 16 shows a graph showing a plot of the acquired flow speed and azimuth data for cross section D-D of wake 1134 when the turbine 11 12 is in the second position. As can be seen from Figures 15 and 16, the wake 1 134 produced by the blades 1120 of the turbine 11 12 is symmetrical about the turbine rotational axis 1 140 and the core 1144 of the wake 1134 - as represented in the graph by the lowest point - is aligned with the rotational axis 1 140 of the turbine 1 1 12. Whereas in the embodiments described above, the sensing arrangement is disposed on the turbine, it will be recognised that the sensing arrangement may be positioned at any other suitable location capable of sensing the wake.

Referring now to Figure 17, there is shown a system 1210 according to an alternative embodiment of the invention. The system 1210 is similar to the systems 1010, 1 1 10 described above with the difference that the sensing arrangement 1232 is located on the ground.

As shown in Figure 17, the turbine system 1210 comprises a turbine 1212 having a tower 1214, a nacelle 1216 and a hub 1218 having a plurality of radially extending blades 1220. The hub 1218 is operatively coupled to an electrical generator 1222 via a drive shaft 1224. In the illustrated embodiment, a gear arrangement 1226 in the form of a gear box is provided, although in other embodiments a gear arrangement may not be provided. In the illustrated embodiment, the turbine 1212 further comprises a controller 1228, the controller 1228 operatively coupled to a yaw drive arrangement 1230 capable of adjusting the angle of the turbine 1212.

In use, the kinetic energy of incident resource (for example air or water) on the blades 1220 drives rotation of the hub 1218 relative to the nacelle 1216, this kinetic energy being transmitted via the drive shaft 1224 (and the gear arrangement 1226 where provided) to the electrical generator 1222 where it is converted into electricity.

As described above, in this embodiment the sensing arrangement 1232 is disposed on the ground and is configured to acquire flow data from a downstream wake 1234 produced by the rotating blades 1220 of the turbine 1212. The sensing arrangement 1232 itself may be of any suitable form and may, for example comprise a Lidar sensing arrangement such as the sensing arrangement 1 132 described above or a Sodar sensing arrangement such as the sensing arrangement 1132 described above, and the sensing arrangement 1 132 may comprise the remote sensing device 10 described above with reference to Figure 1 or the remote sensing device 10' described above with reference to Figures 2 to 4.

It will be recognised that the method and system of the present invention may be used in number of different ways and at different instances during the working life of the energy capture device. For example, the technique may involve short-term application of the sensing arrangement, after which the alignment may be corrected and the sensing arrangement is removed to be used elsewhere. Alternatively the sensing arrangement may be left in-situ for continuous application.

Claims

1. A remote sensing device suitable for use in a system for improving the efficiency of energy capture from an energy capture device by analysis of the downstream fluid wake created by the energy capture device, the remote sensing device comprising:

a source; and

an emitter configured to emit a signal to a remote volume, the emitter comprising one of:

a horizontal array of optical telescopes; and

a scanning arrangement comprising an optical telescope and a rotatable mirror or prism onto which the signal to be emitted is directed and whose orientation is adjustable to scan the signal through a variety of different azimuth angles.

2. The remote sensing device of claim 1 , wherein the remote sensing device comprises a laser system.

3. The remote sensing device of claim 2, wherein the laser system comprises a lidar system.

4. The remote sensing device of claim 1 , 2 or 3, wherein the source comprises a seed laser.

5. The remote sensing device of claim 2, 3 or 4, wherein the source is configured to generate a narrow linewidth continuous wave laser signal with high frequency stability.

6. The remote sensing device of any preceding claim, wherein the source comprises a splitter.

7. The remote sensing device of claim 6, wherein the splitter comprises an optical splitter.

8. The remote sensing device of any preceding claim, wherein the source comprises a modulator.

9. The remote sensing device of claim 8, wherein the modulator comprises an acousto-optic modulator (AOM).

10. The remote sensing device of any preceding claim, wherein the source comprises an amplifier.

1 1. The remote sensing device of claim 10, wherein the amplifier comprises an optical amplifier.

12. The remote sensing device of claim 1 1 , wherein the amplifier comprises a pulsed optical amplifier.

13. The remote sensing device of any preceding claim, wherein the source comprises a circulator.

14. The remote sensing device of claim 13, wherein the circulator comprises an optical circulator.

15. The remote sensing device of any preceding claim, wherein the remote sensing device comprises said array of telescopes and the telescopes of said array are independently connected to the source.

16. The remote sensing device of any preceding claim, wherein the remote sensing device comprises said array of telescopes and comprises a coupler for coupling the telescopes of said array to the source.

17. The remote sensing device of claim 16, wherein the coupler comprises an optical switch.

18. The remote sensing device of claim 16 or 17, when dependent on claim 13, wherein the coupler is configured to make a connection between the circulator and each of the telescopes in isolation.

19. The remote sensing device of any preceding claim, wherein the remote sensing device comprises said scanning arrangement and the scanning arrangement is connected to the source.

20. The remote sensing device of any preceding claim, when dependent on claim 13, wherein the remote sensing device comprises said scanning arrangement and the scanning arrangement is coupled to the circulator.

21. The remote sensing device of any preceding claim, wherein the remote sensing device comprises said scanning arrangement and the mirror of said scanning arrangement comprises a multi-faceted mirror.

22. The remote sensing device of claim 21 , wherein the mirror of said scanning arrangement comprises one of: a hexagonal mirror; and an octagonal mirror.

23. The remote sensing device of any preceding claim, comprising or operatively associated with a receiver configured to detect a return signal.

24. The remote sensing device of claim 23, wherein the receiver comprises a detector.

25. The remote sensing device of claim 23 or 24, wherein the receiver comprises a analogue-to-digital converter.

26. The remote sensing device of claim 23, 24 or 25, wherein the receiver is configured to be interfaced to a processing system, such as a digital processing system.

27. The remote sensing device of any one of claims 24 to 26, when dependent on claim 16, wherein the circulator acts as a splitter to separate the signal to be emitted and returned signal by means of their polarisation, feeding the return signal into the detector.

28. The remote sensing device of claim 25, 26 or 27, when dependent on claim 24, wherein the detector is configured to mix the emitted and returned signals producing an interference signal that is digitised by the analogue-to-digital converter.

29. The remote sensing device of any preceding claim, comprising at least one of: a connector for connecting the source and the emitter;

a connector for connecting the source and the receiver; and.

a connector for connecting the source and the receiver.

30. The remote sensing device of claim 29, wherein at least one of the connector for connecting the source and the emitter, the connector for connecting the source and the receiver, and the connector for connecting the source and the receiver

comprises a signal carrier.

31. The remote sensing device of claim 30, wherein the signal carrier comprises at least one optical fibre, such as a polarisation maintaining optical fibre.

32. The remote sensing device of claim 30 or 31 , wherein the signal carrier comprises an electrical connector.

33. A system comprising:

a sensing arrangement configured to acquire fluid flow data from a downstream wake of an energy capture device, the sensing arrangement comprising a remote sensing device according to any preceding claim; and

34. The system of claim 33, comprising a remote sensng device.

35. The system of claim 33 or 34, wherein the sensing arrangement is mounted or otherwise positioned on the energy capture device.

36. The sensing arrangement of claim 33, 34 or 35, wherein the sensing arrangement is configured to scan the wake from the energy capture device.