EP2630417A2

EP2630417A2 - Absorber tube for a trough collector

Info

Publication number: EP2630417A2
Application number: EP11788016.1A
Authority: EP
Inventors: Andrea Pedretti
Original assignee: Airlight Energy IP SA
Current assignee: Airlight Energy IP SA
Priority date: 2010-10-24
Filing date: 2011-10-24
Publication date: 2013-08-28
Also published as: IL225919A0; MA34660B1; CH703995A2; MA34665B1; CH704005A2; KR20140020827A; TN2013000163A1; CH703996A2; CL2013001114A1; WO2012055055A1; MX2013004580A; KR20130128406A; AU2011320097A1; CL2013001113A1; US20140026944A1; JP2013542398A; US20130247961A1; WO2012055056A2; AU2011320098A1; JP2013545958A

Abstract

The invention relates to a trough collector having a focal area and an absorber tube arranged in the focal area, said absorber tube having an insulating area that extends from its outer surface to the inside, enclosing preferably a transport channel that runs through the absorber tube along its length and carries a heat-transporting medium, and is penetrated by at least one thermal opening that extends radially from the outside through the insulating area to the transport channel. According to the invention, the at least one thermal opening comprises a constriction for radiation passing through it, the focal area being located in the constriction.

Description

Absorber tube for a gutter collector

The present invention relates to a trough collector with a combustion region and an absorber tube arranged in the combustion region.

Trough collectors of the type mentioned find u.a. in solar power plants application.

To date, it has not been able to generate solar power in application of this technology in approximately cost-covering nature because of the not yet overcome disadvantages of photovoltaics. Solar thermal power plants, on the other hand, have been producing electricity on an industrial scale for some time now at prices which, compared to photovoltaics, are close to the current commercial prices for conventionally generated electricity.

In solar thermal power plants the radiation of the sun is mirrored by collectors with the help of the concentrator and focused specifically on a place in which thereby high temperatures. The concentrated heat can be dissipated and used to operate thermal engines such as turbines, which in turn drive the generating generators.

Today, three basic forms of solar thermal power plants are in use: Dish Sterling systems, solar tower power plant systems and parabolic trough systems.

The Dish Sterling systems as small units in the range of up to 50 kW per module have not generally prevailed.

Solar tower power plant systems have a central, raised (on the "tower") mounted absorber for hundreds to thousands of individual mirrors with mirrored to him sunlight, so that the radiation energy of the sun over the many mirrors or concentrators in the absorber concentrated and thus temperatures up to 1300 ° C to be achieved, which is favorable for the efficiency of the downstream thermal machines (usually a steam or Fluentturbinenkraftwerk for power generation). California Solar has a capacity of several MW. The PS20 plant in Spain has an output of 20 MW. Solar tower power plants (in spite of the advantageously achievable high temperatures) to date also found no greater distribution.

Parabolic trough power plants, however, are widespread and have collectors in high numbers, which have long concentrators with small transverse dimension, and thus have not a focal point, but a focal line. These line concentrators today have a length of 20 m to 150 m. In the focal line runs an absorber tube for the concentrated heat (up to 500 ° C), which transports the heat to the power plant. As transport medium z.Bsp. Thermal oil, molten salts or superheated steam in question.

Conventional absorber pipes are manufactured with complex and expensive construction, in order to minimize the heat losses as far as possible. Since the heat transporting medium circulates inside the tube, the solar radiation concentrated by the concentrator first heats the tube, and this then the medium, with the result that the necessarily 500 ° C hot absorber tube radiates heat according to its temperature. The radiation of heat through the network for the heat transport medium can reach 100 W / m, the line length in a large system up to 100 km, so that the heat losses through the piping network for the overall efficiency of the power plant are of considerable importance, as well as on the absorber tubes attributable share of heat losses. WO 2010/078 668 discloses an externally insulated absorber tube whose slot opening provided by the insert in a trough collector is optimized with regard to the heat losses.

Depending on the design of the absorber tube, the term "thermal opening" can be used to denote a physical opening in the external insulation of an absorber tube according to the abovementioned publication. However, the term "thermal opening" also includes in other designs a physically closed area which is constructed for the heat transfer of concentrated solar radiation, wherein, for example, by suitable coatings at the site of heat radiation, a return of heat can be reduced. The person skilled in such constructions are known. Nevertheless, it is necessarily the case that at the location of the thermal opening ultimately no good insulation can be achieved, so the corresponding relevant heat losses must be accepted. It should be added at this point that the term "thermal opening" is further used here also for absorber arrangements in which photovoltaic cells are used which produce electricity upon irradiation. Such Absorber arrangements or absorber tubes are also according to the invention. Absorber tubes according to the present invention, which have holders for photovoltaic cells, then have such holders at the location of the thermal opening. In other words, it is then the case that the thermal openings are designed as holders for photovoltaic cells. In this case, isolation is unnecessary. Also eliminates a transport channel for heat-transporting medium.

The nine SEGS parabolic trough power plants in Southern California together produce an output of approximately 350 MW. The "Nevada Solar One" power plant, which went into operation in 2007, has trough collectors with 182,400 curved mirrors arranged over an area of 140 hectares and produces 65 MW. Andasol 3 in Spain, under construction since September 2009, is expected to be operational in 2011 so that the Andasol 1 to 3 turbines will have a maximum output of 50 MW.

For the entire plant (Andasol 1 to 3), peak efficiency of around 20% and an annual average efficiency of around 15% are expected.

As mentioned, an important parameter for the efficiency of a solar power plant is the temperature of the transport medium heated by the collectors, through which the heat recovered is transported away from the collector and used for conversion into, for example, electricity: higher temperature allows a higher conversion efficiency to be achieved , The realizable in the transport medium temperature in turn depends on the concentration of the reflected solar radiation through the concentrator. A concentration of 50 means that in the focal zone of the concentrator an energy density per m ^{2 is} achieved which corresponds to 50 times the energy radiated from the sun to one m ^{2 of} the earth's surface.

The theoretically maximum possible concentration depends on the geometry of the earth - the sun, ie on the opening angle of the solar disk observed from the earth. From this opening angle of 0.27 ° it follows that the theoretically maximum possible concentration factor for trough collectors is 213. Even with very elaborate, and thus for the industrial use (too) expensive mirrors that are close in cross-section of a parabola and thus produce a focal line area with the smallest diameter, it is not possible today, this maximum concentration of 213 even close to reach , However, a reliably achievable concentration of about 50 to 60 is realistic and already allows the above-mentioned temperatures of about 500 ° C in the absorber tube of a parabolic trough power plant.

In order to approximate as closely as possible the parabolic shape of a gutter collector at a reasonable cost, the Applicant has proposed in WO 2010/037 243 a trough collector which has a pressure cell with a flexible concentrator mounted in the pressure cell. The concentrator is curved differently in different areas and thus comes quite close to the desired parabolic shape. Although this allows to reach a temperature of about 500 ° C in the absorber tube at a reasonable cost for the concentrator.

Reference should also be made to WO 2010/099516 with an absorber tube, which shows a bottleneck in one pass through its isolation. The constriction is located on the inside of the insulation, the passage is designed as a compound parabolic concentrator (CPC). In such an arrangement, for reasons of optics, the focal region of the concentrator of the collector is on the outside of the passage where the passage is at the same time farthest. The CPC serves to continuously reflect radiation that necessarily meets the walls of the passageway throughout the passageway so that it reaches the interior of the absorber tube. This arrangement has the disadvantage that the mirror of the CPC must be cooled continuously, which brings a considerable design effort.

Object of the present invention is to provide a gutter collector for the production of heat on an industrial scale, which has the highest possible efficiency.

This object is achieved on the one hand by a solar collector with the features of claim 1 and an absorber tube with the features of claim 9.

Due to the fact that the thermal opening for radiation passing through has a bottleneck at the location of the firing region, the reflection of heat out of the absorber tube will result minimized, which increases the amount of heat that can be removed and thus increases the efficiency of the trough collector. Since the combustion region lies in the constriction, this has the minimum possible extent, since the path of the concentrated radiation entering the absorber tube has its minimal extent in the combustion region.

Due to the fact that in preferred embodiments the thermal opening widens out of the constriction, the concentrated radiation can diverge again after the firing range and thus reach the transport channel and heat the heat-transporting medium there.

On the other hand, the stated object is also achieved by a solar collector having the features of claim 19 or an absorber tube having the features of claim 21.

Characterized in that a plurality of thermal openings are arranged side by side, run over the length of the absorber tube, each section of a linear concentrator can be assigned a thermal opening. By using several sections, not only can the geometry of the trough concentrator be optimized as such (for better approximation to the parabolic shape, see WO 2010/037 243), but according to the invention additionally also reduce the width of the thermal opening in the absorber tube, to a degree in that the sum of the widths of all thermal openings in the division according to the invention is smaller than the width of a single thermal opening which receives the concentrated radiation of all concentrator sections over its entire width. This is because the concentration of solar radiation in a trough-shaped linear concentrator relatively decreases with increasing width, several sections each have smaller width and therefore higher the concentration of a thermal opening associated with only one section over its entire (and corresponding to the less wide section: even smaller) width is. In the inventive division of a conventional single longitudinal running on the absorber tube thermal opening into a plurality of longitudinal thermal openings can thus either the same amount of heat with a smaller total area of the thermal openings or total of the same area achieve a higher absorbed by the thermal openings amount of heat.

With an overall smaller area, the heat radiation of the absorber tube is reduced accordingly, whereby its efficiency is increased. Of course, instead of the longitudinally extending openings, a plurality of rows of individual thermal openings extending along the absorber tube may also be provided, as described in more detail below. As a result, the entire surface of the thermal openings is additionally reduced in an advantageous manner.

It is understood that the inventive design of the thermal openings with a constriction is not necessarily related to the arrangement of several thermal openings on the absorber tube. Although both arrangements are advantageously combined, i. a plurality of thermal openings provided next to each other, which at least partially have the bottlenecks according to the invention. However, the arrangements can also be realized independently of one another, e.g. several openings next to each other without bottlenecks or even a single, conventional, designed as a longitudinal slot on the absorber tube thermal opening, which is provided with a constriction.

Preferred embodiments of the present invention have the features of the dependent claims.

The invention will be described below with reference to the figures. It shows:

FIG. 1 shows a conventional trough collector,

FIG. 2 a shows a trough collector with a second concentrator arrangement,

FIG. 2b shows a view in a cross-sectional plane of the trough collector of FIG. 2a,

Figure 2c is a view in a longitudinal plane of the trough collector of Figure 2c

3a shows a trough collector with a second concentrator arrangement according to another embodiment 3b shows a section in a cross-sectional plane of the trough collector of Figure 3b,

FIG. 4 shows a view of an absorber tube with its thermal opening,

5a shows a cross section through a first embodiment of the absorber tube of Figure 4,

FIG. 5b shows a cross section through a second embodiment of the absorber tube of FIG. 4,

Figure 6a is a view of an absorber tube according to another embodiment

FIG. 6b shows a longitudinal section over a partial region of the absorber tube of FIG. 6a,

7a shows a view of an absorber tube according to a still further embodiment,

7b shows a longitudinal section over a portion of the absorber tube of Figure 7a, and

Figure 8 is a graph of the difference in power consumption when a row or rows of thermal openings (or photovoltaic cells) are provided on an absorber assembly.

FIG. 1 shows a trough collector 1 of conventional type with a pressure cell 2, which has the shape of a cushion and is formed by an upper, flexible membrane 3 and a lower, flexible membrane 4 concealed in the figure.

The membrane 3 is permeable to the sun's rays 5 which fall in the interior of the pressure cell 2 on a concentrator membrane (concentrator 10, Figure 2a) and are reflected by these as rays 6, to an absorber tube 7, in which a heat-transporting medium circulates which dissipates the heat concentrated by the collector. The absorber tube 7 is held by supports 8 in the focal line region of the concentrator membrane (concentrator 10, Figure 2a).

The pressure cell 2 is mounted in a frame 9, which in turn is mounted in a known manner the daily position of the sun pivotally mounted on a frame. Such solar collectors are described for example in WO 2010/037243 and WO 2008/037108. These documents are expressly incorporated by reference into this specification.

In summary, it can be stated that the radiation path of a trough collector according to FIG. 1 has a focal line region, wherein the absorber tube is arranged at the location of the focal line region.

Although the present invention is preferably used in a trough collector of this type, i. is used with a pressure cell and a clamped in the pressure cell concentrator membrane application, it is in no way limited thereto, but for example, also applicable in trough collectors whose concentrators are designed as non-flexible mirror. Collectors with non-flexible mirrors are used for example in the above-mentioned power plants.

In the figures described below, the parts of the gutter collector which are not relevant to the understanding of the invention are omitted, it being again mentioned here that such omitted parts are formed according to the above-described prior art (pressure cell or non-flexible mirror collectors) are and can be easily determined by the specialist for the specific application.

Figure 2a shows another embodiment of a trough collector, which has not yet become known. A collector 10 designed in principle like the collector 1 of FIG. 1 has a concentrator 11 and an absorber tube 12 mounted on supports 8. Sunbeams 5 fall on the concentrator 11 and are reflected by this as rays 6. The concrete design of the concentrator 11 results in a first radiation path for reflected radiation, which is represented by the beams 6.

The concentrator 11 is, as curved in one direction, a linear concentrator, with the advantage that it can be compared to the parabolic concentrators curved in two directions simpler and also produced with a large area, without having to pay for the frame structure and the day-to-day alignment necessary according to the position of the sun according to prohibitive constructive boundary conditions.

For the orientation in the figure, the arrow 16 indicates the longitudinal direction, the arrow 17 the transverse direction. Accordingly, the concentrator 11 is curved in the transverse direction 17, and not in the longitudinal direction 16.

The radiation path of the concentrator 11 has a focal line area, necessarily, since on the one hand due to the opening angle of the sun whose radiation 5 is not incident parallel, the concentration in a geometrically accurate focal line so that is not possible and also because of an exact pa rabeiförmige curvature of the concentrator is not feasible for a theoretically approximated as far as possible focal line with reasonable cost.

The concentrator 11 is part of a first concentrator assembly of the collector 10, which is formed here from the (as mentioned above to relieve the figure omitted) pressure cell, the organs for maintaining and controlling the pressure and the frame in which the concentrator 11 is clamped. As also mentioned, the omitted elements are known to those skilled in the art.

In the figure, plate-shaped, for concentrated radiation transparent optical elements 20 are arranged in the first radiation path of the concentrator 11 (and thus in the radiation path of the first Konzentratoranordnung), so that the radiation path passes through them. These optical elements 20 break the incident on it (reflected by the concentrator 11) radiation 6 such that the radiation is concentrated 6 after the optical elements 20 as radiation 15 in a focal area. In other words, the second radiation path represented by the radiation 15 of each of the optical elements 20 has a focal point region 21. In the figure, a number of optical elements 20 corresponding to the length of the solar collector are shown, and their focal point regions are shown by way of example in the case of two optical elements 20.

The optical elements 20 are part of a second concentrator arrangement, which is arranged in the first radiation path in front of the focal line area. To the second concentrator Order here include, for example, still carrier 22, which are fixed to the absorber tube 12 and where the optical elements 20 are held in position.

The absorber element embodied here as absorber tube 12 is located at the location of the focal point regions 21 and has a number, at least one, thermal openings 23 for the passage of the concentrated radiation 15 into the interior of the absorber tube 12. The thermal openings 23 are arranged one behind the other over the length of the absorber tube arranged.

FIG. 2b shows a cross-section (arrow 17) through the collector 10 of FIG. 2a with a view of the radiation path projected in this cross-sectional plane and the first and second radiation paths of the two concentrator arrangements, respectively. As mentioned above, all elements of the trough collector 10 which are not essential for the understanding of the invention are known to the person skilled in the art and have been omitted in order to relieve the figure.

In particular, it can be seen that the first radiation path of the first concentrator arrangement (concentrator 11), represented here by the two reflected beams 6, 6 ', converges toward a focal line region 21 at the location of the absorber tube 12. The radiation 6 passes through the optical element 20, wherein its second radiation path, represented here by the two beams 15, 15 ', converges towards the focal point region 21.

The concentration of the first concentration arrangement takes place in the transverse direction (arrow 17).

In the illustrated preferred embodiment, the focus areas 21 of the optical elements 20 are in the focal zone of the concentrator 11, i. in the focal line region of the first concentrator arrangement. As a result, for the view of the cross-sectional plane (not longitudinal direction, see below of FIG. 2c) shown in FIG. 2b, the reflected radiation 6 is not refracted by the optical element 20, i. essentially lying in a straight line. Essentially, because when a beam 6, 6 'passes through the optical element 20, a slight offset of the radiation path 15, 15' relative to the path 6, 6 'can occur, but this is not relevant here.

To relieve the figure again the non-essential elements, here also the carrier 22 (Figure 2a) are omitted for the optical elements 20. FIG. 2 c shows a section through the collector 10 of FIG. 2 a in the longitudinal direction (arrow 16), with a view of the radiation path projected in this longitudinal plane or first and second radiation path of the first and the second concentrator arrangement. However, only part of the longitudinal section over the length of one of the optical elements 20 is shown.

With an assumed viewing direction from right to left (FIG. 2b), FIG. 2c shows the view of the left half of the concentrator 11 (FIG. 2b).

In particular, it can be seen that the first radiation path of the first concentrator arrangement (concentrator 11), represented here by the reflected beams 6, 6 ', runs against a focal line region at the location of the absorber tube 23. The radiation 6 to 6 'passes through the optical element 20, is refracted therethrough in the longitudinal direction 16, wherein the second radiation path of the optical elements 20 (represented by the beams 15, 15') converges toward a respective focal point region 21.

The concentration of the second concentration arrangement takes place in the longitudinal direction (arrow 16).

It can be seen that the second concentrator arrangement has at least one optical element 20 with a second radiation path, wherein at least one focal point region 21 is generated by the at least one optical element 20. It should be noted that the arrangement according to the invention can be implemented for small or very small applications with only one optical element 20 or for industrial applications in collectors with the largest dimensions with tens or hundreds of optical elements 20.

FIGS. 2b and 2c further show that the optical element 20 in the illustrated embodiment is designed as a linear concentrator whose concentration direction is transverse or perpendicular to the concentration direction of the linear concentrator of the first concentrator arrangement.

This further results in that the optically active surfaces (at which the refraction of the light beams is generated) of the optical elements 20 with respect to the first radiation path of the first concentrator arrangement (here the concentrator 11) are aligned such that the path of each individual beam, projected onto a plane perpendicular to the focal line region (shown in FIG. 2b), is a straight line, but is refracted toward the focal point region 21 in a plane lying in the focal line region (shown in FIG. 2c).

The optical elements preferably have a Fresnel structure, which allows them to be formed with a plate-shaped body as shown in FIGS. 2a to 2c. For example, the underside of the plate-shaped body may be flat and the upper surface may be formed with parallel Fresnel steps, wherein the steps in the transverse direction 17 are parallel to each other, so that the focal point region lies above the center of the plate-shaped body.

The design of such a Fresnel lens 30 can be easily made by a person skilled in the concrete case. Alternatively, each optical element 20 may also be designed as a converging lens which extends transversely below the absorber tube 12 and generates the refraction according to FIGS. 2b and 2c. Such formed optical elements 20 can be made, for example, by glazing, in which a metal mold is made and a suitable transparent plastic material (or even glass) is cast.

In summary, it can be stated that the radiation path of a trough collector according to FIGS. 2 a to 2 c has a number of focal point regions arranged in a line, wherein the absorber tube is arranged at the location of the focal point regions.

FIG. 3 a shows a collector 60, whose first concentrator arrangement has a plurality of concentrator sections 61, 62 extending alongside one another and longitudinally. It should be noted at this point that the first concentrator arrangement can have not only two, but for example four, six, eight or more such concentrator sections. In WO 2010/037243 a concentrator arrangement with six sections is described.

Each concentrator section 61, 62 is assigned a row 63, 64 of optical elements 65, 66, wherein in turn each optical element 65, 66 has its own thermal opening 67, 68 in the absorber tube 69. Again, to relieve the figure, the supports for the optical elements 65, 66 and other elements not essential to understanding the invention are omitted. This arrangement has the advantage that the transverse extent (direction 17) of the individual concentrator sections 61, 62 is smaller than would be the case for a single concentrator, so that smaller focal point ranges can be achieved in comparison to a wider concentrator (opening angle of the sun). This in turn leads to smaller thermal openings 67,68, whose entire area is smaller than the area of the thermal openings with only one, but much wider concentrator.

Of course, all optical elements 65, 66 according to the invention are arranged pivotably on the absorber tube 69, as shown by way of example in FIGS. 4 to 5b. Likewise, the optical elements 65,66 as described above, for example, formed as Fresnel lenses.

A suitably designed absorber tube thus has not only one but two or more rows running along its length, each consisting of successive thermal openings 67, 68 (an example of two rows is shown in FIG. 7).

FIG. 3b shows a collector 70 which is slightly modified with respect to FIG. 3a, likewise with two concentrator sections 71, 72 and two rows 73, 74 of optical elements 20 (it may be added here that generally more than two concentrator sections may be present instead of the present one) in the figures exemplified two sections, as disclosed by way of example in the above-mentioned WO 2010/037243). The optical elements 20 of each row 73, 74 are aligned with their respective associated concentrator section 71, 72 and thus arranged obliquely, and thus can be pivoted according to the invention in an oblique plane indicated by the dot-dash lines 75, 76. By this alignment of the optical elements 20, the efficiency of the arrangement improves. The figure further shows a solar beam 80, a reflected beam 81 representing the first radiation path of the concentrate section 71, and a beam 82 (which thus runs past the boundary mirror 50) which runs correctly and passes the second radiation path lateral frame parts 84 and 85, between which the concentrator sections 71, 72 are spanned, Preferably, the width of the strip 83 is selected such that only it is shadowed by the two rows 73, 74 of the optical elements 20. In summary, it can be stated that the radiation path of a trough collector according to FIGS. 3 a and 3 b has a number of focal point regions which are arranged one behind the other in lines, with a plurality of such lines running parallel to one another. The absorber tube is in turn arranged at the location of the focal point areas.

FIG. 4a now shows a view of a preferred embodiment of an absorber tube 20. It is possible to see a schematically illustrated connection piece 21 for a line which leads the heat-transporting medium away from the absorber tube 20 (the connecting piece at the other end of the absorber tube 20 is covered). It can also be seen that a slot opening 22 leading over the length of the absorber tube 20, which forms the outer end of the thermal opening of the absorber tube, and breaks through the outer surface 23 of the absorber tube 20.

FIG. 4b shows a view of a further preferred embodiment of an absorber tube 30 which has a plurality of thermal openings 31, 32. Here are two corresponding to the number of concentrator sections 71, 72 of the collector 70 of FIG. 3b. However, it may also be, for example, six or more, with six corresponding to the number of concentrator sections of the embodiment shown in WO 2010/037243. The thermal apertures 31, 32 extend the length of the absorber tube 30. As noted above, the sum of the widths of the thermal apertures 31, 32 is less than the width of a single thermal aperture (of course, this is not provided by the walkable tab 83 of FIG 3b conditionally but applies to a concentrator with contiguous sections).

FIG. 5a shows a cross section through the absorber tube 20 of FIG. 4. An insulation region 25 extends inwards from the outer surface 23 and encloses a transport channel 26 for heat-transporting medium. The transport channel 26 passes through the absorber tube 20 in length, is connected to the connecting piece at its end and can thus convey the heat-transporting medium.

A thermal opening extending radially from the outside through the insulation region 25 to the transport channel 26 breaks through the insulation region and is designed here as a slot-shaped connection channel 27. The dashed lines 26 'and 23' in the figure show the course of the wall of the transport channel 26 and the course of the outer surface 23, as he would exist without connecting channel. This shows that the connection Channel 27 in cross section has an X - shaped contour, with a constriction 29 at the location of the drawn in the figure point 30. The connecting channel extends from the bottleneck, in the embodiment shown both inwardly and outwardly.

The figure further shows beams 30, 31 and 32, which represent the radiation path of the concentrator of the trough collector 1 (Figure 1). The beams 30, 31 and 32 intersect in the focal line area of the concentrator at the location of the point 30.

Thus, the combustion line region of the trough collector is associated with a thermal opening, which is formed as extending over the length of the absorber tube 20, slot-shaped connecting channel 27 between the outside world and the transport channel 26, wherein the bottleneck 29 of the thermal opening is located in the interior of the connecting channel 27, and wherein the connecting channel 27 widens both inwardly and outwardly.

The illustrated embodiment of the absorber tube 20 makes it possible to provide an external insulation of any desired thickness, for example of rock wool, which is embedded between the transport channel 26 and the outer surface 23, which allows a much more cost-effective production of the absorber tube 20 compared with the absorber tubes used today. In addition, according to the invention, the unavoidably present, heat radiating surface (namely: the surface of the thermal opening, here the surface of the connecting channel 27 at its throat) of the absorber tube 20 are kept minimal, which is important because the heat radiation with the fourth power the temperature rises.

FIG. 5b shows a cross section through a second, preferred embodiment of an absorber tube 35 according to FIG. 4. The constriction 36 of the connecting channel 37 rests against the outer surface 23 of the absorber tube 35. The connecting channel 37 expands inwards and has a V-shaped cross section.

The figure further shows beams 38 and 39, which represent the radiation path of the concentrator of the trough collector 1 (Figure 1). The beams 38 and 39 intersect in the focal line area of the concentrator at the location of the point 40. The embodiment shown in the figure has the above-mentioned advantages of the embodiment of Figure 5a and is also particularly easy to manufacture.

In another embodiment, not shown in the figures, the bottleneck is located on the inside of the isolation area. The connecting channel thus narrows against the inside, the combustion area is located on the inside of the insulation area. The reverse configuration of FIG. 5a is present, the connecting channel has an A-shaped cross-section.

FIG. 6 a shows an absorber tube 50 with a series of thermal openings 51 which is suitable for a trough collector 10 (FIG. 2 a), since a thermal opening in the absorber tube 50 is then assigned to each focal point region 21 of the optical elements 20.

In a longitudinal section through the absorber tube 50, it can be seen that each thermal opening (here, these are designed as connection channels 51 opening in a V-shape) are separated from the adjacent thermal opening by the insulation region 25. Again, the constriction 51 is located on the outer surface 23 of the absorber tube 50. Beams 52, 53 represent the second radiation path of the optical element 20 associated with the illustrated connection channel 51 (FIG. 2a).

Seen in the transverse direction, the connecting channels 51 have a configuration as shown in FIG. 5b (V-shaped).

Alternatively, of course, the individual connecting channels in the longitudinal and cross-section X-shaped or A-shaped (bottleneck on the inside) may be formed, analogous to the representation in Figure 5a.

FIG. 7a shows an absorber tube 100 suitable for a trough collector 60 or 70 according to FIGS. 3a or 3b. The absorber tube 100 here has two rows 101, 102 of thermal openings formed as connecting channels 103. Each of the connection channels 103 is assigned a focal point region 78 (FIG. 3a) or a focal point region of a single optical element 20 (FIGS. 3a and 3b). FIG. 7b shows a cross section through the absorber tube 100 at the location of two adjoining connection channels 103 and 103 '. Shown are rays 105 and 106 representing the second radiation path of an optical element 20 associated with the concentrator section 71 (FIG. 3b). The rays 107, 108, on the other hand, represent the second radiation path of an optical element associated with the concentrator section 72.

Again, the bottlenecks 110 and 111 on the outer surface or outer wall 23 of the absorber tube 100 and are formed in the cross section shown V-shaped (but may also be X-shaped or A-shaped). In longitudinal section, the connecting channels preferably have the configuration of the connecting channels 51 according to FIG. 6b.

The cross section of the absorber tube 100 of Figure 7b corresponds to the cross section of the absorber tube 30 of Figure 4b, correspondingly omitted here a special figure for the cross section of the absorber tube 30 with the associated reference numbers.

Preferably, at least portions of the inner wall of the connecting channels are formed such that they reflect incoming concentrated radiation toward the transport channel. This is advantageous if, due to a faulty geometry in the concentrator arrangements of the trough collector or because of the opening angle of the sun, radiation does not traverse the focal line or focal point area with the intended convergence, but travels outside the focal zone. Then, such "erroneous" radiation is reflected in the transport channel 26 and not absorbed by the isolation region 25. On the other hand, it is also possible not to form the connecting channels behind the constriction with the full opening angle of the incoming radiation and to compensate for this via reflective walls. Even then, according to the invention, the combustion region lies in the constriction, so that the heat radiation of the concentrator through the thermal opening is minimized to the outside.

It should be pointed out once again that although the arrangement according to the invention of several thermal openings in connection with the bottlenecks according to the invention are described in FIGS. 4a to 7b, a plurality of thermal openings or bottlenecks can be realized independently of each other, in which case the respective benefits without the effect of the combination come to fruition. Finally, FIG. 8 shows in a diagram a comparison between the absorber tube 20 of FIG. 4 a and the absorber tube 30 of FIG. 4 b. A denotes the width of the slot opening 22 of the absorber tube 20, B denotes the width of the two slot openings 31, 32 of the absorber tube 30. Both absorber tubes 20, 30 are assigned the same concentrator, wherein the absorber tube 20 with its slot opening 22 is arranged in the focal line area of the entire concentrator is, while the slot openings 30,31 each associated with one half of this concentrator or each focal line region of this half.

The curves over the indicated widths A and B denote the power absorbed by the respective slot openings 22 and 30, 31 via the concentrated radiation.

The difference in the power absorbed by an absorber tube 20 with respect to an absorber tube 30 corresponds to the difference between the hatched area and the two dotted areas. The dotted areas are equal to or slightly larger than the hatched area. Thus, the power consumption of the concentrator 30 with two less wide slot openings 31,31 is equal to or slightly larger than that of the concentrator 20 with only one slot opening 22nd

This effect is due to the aperture angle of the sun, whereupon reflected radiation in the concentrator necessarily scatters into a focal line region, which effect increases with increasing distance of the edge regions of the concentrator.

In summary, the efficiency of the absorber tube and thus of the collector according to the invention can be improved in three steps:

On the one hand, the thermal opening (or the cross-sectional area of the connecting channel 27 open relative to the transport channel 26) is minimized to a constriction, which is reduced to the dimension of the focal line region of conventional trough concentrators.

Then, the thermal opening is resolved into a number of smaller thermal openings, with a total area of the smaller openings that is smaller than the area of the single thermal opening. This is made possible by the use of a second concentrator arrangement which dissolves the focal line region of the trough concentrator into focal areas. Finally, the conventional thermal opening extending the length of the absorber tube is resolved into smaller width thermal openings, and each of the less wide thermal openings is associated with a concentrator section. The same heat input into the absorber tube takes place with a smaller total area of the thermal openings, as is the case with a single thermal opening. In addition, these thermal openings can be provided with a bottleneck.

Claims

claims

A trough collector having a combustion region and an absorber tube arranged in the combustion region, which has an insulating region extending inwards from its outer surface, which preferably encloses a transport channel passing through the absorber tube for heat transporting medium and at least one radially extending from the outside through the Insulation region through to the transport channel extending thermal opening is broken, wherein the at least one thermal opening for radiation passing therethrough has a bottleneck, wherein the focal region lies in the bottleneck.

2. trough collector according to claim 1 wherein the thermal opening after the constriction against continuously widening inwards, such that substantially all occurred in the thermal opening and diverging after the firing range radiation can reach the transport channel directly.

3. Trough collector according to claim 1, wherein the thermal opening is formed as extending from the outer surface of the absorber tube into the transport channel connecting channel, wherein the connecting channel behind the constriction against continuously widening inside and is preferably formed with reflective walls, such that the After the firing range again diverging radiation completely reaches the transport channel substantially without absorption on the reflective walls.

4. trough collector according to claim 1 with one or more focal line areas, each focal line region is associated with a thermal opening, which is formed as extending over the length of the absorber tube, slot-shaped connecting channel between the outside world and the transport channel, the constriction of each thermal opening preferably the outer surface of the absorber tube is located, and then widening the connecting channel towards the inside.

5. trough collector according to claim 1 with one or more focal line areas, wherein each focal line region is associated with at least one thermal opening, which extends over the length of the absorber tube extending, slot-shaped connecting channel between see the outside world and the transport channel is formed, wherein the bottleneck of each thermal opening is located in the interior of the connecting channel, so that the connecting channel widens both against inwardly and outwardly or the bottleneck is provided on the inside of the isolation area.

6. trough collector according to claim 1 having a plurality of rows of adjacent focal areas, each focal point is assigned a single formed as a connecting channel thermal opening, which is separated from the other thermal openings through the isolation area, the bottleneck is preferably located on the outer surface of the absorber tube.

7. trough collector according to claim 1 having a plurality of rows of adjacent focal areas, each focal point is associated with a single formed as a connecting channel thermal opening, which is separated from the other thermal openings through the isolation area, the bottleneck is located in the interior of the connecting channel, and wherein the connecting channel widens from this, both against the inside and against the outside expands or the bottleneck is provided on the inside of the isolation area.

8. Trough collector according to one of claims 1 to 7 wherein at least portions of the inner wall of the connecting channel are formed such that they reflect incoming concentrated radiation against the transport channel.

9. Absorber tube for a gutter collector having an outer surface of its inwardly extending isolation region, which preferably encloses a longitudinally passing therethrough transport channel for heat-transporting medium and at least one radially from the outside through the insulation region to the transport channel extending thermal opening is, wherein the at least one thermal opening in the direction of the passing radiation has a bottleneck and widened from this.

10. absorber tube according to claim 9, wherein the at least one thermal opening is formed as a slot-shaped connecting channel which extends over the length of the absorber tube, wherein the constriction is located on the outer surface of the absorber tube.

11. Absorber tube according to claim 9, wherein the at least one thermal opening is formed as a slot-shaped connecting channel which extends over the length of the absorber tube, wherein the constriction is located in its interior, and wherein the connecting channel from this both against the inside and extended to the outside.

12. absorber tube according to claim 9, wherein a number are provided in a row one behind the other over the length of the absorber tube arranged thermal openings which are separated from each other by the isolation area.

13. An absorber tube according to claim 9 or 10, wherein a plurality of rows of thermal openings are provided in parallel adjacent to each other.

14 absorber tube according to one of claims 9 to 13, wherein each thermal opening is formed as a connecting channel which extends from the outer surface inwardly, the bottleneck is located on the outer surface, and which widens against the inside.

15. An absorber tube according to any one of claims 10 to 14, wherein each thermal opening is formed as a connecting channel which extends from the outer surface inwardly, the constriction is located in its interior, and the connecting channel therefrom from both inwardly against extended outside.

16. absorber tube according to one of claims 9 to 15, wherein at least portions of the inner wall of the connecting channels are formed such that they reflect incoming concentrated radiation against the transport channel out.

17. absorber tube according to claim 16, wherein the reflective portions are formed as a compound Para- bolic Concentrator.

18. Trough collector with a linear concentrator, which is divided into several parallel to each other extending sections, characterized by an absorber tube preferably has an inwardly extending from its outer surface isolation region, which preferably encloses a longitudinally passing through transport channel for heat-transporting medium, and for each of the sections of the linear concentrator at least one thermal opening, these at least one opening per section parallel next to each other and extend over the length of the absorber tube or form per section a series of successively arranged thermal openings mounts.

19. trough collector according to claim 18, wherein the thermal openings are formed as extending from the outer surface of the absorber tube into the transport channel connecting channels, and wherein the connecting channels are separated by the isolation region of each other.

20. Absorber tube for a trough collector which preferably has an inwardly extending from its outer surface isolation region enclosing a longitudinally passing through transport channel for heat-transporting medium or has the holders for photovoltaic cells, characterized by a plurality of parallel adjacent to each other, extending itself over the length of the absorber tube extending thermal openings or through several over the length of the absorber tube running rows of thermal openings.

21. An absorber tube according to claim 17, wherein the thermal openings are formed as extending from the outer surface of the absorber tube into the transport channel connecting channels, and wherein the connecting channels are separated by the isolation region of each other.

22. absorber tube according to claim 17 or 20, wherein two, preferably four and more preferably six extending over the length of the absorber tube thermal openings or rows of openings are provided.

3. Trough collector according to one of the preceding claims, wherein the thermal openings are formed as holders for photovoltaic cells.