AU2007231815B2

AU2007231815B2 - Solar mirror testing and alignment

Info

Publication number: AU2007231815B2
Application number: AU2007231815A
Authority: AU
Inventors: John Lasich
Original assignee: Solar Systems Pty Ltd
Current assignee: Solar Systems Pty Ltd
Priority date: 2001-04-03
Filing date: 2007-11-05
Publication date: 2008-05-15
Anticipated expiration: 2022-04-03
Also published as: AU2007231815A1

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant: Solar Systems Pty Ltd Invention Title: SOLAR MIRROR TESTING AND ALIGNMENT The following statement is a full description of this invention, including the best method for performing it known to us: 2 SOLAR MIRROR TESTING AND ALIGNMENT 0 RELATED APPLICATION z This application is divided from patent application no.

2002244529 filed 3 April 2002, the content of which is incorporated herein by reference in its entirety.

In 00 FIELD OF THE INVENTION SThe present invention relates to a system and method for characterizing the shape of a mirror for use in, for Sexample, a solar power generation system, and for employing C 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.

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.

SUMMARY OF THE INVENTION In a first broad aspect, the present invention provides a method of aligning each of a plurality of mirrors within an array, comprising: 1) determining a preferred pattern of light reflection from the array; 2) obtaining a characterization of the shape of each of the mirrors; 3) simulating the array and light reflection therefrom on the basis of the characterizations, and comparing the simulated light reflection with the preferred pattern of light reflection; and -3- 4) varying the simulated array and repeating step 3) until the simulated light reflection is within z acceptable tolerances of the preferred pattern of light reflection.

The preferred pattern of light reflection from the array Vpreferably includes preferred patterns of light reflection 00 for each mirror in the array.

Thus, there may be a need to produce a certain "shape" of Sbeam at the focus of a set of mirrors. This shape is CI dictated by the needs of the optical receiver placed at the focus. Owing to production constraints, mirrors (such as those for solar concentrators in solar power generation systems) do not have perfect optical surfaces, so the theoretical alignment of a set of mirrors will not produce the anticipated result. Rather than attempting to improve production quality, the present invention determines the character of each mirror, and determines how each mirror should be oriented to produce a composite, reflected light beam that is substantially as prescribed.

Step 4) may comprise varying the simulated orientation of one or more mirrors, or varying the simulated location within the array of one or more mirrors, or both varying the simulated orientation of one or more mirrors and varying the simulated location within the array of one or more mirrors.

Preferably obtaining the characterization of each of the mirrors includes characterizing each of the mirrors.

Preferably the method includes obtaining the characterization of the shape each of the mirrors by characterizing each of a plurality of characterization locations on the respective mirror by observing reflection of a respective light beam from each of the locations (for 4 O example as described in Australian patent application no.

2002244529 filed 3 April 2002) 0 z Preferably the method includes simulating the location of each respective mirror within the array such that mirrors more closely approximating a theoretical shape are located Scloser to a centre of the array than mirrors less closely 00 approximating the theoretical shape. For example, if the M mirrors are designed to be spherical mirrors, those closest to spherical would be located at the edge of the array S(where deviations from spherical would have the greatest 1 deleterious effect owing to higher angles of incidence) and those furthest from spherical would be located at the centre of the array.

In one embodiment, step 1) includes determining preferred patterns of light reflection for each mirror in the array, and the method includes subsequently: reflecting light from each of the mirrors and observing reflected light therefrom; 6) comparing the reflected light with the preferred pattern of light reflection for each respective mirror; and 7) varying the location, orientation or both location and orientation of one or more of the mirrors and repeating steps 5) and 6) until for each mirror the light reflection is within acceptable tolerances of the preferred pattern of light reflection from the respective mirror.

Preferably the array of the mirrors is for use in an energy conversion system, such as a solar power generation system.

In a second broad aspect, the present invention provides an apparatus for determining an alignment each of a plurality of mirrors within an array, comprising computational means (such as a computer provided with a computer program) for performing the method of aligning each of a plurality of 1 00 mirrors within an array as described above.

In a third broad aspect, the present invention provides a 00 method of aligning a mirror, comprising: 1) determining a preferred pattern of light Sreflection from the mirror; 00 2) obtaining a characterization of the shape of M the mirror; 3) simulating the mirror and light reflection C- 10 therefrom on the basis of the characterization, and comparing the simulated light reflection with the preferred pattern of light reflection; and 4) adjusting a simulated orientation of the mirror and repeating step 3) until the simulated light reflection is within acceptable tolerances of the preferred pattern of light reflection.

6 00 BRIEF DESCRIPTION OF THE DRAWINGS i In order that the present invention may be more clearly ascertained, an embodiment will now be described, by way of 00 Cl example, with reference to the accompanying drawing, in S which: Figure 1 is a schematic side view of an apparatus 00 for determining the figure of a mirror according to one C1 embodiment of the present invention; SFigure 2 is a schematic top view of the apparatus for determining the figure of a mirror of figure 1; and -7- O Figure 3 is a view of a solar power generator with an array of the type to be simulated by the simulation O program of the apparatus of figure 1.

z DETAILED DESCRIPTION OF THE INVENTION An apparatus for determining the figure of a mirror Saccording to one embodiment of the present invention is 00 shown generally at 10 in figures 1 and 2 with a mirror 12.

SFigure 1 is a side view of the apparatus 10, which includes a bank 14 of laser sources, a detecting surface in the form Sof target screen 16, a digital camera 18 and a data C 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 8 0 which each reflected beam intersects the target screen 16 may be deduced the gradient of the mirror at each location O at which a beam was incident when a measurement was made.

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

00 It should be noted that as, in this embodiment, Smeasurements are made progressively as the laser source/target screen assembly is translated vertically, the Slocations on the mirror 12 at which gradients are obtained CI 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) 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 -9- C with additional simulated rays impinging the mirror at the locations other than where gradient values have been 0 z 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 Vvalues have been obtained. Even though the mirror may be 00 curved, this approximation should generally be acceptable Mprovided 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 (1 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.

10

O

The simulated orientations of any of the mirrors can then 0 be adjusted and/or the simulated locations of one or more mirrors can be modified, until the desired or an acceptable intensity distributiQn is obtained.

VIn running the simulation program, the mirrors simulated as 00 located towards the periphery of the array of mirrors are Mpreferably those which, when their gradient values were determined, to most closely conform to the design specifications for the mirrors. For example, if the CI 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 11orientations for the mirrors to provide the optimal reflected intensity distribution or "focal shape" for O energy conversion (in the case of a solar concentrator), this field alignment technique should ensure that that optimal arrangement is achieved.

SModifications within the spirit and scope of the invention 00 may readily be effected by persons skilled in the art. It Sis to be understood, therefore, that the invention is not limited to the particular embodiments described by way of Sexample hereinabove.

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, wherein said preferred pattern of light reflection from said array includes preferred patterns of light reflection for each mirror in said array.
3. A method as claimed in either claim 1 or 2, wherein step 4) comprises varying the simulated orientation of one or more mirrors, or varying the simulated location within said array of one or more mirrors, or both varying the simulated orientation of one or more mirrors and varying the simulated location within said array of one or more mirrors.
4. A method as claimed in any one of the preceding claims, wherein said obtaining a characterization of each of said mirrors includes characterizing each of said mirrors.
5. A method as claimed in any one of the preceding claims, including obtaining said characterization of the shape each of said mirrors by characterizing each of a plurality of 13 00 characterization locations on said respective mirror by c-I observing reflection of a respective light beam from each Sof said locations. 00 CI 5 6. A method as claimed in claim i, including simulating the location of each respective mirror within said array Ssuch that mirrors more closely approximating a theoretical 00 shape are located closer to a centre of said array than Smirrors less closely approximating said theoretical shape.
7. A method as claimed in claim 1, wherein step 1) CI includes determining preferred patterns of light reflection for each mirror in said array, and the method includes subsequently: 5) reflecting light from each of said mirrors and observing reflected light therefrom; 6) comparing said reflected light with said preferred pattern of light reflection for each respective mirror; and 7) varying the location, orientation or both location and orientation of one or more of said mirrors and repeating steps 5) and 6) until for each mirror said light reflection is within acceptable tolerances of said preferred pattern of light reflection from said respective mirror.
8. A method as claimed in any one of the preceding claims, wherein said array of said mirrors is for use in an energy conversion system.
9. A method as claimed in any one of the preceding claims, wherein said array is for use in a solar power generation system.
10. An apparatus for determining an alignment each of a plurality of mirrors within an array, comprising computational means for performing the method of aligning 14 00 each of a plurality of mirrors within an array as claimed in any one of claims one of the preceding claims.
11. An apparatus as claimed in claim 10, wherein said 00 CI 5 apparatus comprises a computer provided with a computer program. 00 12. A method of aligning a mirror, comprising: M 1) determining a preferred pattern of light reflection from said mirror; S2) obtaining a characterization of the shape of C said mirror; 3) simulating said mirror and light reflection therefrom on the basis of said characterization, and comparing said 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.
13. A method of aligning each of a plurality of mirrors within an array substantially as hereinbefore described by reference to the accompanying drawing.
14. An apparatus for determining an alignment each of a plurality of mirrors within an array substantially as hereinbefore described by reference to the accompanying drawing. A method of aligning a mirror substantially as hereinbefore described by reference to the accompanying drawing.