Patent Application
20150345832
The present invention can be included in the field of thermosolar technology, more specifically, it relates to dish-type point-based solar concentration systems, in particular, although not necessarily, of dish-type, such as Stirling or AMTEC dishes.
A dish-type point-based solar concentration system, such as those of Stirling dish, has a parabolic concentrator which is equipped with dual-axis tracking, to reflect the incident solar radiation on the surface towards a reflective surface. A solar receiver is located on the focus, which is connected to a Stirling engine or a microturbine. The receptor absorbs the concentrated solar radiation, causing the heating of a fluid until a suitable temperature so that the energy absorbed by the fluid is used in the engine or microturbine to generate electricity, through a generator connected to the engine or microturbine shaft.
There are other dish-type concentration systems where the purpose of the fluid heated in the receiver is that of either generating process vapour or being stored.
In the case of AMTEC (alkali-metal thermal-to-electric conversion) dishes, similar to Stirling dishes, the Stirling engine is replaced by a new regenerative power conversion unit which allows the direct conversion of heat into electricity by the use of an alkaline metal.
In particular, the main components of the Stirling dish are:
Solar concentrator (also called primary reflector): it comprises a parabolic specular surface supported by a structure. Its mission is to concentrate, theoretically in a point, which coincides with the focus of the parabolic specular surface, the solar radiation incident on the specular surface.
Solar receiver: it is a heat exchanger which is positioned in the focus and transfers the solar energy concentrated in said focus towards a working fluid.
Stirling engine or microturbine: it comprises an output shaft and transforms the heat absorbed by the working fluid into mechanical energy to make the output shaft rotate.
Generator: it is coupled to the output shaft and transforms the rotation energy of the output shaft into electrical energy.
Support structure: to support all the mentioned elements and give rigidity and resistance to the assembly.
Tracking system: it enables orienting the assembly of the Stirling dish so that the rays always incide on the reflective surface parallel to the dish axis.
However, the concentration systems known to date have some drawbacks which we will state below.
Stirling dishes are known whose structure is anchored to the ground by a central pivot and a wheel-rail system on foundations in the form of a ring, performing the function of elevation mechanism. This configuration gives said system pointing errors from the foundation, which becomes a key step of the assembly.
Other systems comprise a pedestal several metres high whereon is disposed the concentrator structure and a truss system at which end the Stirling engine is anchored. This “point-based support” system produces a great concentration of stresses in the rotation mechanisms, largely increasing the maintenance and installation cost of the technology, also due to deformations of the pedestal throughout the day.
Another of the disadvantages that dish-type trackers have to date, and which has been an impediment for their serial production in large plants, is the great cost involved in transporting these structures, since they need a large volume in relation to the weight they support.
In short, we have the following disadvantages: heavy and complex structures, which makes the manufacturing of the structure more expensive and complex, as with the transport of the parts forming it, the assembly and the maintenance; inaccuracies in the foundations, which are transferred to the structure operation; high concentration of stresses; and lack of accuracy in the focus of the radiation concentration in the focus.
The aim is to describe a dish-type point-based solar concentration system free from the aforementioned drawbacks.
The present invention resolves the aforementioned drawbacks, in accordance with a first aspect of the invention, by a structure for a dish-type point-based solar concentration system and, according to a second aspect of the invention, by a dish-type point-based solar concentration system including said structure.
The structure of the invention comprises an anchoring sub-structure designed to be anchored to the ground, preferably by piles (either of concrete or metal piles directly anchored to the ground). The anchoring sub-structure provides fixing to the ground for the structure.
It also has a tracking sub-structure, which is connected to the anchoring sub-structure in a rotatory manner with respect to said anchoring sub-structure around an azimuth axis to produce the azimuth tracking of the tracking sub-structure. By way of example, the anchoring sub-structure and the tracking sub-structure are connected through an azimuth crown comprising a casing, fixed to the anchoring sub-structure, and a toothed wheel, internal to the casing, which rotates with respect to the casing around an azimuth axis, and which is linked to the tracking sub-structure. A first engine is in charge of actuating the toothed wheel, so that the rotation of the toothed wheel with respect to the casing drives the tracking sub-structure, generating the azimuth orientation of said tracking structure.
The structure additionally comprises a driving sub-structure, comprising two coaxial hoops, located in parallel planes and connected together by means of tie-rods, and said tie-rods may be oblique and/or perpendicular to the hoops. The hoops are configured from segments which are assembled to mount each one of the hoops. Preferably, the segments are hollow profiles at the ends whereof curved bars are inserted to provide the corresponding fixing between adjacent segments.
The driving sub-structure, once assembled, comprises a receptacle in its contour to house a solar receiver, which will be in connection with a Stirling engine, a microturbine or similar, according to the second object of the invention. The driving sub-structure is linked to the tracking sub-structure, so that it is driven by the azimuth movement of said tracking sub-structure. Likewise, the driving sub-structure rotates with respect to the tracking sub-structure around the axis common to the hoops, to provide the receptacle with elevation tracking.
In particular, the structure may incorporate two pairs of slides, one for each hoop, mounted in the tracking sub-structure, to house the hoops and guide the driving structure in its elevation movement. The slides incorporate rolling elements designed to connect with the hoops, to facilitate the elevation movement.
A second engine causes the rotation of the driving sub-structure with respect to the tracking sub-structure. Preferably, the second engine attacks a transmission (for example, a chain, or a curved rack, linked to at least one of the hoops, to cause said elevation movement.
Therefore, with the movement of the tracking sub-structure by the first engine, together with the movement of the driving sub-structure by the second engine, it achieves dual-axis tracking of the receptacle designed to house the solar receiver, therefore, of the focus of concentration.
The invention also incorporates a connection sub-structure, and a supporting sub-structure, linked to the connection sub-structure, and designed to support a reflection surface in preferably paraboloid form, the focus of which coincides substantially with the receptacle, which defines the solar concentrator of a concentration system according to the second aspect of the invention, as shall be described below.
The connection sub-structure is a modular bar structure, and therefore of great rigidity, which is connected to the driving structure and is designed to support the reflective surface and the supporting sub-structure of said reflective surface.
The supporting sub-structure has the form of a cradle and is joined to the connection sub-structure.
The structure of the invention overcomes the problems of variations in the focus of the paraboloid with respect to the centre of the receiver from the foundations, thanks to a levelling device which provides a decoupling between the receiver surface and the ground, avoiding the transfer of variations of the ground to the structure. The anchoring sub-structure, with its levelling device, replaces the high pedestals of the state of the art thus avoiding the stresses generated due to the ground and the specific foundations.
On the other hand, the Stick-Slip effect is minimized thanks to the use of the slides equipped with rolling elements assisted by bearings. The rotation of the driving sub-structure is subject to greatly reduced errors, since said errors are translated into very low angular differences, due to the high diameter of the hoops. The solution provided makes it possible to dispense with support shafts of great height present in the state of the art and with the previously used system of movements and which had a high concentration of stresses.
Likewise, the driving sub-structure forms a very stable and rigid construction, ideal for housing a Stirling engine or similar with a much higher precision than that provided by other known solutions, such as, for example, the supports in the form of swan's neck, which are a great drawback in terms of vibrations, the starting torque of the engine and even its own weight, making it dimensioned with large consumption of raw materials.
The ease in the rotation of the drum, means that efficiency in engine maintenance is unbeatable, since it is placed in positions very close to the ground avoiding the use of auxiliary lifting machinery.
As previously explained, and as will become clear in the preferred embodiment explained below, both the driving sub-structure, and the connection sub-structure and the supporting sub-structure have been devised to be mounted through simple parts, preferably with a predominantly linear dimension and with the aim of favouring a transport logistics by weight and not by volume.
Said parts can be transported compactly, so that it avoids deformations which may invalidate their function and make its commissioning more expensive or even ruin it. The design has been executed with construction criteria which allows us to apply lean manufacturing techniques for its assembly, in this way achieving an assembly in a known and stable time cycle, and also its quality.
Additionally, the solution proposed on how to produce the driving, connection and supporting sub-structures from simple joints of longitudinal parts which can be stacked in simple configuration (bars or stamped parts), preferably produced in hot-galvanized steel, allows a great use of the material in relation to the resistance and rigidity obtained, and provides advantages in the transport, since the parts can be compactly packaged. Likewise, hot-galvanized steel is a widespread product which is easily acquired, whose capacity of withstanding the passage of time is widely verified.
The assembly of the connection sub-structure and of the supporting sub-structure is devised as a lean manufacturing system of great simplicity which does not require additional investments, without the need to use special tables, nor specific tools for its assembly.
The centre of gravity of the assembly of the driving, connection and supporting sub-structures is, throughout the path, at the intersection of the azimuth axis and of the axis of elevation rotation, avoiding counterweighting the system and considerably reducing the material cost in the structure and that associated to the engines, being able to use first and second engines of very low power to transfer the movement.
To complement the description being made and in order to aid towards a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment thereof, a set of drawings is attached as an integral part of said description wherein, with illustrative and non-limiting character, the following has been represented:
FIG. 1.—Shows a perspective view of a concentration system according to the invention.
FIG. 2.—Shows a perspective view of the azimuth crown.
FIG. 3.—Shows a perspective view of a preferred embodiment of the anchoring sub-structure.
FIG. 4.—Shows a perspective view of a preferred embodiment of the tracking sub-structure.
FIG. 5.—Shows a perspective view of a preferred embodiment of the driving sub-structure.
FIG. 6.—Shows a detailed perspective view of a specific example of assembly of the segments forming the hoops of the driving sub-structure.
FIG. 7.—Shows a side view of the assembly of the connection of the driving sub-structure on the tracking sub-structure.
FIG. 8.—Shows a perspective view of a preferred embodiment of the connection sub-structure mounted on the driving sub-structure.
FIG. 9.—Shows a perspective view of a module comprised in a preferred embodiment of the connection sub-structure.
FIG. 10.—Shows a detailed perspective view of the join of the bars of the module of
FIG. 11.—Shows a perspective view of a preferred embodiment of the supporting sub-structure.
FIG. 12.—Shows a perspective view of the supporting sub-structure of
13.—Shows a detail of the supporting structure showing supporting profiles and clamps to fix the reflective surface.
FIG. 14.—Shows a profile view of a detail of the assembly of the tracking sub-structure on the anchoring sub-structure.
a to 15c.—Schematically show three positions of the structure, showing the ease of access to the solar receiver in the case of maintenance.
FIG. 16.—Shows details of the clamps.
Below, a detailed description of the present invention is described with the aid of said
Below, a list is given of the numerical references used in the description of the preferred embodiment, in correspondence with the figures.
As shown in
In
The tracking sub-structure (20), shown in
The azimuth crown (60) (again see
Again in
Following with
As shown in
As represented in
Once assembled, the driving sub-structure (30) comprises a receptacle (35) in its contour to house a solar receiver (not represented) which can be connected to a Stirling engine or similar (not represented). The driving sub-structure (30) is connected to the tracking sub-structure (20), so that not only is it driven by the azimuth movement of said tracking sub-structure (20), but it is also rotatory with respect to the tracking sub-structure (20) around the axis common to the hoops (31), to provide the receptacle (35) with elevation tracking.
Hence, as shown in
In this way, it achieves that the solar tracking system has two axes due to the combination of the azimuth rotation of the tracking sub-structure (20), and of the elevation rotation of the driving sub-structure (30).
As shown in
The modules (42), as shown in
Each one of the first triangles (43) is connected to one of the vertices of the polygon (preferably hexagon) of the first core (41). From the modules (42) emerge legs (5) which link the connection sub-structure (40) with the hoops (31) of the driving sub-structure (30). It is preferred that the bases (44, 48) of the first (43) and second triangles (47) are located at a lower level than the upper vertices (46) of the corresponding first triangles (43), so that the connection sub-structure (40) has a concave vault-shape which optimizes the transmission of forces, especially of wind.
The supporting sub-structure (50) is fixed on the connection sub-structure (40), as shown in
As observed in
In
For reasons of simplicity, in the figures a further two examples have not been represented which are specular images of the two stated examples.
Once the surface of the invention has been mounted, it is possible to dispose the reflective surface (70), the actuation engines, the Stirling engine or similar, and the solar receiver to obtain a dish-type point-based solar concentration system.
a, 15b, 15c show the ease of access to the solar receiver and to the Stirling engine or similar, in the case of maintenance.
| Number | Date | Country | Kind |
|---|---|---|---|
| P 201231396 | Sep 2012 | ES | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/ES2013/070614 | 9/3/2013 | WO | 00 |
