AU2002244529B2

AU2002244529B2 - Solar mirror testing and alignment

Info

Publication number: AU2002244529B2
Application number: AU2002244529A
Authority: AU
Inventors: John Beavis Lasich
Original assignee: Solar Systems Pty Ltd
Current assignee: Solar Systems Pty Ltd
Priority date: 2001-04-03
Filing date: 2002-04-03
Publication date: 2007-11-22
Anticipated expiration: 2022-04-03

Description

02/11 2007 16:45.FAX 61 3 92438333 GRIFFITH HACK IFAUSTRALIA R1006 (N SOLAR MIRROR TESTING AND ALIGNMENT ZFIELD OF THE INVENTION Cl The present invention relates to a system and method for cha racterizing the shape of a mirror for use in, for example, a solar power generation system, and for employing ON such mirrors characterizations in, for example, aligning each of a plurality of such mirrors within an array for use as a solar concentrator or in a solar power generation system.

Ci BACKGROUND OF THE INVENTION Typically, existing methods for testing mirrors reflect light from the mirror and then adjust the mirror, such as by grinding or mechanical adjustment of a mirror support, until the pattern of light so reflected meets some predetermined standard. However, doing so can be time consuming and adds expense to the manufacture of the mirror.

SUDWARY OF THE INVENTION In a first broad aspect, therefore, the present invention provides a method of characterizing the shape of a mirror, comprising: characterizing each of a plurality of characterization locations on said mirror by observing reflection of a respective light beam from each of said locations; whereby further locations on said mirror can be characterized on the basis of said characterization locations.

Preferably the method includes characterizing the further locations by deducing one or more characteristics of the further locations from one or more of the characterization COMS ID No: ARCS-167295 Received by IP Australia: Time 17:55 Date 2007-11-02 02/11 2007 16:45 FAX 61 3 92438333 GRIFFITH HACK IPAUSTRALIA a007 c-I locations.

O

Z In one embodiment, this may be done by characterizing the cq further locations from one or more of the characterization locations by interpolation, extrapolation or both interpolation and extrapolation, such as by interpolating O between characterization locations or extrapolation from individual characterization locations.

ci ci 10 Thus, the manner in which light can be expected to be reflected from the mirror can be deduced from either merely CI the measured locations, or a combination of both the measured locations and other locations deduced from the measured locations. In the latter case, the characterizations of the further locations will generally approximate the actual characteristics of the mirror at those further locations.

The step of characterizing the further locations on the basis of the characterization locations might involve, for example, interpolating between two or more characterization locations. This might entail defining a polygonal region around each further location, with characterization locations at each vertex, and treating the mirror as flat within each such polygonal region. Alternatively, if the mirror has been fabricated to have a particular shape (such as spherical), this could entail interpolating on the basis of that intended shape. Still alternatively, the method may include defining for each characterization location a respective region and assigning to each region the characterization of its respective characterization location.

For example, if the characterization locations are arranged in a series of rows and columns on the mirror, so that each COMS ID No: ARCS-167295 Received by IP Australia: Time 17:55 Date 2007-11-02 WO 02/082037 PCT/AU02/00428 3 is (at least approximately) at the centre of a rectangle or square (which may be curved, such as where the mirror is a spherical mirror), these rectangles or squares filling the area of the mirror, further locations falling within a particular rectangle or square may be assigned the characteristics of that rectangle or square's characterization location. As will be understood by those in the art, any other suitable combination of characterization locations and area filling regions around those characterization locations may be used in the same manner.

Preferably the method includes calculating how a beam of light would be reflected from said mirror and characterizing the reflected beam of light, on the basis of said characterization locations, on the basis of said further locations or on the basis of both said characterization locations and said further locations.

More preferably said method includes characterizing the shape of a plurality of mirrors, calculating how a beam of light would be reflected from said array of mirrors and characterizing the composite reflected beam of light reflected from said array, on the basis of said characterization locations of each of said mirrors, on the basis of said further locations of each of said mirrors or on the basis of both said characterization locations and said further locations of each of said mirrors.

Thus, the method may include predicting how a, for example, broad beam of light (such as sunlight) would be reflected from the mirror, or from an array of a plurality of mirrors.

The characterizing of the reflected beam or composite reflected beam may comprise predicting its shape at some desired distance, such as the distance at which in use a light receiver would be located relative to said mirror WO 02/082037 PCT/AU02/00428 4 or array of mirrors, whereby said composite reflected beam can be optimized.

Thus, once each of the mirrors has been characterized, an array can be constructed that has the optimal composite reflected beam without having to modify individual mirrors.

That is, each mirror can be put to the best use within the array.

Preferably the method includes adjusting the location, the attitude, or both the location and attitude, of one or more of said plurality of mirrors in said array of mirrors so that said composite reflected beam conforms more closely to a desired composite reflected beam.

Preferably the method involves reflecting a plurality of incident light beams from said mirror, each at a respective characterization location on said mirror, thereby producing respective reflected beams; and detecting each of said reflected beams; whereby said characterization locations can be characterized from the respective pairs of incident and reflected beams.

Preferably the method includes characterizing each characterization location by determining, from each respective pair of incident and reflected beams, the normal vector to said mirror at each of said respective characterization locations, or the gradient of said mirror at each of said respective characterization locations, or both the normal vector to said mirror and the gradient of said mirror at each of said respective characterization locations.

Thus, the method can include determining a vector, such as a normal vector, indicative of the gradient at each characterization location.

WO 02/082037 PCT/AU02/00428 5 Preferably the method includes: 1) locating said mirror opposite a detecting surface; 2) directing a plurality of incident light beams onto said mirror at said respective characterization location such that said beams are reflected to respective detection locations on said surface; and 3) recording, for each of said incident beams, a set of data relating to the respective incident beam and a corresponding detection location; and 4) characterizing from each of said data sets the respective characterization location.

Step 3) may comprise recording, for each of said incident beams, a set of data indicative of the origin of said respective incident beam, a corresponding characterization location, and a corresponding detection location.

Alternatively, step 3) may comprise recording, for each of said incident beams, a set of data indicative of the direction of each of said incident beams, a corresponding characterization location, and a corresponding detection location.

The plurality of incident beams may be directed onto the mirror simultaneously, consecutively, in consecutive groups of beams, each group comprising a plurality of beams, or otherwise. Preferably, however, the plurality of incident beams is directed onto said mirror either simultaneously or in consecutive groups of beams, each group comprising a plurality of beams.

The detecting surface may comprise a screen on which the reflected beams are visible so that their respective detection locations can be observed. Alternatively, the detecting surface could include detecting elements (such as WO 02/082037 PCT/AU02/00428 6 photodetectors) to detect the reflected beams at a plurality of respective detection locations.

Preferably each of said beams of light is a laser beam.

Preferably said method includes providing a plurality of light sources (each preferably a laser source), to provide the incident beams. More preferably said method includes performing steps 2) to altering the relative locations of said plurality of light sources and said mirror, and repeating steps 2) to 4).

Thus, altering the relative locations of (in a preferred embodiment) the lasers could entail moving the lasers, moving the mirror, or moving both the lasers and the mirror.

Preferably the method includes recording the coordinates of the detection location at which each reflected beam is detected.

Thus, these coordinates, once recorded (such as on a computer), can be retrieved for later use.

In a second broad aspect, the present invention provides an apparatus for characterizing the shape of a mirror, comprising: a mirror support for supporting said mirror; a detecting surface located opposite said mirror when said mirror is supported by said mirror support; at least one light source for directing a plurality of incident beams of light onto said mirror at respective characterization locations on said mirror such that said incident beams are reflected as respective reflected beams to respective detection locations on said detecting surface; data recording means for recording, for each of 03/11 2007 13:16 FAX 61 3 32438333 GRIFFITH HACK 14j003/003 o -7- Clsaid incident beams, a set of data indicative of the o respective location of said lighat source, characterization Z location and detection location; end data analysis means for characterizing from each of said data sets the respective characterization location.

Preferably said apparatus includes a plurality of colimaedlight sources, and more preferably each of said light sources is a laser source.

01 C Preferably said apparatus includes means for altering the Cl relative locations of said plurality of light sources and said mirror.

(The specification continues from page 11.) COMS ID No: ARCS-168043 Received by P1 Australia: Time 13:27 Date 2007-11-09 02/11 2007 16:46 F AX 61 3 92438333 GRIFL'T'PU

U

-~IPAUSTRALIA 000oo 0 In another broad aspect, the present invention provides a method of aligning a mirror, comprising: 1) determining a preferred pattern of light Z reflection from said mirror; 2) obtaining a characterization of the shape of sadmirror by characterizing the mirror according to the method described above; ON 3) simulating said mirror and light reflection therefrom on the basis of said characterization, and comparing said simulated light reflection with said pref erred pattern of light reflection; and 8 4) adjusting a simulated orientation of said mirror and repeating step 3) until said simulated light reflection is within acceptable tolerances of said preferred pattern of light reflection.

BRIEF DESCRIPTION OF THE

DRAWINGS

In order that the present invention may be more clearly ascertained, an embodiment will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a schematic side view of an apparatus for determining the figure of a mirror according to one embodiment of the present invention; Figure 2 is a schematic top view of the apparatus for determining the figure of a mirror of figure 1; and Figure 3 is a view of a solar power generator with an array of the type to be simulated by the simulation program of the apparatus of figure 1.

DETAILED DESCRIPTION OF THE

INVENTION

An apparatus for determining the figure of a mirror according to one embodiment of the present invention is shown generally at 10 in figures 1 and 2 with a mirror 12.

Figure 1 is a side view of the apparatus 10, which includes a bank 14 of laser sources, a detecting surface in the form Of target screen 15, a digital camera 18 and a data COMS ID No: ARCS-i 67295 Received by IP Australia: Time (H m) 17:55 Date 2007-11-02 WO 02/082037 PCT/AU02/00428 12 collection computer 20. Figure 2 is a top view, in which the individual laser sources 22a, 22b, etc. constituting the bank 14 of laser sources are shown. The mirror 12 is supported on a simple stand (not shown), while the target screen 16 and the laser sources 22a, 22b, etc. are mounted on a servo-motor driven, vertically translatable mount (also not shown), so that they can be translated vertically in concert. The laser sources 22a, 22b, etc. are mounted such that their respective laser beams 24a, 24b, 24c, etc.

are horizontal.

In use, the bank 14 of laser sources is slowly translated downwards. The laser beams 24a, 24b, 24c, etc. are reflected by the test mirror 12 onto the target screen 16.

Periodically a screen grab is collected from the output of the camera 18; at the same time, the instantaneous locations of the laser sources 22a, 22b, etc. are also collected. Those locations are obtained from the servomotor controller (not shown) controlling the servo-motor, and from the known geometry of the apparatus 10 overall.

At each measurement, the location on the test mirror 12 at which each beam 24a, 24b, etc. impinges the mirror 12 can be deduced from the locations of the laser sources 22a, 22b, etc., in view of the horizontal nature of the beams 24a, 24b, etc. From this information and the locations at which each reflected beam intersects the target screen 16 may be deduced the gradient of the mirror at each location at which a beam was incident when a measurement was made.

Consequently, the angle of reflection for any angle of incidence can subsequently be predicted for each of these locations.

It should be noted that as, in this embodiment, measurements are made progressively as the laser source/target screen assembly is translated vertically, the locations on the mirror 12 at which gradients are obtained WO 02/082037 PCT/AU02/00428 13 are arranged in a grid of rows and columns (though, where the mirror 12 is curved as shown in figures 1 and 2, this grid will also be curved in space) S When this procedure has been completed, the behaviour of the mirror 12 in reflecting light from, say, the sun can be predicted. The apparatus includes a simulation program (not shown) running on computer 20 or on another computer networked to computer For a mirror 12 (such as a spherical mirror that might be employed in a solar power generation system), it may be desirable to predict how light falling on the mirror 12 will be focussed or reflected. Consequently, the simulation program receives the gradient values for the mirror 12, and calculates the intensity distribution of solar radiation (comprising an essentially broad but parallel incident beam) after reflection from the mirror, typically at a predetermined distance from the mirror corresponding to the location of, for example, a solar collector. The simulation program can perform this simulation on the basis of light rays impinging on the mirror at the locations on the mirror's surface at which these gradient values have been determined.

Optionally the simulation program performs the simulation with additional simulated rays impinging the mirror at the locations other than where gradient values have been determined. It does this by treating each measured location as being at the centre of a flat, essentially rectangular region. The regions are rectangular owing to the regular spacing of the locations at which the gradient values have been obtained. Even though the mirror may be curved, this approximation should generally be acceptable provided that the size of the regions (determined by the spacing of the gradient measurements) are relatively small.

The spacing of the gradient measurements can be selected to WO 02/082037 PCT/AU02/00428 14 ensure that this approximation is acceptable.

Subsequently, if the intensity distribution is less than adequate, the simulated orientation of the mirror can be adjusted and the intensity distribution recalculated by the simulation program. This can be repeated until an optimal or acceptable intensity distribution is obtained.

The simulation program can also be used to simulate an array of two or more such mirrors, such as an array of mirrors for a solar power generator. Such a solar power generator is illustrated generally at 30 in figure 3. The generator includes an array 32 of mirrors 34 and a collector 36 (comprising a square array of photovoltaic cells) approximately at the focus of the array 32. Once a grid of gradient values has been determined for each mirror and provided to the simulation program, the simulation program simulates the desired array by treating each mirror as being at a simulated location and orientation within the array. The intensity distribution of the array can then be simulated as described above for a single mirror.

One possible preferred simulation produces a substantially even intensity distribution over the collector so that, in an actual solar power generator, the energy is distributed and the collector does not develop hot-spots.

The simulated orientations of any of the mirrors can then be adjusted and/or the simulated locations of one or more mirrors can be modified, until the desired or an acceptable intensity distribution is obtained.

In running the simulation program, the mirrors simulated as located towards the periphery of the array of mirrors are preferably those which, when their gradient values were determined, to most closely conform to the design specifications for the mirrors. For example, if the WO 02/082037 PCT/AU02/00428 15 mirrors were intended to approximate spherical mirrors, those most closely spherical would be simulated as at the edge of the array of mirrors, where higher angles of incidence of sunlight will occur. Greater deviations from the intended spherical shape can be tolerated in individual mirrors where low angles of incidence (near the centre of the array) are expected.

If the array is to be installed in an actual installation (such as a solar concentrator of a solar power generator), each mirror in the array of mirrors can, according to the present invention, be aligned using a laser source or group of laser sources with respect to a target placed at or near the focal region of the array.

The array is assembled according to the results of the simulation. Then, at the installation site, the array is located with its optical axis pointing upwards, and with the laser source or group of laser sources suspended above the array such that their beams point vertically downwards.

The laser source or sources are shone onto each mirror in turn and the pattern of reflected light on the target observed. The orientation of each mirror is then adjusted until the pattern on the target agrees to an acceptable degree with that predicted in the simulation for that mirror. As the simulation sought to define locations and orientations for the mirrors to provide the optimal reflected intensity distribution or "focal shape" for energy conversion (in the case of a solar concentrator), this field alignment technique should ensure that that optimal arrangement is achieved.

Modifications within the spirit and scope of the invention may readily be effected by persons skilled in the art. It is to be understood, therefore, that the invention is not limited to the particular embodiments described by way of example hereinabove.

WO 02/082037 PCT/AU02/00428 16 For the purpose of this specification the words "comprising", "comprise" or "comprises" are understood to mean the inclusion of a feature but not necessarily exclusion of any other feature.

It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that that prior art forms a part of the common general knowledge in the art, in Australia or in any other country.

Claims

2. A method as claimed in claim 1, including characterizing said further locations by deducing one or more characteristics of said further locations from one or more of said characterization locations.
3. A method as claimed in either claim 1 or 2, including characterizing said further locations from one or more of said characterization locations by interpolation, extrapolation or both interpolation and extrapolation.
4. A method as claimed in claim 2, including characterizing each of said further locations on the basis of said characterization locations by interpolating between two or more of said characterization locations. A method as claimed in any one of the preceding claims, including calculating how a beam of light would be reflected from said mirror and characterizing the reflected beam of light, on the basis of said characterization locations, on the basis of said further locations or on the basis of both said characterization locations and said further locations.
6. A method as claimed in any one of claims 1 to 4, including characterizing the shape of a plurality of COMS ID No: ARCS-167295 Received by IP Australia: Time 17:55 Date 2007-11-02 02/11 2007 16:47 FAX 61 3 92438383 GRIFFITH HACK .IPATJETRALIA o -18- 0mirrors, calculating how a beam of light would be reflected from said array of mirrors and characterizing the composite o reflected beam of light reflected from said array, on the basis of said characterization locations of each of said mirrors, on the basis of said further locations of each of said mirrors or on the basis of both said characterization locations and said further locations of each of said ci mirrors.
7. A method as claimed in either claim 5 or 6, wherein sadcharacterizing of said reflected beam comprises predicting its shape at some desired distance. S. A method as claimed in claim 6, including adjusting the location, the attitude, or both the location and attitude, of one or more of said plurality of mirrors in said array of mirrors so that said composite reflected beam conforms more closely to a desired composite reflected beam.
9. A method as claimed in claim 1, including reflecting a plurality of incident light beams from said mirror, each at a respective characterization location on said mirror, thereby producing respective reflected beams; and detecting each of said reflected beams; whereby said characterization locations can be characterized from the respective pairs of incident and reflected beams. A method as claimed in claim 9, including characterizing each characterization location by determining, from each respective pair of incident and reflected beams, the normal vector to said mirror at each of said respective characterization locations, or the gradient of said mirror at each of said respective characterization locations, or both the normal vector to said mirror and the gradient of said mirror at each of said respective characterization locations. COMS IDNo: ARCS-167295 Received by IP Australia: Time 17:55 Date 2007-11-02 02/11 2007 18:47 FAX 81 3 91438388 GRIFFITH HACK IPAUSTRALIA Qa12
11. A method as claimed in claim 1, including: o 1) locating said mirror opposite a detecting Z surface; 2) directing a plurality of incident light beams onto said mirror at said respective characterization location such that said beams are reflected to respective ci detection locations on said surface; and 3) recording, for each of said incident beams, a set of data relating to the respective incident beam and a ci corresponding detection location; and 4) characterizing from each of said data sets the ci respective characterization location.
12. A method as claimed in claim 11, wherein step 3) comprises recording, for each of said incident beams, a set of data indicative of the origin of said respective incident beam, a corresponding characterization location, and a corresponding detection location.
13. A method as claimed in claim 11, wherein step 3) comprises recording, for each of said incident beams, a set of data indicative of the direction of each of said incident beams, a corresponding characterization location, and a corresponding detection location.
14. A method as claimed in any one of claims 11 to 13, wherein said plurality of incident beams may be directed onto the mirror simultaneously, consecutively, in consecutive groups of beams, each group comprising a plurality of beams, or otherwise. A method as claimed in claim 14, wherein said plurality of incident beams is directed onto said mirror either simultaneously or in consecutive groups of beams, each group comprising a plurality of beams. COMS ID No: ARCS-167295 Received by IP Australia: Time 17:55 Date 2007-11-02 02/11 2007 16:48 FAX 61 3 92438333 GRIFFITH HACK IPAUSTRALIA J013 o16. A method as claimed in any one of claims 11 to wherein said detecting surface comprises a screen on which O the reflected beams are visible so that their respective Z detection locations can be observed. ci
17. A method as claimed in any one of claims 11 to wherein said detecting surface includes detecting elements to detect the reflected beams at a plurality of respective Idetection locations.
18. A method as claimed in any one of claims 11 to 17, Sincluding providing a plurality of light sources to provide said incident beams.
19. A method as claimed in any one of claims 11 to 17, including performing steps 2) to altering the relative locations of said plurality of light sources and said mirror, and repeating steps 2) to 4).
20. A method as claimed in any one of the preceding claims, including recording the coordinates of the detection location at which each reflected beam is detected.
21. An apparatus for characterizing the shape of a mirror, comprising: a mirror support for supporting said mirror; a detecting surface located opposite said mirror when said mirror is supported by said mirror support; at least one light source for directing a plurality of incident beams of light onto said mirror at respective characterization locations on said mirror such that said incident beams are reflected as respective reflected beams to respective detection locations on said detecting surface; data recording means for recording, for each of said incident beams, a set of data indicative of the COMS ID No: ARCS-167295 Received by IP Australia: Time 17:55 Date 2007-11-02 02/11 1007 15:48 FAX 61 3 92438333 GRIFFITH HACK .IPAUSTRALIA t014 -21- 0 respective location of said light Source, characterization location and detection location; and 0 data analysis means for characterizing from each z Of said data sets the respective characterization location. 5 0
22. An apparatus as claimed in claim 21, including a plurality of collimated light sources.
23. An apparatus as claimed in either claim 21 or 22, including means for altering the relative locations of said plurality of light sources and said mirror. 0
24. A method of aligning a mirror, comprising: 1) determining a pref erred pattern of light reflection from said mirror; 2) obtaining a characterization of the shape of said mirror by characterizing said mirror according to the method of any one of claims 1 to 3) simulating said mirror and light reflection therefrom on the basis of said characterization, and comparing Baid simulated light reflection with said preferred pattern of light reflection; and 4) adjusting a simulated orientation of said mirror and repeating step 3) until said simulated light reflection is within acceptable tolerances of said preferred pattern of light reflection. COMS ID No: ARCS-i 67295 Received by IP Australia: Time 17:55 Date 2007-11-02