EP3069178A1

EP3069178A1 - Reflector for solar thermal systems, and method for producing such a reflector

Info

Publication number: EP3069178A1
Application number: EP14805785.4A
Authority: EP
Inventors: Bernd Schuhmacher; Karl-Heinz Kopplin; Winfried Höhn; Lothar Patberg; Mark Hirt; Stephan Drewes
Original assignee: ThyssenKrupp Steel Europe AG; ThyssenKrupp Rasselstein GmbH
Current assignee: ThyssenKrupp Steel Europe AG; ThyssenKrupp Rasselstein GmbH
Priority date: 2013-11-11
Filing date: 2014-11-07
Publication date: 2016-09-21
Also published as: DE102013112378A1; WO2015067368A1; AU2014345935B2; CN105723254A; US10365463B2; AU2014345935A1; DE102013112378B4; MX370883B; US20160266361A1; MX2016004908A

Abstract

The invention relates to a reflector for solar thermal systems, comprising a sheet metal support (5) and a reflective coating (6) which is applied onto the sheet metal support and which is made of at least one reflective metal layer (6.2) and at least one protective layer (6.3) applied onto the reflective layer. The invention additionally relates to a method for producing a reflector for solar thermal systems. The reflector according to the invention for solar thermal systems has a high reflectivity, is robust against mechanical loads, and can additionally be produced in an inexpensive manner. Furthermore, the reflector according to the invention is as lightweight as possible and simultaneously dimensionally stable in that the sheet metal support (5) is made of a sandwich sheet which has an upper and a lower sheet metal cover (5.1, 5.3) and at least one non-metal intermediate layer (5.2) arranged between the upper and lower sheet metal cover. The upper sheet metal cover (5.1) has a smoothed surface (7) onto which the reflective layer (6.2) is applied, and the smoothed surface (7) has an arithmetic average roughness value Ra of less than 0.03 μm prior to applying the reflective layer (6.2).

Description

REFLECTOR FOR SOLAR THERMAL SYSTEMS AND METHOD FOR

MANUFACTURE OF SUCH A REFLECTOR

The invention relates to a reflector for solar thermal systems, with a

metallic support plate and a deposited on the support plate reflective coating, which is composed of at least one metallic reflection layer and at least one applied to the reflection layer protective layer. Of

Furthermore, the invention relates to a method for producing a reflector for solar thermal systems.

Reflectors of the type in question are used for example in solar thermal power plants, such as parabolic trough, Fresnel, Dish Stirling and tower power plants or the like, in which with the help of absorbers, a portion of the solar

Radiation energy is converted into heat. These systems have in common that the solar radiation is concentrated to increase the efficiency of the use of solar energy.

The reflectors are used in solar thermal systems as components of so-called "collectors" to focus on them incident sunlight and a

Absorbers, e.g. an absorber pipe or the like, to concentrate that one

Heat transfer medium leads. On the one hand there is the demand that the

Reflectors have optimal reflectivity in the radiation range of sunlight. On the other hand, the reflectors should be as robust as possible against the mechanical stresses occurring in use and inexpensive to produce. Another particular challenge is the dimensional stability of these

To ensure usually large-area components to achieve the focus of the sunlight in the required accuracy over the entire life of the reflector safely.

In order to design the reflection surface of such a reflector, it is known that a glass carrier in the manner of a conventional mirror on one side with silver or aluminum

CONFIRMATION COPY to coat. Disadvantages are both the high weight and the low elastic deformability and mechanical strength of the glass carrier.

From the European patent application EP 1 154 289 AI it is known a

Reflector body made of aluminum or an aluminum alloy with a

to provide reflective aluminum surface. Alternatively, the reflective surface can also be produced by coating a reflector body with aluminum. A transparent protective layer applied to the reflector surface is intended to protect the reflective surface from environmental influences.

Against the background of the prior art explained above was the

Invention, the object of the invention to provide a reflector for solar thermal systems, which has a high reflectivity, is robust against mechanical stress and can be produced inexpensively. Furthermore, the reflector should be as light as possible and at the same time dimensionally stable. In addition, a procedure for the

Production of such a reflector for solar thermal systems can be specified.

With regard to the reflector, this object has been achieved according to the invention in that the reflector has the features specified in claim 1. With respect to the method, the object has been achieved in that the in claim 12

specified method steps are performed.

The reflector according to the invention is characterized in that the carrier plate is formed from a sandwich sheet having an upper and a lower metallic

Cover plate and at least one interposed, non-metallic

Intermediate layer, wherein the upper cover plate has a smoothed surface on which the reflection layer is applied, and wherein the smoothed surface before the application of the reflection layer is an arithmetic

Mean roughness Ra of less than 0.03 μηι, preferably less than 0.02 μπι. When the term "arithmetic mean roughness Ra" is used, it means the value determined according to DIN EN ISO 4287. With the help of the sandwich structure of the carrier sheet, a rigid construction is achieved with low weight. The at least one arranged between the upper and lower metallic cover plate, non-metallic intermediate layer may for example consist of plastic. Likewise, other foams, adhesives or fillers in the region of the intermediate layer are conceivable, which are suitable for the construction of such a sandwich or composite structure. Due to the low weight of the

Reflectors, the requirements for the reflector supporting support structures and any drives for tracking the reflector in power plant operation, especially in comparison to reflectors with glass slides, can be reduced.

The sandwich structure also has the advantage that the individual components of the carrier sheet can be provided independently of each other. In this way, for example, the material costs can be reduced by the fact that the lower cover plate, which only has a supporting effect within the sandwich structure, can have a lower surface quality or alloy quality than the upper cover plate, whose surface finish has a direct or significantly greater influence on the reflectance of the Reflectors has. Thus, the upper and lower cover plate may be made of different materials, have different thicknesses from each other and / or divergent from each other

Coating systems include. Furthermore, depending on the expected operating conditions, the condition and also the wall thickness of the intermediate layer can be adjusted in order to set an optimal rigidity and / or weather resistance of the reflector. The sandwich construction thus makes it possible in a particularly simple way to achieve a compromise between lightweight design, dimensional stability and cost efficiency.

In addition to the sandwich structure is also for the reflector according to the invention

characterizing that the upper cover plate has a smoothed surface, which before the application of the metallic reflection layer an arithmetic

Mean roughness Ra of less than 0.03 μπι, preferably less than 0.02 μπι has. The low roughness of the smoothed surface favors the application of the

Reflection layer achieving a particularly low arithmetic Mean roughness Ra in the region of the reflection layer. Thus, even very thin layer thicknesses in the nanometer range can be sufficient for the required

Reflection properties trainees surface quality of the metallic

Adjust reflection layer.

Reflective surface layers may be formed, for example, from copper, gold, chromium, nickel or their alloys. In one embodiment of the invention, the reflective layer is made of aluminum, silver, tin, zinc or an alloy containing at least one of these metals. Also, the reflective coating can be constructed of several layers of the above-mentioned materials or their alloys. Thus, for example, first a tin or

Zinc layer are applied to the upper cover plate, which in turn carries an additional reflective layer of aluminum or silver.

The surface of the cover plate is smoothed according to a further embodiment of the invention by rolling, preferably by cold rolling. The cover sheets can be rolled, for example, in a quartz or, in particular when rolling stainless steel sheet, in a Sendzimir stand. In this case, in particular in the last pass, a work roll is used whose coming into contact with the rolling stock

Peripheral surface has an arithmetic mean roughness Ra, which is smaller than that required for the respective surface arithmetic mean roughness Ra. The surface smoothed by rollers has a topography on the basis of which the

Clearly identifies rolling direction. Thus, the roughness characterized by the arithmetic mean roughness Ra shows a pronounced preferential direction, which is aligned parallel to the rolling direction.

The smoothed surface can on the one hand on an uncoated cover plate of the sandwich sheet or on a corresponding cover plate for the preparation of

Sandwich panel are produced so that the metallic reflection layer is applied directly to the smoothed surface of the uncoated cover sheet.

On the other hand, a cover plate can be provided for the sandwich sheet, which already has a surface coating before rolling. So can one For example, already galvanized sheet are cold rolled. Consequently, then the galvanized surface is smoothed in accordance with the invention. Of course, it is also possible to provide any combination of the aforementioned layer systems before rolling on the upper cover plate to the smoothed surface with an arithmetic mean roughness Ra of less than 0.03 μπι, preferably less than 0.02 mm, before applying the To create reflection layer.

The reflection layer and / or the smoothed surface are smoothed by a thermal surface treatment according to a variant of the invention. For example, by purposefully melting the coating of a sheet, such as e.g. a tin pad, the required arithmetic mean roughness Ra are set. A method suitable for this purpose is known, for example, from German Patent Application DE 10 2011 000 984 A1, the content of which is hereby incorporated by reference into the present description. In particular, lasers, short-pulse or ultra-short pulse lasers are used as the energy or heat source. However, it is also conceivable to use any other heat source, the required

Energy input in the area of the surface to be smoothed can afford.

According to a further aspect of the invention, the upper cover plate is made of steel, in particular carbon steel or stainless steel, or of light metal, in particular of aluminum and / or magnesium or their alloys. The top

Cover plate serves as a substrate for the reflection coating after smoothing the surface.

In order to protect the reflective coating from environmental influences, according to one embodiment of the invention, a protective layer, preferably a protective layer, is additionally provided

transparent protective layer, provided. The protective layer or transparent

Protective layer is made in a variant of the invention of silicon oxide and / or titanium oxide. However, the protective layer can also be composed of one or more layers of other inorganic or organic compounds, as known, for example, from European Patent Application EP 1 154 289 A1, the disclosure of which is hereby incorporated by reference into the present specification is included. Additionally or alternatively, an antireflection layer, in particular of T1O2, can be provided, which in itself forms a protective layer or transparent protective layer, or serves to increase the transmission of an underlying transparent protective layer.

The coatings can be applied in a manner known per se in the PVD, CVD or sol-gel process. Furthermore, it is possible to apply the respective layers by magnetron sputtering, in particular high-power pulse magnetron sputtering (HIPIMS). A combination of the coating methods mentioned is conceivable in the construction of the reflective coating. The layer thicknesses of the reflection layer and / or the protective layer produced by these methods are, according to one aspect of the invention, in each case in a range from 50 nm to 5 μm, preferably in a range from 80 nm to 200 nm.

In addition to the coating of the carrier sheet, it is possible according to a further aspect of the invention to provide the reflective coating by one or more films and / or paints, or a combination of one or more films and / or paints and / or coatings. The use of films over the coating has the advantage that the required reflection properties are already largely predetermined by the quality of the film and can be adjusted in a simple manner a consistent quality of the reflective surface.

According to a further embodiment of the invention, the reflector has a wall thickness in a range of 0.5 mm to 5 mm. Due to the sandwich construction is a high rigidity, given at comparatively low weight of the reflector. According to another aspect of the invention, the cover sheet has a thickness in a range of 0.1-4 mm. It can thus be used very thin sheets, which are supported by the at least one non-metallic intermediate layer. The respective sheet thickness can vary depending on the dimensions of the reflector and the

Operating conditions are selected. The reflective coating and the individual layers, such as the metallic reflection layer and the transparent protective layer, can be made as smooth as possible. According to another aspect of the invention, the

Reflective layer and / or the protective layer is an optically active

Rauheitsfeinstruktur and / or at least one interference layer in order to further increase the efficiency of the use of solar radiation. In particular, optically active roughness fine structures can be introduced into the reflective coating by means of short-pulse or ultra-short-pulse laser technology.

The protective layer or transparent protective layer initially protects the metallic reflection layer against abrasive wear, environmental influences and / or (even) from corrosion. Overall, therefore, the upper cover plate on the one hand by the

(Transparent) protective layer and on the other hand by the metallic reflection coating from abrasive wear, environmental influences and / or protected against corrosion. Consequently, the upper cover plate already has a corrosion protection layer, depending on the applied reflective coating. In accordance with one aspect of the invention, an additional anticorrosion layer may also be applied to the upper cover sheet. In this case, the layer system, starting from the upper cover plate, thus has at least three layers

Corrosion protection layer, a metallic reflection layer applied to the corrosion protection layer and a transparent protective layer applied to the metallic reflection layer. The smoothed surface is doing after the

Application of the corrosion layer produced, although also the corrosion layer can already be applied to a smoothed surface.

The coatings described above may also or at least partially be provided on the lower cover plate. In particular, the upper and lower cover plate can be made identical. Thus, according to a further aspect of the invention, the non-metallic intermediate layer facing away from the outside of the upper

Cover plate and / or the lower cover plate provided with a corrosion protection layer. The method according to the invention for producing a reflector for solar thermal systems comprises at least the following method steps:

a. Providing a metallic carrier sheet, which consists of a

Sandwich panel is formed, having an upper and a lower metal cover plate and at least one interposed, non-metallic intermediate layer, wherein the upper cover plate has a smoothed surface and wherein the smoothed surface has an arithmetic mean roughness Ra of less than 0.03 μπι; and

b. Applying a reflective coating on the smoothed

Surface of the carrier sheet, which is composed of at least one metallic reflection layer and at least one protective layer applied to the reflection layer.

According to a variant of the method according to the invention is the smoothed

Surface produced by rolling. For example, by cold rolling a sheet in several rolling passes can be particularly smooth surfaces, especially with very low arithmetic mean roughness Ra produce.

Even before rolling can be applied to the cover plate, a corrosion protection layer. Thus, in this case, the smoothed surface of the

Corrosion protection layer, the substrate for the reflective coating to be applied in the following step.

The smooth surface can alternatively or additionally to the rolls also be produced by a thermal treatment of the layer or surface to be smoothed. Thus, according to another aspect of the invention, a tin layer is applied and the tin layer is melted to produce a smooth surface by means of a laser or heat source. In this case, preferably at least as much of the layer to be smoothed is melted, that elevations and depressions of the

Surface structure of the layer are largely compensated. Apart from a thermal surface treatment by means of a laser, the to be smoothed Tin layer also by heating the cover plate, for example by means of an induction coil, melted and smoothed.

According to another variant of the method according to the invention is the

Reflective layer applied by a PVD, CVD, electrostatic or electrochemical method. The protective layer is also applied according to a further advantageous embodiment of the invention by a PVD, CVD, or electrostatic method, preferably by magnetron sputtering.

In a further advantageous embodiment of the method according to the invention optically effective roughness fine structures are introduced into the reflection layer and / or the protective layer by means of laser processing in order to increase the efficiency in the

Exploitation of solar radiation continues to increase.

The invention will be explained in more detail with reference to an embodiment. Show it:

1 shows a collector for a parabolic trough power plant with a reflector according to the invention in a perspective view.

2 shows the layer structure of a reflector according to the invention from FIG. 1.

Fig. 1 shows a collector 1 for a parabolic trough power plant in a simplified form. In the collector 1, the incident on the concave upper side of a reflector 2 according to the invention solar radiation (not shown) is reflected and concentrated on an absorber tube 3, which carries a heat transfer medium. The reflector 2 is supported by a support structure 4. It is of course also possible to use a reflector 2 according to the invention in other solar thermal systems, such as Fresnel, Dish Stirling or tower power plants. In this case, the reflector may be designed opposite to the concave shape shown here in a flat or planar form. 2 shows the layer structure of a reflector 2 according to the invention for solar thermal systems. The reflector 2 consists of a metallic carrier sheet 5 and a reflective coating 6 applied to the carrier sheet 5. The carrier sheet 5 has an upper cover sheet 5.1, a non-metallic intermediate layer 5.2 and a lower cover sheet 5.3. The reflective coating 6 is made of a

Anticorrosive layer 6.1, a metallic reflective layer 6.2 and 6.3 applied to the reflective layer 6.2 protective layer, preferably constructed transparent protective layer. In a variant of the reflector according to the invention, the metallic reflection layer may simultaneously also constitute a corrosion protection layer, so that including the protective layer 6.3, only two layers are applied to the upper cover sheet 5.1 and yet corrosion protection is provided. Furthermore, the protective layer 6.3 can also represent a corrosion protection layer. In embodiments of the invention, it is also possible to provide a reflective coating formed from a plurality of layers. Thus, in particular, several layers of transparent protective layers can be provided, which are applied to the metallic reflection layer.

By cold rolling a smoothed surface 7 with an arithmetic mean roughness Ra of less than 0.03 μπι, for example, an arithmetic mean roughness Ra in the range of 0.02 to 0.05 μπι has been generated on the upper cover plate 5.1, the upper cover plate 5.1 already before rolling was coated with the corrosion protection layer 6.1. The upper cover sheet 5.1 is rolled in several rolling passes to the required thickness and also smoothed. In particular, in the last pass a roll was used, whose upper cover sheet 5.1

contacting roller surface an arithmetic mean roughness Ra less than 0.02 μπι, preferably less than 0.01 μιτι, more preferably less than 0.4 μπι had. Depending on the nature of the rolls, in particular of the rolls in the last pass, it is of course also possible in one embodiment of the invention to set lower or higher values for the arithmetic mean roughness Ra on the smoothed surface. Likewise, the required surface quality can already be produced in a single pass. The cover plates 5.1, 5.3 can basically be made of any metals or their alloys. In the example shown here, the upper and lower cover plates 5.1, 5.3 are sheet steel. Together with the non-metallic intermediate layer 5.2, for example made of plastic, the cover plates 5.1, 5.3 form a sandwich structure. The individual layers 5.1, 5.2, 5.3 are glued together in a known manner.

The smoothed surface 7 carries a metallic reflection layer 6.2, the

is formed for example of aluminum or tin. On the metallic reflection layer 6.2 is applied a protective layer, preferably transparent protective layer 6.3, which is e.g. made of SiOx. In this way, the metallic

Reflective layer 6.2 protected against mechanical wear and also against the weather.

reference numeral

1 collector

2 reflector

3 absorber tube

4 support structure

5 carrier sheet

5.1 upper cover plate

5.2 non-metallic intermediate layer .3 lower cover plate coating

.1 corrosion protection layer

.2 metallic reflection layer .3 protective layer

smoothed surface

Claims

claims

Reflector for solar thermal systems, comprising a metallic support plate (5) and a reflective coating (6) applied to the support plate (5), comprising at least one metallic reflection layer (6.2) and at least one protective layer (6.3) applied to the reflection layer (6.2). is constructed, characterized in that

the carrier sheet (5) is formed from a sandwich sheet which has an upper and a lower metallic cover sheet (5.1, 5.3) and at least one non-metallic intermediate layer (5.2) arranged therebetween, the upper cover sheet (5.1) having a smoothed surface (5). 7) having an arithmetic mean roughness Ra of less than 0.03 μιη, on which the

Reflective layer (6.2) is applied.

Reflector according to claim 1,

characterized in that

the reflective layer (6.2) is made of aluminum, silver, tin, zinc or an alloy containing at least one of these metals.

Reflector according to one of claims 1 to 2,

characterized in that

the smoothed surface (7) of the upper cover sheet (5.1) is formed by at least one tin layer.

Reflector according to one of claims 1 to 3,

characterized in that

the upper cover plate (5.1) is made of steel or light metal. Reflector according to one of claims 1 to 4,

characterized in that

the protective layer (6.3) is made of silicon oxide and / or titanium oxide.

Reflector according to one of claims 1 to 5,

characterized in that

the layer thickness of the reflection layer (6.2) and / or the layer thickness of the protective layer (6.3) is in the range of 50 nm to 5 μπι.

Reflector according to one of claims 1 to 6,

characterized in that

the upper and / or the lower cover plate (5.1, 5.3) have a thickness in the range of 0.1 mm to 4 mm.

Reflector according to one of claims 1 to 7,

characterized in that

the reflective layer (6.2) and / or the protective layer (6.3) has an optically effective roughness fine structure and / or at least one interference layer.

Reflector according to one of claims 1 to 8,

characterized in that

the at least the outside of the upper cover plate (5.1) facing away from the non-metallic intermediate layer (5.2) and / or the lower cover plate (5.3) is provided with a corrosion protection layer (6.1).

Method for producing a reflector for solar thermal systems, comprising the following method steps:

a. Providing a metallic support plate (5), which consists of a

Sandwich panel is made, which has a top and a bottom metallic Cover plate (5.1, 5.3) and at least one interposed non-metallic intermediate layer (5.2), wherein the upper cover plate (5.1) has a smoothed surface (7) and wherein the smoothed surface (7) has an arithmetic mean roughness Ra of less than 0, 03 μπ \ has; and

b. Applying a reflective coating (6) on the smoothed

Surface (7) of the carrier sheet (5), which is constructed from at least one metallic reflection layer (6.2) and at least one protective layer (6.3) applied to the reflection layer (6.2); That is, the smoothed surface (7) is produced by rolling.

11. The method according to claim 10, characterized in that before rolling a corrosion protection layer (6.1) is applied to the cover plate (5.1).

12. The method according to any one of claims 10 to 11, characterized in that applied to the upper cover sheet, a tin layer and the tin layer to produce a smooth surface by means of a laser or a

Heat source is melted.

13. The method according to any one of claims 10 to 12, characterized in that the reflection layer (6.2) by a PVD, CVD, electrostatic or electrochemical method is applied.

14. The method according to any one of claims 10 to 13, characterized in that the protective layer (6.3) by a PVD, CVD, or electrostatic method, preferably applied by magnetron sputtering.

15. The method according to any one of claims 10 to 14, characterized in that in the reflection layer (6.2) and / or the protective layer (6.3) by means of

Laser processing optically effective Rauheitsfeinstrukturen be introduced.