Parabolic trough solar collector

Abstract

The invention relates to a parabolic-cylindrical solar collector (1) comprising: - a parabolic-cylindrical reflector (200) consisting of a matrix array of reflective tiles with a parabolic cross-section (210), arranged in rows and columns; - an absorber tube arranged along the linear focus of said reflector and inside which a heat transfer fluid circulates; - a frame (100) supporting said absorber tube and said reflector, said frame comprising an elongated central torsional body (110) oriented parallel to the linear focus of said reflector and a plurality of curved support arms (120) extending symmetrically in pairs on either side of this elongated central body and to which said reflective tiles are fixed; characterized in that each of said reflective tiles comprises a concrete base covered on its concave upper face by a mirror. Figure to be published with the abbreviation: Fig. 2

Description

Title of the invention: Cylindrical-parabolic solar collector technical field

[0001] The present invention relates to the field of solar energy capture and more particularly to a parabolic-cylindrical type solar collector. Previous technique

[0002] Due to its abundant availability, its renewable nature, its reduced environmental impact compared to fossil fuels and its ability to be used in remote locations or places not connected to the electrical grid, solar energy has many advantages.

[0003] Among the various technological solutions aimed at capturing some of this energy, solar collectors make it possible to capture solar radiation and transmit its thermal energy to a heat transfer fluid in the form of heat.

[0004] In particular, cylindrical-parabolic type collectors are known which include a cylindrical-parabolic reflector focusing the captured light rays towards an absorber tube arranged along the linear focus of this reflector.

[0005] The tube contains a heat transfer fluid, usually oil or water, which circulates to absorb the heat generated by sunlight. The absorbed heat can then be used to produce steam, which can be used to generate electricity using a steam turbine or to provide heat to industrial processes or heating systems.

[0006] The main advantage of parabolic-cylindrical collectors lies in their ability to concentrate sunlight on a narrow linear area, which allows for higher temperatures and better solar energy conversion efficiency.

[0007] Furthermore, parabolic trough collectors can be used in a modular manner and combined to form large-scale solar collection assemblies capable of producing a significant amount of electricity or heat.

[0008] Such a cylindrical-parabolic type collector classically comprises a frame supporting the absorber tube and a matrix network of reflective tiles with a cross-section in a portion of a parabola, arranged in rows and columns so as to constitute the cylindrical-parabolic reflector.

[0009] As disclosed, for example, by document WO 2013 / 084016 A1, the support frame generally comprises a central torsionally elongated body oriented parallel to the linear focus of the parabolic cylindro-reflector and enabling limit reflector deformations due to torsional stresses caused by its own mass and external forces such as wind.

[0010] Made of galvanized steel or aluminium, this elongated central body is generally in the form of a cylindrical tube or a tubular frame.

[0011] Such a support frame also includes a plurality of curved support arms extending symmetrically in pairs on either side of this elongated central body in directions perpendicular to the linear focus of this reflector and on which the reflective slabs are fixed.

[0012] Made for example from welded metal tubes or from a stamped sheet metal side, these arms make it possible to distribute the load and rigidity evenly along the surface of the reflector.

[0013] The chassis is further generally mounted pivoting around a longitudinal axis parallel to the linear focus of the parabolic cylindro-reflector by means of pylons rigidly anchored to the ground via concrete foundations.

[0014] Reflective slabs are classically formed by a mirror comprising a "thick" glass substrate (thickness of at least 4 millimeters) so as to present a certain resistance to deformation, as well as a reflective layer generally of silver applied against the convex underside of this substrate.

[0015] Generally fixed at four points to two adjacent support arms, these reflective slabs unfortunately tend to deform at their four corner areas in strong wind, which leads to their defocusing and a significant reduction in the solar energy absorbed by the heat transfer fluid circulating in the absorber tube, which can lead to the solar collector stopping.

[0016] It is also known to produce these reflective slabs from an aluminium sheet on which a reflective polymer film is glued, these sheets then being mounted to slide along curved guide rails provided on the support frame so as to give them a parabolic cross-section profile.

[0017] Unfortunately, these reflective aluminium slabs also tend to warp, which also leads to problems with focusing the light rays onto the absorber tube.

[0018] In addition, these reflective tiles are particularly difficult to install because they require, in particular, the use of lifting platforms to support the aluminum rolls.

[0019] We also know of reflective slabs developed by the German company ToughTrough® and made up of a reflective coating based on a "thin" glass substrate of about one millimeter thick covering a polyurethane foam core on the back of which is affixed a composite back layer made of steel and glass fibers.

[0020] The German company Solariite® offers reflective slabs made of a hollow base in composite resin / fiberglass material, this base being filled with a foam core and covered with a mirror based on a "thin" glass substrate.

[0021] These latter types of reflective slabs made of composite material are unfortunately particularly expensive to produce. Furthermore, due to their relatively low mass, the anchoring pylons of collectors equipped with these slabs must be combined with more massive concrete foundations to ensure adequate anchoring to the ground.

[0022] Recently, a new type of parabolic trough solar collector was developed by an international consortium within the framework of the CONSOL® project. This collector comprises a support frame consisting of a one-piece parabolic trough concrete shell on which rests a reflector made of several flexible aluminum sheets coated with a reflective coating and glued to the concave upper surface of this support shell.

[0023] Although this latter solution may seem attractive at first glance, the construction of such a concrete shell proves to be particularly complex and costly to implement. Furthermore, due to its size and mass, this shell cannot be transported and must therefore be constructed on site. Description of the invention

[0024] The present invention therefore aims to remedy at least partially the aforementioned drawbacks.

[0025] To this end, it proposes a parabolic-cylindrical solar collector comprising: - a parabolic cylindrical reflector consisting of a matrix network of reflective tiles with a parabolic cross-section, arranged in rows and columns; - an absorber tube arranged along the linear focus of said reflector and inside which a heat transfer fluid circulates; - a frame supporting said absorber tube and said reflector, said frame comprising an elongated central torsion body oriented parallel to the linear focus of said reflector and a plurality of curved support arms extending symmetrically in pairs on either side of this elongated central body and to which said reflective slabs are attached.

[0026] According to the invention, each of said reflective slabs comprises a concrete base covered on its concave upper face by a mirror.

[0027] Such a conformation of the reflective slabs forming the reflector ensures excellent mechanical rigidity, making it possible to avoid any risk of deformation and defocusing even in the event of strong winds.

[0028] Moreover, the cost price of the parabolic trough according to the invention is particularly reasonable in comparison in particular to parabolic troughs whose reflector is made up of slabs with a base made of composite material.

[0029] Finally, due to the greater mass of its concrete base slabs, the parabolic cylindrical collector naturally has better ground anchoring, which makes it possible to reduce the volume and mass of the buried foundations.

[0030] For reasons of cost and ease of manufacture, the base of each said reflective slab preferably has a flat underside.

[0031] In order to limit the mass of the reflective slabs, their base advantageously has a thickness of less than or equal to 50 millimeters at the thinnest area, this thickness preferably being between 30 and 40 millimeters.

[0032] In order that these reflective slabs exhibit excellent resistance to bending, their base is preferably made of reinforced concrete.

[0033] In order to avoid any risk of corrosion, it is also possible to make these bases alternatively out of fiber-reinforced concrete.

[0034] According to a first preferred embodiment, the mirror of each said reflective slab preferably comprises a transparent substrate covered on its convex underside with a reflective layer

[0035] This transparent substrate is preferably made of glass because of its excellent light transmission combined with a controlled cost price.

[0036] In order to have a certain flexibility allowing it to be cold-bent, this transparent substrate advantageously has a thickness of less than or equal to two millimeters.

[0037] According to a second preferred embodiment, the mirror of each said reflective slab is constituted by a reflective coating directly affixed against the concave upper face of said base.

[0038] In order to enable the reflector to follow the sun in its daily course, the frame is advantageously mounted pivoting around a longitudinal axis parallel to the linear focus of said reflector by means of two pylons arranged near the two longitudinal ends of this frame.

[0039] Furthermore, the height of said pylons defining the distance between the ground and said longitudinal pivot axis of said chassis is preferably defined so as to allow the latter to pivot through 360°.

[0040] Finally, this pivoting articulation of said chassis vis-à-vis said pylons is ensured for example by means of two cylindrical pins projecting at the two longitudinal ends of said elongated torsion body and cooperating with two rotating joints arranged at the tops of said pylons.

[0041] The invention also relates in a second aspect to a solar collection assembly formed of at least one alignment of several such parabolic-cylindrical solar collectors. Brief description of the drawings

[0042] The description of the invention will now be continued by a detailed description of an example embodiment, given below by way of illustration but not limitation, with reference to the accompanying drawings, on which: - [Fig.1] is a perspective view of a parabolic cylindrical solar collector according to the invention; - [Fig. 2] shows an exploded perspective view from another angle of the parabolic-cylindrical solar collector according to the invention; and - [Fig.3] represents a cross-sectional view of one of the reflective slabs forming the parabolic cylindro-reflector. Description of the implementation methods

[0043] Figures 1 and 2 represent a parabolic cylindrical solar collector 1 according to the invention.

[0044] An orthogonal frame XYZ comprising three axes perpendicular in pairs is defined with respect to this solar collector 1, namely: - an X axis, defining a longitudinal, horizontal direction, parallel to the linear focus of this solar collector 1; - a Y-axis, defining a horizontal, transverse direction, which, together with the X-axis, defines a horizontal XY plane, and - a Z-axis, defining a vertical direction, perpendicular to the horizontal XY plane.

[0045] In the remainder of the description and with reference to the frame of reference defined above, the terms "Longitudinal" or "longitudinally" will refer to a direction parallel to the X axis, the terms "transverse" or "transversely" will refer to a direction parallel to the Y axis, and the terms "vertical" or "vertically" will refer to a direction parallel to the Z axis.

[0046] On the other hand, the terms "front" and "rear" will be used to specify the longitudinal positioning of certain elements relative to the orientation of the X axis. Similarly, the terms "upper" and "lower" will be used to specify the relative position of certain elements relative to the orientation of the Z axis.

[0047] The terms "external" and "internal" will be used to define the relative position of an element with reference to the median vertical longitudinal plane of the solar collector 1. The element closest to this plane will thus be described as internal, as opposed to the other element further from this same plane, which will be described as external.

[0048] Finally, the term "substantially" indicates that a slight deviation from a predetermined nominal orientation is permitted, while remaining within the scope of the invention. For example, "substantially vertical" indicates that a deviation of approximately 10° to 20° from a strictly vertical orientation is permitted within the scope of the invention.

[0049] With reference to these figures 1 and 2, the parabolic-cylindrical solar collector 1 comprises a frame 100 supporting a parabolic-cylindrical reflector 200 and an absorber tube 300 extending along the linear focus of this reflector 200 in order to receive the light rays captured and reflected by the latter.

[0050] Inside this absorber tube 300, a heat transfer fluid circulates, typically consisting of oil or water and designed to absorb the heat generated by the light rays striking this tube.

[0051] The chassis 100 conventionally comprises an elongated central torsional body in the form of a beam 110, oriented parallel to the linear focus of the cylindrical-parabolic reflector 200 and allowing to limit the deformations of this reflector 200 due to the torsional forces which it undergoes due to its own mass and external forces such as wind.

[0052] According to alternative embodiments not shown, the elongated central body 110 of the support chassis 100 can be shaped differently, for example taking the form of a cylindrical tube or a tube with a polygonal cross-section (for example, square or hexagonal).

[0053] This chassis 100 also includes a plurality of curved lateral support arms 120 extending symmetrically in pairs on either side of the elongated central torsion body 110 to which they are rigidly fixed and in directions perpendicular to the linear focus of the reflector 200.

[0054] In this case, these support arms 120 are sixteen in number (eight on each side of the elongated central torsion body 110) being distributed at regular intervals along the latter.

[0055] The support frame 100 is further mounted pivoting around a longitudinal axis A parallel to the linear focus of the parabolic cylindro-reflector 200 by means of two pylons 400 arranged near the two longitudinal ends of this frame 100.

[0056] As illustrated by [Fig. 2], the pivoting articulation of this support frame 100 vis-à-vis these two pylons 400 is advantageously ensured by means of two cylindrical metal pins 111 protruding from the two longitudinal ends of the elongated central torsion body 110 and cooperating with two rotating joints 410 arranged at the tops of the pylons 400.

[0057] Each pin 111 extends in this case from a respective metal plate 112 fixedly attached by screwing onto a longitudinal end of the elongated central torsion body 110.

[0058] According to alternative embodiments not shown, these transmission means may differ by being, for example, of the worm gear type.

[0059] The height of the pylons 400 defining the distance between the ground and the pivot axis A of the chassis 100 (and therefore of the reflector 200) will advantageously be defined so as to allow this reflector 200 to pivot through 360° in order to follow the sun in its daily course and thus capture solar radiation under optimal conditions.

[0060] As illustrated by [Fig.2], the parabolic cylindrical reflector 200 consists of a matrix array of nxm reflective tiles 210 with a section in a portion of a parabola, arranged in n longitudinal lines parallel to the linear focus of this reflector 200 and m transverse columns.

[0061] Advantageously having a longitudinal dimension at least twice greater than its transverse dimension, each reflective slab 210 is fixed to two adjacent support arms 120.

[0062] In the embodiment illustrated in the figures, the reflector 200 consists of twenty-four reflective slabs 210 arranged in six longitudinal lines (n equal to 6) and four transverse columns (m equal to 4), these slabs 210 each having dimensions of about three meters long by 0.9 to 1.25 meters wide, so that this reflector 200 extends longitudinally over about twelve meters with a transverse opening of about six meters.

[0063] According to alternative embodiments not shown, the dimensions of each reflective tile 210, as well as the number of rows n and / or columns m, may differ depending, in particular, on the desired dimensions of the reflector 200 in length and / or opening. It should be noted, with reference to [Fig. 2], that the width of these tiles 210 increases advantageously with their transverse spacing relative to the elongated central torsional body 110.

[0064] According to the invention and as illustrated in the section view of [Fig.3], each reflective slab 210 comprises a concrete base 211 covered on its concave upper face by a mirror 212.

[0065] For reasons of ease and cost of manufacture, the base 211 has a flat lower face so as to allow the concrete to be poured into a formwork open at the top and whose convex lower face has a profile in the form of a portion of parabola corresponding to the one we wish to give to the concave upper face of this base 311.

[0066] In order to limit the mass of the reflective slabs 210, this base 211 will advantageously have at its thinnest area a thickness e less than or equal to 50 millimeters and preferably between 30 and 40 millimeters.

[0067] Furthermore, and in order that these reflective slabs 210 exhibit excellent resistance to bending, their base 211 will preferably be made of reinforced concrete with, for example, stainless steel or galvanized steel reinforcement to protect it from corrosion.

[0068] In order to avoid any risk of corrosion, it is also possible to make these bases 211 in fiber-reinforced concrete although this may negatively impact the cost price and the resistance to bending.

[0069] Fixedly affixed by gluing to a corresponding base 211 by suitable means (for example epoxy or polyurethane glue or even double-sided adhesives), the mirror 212 of each reflective slab 210 advantageously comprises a transparent substrate covered on its convex underside with a reflective layer for example of silver.

[0070] Preferably made of glass due to its excellent light transmission combined with a controlled cost price, this transparent substrate advantageously has a thickness less than or equal to two millimeters and even more advantageously less than or equal to one millimeter.

[0071] The use of such a transparent “thin” glass substrate with a certain degree of flexibility thus allows its cold bending by gravity, which proves to be particularly advantageous from an economic point of view.

[0072] The mirrors 212 may also include at least one protective layer, in particular a copper or tin layer applied against the reflective layer so as to prevent its tarnishing and to allow the bonding of this mirror 212 against the base 211.

[0073] According to alternative embodiments, the mirrors 212 of the reflective slabs 210 can be constituted differently.

[0074] Each mirror 212 can thus comprise an aluminum substrate covered on its concave upper face with a thin reflective layer deposited, for example, by a physical vapor deposition process (commonly referred to by the English acronym PVD for "Physical Vapor Deposition"). One or more protective layers can also be applied to this reflective layer.

[0075] This thin reflective layer can for example be made up of a reflective polymer film such as the "Solar Mirror Film 1100" produced by the American company 3M®.

[0076] According to another embodiment, the mirror 212 of each reflective slab 210 can be constituted by a reflective coating directly affixed against the concave upper face of the base 211 of this slab 210.

[0077] Many embodiments are of course conceivable and it is recalled in this regard that the present invention is not limited to the embodiments described and represented, but also encompasses all the execution variants within the reach of a person skilled in the art.

Claims

Demands

1. Cylindrical-parabolic type solar collector (1) comprising: - a cylindrical-parabolic reflector (200) consisting of a matrix array of reflective tiles with a cross-section in a portion of a parabola (210), arranged in rows and columns; - an absorber tube (300) arranged along the linear focus of said reflector (200) and inside which circulates a heat transfer fluid; - a frame (100) supporting said absorber tube (300) and said reflector (200), said frame (100) comprising an elongated central torsional body (110) oriented parallel to the linear focus of said reflector (200) and a plurality of curved support arms (120) extending symmetrically in pairs on either side of this elongated central body (110) and to which said reflective slabs (210) are fixed;characterized in that each of said reflective slabs (210) comprises a corresponding concrete base (211) covered on its concave upper face by a mirror (212).

2. Solar collector (1) according to claim 1, characterized in that the base (211) of each said reflective slab (210) has a flat lower face.

3. Solar collector (1) according to any one of claims 1 or 2, characterized in that the base (211) of each said reflective slab (210) has at its thinnest area a thickness (e) less than or equal to 50 millimeters.

4. Solar collector (1) according to claim 3, characterized in that said thickness (e) is between 30 and 40 millimeters.

5. Solar collector (1) according to any one of claims 1 to 4, characterized in that the base (211) of each said reflective slab (210) is made of reinforced concrete.

6. Solar collector (1) according to any one of claims 1 to 4, characterized in that the base (211) of each said reflective slab (210) is made of fiber-reinforced concrete.

7. Solar collector (1) according to any one of claims 1 to 6, characterized in that the mirror (212) of each said reflective slab (212) comprises a transparent substrate covered on its convex underside with a reflective layer.

8. Solar collector (1) according to claim 7, characterized in that said transparent substrate is made of glass.

9. Solar collector (1) according to any one of claims 7 or 8, characterized in that said transparent substrate has a thickness less than or equal to two millimeters.

10. Solar collector (1) according to any one of claims 1 to 6, characterized in that the mirror (212) of each said reflective slab (212) is constituted by a reflective coating directly affixed against the concave upper face of said base (211).

11. Solar collector (1) according to any one of claims 1 to 10, characterized in that said frame (100) is mounted pivoting about a longitudinal axis (A) parallel to the linear focus of said reflector (200) by means of two pylons (400) arranged near the two longitudinal ends of this frame (100).

12. Solar collector (1) according to claim 11, characterized in that the height of said pylons (400) defining the distance between the ground and said longitudinal pivot axis (A) of said chassis (100) is defined so as to allow the latter to pivot through 360°.

13. Solar collector (1) according to any one of claims 11 and 12, characterized in that the pivoting articulation of said chassis (100) vis-à-vis said pylons (400) is ensured by means of two cylindrical pins (111) projecting at the two longitudinal ends of said elongated torsion body (110) and cooperating with two rotating joints (410) arranged at the tops of said pylons (400).

14. Solar collection assembly consisting of at least one alignment of several parabolic-cylindrical solar collectors according to any one of claims 1 to 13.

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