CH704007A1 - Solar collector comprises first concentrator arrangement having first radiation path with combustion line portion, which exhibits incident solar radiation alternately in operating region, and absorber arrangement for concentrated radiation - Google Patents

Abstract

Solar collector comprises a first concentrator arrangement having a first radiation path with a combustion line portion, which exhibits incident solar radiation (5) alternately in an operating region, and an absorber arrangement for concentrated radiation. The first concentrator arrangement comprises many concentrator sections with a focal line area, and a second concentrator arrangement is provided with many rows of additional concentrators along the length of the absorber arrangement, which are arranged behind one another. Solar collector comprises a first concentrator arrangement having a first radiation path with a combustion line portion, which exhibits incident solar radiation (5) alternately in an operating region, and an absorber arrangement for concentrated radiation. The first concentrator arrangement comprises many concentrator sections with a focal line area, and a second concentrator arrangement is provided with many rows of additional concentrators along the length of the absorber arrangement, which are arranged behind one another. The additional concentrators of each row respectively exhibit an associated focal line area and are arranged in the first radiation path before the respective focal line area, and the additional concentrators have a second radiation path, each with a focal line area. The collector exhibits a device for running the alignment in an alignment region of additional concentrators against an actual path of a radiation of concentrator section of the first concentrator arrangement. A thermal opening is associated with each row of additional concentrator, respectively along the length of the absorber arrangement, which is arranged on the absorber arrangement in adjacently extending rows. The device is provided for aligning the running additional concentrators, whose focal point areas are fixed in its associated thermal opening. An independent claim is also included for an absorber tube (7), where the absorber arrangement is formed as an absorber tube, and is completely insulated on the outside including the areas situated between the thermal openings.

Description

The present invention relates to a solar collector according to claim 1.

Radiation collectors or concentrators of the type mentioned u.a. in solar power plants application.

To date, it has not been able to produce 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 focused 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, increased (on the "tower") mounted absorber for hundreds to thousands of individual mirrors with mirrored to him sunlight, so the radiation energy of the sun over the many mirrors or concentrators concentrated in the absorber and so Temperatures up to 1300 ° C to be achieved, which is favorable for the efficiency of the downstream thermal machines (usually a steam or fluid turbine power plant 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 common and have collectors in high numbers, which have long concentrators with small transverse dimension, and thus do not have 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. The transport medium is e.g. Thermal oil, molten salts or superheated steam in question.

The 9 SEGS parabolic trough power plants in Southern California together produce an output of about 350 MW. The "Nevada Solar One" power plant, which went online 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 overall system (Andasol 1 to 3), a peak efficiency of about 20% and an annual average efficiency of about 15% is expected.

As mentioned, an essential parameter for the efficiency of a solar power plant, the temperature of the heated by the collectors transport medium through which the heat is transported away from the collector and used for the conversion into, for example, electricity: with higher temperature can be a higher efficiency at to achieve the conversion. 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 m2 corresponding to 50 times the energy radiated from the sun to one m2 of the earth's surface is achieved.

The theoretically maximum possible concentration depends on the geometry of the earth-sun, i. from 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 industrial use (too) expensive mirrors are well approximated 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 only almost 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 panel at a reasonable cost, the Applicant has proposed in WO 2010/037 243 a trough collector having a pressure cell with a flexible, clamped in the pressure cell concentrator. The concentrator is curved differently in different areas and thus comes quite close to the desired parabolic shape. Although this makes it possible to achieve a temperature of about 500 ° C in the absorber tube at a reasonable cost for the concentrator, but not a once again increased process temperature in the absorber tube.

Accordingly, it is the object of the present invention to provide a gutter collector for the production of heat on an industrial scale, which allows to produce even higher temperatures in the transport medium.

This object is achieved by a solar collector with the features of claim 1.

Characterized in that reflected by the second concentrator arrangement, the reflected solar radiation is no longer reflected in a focal line area, but in at least one focal area, results in a concentration in one-dimensional trough concentrator, which is two-dimensional, namely a concentration over the length of the collector in a focal line and then across its width in at least one focus area. This increases the theoretically possible maximum concentration to more than 40 000. Of course, this maximum possible concentration can not be reached here. However, a small realization of this enormous potential allows to increase the temperatures in the transport medium of the task according to and thus to improve the efficiency of the power plant (or even a smallest heat generating unit).

Characterized in that the at least one concentrator of the second concentrator is continuously aligned with respect to the current, first radiation path, losses in the second concentrator can be avoided due to, for example, the time of day according to obliquely incident solar radiation and a high efficiency of the arrangement at any time be ensured ,

In a preferred embodiment, the focal point region of the at least one concentrator of the second concentrator assembly remains stationary and thus at a constant location on the absorber tube. This, in turn, despite changing incident solar radiation to reduce the thermal opening of the absorber tube to the cross section of the incoming radiation path, with the result that the relevant heat losses of the absorber tube decrease and increases the efficiency of the solar power plant.

Accordingly, the present invention also relates to an absorber tube having the features of claim 10.

Characterized in that a number of spaced-apart thermal openings are provided, a larger area of the absorber tube can be isolated, with the result that decreases in operation, the heat radiation. Since the heat radiation increases with the fourth power of the temperature, this is particularly advantageous in the case of the solar collector according to the invention for producing higher temperatures.

Particular embodiments of the present invention are described in more detail with reference to the figures.

It shows: <Tb> FIG. 1 schematically shows a conventional trough collector, as used in solar power plants, <Tb> FIG. 2a schematically shows the structure of a trough collector according to the present invention, <Tb> FIG. 2b shows a cross section through the trough collector of FIG. 2a, FIG. <Tb> FIG. 2c <sep> a longitudinal section through the trough collector of Fig. 2a, <Tb> FIG. 3 schematically shows the direction of the solar radiation incident on the time of day, <Tb> FIG. 4 <sep> a preferred embodiment of the present invention, <Tb> FIG. 5a shows a particularly preferred modification of the embodiment of FIG. 4 in a longitudinal view, FIG. <Tb> FIG. 5b <sep> the embodiment of FIG. 5a in a cross-sectional view, <Tb> FIG. 6a <sep> is a view of another embodiment of the present invention, <Tb> FIG. Fig. 6b <sep> is a cross-sectional view of the embodiment of Fig. 6a, <Tb> FIG. 7a <sep> a cross section through an additional embodiment of the invention, and <Tb> FIG. 7b <sep> is a detail view of the embodiment of FIG. 7a

Fig. 1 shows a trough collector 1 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 concealed in the Fig., Lower flexible membrane 4.

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, Fig. 2a) and are reflected by these as rays 6, towards an absorber tube 7, in which 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, FIG. 2 a).

The pressure cell 2 is mounted in a frame 9, which in turn is mounted according to the daily position of the sun in a known manner pivotally mounted on a frame.

Such solar panels are described for example in WO 2010/037243 and WO 2008/037 108. These documents are expressly incorporated by reference into this specification.

Although the present invention is preferably embodied in a trough collector of this kind, i. E. 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, each of the not relevant to the understanding of the invention parts of the trough collector are omitted, and here again mentioned that such omitted parts according to the above-described prior art (collectors with pressure cell or those with non-flexible Mirrors) are formed and can be easily determined by the skilled person for the specific application.

Fig. 2a shows a preferred embodiment of the invention. A collector 10 formed 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 affecting the frame structure and the necessary orientation over the day, according to the position of the sun, results in prohibitive constructive constraints.

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 a precise parabolic curvature of the concentrator for a theoretically as close as possible approximated focal line with reasonable cost is not feasible.

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 Fig. Omitted) pressure cell, the organs for maintaining and controlling the pressure and the frame in which the concentrator 11 is stretched. 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 concentrator), 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 ranges 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 region. The second concentrator arrangement here includes, for example, still carriers 22, which are fixed to the absorber tube 12 and at which the optical elements 20 are held in position.

The absorber element formed 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.

2b shows a section in the transverse direction (arrow 17) through the collector 10 of Fig. 2a with a view of the beam path projected in this cross-sectional plane and the first and second radiation paths of the two concentrator arrangements. As mentioned above, all elements of the trough collector 10 which are not essential to the understanding of the invention are known to the person skilled in the art and have been omitted for the purpose of relieving 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 the second radiation path, represented here by the two beams 15, 15, converges toward 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 line area of the concentrator 11, i. in the focal line region of the first concentrator arrangement. Thus, 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 with respect 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 (Fig. 2a) are omitted for the optical elements 20.

Fig. 2c shows a section through the collector 10 of Fig. 2ain longitudinal direction (arrow 16), with a view of the beam path projected into 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. 2 b), FIG. 2 c shows the view of the left half of the concentrator 11 (FIG. 2 b).

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, and the second radiation path of the optical elements 20 (represented by the rays 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 follows 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 here 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.

From FIGS. 2b and 2c it is also clear 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.

Thus, it follows that the optically active surfaces (where the refraction of the light beams is generated) of the optical elements 20 with respect to the first radiation path of the first concentrator assembly (here the concentrator 11) are aligned such that the path of each beam projected onto a plane perpendicular to the focal line region (shown in FIG. 2 b) 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. 2 c).

Preferably, the optical elements have a Fresnel structure, which allows them to form with a plate-shaped body as shown in Figures 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 may be made, for example, by casting, in which a metal mold is made and a suitable transparent plastic material (or glass) is cast.

Fig. 3 shows the collector 10 and the orbit 30 of the sun from morning to evening. Shown are solar rays 31, 32 and 33, incident on the concentrator 11 at the same place and are reflected by this in the first radiation path depending on the time of day as rays 31, 32 and 33. In other words, the solar radiation alternately falls on the concentrator 11 over the time of day, i. the first Concentratorandordnung, so that its first radiation path changes continuously with the time of day, wherein the current first radiation path in the morning by the beam 31, at noon by the beam 32 and in the evening by the beam 33 is represented. Accordingly, the focal line region of the concentrator 11 is displaced only in its longitudinal axis (direction 16), but not transversely thereto. However, this is disadvantageous because the beams 31 and 33 obliquely fall on the optical element 20 (Figures 2a and 2c) and therefore partially enter this and are refracted according to the invention, but are also partially reflected by the surface of the optical element the efficiency of the solar collector 10 is negatively affected because the reflected rays do not reach the focal point area. This effect is close to zero in the case of the beam 32, and becomes larger the more obliquely the beams 31 or 33 fall on the lower surface of the optical element 20.

4 now shows an arrangement according to the invention which increases the average efficiency of the second concentrator arrangement. The FIG. 2c shows a section through the collector 10 in the longitudinal direction (arrow 16) analogously to FIG. 2, only a part of the longitudinal section being illustrated in order to explain the conditions in more detail with reference to an arbitrary optical element 20 of the collector 10 (FIG ,

The optical element 20 is pivotally connected via a carrier pair 40,40 (of which only the front in the image plane carrier 40 is visible) pivotally on its part fixed to the absorber tube 12 arranged carriers (of which only the front in the image plane carrier 41st Is visible) hinged. Thereby, it can be pivoted in the direction of the double arrow 42, in each case so that it is aligned with respect to the current radiation path of the first concentrator arrangement, i. is perpendicular to the current first radiation path. In the figure, the actual radiation path is represented by the beams 31 and 31 **. The second radiation path is represented by the rays 15 and 15 **.

The pivoting movement is triggered by a movable in the direction of the double arrow 47 lever 48 which is connected to the optical element 20 (and all other optical elements of the collector 10). A not shown to relieve the figures control of the collector 10 can drive a drive, also not shown, for the lever 48, so that the orientation of the optical element 20 is done properly at any time during the day. The feed area of the lever 48 defines an alignment area for the optical elements 20 that corresponds to the daytime radiation conditions prevailing at the location of the collector 10 (FIG. 3).

The carrier pairs with the carriers 40,40 and 41,41 and the lever 47 with the associated drive and its control are means to the at least one concentrator (in the illustrated embodiment: the optical elements 20) of the second Concentrator arrangement with respect to a current first radiation path of the first concentrator arrangement continuously, the time of day to align accordingly.

An advantage of the preferred embodiment shown in the figure is that the Verschwenkachse 43 is placed in the region of the thermal opening 45 by the carrier pair with the carrier 41, with the result that the dashed line indicated focal point area 46 over the entire Ausrichtbereich of the optical element 20 (or alignment area of the at least one concentrator of the second concentrator arrangement) is held fixed in a fixed position.

Since the absorber tube 12 is fixed relative to the concentrator 11, this is also the case for the focal point region 45. In other words, by the arrangement shown, the focus area 45 of the concentrator of the second concentrator assembly (the optical element 20) is over the entire alignment range relative to a position relative to a concentrator portion of the first concentrator assembly (here the portion of the concentrator 11 shown in the figure) kept fixed.

This arrangement allows the thermal openings 45 to be reduced to the extent of the fixed focal area 46, i. to those dimensions which result from the alternating orientation of the radiation (FIG. 3) as a whole. If the optical element 20 were not aligned according to the invention, the thermal opening would have to have a length which corresponds to the displacement of the focal point area over the time of day. With a long tanning time over day, this could even cause the individual thermal openings to touch, i. the absorber tube would have a thermal opening extending through its length. A corresponding and inventively avoidable heat loss would be the result.

5a shows a further embodiment according to the present invention, the embodiment according to FIG. 4 being supplemented by two limiting mirrors 50, 51. A preferred arrangement of such mirrors is known to those skilled in the art as Compound Parabolic Concentrator. To the knowledge of the applicant Compound Parabolic Concentrators have not been used in solar collectors with linear concentrators. In a compound parabolic concentrator, mirrors 50, 51 have a profile corresponding to a branch of a parabola, with the focal point of that parabola at the bottom of the opposite mirror. The boundary mirrors 50,51 are here attached on the one hand to the optical element 20 and on the other hand to an upper bracket 58, fixed relative to the optical element 20 and arranged pivotably therewith.

By means of these limiting mirrors 50, 51 a scattering of the radiation reflected in the first radiation path is corrected. The scattering results on the one hand from the opening angle of the sun, with the result that the solar radiation is not incident as parallel radiation, and on the other hand from the concentrator 11 itself, whose surface is not geometrically ideal to produce reasonable costs, resulting in a further disturbance of the beam path Has. Likewise, errors in the optical element 20 may cause a disturbance in the second radiation path that is corrected by the boundary mirrors 50, 51.

In the figure, a beam 31 ** is drawn in the first radiation path and a beam 15 ** in the second radiation path. It is assumed that the beam 31 ** is the reflected beam of a beam originating from the center of the sun, and that the concentrator 11 is geometrically ideally formed at the location of the rejection. Accordingly, the beam 15 ** passes ideally through the center of the focal region 46.

Further drawn in the figure is a beam 53 in the first radiation path and a beam 54 in the second radiation path. Here, it is assumed that the beam 53 is the reflected beam of a beam originating from the edge of the sun, and / or that the concentrator 11 has a geometric deviation at the location of the reflection. Accordingly, the beams 31 ** and 53 are not parallel, and further, the beam 54, despite refraction in the optical element 20 (or because of a defect in the optical element 20), is not directed to the focus area 46, but would miss it. as indicated by the dashed line 47.

The beam 54 correspondingly strikes the boundary mirror 50 and is reflected by it as a beam 55 in the focal point area 46.

This reflection at the boundary mirror 50 results in that all the radiation impinging on it within the framework of its acceptance angle is concentrated on the focal point area 46. In other words, the boundary mirrors 50, 51 represent a third concentrator arrangement having a third radiation path whose focal point region is located at the location of the focal region 46 of the second radiation path.

Fig. 5b shows a view of the arrangement of Fig. 5ain in a section along the plane AA of Fig. 5a. Visible are the underside of the optical element 20, the back of the boundary mirror 50, wherein the impact point of the beam 54 is marked by the cross drawn there.

At this point it should be noted that the figure shows the application of the limiting mirrors 50, 51 in longitudinal section through the collector 10, that is to say that their surface extends transversely, in the direction 17. However, the boundary mirrors may also be aligned with their surface longitudinally, in the direction 16, so that the beam path, for example, by non-parallel incident radiation of the sun, due to errors in the curvature of the concentrator 11 in the transverse direction (direction 17) or transversely effective errors in optical element 20 can be corrected by further concentration in a third radiation path.

In a further preferred embodiment, limiting mirrors are provided for the correction of the radiation path in the longitudinal and in the transverse direction.

Fig. 6 shows a collector 60, the first concentrator arrangement comprises a plurality of juxtaposed and longitudinal concentrator sections 61, 62. 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.

A sun ray 70 is reflected in the concentrator section 61 as a beam 71 (first radiation path of the concentrator section 61), refracted by the optical element 65, and refracted as a beam 72 (second radiation path of the optical element 65) into a focus region not visible in FIG Directed location of the hidden thermal opening 67.

Similarly, a sun ray 74 is reflected in the concentrator portion 62 as a beam 75 (first radiation path of the concentrator portion 62), refracted by the optical element 66, and as a beam 76 (second radiation path of the optical element 66) into a focus region 78 at the location of the thermal Opening 68 steered.

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 with 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 the 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.

FIG. 6b shows a collector 70 slightly modified in comparison with FIG. 6a, likewise with two concentrator sections 71, 72 and two rows 73, 74 of optical elements 20. The optical elements 20 of each row 73, 74 are assigned to their respective ones Concentrator 71.72 aligned and thus arranged obliquely, and thus according to the invention in an inclined direction indicated by the dash-dotted lines 75,76 inclined plane according to the invention. By this alignment of the optical elements 20, the efficiency of the arrangement improves. The figure further shows a sunbeam 80, a reflected beam 81 representing the first radiation path of the concentrator section 71, and a beam 82 correctly traveling (which thus passes the boundary mirror 50. Further, the figure shows a preferably walkable strip 83 as well as lateral frame parts 84 and 85, between which the concentrator sections 71, 72 are spanned, Preferably, the width of the strip 83 is selected so that only it is shadowed by the two rows 73, 74 of the optical elements 20.

Figs. 7a and 7b show another embodiment of the present invention in which the second concentrator assembly does not have a transparent optical element but a mirror. In Fig. 7a, a solar collector 100 is shown, with a pressure cell 101 of known type, clamped in a frame 102, which in turn is mounted for tracking the sun pivotally mounted on a base 103.

In the pressure cell 101, a first concentrator arrangement with a multi-part concentrator, consisting of the sections 104 and 105, wherein according to the invention a here also two-part second concentrator arrangement is provided with mirrors 106 and 107. Each mirror 106, 107 is in the radiation path The incident solar radiation is represented by the beams 110, 111, the radiation path of the concentrator sections 104 and 105 by the reflected beams 112, 113. The mirrors 106, 107 are located in the radiation path in front of the focal line region of the respective concentrator section 104, 105. The radiation path of the mirrors 106, 107 for the reflected solar radiation 112, 113 is represented by the radiation 114, 155 reflected by the mirrors. According to the invention, this reflected radiation 114, 115 is concentrated by the mirrors 106, 107 into a focal point region 116 which lies at an associated opening of the absorber tube.

The curvature of the mirrors 106, 107 required for this purpose is shown schematically in FIG. 7 b. The mirrors 106, 107 may alternatively be provided with a Fresnel structure, particularly preferably with a Fresnel lattice structure. FIG. 7b shows a view of a part of the solar collector 100, the viewing direction approximately corresponding to the arrow direction for the reference symbol 100 in FIG. 7a. To relieve the FIG., Only the absorber tube 120, one of the thermal openings 121 and a mirror 107 assigned to this opening 121 are shown. Adjacent and identically formed mirror 107, which line up under the absorber tube 120 along its entire length (arrow 16) are indicated by dashed lines, wherein each mirror 107 in turn has an opening 121 associated therewith.

The mirror 107 is curved (concave) in the longitudinal direction 16 so that, viewed in the longitudinal direction, all the incident rays 113 are concentrated on the focal point region 116, while the mirror 107 is also (concave) curved in the transverse direction 17, so the concentration on the focal region 116 in the transverse direction also takes place.

Fig. 7c shows the arrangement of Figs. 7a and 7b, wherein means according to the invention are provided to align the mirror 107 in an alignment region with respect to a current radiation path of the first concentrator arrangement. These means have a bearing 122, on which the mirror 107 is pivotably mounted about a pivot axis 123, wherein the pivoting movement is triggered by a lever 124 which is activated by a drive, not shown for relieving the FIG.

The mirrors may preferably have a Fresnel lattice structure, which the person skilled in the art can determine in a specific case so that the inventive success occurs. Such mirrors can also be produced as castings, wherein, for example, the effective optical surface of the cast part can be mirrored by a suitable coating.

It is advantageous to the arrangements shown in the figures that the second concentrator arrangement can be arranged in a pressure cell, so that it is protected from contamination. Basically, this saves the considerable effort for cleaning, not protected by the pressure cell, finely graduated Fresnel grating structures in the mirrors can not be completely cleaned even with very large cleaning effort, which must lead to losses in the performance of the collector.

Conventional absorber pipes are manufactured with more expensive and more expensive construction in order to minimize the heat losses as much 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. In WO 2010/078 668 an externally insulated absorber tube is disclosed, which is optimized by the use in a gutter collector slot opening in terms of 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.

The present invention now allows beyond the stated object to use an absorber tube, wherein the surface of the thermal opening is divided into individual, small openings and is reduced to a substantially reduced total area. Thus, the heat losses of the corresponding absorber tube are significantly reduced.

This results in a synergy with the concentrated according to the present invention in focal areas radiation: on the one hand, the possible temperature in the absorber tube is increased, and on the other hand, the heat losses from the absorber tube are reduced, which is particularly significant here, since the heat losses mainly by Heat radiation take place, which increases with the fourth power of the temperature.

Usually, a trough collector is positioned lengthwise in the east-west direction and can be aligned in height according to the daily position of the sun. As a result, the sun's rays, apart from noon, obliquely into the channel and are reflected obliquely. The beam path shown in FIG. 4 thus corresponds to a certain time over noon.

On the one hand, therefore, the thermal openings 29 in the absorber tube 28 as longitudinally extending, spaced apart slots can be provided along which the respective focus area of the time of day can migrate accordingly. Although the heat radiation is then still reduced, but not in the measure, as is the case when each thermal opening 29 is reduced substantially to the extent of the radiation path entering there.

Accordingly, another, not shown in the figures embodiment of the invention provides that an absorber tube provided with substantially reduced to the extent of the incoming radiation path thermal openings and longitudinally displaceable longitudinally mounted (direction 16 in Fig. 4) in the trough collector is such that the thermal openings can in turn follow the radiation path following the daily east-west movement of the sun, so that the above-mentioned formation of the thermal openings 29 is unnecessary as slits.

A concrete embodiment of a solar collector, for example according to FIGS. 2 to 4, with an absorber tube according to FIG. 10, has a trough collector with a concentrator of 50 m length, wherein the concentrator has two parallel regions (FIG. 3) of 4 m width which are curved so that their focal line area is located at a distance of 3 m. The curved optical elements (FIG. 7a) have a radius of curvature of 200 mm and a length of 200 mm. Correspondingly, approximately 250 optical elements are provided over the length of the absorber tube, the absorber tube (FIG. 10) having 250 thermal openings.

Claims (19)

A solar collector having a first concentrator arrangement having a first radiation path with a focal line region for solar radiation incident thereon in an operating region and having a concentrated radiation absorber arrangement characterized by a second concentrator arrangement having at least one in the first radiation path in front of the focal region thereof , in turn, a second radiation path having a focal point area further concentrator, wherein the second concentrator arrangement comprises means for the current alignment in an alignment region of the at least one concentrator with respect to a current radiation path of the first concentrator. 2. Solar collector according to claim 1, wherein the means for aligning the at least one further concentrator are formed, whose focal point over the entire alignment region relative to a relative to a concentrator section of the first concentrator arrangement fixed position, preferably at the location of a further concentrator associated thermal opening of the absorber assembly to keep it fixed. 3. The solar collector according to claim 1, wherein the second radiation path is delimited between the at least one further concentrator and its focal point area by limiting mirrors arranged laterally in the radiation path, which have a third radiation path for radiation concentrated by the at least one further concentrator, with a focal point region is located at the location of the focal area of the second radiation path. 4. Solar collector according to claim 3, wherein the limiting mirrors have a compound Parabolic Concentrator. 5. Solar collector according to one of claims 1 to 3, wherein the at least one further concentrator of the second concentrator arrangement is designed as transparent to solar radiation optical element, which preferably has a Fresnel structure, particularly preferably a Fresnel lattice structure. 6. Solar collector according to one of claims 1 to 3, wherein the at least one further concentrator of the second concentrator arrangement is formed as a mirror which preferably has a Fresnel structure, particularly preferably a Fresnel lattice structure. 7. Solar collector according to claim 1, wherein the second concentrator arrangement is mounted on the absorber element. 8. A solar collector according to claim 2 and 6, wherein the at least one further concentrator of the second concentrator arrangement is connected to a pivotable on the absorber element arranged carrier arrangement, and wherein the pivot axis is located in the focus area of the other concentrator. 9. The solar collector of claim 1, wherein the absorber element is formed as an absorber tube with a number of thermal openings and wherein each of the at least one further concentrator is associated with a thermal opening. 10. Solar collector according to claim 7 and 8, wherein the focal point region of the at least one further concentrator in the thermal opening, at the location of their smallest extension. 11. absorber tube for a solar collector characterized by a number of spaced, arranged over the length of the tube thermal openings for receiving concentrated solar radiation. 12. An absorber tube according to claim 10, wherein the thermal openings are arranged in a plurality of parallel to each other over the length of the absorber tube rows, and preferably at the same height of the absorber tube, the thermal openings of each row side by side in a group, and group by group follow each other over the length of the absorber tube each other. 13. An absorber tube according to claim 10 or 11, wherein the thermal openings are arranged in six rows. 14. The absorber tube according to claim 10, wherein the absorber tube is completely externally insulated, including the areas located between the thermal openings. 15. The absorber tube of claim 10, wherein the thermal openings form a concentrated radiation communication channel between the outside world and a transport channel for the heat transporting medium extending inside the absorber tube, and wherein the communication channel narrows to a throat having a minimum cross section. 16. absorber pipe according to claim 14, wherein the bottleneck is located on the outside of the connecting channel and this widens steadily inwards. 17. absorber tube according to claim 15, wherein the channel is seen in cross-section of the absorber tube widened with an opening angle between 100 ° and 15 °, preferably 90 °, particularly preferably 40 °, and wherein it is in longitudinal section preferably between 100 ° and 60 °, more preferably 90 ° widened. 18. absorber pipe according to claim 14, wherein the constriction is located in the interior of the channel and this opens against outside and against inside with an opening angle in cross section. 19 absorber tube according to claim 15, wherein the inside of the connecting channel is mirrored, such that concentrated incident radiation is reflected in the transport channel.