DK202070419A1 - Method for identifying a wind turbine causing shadow flicker - Google Patents

Abstract

The invention relates to a method for identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker. When shadow flicker is identified at a position of a person, information is generated comprising the position of the person. The information is used to identify the wind turbine causing the shadow flicker and to pause the wind turbine causing the shadow flicker.

Description

DK 2020 70419 A1 1

METHOD FOR IDENTIFYING A WIND TURBINE CAUSING SHADOW FLICKER

FIELD OF THE INVENTION The present invention relates to a method identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker.

BACKGROUND OF THE INVENTION A wind turbine may cause a shadow at a person, when the sun is shining. When the rotor of the wind turbine is rotating, the shadow may flicker. This may occur if the sunlight hitting the person passes through the rotor plane of a wind turbine in operation. The shadow flicker may be a nuisance for the person. A way to mitigate the shadow flicker is to pause the wind turbines; however, paused wind turbines are not producing power, which is undesirable.

It is therefore desirable to have a method that can identify a wind turbine causing shadow flicker. Thus, it gives the possibility only pausing a wind turbine, if it is causing the shadow flicker and thereby minimising lost power production.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved method to determine shadow flicker from a wind turbine.

In particular, it may be seen as an object of the present invention to provide a method to identify a wind turbine causing shadow flicker at a person and thereby making it possible to take appropriate measures to mitigate the shadow flicker. Thus, the above-described objects and several other objects are intended to be obtained in a first aspect of the invention by providing a method for identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker, the method comprising the steps of: — identifying shadow flicker at a position of the person, — generating information comprising the position of the person affected by shadow flicker,

DK 2020 70419 A1 2 — identifying the wind turbine causing the shadow flicker by use of the information and the position of the sun, and — pausing the wind turbine causing the shadow flicker.

The invention is particularly, but not exclusively, advantageous for identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker. Shadow flicker anywhere in a vicinity of a wind park may affect a person. It will be advantageous that a person being outdoor and away from home may have the opportunity to mitigate shadow flicker. The person affected by shadow flicker may be involved in any kind of outdoor activity, for instance the person may be outside walking, fishing, playing ball or visiting a tourist destination or any other kind of outdoor activity.

Shadow flicker is identified at the position of a person, in one embodiment the shadow flicker is identified by the person himself, being affected and annoyed by the shadow flicker.

A person being affected by shadow flicker may generate information comprising the position of the person and the person may transmit the information to a central control system. This may be done by a phone call or by an app on a mobile phone.

In an alternative embodiment, a remote detector may detect the shadow flicker. The remote detector may be placed at a position where shadow flicker may occur and people often are present, for instance at a tourist attraction. The remote detector may detect both the shadow flicker and the presence of a person and generate information comprising the position of the remote detector. The remote detector may transmit the information to a central control system or directly to a wind park controller.

The information is used to identify the wind turbine causing the shadow flicker at the position of the person. From the position of the sun and the positions of wind turbines in the vicinity, the position of the shadow may be estimated, and it may be estimated whether the shadow caused by a wind turbine actually hits the person. The shadow flicker may be caused by a wind turbine located in a wind

DK 2020 70419 A1 3 park. The step may be to estimate the position of the shadow for each wind turbine in a wind park near the person, and identify whether one or more of the wind turbines is causing shadow flicker to hit the person. It is to be understood that the position of the sun may be determined based on the time and preferably the date. This could be based on a table defining the presence of the shadow based in the hour of the day and if needed the date. When identifying the wind turbine causing the shadow flicker, the wind turbine may be paused to mitigate the shadow flicker. In one example, pausing the wind turbine causes the rotor to stop moving. In another example, pausing the wind turbine still allows the rotors to rotate slowly; the shadow flicker is still mitigated. In yet another example the shadow flicker is mitigated by yawing the wind turbine. These examples may be combined in any suitable way.

According to an embodiment, the method comprises that the person affected by shadow flicker generates the information. When shadow flicker from a wind turbine affects a person, the person may have a possibility to stop the shadow flicker by requesting the wind turbine to be paused.

This may be service provided by the operator of a wind park, where a person affected by shadow flicker may transmit information comprising the position of the person, and then the operator or a computer-controlled system of a wind park may take measures to mitigate the shadow flicker.

The person affected by shadow flicker may generate and transmit information from anywhere he may be, typically away from home. According to an embodiment, the method comprises that a mobile phone and an app on the mobile phone is used to generate the information.

When being outside the person may have a mobile phone, the mobile phone may be used to generate information about being affected by shadow flicker. The information may be generated by making a call to a phone number that may be applied by the operator of the wind park, for instance the number may be published on a webpage for the wind park with information about how to mitigate

DK 2020 70419 A1 4 shadow flicker. Alternatively, the mobile phone may have an app used to generate the information about shadow flicker. According to an embodiment, the method comprises that a remote detector is generating the information when detecting the presence of a person and shadow flicker is also detected. A remote detector can generate the information about shadow flicker. At a location often visited by people, for instance a tourist designation, as a service, a remote detector may be set up. The remote detector may detect shadow flicker and it may detect people present at the same time and generate information that may be transmitted to the central control system or the wind park controller. According to an embodiment, the method comprises that the remote detector detects the presence of a person by the presence of a mobile phone. The remote detector may detect the presence of a person by discovering the presence of a mobile phone. This may be done by registering a nearby Bluetooth connection. Alternatively, a movement detector may be used to detect that a person is present, but a movement detector may be tricked by animals or other moving objects and therefore not as reliable as detecting the presence of a mobile phone. Alternatively, a button on the remote detector that can be activated by a person may be used to detect the presence of people.

According to an embodiment, the method comprises that the position of the person is determined using GPS. The mobile phone or the remote detector may use GPS to determine the position and include the GPS position in the information about shadow flicker. Using GPS is providing a very reliable position of the person affected by shadow flicker. The app in the mobile phone or the remote detecter may be used to record the rotation of the blades of the wind turbine. The mobile phone app or the remote detector may generate further information. The further information detected by the app by recording the rotation of the blades may be the speed of the rotation

DK 2020 70419 A1 of the blades and the frequency of the shadow flicker. Further, the app may detect the time, when a blade is in a vertical position. From the position of the sun and the wind turbine position, the position of the 5 shadow can be estimated, and it can be estimated whether the shadow caused by a wind turbine is actually hitting the position of the person. The step is to estimate the position of the shadow of the wind turbine. If the wind turbine is located in a wind park, the position of the shadow for each wind turbine in the wind park can be estimated and it can be identified whether one or more of the wind turbines is causing a shadow to hit the person.

From the wind turbine identified as causing shadow flicker at the position of the person operational data can be generated. The operational data may comprise the rotational speed of the rotor of the wind turbine and it may comprise the position of the rotor at a given time for instance by a sensor at the tower registering the time when a rotor blade is passing the tower.

Finally, it can be verified that the target wind turbine generates the shadow flicker by comparing the information from the mobile phone app and the operational data.

According to an embodiment, the method comprises that the information comprises detected oscillations in the light intensity at the location of the person.

The information represents the shadow flicker at the location of the person. The information may comprise the detected oscillations in the light intensity; the oscillations may be represented by a frequency of the oscillations of the light intensity caused by the shadow flicker.

When detecting oscillation in the light intensity, the difference between a highest light intensity and the lowest light intensity may have to be higher than a threshold value, avoiding small oscillations that is not a nuisance to the person, causing the target wind turbine to be paused. In an embodiment, the information may be determined and recorded by a remote detector at, or near, the location of the person.

DK 2020 70419 A1 6 According to an embodiment, the method comprises that each wind turbine comprises a rotor, and the operational data comprises the rotor speed of the at least one target wind turbine.

The rotor speed may be used to determine the frequency of the shadow flicker caused by the wind turbine. The frequency determined from the rotor speed may then be compared to the frequency in the oscillation of the shadow flicker at the location of the person. If the frequency of the detected oscillations and the rotor speed do not match, the target wind turbine is taken not to cause the determined shadow flicker, and the target wind turbine therefore do not need to be paused. According to an embodiment, the method comprises that each wind turbine comprises a rotor, and the operational data comprises the angular position of a blade of the rotor of the at least one target wind turbine.

In a wind park, all wind turbines may be rotating the rotors substantially with the same rotor speed and therefore causing the same oscillations in the light intensity. It may therefore be advantageous to verify the target wind turbine, among a plurality of wind turbines, by comparing the angular position of the blades of the rotor to the information from the mobilde phone or the remote detector. Preferably, the operational data from the wind turbines, as well as the information from the mobile phone or remote detector, have a synchronous time registration making it easier to compare the angular position of a blade and the shadow flicker occurring at the position of the person.

According to an embodiment, the method comprises that the verifying involves determining, if the oscillations in the light intensity and the angular position of the blades are synchronic.

The advantage, of using the angular position of the rotor blades, is that the angular position may be different for different wind turbines, making it possible to distinguish between different wind turbines to verify the target wind turbine. Then it also can be verified that the wind turbine, actually causing the shadow, is the same wind turbine that is identified by using the position of the sun to

DK 2020 70419 A1 7 determine that the shadow hits the person. Especially, if more than one wind turbine may cause a shadow, the wind turbine causing the shadow flicker can be identified by determine synchronicity between the oscillations and the rotor positions.

According to an embodiment, the method comprises that the information is transmitted to a central control system. The mobile phone, the remote detector, or any other suitable device transmit, when identifying shadow flicker, the collected information comprising the position of the person to a central control system. The central control system may be located anywhere, for instance at the head quarter of the wind park operator or at the wind park. The central control system may also be a system shared by more wind park operators so that a person affected by shadow flicker can transmit a message to a central control system without having to find out contact information for the specific wind park wherein the wind turbine causing shadow flicker is located.

According to an embodiment, the method comprises that an instruction is transmitted to a wind park controller, which pauses the wind turbine causing the shadow flicker.

According to an embodiment, the method comprises that the instruction to pause the wind turbine causing shadow flicker is transmitted by the central control system to the wind park controller.

When shadow flicker at the position of a person is identified and information about the shadow flicker is transmitted, an instruction to mitigate the shadow flicker is transmitted to the wind park controller for the wind park, wherein the wind turbine causing the shadow flicker is located. The instruction may comprise the identity of the wind turbine causing shadow flicker. Alternatively, the instruction comprises the position of the person affected by shadow flicker and the wind park controller identifies the wind turbine causing the shadow flicker.

DK 2020 70419 A1 8 According to an embodiment, the method comprises that further information is generated when the person has moved away from the position of shadow flicker.

When a person has moved away from the position where shadow flicker was reported, further information is generated that the shadow flicker no longer affects the person.

This information may be generated from the remote detector, set up at the location, that no longer any people are present.

Alternatively, the further information that the phone and the person carrying it, now have moved outside the area, where shadow flicker was reported, may be generated by the app on the mobile phone.

The further information may then be transmitted to the central control system.

According to an embodiment, the method comprises that it is assumed the person has moved away from the position of shadow flicker, if no information about shadow flicker have been transmitted for a period.

When transmitting information about shadow flicker by an app on a mobile phone or by a remote detector, the information preferable may be transmitted again after a period, for instance after 10 or 20 or 30 minutes, to confirm the person is still in the position where he was affected by shadow flicker.

If such a transmission is not transmitted, then it can be assumed the person has move away from the position of shadow flicker.

It is preferable to retransmit the information after a period to confirm a person is still being in the position where shadow flicker affected him, because further information transmitted that shadow flicker is no longer affecting a person may be lost or not transmitted causing the wind turbine to be paused longer than needed.

According to an embodiment, the method comprises that normal operation of the wind turbine is resumed, when the person has moved away from the position of shadow flicker.

According to an embodiment, the method comprises that wherein normal operation of the wind turbine is resumed, when the shadow causing shadow flicker, due to the movement of the sun, has moved away from the original position of shadow flicker.

DK 2020 70419 A1 9 When a wind turbine has been paused, the shadow of the wind turbine may still be observed, and when it is determined that the shadow is moved away or disappeared, then the wind turbine again can be activated and resume normal operation because the target wind turbine no longer risks causing shadow flicker. The risk of shadow flicker disappears, when the sun has moved sufficiently, for the shadow to move away from the position of the person, or the shadow can disappear because clouds have appeared, between the sun and the person, so no risk of shadow flicker is anymore being determined.

In an embodiment, the pausing of the wind turbine may be delayed, e.g. a few minutes, to ensure that the shadow flicker is continuous, and not just caused by, for instance, a short opening in the clouds allowing sun light to hit the person just to disappear again shortly after. For instance, the requirement may be that the shadow flicker information is transmitted twice with a period between to ensure the shadow flicker is continuously affecting a person. This may be done to avoid continuously pausing and starting the wind turbine verified to cause the shadow flicker. Alternatively, the wind turbine may be paused immediately.

In a second aspect, the invention relates to a central control system for identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker, wherein — the central control system receives information comprising the position of the person affected by shadow flicker, — the wind turbine causing the shadow flicker by use of the information and the position of the sun is identified, and — the wind turbine causing the shadow flicker is paused. The detector system to determine shadow flicker according to the second aspect of the invention may be modified to perform the method steps as mentioned above according to the first aspect.

DK 2020 70419 A1 10 A third aspect of the invention relates to a control system for determining shadow flicker of a wind turbine, where the control system is arranged to perform the steps according to the method of the first aspect.

A fourth aspect of the invention relates to a computer program product comprising software code adapted to control a wind turbine when executed on a data processing system, the computer program product being adapted to perform the method of the first aspect.

In general, the various aspects and embodiments of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which Fig. 1 illustrates a wind turbine, Fig. 2 illustrates a wind turbine in a wind park causing shadow flicker at a position of a person, Fig. 3 illustrates a central control system according to an embodiment of the invention, Fig. 4 illustrates wind turbines configured as multi-rotor wind turbines.

DETAILED DESCRIPTION OF AN EMBODIMENT Fig. 1 shows a wind turbine 100 (also commonly referred to as a wind turbine generator, WTG) comprising a tower 101 and a rotor 102 with at least one rotor blade 103. Typically, three blades are used, but a different number of blades can also be used. The blades 103 are connected with the hub 105, which is arranged to rotate with the blades. The rotor is connected to a nacelle 104, which is mounted on top of the tower 101 and being adapted to drive a generator situated

DK 2020 70419 A1 11 inside the nacelle 104 via a drive train. The rotor 102 is rotatable by action of the wind. The wind induced rotational energy of the rotor blades 103 is transferred via a shaft to the generator. Thus, the wind turbine 100 is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator.

Fig. 2 shows a wind park 201 comprising a plurality of wind turbines 100. When the sun 202 is shining, the wind turbines 100 cause shadows 203, which may, when the sun 202 is in a certain position, hit a person 204. When the rotor 102 is rotating, the shadow 203 may cause shadow flicker, affecting the person 204. When shadow flicker affects a person 204, he can use his mobile phone 207 to transmit information to a central control system 206 that shadow flicker affects him, the information comprising the GPS position. Alternatively, a remote detector 205 can determine shadow flicker by changes in light intensity, and create and transmit information about shadow flicker to the central control system 206. The remote detector 205 may be a stationary detector, for instance placed at a location where shadow flicker may occur and where there often are people, for instance at a tourist destination. The remote detector 205 may comprise a camera, using the camera to record the shadow flicker. Fig. 3 shows a diagram illustrating a possible implementation of the functionality of the invention. When shadow flicker has been identified 301, either by a person 207 or by a remote detector 205, information is generated 302 and transmitted to the central control system 206. When the central control system 206 receives the information about shadow flicker, the information is used to identify 303 the wind turbine 100 causing the shadow flicker. When the wind turbine 100 causing shadow flicker is identified, an instruction is transmitted to the wind turbine pausing 304 the wind turbine 100.

When the wind turbine 100 is paused 304, the situation is monitored to determine whether a risk of shadow flicker is still occurring 305. If a risk of shadow flicker is still occurring 305, the system waits 307 for a period, before it again is checked whether a risk of shadow flicker is still occurring 305, alternatively, the system waits 307 for receiving further information that no risk of shadow flicker is

DK 2020 70419 A1 12 occurring any longer. When a risk of shadow flicker no longer is occurring, the wind turbine resumes normal operation 306. The system may wait for a period of 10 minutes, 20 minutes, 30 minutes before the system checks whether the risk of shadow flicker still occurs. For instance, the system may determine, when the sun has moved so much that the shadow of the wind turbine has moved so much that there is no risk that shadow flicker still will affects the person, and the wind turbine resumes normal operation.

The system may also track the position of the person affected by shadow flicker. Tracking the position of the person may be done by tracking the movement of the mobile phone used for reporting shadow flicker. In addition, a build in timer in the system may allow the wind turbine to resume normal operation, if for instance after 30 minutes no new message has been received that shadow flicker still risks occurring, if the wind turbine is restarted.

The person affected by shadow flicker may be able to send a message to the system, for instance by using the app on the mobile phone, when he leaves the area, where the person reported shadow flicker. Alternatively, the mobile phone app may automatically send a message to the system, when the mobile phone register that it has moved a distance, for instance 50 meters or 100 meters away from the position where shadow flicker was reported. If a remote detector was detecting the shadow flicker, the remote detector may send a message when there is no longer any persons detected by the remote detector.

Fig. 4 shows alternative wind turbines 100 configured as multi-rotor wind turbines. Multi-rotor wind turbines comprises a plurality of nacelles 104. The nacelles 104 can be supported, as illustrated in the upper drawing, via a tower 101 and support arms 106 extending outwardly from the tower 101 so that the nacelles are placed away from the tower and on opposite sides of the tower. Alternatively, as illustrated in the lower drawing, the nacelles 104 can be supported by angled towers 101 extending from a foundation 130, e.g. a ground or floating foundation, so that two or more nacelles 104 are sufficiently separated from each other at a given height. Embodiments of the present invention may also be used with multi-rotor wind turbines. The method can be used to not only

DK 2020 70419 A1 13 identify a specific multi wind turbine is causing shadow flicker, but also be used to determine the specific rotor or rotors causing the shadow flicker. In this way in can be ensured that only the rotors causing the shadow flicker are paused.

The invention can be implemented by means of hardware, software, firmware or any combination of these. The invention or some of the features thereof can also be implemented as software running on one or more data processors and/or digital signal processors.

The individual elements of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way, such as in a single unit, in a plurality of units or as part of separate functional units. The invention may be implemented in a single unit, or be both physically and functionally distributed between different units and processors.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is possible and advantageous.

Claims (15)

DK 2020 70419 A1 14 CLAIMS

1. A method for identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker, the method comprising the steps of: — identifying shadow flicker at a position of the person, — generating information comprising the position of the person affected by shadow flicker, — identifying the wind turbine causing the shadow flicker by use of the information and the position of the sun, and — pausing the wind turbine causing the shadow flicker.

2. A method according to any of the preceding claims, wherein the person affected by shadow flicker generates the information.

3. A method according to any of the preceding claims, wherein a mobile phone and an app on the mobile phone is used to generate the information.

4, A method according to any of the preceding claims, wherein a remote detector is generating the information when detecting the presence of a person and shadow flicker is also detected.

5. A method according to claim 4, wherein the remote detector detects the presence of a person by the presence of a mobile phone.

6. A method according to any of the preceding claims, wherein the position of the person is determined using GPS.

7. A method according to any of the preceding claims, wherein an instruction is transmitted to a wind park controller, which pauses the wind turbine causing the shadow flicker.

8. A method according to any of the preceding claims, wherein the information is transmitted to a central control system.

DK 2020 70419 A1 15

9. A method according to claim 8, wherein the instruction to pause the wind turbine causing shadow flicker is transmitted by the central control system to the wind park controller.

10.A method according to any of the preceding claims, wherein further information is generated when the person has moved away from the position of shadow flicker.

11.A method according to any of the preceding claims, wherein it is assumed the person has moved away from the position of shadow flicker, if no information about shadow flicker have been transmitted for a period.

12.A method according to any of the preceding claims, wherein normal operation of the wind turbine is resumed, when the person has moved away from the position of shadow flicker.

13.A method according to any of the preceding claims, wherein normal operation of the wind turbine is resumed, when the shadow causing shadow flicker, due to the movement of the sun, has moved away from the original position of shadow flicker.

14. A central control system for identifying a wind turbine, causing shadow flicker affecting a person and mitigating the shadow flicker, wherein — the central control system receives information comprising the position of the person affected by shadow flicker, — the wind turbine causing the shadow flicker by use of the information and the position of the sun is identified, and — the wind turbine causing the shadow flicker is paused.

15.A computer program product comprising software code adapted to control a wind turbine system when executed on a data processing system, the computer program product being adapted to perform the method of any of the claims 1-13.