WO2018154497A1

WO2018154497A1 - Concentrated solar system

Info

Publication number: WO2018154497A1
Application number: PCT/IB2018/051133
Authority: WO
Inventors: Giovanni Murgia
Original assignee: Suberia Systems Srl
Priority date: 2017-02-27
Filing date: 2018-02-23
Publication date: 2018-08-30
Also published as: IT201700021827A1

Abstract

Concentrated solar system (100) comprising: a conversion apparatus (110), wherein a heat transfer fluid flows in a duct and absorbs thermal energy irradiated onto said duct; a concentration structure (120) adapted to receive solar radiations and convey them onto said conversion apparatus (110), thus supplying said thermal energy. Said concentration structure (120) comprises: a plurality of reflective panels (130); a modular support structure (140) for said reflective panels (130). Each module (1) of said modular structure (140) comprises first and second frames, each one comprising: a pair of uprights (2); a crossmember (3); a pair of upper beams (5), each one extending from one end of said crossmember (3) to join with the other upper beam at the opposite end, so as to form, together with said crossmember (3), a substantially triangular structure. Each module (1) of said modular structure (140) further comprises a pair of longitudinal beams (4), each longitudinal beam (4) connecting corresponding ends of said crossmembers (3), so that said pair of longitudinal beams (4) form, together with said crossmembers, a substantially rectangular structure. Each module (1) of said modular structure (140) finally comprises a top beam (6) supported by the upper ends of the upper beams (5). Each one of said uprights (2), crossmembers (3), upper beams (5), longitudinal beams (4), top beams (6) is provided as a cut-to- size metal tube having a circular cross-section.

Description

CONCENTRATED SOLAR SYSTEM'

DESCRIPTION

[TECHNICAL FIELD]

The present invention relates to a concentrated solar thermal system.

[PRIOR ART]

In CSP (Concentrated Solar Power) and CST (Concentrated Solar Thermal) systems, solar concentration is achieved by means of an optical system consisting of reflecting surfaces moved by suitable drives that allow them to follow the apparent motion of the sun and to direct the solar radiation beams, via the optical reflection mechanism, towards a linear receiver, e.g. linear parabolic troughs and Fresnel reflectors, or towards a punctiform receiver, e.g. solar tower or solar dish systems.

Linear parabolic concentrators are made up of long lines of linear parabolic reflectors that concentrate the solar radiation incident on a linear receiver integral with the parabolic reflector and positioned along the latter' s focal axis. Such linear receiver comprises a duct, referred to as receiver or absorber tube, into which a thermovector fluid flows, which is then heated and transfers heat to a thermoelectric plant for power generation or to another plant directly using this thermal energy.

In Fresnel reflector systems, solar concentration is achieved by means of long parallel rows of reflectors equidistant from the ground and moved by suitable drives. Fresnel reflectors have a flat or slightly curved geometry for better focusing capability. The linear receiver, which is similar to the one used in parabolic reflectors, is fixed and is not integral with the optical system that concentrates the solar radiation.

In solar tower systems, an optical system, typically consisting of individually driven flat square mirrors capable of turning about two perpendicular axes, directs the reflected beam of solar radiation towards a punctiform receiver located at a height of several tens of metres.

Just like solar tower systems, solar dish systems concentrate the solar radiation towards a punctiform receiver. In this case, however, the punctiform receiver is located at the geometric focus of the optical system and is integral therewith. In solar dish systems, the dish is sometimes made up of a number of smaller reflecting elements, mechanically integral with one another and driven by a single biaxial drive.

Notwithstanding the clear differences in the configurations of the various optical systems employed in CSP and CST systems, they must have some fundamental characteristics, such as:

(i) high reflectivity of the reflecting surfaces,

(ii) high geometric precision of the reflecting surface,

(iii) high mechanical rigidity,

(iv) low weight,

(v) long life, which must be aligned with the lifetime of CSP and CST systems, i.e. approx. 25 years, and

(vi) low cost.

The efficiency of a concentrated solar thermal system as a whole mainly depends on the optical performance of the reflector, i.e. its capability of effectively concentrating the solar radiation incident on the surface of the receiver.

To achieve effective concentration, it is not sufficient that the mirror surfaces are highly reflective, rigid and precisely curved, since they must also be positioned correctly and be capable of accurately following the apparent motion of the sun (solar tracking) . In order to obtain such characteristics, the mechanical structure that supports the reflective panels, briefly referred to as support structure, must be sufficiently rigid from a structural viewpoint, in order not to jeopardize the optical-geometrical precision in strong-wind conditions or during the movements occurring while tracking the sun or, more simply, because of the elastic deformations caused by the weight of the panels themselves.

A general indication about the precision required from a metallic support structure for solar concentrators, expressed in terms of angular and linear offsets relative to the theoretical geometric positions (i.e. those indicated in the working drawings), is, respectively, 1 mrad (milliradians ) for angular offsets and approx. lmm/m (millimetres per metre) for linear ones. This implies that the various elements constituting the metallic support structure must be assembled in an accurate manner, with small position tolerances, and by using high-precision mechanical joints.

Another fundamental property of the support structure is its service life, i.e. its capability of keeping its mechanical properties and its performance unchanged throughout the life of the solar system.

Finally, since this is a component to be used within a technology aimed at energy production from renewable sources, another important characteristic is a low environmental impact, as concerns both its production and its disposal at the end of its service life. Therefore, the metallic support structure, which, together with the reflective panels, is the biggest and heaviest component of a concentrated solar system, should preferably be made of recyclable and/or renewable materials that are safe for both the health and the environment .

Fabrication of metallic structural elements that can be assembled with high precision to form rigid, long-lasting and geometrically precise structures is possible through the use of different techniques, most of which imply, however, slow and costly processing, such as milling and drilling by means of numerical-control machine tools, grinding, turning, etc.

The use of the above-mentioned metal processing techniques would not make it possible to meet the extremely stringent cost restraints of CSP and CST systems. In fact, as aforesaid, the support structure is one of the two biggest components of a CSP/CST system - the other being the reflector assembly - and its cost strongly affects the total cost of this technology. The necessity of limiting the cost of the support structure, while still meeting the above-described requirements of mechanical strength, precision, duration and installation simplicity, is what makes it difficult to design an effective and competitive solution for support structures of CSP/CST systems. Moreover, the low cost of the metal structure must not affect the basic requirements of mechanical strength, life and precision, nor can it be compensated for by complex assembling and processing during the implementation stage. The implementation cost of the metal structure must be limited to a fraction of the cost of the finished material, e.g. 30%-50%.

To make a metallic support structure for a concentrated solar system with Fresnel mirrors that at the same time possesses all of the above-mentioned mechanical, geometrical, physical, economical and environmental characteristics required by the application is therefore a problem that cannot be easily solved.

[OBJECTS AND SUMMARY OF THE INVENTION]

It is the object of the present invention to provide a support structure for solar concentrators with Fresnel mirrors to be used in CST and CSP systems, which can ensure sufficient mechanical strength (to traction, compression, torsion, shear) and sufficient fatigue strength, high geometric precision for assembly, low weight, a sufficiently long service life, installation simplicity, and low costs of the semifinished products and finished components.

In order to obtain all of the above-mentioned qualities, three implementation choices have been made, which differentiate said technical solution from what has been so far proposed in similar CSP/CST systems:

1) the metallic support structure is made up of tubes having a circular cross-section cut to size in the transverse direction (i.e. orthogonally to the tube axis);

2) tube-to-tube joints are effected by means of commercial joints made of malleable cast-iron secured by means of a set screw, with the only exception of coaxial tube-to-tube joints, which are preferably made by using a commercial friction joint made of cold-pressed steel;

3) the components of the metal structure (tubes and joints) are subjected to no additional mechanical processing neither before nor during installation, besides the cutting to size specified in 1) .

Since cutting to size is a very fast and simple operation, the final price of the finished material (the cut-to-size tube) turns out to be only marginally higher than the price of the initial semifinished product (the tube not yet cut) . In addition, the elimination of any further mechanical machining during the installation stage, such as welding, drilling, boring, etc., simplifies the assembly work and keeps the installation costs low. Finally, the circular tubular sections offer, compared to metal sections having different geometric cross-sections, higher inertia to lateral deflection (peak load) relative to the axis in any direction. This allows achieving the target performance in terms of mechanical strength, the selected material being the same, by using lighter, and hence less expensive, elements. Assuming the above-mentioned design constraints, a structural solution has been conceived which allows the metallic support structure to achieve also the other objects of the invention, i.e.: high mechanical strength, fatigue strength, geometric precision, long life, low weight, recyclability and low disposal costs.

The invention relates to a concentrated solar system equipped with a modular tubular metallic support structure, the base module of which consists of two simple tubular frames formed by two uprights and a crossmember, rigidly connected at the frame nodes by two longitudinal beams to form a rectangular tubular structure with the uprights lying on the horizontal plane, i.e. the anchorage plane. At the nodes of said rectangular structure a triangular structure is connected, formed by two upper beams preferably of the same material and diameter as those of the beams of the rectangular frame .

The modular unity of the structure is completed by a top beam, i.e. a beam that is parallel to the horizontal anchorage plane, which connects the vertices of the triangular structures; said top beam is also made up of tubes having the same characteristics as the other beams described so far.

The support structure comprises metal tubes having a circular cross-section of various length and commercial joints made of malleable cast-iron or cold-pressed steel (such as, for example, scaffolding joints) . Tube-to- joint anchorage is effected by means of steel set screws, for joints made of malleable cast-iron, or by friction with fastening bolts, for joints made of cold-pressed steel. The tubes of the structure comprise the following preferred but non-exclusive properties: non-welded hollow steel tubes with a circular profile, preferably all having the same outside diameter of 48.3 mm or l'l/2 inches (i.e. the standard size of structural scaffolding tubes), protected against oxidation by galvanizing.

The material of the tubes is preferably galvanized, hot- rolled, fine-grain, non-alloy steel for structural use, but various non-alloy or alloy steel types can be used, with different grain sizes, subjected to forming and corrosion protection treatments, provided that all the tubular beams of the structure must have minimum mechanical characteristics (expansion, tensile strength, yield and resilience) to meet the design specifications. By way of example, aluminium tubes may be used instead of steel ones.

In the above-described support structure, the crossmembers (i.e. the base beams of the triangular structures) are the beams whereon the reflectors rest. More specifically, they support the bearings and/or the actuators that support the drive shafts of the solar tracking mechanism, whereon the reflectors are in turn integrally connected. In the apical part of the structure, the top beam supports the elements that receive the concentrated solar radiation. Said elements essentially consist of the evacuated receiver tube and the CPC (Compound Parabolic Concentrator) secondary reflector. The whole tubular structure further comprises some oblique reinforcement beams, called diagonal beams, that are mainly subjected to tensile or compressive strains according to the typical scheme of reticular structures. In particular, a diagonal beam connects each upright of the structure to the crossmember connected thereto. As aforementioned, the reflectors and the solar tracking mechanical assembly, i.e. most of the concentrator's weight, rest on the crossmember. Said diagonal element limits the inflection of the crossmember by countering the static thrusts (the weight of the reflectors) and the dynamic thrusts (wind pressure on the reflectors' surface) . The structure further comprises a diagonal beam that connects the crossmember to the upper beams. This diagonal element reduces the inflection of the upper beams. Other reinforcement diagonal tubular elements may also be included in the support structure, though not expressly described and illustrated herein.

The support structure module described so far can be further extended by adding two tubular beams, the function of which is to extend the crossmember. The two tubes are symmetrically anchored to the two upper beam-crossmember nodes and are oriented coaxially to the crossmember. The inflection of the extension beams is supported by the addition of two further diagonal tubes that connect said extensions to the upright adjacent thereto. The function of the extensions is to increase the length of the support base for the rows of Fresnel reflectors, so that a greater number of reflector rows can be housed in the support structure.

The modules can be replicated indefinitely along the longitudinal direction, i.e. along the direction of the top beam and of the longitudinal beams, up to the desired length of the row of the solar concentrator. At the beginning and at the end of the row of the solar concentrator, i.e. in its outermost modules, a reinforcement tube is added, which joins the connection node between the top beam and the outermost triangular structure to the support plane of the structure (where it will be anchored, by means of suitable hooks and/or flanges, to the foundation structure) . Said final beam increases the mechanical strength of the various triangular structures lying in succession along the entire concentrator row, as well as their resistance to deformations generated by strains in a direction parallel to the top beam.

The minimum precision required for cutting to size tubular sections may be +/- 1.00mm, although greater precision, around +/- 0.5mm, can be easily obtained even when using simple machine tools without numerical control. In order to avoid that assembling the structure might add further inaccuracy to that caused by the production tolerances of its components (the cut-to-size tubes and the joints), it is necessary and sufficient that all tubes are positioned "in abutment" in the joints, and that the set screws of the joints, if they can take two or more functionally equivalent positions, are oriented according to a predefined scheme. By following these simple guidelines during the assembly process, due to the composition of the intrinsic geometric constraints in the structure, the latter can be assembled quickly without requiring any further adjustment and/or setting, ensuring a positioning tolerance within +/- lmm/m. For instance, the conditions of perpendicularity between the longitudinal beam and the crossmember (i.e. the conditions of rectangularity of the structure) are imposed by the particular tube-to-tube joints positioned at the nodes of the rectangular frame, as will be further described in the detailed description of the invention. Should such a joint be unavailable and need to be replaced with two joints not ensuring mutual perpendicularity of the tubes connected thereto, the condition of perpendicularity can nevertheless be imposed through the use of assembly jigs. In the specific case mentioned above, a diagonal beam may be temporarily installed, arranged along the geometric diagonal of the rectangular frame, also made up of cut-to-size tubes and joints positioned "in abutment" at the head and tail of said tubes. Such a tubular structure can only be assembled when the longitudinal beams and the crossmembers are orthogonal to each other. Once the condition of orthogonality has been ensured, the positions of the beams are fixed by tightening the joints, and the diagonal beams acting as an assembly jig, positioned along the geometric diagonal of the frame, can then be removed.

The only tools necessary for assembling the structure are a hexagonal wrench for tightening the set screws of malleable cast-iron joints and a suitably sized wrench for the bolts of cold-pressed steel joints. Preferably, tightening should be effected by using a torque wrench, in order to apply the appropriate tightening torque to set screws and bolts.

The mechanical strength and fatigue strength of the structure depend on several factors including: diameter, thickness and material of the tubes and geometric characteristics of the structure (e.g. beam length, position of the tubes relative to the direction of the main strains, presence of diagonal reinforcement elements, etc.) .

The size of the structure is variable and is mainly determined by the width and number of supported rows of reflectors (and hence the effective aperture of the optical concentrator) . The material and diameter of the tubes being equal, the number of diagonal reinforcement elements will increase as a function of the dimensions of the structure module, and more specifically of the length of the crossmembers and longitudinal beams and the height of the top beam relative to the plane defined by the longitudinal beams and the crossmembers. The addition of further diagonal reinforcement elements to those already present in the above- described base module may be evaluated on the basis of the results of structural calculations made for a specific implementation during the design stage.

These and other objects are substantially achieved through a concentrated solar system as described in the appended claims .

[BRIEF DESCRIPTION OF THE DRAWINGS ]

Further features and advantages will become more apparent from the following detailed description of some preferred but non-limiting embodiments of the invention.

This description will refer to the annexed drawings, which are also provided merely as explanatory and non-limiting examples, wherein:

- Figure 1 shows an isometric perspective view of a support structure module included in a system according to the present invention;

- Figure 2 shows an isometric perspective view of the base of the module of Figure 1, wherein a diagonal beam is used during assembly in order to impose orthogonality of the sides of the quadrilateral;

- Figure 3 shows an isometric perspective view of the terminal module of a support structure according to the present invention;

- Figure 4 shows a perspective view and corresponding orthogonal sections of some details of Figure 1;

- Figure 5 shows a perspective view and corresponding orthogonal sections of some details of Figure 1;

- Figure 6 shows a perspective view and corresponding orthogonal sections of some details of Figure 1;

- Figure 7 shows a perspective view and corresponding orthogonal sections of some details of Figure 1;

- Figure 8 shows a perspective view and corresponding orthogonal sections of some details of Figure 3;

- Figure 9 shows a simplified block diagram of a system using panels made in accordance with the invention;

- Figure 10 shows an isometric perspective view of the module of Figure 1, whereon reflective panels and the conversion apparatus are mounted.

[DETAILED DESCRIPTION OF THE INVENTION]

With reference to the annexed drawings, 100 designates a concentrated solar system in accordance with the present invention.

The system 100 (Figure 9) preferably comprises a conversion apparatus 110, in which a heat transfer fluid flows in a duct and absorbs thermal energy irradiated onto said duct .

The system 100 further comprises a concentration structure

120 adapted to receive solar radiations and convey them onto the conversion apparatus 110, thus supplying said thermal energy .

The concentration structure 120 comprises a plurality of reflective panels 130 and a modular support structure 140 for said reflective panels 130. The reflective panels 130 are preferably Fresnel reflectors. Such reflectors may have a flat or slightly curved geometry .

Preferably, the reflective panels 130 are arranged in a plurality of parallel rows, so as to form a sort of matrix.

Preferably, the reflective panels 130 are associated with respective actuators, which allow the panels to be moved in order to follow the apparent motion of the sun.

The reflective panels 130 are arranged in such a way as to receive solar radiations and direct them towards the conversion apparatus 110.

The support structure 140 comprises a plurality of modules 1, all having substantially the same structure.

Figure 10 shows a module 1, whereon a plurality of rows of panels 130 are mounted.

Note that the structural elements of the module 1, and in particular the crossmembers 3, which will be described below, preferably support the bearings and/or the actuators that support the transmission shafts of the solar tracking mechanism, whereon the panels 130 are in turn firmly connected .

Each module 1 comprises first and second frames la, lb, which are substantially equal to each other.

Each one of said first and second frames la, lb comprises a pair of uprights 2, a crossmember 3 and a pair of upper beams 5. Each upper beam 5 extends from a respective end of the crossmember 3, so as to meet, at the opposite end, the other upper beam 5.

Each module 1 further comprises a pair of longitudinal beams 4 fixed at the upright-crossmember nodes to form a frame having a rectangular structure. Preferably, each module 1 comprises also a top beam 6 supported by the upper ends of said upper beams 5.

Preferably, said conversion apparatus 110 is supported by the top beam 6. In other words, one or more components of the conversion apparatus 110 are borne/supported by the top beam 6.

Advantageously, the conversion apparatus 110 may be hung to the top beam 6.

The Applicant has observed that when the system is in operation the conversion apparatus 110 reaches very high temperatures (around 200 °C-300 °C) , which cause it to undergo structural deformations, typically along the longitudinal direction. This can be taken into account by hanging the conversion apparatus 110 to the top beam 6 by means of sliding bearings, which will allow the apparatus to expand without generating any additional strains on the support structure 140.

The various elements so far described (uprights 2, crossmembers 3, upper beams 5, longitudinal beams 4, top beam 6) are tubes having a circular cross-section, preferably with an outside diameter of 48.3mm or l'-l/2 inches, cut to size orthogonally to the tube axis.

In general, said elements are cut-to-size metal tubes having a circular cross-section, all having substantially the same inside diameter and outside diameter.

Note that also the beams that will be described hereinafter (diagonal beams 7, extension beams 8, reinforcement beams 9, 10) are preferably cut-to-size metal tubes with a circular cross-section having the same inside diameter and outside diameter as the elements already described . Preferably, the tube-to-tube junctions are effected by means of commercial joints made of malleable cast-iron and secured by means of a set screw, with the only exception of coaxial tube-to-tube junctions, which are preferably effected by means of a commercial friction joint made of cold-pressed steel ;

Note that the components of the metal structure (tubes and joints) are subjected to no additional mechanical machining neither before nor during the installation, besides the cutting to size necessary for giving the element the desired axial length.

The preferred nominal diameter of the tubular beams is the one typically used for scaffolding, i.e. 1'- 1/2 (one inch and a half), corresponding to an outside diameter of 48.3 mm, but it is possible to use tubes having a nominal diameter ranging from l'-l/4 to 2' (one inch and a quarter to two inches), i.e. having an outside diameter ranging from 42 to 61 mm.

As aforementioned, the tubes are rigidly connected to one another or, as far as the uprights 2 are concerned, to the support plane through commercial joints made of malleable cast iron and secured by means of a set screw, with the exception of coaxial tube-to-tube junctions, for which it is preferable to use friction joints made of cold-pressed steel and fastening bolts, like, for example, scaffolding joints.

The anchorage of the upright 2 to the support plane is preferably effected through the joint 12, which has a fastening flange and a blind bottom, as detailed in Figure 5. The joint has two holes in the fastening flange, which are suitable for tightening by means of screws and bolts or chemical anchors. Other types of joints may be effectively used as well, such as, for example, the joints 12a and 12b shown in Figure 5, which differ from the joint 12 in the number of anchorage holes, in the case of the joint 12a, or in the type of anchorage element, in the case of the joint 12b. In particular, the joint 12b is suitable for immersion and inclusion into a concrete footing or plinth.

The fastening joint 13 connects the upright 2 to two crossmembers 3 and two longitudinal beams 4 adjacent thereto. The joint 13 has a 5-way cross-like shape, four ways being coplanar cavities orthogonal to one another, and one way being a through cavity located at the centre of the cross in the direction orthogonal to the plane passing through said four cavities, as shown in detail in Figure 4.

Due to the particular geometry of the joint 13, mutual orthogonality between the crossmember 3 and the longitudinal beam 4 is attained as they are fixed to the joint, without requiring any further adjustment. The joint 13 may be replaced with two three-way cross-shaped joints 13c (Figure 4), two ways of which are coaxial and one is an orthogonal through cavity. The first one of the two joints 13c effects the connection between the upright 2 and two crossmembers 3, and the second one effects the connection between the same upright

2 and two longitudinal beams 4. In this case, the crossmembers

3 and the longitudinal beams 4 will lie in geometric planes parallel to but no longer coinciding with each other. Perpendicularity between crossmembers and longitudinal beams will be obtained via an adjustment to be carried out while assembling the structure, and will require suitable tools, e.g. the mounting jig 19 shown in Figure 2. The latter can be easily obtained from a cut-to-size tubular beam, like structural beams. At the ends of the tubular jig, the joints 13d (Figure 4) have to be positioned in a "T" fashion with one through cavity and one blind cavity orthogonal thereto, and the through cavity of one of the two joints is fitted onto one of the four uprights 2, e.g. the upright 2a in Figure 2; then, by adjusting the angles between upright and crossmember and between upright and longitudinal beam, the position of the upright 2c, i.e. the one opposite to 2a along the diagonal direction, is brought to coincide with the centre of the through cavity of the second joint 13d. Because the length of the jig, calculated as the distance between the centres of the through cavities of the opposite joints 13d, is exactly the length of the geometric diagonal of the rectangular frame to be constructed, rectangularity of the quadrilateral will be ensured when the upright 2c is fitted into the through seat of the joint 13d.

When the ends of the crossmember 3 coincide with the upright-crossmember junction nodes, i.e. in those cases wherein the crossmember is not extended past said node, the joint 13 can be effectively replaced with the joint 13a (Figure 4), i.e. a four-way T-shaped joint with one through cavity and three coplanar cavities. As described in regard to the replacement of the joint 13 with two joints 13c, also the joint 13a may be replaced with two joints, e.g. the joints 13c and 13d. In this latter case, the joint 13c effects the connection between two consecutive longitudinal beams 4 and the upright 2, and the joint 13d effects the junction between the upright 2 and the crossmember 3. Finally, when the metal structure module is in the terminal position, as shown in Figure 3, in which case there is no need for a junction between two consecutive longitudinal beams, the joint 13a or, as an alternative, the two joints 13c and 13d may be used instead of the joint 13 shown in the drawing. Should not even the crossmember extensions be present, one may use the joint 13b, which is a three-way 90-degree angular joint with one through cavity, or, as an alternative, two joints 13d.

Regardless of which variant among the ones described above will be adopted for the junction between uprights and crossmembers and longitudinal beams, it is preferable that a ring 14, made of malleable cast iron and provided with a fixing set screw, is secured to the upright in abutment with the bottom edge of said joints. The function of the ring 14 is to prevent the overlying joints from sliding along the upright due to an insufficiently tightened fixing set screw. The ring may also be used as a reference and adjustment element when positioning the overlying joints in the vertical direction (i.e. along the upright) .

The dimensions of the support structure module are defined by the length of the distances between: A) two adjacent uprights in the direction of the crossmember, B) the end of the crossmember extension and the adjacent upright in the direction of the same crossmember, C) adjacent uprights in the direction of the longitudinal beam, and D) the axis of the top beam and the plane defined by the crossmembers.

The minimum and maximum lengths of said distances are: 1-6 metres for distance A) , 0-4 metres for distance B) , 3-6 metres for distance C) , and 1-6 metres for distance D) . Once said distances have been set, the lengths of the other beams are determined as well. The tubes of the structure preferably have a length equal to or shorter than 6 metres, because this is the standard length of steel sections. When the tubular beams of the structure are longer than 6 metres, a linear junction between two tubes becomes necessary, which is preferably effected by means of friction joints 18 (Figure 7) made of cold-pressed steel. The diameter, thickness and material of the tubes being equal, the mechanical strength of the structure will decrease as the above-listed characteristic distances increase. When the beam deformations, mostly due to static thrusts, caused by the reflectors' weight, and dynamic thrusts, caused by the wind pressure on the reflectors' surface, exceed the design limits, or anyway when the mechanical stresses acting upon the structure approach the ultimate tensile stress, the structure can be reinforced with the addition of further diagonal tubular elements, as in reticular structures. In the present invention, circular sections having the same diameter, thickness and material as the structural beams are used also for the diagonal elements. The number and position of the diagonal elements depend on specific structural requirements of the support structure module of the present invention.

For example, the inflection of the crossmember is limited through the use of two diagonal tubular beams 7, one end of which is fixed to the base of the upright 2, just above the joint 12 or the joint employed as an alternative, and the other end is fixed to the crossmember 3 near the centre thereof, i.e. near the point of maximum inflection. The diagonal beam 7 is mostly subject to axial forces applied to the nodal points. While supporting the inflection of the crossmember, the diagonal beams 7 are subject to compression (or traction, if inflection occurs in the direction opposite to the weight, e.g. if the crossmember is subject to overturning forces generated by the wind) . The structural assembly consisting of the upright, the crossmember and the diagonal beams recalls the scheme of a reticular structure in which the uprights and the diagonal beams are internal stiffening elements that are mainly subject to axial forces and only little deformation, and the crossmember is the upper bar (or chord) , although this scheme does not include the lower bar.

The diagonal beams 7 are fixed at the above-specified nodes by means of two combined joints 15, one with a blind cavity and the other with a through cavity, connected by means of a pin to form a hinge, as shown in detail in Figure 6.

As aforementioned, the structure comprises further diagonal reinforcement tubes acting mechanically in a way similar to the diagonal beams 7 and, just like the latter, connected to the structure through the hinge joints 15.

The rectangular tubular frame so far described supports a truss-shaped tubular structure wherein the nodes of the two upper beams 5 are fixed one to the upright 2 and the other to the top beam 6. The connection between the upright 2 and the top beam 5 is effected either by means of a variable-angle T- shaped joint 16 (Figure 6) or by means of the hinge joint 15 already described. With the joint 16, the angle at the node between the upper beam and the crossmember may vary from a minimum value of 30 degrees to a maximum value of 60 degrees, whereas the hinge joint 15 allows any junction angle.

The connection between the two upper beams 5 and the top beam 6 is effected by means of two T-shaped joints 17 coupled together and lowered to form an articulation, wherein each joint is similar to the joint 13d but, unlike the latter, the through cavity is modified so that the two blind cavities can be coplanar and at the same time perpendicular to the direction of the axis of the two through cavities. With reference to the axes of the two blind cavities, the articulation 17 forms an angle that may vary from a minimum value of approx. 46° to a maximum value of approx. 314° (i.e.: 360° minus 46°) .

The top beams 6 are joined together without solution of continuity throughout the length of the metallic support structure. Said joints 18 may either be internal to the module 1 or be positioned at the modules' junction node along the top beam. Unlike all other tube-to-tube junctions made of malleable cast iron with a fixing set screw described so far, the joint 18 is preferably a friction joint made of cold- pressed steel with a fastening bolt, similar to tubular scaffolding and/or framework joints. A joint 18a shaped like an external sleeve and made of malleable cast iron may be used as an alternative, but such a joint will not ensure the same mechanical performance as the joint 18.

The top beam 5 preferably consists of a single continuous tube. However, (a) when its length exceeds 6 metres, i.e. the standard length of the initial tubular section (not yet cut to size) , and (b) when it is necessary to change direction in the connection between the upright 2 and the top beam 6, the upper beam 5 must be made up of two joined tubular beams. In case (a) , the coaxial junction is preferably effected by means of the joint 18 or 18a, also used for joining the top beams. In case (b) , the variable-angle elbow joint 18b is used, which can join the sections of upper beam 5 at angles that may vary from a minimum value of 120° to a maximum value of 165° (the 180° angle corresponds to a coaxial tube-to-tube junction) .

When the Fresnel concentrators are formed by numerous rows of reflectors, in such a number that all of them cannot be housed in the space of the crossmember 3 internal to the uprights, it is possible to extend said beam symmetrically by adding two further tubular beams 8, coaxial to the crossmember and rigidly connected thereto, preferably by means of joints 13 or a combination of joints 13a and/or 13c, as previously described. A further diagonal beam 9 connecting the extension beam 8 to the upright 2 adjacent thereto will allow the extension beam to transmit the strains to a second joint node. Hinge joints 15 are used for fixing the tubular beams 9.

The structure may comprise further diagonal elements performing reinforcement and stiffening functions. Figure 1 shows, by way of example, the reinforcement beams 10 and 11. Hinge joints 15 are used, as for the other diagonal reinforcement elements 7 and 9 previously introduced.

The outer support structure modules 20 illustrated in Figure 3, i.e. those placed at the beginning and at the end of the linear concentrator with Fresnel mirrors, show some differences compared to the inner modules. In fact, there is a vertical tube 21 that secures the top beam to the anchorage and support plane of the structure. The purpose of this additional tubular element is to limit the deformations generated by the strains oriented along the direction of the top beam 6. If the vertical tube is positioned orthogonally to the support plane (being therefore also perpendicular to the top beam) , it can be anchored to the support plane by means of the same joint 12 as used for the uprights 2, or its variants 12a and 12b. As regards the joint that secures the vertical tube 21 to the keystone 6, several solutions may be adopted, such as, for example, the cross-shaped joint with overlapping arms 22, or the 90° elbow joints 22a, or the T-shaped joint 13d. However, the preferred positioning of the tube 21 is diagonal, so that the beam will be mostly subject to compressive and tensile stresses. In this case, the fixing to the top beam 6 can preferably be effected by means of the hinge joint 15, whereas anchorage to the ground can be effected by means of a hinge joint 23 (Figure 8) similar to the joint 15, wherein one of the two parts making up the hinge joint is a perforated flange suitable for anchorage to the support plane by means of anchors, chemical anchors, or screws and bolts.

Claims

1. Concentrated solar system comprising: a) a conversion apparatus (110), wherein a heat transfer fluid flows in a duct and absorbs thermal energy irradiated onto said duct;

b) a concentration structure (120) adapted to receive solar radiations and convey them onto said conversion apparatus (110), thus supplying said thermal energy;

wherein said concentration structure (120) comprises:

c) a plurality of reflective panels (130) ;

d) a modular support structure (140) for said reflective panels (130), wherein each module (1) of said modular structure (140) comprises:

d.i. first and second frames (la, lb), each one comprising a pair of uprights (2) ; a crossmember (3) ; a pair of upper beams (5), each one extending from one end of said crossmember (3) to join with the other upper beam at the opposite end, so as to form, together with said crossmember (3), a substantially triangular structure;

d.ii. a pair of longitudinal beams (4), each longitudinal beam (4) connecting corresponding ends of said crossmembers (3), so that said pair of longitudinal beams (4) form, together with said crossmembers, a substantially rectangular structure;

d.iii. a top beam (6) supported by the upper ends of said upper beams (5) ,

wherein each one of said uprights (2), crossmembers (3), upper beams (5), longitudinal beams (4), top beam (6) is provided as a cut-to-size metal tube having a circular cross-section.

2. System according to claim 1, wherein each one of said uprights (2), crossmembers (3), upper beams (5), longitudinal beams (4), top beam (6) has substantially the same inside diameter and the same outside diameter.

3. System according to claim 1 or 2, wherein each one of said tubes (2, 3, 4, 5, 6) is connected to one or more of the other tubes by means of one or more joints made of malleable cast iron or a friction joint made of cold-pressed steel.

4. System according to any one of the preceding claims, wherein one or more of said modules comprises one or more reinforcement beams (10), each one having a first end fixed to the crossmember (3) and a second end fixed to one of the upper beams (5) of said module,

said one or more reinforcement beams (10) consisting of cut-to-size metal tubes having a circular cross-section.

5. System according to any one of the preceding claims, wherein one or more of said modules comprises one or more diagonal beams (7), each one having a first end fixed to an upright (2) and a second end fixed to the crossmember (3) of said module,

said one or more diagonal beams (7) consisting of cut-to- size metal tubes having a circular cross-section.

6. System according to any one of the preceding claims, wherein one or more of said modules comprises at least one extension beam (8) for extending said beam (3) axially from a respective upright (2),

said at least one extension beam (8) consisting of a cut- to-size metal tube having a circular cross-section.

7. System according to claim 6, wherein said module comprises at least one additional reinforcement beam (9) having a first end fixed to said extension beam (8) and a second end fixed to the respective upright (2), said at least one additional reinforcement beam (9) consisting of a cut-to-size metal tube having a circular cross-section.

8. System according to any one of the preceding claims, wherein said system comprises a plurality of modules (1) arranged next to each other in the direction defined by the axial development of said longitudinal beams (4) .

9. System according to any one of the preceding claims, wherein said conversion apparatus (110) is supported by said top beam (6) .

10. System according to any one of the preceding claims, wherein at least one of said uprights (2) is provided with a ring (14) for holding in position one or more joints mounted along said at least one upright (2), said ring (14) being preferably made of malleable cast iron and being secured by means of a set screw.