According to the title of this specification, the present invention relates to a new solar reflector for solar power concentration power plants or the like and the method for producing it.
It is one of the main elements used in solar power plants. Said element is used in these power plants to collect direct solar radiation and concentrate it on a receiving system, where the radiant energy, through a process, is converted into electric energy suitable for the use and/or storage thereof. Nevertheless novel applications in different fields of solar energy can be derived from this invention, generating a new range of customized and need-based products, such as for example small solar thermal cells suitable for dwellings and buildings.
The new reflector is applicable to new and customized electric or thermal generation units, such as:
Solar thermal concentration systems (STCS) are based on harnessing direct solar energy to convert it into electric energy. These generation systems are called solar power plants. They use different technologies among which the following stand out:
Parabolic trough collector (PTC) system
Parabolic dish or paraboloid of revolution (PD) systems
Central receiver or tower systems (CRS)
A parabolic trough power plant (hereinafter PTPP) represents the most developed technology. It consists of collecting direct solar radiation through the parabolic trough reflective mirrors. The direct radiation is concentrated in an absorption tube through which there circulates special oil which is progressively heated, reaching about 400° at the end of the loop. This heat is used to generate steam which generates electricity through a turbine. A parabolic trough collector is about 150 m in length and is made up of several segments or modules the length of which is about 12 m. Each segment consists of 28 mirrors curved in one of the dimensions thereof with a parabolic shape which concentrates on its focal line all the solar radiation impinging on the aperture plane thereof.
In the state of the art, the reflective component used in all the mentioned installations is formed by low iron content glass mirrors. There are different thicknesses depending on the required curvature of the glass. A thin silver film protected by means of a copper film and a coat of epoxy paint or protective lacquer is deposited on the rear face. Depending on the thickness of the glass on which the reflective silver film is deposited, two different types of mirrors are obtained: thick glass mirrors (3-5 mm thick) and thin glass mirrors (1.5-3 mm thick). Although this technology is considered the most developed, there are still many aspects to be improved which mainly relate to optimizing the system, reducing and improving the cost of glass mirrors and of other components, as well as optimizing operating and maintenance jobs. Although glass reflectors are currently used due to their greater durability and reflectivity, they have still not been improved enough and their high production and maintenance cost make it a type of technology that is still too expensive. On the other hand, the performance is reduced due to the efficiency losses they suffer. Environmental factors tint the glass, affecting the reflectivity of the reflectors and the transmissivity of the glass cover of the absorption tube. Maintaining the theoretical optical definition further involves considerable difficulty, because they are very large and weak parts, which can involve considerable efficiency losses of the collector.
Parabolic dish (PD) or paraboloid of revolution technology defines a parabolic dish system consisting of a reflector formed by a set of mirrors forming and approximating the shape of a large-diameter paraboloid of revolution with an external combustion engine/receiver located in its focal area, where all the solar radiation collected by the aperture of the paraboloid is concentrated.
Parabolic dishes are built with a tensioned membrane or with facets discretely approaching the geometry of the paraboloid. The reflective surface is obtained on the basis of glass mirrors or reflective films.
This technology is currently in the developmental stage. There are working prototypes, although the high cost of both the mirrors and of the assembly makes their massive introduction on the electric generation market non-viable for now.
Central or tower receivers (CRS) are in the developmental stage. They use a circular arrangement of large mirrors having an individual path (heliostats) for concentrating sunlight in a central receiver assembled at the top of a tower, where the radiant energy is converted into electric energy.
The reflectors used in this technology are flat reflectors (although the application of new models is being researched) arranged on a support structure spaced at determined distances from one another.
Concerning the production method for producing current reflectors and the characteristics of each material used:
The production method is focused on the reflectors used in parabolic trough power plants because they are currently used and are more developed.
The thick glass, one of the base supports used for the reflectors, is hot-curved so that it adopts the parabolic shape it must have, such that the mirrors can be placed directly on the metal structure of the collector.
When the thickness of glass is small, the mirror is flexible enough to be cold-curved and can be adhered directly on a support made from a metal or plastic plate which assures the curvature of the concentrator. In other words, the parabolic trough shape is provided by the mentioned plate on which the mirrors having a small thickness are adhered.
Silver or aluminum foil, another layer of copper and another layer of epoxy paint or protective lacquer are adhered to the glass on the rear portion of the exposed portion to finally insert ceramic parts therein to fix it to the structure, assuring and providing sufficient stability and rigidity, in addition to maintaining the optical definition of the mirror. Other support means for the reflective film, even though they are not used in industrial applications, are:
Sheet metal. High mirror reflectivity polished aluminum sheets in which the support material in turn acts like a reflective element are used. It is low-cost, but it has low durability because the surface deteriorates more quickly, therefore the reflectivity decreases, in addition to the optical alterations caused by temperature differences. They are not normally used for long-duration industrial applications.
Plastic. An extruded flat plate which can have different thicknesses of plastic material on which aluminum or silver foil is deposited on its front face. The parabolic shape must be provided by a stronger support on which the mentioned plate will be adhered. This is also the case of thin glass mirrors. These means are not long-lasting when exposed to the weather because the reflective surface directly erodes.
The support means described above (glass, sheet metal and plastic) are the three most significant types of reflective mirrors with respect to the material.
The characteristics reflective mirrors must comply with are:
The invention relates to a new mirror model made from injected thermoplastic material and the system used for obtaining the reflective surface, as well as the protection thereof, in addition to the production method for producing the assembly.
The objective is to reduce the high economic cost, maintaining the same performance of the collector or increasing it. It is necessary and urgent to achieve maximum solar radiation harnessing simply and economically.
A first and the most important aspect of the invention relates to the material used for the base support of the reflector, made from injected thermoplastic and configured to be coupled in current solar power concentration power plants. It maintains the same optical definition or a new definition if required. Its thickness can range between 1-7 mm, not including the reinforcing ribs giving it dimensional stability.
In addition to the raw material price, the use of thermoplastic is based on the advantages it offers, such as its transformation in an injection mold. This production mode allows obtaining any part no matter how complex it is in a very widespread process today, providing great improvements concerning production rates and possibilities of incorporating it to automated processes, whereby achieving very competitive prices.
A second aspect of the invention relates to the mode of obtaining the reflective surface, which is different from those currently used. It is obtained as a result of the direct deposition of materials such as aluminum, silver, chrome, stainless steel, etc., on the front visible face. The reflectors made from thermoplastic material are introduced inside a high-vacuum metal plating hood, where the metal cladding process is carried out by means of sublimation and deposition. These types of metal plating processes are not nor do they comprise ordinary galvanization processes because they confer fewer technical properties suited to the applications herein present, in addition to being highly contaminating and harmful to human health.
During the cladding process, satellites (part bearing systems) rotate around the source of evaporation and about the very axis to uniformly plate complex surfaces as well. The vacuum further assures an ideal condition for obtaining a perfectly uniform and compact cladding. For shiny molded plastic materials (also called mirror-like materials), deposition takes place directly after a prior plasma treatment in the process chamber, providing a shiny and glazed mirror effect.
Another similar cladding process whereby a suitable reflective surface can be obtained is metal plating through the sputtering method. In this process, an indestructible bond is formed between the film and the substrate or base because they become welded at the molecular level, providing a metallic effect with high abrasion resistance.
In the third place, after metal plating, the reflective surface is protected by means of the application or applications of completely transparent fluids with the necessary hardness once catalyzed to withstand the weather directly thereon. To that end, in a special dust-free facility (“clean room”) a specific preparation treatment is previously applied to the parts, before the mentioned applications. Finally, a curing and drying treatment is performed, leaves it with the necessary technical characteristics to comply with technical requirements.
In synthesis, the main features of the invention are:
Constructing the reflector with any optical definition of the following types:
Images or drawings which help to better understand the invention and processes described and which expressly relate to an embodiment of said invention as a non-limiting example thereof are briefly described below:
Referring to the reference numbers used in the drawings, it can be seen that
The production of current reflectors is conditioned to the way the reflective surface thereof, as well as the protection thereof against external agents, are obtained. The most widespread way today consists of adapting a mirror to the optical definitions used, the mirror comprising special characteristics such as specific glass, silver or aluminum foil, support and attachment elements, in addition to fixing or anchoring points for fixing or anchoring to the support structures that are usually made from ceramic and are disposable when their service life ends.
Implementing the process described above involves very high production and raw material costs, resulting in a very substantial final price for the reflector that decisively conditions the viability of projects as a whole.
The new reflector 5, object of the invention, such as the one shown in
This product can be produced in a completely automated continuous flow cell which would consist of the following elements:
The technical features of the new reflector, i.e., for the concentration and harnessing of solar radiation, are substantially better due to the new characteristics it complies with:
The reflector 5 has a general thickness ranging between 1-7 mm, in addition to a structure of reinforcing ribs in the rear portion autonomously assuring the dimensional stability of the optical definition of the front face (reflective surface) (see
Concerning the fixing of the new reflector 5, there can be between one and six fixing points in the new reflectors or they can be adapted to the number of such points in the reflector that need to be replaced. The way of fixing the fixings consists of inserting a bushing 6 with a threaded hole 7 in the mold at each of the points. The mentioned insertion in the mold is done before injecting the plastic, so once the plastic is injected, all the bushings 6 are overmolded, the overmolded thermoplastic material 8 thereby being part of the assembly (
The threaded holes 7 of the bushings 6 allow accurate regulation during the assembly, introducing therein threaded bolts and their lock nuts which would be fixed to the support structure 3.
The reflective surface is obtained as follows (
1. Base material 9 made from thermoplastic material obtained in an injection mold with a mirror finish on a useful face.
2. Preparation treatments for preparing the useful face before metal plating (for example plasma, etc.).
3. Optionally applying primer 10 on the useful face with a fluid that can optimize the adhesion of the metal plating 11.
4. Deposition of a reflective metal on the useful face by means of the process of introducing the reflector support in a high-vacuum hood, being able to apply two different processes, sublimation or sputtering, thereby obtaining a face having high reflectivity sputtering.
5. Protecting the metal plated surface by means of one or several applications 12 of special protective fluids which become hard and transparent when catalyzed, being applied in specific cabinets after introducing the already metal plated reflector.
6. Quality control operation:
The industrialization leads to the mass production in a completely automated cell consisting of the following elements:
The new reflector can be reused once its service life has ended, with the same features as the original.
The new reflector 5 can be constructed with any optical definition:
In a comparative analysis with other existing patents, it can be established that:
Patent WO 2007/108837 “Method of making reflector for solar collector or the like and corresponding product” only relates to a single optical definition (parabolic trough), in addition to including glass in all its versions, these aspects being the main differences with the reflector 5 at hand, in addition to achieving reflection by providing an independent foil formed in part by the reflective material, and this foil can be the object of another patent.
The reflector of Patent WO 2007/108837 “Method of making reflector for solar collector or the like and corresponding product” consists of completely flat plates, obtaining the optical definition by “thermoforming” or cold bending and subsequently adhering to previously thermoformed plates, in both cases, this method does not provide the necessary consistency in such large parts for the accurate maintenance of the optical definition, providing this deficiency to the structure of the collector during the fixing.
Another fundamental and novel aspect is the final cost of the product. The new reflector 5 is initially estimated to be 40% cheaper than current reflectors.
The reflector 5 can replace any of those on the market, respecting the fixings, the position of the absorption tube in the case of the parabolic trough collector, as well as those used in the tower power plants and Stirling dishes, reducing the number of facets in addition to modifying the definition thereof, being able to form them as “pieces of paraboloids of revolution”, along with what this involves concerning the performance and final price of the assembly.
Since Fresnel definitions can be reinforced in a determining manner as they are formed in an injection mold like the catadioptric elements of automobiles and the lines of research, which are open concerning this definition, are more economical.
Number | Date | Country | Kind |
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P200900270 | Jan 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/ES09/00482 | 10/5/2009 | WO | 00 | 10/12/2011 |