WO2014068452A2

WO2014068452A2 - A method for manufacturing a reflector for solar plants

Info

Publication number: WO2014068452A2
Application number: PCT/IB2013/059597
Authority: WO
Inventors: Antonino Toro
Original assignee: Fabbrica Energie Rinnovabili Alternative S.R.L.
Priority date: 2012-11-05
Filing date: 2013-10-24
Publication date: 2014-05-08
Also published as: ITMI20121880A1; WO2014068452A3

Abstract

Method for the production of a reflecting mirror in a single piece for a concentrating solar plant, of the Fresnel type, said mirror being provided with only one curvature axis, comprising the steps of: a. preparing a single plate of deformable material that is at least elastically deformable, so that said plate is provided with at least one optically reflective surface; b. preparing a die having a shape opposite to that of the mirror to be produced for a Fresnel solar plant; c. prearranging means for defining a hollow with said single plate; said single plate partially delimiting said hollow, and said means being provided with at least one through hole of fluidic communication; d. coupling, substantially by sealing, said means for defining a hollow to said single plate, said plate being in its own substantially not - deformed condition; e. joining said single plate of deformable material in a substantially not - deformed condition, coupled with said means for defining a hollow, to said die, with said at least one optically reflective surface partially engaging said die; f. injecting into said hollow, through said at least one through hole, at least one plastic filling material in a fluid, or fluidized, state, in order to move said at least one reflective surface from a position partially engaged with said die to a position totally engaged with said at least one reflective surface against said die; said at least one plastic filling material being adhesive, at least when solidified, to said single plate; g. solidifying said at least one plastic filling material; h. drawing out from said die said single plate permanently deformed as a mirror for a Fresnel solar plant.

Description

"A method for manufacturing a reflector for solar plants"

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FIELD OF THE INVENTION

The present invention relates to a method for realizing a reflecting mirror with a given curvature, by deformation in a die of a plate made of deformable material, provided with at least one optically reflective surface. Preferably, such a curved reflecting mirror has application in thermodynamic solar plants of the so-called "Fresnel" typology, i.e. wherein linear Fresnel reflectors are employed for conveying the sun light rays towards a proper collector.

Such plants are composed by rows of linear mirrors, with relatively low curvature which, when conveniently tilted and oriented to the sun, reflect and concentrate the solar radiation towards a collector (receiver tube) for heating a fluid, of which thermodynamic properties are exploited in a known way in order to produce, for example, electric power. The above-mentioned mirrors can be further mounted on handling mechanisms able to move and/or tilt the mirrors themselves along their own longitudinal axis, in order to follow the sun motion, and thus keep substantially constant the solar radiation reflected to the collector.

BACKGROUND ART

It is a known technique to realize reflecting mirrors, by elastic or plastic (i.e. permanent) deformation, of a substantially flat plate, provided with at least one surface reflecting the light.

A known implementation method (see WO 2010/052282 Al) provides, for example, the implementation of a reflector of solar rays by the side-by-side installation of several plates made of reflective material arranged inside a supporting structure. Initially such plates, of substantially rectangular and elongated shape, have a substantially flat profile; during the production, the plates are arranged side-by-side, without interruption, at the largest sides above a previously realized convex shape die (which is thus directly contacting the reflective surface of the plates themselves). Once arranged on the die, the plates are constrained to the mentioned supporting structure and their relative position is therefore made permanent by injection, and subsequent solidification, of polyurethane foam inside the supporting structure itself. Such a production method needs long preparation times without, on the other hand, assuring that the produced reflector is reliable and accurate.

It results, in fact, that the side-by-side arrangement of a plurality of flat sheets on a convex shape die results in unavoidable inaccuracies both during the preparation of the printing step, and during the deforming step during the printing itself. Note also that, at the end of the latter step, it has to be verified that the plates are side-by-side arranged one with another as much as possible and that gaps are absent therebetween. In case these two conditions are not fulfilled, which is also a frequent situation, the manual junction of plates has to be implemented by a reflective glue or other filling material, thus increasing costs and production times, as well as decreasing the accuracy of the result.

According to another method for the production of such mirrors, known from the patent application US 2009/0260753 (SELIG et AL.), a flexible flat plate, provided with a reflective surface, is fixed to a supporting frame provided with adhesive means, by a convex die compressing the flat plate against the same adhesive means on the supporting frame. The convex die compression establishes its own shape to such a deformable plate, and therefore to the underlying adhesive means. When the adhesive means solidify (for example by cross-linking, in case such adhesive means are of polymeric type), the concave die is removed, and the flat plate, retained by the already solidified adhesive means, keeps its own deformed configuration.

On the other hand such a production method, while highly cost effective, can lead to a not accurate deformed configuration of the reflective plate constituting the mirror, for example due to unexpected dimensional shrinkages, or deformations, of adhesive means, or to the lack - over time - of one or more of the points for anchoring to the plate frame, provided by the same adhesive means, due to inaccuracy in the application of such adhesive means, impacts, wear, crystallization of the adhesive means, etc.

According to another known method for implementing such mirrors, disclosed in GB-A-0430321, in name of VEREINIGTE DEUTSCHE METALLWERKE, a flat plate made of reflective material is inserted in a box-shaped die and retained, at its peripheral edge, to the die itself, so as to define, with the latter, a fluidic sealed chamber, of which the plate constitutes at least part of a wall. The subsequent filling of such a chamber by a pressurized fluid, generates at first the elastic deformation of the flat plate, uniformly on the whole surface, and afterwards the desired plastic deformation thereof.

Such a method imposes that the material constituting the reflecting plate is plastically deformable, and in this way limits the use of this method only to some classes of materials, and further does not allow any effective control on the plate curvature, during its deformation.

Finally, the international patent application WO 03/051554 Al, in name of UNIVERSITY OF DURHAM, teaches inserting a flat plate provided with a reflective surface coupled to a die of desired curvature, and applying a suctioned flow, with proper speed and flow rate, to holes present in such a die, so as to deform the above said flat plate on the die, until the plate perfectly adheres to the die itself. During such an operation, the method described in WO 03/051554 Al provides that a supporting element (or frame) is joined to the plate, the latter being kept deformed by the suction on the die by an adhesive material.

The method described in WO 03/051554, while being rather effective in obtaining the desired curvature of the reflecting mirror, shows to be rather complicated, as well as expensive, and provides the use of complex apparatuses, such as the suctioning equipment, hard to implement.

It is therefore an object of the present invention to provide a method for the production of a reflecting mirror, by deformation in a die of a single plate of at least plastically deformable material and provided with at least one optically reflective surface, which is free from the above pointed out drawbacks of the known prior art. It is a further object of the present invention to provide a method for the production of a reflecting mirror of the above mentioned type, which results simple, easily adaptable to the different required curvatures and which, at the same time, leads to the effective implementation of mirrors with the desired, highly stable curvature over time.

A further object of the present invention is to realize a reflecting mirror, preferably to be used in thermodynamic solar plants, which is dimensionally accurate, while being economic.

SUMMARY OF THE INVENTION

These and other objects are obtained by the method for producing a reflecting mirror according to the first independent claim and the subsequent dependent claims, and by the reflecting mirror according to the eleventh claim and the subsequent claim dependent therefrom.

According to the present invention, the method for the production of a reflecting mirror provided with only one curvature axis, to be used in a concentrating solar plant of Fresnel type, i.e. with Fresnel reflectors, comprises the steps of:

a. preparing a single plate of a material that is at least elastically deformable, so that the plate is provided with at least one optically reflective surface;

b. preparing a die having a shape opposite to that of the mirror to be produced for a Fresnel solar plant;

c. prearranging means for defining a hollow with the single plate; such a single plate partially delimiting the hollow and the means being provided with at least one through hole of fluidic communication;

d. coupling, substantially by sealing, the means to the single plate, the plate being in its own substantially not-deformed condition;

e. joining the single plate of deformable material still in a substantially not-deformed condition, and coupled with the means for defining a hollow, to the die, with the afore said at least one optically reflective surface partially engaging the die;

f. injecting into the hollow, through the through hole, at least one plastic filling material in a fluid, or fluidized, state, in order to move the at least one reflective surface from a position partially engaged with the die to a position totally engaged of the reflective surface against the die; the afore said at least one plastic filling material being adhesive, at least when solidified, to the afore said single plate;

g. solidifying the plastic filling material; and

h. drawing out, from the die, the single plate permanently deformed as a mirror, to be used for a Fresnel solar plant.

Such a method, as it will be evident to a field technician, allows using a filling material that can be injected and solidified, such as for example polyurethane (PUR), for both deforming, on a die with desired geometry, an even flat single plate with a reflective surface, and retaining deformed such a plate once solidified.

In the step d), the substantially not-deformed, generally flat, condition of such a single plate makes particularly easy the coupling by sealing with the mentioned means, conversely to what happens by the use of one or more plates possibly already characterized by their own curvature.

In addition, the production of a reflecting mirror in a single piece, i.e. not composed by several sheets arranged side-by-side, simplifies and speeds up the step e) wherein the single plate is joined to the die and, at the same time, entails the use of a die easier to produce.

According to a preferred aspect of the present invention, the method provides as well that the above mentioned means for defining a hollow comprise a box-shaped counter-die, which can be substantially coupled by sealing to the die and/or to the above mentioned plate, and wherein such a counter-die is provided with at least one through hole of fluidic communication; so that the above mentioned step of d) coupling the means, in order to define a hollow, to the single plate comprises as well the step of:

d.l) putting the counter-die in a substantially sealed coupling with the single plate of deformable material, still in its substantially not-deformed condition, to define the hollow mentioned above.

According to a further preferred aspect of the present invention, the herein claimed method provides that the means for defining a hollow further comprise at least one supporting frame for the single plate; wherein such a supporting frame can be coupled to the single plate; and is in fluidic communication with the afore said counter-die.

According to this aspect of the present invention, the method comprises, before the step d.l) of putting the counter-die in a substantially sealed coupling to the die and the single deformable plate, the further step of:

d.0) coupling the afore said supporting frame to the plate of deformable material, still in a substantially not-deformed condition; and wherein the plastic filling material is adhesive also to the afore said frame. This way, the above mentioned step of h) drawing out the single deformed plate, comprises as well the step of drawing out such a supporting frame, joined to the single plate by the solidified plastic filling material.

Finally, according to another aspect of the present invention, a reflecting mirror is provided for concentrating solar implants of the Fresnel typology, having only one curvature axis, obtained by the above described method for the production of a reflecting mirror, comprising a single plate with a reflective surface, wherein such a plate, suitably deformed and with the expected curvature, is adhering to a solidified plastic material.

Such a reflecting mirror can preferably comprise at least one supporting frame joined to such a single plate, provided with a reflective surface, by the afore-said solidified plastic material, simultaneously adhering to the plate and to the supporting frame. BRIEF DESCRIPTION OF THE FIGURES

A preferred embodiment of the method according to the present invention will be now described, for illustration purposes only and without any limitation to what claimed later, referring to the attached figures, in which:

figure 1 is a scheme of a possible application of the reflecting mirrors object of the present invention in a thermal solar power plant, of the Fresnel typology;

figures 2 to 5 are schematic side section views of an apparatus and the elements which can be used for the production of a reflecting mirror according to a particular embodiment of the method according to the present invention, according to the different steps thereof;

figure 6 is a sectional schematic view of a reflecting mirror obtained through the method depicted in figures 2 to 5; and

figure 7 is a schematic exploded view of the reflecting mirror of figure 6. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE PRESENT INVENTION

Referring at first to figure 1, the reflecting mirrors 1, object of a particular aspect of the present invention, are provided with suitable geometry, and in particular only with a mild curvature (concavity) with respect to only one curvature axis, in order to act as Fresnel linear reflectors, and thus preferably have application in thermal solar plants of Fresnel type. In such a type of solar plant, the sun rays 100 are reflected by the mirrors 1, provided with the mentioned curvature, towards a collector 200 that is usually constituted of a heat absorbing tube bundle, or a tank, wherein a fluid, for example a heat-transfer fluid or a fluid subjected to a phase change, is circulated inside a circuit provided with devices for converting, directly or indirectly, the mechanical and/or thermal energy of such a fluid in electric power.

Note that typical geometries of such a mirror 1 are those for which the radius of curvature is comprised between 6m and 30 m, and the length and width of such a mirror are respectively comprised between 1 m and 6 m and between 0.4 m and 1.5 m.

In such a plant, it is known that the reflecting mirrors 1 can be mounted on apposite supporting frames, which in their turn can be constrained to suitable handling means, usually automatically activated. Such handling means are configured such to move the mirrors 1 during the day, so that latter will follow the relative position of the sun 100, in order to effectively reflect the sun light towards the afore said collector 200 in any instant of the day.

However, in order to realize an effective reflection of the light rays from the mirrors 1 to the collector 200, it is extremely important that the curvature of the mirrors 1, which depends on their distance from the collector 200, is extremely accurate and precise. That is, in order to obtain a high concentration of sun rays reflected by the various mirrors 1 towards the collector 200, setting previously the correct theoretical curvature of the various mirrors 1 as a function of their distance from the collector 200 itself and thus realizing the various mirrors 1 with an identical curvature is extremely important, or at least as similar as possible to the theoretical curvature set up during the designing step.

The method according to the present invention achieves, among the others, the object of producing reflecting mirrors 1 adapted to be used in a solar plant of the above described type, which have a high precision in their curvature, without thereby requiring excessive costs for their production. Such a method, as it will be better explained in the following, preferably provides that, after a single plate of at least elastically deformable material has been prepared, provided with at least one optically reflective surface, and a relative die having shape opposite to that of the mirror to be produced, the following steps are carried out:

- prearranging means for defining a hollow jointly to said single plate; wherein said means, which can take the shape of a removable counter-die and/or a supporting frame for the produced mirror, have at least one through hole for injecting at least one plastic filling material (for example polyurethane) into the hollow;

coupling, and preferably constraining, by sealing such means in order to define a hollow to the single plate, wherein the latter is in its own substantially not deformed condition; then

joining the single plate of deformable material in a substantially not- deformed condition, coupled with the means for defining a hollow, to the die, in such a way that the optically reflective surface of the plate is partially engaging the die; and then

injecting into the hollow at least one plastic filling fluid material, able to deform the plate against the die and, once solidified, to adhere at least to the plate; and

drawing out the plate after the solidification of the plastic filling material.

More in particular, according to a preferred aspect of the present invention, referring to figure 2, the particular method for producing reflecting mirrors from a single plate 5 provided with at least one reflective surface, here described, provides the preliminary steps of:

- preparing a die 2, having the geometry, and in particular the curvature, which the reflecting mirror 1 in progress is desired to have (step (b));

then preparing a counter-die 3a, 3b, 4, shaped in such a way to be coupled substantially by sealing to the die 2, and to the single plate 5, so that to realize a hollow 7 (see also figures 3 and 4) which is delimited, partly, by the plate 5 itself (step (c)).

Note that the counter-die drafted in figure 2, according to a particular aspect of the present invention, can be constituted of a plurality of modular walls 3a, 3b, 4 that, once mutually assembled, preferably constitute a box-shaped counter-die, able to be coupled by sealing to the die 2 and to the single plate 5 that is in its own substantially not-deformed condition.

Such a counter-die 3 a, 3 b, 4 can thus constitute, in this particular embodiment of the process according to the invention, the afore said means for defining a hollow 7 jointly to the plate 5 and the latter is thus coupled, or constrained, in its own not- deformed condition to such means.

Note that the constraint of the plate 5 to the counter-die 3a, 3b, 4 and/or, as it will be seen, to a supporting frame 6, is made particularly easy just by the not-deformed condition of such a plate 5, that is in a substantially flat condition.

The hollow 7 that is realized in the sealed coupling of the counter-die 3a, 3b, 4 to the die 2 and to the single plate 5, according to what provided by the method according to the present invention, is substantially fluidically sealed with respect to the outer environment, except for the presence of at least one through hole 8 (see figure 3) allowing, as it will be seen, the passage of fluids from the outside to the inside of such a hollow 7. The die 2, according to known art, can be made of metal material, starting from a whole blank, through chip removal machining, preferably carried out automatically by a numerically controlled machine tool. Such a die 2 can alternatively be made of other suitable material (for example of a thermosetting polymeric material), according to any known art, able to provide the die 2 with the desired geometry. The die 2 is however shaped so that to have only one curvature axis through which the single curvature of the reflecting mirror is characterized. The single plate 5, according to a particular aspect of the present invention, is preferably a flat plate, provided with at least one usually metal, and at least elastically deformable, reflective surface.

In particular, the single flat plate 5 can be made, similarly to the domestic reflecting mirrors, of a substantially transparent glass with a surface reflecting the sun rays composed of a silver layer, conveniently deposited on the glass, which is covered by an additional resin layer (paint) adapted to protect silver against oxidation. Note that, in this case, the reflective surface of the single plate 5, consisting of the silver metal layer, is surmounted by the glass.

According to known embodiments of the single plate 5, this can alternatively be constituted of an aluminium plate, usually provided with a mechanically and/or chemically treated surface for increasing the reflectivity thereof, or it can be a plastic or metal plate, to which a reflective film is applied, generally of synthetic material, by an adhesive layer.

In any case, the single plate 5 does not need to have high mechanical resistance features, but needs to have only a highly reflective surface and to be deformable, at least elastically, without reaching its rupture too quickly during its deformation. As visible in figure 2, according to an optional, but preferred, aspect of the method according to the present invention, a supporting frame 6 can be preventively realized, for example made of metal (such as aluminium or steel) or plastic material, realized by a substantially U-shaped thin profile plate. Such a supporting frame 6, if present, and as it will be evident from the following, has to be in fluidic communication with the above described hollow 7, and in particular with the corresponding through hole 8, so that the input of a fluid between the supporting frame 6 and the single plate 5 is possible.

The supporting frame 6, according to a particular aspect of the present invention, can be constituted of a metal, or plastic, substantially smooth foil, or of a metal, or plastic foil provided with at least one surface comprising knurls, webs or the like, or however with high roughness, preferably intended to contact the afore said fluid that will be introduced between the supporting frame 6 itself and the reflective plate 5. According to another aspect of the present invention, not shown in figures, in case wherein the supporting frame 6 comprises a substantially thin U-shaped profile plate, the supporting frame 6 can comprise one or more closing heads too, constituted of metal, or plastic, plates intended to be coupled to such a thin U-shaped profile plate at the free edges of the latter, that is at the edges of the thin U-shaped profile plate not engaged with the reflecting plate 5.

Further note that, although a printing apparatus has been described heretofore provided with a die 2 made in a single piece and a fixed counter-die 3a, 3b, 4 provided with modular walls, any other geometry and configuration of the die and relevant counter-die can be equally used, as long as die and counter-die, once reciprocally assembled, are able to define the above said substantially sealed hollow 7, of which at least one wall is constituted of the single plate 5.

For example, the counter-die 3 a, 3 b, 4 can provide an upper, movable, wall 4 and in case subjected to an elastic thrust exerted by springs and facing towards the die 2, able to balance possible dimensional and geometrical variations in the coupling between supporting frame 6 and single plate 5, during the deforming step of the plate 5 itself.

More in general, alternatively to the afore said counter-die 3a, 3b, 4 and/or to the supporting frame 6, the method according to the present invention can provide the use of any known mechanical means able to define, when coupled substantially by sealing to at least the single plate 5, a hollow 7, provided with at least one through hole 8 of fluidic communication with the outer environment and wherein at least part of a wall is constituted by the same plate 5 in its own not-deformed condition.

Therefore, as said, the particular method herein described provides that the supporting frame 6 is coupled to the single not-deformed plate 5, and that the box- shaped counter-die 3 a, 3 b, 4 is assembled and coupled by sealing to the plate 5 (step (d)). In this way, as just visible in the scheme of figure 3, among the single plate 5, the supporting frame 6 and the counter-die 3a, 3b, 4, a hollow 7 is created, having its own lower wall constituted of the same flat plate 5. Such a hollow 7, as already mentioned, is substantially fluidically sealed, except for a through hole 8, intended for the communication of the hollow 7 with the outside.

As already mentioned, if the supporting frame 6 comprises a substantially thin U- shaped profile plate, according to a particular embodiment of the method of the present invention, ending heads can be inserted within the counter-die 3a, 3b, 4, constituted of metal or plastic plates, not shown, intended to engage the free edges of the thin profile plate. Such heads constitute the ending walls of the hollow 7.

Note that, in case the supporting frame 6 is a U-shaped, or however not box-shaped, metal plate and thus not able to define the hollow 7 in its own with the plate 4, and therefore such a hollow 7 is defined by the plate 4, by the supporting plate 6 and by the counter-die 3a, 3b, 4, it is advantageous to provide that the inner walls of the counter-die 3 a, 3 b, 4 are not able of adhering to the above said plastic filling material (for example polyurethane PUR), once solidified, conversely to the fact that it is convenient that such a plastic filling material, once solidified, adheres both to the plate 4, and to the supporting plate 6.

Note finally that, as it can be noted from figure 3, with respect to the die 2 the single flat plate 5 is preferably arranged under the supporting frame 6 and the box-shaped counter-die 3 a, 4b, 4.

Since the plate 5 is constrained in its own typically flat not-deformed position, to the means for creating a hollow, for example to the supporting frame 6 and/or to the above described counter-die 3a, 3b, 4, such means can be shaped according to an advantageously simple and cost effective shape.

Due to the method according to the present invention, the deformation of the plate 5 can be advantageously carried out and entirely completed during the printing step on the die 2. A disadvantageous step of pre-forming the plate 5 according to a geometry adapted to its arrangement on the die 2 is therefore avoided and, at the same time, additional machining on the product upon the deformation step is not required.

The method for the production of reflecting mirrors in a concentrating solar plant of Fresnel type, according to a particular aspect of the present invention, thus provides the subsequent step of arranging, over the die 2 also referring to figure 3, the single plate 5 coupled -i.e. preferably made integral- to the counter-die 3a, 3b, 4 and/or to the supporting frame 6, in substantially not-deformed, i.e. preferably flat, condition and in such a way that its own reflective surface is facing towards, and partially rested on, the die 2. Note that, according to a particular embodiment of the method of the present invention, herein not described, the coupling of the single plate 5 to the die 2 can be carried out with the only coupling of the counter-die 3a, 3b, 4, to the plate 5, without necessarily the presence of the supporting frame 6, as well as, in an alternative implementation of this method, the single plate 5 can be coupled only to a particular supporting frame 6, in this case having a substantially box-shaped and provided with the afore mentioned through hole 8, the use of the counter-die 3a, 3b, 4 not being required. Therefore, according to such alternative embodiments of the method according to the present invention, the counter-die 3a, 3b, 4 or the supporting frame 6 constitute the afore said means for defining the hollow 7, respectively.

The following steps of the method herein described, also referring to figures 4 and 5, provide a plastic filling material 9 being injected into the hollow 7, through the through hole 8, in a fluid or fluidized state, which should be able to expand within the hollow 7 itself in order to switch the plate 5 from its own not-deformed, and partially engaging the die 2, condition to a position totally engaging the reflective surface against the die 2 itself so that to form the only curvature axis of the mirror 1. The plastic filling material 9, for example constituted of a polyurethane (PUR) preferably with density comprised between 36 and 50 Kg/m³, injected in its own molten state, should have the characteristic to be adhesive at least to the single plate 5, and in the herein described method, also to the supporting frame 6, preferably during its own solidification.

It is not needed, on the other side, in the particular embodiment of the method of this invention here described, that the plastic filling material 9 adheres to the inner walls of the counter-die 3a, 3b, 4, which have thus to be substantially refractory to the adhesion of the material 9 (for example PUR).

Note that, for the realization of the method according to the present invention, any other filling material 9 can be used which has the characteristic of being able to be injected in a fluid, or fluidized, state also by an appropriate inert operating fluid, within the afore said hollow 7 and which, at least during its own solidification, adheres at least to the plate 5.

Preferably, such a filling material 9 is constituted of a foaming material, in order to result, once solidified, particularly light, besides assuring an optimal filling of the hollow 7 between the supporting frame 6 and the single deformed plate 5.

The solidification of the filling material 9 (step (g)), which in the case of use of a PUR or any thermoplastic material, is simply carried out by cooling, of course depends on the used material 9, which alternatively can be a thermosetting plastic material, thus solidified by high temperature heat intake, or a polymeric material that can be solidified by cross-linking, for example obtained with a chemical catalyst. At the end of the solidification, and possible foaming, of the filling material 9, during which the originally flat plate 5 is kept deformed on the die 2 by the same material 9, the single plate 5 can be therefore drawn out (step (h)) from the die 2 and the counter-die 3a, 3b, 4, joined to its own supporting frame 6 by the same material 9, and kept in the deformed configuration given by the die 2, in case the plate 5 did not undergo a plastic deformation during the previous printing step, still due to the filling material 9 conveniently solidified.

As mentioned, since the die 2 has a single curvature axis, also the mirror 1, i.e. the final product, has a single curvature axis, which provides the mirror 1 with the typical elongated concave configuration ("manger-like").

Furthermore, the adhesion of the filling material 9 both to the frame 6 and to the plate 5, and its solidification, allow not only to keep the reflective plate 5 in the correct curvature, given by the die 2, but also to retain the frame 6 and the plate 5 itself substantially permanently joined.

Therefore, as visible in figures 6 and 7, from the above described method a reflecting mirror 1 in a single piece is obtained, comprising a single plate 5, provided with an outer reflective surface and shaped according to a desired geometry, joined to a supporting frame 6 due to a filling material 9, preferably constituted of a foamed plastic material.

In case of use of closing heads in conjunction with a supporting frame 6 comprising a substantially thin U-shaped profile plate, as mentioned above, such heads have to be adhesive as well to the plastic filling material 9, so that to be joined both to the supporting frame 6 and to the single reflective plate 5, when such a plastic filling material 9 is solidified.

Such heads, not shown, can be conveniently shaped in order to interface the mirror 1 with the so obtained respective supporting frame 6, with possible means for handling the mirror 1 present in the solar plants of thermal type, in order to allow the same mirror 1 to follow the relative position of the sun.

Note that, in case the method according to the present invention does not provide the use of a supporting frame 6, at the end of the injecting and solidifying steps of the filling material, after the counter-die 3a, 3b, 4 has been removed, the drawing out of a reflecting mirror 1 would be obtained with its respective single plate 5 retained in its desired deformed configuration by the filling material 9, which would also constitute a support for such a reflective plate 5.

In case an alternative embodiment of the method according to the present invention would not provide the use of a counter-die 3 a, 3b, 4, but only the use of a supporting and conveniently configured frame 6, at the end of the above described injecting and solidifying steps of the material 9, a reflecting mirror 1 would be obtained, similar to that illustrated in figures 6 and 7 here attached, but provided with a supporting frame 6 of box-shaped type.

By way of example, the above described method can be used for the realization of a mirror for thermal solar plants of Fresnel type, starting form a single flat glass plate, with dimensions 0.7 x 5 m, having a silver reflective layer of 3 mm thickness, to be curved with radius of curvature of 18000 mm, and from a frame made of zinc-coated plate with 0.6 mm thickness, by the use of foamed polyurethane with about 40 Kg/m³ density, as a filling material.

Claims

1. Method for the production in a single piece of a reflecting mirror for a concentrating solar plant of the Fresnel type, said mirror being provided with only one curvature axis, comprising the steps of:

a. preparing a single plate of a material that is at least elastically deformable,, so that said plate is provided with at least one optically reflective surface;

c. prearranging means for defining a hollow with said single plate; said single plate partially delimiting said hollow, and said means being provided with at least one through hole of fluidic communication;

d. coupling, substantially by sealing, said means for defining a hollow to said single plate, said plate being in its own substantially not - deformed condition;

e. joining said single plate of deformable material in a substantially not - deformed condition, coupled with said means for defining a hollow, to said die, with said at least one optically reflective surface partially engaging said die;

f. injecting into said hollow, through said at least one through hole, at least one plastic filling material in a fluid, or fluidized, state, in order to move said at least one reflective surface from a position partially engaged with said die to a position totally engaged with said at least one reflective surface against said die; said at least one plastic filling material being adhesive, at least when solidified, to said single plate;

g. solidifying said at least one plastic filling material;

h. drawing out from said die said single plate permanently deformed as a mirror for a Fresnel solar plant.

2. Method according to claim 1, wherein said means for defining a hollow comprise a supporting frame for said single plate; said supporting frame being able to be coupled substantially by sealing to said single plate, when said single plate is in its own not - deformed condition, in order to form said hollow, said frame being provided with at least one hole of fluidic communication; and wherein said at least one plastic filling material is adhesive, at least when solidified, also to said supporting frame.

3. Method according to claim 1, wherein said means for defining a hollow comprise a box-shaped counter-die, connectable substantially by sealing with said die and/ or with said single plate, said counter-die comprising at least one through hole of fluidic communication; and wherein said step d) of coupling said means for defining a hollow to said single plate comprises the step of:

d.l) putting said counter-die in a sealed coupling with said single plate to define said hollow, said plate being in its own substantially not - deformed condition.

4. Method according to claim 3, wherein said means for defining a hollow comprise a supporting frame for said single plate; said supporting frame being able to be coupled to said single plate; and wherein said counter-die and said supporting frame are in fluidic communication one with the other; the method comprising, before said step of d.l) putting said counter-die in a sealed coupling with said die and said single plate, the step of:

d.0) coupling said supporting frame with said plate of deformable material, said plate being in its own substantially not-deformed condition;

wherein said at least one plastic filling material is also adhesive to said frame; and wherein said step of h) drawing out said single plate comprises the step of drawing out also said supporting frame, joined to said single plate by said solidified plastic filling material.

5. Method according to any one of the preceding claims, characterized in that said step of g) solidifying said at least one plastic filling material is obtained by cooling.

6. Method according to any one of the preceding claims, characterized in that said at least one plastic filling material is a thermoplastic material.

7. Method according to claim 6, wherein said thermoplastic material is a polyurethane.

8. Method according to claim 7, wherein said polyurethane (PUR) has a density comprised between 36 and 50 Kg m .

9. Method according to claim 6, 7 or 8, wherein said thermoplastic material is injected at its melting point.

10. Method according to any one of the preceding claims, characterized in that said single plate of deformable material comprises at least one layer of metal material.

11. Method according to claim 2 or 4, characterized in that said supporting frame comprises a plate with a substantially thin U-shaped profile made of metal and/or plastic material.

12. Method according to claim 11, wherein said at least one supporting frame comprises as well at least one closing head connectable to at least one end of said plate with a thin profile, not intended to be engaged with said single plate with a reflective surface.

13. Method according to any one of claims 2, 4, 11 or 12, wherein said supporting frame comprises knurled or cross-linked or with high roughness surfaces.

14. Reflecting mirror for concentrating solar plants of the Fresnel type, having only one curvature axis, obtained by the method for the production of a reflecting mirror according to one or more of the preceding claims, comprising a single plate with a reflective surface, said plate being bonded to a solidified plastic material.

15. Reflecting mirror according to claim 14, comprising a supporting frame joined with said single plate with a reflective surface by said solidified plastic material, bonded to said single plate and said supporting frame.