WO2010035083A2

WO2010035083A2 - Solar reflector with metal sheet cellular support structure, and process for making such reflector

Info

Publication number: WO2010035083A2
Application number: PCT/IB2009/006249
Authority: WO
Inventors: Dario Amidei
Original assignee: O.C.A.P. S.P.A.
Priority date: 2008-09-26
Filing date: 2009-09-22
Publication date: 2010-04-01
Also published as: ITTO20080706A1; WO2010035083A3

Abstract

The solar reflector (10; 110) comprises a mirror (14; 114) and a supporting structure (16; 116) made of sheet metal supporting the mirror (14;114), wherein the supporting structure (16; 116) comprises a first metal sheet (18; 119) having a plurality of truncated cone-shaped bosses (22; 122a, 122b) obtained by pressing or drawing from a flat metal sheet, and a second metal sheet (20; 120) arranged above the first metal sheet (18; 119) and securely joined to the latter by means of permanent connections (26; 126) so as to give the supporting structure (16; 116) a cellular or honeycomb configuration. The permanent connections (26; 126) are obtained by means of clinching, spot welding, projection welding, laser welding or gluing. The mirror (14; 114) is securely joined to the second metal sheet (20; 120) by means of gluing or mechanical connection.

Description

"SOLAR REFLECTOR WITH CELLULAR SHEET METAL SUPPORTING STRUCTURE AND PROCESS FOR MAKING SUCH REFLECTOR"

Field of the invention [1] The present invention refers to a solar reflector for a thermodynamic solar energy plant for the production of heat at high temperature.

According to a further aspect, the present invention refers to a process for the manufacture of a solar reflector for a thermodynamic solar energy plant for the production of heat at high temperature. State of the art

[2] Thermodynamic solar energy, or concentrating solar power, is a known technology for exploiting solar energy which allows the generation of heat at high temperature (currently up to 600°) for use in the production of electricity and/or as process heat for industrial uses. A thermodynamic solar energy plant consists of a plurality of solar collector modules (one of which is schematically illustrated in the figure of the attached drawings), each of which comprises basically a solar reflector 10 and a receiver tube 12. The solar reflector 10 includes a glass mirror with high reflecting power and a supporting structure to which the mirror is fixed. The mirror is advantageously a linear parabolic mirror (i.e. in the form of a paraboloid with single curvature or parabolic cylinder), but can also be a convex parabola mirror or a flat mirror. The solar reflector 10 is supported by pillars 13 so that it can oscillate around a horizontal oscillation axis to follow the path of the sun. The receiver tube 12 is positioned with its axis coinciding with the focal axis of the mirror 10, so that the sun's rays are concentrated by the mirror 10 on the receiver tube 12 and heat a heat transfer fluid contained in it. The heat transfer fluid running in the receiver tube 12 absorbs the energy transmitted by the sun's rays concentrated on the tube by means of the solar reflector 10 and conveys it to a storage tank (not shown) in which the heat is accumulated to compensate for periods in which there is very little or no sun. The storage tank communicates with a heat exchanger (also not shown) which generates steam used for example to drive turbines connected to alternators for the production of electrical current. [3] The supporting structures for the mirrors of the solar reflectors are typically large-dimension structures (for example 12 metres long and 6 metres wide) produced for example in sheet metal and must be designed so as to ensure the necessary rigidity and stability for the mirrors during their operation. [4] One of the technologies currently used for the production of said supporting structures is the sandwich technology, in which the supporting structure consists of two fine metal surface sheets and an internal metallic honeycomb structure and in which the metal sheets are secured to the honeycomb structure by means of application of adhesive and heating in an oven to harden the adhesive. This technology is, however, fairly expensive and suited to the manufacture of small and medium-sized production batches. [5] Given the current incentive to the development of renewable energy, in particular thermodynamic solar technology, or concentrating solar power, there is likely to be an increasing demand for solar collector modules and therefore supporting structures for solar reflector mirrors. For a plant for the production of electricity with power of 1 ,000 MW, over 11 million square metres of modular components are necessary (for example 3 metres long by 1.2 metres wide) for supporting structures in the form of a half-cradle for the solar reflectors. To achieve the objective of constructing a plant of the type indicated above in a period of two years, a modular support would have to be produced in less than 2.5 seconds. Such an objective cannot be achieved with the technologies currently known for production of the supporting structures for solar reflector mirrors.

[6] A first object of the present invention is to provide a solar reflector with sheet metal supporting structure which can be produced rapidly and at low cost in the context of a completely automated production system. Summary of the invention

[7] This object is fully achieved according to the present invention by a solar reflector having the characteristics defined in the attached independent claim 1. [8] Preferred embodiments of the solar reflector according to the invention are specified in the dependent claims from 2 to 9. [9] A further object of the present invention is to provide a process for the manufacture of a solar reflector with sheet metal supporting structure which can be implemented in a completely automated manner.

[10] This further object is fully achieved according to the present invention by a process for the manufacture of a solar reflector having the characteristics defined in the attached independent claim 10.

Preferred modes of implementation of the process for the manufacture of a solar reflector according to the invention are specified in the dependent claims from 11 to 14. [11] In short, the invention is based on the idea of producing a supporting structure for the mirror of a solar reflector made of sheet metal with cellular or honeycomb structure, the supporting structure comprising a first metal sheet having a plurality of bosses obtained by pressing or drawing from a flat metal sheet and a second metal sheet positioned above the first one and securely joined to it by means of permanent connections.

[12] In general in the present description the term "boss" has the meaning currently used in the field of pressing and welding of sheet metal and/or sheet metal assembly and indicates a stud, boss or protuberance with a substantially squat and possibly rounded form. Preferably the ratio between the maximum length LUMX and width LAMX of the base of the boss is substantially equal to or below four, and more preferably equal to or below three (Figures 15A-15D). [13] Preferably, the number and dimensions of the bosses of the first metal sheet are chosen so that the production of said bosses by pressing or drawing causes stretching of the entire metal sheet, or at least a large part of it, with the consequent effect of stiffening the metal sheet itself and in particular increasing its resistance to elastic instability. List of the Figures

[14] The characteristics and advantages of the present invention will become clear from the following detailed description, provided purely by way of non- limiting example with reference to the accompanying drawings, in which:

[15] figure 1 schematically shows a typical example of a solar collector module for a thermodynamic solar energy plant; figure 2 is a longitudinal section view of a supporting structure for a solar reflector with linear parabolic mirror according to a first preferred embodiment of the present invention; figure 3 is a longitudinal section view of a drawn metal sheet for production of the supporting structure of figure 2; figure 4 is a longitudinal section view of a forming jig for production of the supporting structure according to figure 2; figure 5 is a longitudinal section view of a solar reflector with linear parabolic mirror comprising the supporting structure of figure 2; figure 6 is a perspective view of a supporting structure for a solar reflector with linear parabolic mirror according to a second preferred embodiment of the present invention, in which the upper metal sheet is shown in a transparent manner; figure 7 is a longitudinal section view of the supporting structure of figure 6; figure 8 is a longitudinal section view of a solar reflector with linear parabolic mirror comprising the supporting structure of figure 6; figure 9 is a longitudinal section view of a solar reflector with linear parabolic mirror comprising a supporting structure according to a third preferred embodiment of the present invention; figure 10 is a longitudinal section view of a double-drawn metal sheet for manufacture of the supporting structure of figure 9; figure 11 is a longitudinal section view of a forming jig for production of the supporting structure according to figure 9; figure 12 is a longitudinal section view of a solar reflector with flat mirror comprising a supporting structure according to a fourth preferred embodiment of the present invention; figure 13 is a longitudinal section view of a solar reflector with flat mirror comprising a supporting structure according to a fifth preferred embodiment of the present invention; figure 14 is a longitudinal section view of a solar reflector with flat mirror comprising a supporting structure according to a sixth preferred embodiment of the present invention; figures 15A-15D are each a perspective view of variations of bosses which can be used to produce the present invention, and show respectively a truncated pyramid boss with square base (Figure 15A), truncated cone boss with elliptical base (Figure 15B), truncated pyramid boss with hexagonal base

(Figure 15C) and truncated pyramid boss with lobed base (Figure 15D); figure 16 shows a view, in section according to the plane A-A or B-B, of a supporting structure for a solar reflector according to a seventh preferred embodiment of the present invention; figure 17 shows a plan view of the intermediate metal sheet, provided with bosses, of the supporting structure of figure 16. Detailed description

[16] Referring initially to figure 5, a solar reflector for a thermodynamic solar energy plant according to a first preferred embodiment of the present invention is indicated overall by 10 and fundamentally comprises a linear parabolic mirror 14 made of glass with high reflecting power and a supporting structure or cradle 16 supporting the mirror 14. [17] The supporting structure 16 consists of a pair of metal sheets 18 and 20, lower and upper respectively, each of which is obtained from a flat metal sheet with thickness S (shown in figure 3), in which a plurality of roughly truncated cone-shaped bosses 22, spaced at a constant pitch P, having constant height H and a substantially flat bottom 24 are formed by drawing. According to this first embodiment, the bosses 22 all extend on the same side with respect to the plane of the metal sheet 18, 20. With reference also to figure 2, the two metal sheets 18 and 20 of the supporting structure 16 are arranged with respect to each other with the bottoms 24 of the respective bosses 22 in contact and are securely joined to each other at the level of said bottoms by means of permanent connections 26, for example by means of clinching (or cold welding), spot welding, projection welding, laser welding or gluing, riveting, nailing, crimping, or hot or cold plastic deformation in general. The supporting structure 16 therefore has a so-called cellular or honeycomb structure. [18] With reference to figure 4, the supporting structure 16 is produced by arranging the two metal sheets 18 and 20, with the bottoms 24 of the respective bosses 22 in contact, between respective forming jigs 28 and 30, so that the metal sheets take on the desired curved profile, and joining the metal sheets by means of the permanent connections 26 using suitable connection instruments 32, for example clinching tools, electrodes for welding (spot, projection or laser welding), adhesive applicators, riveters, nailers, crimpers or tools for performing cold or hot plastic deformation in general.

In the case of permanent connections obtained by means of clinching, spot welding or projection welding, one of the two metal sheets has, at the bottoms of the bosses in which said connections are provided, holes or apertures (not shown) for the passage of one of the two clinching or welding tools. [19] The structural rigidity of the supporting structure 16 thus obtained depends on the thickness S of the metal sheets 18 and 20, on the distance (indicated by A in figure 2) between them, on the pitch P and on the shape of the bosses 22, as well as on the elastic modulus of the metallic material used. [20] Once the supporting structure 16 has been obtained, a fine flexible sheet of glass with high reflecting power forming the mirror 14 is positioned on the supporting structure and fixed to it, by means of structural adhesives or other mechanical connection methods, in the contact zones (indicated by 34 in figure 5) between the lower surface of the mirror 14 and the upper surface of the supporting structure 16. Obviously all the operations described above, i.e. drawing of each of the two metal sheets, shaping and joining of the two metal sheets to form the supporting structure and lastly positioning and fixing of the glass on the supporting structure, can be easily automated and therefore the solar reflector subject of the present invention is particularly suited to being mass-produced in an automated production plant, with evident benefits in terms of reduction of costs and manufacturing times with respect to the solutions currently adopted.

[21] While in the embodiment described above with reference to the figures from 2 to 5, the supporting structure of the solar reflector has a substantially symmetrical profile with respect to the curved line passing through the connections between the two metal sheets, the second preferred embodiment of the present invention, shown in figures 6 to 8, proposes a supporting structure with two metal sheets having an asymmetrical configuration. [22] With reference to figures 6 to 8, in which parts and elements identical or corresponding to those of figures 2 to 5 have been attributed the same reference numbers, the supporting structure 16, designed also in this case to support a linear parabolic mirror 14, consists of a lower metal sheet 18 with thickness S having a plurality of bosses 22, like the lower metal sheet of the embodiment previously described, and a flat (or, better, non-drawn) upper metal sheet 20, securely joined to the lower metal sheet 18 by means of permanent connections 26 of the type described above with reference to the first embodiment. With respect to the first, this second embodiment has the advantage that the supporting structure 16 provides a continuous supporting and fixing surface for the mirror 14 and is therefore able to guarantee fewer deformations of the mirror following the stress to which it is subjected in use. [23] In both the first and second embodiments described above, the two metal sheets 18 and 20 constituting the supporting structure 16 can have the same thickness S or different thicknesses, according to the required rigidity. [24] As can be seen from figure 6, the bosses 22 are uniformly distributed over the entire surface of the lower metal sheet 20 and are chosen in appropriate numbers and dimensions such that obtaining of said bosses by means of pressing or drawing starting from a flat metal sheet causes stretching of the entire metal sheet, or at least a large part of it, with the consequent effect of stiffening the metal sheet itself and in particular increasing its resistance to elastic instability.

[25] Figures 9 to 11 , in which parts and elements identical or corresponding to those of figures 2 to 8 have been attributed the same reference numbers, increased by 100, illustrate a third embodiment of a solar reflector according to the invention, comprising a supporting structure with three metal sheets, i.e. an example of shell with honeycomb structure.

[26] With reference to figure 9, the solar reflector, indicated overall by 110, comprises a linear parabolic mirror 114 made of glass with high reflecting power and a supporting structure 116 supporting the mirror 114. The supporting structure 116 consists of three metal sheets 118, 119 and 120, to be precise a pair of flat (or, better, non-drawn) external metal sheets 118 and 120, lower and upper respectively, and a double-drawn metal sheet 119 positioned between the two external metal sheets 118 and 120. [27] As illustrated in greater detail in figure 10, the intermediate metal sheet 119 is a flat metal sheet in which a series of substantially truncated cone- shaped lower bosses 122a are provided by means of drawing, equally spaced at a constant pitch P, having constant height Ha and a substantially flat bottom 124a, and a series of substantially truncated cone-shaped upper bosses 122b, equally spaced at the same pitch P as the lower bosses 122a, having constant height Hb and a substantially flat bottom 124b. The lower bosses 122a and upper bosses 122b protrude in opposite directions from opposite faces of the same metal sheet 119. Preferably, the height Ha of the lower bosses 122a is equal to the height Hb of the upper bosses 122b, but different heights can naturally be provided according to specific needs in terms of geometry and/or rigidity of the supporting structure.

[28] The two external metal sheets 118 and 120 are securely joined to the intermediate sheet 119 at the bottoms 124a of the lower bosses 122a and at the bottoms 124b of the upper bosses 122b respectively by means of permanent connections 126, for example by means of clinching (or cold welding), spot welding, projection welding, laser welding, gluing or the other types of permanent connection previously described.

[29] With reference to figure 11 , the supporting structure 116, another example of a shell structure, is obtained by arranging the three metal sheets 118, 119 and 120, with the bottoms 124a of the lower bosses 122a of the intermediate metal sheet 119 in contact with the upper surface of the lower metal sheet 118, and with the bottoms 124b of the upper bosses 122b of the intermediate metal sheet 119 in contact with the lower surface of the upper metal sheet 120, between respective forming jigs 128 and 130, so that the set of the three metal sheets assumes the desired curved profile, and joining the three metal sheets by means of the permanent connections 126 using appropriate connection instruments (not shown), for example clinching tools, electrodes for welding (spot, projection or laser welding) or adhesive applicators. In the case of permanent connections provided by means of clinching, spot welding or projection welding, one of the two metal sheets has, in the bottoms of the bosses in which said connections are provided, holes or apertures (not shown) for the passage of one of the two clinching or welding tools. [30] The structural rigidity of the supporting structure 116 thus obtained depends fundamentally on the thickness of the metal sheets 118, 119 and 120, on the distance between the two external metal sheets 118 and 120 (in other words the sum of the heights Ha and Hb of the bosses 122a and 122b of the intermediate metal sheet 119), on the pitch P and on the shape of the bosses 122a and 122b, as well as on the elastic modulus of the metallic material used. Once the supporting structure 116 has been obtained, a fine flexible sheet of glass with high reflecting power forming the mirror 114 is placed on the supporting structure and fixed to it, by means of structural adhesives or other mechanical connection means. As in the embodiment illustrated in figure 8, also in this case the advantage is that of having a continuous resting surface for the mirror 114 formed of the upper metal sheet 120. [31] The figures 12, 13 and 14 lastly show in longitudinal section three preferred embodiments of a flat solar reflector according to the invention. [32] The embodiment shown in figure 12, in which parts and elements identical or corresponding to those of figure 5 have been attributed the same reference numbers, differs from the embodiment of figure 5 substantially due only to the fact that it has a flat instead of a linear parabolic configuration. It too, therefore, has a supporting structure consisting of a pair of drawn metal sheets, securely joined at the bottoms of the respective bosses. For the details on the structural characteristics of the solar reflector of figure 12, and on the steps of the process for the manufacture of said solar reflector, refer to the preceding description of the embodiment shown in figures 2 to 5.

[33] The embodiment shown in figure 13, in which parts and elements identical or corresponding to those of figure 8 have been attributed the same reference numbers, differs from the embodiment of figure 8 substantially due only to the fact that it has a flat instead of a linear parabolic configuration. It too, therefore, has a supporting structure consisting of a drawn lower metal sheet and a flat upper metal sheet securely joined to the lower metal sheet at the upper flat portions of the latter. For the details of the structural characteristics of the solar reflector of figure 13, and the steps of the process for the manufacture of said solar reflector, refer to the preceding description of the embodiment shown in figures 6 to 8.

[34] The embodiment shown in figure 14, in which parts and elements identical or corresponding to those of figure 11 have been attributed the same reference numbers, differs from the embodiment shown in figure 11 substantially only due to the fact that it has a flat instead of a linear parabolic configuration. It too, therefore, has a supporting structure consisting of a pair of flat external metal sheets, lower and upper respectively, and a double-drawn intermediate metal sheet, securely joined to the two external metal sheets at the bottoms of their bosses. For the details of the structural characteristics of the solar reflector of figure 14, and the steps of the process for the manufacture of said solar reflector, refer to the preceding description of the embodiment of figures 9 to 11. [35] As said previously with reference to the first embodiment shown in figures 2 to 5, the main advantage of the solar reflector subject of the present invention is the possibility of being manufactured at low cost and rapidly via a completely automated manufacturing process. The three main phases of the manufacturing process, i.e. pressing of the bosses (drawing) on one or two metal sheets, joining (plus any forming) of the metal sheets to form the supporting structure and, lastly, laying and fixing of the glass on the supporting structure, can be performed on complete modular type production lines comprising automated work units with a high production rate and robots for loading the semi-finished pieces and discharging the finished products. The complete automated production lines are furthermore quick and easy to assemble and disassemble and can therefore be transported and installed each time on the various thermodynamic solar energy plant construction sites.

[36] The bosses are able to give the supporting structure in which they are assembled a rigidity substantially equal at least in two transverse directions X and Y unlike, for example, the linear ribs described in the documents GB2104238 and US6035850. Furthermore the bosses according to the present invention can be obtained from a coil or continuous strip of sheet metal by means of roll forming or progression tools and said roll forming or progression tools can be of smaller dimensions than those necessary to produce, for example, the linear ribs described in the documents GB2104238, US6035850 and DE3134690, with the same dimensions of the metal sheet to be pressed.

[37] The permanent connection - for example by means of welding, gluing, clinching or the other methods referred to above - of three or more overlapped metal sheets, of which at least the central sheet is bossed, as in the embodiments of Figures 9 and 11 , for example, allows the production of shells with substantially self-supporting honeycomb structure, i.e. able to substantially preserve their shape for example the parabolic cylinder shape shown (Figure 1) also after being removed from the above-mentioned forming jigs. [38] Naturally, without prejudice to the principle of the invention, the embodiments and the construction details can be widely varied with respect to what has been described and illustrated purely by way of non-limiting example, without departing from the scope of the invention as defined in the attached claims.

[39] For example, although in the embodiments described and illustrated here substantially truncated cone-shaped bosses are used having a substantially flat bottom, bosses of different shape can also be used, for example semi-spherical bosses therefore having a curved instead of a flat bottom. The bosses can be arranged according to a variable pitch P, for example progressively variable moving from the centre towards the outside of the supporting structures 16, 116 or other supporting shells, for example moving perpendicular to the directrix lines of the parabolic cylinder; this gives said supporting structures a rigidity varying progressively from the centre towards the ends, reducing where possible the density of the bosses and consequently the number of permanent connections to be made and the production times. Analogously also the heights of the bosses - e.g. Ha and Hb - can vary progressively on the supporting structure 16, 116 or other shell.

[40] The Figures 15A-D show some further examples of "bosses" that can be used in the present invention: truncated pyramid with square base (Figure 15A), truncated cone with elliptical base (Figure 15B), truncated pyramid with hexagonal base (Figure 15C) and truncated pyramid with lobed base (Figure 15D).

[41] The Figures 16, 17 show generically convex bosses - e.g. dome-shaped or in sinusoidal transverse sections - upper A and lower B which alternate. Advantageously, in this embodiment as in the others, for the production of mirrors with single curvature, the bosses according to the invention are arranged according to a square or rectangular mesh grid (Figure 17): said arrangement avoids unduly increasing the flexional rigidity of the bossed metal sheet even if the bosses are very close to one another, and said metal sheet can be bent and arranged on the forming jigs 28, 30 without inducing excessive internal tensions and adapting very well to the form of the jigs; in this way supporting structures 16, 116 or other honeycomb structure shells can be produced with considerable dimensional accuracy. In said regard in order to produce linear parabolic mirrors, one of the directrixes of said grid is advantageously arranged parallel to the generatrixes of the mirror surface.

Claims

1. Solar reflector (10; 110), particularly for thermodynamic solar energy plant, comprising a mirror (14; 114) and a supporting structure (16;116) made of sheet metal supporting the mirror (14;114), characterised in that the supporting structure (16; 116) comprises a first metal sheet (18; 119) having a plurality of bosses (22; 122a, 122b) obtained by pressing or drawing from a flat metal sheet, and a second metal sheet (20; 120) arranged above the first metal sheet (18; 119) and securely joined to the latter by means of permanent connections (26; 126) so as to give the supporting structure (16; 116) a cellular or honeycomb structure, and in that the mirror (14; 114) is securely joined to the second metal sheet (20; 120).

2. Solar reflector (10) as claimed in claim 1 , wherein also the second metal sheet (20) has a plurality of bosses (22) obtained by pressing or drawing from a flat metal sheet and wherein the first and the second metal sheet (18; 20) are joined to each other at the bottoms (24) of the respective bosses (22).

3. Solar reflector (10) as claimed in claim 2, wherein both the bosses (22) of the first metal sheet (18) and the bosses (22) of the second metal sheet (20) are spaced at a constant pitch (P), have a constant height (H) and if necessary have a shape chosen from the following: roughly truncated cone shape, truncated cone-shaped with elliptical or ovoid base, semi-spherical, truncated pyramid, truncated pyramid with square base, truncated pyramid with hexagonal or polygonal base, truncated pyramid with lobed base, boss with substantially polygonal, elliptical, ovoid or lobed base.

4. Solar reflector (10; 100) as claimed in claim 1 , wherein the second metal sheet (20; 120) is a non-drawn sheet, thus providing a continuous supporting and fixing surface for the mirror (14; 114).

5. Solar reflector (100) as claimed in claim 4, wherein the first metal sheet (119) has a first series of lower bosses (122a) and a second series of upper bosses (122b), wherein the second metal sheet (120) is securely joined to the first metal sheet (119) by means of permanent connections (26; 126) at the bottoms (124b) of the upper bosses (122b) of the latter and wherein the supporting structure (116) furthermore comprises a third non-drawn metal sheet (118) securely joined to the first metal sheet (119) by means of permanent connections (26; 126) at the bottoms (124a) of the lower bosses (122a) of the latter.

6. Solar reflector (100) as claimed in claim 5, wherein the lower bosses (122a) of the first metal sheet (119) are spaced at a constant pitch (P), have a constant height (Ha) and if necessary have a shape chosen from the following: roughly truncated cone shape, truncated cone-shaped with elliptical or ovoid base, semi-spherical, truncated pyramid, truncated pyramid with square base, truncated pyramid with hexagonal or polygonal base, truncated pyramid with lobed base, boss with substantially polygonal, elliptical, ovoid or lobed base.

7. Solar reflector (100) as claimed in claim 5 or claim 6, wherein the upper bosses (122b) of the first metal sheet (119) are roughly truncated cone-shaped or semi-spherical shaped, are spaced at a constant pitch (P) and have a constant height (Hb).

8. Solar reflector (100) as claimed in claims 6 and 7, wherein the pitch (P) of the lower bosses (122a) is equal to the pitch (P) of the upper bosses (122b).

9. Solar reflector (10; 100) as claimed in any one of the preceding claims, wherein said permanent connections (26; 126) are obtained by means of any one of the following connection methods: clinching, spot welding, projection welding, laser welding, gluing, riveting, nailing, crimping, hot or cold plastic deformation.

10. Process for the manufacture of a solar reflector (10; 110) particularly for a thermodynamic solar energy plant, the reflector (10; 110) comprising a mirror (14; 114) and a supporting structure (16; 116) made of sheet metal supporting the mirror (14; 114), characterised in that it comprises the steps of: a) producing by pressing or drawing a plurality of bosses (22; 122a, 122b) in a first metal sheet (18; 119); b) arranging a second metal sheet (20; 120) on the first metal sheet (18; 119); c) securely joining the second metal sheet (20; 120) to the first metal sheet (18; 119) by means of permanent connections (26; 126) at the bottoms (24; 124a, 124b) of the bosses (22; 122a, 122b), thus giving the supporting structure (16; 116) a cellular or honeycomb structure; d) arranging the mirror (14; 114) on the second metal sheet (20; 120); and e) securely joining the mirror (14; 114) to the second metal sheet (20; 120).

11. Process as claimed in claim 10, furthermore comprising, between steps b) and c), step b1) of arranging the first (18, 119) and the second metal sheet (20; 120) between respective forming jigs (28, 30; 128, 130) so as to impart to the supporting structure (16; 116) a given curved profile.

12. Process as claimed in claim 10 or claim 11 , furthermore comprising, before step b), step a1) of producing by pressing or drawing a plurality of bosses (22) also in the second metal sheet (20).

13. Process as claimed in claim 10 or claim 11 , wherein in step a) a first series of lower bosses (122a) and a second series of upper bosses (122b) are produced in the first metal sheet (119) by pressing or drawing, wherein in step c) the permanent connections (126) between the first metal sheet (119) and the second metal sheet (120) are provided at the bottoms (124b) of the upper bosses (122b), and wherein the process furthermore comprises, before step d), step c1) of providing a third metal sheet (118) and securely joining it to the first metal sheet (119) by means of permanent connections (126) at the bottoms (124a) of the lower bosses (122a) of the latter.

14. Process as claimed in any one of the claims from 10 to 13, wherein said permanent connections (26; 126) are obtained by means of any one of the following connection methods: clinching, spot welding, projection welding, laser welding, gluing, riveting, nailing, crimping, hot or cold plastic deformation.