Solar absorber

Abstract

The invention relates to a solar absorber (1) for use in a solar power plant, the solar absorber (1) having at least one main body (2) which is accommodated in a sheath housing (3), the main body (2) being formed from a plurality of metal foils, a first metal foil being smooth and a second metal foil being at least partially structured, the first metal foil being flat and the second metal foil being at least partially structured, the metal foils are stacked on one another and a plurality of flow channels (8), which can flow through the gas inlet side (6) to the gas outlet side in a main flow direction (7), are formed between the metal foils, the sheath housing (3) being connected to a funnel (4), to which the coupling tube (5) is connected, and a fluid can flow through the flow channels (8) along the funnel (4) to the coupling tube (5).

Description

Technical Field

[0001] The present invention relates to a solar absorber for use in a solar power generation facility. Background Art

[0002] A solar absorber is a device which is designed to be irradiated with (focused) sunlight and which is therefore subject to a significant thermal load when used in a solar power plant. The solar absorber can absorb a portion of the heat thus obtained.

[0003] The device provided for this purpose has at least one matrix (sometimes referred to as a substrate) that is accommodated in a sheath tube or housing. The matrix is ​​formed from a plurality of metal foils, a first metal foil being (substantially) smooth and a second metal foil being at least partially structured. The metal foils can be stacked on top of one another, and a plurality of flow channels are formed between them, through which a gas flow can flow in the main throughflow direction from the gas inlet side to the gas outlet side.

[0004] In the field of solar thermal power generation facilities, in particular in facilities using so-called air receiver technology, solar absorbers with volumetric receivers made of silicon carbide (SiSiC) are used. The solar absorber has a porous / air-flowable structure, which forms a plurality of preferably rectangular or square flow channels. The porosity in the prior art corresponds to approximately 80 cells per square inch (cpsi). The material wall thickness of the bridge between the individual flow channels is approximately 0.75 mm. The absorber is preferably inserted into a funnel-shaped part with a connecting tube made of silicon carbide and connected thereto. The flow channels extend in a horizontal and vertical arrangement. By focusing the energy source (for example a highly beamed light beam), the medium flowing in the flow channel can be heated, whereby energy can be obtained.

[0005] A particular disadvantage of the solutions according to the prior art is that the flow channel is generally poorly flowed through in the edge region, whereby elevated temperatures can occur in this region, which can also lead to local overheating, which can cause damage and even failure of the absorber.

[0006] Another disadvantage is that, due to the materials used and the large temperature differences between the absorber and the retaining tube, there is a risk that the entire absorber module could fall off. To counteract this, a completely circumferential air gap is often formed around the absorber. This air gap results in the loss of potentially usable absorber surface and makes it unusable. This is particularly significant because conventional solar thermal systems sometimes have tens of thousands of absorbers installed, resulting in a significant amount of unused absorber surface due to the air gap.

[0007] The silicon carbide used is particularly sensitive to thermal shocks. However, large temperature fluctuations, such as those caused by cloud cover, are to be expected, especially in everyday use. This material, in particular, does not allow for elastic deformation, so severe thermal cycling can lead to permanent damage. Summary of the Invention

[0008] The object of the present invention is therefore to at least partially solve the problems described with reference to the prior art and in particular to create a device or a solar absorber which is improved in terms of its temperature resistance and / or has more favorable thermal conductivity.

[0009] The object of the solar absorber is achieved by a solar absorber with the features of claim 1. Advantageous improvements are indicated in the dependent claims. The features listed individually in the claims can be combined arbitrarily with each other and / or with the contents of the description. The description, in particular in conjunction with the drawings, explains the invention and indicates additional implementation variants. This is facilitated by a device for use in a solar power plant, referred to herein as a solar absorber, wherein the solar absorber has at least one base body accommodated in a sheath housing. The base body consists of a plurality of metal foils, wherein a first metal foil is smoothly constructed and a second metal foil is at least partially structured. The metal foils are stacked on one another and a plurality of flow channels are constructed between them, through which a gas can flow in the main flow direction from the gas inlet side to the gas outlet side. The sheath housing is connected to a funnel-shaped part to which a connecting pipe is connected, wherein the fluid can flow along the funnel-shaped part to the connecting pipe through the flow channels.

[0010] The structure and shape of the solar absorber can be easily adapted to the structural constraints of the receiver in the solar power plant. The solar absorber particularly preferably has a square cross-section, but other structural shapes (such as rectangular, oval, or hexagonal shapes) are also possible. The provided sheath housing has essentially the same cross-section as the base body and is therefore preferably also square, rectangular, or hexagonal. The sheath housing can also be designed as a sheath tube.

[0011] In particular, the base body is designed to rest against the jacket housing or be directly connected to it, i.e., in particular, without an air gap surrounding it (but not allowing axial flow through it). In other words, this means that the flow channel is arranged up to the jacket housing; therefore, there are no (separate or additional) cooling channels between the base body and the jacket housing. Consequently, the entire inner cross-section of the jacket housing can serve as an absorber for (end-side) solar energy input.

[0012] The base body can be arranged so as to be partially inserted into or extend into the jacket housing. In particular, the jacket housing only partially covers the base body, i.e., in the base body section facing the funnel. The base body section enclosed by the jacket housing can be approximately half the axial length of the base body. In particular, the jacket housing can be designed to have a smaller axial length than the funnel and / or the coupling tube. The jacket housing can be constructed integrally with the funnel. The funnel and the coupling tube can be constructed integrally. The jacket housing, the funnel, and / or the coupling tube can be designed separately and joined to one another.

[0013] The solar absorber, together with the funnel and the connecting pipe, forms a ready-to-install unit. Several of these solar absorbers can be assembled (adjacently or in a single plane) and together form a solar power plant. The size of the solar power plant can be scaled to the number of solar absorbers.

[0014] The entire irradiated surface, formed by the corresponding gas inlet side of the solar absorber (or substrate), is (axially) penetrated by flow, thus ensuring optimal utilization of the structural space and thereby increasing overall efficiency. The gas inlet side forms the entrance into the numerous flow channels formed by the substrate. Irradiating the surface with focused light results in intense heating of the gas inlet side and, consequently, the entire substrate. Thermal energy can be transferred from the heated substrate to the medium, such as air, flowing through the flow channels. The thermal energy incorporated into the air flowing through the flow channels can ultimately be used to generate electrical current.

[0015] The surrounding air gaps present in conventional systems can be reduced or completely avoided. This can be achieved by placing directly adjacent substrates with their jacket housings directly against one another, preventing any flow from bypassing the substrates. This improves the efficiency of the system.

[0016] The thin first and second metal foils (particularly relative to the jacket housing) have very good axial and radial thermal conductivity, thereby enabling particularly uniform and rapid heating of the base body. In particular, the formation of so-called hot spots can be avoided. The base body formed from metal foils also offers a certain flexibility, as the foils can partially move relative to one another, or the entire base body can expand or contract. This allows for the absorption of stresses that can arise, for example, from thermal shocks.

[0017] The base body is preferably produced from alternating (metal) corrugated and smooth layers, which are stacked one on top of the other and inserted into the jacket housing and connected thereto. The base body preferably has a cell density of 80 to 1600 cpsi (cells per square inch), particularly preferably 200 to 800 cpsi, and most preferably 500 to 700 cpsi.

[0018] Due to the very low wall thickness of the metal foil, even with a low pore density and thus a high porosity of the base body, a large geometric surface is obtained compared to systems from the prior art, thereby achieving increased efficiency. The foil used preferably has a thickness of 20 μm to 250 μm (micrometers), particularly preferably 30 μm to 100 μm, and very particularly preferably 50 μm to 80 μm.

[0019] The solar-weighted absorption rate is between 95% and 96%, and at a temperature of 700 degrees Celsius and 641kW / m 2 At a flux density of 100 nm, the thermal efficiency is approximately 90%. Compared to the solutions known from the prior art, this corresponds to an improvement in absorption of 5% and an improvement in thermal efficiency of 6% to 7%.

[0020] During continuous operation, the absorber or the metal foil develops a protective dark oxide layer which, in addition to protecting the metal foil, also increases the absorption rate, thereby improving the thermal efficiency.

[0021] It is particularly advantageous if the jacket housing has a shorter (axial) extension in the main flow direction than the base body. The jacket housing is designed to be shorter in the main flow direction than the base body itself. This results in the base body protruding beyond the jacket housing. Consequently, the jacket housing is set back behind the gas inlet side formed by the base body, so that it is located in an area shielded by the base body. By arranging multiple solar absorbers directly adjacent to each other, the jacket housing is not directly exposed to radiation with beamed light. This reduces the likelihood of damage to the jacket and thus actively avoids deformation of the jacket housing. The shortening of the jacket housing relative to the base body on the gas inlet side is preferably in the range of between 0% and 90%, particularly preferably in the range of between 20% and 80%, and most preferably in the range of between 30% and 70%.

[0022] It is also advantageous to arrange a corrugated third metal foil between the base body and the jacket housing, which has a significantly stronger structure than the second metal foil. The third metal foil can also be part of the base body itself. The structure can be characterized by wavelength and wave height, so that the wavelength and / or wave height of the corrugated third metal foil is greater than the wavelength and / or wave height of the first and second metal foils in the inner or adjacent regions of the base body.

[0023] The third metal foil has a structure, in particular a corrugation. The third metal foil is arranged circumferentially around the base body or as an edge region of the base body, and thus forms an additional (axially permeable) flow channel between the jacket housing and the (inner) base body. Because the pore density is lower due to the stronger structure, the porosity in the area of ​​the third metal foil is significantly higher. The high porosity in the area of ​​the third metal foil increases the flexibility of the base body assembly, especially in the case of thermal shock loads. In addition, the base body cools faster and more strongly in the area close to the jacket due to the higher flow achieved by the generally lower back pressure in this area. As a result, the jacket temperature drops quickly or remains at a low level, thereby reducing the deformation of the jacket and thus possibly avoiding damage.

[0024] Furthermore, the wraparound position of the third metal foil improves the quality of the connection between the base body and the jacket, in particular at the vertical sides where the foil leads contact the jacket. The foil thickness of the third metal foil, which forms the so-called compensation layer, is preferably 20 μm to 250 μm (micrometers), particularly preferably between 50 μm and 150 μm, and most preferably between 80 μm and 120 μm.

[0025] The base body is firmly connected to the third metal foil or the compensation layer. The jacket housing is designed to be shorter, so that the base body and the compensation layer protrude beyond the jacket housing on the gas inlet side.

[0026] The corrugated third metal foil can be wound around the base body in the circumferential direction and form flow channels running parallel to the main throughflow direction between the base body and the jacket housing.

[0027] Compared to the second metal foil, the first metal foil can have a shorter extension along the main flow direction of the substrate. Due to the shortened first metal foil (which is a smooth metal foil), a higher porosity is generated in the area of ​​the shortened first metal foil than in the remaining areas of the substrate.

[0028] The first metal foil can terminate flush with the second metal foil at the gas outlet side, and the first metal foil can be arranged offset relative to the second metal foil in the main flow direction at the gas inlet side. This increases the porosity at the gas inlet, allowing for greater absorption of radiation energy. This is particularly applicable to energy originating from radiation incident on the gas inlet side of the absorber at an angle, thereby improving thermal efficiency.

[0029] The inlet section represents the section of the base body having increased porosity due to the shortened first metal foil. The length of this inlet section is preferably 0 mm to 40 mm (millimeters), particularly preferably 2 mm to 20 mm, and most particularly preferably 5 mm to 10 mm.

[0030] The base body can protrude beyond the jacket housing with its gas inlet side. This increases the porosity, in particular in the region irradiated primarily by the beamed radiation, thereby promoting heating of the base body and thus increasing the efficiency.

[0031] It can also be advantageous to arrange multiple base bodies one after the other in the main flow direction. Each base body can have a different pore density and, therefore, a different porosity. By cascading individual base bodies one or more times over the length of the absorber, it is possible to have axial regions with different porosities in the absorber, allowing the absorber to be specifically designed in a manner that is most advantageous for optimal efficiency. In particular, a high porosity in the region on the gas inlet side is advantageous.

[0032] Furthermore, it is advantageous if the base body forming the gas inlet side has a first metal foil which is shortened in comparison to a second metal foil.

[0033] According to another aspect, a solar absorber of the type presented here is used to improve the solar-weighted absorption rate and / or thermal efficiency of a solar power plant. For further details of this use, reference is made to the described application description and / or effects or advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention and its background are explained in detail below based on exemplary embodiments with reference to the accompanying schematic drawings. It should be noted that elements marked with the same reference numerals in the drawings may have the same characteristics, unless otherwise explicitly stated. The illustrated elements of the drawings may be further characterized by facts from other drawings and / or the description and / or the claims (and vice versa), unless this is explicitly excluded below. In the drawings:

[0035] Figure 1 shows a cross-section through an absorber with a base body housed in a jacket housing and a connected funnel and connecting tube, and

[0036] Figure 2 The figure shows a plan view onto the main body with a circumferentially extending compensation layer between the main body and the jacket housing. DETAILED DESCRIPTION

[0037] Figure 1 A section through a solar absorber 1 is shown. The solar absorber has a base body 2 held in a jacket housing 3. The jacket housing 3 is connected to a funnel 4, to which a connecting pipe 5 is connected.

[0038] The main body 2 forms a gas inlet side 6 which projects beyond the jacket housing 3 in the main throughflow direction 7. Figure 1It is not apparent how the first metal foil (smooth layer) is shorter than the second metal foil (corrugated layer) and thus produces an increased porosity in the region of the gas inlet side 6. In other words, the smooth layer does not extend as far as the gas inlet side 6, but rather, for example, extends in the (axial) region between the end edge of the corrugated layer and the end edge of the jacket housing 5.

[0039] Air can flow through the solar absorber 1 along the flow channel in the base body 2 toward the funnel 4 and ultimately toward the connecting pipe 5 , wherein the air absorbs thermal energy from the base body 2 and is thereby heated.

[0040] Figure 2 The figure shows a top view of the gas inlet side 6 of the base body 2. It can be seen that the base body 2 forms a plurality of flow channels 8, which are formed between a first metal foil and a second metal foil. Consequently, the pore density in the region of the base body 2 is higher than the pore density created by a third metal foil 9 between the base body 2 and the jacket housing 3. The third metal foil 9 extends circumferentially around the base body 2 and has a much coarser structure than the at least partially structured second metal foil of the base body.

[0041] Figure 1 and Figure 2 The embodiments described are particularly not to be construed as limiting and serve to illustrate the inventive concept.

[0042] Reference Number List

[0043] 1 Solar absorber

[0044] 2 Matrix

[0045] 3 Sheath shell

[0046] 4 Funnel-shaped piece

[0047] 5 Connecting pipe

[0048] 6 Gas inlet side

[0049] 7 Main flow direction

[0050] 8 flow channels

[0051] 9 Third Metal Foil

Claims

1. A solar absorber (1) for use in a solar power generation facility, wherein: The solar absorber (1) has at least one base body (2) which is accommodated in a jacket housing (3), wherein the base body (2) is composed of a plurality of metal foils, wherein a first metal foil is smoothly constructed and a second metal foil is at least partially structured, wherein the metal foils are stacked on one another and a plurality of flow channels (8) are constructed between the metal foils, through which a gas can flow in a main flow direction (7) from a gas inlet side (6) to a gas outlet side, and is characterized in that the jacket housing (3) is connected to a funnel-shaped part (4) to which a connecting pipe (5) is connected, wherein a fluid can flow through the flow channels (8) along the funnel-shaped part (4) to the connecting pipe (5).

2. The solar absorber (1) according to claim 1, characterized in that Compared to the main body (2), the jacket housing (3) has a shorter extension in the main throughflow direction (7).

3. A solar absorber (1) according to any one of the preceding claims, characterised in that A corrugated third metal foil (9) is arranged between the base body (2) and the jacket housing (3), which third metal foil has a significantly stronger structuring than the second metal foil.

4. The solar absorber (1) according to claim 3, characterized in that The corrugated third metal foil (9) is wound around the base body (2) in the circumferential direction and forms a flow channel extending parallel to the main throughflow direction (7) between the base body (2) and the jacket housing (3).

5. A solar absorber (1) according to any one of the preceding claims, characterised in that Compared to the second metal foil, the first metal foil has a shorter extension in the main throughflow direction (7) of the base body (2).

6. The solar absorber (1) according to claim 5, characterized in that The first metal foil and the second metal foil end flush on the gas outlet side, and the first metal foil is arranged offset relative to the second metal foil on the gas inlet side (6) in the main throughflow direction (7).

7. A solar absorber (1) according to any one of the preceding claims, characterised in that The main body (2) projects beyond the jacket housing (3) with its gas inlet side (6).

8. A solar absorber (1) according to any one of the preceding claims, characterised in that A plurality of substrates are arranged in sequence along the main flow direction (7).

9. The solar absorber (1) according to claim 8, characterized in that The base body (2) forming the gas inlet side (6) has a first metal foil which is shortened compared to the second metal foil.

10. Use of a solar absorber (1) according to any one of the preceding claims for improving the solar-weighted absorptivity and / or thermal efficiency of a solar power plant.

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