Receiver system for solar installations and solar installation

Abstract

A receiver system (1) for solar installations (100), comprising at least one first receiver (3) having a hollow chamber and having a first aperture (5), a high-temperature process being solar-thermally operable in the hollow chamber, and comprising at least one second receiver (7), which annularly surrounds the at least one first receiver (3), a heat-transfer medium being heatable by means of the at least one second receiver (7).

Description

[0001] Receiver system for solar power plants as well as solar power plants

[0002] The present invention relates to a receiver system for solar power plants and to a solar power plant with such a receiver system.

[0003] For the most efficient provision of solar high-temperature heat for solar thermochemical processes, only concentrating solar technologies are suitable, as only these can currently provide the required temperature level in a stationary receiver, which is usually designed as a hollow chamber receiver. Such solar systems consist of numerous biaxially controlled mirrors (heliostats) that direct sunlight onto one or more receivers, which are stationary on one or more towers. In the receivers, the high-temperature heat generated in this way is absorbed by a suitable heat transfer medium and made available for use.

[0004] When using solar energy in solar tower systems, it is important to note that the sun appears from Earth as a circular light source with a diameter of approximately 10 mrad. This angle results from the ratio of the sun's diameter (~1.4 million km) to the average distance from Earth, which is approximately 1:100.

[0005] 150 million km). This means that every beam of light directed from a heliostat to the receiver spreads out at this angle, even under ideal conditions. In some solar tower power plants, the average beam path from the heliostats to the receiver is approximately 1 km, and consequently, the diameter and height of the receivers would each need to be on the order of 10 m.

[0006] The projection area of ​​the receiver visible to the heliostat is referred to in the scientific community as the aperture. The portion of solar radiation that does not reach the receiver is called scattered radiation or spillage. Providing high-temperature heat (temperature level > 1000 °C) requires a particularly high energy density of solar radiation (flux density), while at the same time the apertures should be as small as possible to minimize radiation losses, although this increases the spillage.

[0007] Even with high accuracy of the mirror surface and control, the heliostats generate an approximately Gaussian flux density distribution at the aperture plane, with a peak at the target point. This results in a comparatively low radiation flux density at the edges. Simulations have shown, however, that a large proportion (>80%) of the radiation does not reach the aperture and remains almost unused, requiring cooling to dissipate it and prevent damage to the structures surrounding the receiver. Due to the lower flux density towards the edges, increasing the aperture is not practical, as this would lead to excessively high additional radiation losses.

[0008] To reduce radiation losses due to spillage, secondary concentrators surrounding the aperture can be used. However, these often involve significant design complexity, particularly regarding the necessary cooling, as well as considerable maintenance effort for cleaning, with only moderate additional benefits. Even with secondary concentrators, spillage can still account for approximately 80%.

[0009] The receivers described above are part of the applicant's general knowledge, but do not refer to a specific, published state of the art.

[0010] The object of the present invention is to provide a receiver system for solar power plants that enables improved utilization of concentrated solar radiation compared to previously known receivers. It is further an object of the present invention to provide a solar power plant with such a receiver.

[0011] The receiver system according to the invention is defined by the features of claim 1.

[0012] The solar system according to the invention is defined by the features of claim 10.

[0013] The receiver system for solar thermal systems according to the invention comprises at least one first receiver with a hollow chamber and a first aperture, wherein a high-temperature process can be operated solar-thermally within the hollow chamber. The invention is characterized in that the receiver system comprises at least one second receiver that surrounds the at least one first receiver in a ring-like manner, and wherein a heat transfer medium can be heated by means of the at least one second receiver. By means of the at least one second receiver that surrounds the first receiver in a ring-like manner, the solar radiation that does not reach the aperture of the first receiver, and which remained unused as spillage in previous receivers, can be at least partially utilized by the second receiver, in that this solar radiation is at least partially absorbed by the second receiver and used to heat a heat transfer medium.

[0014] The receiver system according to the invention can thus operate a high-temperature process using the first receiver, achieving operating temperatures of, for example, > 1000 °C. Lower temperatures, for example < 1000 °C, such as between 500 °C and 1000 °C, can be generated using the at least one second receiver.

[0015] The at least one first receiver can therefore be, for example, a solar-thermochemical receiver, with the corresponding reactions being carried out using solar thermal energy in the hollow chamber. The hollow chamber of the at least one first receiver can thus be designed, in particular, as a reactor for thermochemical reactions. The at least one second receiver can, for example, be a solar-thermal receiver.

[0016] By means of the receiver system according to the invention, the concentrated solar radiation occurring as spillage with respect to the at least one first receiver, which has a lower flux density than at the center of the concentrated radiation, can thus be advantageously used by the at least one second receiver to heat the heat transfer medium. This significantly increases the efficiency of the receiver system according to the invention and, moreover, reduces or eliminates the need for complex cooling measures around the at least one first receiver. The heat transfer medium heated by the at least one second receiver can, for example, be used as heat, for generating electricity, or for preheating a material for the high-temperature process carried out in the first receiver.

[0017] The first receiver can be used for processes such as calcination or metallurgical processes. It is also possible to perform synthesis processes of fuels (solar fuels) such as hydrogen, methanol, ammonia, or kerosene. The cavity of the first receiver can be configured as a reactor.

[0018] The receiver system according to the invention can also provide several first receivers which are jointly surrounded in a ring-like manner by at least one second receiver. In other words, several first receivers are arranged close together centrally on the target area for the concentrated solar radiation, with the at least one second receiver jointly surrounding the several first receivers in a ring-like manner.

[0019] Of course, it is also possible for several second receivers to be provided, which surround the at least one or more first receivers in a ring-like manner. The invention can also provide for several first receivers, each of which is surrounded in a ring-like manner by at least one second receiver. In this embodiment, the first receivers are arranged at a distance from one another on the target surface and each is surrounded in a ring-like manner by one or more second receivers. In such an arrangement of the receiver system according to the invention, it can be provided during operation that a portion of the solar radiation is focused onto one of the first receivers at a time.

[0020] Preferably, the at least one second receiver is designed as an open, volumetric receiver. This design has proven particularly advantageous because open, volumetric receivers can advantageously utilize solar radiation, even at lower flux densities, to heat a heat transfer medium. Preferably, the open, volumetric receiver uses air as the heat transfer medium. Furthermore, an open, volumetric receiver has the advantage of typically being modular in design, thus allowing it to be advantageously arranged around the at least one first receiver or the multiple first receivers.

[0021] Preferably, the at least one second receiver has several absorbers arranged in a ring around the at least one first receiver or around one of the first receivers, wherein, during operation, the receiving surfaces of the absorbers are exposed to solar radiation and air can flow through the absorbers. The configuration with multiple absorbers has the particular advantage that, on the one hand, a flexible arrangement of the absorbers around the at least one or the first receivers is possible, and, on the other hand, flexible operation is also possible, for example, by adjusting the volume flow of air through individual absorbers depending on the radiation flux density reaching the absorbers.

[0022] The absorbers can be designed to each have a support body with a porous absorber body, the absorber body forming the respective receiving surface. The porous absorber body can be made, for example, of ceramic honeycomb structures, wire mesh, or a metallic foam. Such materials have proven effective in forming a porous structure that is both heatable by solar radiation and advantageously permeable to air.

[0023] In the receiver system according to the invention, it can also be provided that the at least one second receiver is configured as a cavity with a second aperture, wherein absorber tubes for conveying the heat transfer medium are arranged in the cavity. The at least one second receiver can thus, as an alternative to the configuration as an open, volumetric receiver, be configured as a cavity into which the radiation enters to heat the absorber tubes arranged in the cavity and the heat transfer medium conveyed therein. The at least one second receiver can therefore be configured as a type of cavity receiver.

[0024] In one embodiment of the receiver system according to the invention, the at least one first receiver may have a secondary concentrator surrounding the first aperture. Thus, the first receiver may have a secondary concentrator surrounding the first aperture to improve the introduction of radiation into the cavity. The secondary reflector may be cooled by a cooling device.

[0025] Preferably, a plate transparent to solar radiation is arranged at the first aperture, at least partially closing it. Solar radiation can advantageously be introduced into the cavity via the transparent plate, while simultaneously reducing or preventing exchange between the interior of the cavity and the atmosphere. With a transparent plate that completely closes the first aperture, a desired atmosphere can thus be created and maintained within the cavity. Similarly, a negative pressure can be created within the cavity. For example, an oxygen-depleted atmosphere can be generated in the first cavity for certain thermochemical reactions.

[0026] In the context of the invention, a plate transparent to solar radiation is understood to be a plate which has a hemispherical solar transmittance (AM 1,5) of at least 85% for solar radiation.

[0027] The invention further relates to a solar power plant with at least one solar tower on which a receiver system according to the invention is arranged, and with a heliostat field with several heliostats that can be focused on the receiver system.

[0028] The heliostats can be designed to focus on the first aperture of the first receiver. It is also possible for the receiver system to have multiple first receivers, with a portion of the heliostats being focusable on the first aperture of each of the first receivers.

[0029] The invention will be explained in more detail below with reference to the following figures. These show:

[0030] Fig. 1 shows a schematic view of a solar power system according to the invention with a receiver system according to the invention.

[0031] Fig. 2 is a schematic top view of a first embodiment of a receiver system according to the invention and

[0032] Fig. 3 shows a schematic top view of a second embodiment of a receiver system according to the invention.

[0033] Figure 1 schematically illustrates a solar power system 100 according to the invention. Sunlight is reflected via heliostats 110 of a heliostat array 120 onto a receiving surface la of a receiver system 1 according to the invention, which is arranged on a solar tower 105. The heliostats 110 generate an approximately Gaussian flux density distribution of the solar radiation on the receiving surface la with a peak in the center, the flux density decreasing towards the edge.

[0034] Figures 2 and 3 show two embodiments of the receiver system 1 according to the invention schematically in a top view.

[0035] To advantageously utilize the flux density distribution of concentrated solar radiation generated by the heliostats 110, the receiver system 1 according to the invention has a centrally arranged first receiver 3. This receiver can, for example, be configured with a hollow chamber and a first aperture 5. A high-temperature solar thermal process can be operated in the hollow chamber of the first receiver 3. For example, a solar thermochemical process can be operated with the first receiver 3. A second receiver 7 is arranged annularly surrounding the aperture 5 of the first receiver 3. The second receiver 7 is configured as a solar thermal receiver and serves to heat a heat transfer medium. In the embodiment shown in the figures, the second receiver 7 is configured as an open, volumetric receiver.The second receiver 7 has several absorbers 9 arranged side by side in multiple rows, forming a ring around the first aperture 5 of the first receiver 3. Each absorber 9 has a support body with a porous absorber body, the porous absorber body forming a receiving surface 9a for solar radiation. Air can flow through the porous absorber body. During operation, air located in front of the receiving surfaces 9a is drawn in by the absorbers 9 and heated by the porous absorber bodies warmed by the solar radiation.

[0036] The design of the second receiver 7 as an open, volumetric receiver offers the particular advantage that the different flux density distribution of the solar radiation can be advantageously used for heating the heat transfer medium, since the volume flow of the heat transfer medium (air) drawn in through the individual absorbers 9 is controllable. Thus, a relatively uniform temperature of the heated heat transfer medium can be achieved.

[0037] Furthermore, the design of the second receiver 7 with several absorbers 9 offers the advantage that a ring-shaped arrangement of the second receiver 7 around the first receiver 3 can be created in a structurally simple way.

[0038] Figure 3 schematically shows a second embodiment of the receiver system 1 according to the invention. In the receiver system 1 shown in Figure 3, the first receiver 3 has a secondary concentrator 11 around the aperture 5. The second receiver 7 is designed in a comparable form to the embodiment shown in Figure 2 and also has several absorbers 9 forming receiving surfaces 9a. In the embodiment shown in Figure 3, the second receiver 7 is also designed as an open, volumetric receiver.

[0039] In the receiver system 1 according to the invention, the aperture 5 of the first receiver can be designed to be comparatively small without causing energy disadvantages due to excessive spillage, since the spillage can be advantageously used thermally by the second receiver 7.

[0040] The heat transfer medium heated in the second receiver 7, for example air, can be used to provide heat or to generate electricity. It is also possible to use the heated heat transfer medium to preheat reaction material used in the first receiver. List of references

[0041] Receiver system first receiver

[0042] Aperture of second receiver

[0043] Absorber a Receiving surface 1 Secondary concentrator 00 Solar system 05 Solar tower 10 Heliostat 20 Heliostat field

Claims

Claims 1. Receiver system (1) for solar systems (100), comprising at least one first receiver (3) with a hollow chamber and with a first aperture (5), wherein a high-temperature process can be operated solar thermally in the hollow chamber, characterized by at least one second receiver (7) which surrounds the at least one first receiver (3) in a ring shape, wherein a heat transfer medium can be heated by means of the at least one second receiver (7).

2. Receiver system according to claim 1, characterized by several first receivers (3) which are jointly surrounded in a ring shape by the at least one second receiver (7).

3. Receiver system according to claim 1 or 2, characterized by several first receivers (3) each being surrounded in a ring shape by at least one second receiver (7).

4. Receiver system according to one of claims 1 to 3 characterized in that the at least one second receiver (7) is designed as an open volumetric receiver.

5. Receiver system according to claim 4, characterized in that the at least one second receiver (7) has several absorbers (9) which are arranged in a ring-like manner surrounding the at least one first receiver (3) or in a ring-like manner surrounding one of the first receivers (3), wherein in operation receiving surfaces (9a) of the absorbers (9) are exposed to solar radiation and the absorbers (9) are permeable to air.

6. Receiver system according to claim 5, characterized in that the absorbers each have a carrier body with a porous absorber body, wherein the absorber body forms the respective receiving surface (9a).

7. Receiver system according to one of claims 1 to 3 characterized in that the at least one second receiver (7) has a cavity with a second aperture, wherein absorber tubes for conveying the heat transfer medium are arranged in the cavity.

8. Receiver system according to one of claims 1 to 7, characterized in that the at least one first receiver (3) has a secondary concentrator (11) surrounding the first aperture (5).

9. Receiver system according to one of claims 1 to 8, characterized in that a plate transparent to solar radiation is arranged at the first aperture (5) which at least partially closes the aperture (5).

10. Solar power plant (100) with at least one solar tower (105) on which a receiver system (1) according to one of claims 1 to 9 is arranged, and with a heliostat field (120) with several heliostats (110) that can be focused on the receiver system (1).

11. Solar system according to claim 10, characterized in that the heliostats (110) are focusable on the first aperture (5) of the first receiver (3).

12. Solar system according to claim 10, characterized in that the receiver system (1) has several first receivers (3), wherein a portion of the heliostats (110) can be focused on the first aperture (5) of one of the first receivers (3).

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