AU2016208290A1 - Closed loop control system for heliostats - Google Patents

Abstract

- 22 CLOSED LOOP CONTROL SYSTEM FOR HELIOSTATS Abstract Described herein is a control system for a solar energy collection apparatus (1). The apparatus includes a plurality of individually angularly controllable heliostats (3) disposed 5 adjacent to a central receiver (5). The heliostats are able to be tilted to reflect solar energy towards a target region of the central receiver (5) as a beam of solid angle. The control system includes a measuring device (23) capable of being scanned across a surface of the central receiver (5) including the target region. The measuring device (23) includes a distribution (31) of photo sensors (33) configured to sense the presence of the beam from 10 each heliostat. The control system further includes a controller (21) for performing a closed-loop control procedure (43) to iteratively vary a pointing direction of each heliostat to bring the respective beam into the target region. ---- --- 33 Figure 2

Description

- 1 - 2016208290 26 Μ 2016

CLOSED LOOP CONTROL SYSTEM FOR HELIOSTATS RELATED APPLICATIONS AND PATENTS

[0001] PCT Patent Application PCT/AU2015/000066 entitled “Monitoring and measuring of multiple light sources especially heliostats”. 5 [0002] PCT Patent Application PCT/AU2011/001687 entitled “Heliostat calibration and control”, published as WO 2012/083383 A1.

[0003] Australian Patent 2012203230 entitled “Heliostat calibration and control”, which is a national application of PCT/AU2011/001687.

[0004] Australian Patent 2012203231 entitled “Heliostat control”, which is a national 10 application of PCT/AU2011/001687.

[0005] Australian Patent 2012203234 entitled “Heliostat control”, which is a national application of PCT/AU2011/001687.

[0006] Chinese Patent Application 4782/CHENP/2013 entitled “Heliostat control”, which is a national application of PCT/AU2011/001687. 15 [0007] US Patent Application 4782/CHENP/2013 entitled “Heliostat control”, which is a national application of PCT/AU2011/001687.

[0008] South African Patent 2013/05428 entitled “Heliostat control”, which is a national application of PCT/AU2011/001687.

TECHNOLOGY 20 [0009] The present invention relates generally to solar energy collection systems such as heliostat systems. More specifically, embodiments of the present invention relate to a control system for a solar energy collection system including a plurality of heliostats configured to direct solar energy onto one or more solar receivers.

[0010] While some embodiments will be described herein with particular reference to 25 that application, it will be appreciated that the invention is not limited to such a field of use, and is applicable in broader contexts.

BACKGROUND

[0011] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of 30 common general knowledge in the field. - 2 - 2016208290 26 Jul2016 [0012] Solar energy collection systems incorporating heliostats include a control system which is responsible for controlling the angle of each heliostat to efficiently direct solar energy onto a central energy collector. Current known control systems require redirecting subsets of the heliostats temporarily to a secondary target for recalibration and 5 subsequently redirecting the heliostats back to a primary target based on calibration data. The result is to provide each heliostat with precise steering coordinates which should ideally calibrate the heliostat.

[0013] The accuracy and hence performance of these systems is restricted by several limitations resulting from non-ideal properties of the control system. These non-ideal 10 properties include: [0014] A non linear response of the heliostat control aiming system to input control signals. For example, the aiming system may have hysteresis between control signals and pointing direction. Further, the aiming system may incorporate elements with dynamic characteristics like a mechanism which integrates or differentiates the control signal with 15 respect to time and may have unknown gains, constants etc.

[0015] A non deterministic response of the heliostat control aiming system to control signals. For example, the system may be susceptible to noise or other non deterministic perturbations. The system may also respond differently throughout its lifetime perhaps due to poorly understood responses to different climatic conditions such as temperature, 20 humidity or rainfall, or due to variable quality system components being in different states of wear.

[0016] To address the above accuracy restrictions, closed-loop control of heliostats has been proposed.

[0017] In “Closed loop control of heliostats”, Kribus, A et al. Energy , 2004, 29, (5-6), 25 905-913, closed loop control is provided using cameras placed around the receiver.

[0018] In “Closed-loop control for power tower heliostats”, Convery, M. R., Proc. of SPIE 2011, heliostats are vibrated using piezoelectric actuators and vibration frequency is used to identify heliostat signals on the receiver.

[0019] PCT Publication WO 2012/125748-A2 relates to a method for concentrating 30 sunlight onto a target and observing optically modified and distributed sunlight to actuate a light redirecting element in a manner that concentrates redirected sunlight into a target portion. -3- 2016208290 26 Μ 2016 [0020] PCT Publication WO 2012/125751 relates to a method for concentrating sunlight from a light source onto a receiver and involves utilizing observed diffracted sunlight in a closed loop control system to actuate light redirecting elements in a manner that concentrates sunlight onto target. 5 [0021] PCT Publication WO 2012/117123 relates to a heliostat with a closed-loop control system that is retroactively supplied by signals from sensors that compare signals at all times. These signals control a primary drive and secondary drive in order to achieve a desired pointing condition at a target.

[0022] US Patent 9,010,317 relates to a closed-loop tracking system, e.g. a solar 10 tracking system, for controlling orientation of heliostat mirrors. The tracking system concurrently transmits and receives signal beams from optical elements by a signal beam target.

[0023] US Patent Application Publication 2012/174909 relates to a system for controlling a heliostat that is used as a source of heat to drive turbine engine for producing 15 solar power, in solar power system at solar power plant, has camera for receiving sunlight reflected from reflective element.

[0024] All of the above closed-loop systems rely on secondary beams or optical devices mounted on the heliostats themselves. The addition of hardware on each heliostat device significantly increases the complexity and cost of the system, and also increases 20 the likelihood of hardware failures in the system.

[0025] Therefore, there is a desire for more efficient control systems in heliostat based solar energy collection apparatus.

SUMMARY OF THE INVENTION

[0026] In accordance with a first aspect of the present invention there is provided a 25 method for controlling a pointing direction of a heliostat in a solar energy collection apparatus, the method including the steps of: a) pointing a heliostat in a direction such that incident solar energy is reflected towards a target region of a solar energy receiver as a beam of solid angle; b) sensing the presence of the beam from the heliostat using a distribution of 30 sensors intercepting the path of the beam at regular intervals of time; c) during the intervals, performing a closed-loop control procedure to iteratively vary the pointing direction of the heliostat to bring the beam into the target region . -4- 2016208290 26 Jul2016 [0027] In one embodiment the distribution of sensors is located on an arm that is movable about a surface of the receiver.

[0028] In one embodiment step c) includes the substep: c)i) estimating a current position of the beam on the receiver. 5 [0029] In one embodiment step c) includes the substep: c)ii) comparing the estimated current position of the beam with a position of the target region to derive a position vector.

[0030] In one embodiment step c) includes the substep: c)iii) calculating a pointing direction adjustment signal based on the position 10 vector, the pointing direction adjustment signal being provided to an actuator control system of the heliostat to vary the pointing direction.

[0031] In one embodiment the estimated current position of the beam is determined by a beam profile as sensed by the distribution of sensors.

[0032] In one embodiment the predetermined intervals are in the range of 0.1 seconds 15 to 1 minute. Preferably the predetermined intervals are regular intervals of time.

[0033] In one embodiment step a) is performed based on stored pointing coordinates. In another embodiment, in step a), the heliostat is pointed at a position that is calculated based on a modified previously determined position. In some embodiments, step a) is performed based on reference to an external field. 20 [0034] Preferably the method according to the first aspect is performed on multiple heliostats simultaneously.

[0035] In one embodiment the distribution of sensors is capable of angularly distinguishing beams from separate heliostats.

[0036] In accordance with a second aspect of the present invention there is provided a 25 control system for a solar energy collection apparatus, the apparatus including a plurality of individually angularly controllable heliostats disposed adjacent to a central receiver, the heliostats being able to be tilted to reflect solar energy towards a target region of the central receiver as a beam of solid angle, the control system including: a measuring device capable of being scanned across a surface of the central 30 receiver including the target region, the measuring device including a distribution of photo sensors configured to sense the presence of the beam from the heliostat; and -5- 2016208290 26 Jul2016 a controller for performing a closed-loop control procedure to iteratively vary a pointing direction of the heliostat to bring the beam into the target region.

[0037] In one embodiment the closed-loop control procedure includes the substep: c)i) estimating a current position of the beam on the receiver. 5 [0038] In one embodiment the closed-loop control procedure includes the substep: c)ii) comparing the estimated current position of the beam with a position of the target region to derive a position vector.

[0039] In one embodiment the closed-loop control procedure includes the substep: c)iii) calculating a pointing direction adjustment signal based on the position 10 vector, the pointing direction adjustment signal being provided to an actuator control system of the heliostat to vary the pointing direction.

[0040] In one embodiment the controller is further configured to perform an initial pointing procedure to point the heliostat in the general direction of the target region.

[0041] In one embodiment the initial pointing procedure is performed based on stored 15 pointing coordinates. In another embodiment, in the initial pointing procedure, the heliostat is pointed at a position that is calculated based on a modified previously determined position. In some embodiments the initial pointing procedure is performed based on reference to an external field.

[0042] In accordance with a third aspect of the present invention there is provided an 20 apparatus for monitoring and/or measuring multiple directional radiative sources, each radiative source directing radiation as a beam of limited solid angle, comprising: a measuring device having the capability to angularly distinguish the directional radiative sources from one another; means to scan the measuring device across or through a zone on which at least 25 50% of the radiation beam from each radiative source impinges; and means to record a set of multiple images respectively detected at the measuring device at successive positions of the measuring device during said scan; a controller for performing a closed-loop control procedure to iteratively vary pointing directions of the respective radiative sources to bring the beams into the target 30 region, wherein the radiation from the multiple directional radiative sources recorded at different positions of the measuring device as the measuring device is scanned across the -6- 2016208290 26 Jul2016 zone and the positions are sufficiently distinguishable in said set of multiple images to permit simultaneous measuring and/or monitoring of the directional radiative sources during a single scan of the measuring device across or through said zone.

[0043] In one embodiment the measuring device includes an array of sensors each 5 having multiple radiation responsive pixels and, at each position of the array, radiation from the multiple directional radiative sources is recorded at different respective subsets of the pixels and the subsets are sufficiently distinguishable in said set of multiple images to permit simultaneous measuring and/or monitoring of the directional radiative sources during a single scan of the array of sensors across or through said zone. 10 [0044] In one embodiment the measuring device includes an array of tiltable mirrors configured to direct the radiation onto one or more sensors. In another embodiment the measuring device includes an array of single pixel cameras having an associated computer controller.

[0045] In one embodiment the subsets are mutually exclusive. In another embodiment 15 the subsets share one or more common pixels.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Example embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: [0047] Figure 1 is a schematic plan view of a solar energy collection system utilising a 20 circular field of heliostats; [0048] Figure 2 is a schematic diagram illustrating the direction of solar energy onto an array of photo sensors; [0049] Figure 3 is a perspective view of an alternative embodiment receiver having a substantially flat aperture; 25 [0050] Figure 4 is a process flow diagram illustrating the primary steps in a heliostat calibration method according to the invention; [0051] Figure 5 is a diagrammatic representation of the closed-loop control system; and [0052] Figure 6 is a sequence representation of a beam being steered to a target 30 region in three iterations of the closed-loop control. -7- 2016208290 26 Jul2016

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview of the solar energy collection system [0053] Referring to Figure 1 there is illustrated a plan view of a solar energy collection system 1 including a plurality of heliostats 3 disposed in radially separated circumferential 5 arrays about a substantially cylindrical central solar energy receiver 5. Typical solar energy collection systems include several hundred heliostats and may be formed into circular fields as in Figure 1 or into square or other shaped fields.

[0054] As illustrated in Figure 2, receiver 5 is mounted on a tower 7 so as to be vertically elevated above the substantially horizontally disposed field of heliostats. In 10 operation, the heliostats are positioned to reflect and focus solar energy from the Sun onto a receiving surface 9 of receiver 5. Receiving surface 9 is designed to receive directed beams of solar energy from each of the field of heliostats and use the concentrated solar energy to perform useful work, for example by generating electricity. It will be appreciated that various techniques are known for converting the received solar energy into useful 15 work and, for simplicity, these techniques are omitted from this description. It will also be appreciated that heliostat-based solar energy collection systems are available in various other forms including non-circular heliostat fields, non-cylindrical receivers and even multiple receivers.

[0055] The heliostats used in system 1 may be of any conventional heliostat design. By 20 way of example, suitable heliostats are described in WO 2012/083383 A1 and these types of heliostats will be used in the following description. As best shown in Figure 2, each heliostat 11 includes a shallow concave rectangular mirror 13 fixed in a frame 15 which is pivotally mounted to a supporting post 17. Typical dimensions of the mirror are 2.4 meters by 1.8 meters and typical focal lengths of the mirrors are in the range of 15 to 1000 meters 25 depending on the size of the field and their position in the field.

[0056] Heliostats 11 also include an actuator system 19, such as that described in WO 2012/083383 A1, which is responsive to control signals from a central controller 21 to selectively orient the mirror in two dimensions. In the heliostats illustrated in Figure 2, the actuator system 19 of each heliostat comprises a pair of linear actuators for respectively 30 controlling the inclination and declination of the heliostat's reflecting mirror. The angular position of each heliostat, both inclination and declination, is determined by controller 21, which may comprise a suitable computer system. Controller 21 is operably coupled to the actuators of all of the heliostats to simultaneously, sequentially or otherwise control the -8- 2016208290 26 Μ 2016 orientation angle or pointing direction of each of the heliostats. Furthermore, controller 21 may be operably coupled to feedback sensors (such as magnetic sensors) by which the controller is kept informed of actual angular position co-ordinates of each heliostat and to sensor distribution 31. However, the operation of the present invention lessens or 5 removes the need for such open-loop control of heliostats and, in some embodiments, these feedback sensors are omitted. Controller 21 may also be responsible for controlling the position and speed of arm 29 through the actuatable mechanism. In other embodiments the control system for the measuring device may be separate to the heliostat control system, but able to communicate with each other. Further embodiments 10 may use other control system topologies. The scanning of arm 29 and sensors 33 is independent to the angular positioning of the heliostats.

[0057] Referring still to Figure 2, a measuring device 23 is mounted proximate to the central receiver 5, in this embodiment rotating about an axial rotation point 25. Device 23 includes substantially horizontally extending mounting 27, which is integrally or releasably 15 attached to a substantially vertically extending arm 29. Mounted to arm 29 is a spatial array or other distribution 31 of photo sensors 33, each having a sub-array of light responsive pixels as illustrated by the inset in Figure 2. Arm 29 is positioned at a distance from the surface of receiver 5 that is in the range of 10 cm to 20 m. Rotation of arm 29 about receiver 5 sweeps distribution 31 through the path of the beams from the respective 20 heliostats in the field. The sensors 33 measure light intensity at a predetermined sampling frequency such that the samples map the entire light field around the receiver, allowing calculation of irradiance maps on the swept surface for each heliostat. In some embodiments, arm 29 may extend above the top of receiver 5 and/or below the bottom of receiver 5 to detect beams not aligned with receiver 5. 25 [0058] In the illustrated embodiment, distribution 31 is a one dimensional linear array of substantially equally vertically spaced apart sensors 33. The horizontal sweeping motion of measurement device 23 provides a two dimensional array of sample points to be obtained. However, it will be appreciated that, in other embodiments, distribution 31 may take other forms. In general, sensors 33 need not be separated by the same distance but 30 may be disposed in a linear or two dimensional distribution having different distances therebetween. In some embodiments, the distribution may be two dimensional and have a high density of sensors on a region of arm 29 corresponding to a central receiver region and a lower density of sensors on a region of arm 29 corresponding to peripheral receiver regions. -9- [0059] In other embodiments, measuring devices other than pixel arrays are utilised. In some other embodiments, detectors at positions in array 30 are replaced with similarly sized and oriented measuring devices capable of measuring radiance as a function of two angular dimensions. In one alternative embodiment (not illustrated) a similarly sized and oriented two-dimensional array of electrically tiltable mirrors, lenses, mirror/lens combinations and or/a mirror or lens with different angular reflecting regions directing light to respective optical sensors or a single optical sensor having multiple radiation responsive pixels. The mirrors or lenses may convey light in series or in parallel to the optical sensor. The mirrors/lenses may be scanned to measure incoming light simultaneous to the scanning of the overall detector array. In another alternative embodiment (not illustrated) the detector includes an array of single pixel cameras, each capable of spatially and angularly distinguishing light through post-processing of the received light signal at a processor (for example, by way of compressive imaging techniques).

[0060] In Figure 2, the focussed solar energy from heliostat 11 is illustrated as a Gaussian beam spot 35 on distribution 31.

[0061] It should be noted that Figure 2 is not drawn to scale for the purpose of clarifying specific aspects of the system. In particular, the scale of arm 29, distribution 31 and beam 35 are substantially increased for clarity. In practice, it will be appreciated that the beam size may be much smaller or larger than the size of receiver 5. In preferred embodiments, sensors 33 can be considered as digital camera sensors.

[0062] Mounting 27 includes an electronically actuatable mechanism (not shown) for scanning or sweeping arm 29 and sensor distribution 31 circumferentially around the receiver in a direction indicated by the arrow. The scanning motion ensures that, at any one time, distribution 31 passes between the receiver and a subset of heliostats currently facing the array to intercept beams reflected from that subset. If and when necessary, arm 29 is able to be positioned out of alignment with receiver 5 so as to not be in the path of the heliostat beams.

[0063] In an alternative embodiment illustrated in Figure 3, receiver is square in shape. In this embodiment, the actuatable mechanism is configured to sweep distribution 31 across the receiver in a linear fashion in both a forward and reverse direction. In other embodiments (not illustrated), arm 29 extends substantially horizontally and is actuatably moveable in a vertical direction. In an embodiment having a cylindrical receiver surface, - 10- 2016208290 26 Jul2016 arm 29 is in the form of a substantially cylindrical collar which is moveable vertically about the receiver.

[0064] In some embodiments, an actuator system is provided for advanced movement of measurement device 23. In one embodiment, mounting 27 is telescopically or linearly 5 actuatable to move arm 29 closer or further from the surface of receiver 5 in a radial or other plane. In another embodiment, arm 29 is hingedly or pivotally mounted to mounting 27 and an actuator is configured to selectively rotate arm 29 vertically about the hinge/pivot point and out of the path of the heliostat beams.

[0065] The actuatable mechanism is configured to incrementally move or progress 10 arm 29 across the surface of receiver 5 at a speed and direction determined by a control signal from controller 21 or a separate controller. During a predetermined period of time, different subsets of sensors 31 and their respective pixels detect the local optical power of the individual beams from various adjacent heliostats in the field. By scanning around receiver 5, distribution 31 is able to detect and measure the beams of all heliostats in the 15 field, allowing application of a closed-loop heliostat control method as described below.

[0066] The two dimensional nature of the sensors and pixels allows the overall beam profile (such as a Gaussian beam profile) to be determined and the different beams to be angularly distinguished and mapped to a particular heliostat for individual control.

Closed loop control procedure 20 [0067] Referring now to Figure 4, there is illustrated the primary steps in a heliostat calibration method 40 for a system such as system 1. Figure 4 illustrates diagrammatically the control system 50 that performs method 40, with the primary control centred around controller 21. It will be appreciated that the control methodology described below is able to be performed on multiple heliostats simultaneously by angularly distinguishing the 25 different associated beams using distribution 31.

[0068] Method 40 provides for regularly calibrating or recalibrating a pointing direction of each heliostat such that a heliostat reflects and focuses incident solar radiation onto a target region of receiver 5. The target region may be defined as a set of two dimensional coordinates that defines an ideal pointing direction for that heliostat or a range of two 30 dimensional coordinates that indicates a two dimensional region on receiver 5 in which that heliostat should direct the focussed solar radiation. In operation, each heliostat may be assigned a different target region on receiver 5 so that focussed solar energy is -11 - 2016208290 26 Jul2016 distributed appropriately across the surface of receiver 5 to prevent overheating and associated faults. The target regions of separate heliostats may overlap or may be mutually exclusive.

[0069] The calibration method illustrated in Figure 3 is performed periodically on 5 heliostats adjacent to distribution 31 as the array scans or sweeps around receiver 5.

[0070] Initially, at step 41 a check is performed as to whether the beam of solar energy for a heliostat is detected at the sensor array upon initial commencement of the control method. This check is performed as the beam may still be in close alignment with the desired target region from a previous calibration loop. If at least part of the beam is initially 10 detected at distribution 31, control proceeds directly to a closed-loop control subroutine. If, however, the beam is not detected at distribution 31, an initial step 42 of pointing of the heliostat must be performed.

[0071] At step 42, controller 21 controls actuator system 19 of heliostat such that the corresponding beam of incident solar energy is reflected towards the target region of 15 receiver 5.

[0072] Step 42 may represent an initialisation procedure that is performed upon startup of the system to direct the beam of solar energy in the general direction of receiver 5 and distribution 31. Step 42 may not need to be subsequently performed unless the beam of solar energy is inadvertently directed away from receiver 5 during the course of 20 operation. Step 42 may also be performed as a secondary aiming method when the primary closed-loop control angular measuring system is not available for reasons such as a loss of sunlight or limitations on the area monitored by the monitoring system.

[0073] The initial pointing in step 42 may be performed based on a number of techniques using reference data stored in a database 52. In one embodiment, a reference 25 pointing direction is associated with that particular heliostat based on the current sun position (determined from the time of day, time of year and latitude and longitude of the heliostat) and this is used during initial pointing or when the associated beam direction becomes unknown. In another embodiment, when the heliostat beam strays off target, a dead reckoning procedure may be implemented based on a previously determined 30 position. In this dead reckoning procedure, a new orientation of a heliostat is determined by modifying a previous position of that heliostat by known information such as the current position of the sun and time elapsed since a previous measurement. Further positioning control may be provided based on reference to an external field such as gravity. - 12- [0074] Steps 41 and 42 may be iterated until the beam is detected at sensor distribution 31. Once the beam is detected by one or more pixels of sensor distribution 31, closed-loop control 43 can commence.

[0075] At step 44, an initial estimate of the position of the beam centre is performed based on the particular sensors and pixels which have been illuminated. This estimation may be based on a stored beam profile which specifies a beam shape and intensity profile such as a Gaussian. With this information, a centre of the beam can be estimated. For example, referring to panel A) of Figure 6, a Gaussian beam is incident on several lower sensors of distribution 31 but the beam centre still lies off distribution 31. By detecting the intensity variation of the partial beam across pixels of the illuminated sensors, controller 21 is able to estimate the likely position of the centre of the beam. The detected illumination from distribution 31 is fed to controller 21 as sensor array observations 54, as illustrated in Figure 5.

[0076] At step 45, the estimated position of the centre of the beam is compared with the stored position of the desired target region of that beam. This allows controller X to derive a position vector indicative of the direction and distance between the current beam position and desired beam position (target region). Decision 46 is made as to whether the beam centre is within the target region (as defined by a minimum proximity requirement). If the beam centre is within the target region, processing ends until calibration is required again at a later time. If, the beam centre is not within the target region, processing proceeds to step 47.

[0077] At step 47, controller 21 calculates an actuator control signal in the form of a pointing direction adjustment signal based on the position vector determined in step 46. When applied to the heliostat actuator system 19, the pointing direction adjustment signal varies the heliostat pointing direction to bring the beam into closer proximity with the target region.

[0078] After the variation in pointing direction is applied, processing returns to step 44 where the new position of the beam is determined. This closed-loop procedure continues iteratively until the beam is determined to be within the target region of receiver 5 for that beam. This will often require several iterations. Figure 6 illustrates an example scenario where the closed-loop control procedure steers the beam into the target region in three iterations of the loop. 2016208290 26 Jul2016 - 13- [0079] As measuring device 23 rotates relative to receiver 5, while the target region is fixed on receivers, the relative position of distribution 31 relative to receivers must be known to controller 21 at all times to perform accurate heliostat control.

[0080] Procedure 40 is performed iteratively as arm 29 and distribution 31 is scanned 5 or swept across the surface of receiver 5 and may be performed simultaneously on multiple heliostats in a common region adjacent the current position of distribution 31. The speed at which arm 29 is able to sweep through the beams about receiver 5 is determined by the processing speed of the control system. A control system having a faster processor permits a higher sampling frequency, which allows for faster closed-loop control and faster 10 heliostat calibration. This, in turn, allows for faster scanning of arm 29.

[0081] Recalibration of each heliostat is performed by successive sweeps of arm 29. By way of example, arm 29 may scan around receiver 5 continuously with a scanning period of several seconds such that each heliostat is recalibrated at least as fast as the heliostats need to move to track the sun. Alternatively, arm 29 may scan around 15 receiver 5 periodically at specific time periods and, between these periods, arm 29 is maintained out of the path of the heliostat beams. In embodiments utilising a single sided receiver, arm 29 and distribution 31 may be parked outside the path of the beams and then rapidly swept through the beams at regular intervals to manage the amount of light that is blocked. Successive sweeps of arm 29 may be at regular or irregular intervals. 20 [0082] The overall energy loss due to occlusion of the beams by arm 29 is determined by the physical dimensions of arm 29, the distance of arm 29 from the surface of receiver 5, the sweep speed of arm 29 and the period of successive sweeps of arm 29.

Conclusions [0083] It will be appreciated that the above described invention provides significant 25 advances in the control of heliostats in a solar energy collection system. For given system hardware, the invention allows for greater pointing accuracy of heliostats which translates to increased efficiency in energy collection. Conversely, for a given efficiency, the invention allows for relaxation of the hardware requirements such that relatively simple design heliostats can be controlled by relatively crude control hardware. Furthermore, the 30 invention requires no additional hardware to be added to the heliostats for an existing system. - 14-

Interpretation [0084] As used herein, except where the context requires otherwise, the terms “scanning” or “sweeping” mean the act of moving over or across an object with a detector (e.g. an array of sensors).

[0085] Use of terms “solar”, “solar energy”, “sunlight” “light” and the like in this specification are intended to refer to electromagnetic radiation covering one or more of the visible, ultra-violet and infra-red wavelength ranges.

[0086] As used herein, the terms “solid angle” mean a two-dimensional angle subtended in three-dimensional space.

[0087] As used herein, the terms “closed-loop control” related to control in which the output has an effect on the input quantity in such a manner that the input quantity will adjust itself based on the output generated.

[0088] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing," "computing," "calculating," “determining”, analysing” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities into other data similarly represented as physical quantities.

[0089] In a similar manner, the term "controller" may refer to any device or portion of a device that processes electronic data, e.g., from registers and/or memory to transform that electronic data into other electronic data that, e.g., may be stored in registers and/or memory. A “computer” or a “computing machine” or a "computing platform" may include one or more processors.

[0090] The methodologies described herein are, in one embodiment, performable by one or more processors that accept computer-readable (also called machine-readable) code containing a set of instructions that when executed by one or more of the processors carry out at least one of the methods described herein. Any processor capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken are included. Thus, one example is a typical processing system that includes one or more processors. Each processor may include one or more of a CPU, a graphics processing unit, and a programmable DSP unit. The processing system further may include a memory subsystem including main RAM and/or a static RAM, and/or ROM. A bus - 15- 2016208290 26 Jul2016 subsystem may be included for communicating between the components. The processing system further may be a distributed processing system with processors coupled by a network. If the processing system requires a display, such a display may be included, e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT) display. If manual data entry is 5 required, the processing system also includes an input device such as one or more of an alphanumeric input unit such as a keyboard, a pointing control device such as a mouse, and so forth. The term memory unit as used herein, if clear from the context and unless explicitly stated otherwise, also encompasses a storage system such as a disk drive unit. The processing system in some configurations may include a sound output device, and a 10 network interface device. The memory subsystem thus includes a computer-readable carrier medium that carries computer-readable code (e.g., software) including a set of instructions to cause performing, when executed by one or more processors, one of more of the methods described herein. Note that when the method includes several elements, e.g., several steps, no ordering of such elements is implied, unless specifically stated. The 15 software may reside in the hard disk, or may also reside, completely or at least partially, within the RAM and/or within the processor during execution thereof by the computer system. Thus, the memory and the processor also constitute computer-readable carrier medium carrying computer-readable code.

[0091 ] Furthermore, a computer-readable carrier medium may form, or be included in a 20 computer program product.

[0092] In alternative embodiments, the one or more processors operate as a standalone device or may be connected, e.g., networked to other processor(s), in a networked deployment, the one or more processors may operate in the capacity of a server or a user machine in server-user network environment, or as a peer machine in a 25 peer-to-peer or distributed network environment. The one or more processors may form a personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. 30 [0093] Note that while diagrams only show a single controller and a single database, those in the art will understand that many of the components described above are included, but not explicitly shown or described in order not to obscure the inventive aspect. For example, while only a single controller is illustrated, the term "controller" shall also be taken to include any collection of machines that individually or jointly execute a set - 16- 2016208290 26 Jul2016 (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. Similarly, the term “database” may refer to a single locally accessed database, or share data resources accessed locally or remotely over a server.

[0094] One embodiment of the methods described herein is in the form of a computer-5 readable carrier medium carrying a set of instructions, e.g., a computer program that is for execution on one or more processors, e.g., one or more processors that are part of web server arrangement. Thus, as will be appreciated by those skilled in the art, embodiments of the present invention may be embodied as a method, an apparatus such as a special purpose apparatus, an apparatus such as a data processing system, or a computer-10 readable carrier medium, e.g., a computer program product. The computer-readable carrier medium carries computer readable code including a set of instructions that when executed on one or more processors cause the processor or processors to implement a method. Accordingly, aspects of the present invention may take the form of a method, an entirely hardware embodiment, an entirely software embodiment or an embodiment 15 combining software and hardware aspects. Furthermore, the present invention may take the form of carrier medium (e.g., a computer program product on a computer-readable storage medium) carrying computer-readable program code embodied in the medium.

[0095] The software may further be transmitted or received over a network via a network interface device. While the carrier medium is shown in an example embodiment 20 to be a single medium, the term "carrier medium" should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term "carrier medium" shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by one or more of the processors and that 25 cause the one or more processors to perform any one or more of the methodologies of the present invention. A carrier medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical, magnetic disks, and magneto-optical disks. Volatile media includes dynamic memory, such as main memory. Transmission media includes coaxial cables, 30 copper wire and fiber optics, including the wires that comprise a bus subsystem. Transmission media also may also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. For example, the term "carrier medium" shall accordingly be taken to include, but not be limited to, solid-state memories, a computer product embodied in optical and magnetic media; a medium - 17- bearing a propagated signal detectable by at least one processor or one or more processors and representing a set of instructions that, when executed, implement a method; and a transmission medium in a network bearing a propagated signal detectable by at least one processor of the one or more processors and representing the set of instructions.

[0096] It will be understood that the steps of methods discussed are performed in one embodiment by an appropriate processor (or processors) of a processing (e.g., computer) system executing instructions (computer-readable code) stored in storage. It will also be understood that the invention is not limited to any particular implementation or programming technique and that the invention may be implemented using any appropriate techniques for implementing the functionality described herein. The invention is not limited to any particular programming language or operating system.

[0097] 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 disclosure. 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. 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.

[0098] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[0099] In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term - 18- that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

[00100] It should be appreciated that in the above description of example embodiments of the disclosure, various features of the disclosure 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 claims require 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 disclosure.

[00101] 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 disclosure, 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.

[00102] In the description provided herein, numerous specific details are set forth. Flowever, it is understood that embodiments of the disclosure 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.

[00103] Thus, while there has been described what are believed to be the best modes of the disclosure, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the disclosure, and it is intended to claim all such changes and modifications as fall within the scope of the disclosure. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present disclosure.

Claims (21)

1. We claim:

   1. A method for controlling a pointing direction of a heliostat in a solar energy collection apparatus, the method including the steps of: a) pointing a heliostat in a direction such that incident solar energy is reflected towards a target region of a solar energy receiver as a beam of solid angle; b) sensing, the presence of the beam from the heliostat using a distribution of sensors intercepting the path of the beam at predetermined intervals of time; c) during the intervals, performing a closed-loop control procedure to iteratively vary the pointing direction of the heliostat to bring the beam into the target region.
2. 2. A method according to claim 1 wherein the distribution of sensors is located on an arm that is movable about a surface of the receiver.
3. 3. A method according to claim 1 or claim 2 wherein step c) includes the substep: c)i) estimating a current position of the beam on the receiver.
4. 4. A method according to claim 3 wherein step c) includes the substep: c)ii) comparing the estimated current position of the beam with a position of the target region to derive a position vector.
5. 5. A method according to claim 4 wherein step c) includes the substep: c)iii) calculating a pointing direction adjustment signal based on the position vector, the pointing direction adjustment signal being provided to an actuator control system of the heliostat to vary the pointing direction.
6. 6. A method according to any one of claims 3 to 5 wherein the estimated current position of the beam is determined by a beam profile as sensed by the distribution of sensors.
7. 7. A method according to any one of the preceding claims wherein the predetermined intervals of time are in the range of 0.1 seconds to 1 minute.
8. 8. A method according to any one of the preceding claims wherein the predetermined intervals are regular intervals of time.
9. 9. A method according to any one of the preceding claims wherein step a) is performed based on stored pointing coordinates.
10. 10. A method according to any one of claims 1 to 6 wherein in step a) the heliostat is pointed at a position that is calculated based on a modified previously determined position.
11. 11. A method according to any one of claims 1 to 4 wherein step a) is performed based on reference to an external field.
12. 12. A method according to any one of the preceding claims performed on multiple heliostats simultaneously.
13. 13. A method according to claim 12 wherein the distribution of sensors is capable of angularly distinguishing beams from separate heliostats.
14. 14. A control system for a solar energy collection apparatus, the apparatus including a plurality of individually angularly controllable heliostats disposed adjacent to a central receiver, the heliostats being able to be tilted to reflect solar energy towards a target region of the central receiver as a beam of solid angle, the control system including: a measuring device capable of being scanned across a surface of the central receiver including the target region, the measuring device including a distribution of photo sensors configured to sense the presence of the beam from the heliostat; and a controller for performing a closed-loop control procedure to iteratively vary a pointing direction of the heliostat to bring the beam into the target region.
15. 15. A control system according to claim 14 wherein the closed-loop control procedure includes the substep: c)i) estimating a current position of the beam on the receiver.
16. 16. A control system according to claim 15 wherein the closed-loop control procedure includes the substep: c)ii) comparing the estimated current position of the beam with a position of the target region to derive a position vector.
17. 17. A control system according to claim 16 wherein the closed-loop control procedure includes the substep: c)iii) calculating a pointing direction adjustment signal based on the position vector, the pointing direction adjustment signal being provided to an actuator control system of the heliostat to vary the pointing direction.
18. 18. A control system according to any one of claims 14 to 17 wherein the controller is further configured to perform an initial pointing procedure to point the heliostat in the general direction of the target region.
19. 19. A control system according to claim 18 wherein the initial pointing procedure is performed based on stored pointing coordinates.
20. 20. A control system according to claim 18 wherein, in the initial pointing procedure, the heliostat is pointed at a position that is calculated based on a modified previously determined position.
21. 21. A control system according to claim 16 wherein the initial pointing procedure is performed based on reference to an external field.