AU2014203701B2 - Monitoring and measuring of multiple light sources, especially heliostats - Google Patents

Abstract

Monitoring and measuring of multiple light sources, especially heliostats Abstract Described herein are methods and apparatus for monitoring and measuring multiple lights sources such as heliostats. One embodiment provides an apparatus for monitoring and/or measuring multiple directional light sources, each directing light as a beam of limited solid angle. The apparatus comprises a distribution of light responsive pixels defined by individual or multiple photodiodes. The apparatus also comprises an optical arrangement including multiple apertures distributed over an area on which at least 50% of the light beam from each light source impinges, wherein the apertures are arranged to direct light from the multiple directional light sources to different respective subsets of the pixels. The aperture arrangement and pixels are sized and located so that the subsets are sufficiently distinguishable to permit simultaneous monitoring and/or measuring of the directional light sources.

Description

Abstract

Described herein are methods and apparatus for monitoring and measuring multiple lights sources such as heliostats. One embodiment provides an apparatus for monitoring and/or measuring multiple directional light sources, each directing light as a beam of limited solid angle. The apparatus comprises a distribution of light responsive pixels defined by individual or multiple photodiodes. The apparatus also comprises an optical arrangement including multiple apertures distributed over an area on which at least 50% of the light beam from each light source impinges, wherein the apertures are arranged to direct light from the multiple directional light sources to different respective subsets of the pixels. The aperture arrangement and pixels are sized and located so that the subsets are sufficiently distinguishable to permit simultaneous monitoring and/or measuring of the directional light sources.

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2014203701 07 Jul 2014

Monitoring and measuring of multiple light sources, especially heliostats

Field of the invention [0001] This invention relates generally to the monitoring and/or measurement of the orientation of multiple directional light sources. The invention enables measurement of radiation intensity over an array of ray angles and positions. One use is to simultaneously measure a pattern of intensity falling on a planar surface from each of multiple light sources. The invention is particularly, though not exclusively, useful in the calibration and control of the heliostats of a solar field. Such a solar field may typically be in a solar energy collection apparatus of the kind having a central solar energy receiver, typically on a tower, and an array of heliostats mounted for angular adjustment to optimally receive a beam of sunlight and direct it to the central receiver. Solar energy collection apparatus of the aforementioned kind is referred to herein as a central receiver solar energy collection system.

Background of the invention [0002] A challenge with central receiver solar energy collection systems is the trade off, in relation to the heliostats, between manufacturing cost and manufactured accuracy. A large solar field may have many hundreds, even tens of thousands, of heliostats and so the overall economic performance of the system may be dependent upon achieving a low unit cost in the manufacture of each heliostat, including the actuator configuration for angularly adjusting the heliostat. On the other hand, inexpensive manufacture will generally come with high tolerances that will give rise to substantial variations in the optical characteristics across the heliostats of a large field. One way to address this issue is to obtain a geometrical calibration or characterisation of each heliostat mirror, for example by measuring the location of the centre of the heliostat image. The location of this point can be used to calibrate or adjust each of the two angular positioning systems on each heliostat. Ideally the image shape could be measured on the receiving surface during operation. However, the receiver in a central receiver system is operating at high temperatures and is a hostile place for measuring equipment. The reflectivity can be non uniform and the surface can be non planar.

[0003] United States patent 4,564,275 provides a calibration technique which eliminates resurveying and field work and provides a method of aligning a single heliostat or a number of heliostats at the same time. The technique relies on changing the aim point from the receiver to a reference position on a target, with a radiometer used to determine the beam centroid error

2014203701 07 Jul 2014 which is then used to re-align the heliostat. A problem with this technique is that it does not address the calibration of inexpensive and inaccurate heliostats.

[0004] PCT Patent Application Publication WO 2012/083383 by the present applicant discloses solar energy collection apparatus including a solar energy receiver defining a primary target to receive directed sunlight from a field of angularly adjustable heliostats. A controller operably coupled to an actuator arrangement for effecting angular adjustment of each heliostat is configured to sequentially cause, during operation of the apparatus, a temporary angular adjustment of the respective heliostats so as to direct the beam of sunlight received at each heliostat to a secondary target for a predetermined period of time. A representation of each diverted beam at the secondary target is recorded by a camera and deviation of a parameter of the image, for example the location of the centroid of the image, from a reference norm provides a basis for angularly adjusting the corresponding heliostat to improve its targeting accuracy on the primary target.

[0005] This latter calibration mechanism is suitable for small, inaccurately constructed heliostats. Frequent measurement of the image centroid on the secondary target during operation allows the system operator to maintain a model of the heliostat geometry.

[0006] United States Patent Application Publication 2012/0174909 describes a system for aligning heliostats using a ring of cameras around the central target. The cameras are designed to measure the imbalance of light reflecting off each heliostat from the circum solar region of the solar image. US Patent Application Publication 2013/0021471 describes a similar approach to US 2012/0174909.

[0007] Two issues have been identified with these approaches. Solar fields of tens or hundreds of megawatt capacity have been proposed, and these fields could consist of tens of thousands of small heliostats. In this case, the requirement to separately calibrate the heliostats regularly can be problematic because the calibration or secondary target is a shared resource. There will be a long time between calibration points for a heliostat while all of the other heliostats are being separately calibrated. There are practical limits to the number of calibration targets as they all need to be a similar size to the receiver making many targets unwieldy.

[0008] The second issue arises when a small heliostat is a long distance from the receiver: the image it forms on a white surface may be many times less intense than ambient light. Designing a system capable of accurately measuring the heliostat image under these conditions would present significant challenges.

[0009] United States Patent Application Publication 2013/0139804 describes a system for characterising a surface of a single heliostat. Each heliostat is scanned incrementally across a multiple pixel camera, with an image snapshot taken at each scanned position. By associating

2014203701 07 Jul 2014 pixels with sections of the heliostat surface, the geometry of the surface can be defined, and this information employed to optimise the energy flux of the solar receiver.

[0010] PCT Patent Application Publication WO 2009/152573 describes a method and apparatus for calibrating heliostats. Calibration is performed by comparing, at the primary receiver, the flux distributions corresponding to a plurality of mirrors at first and second mirror angles. This technique is not capable of spatially distinguishing the individual mirror contributions, only their overall contributed flux. Furthermore, the camera devices for measuring the flux distributions are located at the primary receiver where a high flux intensity is focussed. As such, the cameras must be significantly robust to withstand very high temperatures. Such robust cameras are generally quite expensive and may still be subject to short operating lifetimes.

[0011] It is a general object of the preferred embodiments of the invention to provide for the improved monitoring and/or measurement of the orientation of multiple direction light sources. In a particular application of interest, it is an object of the invention to provide for the calibration and adjustment of multiple spaced light sources in the form of heliostats in a solar field, in a manner that, at least in part, addresses the aforementioned problems with current calibration systems that entail the receipt of the solar light image from the heliostat onto a secondary target.

[0012] Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention [0013] In one aspect, the invention provides apparatus for monitoring and/or measuring multiple directional light sources each directing light as a beam of limited solid angle, the apparatus comprising:

a distribution of light responsive pixels;

an optical arrangement including multiple apertures distributed over an area on which at least 50% of the light beam from each light source impinges, wherein the apertures are arranged to direct light from the multiple directional light sources to different respective subsets of the pixels, the aperture arrangement and pixels being sized and located so that the subsets are sufficiently distinguishable to permit simultaneous monitoring and/or measuring of the directional light sources.

2014203701 07 Jul 2014 [0014] Advantageously, in one embodiment, the apparatus further includes a controller configured to receive and store in memory data in relation to said different subsets of the pixels for reference orientations of the respective light sources, to subsequently receive and record updated data in relation to respective subsets of pixels simultaneously illuminated by the respective light source, and to compare the updated data with the data in memory for the reference orientations of the light sources.

[0015] In an embodiment, the controller is further configured to output light source orientation correction signals responsive to differences detected in the comparing step.

[0016] In another embodiment, useful with multiple light sources that are elements of a larger, e.g. substantially continuous, light source, the apparatus includes a controller configured to receive and store in memory data in relation to said different subsets of the pixels, and to process the data to characterise the light sources, e.g. the amount of light emanating therefrom or the relative slope of the respective elements of a larger light source.

[0017] In the first aspect, the invention further provides a method for monitoring and/or measuring multiple directional light sources each directing light as a beam of limited solid angle, the method comprising: receiving light from the multiple directional light sources at different respective subsets of pixels in a distribution of light responsive pixels via apertures of an optical arrangement that includes multiple apertures distributed over an area on which at least 50% of the light beam from each light source impinges, wherein the optical arrangement and pixels are sized and located so that said subsets are sufficiently distinguishable to permit simultaneous monitoring and/or measuring of the directional light sources.

[0018] Advantageously, the method further includes:

storing in memory, data in relation to said different subsets of the pixels for reference orientations of the respective light sources; and subsequently receiving and recording updated data in relation to respective subsets of pixels simultaneously illuminated by the respective light sources, and comparing the updated data with the data in memory for the reference orientations of the light sources.

[0019] The method preferably further includes outputting light source orientation correction signals responsive to differences detected in the comparing step.

[0020] In an application of the first aspect of the invention, the multiple directional light sources are heliostats in a solar field. The heliostats simultaneously illuminating each subset of pixels are not adjacent in the field, typically having sufficient spacing to avoid any pixels being illuminated by multiple heliostats.

2014203701 07 Jul 2014 [0021 ] The multiple directional light sources may be discrete light sources, or elements of a larger, e.g. continuous, light source. The multiple directional light sources may be active light generators, or passive reflectors or transmitters of light. Heliostats are typical of the latter class.

[0022] In a second aspect, the invention provides a solar energy collection apparatus comprising:

a solar energy receiver defining a primary target to receive directed sunlight;

a field of heliostats mounted for angular adjustment to optimally receive a beam of sunlight and direct it to the primary target of the solar energy receiver;

at least one actuator to effect the angular adjustment of each heliostat of the field;

a secondary target at or spaced from said primary target disposed so as not to be intercepted by said optimally received and directed beams of sunlight; and a controller operably coupled to the at least one actuator and configured to cause, during operation of the solar energy collection apparatus, a temporary angular adjustment of the respective heliostats so as to temporarily divert the beam of sunlight received at each heliostat to the secondary target;

wherein the secondary target comprises the apparatus according to the first aspect comprising a distribution of light responsive pixels and the optical arrangement that includes multiple apertures arranged to simultaneously direct beams in the form of sunlight from directional light sources in the form of plural, preferably multiple, spaced apart heliostats of the solar field to different respective subsets of the pixels, the arrangement and pixels being sized and located so that the subsets are sufficiently distinguishable to permit simultaneous optical characterisation of said plural spaced apart heliostats.

[0023] The secondary target is preferably the apparatus according to the first aspect, with the multiple directional light sources comprising heliostats.

[0024] Advantageously, the apparatus of the second aspect of the invention further includes a controller configured to receive and store in memory data in relation to said different subsets of the pixels for reference angular positions of the respective heliostats, to subsequently receive and record updated data in relation to respective subsets of pixels, simultaneously illuminated by the respective heliostats, to compare the updated data with the data in memory for the reference angular positions of the heliostats, and to output angular position correction signals for the respective heliostats responsive to differences detected in the comparing step.

[0025] In the second aspect, the invention further provides a method of solar energy collection, comprising:

receiving at a primary target defined by a solar energy receiver, beams in the form of sunlight directed from directional light sources in the form of heliostats of a field of heliostats

2014203701 07 Jul 2014 mounted for angular adjustment to optimally receive a beam of sunlight and direct it to the primary target of the solar energy receiver;

causing, during operation of the field, a temporary angular adjustment of the respective heliostats so as to temporarily divert the beam of sunlight received at each heliostat to a secondary target at or spaced from the primary target, wherein the secondary target includes a distribution of light responsive pixels and an optical arrangement that includes multiple apertures arranged to simultaneously direct sunlight from plural, preferable multiple, spaced apart heliostats of the solar field different respective subsets of the pixels, the optical arrangement and pixels being sized and located so that the subsets are sufficiently distinguishable to permit simultaneous optical characterisation of said plural spaced apart heliostats;

receiving and storing in memory data in relation to said different subsets of the pixels, for reference angular positions of the respective heliostats;

subsequently receiving and recording updated data in relation to respective subsets of pixels simultaneously illuminated by the plural, preferably multiple, spaced apart heliostats;

comparing the updated data with the data in memory for the reference positions of the heliostats, and outputting angular position correction signals for the respective heliostats responsive to differences detected in the comparing step.

[0026] In the second aspect of the invention, the optical arrangement is preferably a multiaperture optical arrangement.

[0027] The second aspect is preferably encompassed by the first aspect of the invention, with the multiple directional light sources being heliostats.

[0028] In some aspects of the invention, the subsets of pixels are preferably sufficiently distinguishable through no pixel of each subset being illuminated by more than one of the directional light sources.

[0029] Each of the subsets of pixels may be further distinguishable through having no overlap with adjacent subsets of pixels, i.e no pixel common to any two or more of the subsets.

[0030] In an embodiment, the spacing between each subset of pixels is at least one pixel. This spacing may be at least two pixels, or it may be three pixels or more.

[0031] In both the first and second aspects, the distribution is preferably a two dimensional distribution which is preferably an array. Preferably, the array of light responsive pixels is a rectangular (e.g. a square) array. In another embodiment, the distribution may include plural arrays of light responsive pixels, in which case each of the plural arrays may be a rectangular array. In another embodiment, the distribution may be a circular or hemispherical distribution of light responsive pixels.

2014203701 07 Jul 2014 [0032] The subsets of pixels may include a single pixel or a plurality of pixels. In one embodiment, the subset includes a square array of pixels. The subsets are preferably sufficiently distinguishable such that the directional light sources are simultaneously spatially resolved from one another.

[0033] In both the first and second aspects of the invention, the distribution of light responsive pixels is preferably generally co-planar. Conveniently, the distribution may typically comprise an array or multiple subarrays of pixels arranged in a coplanar configuration, in which case the aperture arrangement may comprise a 1:1 array of apertures associated with the subarrays of pixels. Each subarray may be, for example, a discrete digital camera sensor array, e.g. a photodiode array in a CCD or CMOS arrangement. The subarrays of pixels are typically equi-spaced square array, as is, preferably, the array of apertures.

[0034] The light responsive pixels are each preferably responsive to provide a measure of the light incident on the pixel. They array of light response pixels may comprise, for example, a photodiode array in a charge-coupled device (CCD) or CMOS arrangement.

[0035] The invention extends to a solar energy collection apparatus or method according to the second aspect of the invention in which the secondary target is an apparatus according to the first aspect.

[0036] In the second aspect, the secondary target may be spaced apart from the first target by a distance in the range of 2 m to 10 m.

[0037] In a third aspect, the invention provides system for simultaneously calibrating an angular position of a plurality of spaced-apart heliostats, each heliostat being configured to reflectively direct a beam of light in a predetermined direction based on its angular position, the system including:

a controller operatively associated with a system of actuators to selectively adjust the angular position of the heliostats to simultaneously direct the respective beams to an array of spaced apart light responsive pixels such that the beams from separate heliostats are directed to different respective subsets of the pixels and are capable of being distinguished from each other; and a database to record a measured irradiance at each subset of pixels;

the controller further adapted to:

calculate an ideal angular position of each heliostat for which the irradiance on a target is maximised;

compare the ideal angular positions for each heliostat to previous angular positions and determine an angular adjustment based on the comparison; and apply the angular adjustment to the respective heliostats.

2014203701 07 Jul 2014 [0038] In the third aspect, the invention further provides a method of simultaneously calibrating an angular position of a plurality of spaced-apart heliostats, each heliostat being configured to reflectively direct a beam of light in a predetermined direction based on its angular position, the method including the steps:

selectively adjusting the angular position of the heliostats to direct the respective beams, simultaneously if required, to an array of spaced apart light responsive pixels such that the beams from separate heliostats are directed to different respective subsets of the pixels and are capable of being distinguished from each other;

recording a measured irradiance at each subset of pixels during the sweep; calculating an ideal angular position of each heliostat for which the irradiance on a target is maximised;

comparing the ideal angular positions for each heliostat to previous angular positions and determining an angular adjustment based on the comparison; and applying the angular adjustment to the respective heliostats.

[0039] As used herein, except where the context requires otherwise, the term comprise and variations of the term, such as comprising, comprises and comprised, are not intended to exclude further additives, components, integers or steps.

Brief description of the drawings [0040] Preferred embodiments of the invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a simplified diagram of a central receiver solar energy collection system, according to an embodiment of the invention;

Figure 2 is a perspective view from below of the tower mounted central receiver and the secondary target;

Figure 3 is a functional block diagram of the main components of a solar energy collection system, including the controller;

Figure 4 is a rear perspective view of a typical heliostat; and

Figure 5 is a schematic diagram depicting a secondary target according to an embodiment of the invention and its interaction with a representative heliostat.

Detailed description of the embodiments [0041] The present invention has particular utility in the operation of a central receiver solar energy collection system utilising inexpensively manufactured heliostats. Such a system 10 is depicted in Figures 1 and 2. The system comprises a central solar energy receiver 12 mounted in cantilevered fashion from a tower 11 above and in front of a large array or field 18 of

2014203701 07 Jul 2014 horizontally spatially separated heliostats 15. Heliostats 15 are mounted for angular adjustment to optimally receive a respective beam of sunlight 200 and to direct the beam, as a directed beam 202, to the solar receiver 12. As best shown in Figure 2, receiver 12 has an aperture 13 that defines a primary target to receive the directed beams of sunlight from the heliostats during operation of the system.

[0042] An optimally receiving position in this context is the two dimensional angular position of the heliostat determined by a central controller, discussed further below, to be the appropriate position at the particular time on the particular date at which the respective heliostat makes a desired contribution to the energy flux incident on the receiver target 13. In general, the objective is to best approximate the desired flux levels and flux distribution at the receiver.

[0043] Receiver 12 hangs downwardly from a supporting cantilever framework 19 fixed to tower 11. However, it will be appreciated that, in other embodiments, receiver 12 is supportively mounted to tower 11 by other types of frameworks. Also fitted to framework 19, by being suspended between a pair of inclined struts 31, is a secondary or auxiliary target 30 (Figure 3). The secondary target is, in this case, spaced vertically from the primary target and disposed so as not to be intercepted by the optimally received and directed beams of light from the heliostats. Preferably, secondary target 30 is located several metres from receiver 12 so that it is outside the radiation spill area of receiver 12 but does not require significant angular deviation of the heliostats from their trajectory during normal operation. In exemplary embodiments, secondary target 30 is spaced apart from receiver 12 by a distance in the range of 2 to 10 metres and preferably by a distance of 5 metres.

[0044] Each heliostat 15, has an individual actuator system 21 typically comprising a pair of linear actuators 60, 62 (Figure 3) for respectively controlling the inclination and declination of the heliostat's reflecting surface. The angular position of each heliostat, both inclination and declination, is determined by a central controller 40 (Figure 3) which may comprise a suitable computer system. This controller is operably coupled to the actuators 60, 62 of all of the heliostats, to magnetic sensors 80 by which the controller is kept informed of actual angular position co-ordinates of each heliostat, and to secondary target 30. As well as activating and deactivating the system 10 into and out of operation, controller 40 is programmed to carry out a number of calibration and control tasks in order to optimise the convertible energy received at primary target aperture 13.

[0045] A suitable heliostat 15 with respective actuators 60, 62 is illustrated in Figure 4. Heliostat 15 is indicative of a typical device incorporated into system 10. However, it will be appreciated that other types and designs of heliostat or combinations of different heliostats can be incorporated into system 10. Heliostat 15 includes a large concave mirror fixed by adhesive ίο

2014203701 07 Jul 2014 to a backing frame 20 of rectangular profile. Frame 20 is mounted atop a stand or post 70, by means to be described, and comprises a central hub 23 and ribs 22 that extend radially from central hub 23 to peripheral edge beams 22a. The ribs 22 are fastened to corresponding flat radial arms 25 of hub 23. The mirror 14 lies on the concave side. The dimensions of the components are determined by a frame pattern which is generated by software. Fasteners such as thread forming screws, rivets, spot welding or bolted joints are used throughout the frame 20.

[0046] The mirror 14 is glued directly to the frame 20 using a polyurethane based adhesive applied to folded tabs on the inner edge flanges 28 of all the ribs 22, which collectively define a shallow concave paraboloid shape. The mirror is typically made of 3mm thick glass having a high reflectivity surface, such as a plastic composite, and a low iron content to reduce energy absorption. Suitable such glasses include those manufactured by Sencofein or Miralite Solar Premium manufactured by Saint Gobain.

[0047] The pair of linear screw actuators 60, 62 by which the heliostat orientation is controlled are positioned substantially parallel, so that they both extend generally perpendicular to the mirror 14. This prevents the actuators 60, 62 from colliding during operation whilst giving a greater range of optimal angle to the heliostat 12. The actuators 60, 62 include individual offthe-shelf DC motors 65.

[0048] The actuators 60, 62 are arranged to provide control in two orthogonal directions so that the focusing point can be maintained for any angle of incident light. One axis is controlled east to west, i.e. side to side, and the other north to south, i.e. upward tilt. However, one axis is controlled relative to the other axis. Specifically, side-to-side rotation occurs about an intermediate mount in the form of a frame support bracket 66, which is itself rotated up or down: this arrangement minimises the amount of space taken up by each heliostat 12.

[0049] The frame 20 is connected to support bracket 66 at vertically spaced hinges for rotation about an upright axis joining the hinges. The first linear actuator 60 is mounted between the mirror frame 20 and an arm 64 that projects laterally rearwardly from support bracket 66, for controlling this side-to-side or east-west rotational movement. Bracket 66 is pivotally attached in turn, by a bracket pin 68, to the top of post 70. Pin 68 defines an inclination axis about which the tilt angle of bracket 66, and thereby of frame 20, is adjustable. The aforementioned upright axis is generally orthogonal to the inclination axis. Arm 64 is rigidly connected to the bracket 66 as close to the inclination axis as possible.

[0050] Second actuator 62 extends between post 70 and an attachment point at the lower end of bracket 66 for effecting adjustment of the tilt or inclination of the mirror. The angle of the arm 64 to the bracket 66 is selected to provide optimum actuator geometry, with different angles for each heliostat according to positions in the field. The bracket 66 may further include a π

2014203701 07 Jul 2014 number of different attachment points for the actuator 62 also selectable to provide the optimum angle according to the individual heliostat's position in the field.

[0051] As shown in Figure 3, magnetic sensors 80 mounted adjacent each heliostat and are used to measure the respective orientation or positional angles of each heliostat, defined by inclination and lateral orientation or declination. In some embodiments, magnetic sensors 80 are only operatively associated with a subset of the heliostats. These sensors are inexpensive low precision (~8 bit) encoders, e.g. hall effect encoders. Furthermore these encoders are deployed to determine motor shaft position rather than directly measuring the angular location of the mirror assembly.

[0052] System 10 is activated into operation by controller 40 using the actuators 60, 62 to bring the heliostats to substantially their optimum orientation at which all optimally receive a respective beam of sunlight and direct it to the primary target 13 of the solar energy receiver 12. When this concentrated composite beam is not being utilised to provide heat energy for the power plant coupled to the receiver, the system must be deactivated out of operation by adjusting the heliostats away from their optimal position to random uncorrelated orientations that do not result in any collectively focused sunlight.

[0053] According to an embodiment of the invention illustrated in Figure 5, secondary target 30 comprises a square array 101 of substantially equally spaced apart discrete digital camera sensors 102 each including a planar array of light responsive pixels defined by individual or multiple photodiodes. Exemplary arrays of light responsive pixels include a charge coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) arrangement. Looked at from an alternative perspective, this arrangement comprises an array of light responsive pixels arranged in subarrays or subgroups 102 of the pixels. The pixels are each responsive to provide a measure of light incident on the pixel.

[0054] In general, sensors 102 need not be disposed in an ordered arrangement such as an array but may be arranged in any spatial distribution having equal or different distances therebetween. In other embodiments, sensors 102 are arranged in other two dimensional distributions not necessarily having ordered vertical columns and horizontal rows. For example, in one embodiment sensors 102 are arranged in a substantially circular distribution having concentric arrays of monotonically increasing radius from a central point.

[0055] Disposed in front of the array of light responsive pixels is an aperture arrangement 105 in which there is a single aperture 104 in 1:1 correspondence with the respective camera sensors or pixel subarrays. In some embodiments, arrangement 105 includes coupling optics such as one or more lenses. In a simple exemplary layout, the aperture arrangement may be provided by a machined sheet of metal 100 with an array of pinholes 104 in it. The actual

2014203701 07 Jul 2014 apertures may have one of a number of shapes including circular, square or rectangular. The pixel subarrays 102, which may be viewed as separate respective sensor elements, are arranged behind each pinhole 104 so that all pixels are aligned in the same plane with the same offset from their respective pinholes.

[0056] The pixel subarrays or sensors 102 are electrically coupled to controller 40 with appropriate electronics for recording data representative of the intensity and location of light received at each sensor.

[0057] It will be appreciated that any selected heliostat 15 in the field 18, if angularly adjusted by controller 40 so as to direct its received sunlight 200 toward secondary target 30 as a beam 202 that illuminates the target as an image 115, will illuminate a respective different subset 110 of the pixels. If one chooses a number of sufficiently spaced heliostats in the field, and the aperture arrangement 105 is appropriately sized and located, these subsets of pixels 110 - one or more 103 in each of the subarrays 102 - are sufficiently distinguishable to permit simultaneous optical characterisation of the spaced heliostats. The term ‘sufficiently distinguishable’ is intended to mean that two or more heliostat beams are able to be simultaneously spatially resolved or distinguished from one another such that each corresponding heliostat can be characterised. This does not imply that the beams are actually spatially separated and significant overlapping of the beams is likely where simultaneous characterisation is performed. The limit of resolution or distinguishability is determined by the particular characteristics (including size, shape and position) of sensors 102 and apertures 104.

[0058] The required spacing between heliostats can be readily determined through correlating the spacing of the heliostats with the required minimum spacing between each of the subsets of pixels 110.

[0059] In the earlier described prior art calibration and adjustment system, each heliostat in the field must be singularly and in turn directed to the secondary target. With the arrangement of the present invention, a substantial number of sufficiently separated heliostats can be simultaneously directed to the secondary target so that the respective subsets of illuminated pixels of the subarrays will be distinguishable for each heliostat. Preferably, the number of heliostats that may be simultaneously checked and adjusted is at least 5 and more preferably 10 or more.

[0060] As mentioned earlier, controller 40 is programmed to carry out a number of calibration and control tasks in order to optimise the convertible energy received at primary target aperture 13. The first of these tasks is the calibration of each heliostat and the second is to effect an angular adjustment of the heliostat in response to the calibration. During the calibration phase, by means of control signals from controller 40 to heliostat actuators 60, 62, one heliostat

2014203701 07 Jul 2014 at a time has its angular position shifted. The system is calibrated by recording the relative magnitude of maximum response that can be generated by sweeping each heliostat in turn over the pixel array with a constant direct irradiance. The light responses from each heliostat subarray 102 are then sampled to provide a sample image for each subarray, and these sample images are then assembled as a subset of pixels to produce a reference image for each heliostat - from which is deduced a reference position for the heliostat. In an alternative embodiment, the total irradiance measured by the pixels of each subarray is determined and the reference position is determined from the measure total irradiances.

[0061] Repetition of this process across all heliostats in turn during commissioning of the apparatus constitutes an ‘instantaneous’ calibration of each heliostat.

[0062] The update phase (calibration and adjustment) of monitoring heliostat annular position and making on the run adjustment at regular intervals is effected by a controller managed program of sequentially angularly directing groups of well-spaced heliostats away from the primary target during operation of the field, and directing their reflected beam to the secondary target 30, thereby receiving and recording updated data in relation to respective subsets of pixels simultaneously illuminated by the respective heliostats. The updated data is then compared with the data in memory for the earlier determined reference positions of the heliostats, and, if necessary, angular position correction or adjustment signals responsive to differences detected in the comparing step are determined and stored in a database or memory associated with controller 40.

[0063] In an optimum arrangement, the subsets of pixels are mutually exclusive, i.e there are no pixels common to any two subsets. It is preferable that there be at least a full pixel separation of adjacent pixels of respective subsets so as to reduce or eliminate interference from adjacent heliostat beams. This is because it would be impractical to ensure that pixel boundaries fall between heliostat beams. In an alternative arrangement, subsets of pixels might share one or more common pixels at the expense of some degree of interference between adjacent heliostat beams: these subsets can still be distinguishable provided there are sufficient pixels not common for the respective heliostats to be capable of being distinguished and characterised. That is, different heliostat beams may be able to be simultaneously spatially resolved even when their images (as detected by sensors 102) partially overlap. The amount of overlap of pixels permitted is determined by the limit of resolution of the optical arrangement defined by the distribution of sensors 102 and apertures 104.

[0064] Because the camera pixels of interest are not significantly influenced by ambient light, the earlier mentioned problem arising when heliostats are distant and the secondary target image much less intense than ambient light, is substantially resolved.

2014203701 07 Jul 2014 [0065] The method and apparatus of the invention may be employed to characterise the shape (in terms of a directivity or response profile) of an individual heliostat. If there are sufficient pixels per angle of incidence the described configuration can be used to measure the amount of light coming from various parts or elements of the mirror surface, on each camera. This allows the relative slope of elements across the mirror surface to be determined, effectively measuring the mirror shape including the mirror curvature and focal length.

[0066] Preferably, the angle per pixel is between 1 x10-6 and 1.0 degrees. The lower limit is likely to be limited by the pixel density of CCD elements in combination with the field of view.

[0067] A further application is to use these measurements to calculate adjustments in the ‘canting’ of large multi faceted heliostats, the relative angular adjustment of individual, sometimes flat, facets in a large heliostat.

[0068] In the heliostat calibration application described above, it is advantageous for the field of view of each camera to include the whole field of heliostats and sufficient angular resolution to resolve individual heliostats, limitations in camera angular resolution mean that covering a large field of view with high resolution might be optimally achieved using a distribution of cameras with varying optical alignment [0069] In the reflector surface characterisation case, it is advantageous to achieve higher angular resolution to be able to have many pixels over the mirror surface, with a field of view only covering a single heliostat. An implementation may have the CCD elements further from the aperture plane in the optical axis than for the heliostat calibration application and the whole assembly would need to be aimed at the heliostat of interest.

[0070] The invention more generally can be considered as an angularly selective imaging element - capable of measuring the intensity over a surface and over an angular range of incidence angles.

[0071] In an alternative application, the invention could be used for modern cinematography employing a mixture of computer generated imagery and conventional filming to accurately measure lighting patterns intended to intercept specular computer generated surfaces. For example, a specularly reflective computer generated object could be inserted into a complex scene involving multiple light sources, shadows etc, by measuring light in the scene using an embodiment of the present invention and then applying that light field during rendering of the computer generated object.

[0072] An embodiment could enable a novel camera technology capable of forming a focus without lenses, by applying algorithms to the camera data. Alternatively, all camera data could

2014203701 07 Jul 2014 be captured to enable focussing and changing depth of field to be performed during post processing.

[0073] Reference throughout this specification to “one embodiment”, “some embodiments” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in some embodiments” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0074] As used herein, the term “exemplary” is used in the sense of providing examples, as opposed to indicating quality. That is, an “exemplary embodiment” is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

[0075] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0076] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0077] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0078] Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms coupled and connected, along with their derivatives, may be used. It should be understood that these terms are not

2014203701 07 Jul 2014 intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. Coupled may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[0079] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. Functionality may be added or deleted from the schematic diagrams and operations may be interchanged. Steps may be added or deleted to methods described within the scope of the present invention.

2014203701 07 Jul 2014

Claims (20)

1. An apparatus for monitoring and/or measuring multiple directional light sources each directing light as a beam of limited solid angle, the apparatus comprising:

a distribution of light responsive pixels;

an optical arrangement including multiple apertures distributed over an area on which at least 50% of the light beam from each light source impinges, wherein the apertures are arranged to direct light from the multiple directional light sources to different respective subsets of the pixels, the aperture arrangement and pixels being sized and located so that the subsets are sufficiently distinguishable to permit simultaneous monitoring and/or measuring of the directional light sources.

2. A method for monitoring and/or measuring multiple directional light sources each directing light as a beam of limited solid angle, the method comprising:

receiving light from the multiple directional light sources at different respective subsets of pixels in a distribution of light responsive pixels via apertures of an optical arrangement that includes multiple apertures distributed over an area on which at least 50% of the light beam from each light source impinges, wherein the optical arrangement and pixels are sized and located so that said subsets are sufficiently distinguishable to permit simultaneous monitoring and/or measuring of the directional light sources.

3. The method according to claim 2 further including the steps of:

storing in memory, data in relation to said different subsets of the pixels for reference orientations of the respective light sources; and subsequently receiving and recording updated data in relation to respective subsets of pixels simultaneously illuminated by the respective light sources, and comparing the updated data with the data in memory for the reference orientations of the light sources.

4. The method according to claim 3 further including the step of outputting light source orientation correction signals responsive to differences detected in the comparing step.

5. The method or apparatus according to any one of the preceding claims wherein the light sources are discrete light sources.

6. The method or apparatus according to any one of claims 1 to 4 wherein the light sources are elements of a single light source.

7. A solar energy collection apparatus comprising:

a solar energy receiver defining a primary target to receive directed sunlight;

2014203701 07 Jul 2014 a field of heliostats mounted for angular adjustment to optimally receive a beam of sunlight and direct it to the primary target of the solar energy receiver;

at least one actuator to effect the angular adjustment of each heliostat of the field;

a secondary target at or spaced from said primary target disposed so as not to be intercepted by said optimally received and directed beams of sunlight; and a controller operably coupled to the at least one actuator and configured to cause, during operation of the solar energy collection apparatus, a temporary angular adjustment of the respective heliostats so as to temporarily divert the beam of sunlight received at each heliostat to the secondary target;

wherein the secondary target comprises the apparatus according to claim 1 comprising the distribution of light responsive pixels and the optical arrangement that includes multiple apertures arranged to simultaneously direct beams in the form of sunlight from directional light sources in the form of plural, preferably multiple, spaced apart heliostats of the solar field to different respective subsets of the pixels, the arrangement and pixels being sized and located so that the subsets are sufficiently distinguishable to permit simultaneous optical characterisation of said plural spaced apart heliostats.

8. The apparatus according to claim 7 further including a controller configured to receive and store in memory data in relation to said different subsets of the pixels for reference angular positions of the respective heliostats, to subsequently receive and record updated data in relation to respective subsets of pixels, simultaneously illuminated by the respective heliostats, to compare the updated data with the data in memory for the reference angular positions of the heliostats, and to output angular position correction signals for the respective heliostats responsive to differences detected in the comparing step.

9. The apparatus according to claim 7 or claim 8 wherein the secondary target is spaced apart from the first target by a distance in the range of 2 m to 10 m.

10. A method of solar energy collection according to any one of claims 2 to 6, comprising:

receiving, at a primary target defined by a solar energy receiver, beams in the form of sunlight directed from directional light sources in the form of heliostats of a field of heliostats mounted for angular adjustment to optimally receive a beam of sunlight and direct it to the primary target of the solar energy receiver;

causing, during operation of the field, a temporary angular adjustment of the respective heliostats so as to temporarily divert the beam of sunlight received at each heliostat to a secondary target at or spaced from the primary target, wherein the secondary target includes a distribution of light responsive pixels and an optical arrangement that includes multiple apertures arranged to simultaneously direct sunlight from plural, preferable multiple, spaced

2014203701 07 Jul 2014 apart heliostats of the solar field to different respective subsets of the pixels, the optical arrangement and pixels being sized and located so that the subsets are sufficiently distinguishable to permit simultaneous optical characterisation of said plural spaced apart heliostats;

receiving and storing in memory data in relation to said different subsets of the pixels, for reference angular positions of the respective heliostats;

subsequently receiving and recording updated data in relation to respective subsets of pixels simultaneously illuminated by the plural, preferably multiple, spaced apart heliostats; and comparing the updated data with the data in memory for the reference positions of the heliostats, and outputting angular position correction signals for the respective heliostats responsive to differences detected in the comparing step.

11. The method or apparatus according to any one of the preceding claims, where said subsets are mutually exclusive.

12. The method or apparatus according to claim 11 wherein said subsets are spaced apart from each other by a spacing of at least one pixel.

13. The method or apparatus according to any one of claims 1 to 11, wherein said subsets share one or more common pixels.

14. The method or apparatus according to any one of the preceding claims wherein the distribution is an array of light responsive pixels.

15. The method or apparatus according to claim 14 wherein the array is a rectangular or square array.

16. The method or apparatus according to any one of claims 1 to 13 wherein the distribution includes plural arrays of light responsive pixels.

17. The method or apparatus according to claim 16 wherein the each of the plural arrays is a rectangular or square array.

18. The method or apparatus according to any one of the preceding claims wherein the subsets include a single pixel.

19. The method or apparatus according to any one of claims 1 to 18 wherein the subsets include a plurality of pixels.

20. The method or apparatus according to any one of the preceding claims wherein the subsets are sufficiently distinguishable such that the directional light sources are simultaneously spatially resolved from one another.

2014203701 07 Jul 2014