Absorber unit, mirror unit and solar collector or solar installation

Abstract

The invention relates to an absorber unit (3) which comprises at least one heater element (28), a transparent enclosure and a mount (29) for the enclosure, the mount (29) comprising an inner tube (32) and an outer tube (31). The invention also relates to a mirror unit which comprises at least one reinforcement (1) having a concave reinforcement element (1a), wherein an upper mirror (14) is fastened to an inner side (55) of the reinforcement element (1a) and / or a lower mirror (15) is fastened to an outer side (56) of the reinforcement element (1a). The invention also relates to a solar collector or solar installation comprising at least one support arm for receiving a mirror unit and / or an absorber unit.

Description

[0001] Mirror unit for solar energy generation

[0002] The subject of the invention is an overall unit, here referred to as a mirror unit, comprising an absorber unit, mirror, support arm, and an automatic cleaning device, including all wiring, insulation, and specific details of individual components. These mirror units can be mounted on various supports, in particular tracking frames. For example, there are collector systems with two, four, and eight mirror units. There are several variants of solar heaters. For example, there are absorber units that provide instantaneous water heaters for heating liquid and gaseous heat transfer media. Another variant, for example, provides a solar heater for evaporating condensate.

[0003] A key objective of the invention is to generate high-temperature heat with the lowest possible thermal losses and to transmit this heat via appropriately insulated lines or to transport it to a station. All lines are laid inside the support arms and can be encased in high-temperature insulation. Additional foam filling of the interior provides further thermal insulation and enables the lines to be positioned ready for connection. The system is designed to withstand temperatures of up to 400°C and pressures of up to 50 bar. The selection of suitable materials can be made depending on the temperature requirements. It is important to consider the thermal expansion of the lines by providing expansion compensators. The frame of a glass dome of the mirror unit should not come into contact with heated parts. Thermal bridges from the lines to the suspensions and between the lines must be avoided or minimized.The mirrors concentrate the sun's radiation approximately 25 times. Depending on the angle of incidence on the mirror (top or center), a steradian of 5 to 15° around the sun's core radiation is captured. This also captures diffuse radiation in the sun's immediate vicinity. The absorber glass can be shaped accordingly so that direct radiation strikes the glass surface essentially perpendicularly in all areas.

[0004] A knock-out criterion for many mounted systems is often the free wind attack surface. In systems with eight mirror units, the outer mirrors can swivel 180° and form a seal against the inner mirrors. This allows an ideal protective position with half the wind attack surface. To withstand extreme wind loads of 150 to 250 km / h, the mirrors can also be removed. A decisive criterion is the quick and easy assembly and disassembly of the mirrors. One object of the invention is achieved by an absorber unit for a solar collector or a solar system, wherein the absorber unit has at least

[0005] • a heating element, which heating element for guiding a

[0006] heat transfer medium,

[0007] • a translucent frame, in which frame the at least one

[0008] Heating element, preferably all heating elements, is or are arranged, and

[0009] • comprises a holder for the casing, the holder comprising an inner pipe and an outer pipe radially spaced from the inner pipe, the casing being fastened to the outer pipe, and a supply line and / or a return line for the heat transfer medium being guided in the inner pipe. Damage to the casing due to the effects of heat and corresponding expansion stresses can thus be avoided, since the casing is not attached to the hot part of the holder, which part accommodates the hot supply line, but to a comparatively cold part of the holder, which cold part is formed by the outer pipe, the outer pipe being separated / heat-insulated from the inner pipe by a (vacuum) annular gap. The casing is usually made of glass and is intended to be transparent for at least one spectral range of electromagnetic radiation.

[0010] Preferably, the frame is formed by a glass dome. This provides the frame with the desired optical properties with regard to the required light transmission while also providing a certain degree of stability and fracture resistance.

[0011] Preferably, an annular gap, in particular a vacuum annular gap, is formed between the inner tube and the outer tube. This annular gap opens into a receiving volume of the enclosure, and the inner tube is sealed, preferably vacuum-tight, at an end facing the receiving volume. This allows the efficiency of the absorber unit to be increased due to the thermal insulation and the avoidance of thermal bridges.

[0012] It is preferably provided that a receptacle for the heating element, in particular a welding receptacle, closes the inner tube at its end facing the receiving volume, preferably in a vacuum-tight manner. This allows the thermal insulation to be improved even further; at the same time, the receptacle enables a stable arrangement of the heating elements in the receiving volume of the enclosure. It is preferably provided that the annular gap is closed, preferably in a vacuum-tight manner, at an end of the holder facing away from the receiving volume. This means that heat is conducted from the hot end of the inner tube, which hot end can be arranged in the receiving volume or faces this, to the cold end of the outer tube, at which cold end the enclosure engages oris arranged, is possible; however, the distance between these two areas is kept to a maximum by the connection of the inner pipe to the outer pipe being arranged only at the end, so that - if a material with a correspondingly poor thermal conductivity is selected - no noticeable heating of the end of the outer pipe used to fasten the casing can occur.

[0013] Preferably, the inner tube is welded to the outer tube at the end of the bracket facing away from the receiving volume. This ensures a particularly stable connection between the inner and outer tubes, which simultaneously enables the described advantages of secure fastening of the enclosure.

[0014] Preferably, the inner tube extends beyond the outer tube with its end facing the receiving volume. This allows the inner tube to extend into the receiving volume of the enclosure, allowing a more stable and exposed arrangement of the heating element (or all heating elements). This further improves the efficiency of the absorber unit, or of a solar system or solar collector comprising the absorber unit.

[0015] Preferably, the heating element is formed by or comprises a heat exchanger. Preferably, the heating element is formed by or comprises a continuous-flow heater with coiled tubing. Preferably, the heating element is formed by or comprises a two-phase thermosiphon. Preferably, the heating element is formed by or comprises a heat pipe. In this way, particularly efficient heating of the heat transfer medium can be achieved.

[0016] Preferably, the heat pipe comprises a pressure vessel, a capillary suction layer or lining, an outer tube for discharging the heat transfer medium from the pressure vessel, wherein the outer tube has an outlet opening opening outside the pressure vessel, and an inner tube for supplying the heat transfer medium into the pressure vessel, wherein the inner tube has a first outlet, in particular a lower outlet, and a second outlet, in particular an upper outlet, wherein the first outlet and second outlet open inside the pressure vessel. This advantageous embodiment of the heat pipe enables particularly efficient energy or heat recovery by the absorber unit.

[0017] Preferably, a distribution unit is provided with several, for example five, receptacles, in or to which a heat pipe is fastened in each receptacle, wherein the distribution unit establishes a (fluidic) connection between the inner tube and the outer tube of the heat pipes accommodated in or on the receptacles, on the one hand, and the supply line and the return line, on the other. In this way, on the one hand, a particularly stable and exposed mounting of the heating elements in the receiving volume of the absorber element can be realized, while at the same time also a simple, tight, and reliable fluidic connection between the supply and return lines and the individual heating elements can be realized.

[0018] Preferably, the distribution unit forms the receptacle for the heating element. Thus, the distribution unit simultaneously assumes the function of the receptacle-side closure of the inner tube.

[0019] Preferably, the absorber unit comprises at least one reflector, with the at least one heating element, preferably each heating element, being arranged between the reflector and the enclosure. This ensures the most uniform heating possible of the heating elements in the receiving volume of the absorber unit.

[0020] Preferably, the reflector is attached to the heater element mount or to the distribution unit, and the reflector extends in the longitudinal direction of the heater element. This allows for stable and reliable mounting of the reflector and, at the same time, high efficiency of the absorber unit.

[0021] Preferably, the at least one heating element, preferably all heating elements, is / are connected to heat-conducting fins or formed integrally with them in order to increase the proportion of solar radiation absorbed by the heating element. The heat-conducting fins are preferably made of a highly thermally conductive material and enable even more efficient use of the energy flow entering the enclosure. Preferably, the heat-conducting fins of adjacent heating elements touch one another or are formed integrally with one another. This further increases the efficiency of the absorber unit.

[0022] Preferably, the heat-conducting wings have solar cells on an outer side facing the enclosure, preferably this outer side is completely covered with solar cells. In this way, photovoltaics can also be used in addition to thermal energy generation.

[0023] Preferably, the bracket is provided with a counterflange for screwing the absorber unit to a retaining flange of a support arm of the solar collector or solar system and / or retaining bolts for engaging in guide slots of a support arm of the solar collector or solar system and / or guide slots for receiving retaining bolts of a support arm of the solar collector or solar system. This allows for a particularly simple and reliable attachment of the absorber unit to the support arm.

[0024] Preferably, a line outlet of the flow line and / or the return line (located away from the enclosure) has a thread for attaching one or more sliding sleeves to sealably connect the flow line and / or the return line to the internal piping of a support arm of the solar collector or solar system. The attachment option for sliding sleeves allows them to be used as expansion compensators, which absorb the thermal expansion of the lines from the support arm and / or the line outlet of the flow line and / or the return line. This improves the tightness of the solar system or collector and prevents leaks or losses.

[0025] One object of the invention is achieved by a mirror unit for a solar collector or a solar system, wherein the mirror unit comprises at least one stiffener with a concave stiffening element, wherein an upper mirror is fastened, in particular glued, to an inner side of the stiffening element and / or a lower mirror is / are fastened, in particular glued, to an outer side of the stiffening element, wherein the mirror unit further comprises a closure element, which closure element is connected to the stiffening element or is formed integrally therewith and forms a closure opening, wherein the closure element has means for releasably fastening the mirror unit to a support arm of the solar collector or the solar system. The closure element enables particularly simple assembly and disassembly of the mirror unit on the support arm or the solar system / the solar collector.The stiffening element provides structural reinforcement, particularly in the part of the mirror unit that provides attachment to the support arm. However, the fact that this stiffening is only provided in a (central) section of the mirror unit(s) allows for weight savings. The closure opening also allows for the passage of other components of the solar system / solar collector, such as the absorber unit, which can be attached to the support arm before the mirror unit is attached. In particular, this design also enables separate handling, particularly assembly and disassembly, of the mirror unit and absorber unit.

[0026] Preferably, the stiffener, in particular the stiffening element, only partially abuts the upper mirror and / or the lower mirror. Thus, structural reinforcement of the mirror unit is provided only in the area providing attachment, while outside of this area, corresponding reinforcements (which have a negative impact on the overall weight) can be dispensed with. This allows the overall weight of the mirror unit to be significantly reduced. Preferably, the stiffener or the stiffening element overlaps the upper mirror and / or the lower mirror only in a partial area, which partial area forms no more than 30%, preferably no more than 20%, in particular less than 10%, of an outer surface of the upper mirror and / or the lower mirror.

[0027] Preferably, a filling, in particular a foam filling, is arranged between the upper mirror and the lower mirror. This can protect the mirror surface and increase the stability of the mirror unit.

[0028] Preferably, the closure opening, in particular the closure element, is welded to the stiffener, in particular the stiffening element, or connected to the stiffener, in particular the stiffening element, by die-casting. The stiffening element can be formed, for example, as a welded part, an (aluminum) die-cast part, or a (plastic) injection-molded part. This allows the closure element and stiffening element to be connected to each other in a particularly reliable and stable, yet cost-effective manner.

[0029] It is preferably provided that the closure element has a, preferably circumferential, guide recess, which guide recess is designed to receive one or more bolts of a holding flange of the support arm and comprises a stop, in particular a jaw, for defining a stop position of a bolt, and the closure element further has a locking element, in particular a locking bolt, for locking the bolt in the stop position. The mirror unit can be mounted with an upper limit of the guide recess, i.e. with the closure element, on or on the bolt of the holding flange. This embodiment allows for a particularly simple fastening, which can be established and released again in a time-saving manner, namely by means of a bayonet lock.

[0030] Preferably, the closure element has insertion openings to allow the bolts to be inserted into the guide recess. The arrangement of the guide recesses also allows a desired rotational position to be defined, in which rotational position the mirror unit is to be connected to the retaining flange. This facilitates the coordination of the mirror unit and the absorber unit.

[0031] Preferably, the lower mirror covers the rear side of the upper mirror facing the stiffener only in sections or segments. This allows for cost savings, as the costs for the deep-drawing tool for a segment are many times lower than for a full mirror. Furthermore, the degree of deformation can be kept relatively low.

[0032] One object of the invention is achieved by a solar collector or a solar system, comprising at least one support arm for receiving a mirror unit and / or an absorber unit, wherein the support arm has at least one support tube, which support tube is connected to a post or a tracking unit of the solar collector or the solar system, and at least one retaining flange for releasably fastening the mirror unit to the support arm, wherein the retaining flange has at least one radially projecting retaining bolt on one end face. In this way, a bayonet lock can be created between the support arm and the mirror unit; the retaining bolt(s) can engage in the guide recess of the closure element when the mirror unit is placed on the retaining flange, and by locking at least one retaining bolt, the mirror unit can be fixed in a specific rotational position on the retaining flange.After releasing the lock and rotating the mirror unit in the opposite direction, it can be lifted off the mounting flange again. Preferably, the mounting flange has through holes to allow a screw connection between the support arm and a mating flange of the absorber unit. This ensures secure attachment of the absorber unit.

[0033] Preferably, the support arm has at least one guide slot to enable a bayonet connection between the support arm and a mount for the absorber unit. This ensures rapid assembly and disassembly of the absorber unit on or from the support arm.

[0034] Preferably, the end face of the retaining flange is covered at least partially, preferably over its entire surface, by a seal, with the retaining bolts penetrating a sealing element of the seal. This seal can protect the closure element of a mirror unit attached to the retaining flange from water ingress and contamination on the end face.

[0035] Preferably, the seal has a projection adjoining the front sealing element and extending radially outward. This projection forms a sealing lip that engages under the retaining bolts. This prevents water from entering through the insertion openings of the closure element.

[0036] Preferably, a mirror unit according to one of the described embodiments is fastened to the support arm, wherein the retaining flange is received in the closure opening of the mirror unit and at least one, preferably all, retaining bolts is / are received in the closure element of the mirror unit. Thus, the retaining bolts of the retaining flange are located within the guide recess and enable the mirror unit to be mounted on the support arm. Furthermore, the locking of at least one bolt to the stop of the guide recess prevents rotation of the mirror unit relative to the retaining flange and thus—since the insertion openings are arranged outside the stop position / stop position of the bolts—also prevents (accidental) loosening of the connection between the mirror unit and the retaining flange.

[0037] Preferably, an absorber unit according to one of the described embodiments is attached to the support arm, wherein the counterflange is screwed to the retaining flange and / or wherein at least one of the retaining bolts of the absorber unit engages in a guide slot of the support arm to form a bayonet lock between the absorber unit and the support arm. Thus, the absorber unit can be mounted on or removed from the support arm independently of the mirror unit.

[0038] Preferably, the diameter of the closure opening of the mirror unit is selected such that the absorber unit can be passed through the closure opening. This allows the mirror unit and absorber unit to be assembled and disassembled in any order.

[0039] Preferably, the diameter of the closure opening is selected to be larger than the diameter of the enclosure, in particular the glass dome. Thus, the absorber unit can be mounted on the support arm, for example, before attaching the mirror unit, without the risk of damage. Likewise, the mirror unit can be removed from the support arm before the absorber unit. Overall, this simplifies or improves the handling of the solar system / solar collector according to the invention.

[0040] The mirrors can have a central stiffener with a ring-shaped quick-release fastener so that they can be mounted and dismounted on a support flange of the support arm purely by twisting, whereby the diameter of the ring-shaped closure opening is larger than the maximum diameter of the glass dome.

[0041] This allows the mirrors to be threaded in and out over the absorber units. When the mirrors are facing downwards, they can be easily removed or installed by two people, with a weight of approximately 25 to 30 kg. Because the mirror and absorber unit are mounted independently, the hydraulic circuit does not need to be opened. The support arm's retaining flange and the central stiffener (mirror stiffener) form a bayonet lock, which can be opened by rotating the mirror by a slight angle after releasing a locking bolt. The bayonet lock is sealed, with a gasket providing centering. Further details can be found in the figure description.

[0042] The absorber units can be attached to the support arm. This can be achieved through a sealed flange connection with through holes in the support flange, or also through a bayonet lock. The hydraulic connection can be established via two sealing elements, particularly sliding sleeves, which can be screwed onto the line outlets of the absorber. The sealing elements, particularly sliding sleeves, are sealed when screwed in and serve as expansion compensators, absorbing the thermal expansion of the lines from the support arm.

[0043] Regardless of the heater variant used, the glass dome is enclosed or attached to the outer pipe of a pipe-in-pipe system, which forms a vacuum annular gap. The inner pipe can protrude slightly beyond the outer pipe and be connected or welded in a vacuum-tight manner to the welding socket of the solar heater. The supply and return lines can be led from the welding socket through the inner pipe into the outside space. Threads are provided at the pipe ends for screwing the sliding sleeves. The annular gap between the inner and outer pipes can be sealed vacuum-tight at the lower pipe ends. The welding sockets of the solar heaters form thermal bridges to the outside. Since the heat flow through the double-walled pipe with poor thermal conductivity (e.g. stainless steel) has a long way to go before it reaches the fastening, be it a bayonet lock or mounting flange, or before it reaches the glass enclosure, these areas can be considered "cold".The heat flow is minimal. Damage to the glass frame due to heat exposure and the associated tensile stresses can be ruled out.

[0044] The mirrors should be as light as possible, yet rigid and dimensionally stable. A sandwich construction, with, for example, plastic foam filling between the upper and lower mirrors, is advantageous in this regard. The upper and lower mirrors could be manufactured using the same tool. Due to its low weight, reflectivity, and deformation properties, aluminum appears to be a suitable material for deep drawing. The sheet material can be mirrored (upper mirror) or anodized (lower mirror) before deep drawing. The mirrors could be composed of upper and lower mirror segments that are glued together in an overlapping manner. This offers advantages in manufacturing and in terms of tool costs. The mirror segments can be glued to the mirror stiffener over a large area or attached in another way. The mirror stiffener can be a welded part or a die-cast aluminum part.Rubber strips can be glued to the ends of the mirrors as a protective finish. The mirrors can be securely stacked along these edges. Designing the mirrors with double-walled panels and foam filling the space between them not only provides reinforcement but also has the advantage that hail damage only occurs on the outside, while the mirror surface remains intact. Further details can be found in the figure description (Fig. 7, Fig. 8). The absorber units can be designed in a modular manner, allowing different solar heaters to be used with consistent external and connection dimensions. Spiral heaters can be used to heat heat transfer media without a change in state, such as water, seawater, thermal oil, steam, compressed air, etc. These are very pressure-resistant and have a high heat transfer rate. The manufacture of such spiral heaters is very simple.Deposits in the pipes can be easily removed by flushing with chemically reactive liquids (acids, bases). The material selection can be tailored to the process media. This enables open processes, as is often advantageous in the food industry or in water treatment plants. Heat pipes, in particular heat pipes that independently draw in the condensate via capillary action, can be used to generate process steam. With direct evaporation, processes can be very precisely regulated to the desired temperature. The main application will be in industry. Important areas of application will be solar power generation, seawater desalination, and hydrogen production. In hydrogen production, saturated steam is generated at 30 bar.A portion of the generated steam is fed into the electrolysis station to separate hydrogen, while the remaining steam (>90%) is converted into electricity. Both the electrolysis station and the steam engine can optimally adapt to fluctuating load conditions, as is common in solar energy. Another interesting application is the generation of electricity and heat in combination with fossil and biogenic fuels. Details on the heat pipes can be found in the figure description.

[0045] It is also possible to use refrigerants as heat transfer media. For example, in absorption chillers, the refrigerant can be evaporated directly in the collectors. This eliminates the need for expensive heat exchangers in the absorption systems and leads to improved performance.

[0046] The special mirror shape makes it possible to install PV elements on the absorber surfaces, as the incident radiation intensity on the power-generating surface is largely constant. The solar heater for evaporation is already modular and suitable for assembly. With evaporation, the PV elements can be cooled evenly to the lowest possible temperatures. At cooling temperatures below 85°C, a refrigerant can be used, as water vapor has a specific volume that is too high in the lower temperature range to pass through the pipes. The hydraulic circuit serves for cooling, provided the waste heat is not additionally utilized. This is to be considered an exception to the high-temperature systems. Details can be found in the figure description. Automatic cleaning: In industrial applications, system blocks with a heating output of up to 1 MW are required.It is advisable to provide automatic cleaning here, as manual cleaning represents a considerable cost factor. In collector systems with eight mirror units, the mirrors can close each other off to form a closed interior space. Cleaning can be carried out using nozzle heads that rotate around the central mirror axis, similar to the principle of a dishwasher. The lines with the nozzles provided for this purpose, referred to here as the nozzle unit, can be attached to a free-running rotating ring on the inside of the mirror. Free-running means that the rotating ring with the nozzle unit begins to rotate without its own drive due to the impulse force when the nozzle is pushed out. An inner ring can be permanently connected to the flange for the bayonet lock and have a channel recess on the outside. The cleaning water can be supplied into the channel recess. When the (outer) rotating ring is pushed over, the channel closes.The axial position of the rotating ring can be secured by guide pins supported in the duct wall. The guide pins can have holes through which the cleaning water reaches the nozzle units. Seals between the rotating ring and inner ring are not required, but can be provided. A small amount of leakage (up to 10%) is perfectly acceptable and can even be advantageous. This way, a gap between the inner ring and the rotating ring is water-lubricated, which reduces rotational resistance. In order to thread the mirror out over the absorber, the nozzle units can be removed. Therefore, a plug-in system with a stuffing box seal is recommended for connecting the nozzle units to the mirror. Further details can be found in the figure description.

[0047] Short description of the characters

[0048] Preferred embodiments of the present invention are described in more detail below with reference to schematic drawings; however, the following description is not intended to exhaustively represent or restrict the inventive concept. In the drawings:

[0049] Fig. 1 a mirror unit in exploded view,

[0050] Fig. 2 the mirror unit in assembled state,

[0051] Fig. 3a, 3b two variants of a central stiffener for the mirror attachment,

[0052] Fig. 4a, 4b a bayonet lock,

[0053] Fig. 5 a section of a support arm with the retaining flange for the bayonet lock,

[0054] Fig. 6a, 6b a section of the support arm with a connecting flange, Fig. 7 two mirror variants in assembly with the stiffener,

[0055] Fig. 8 the segmental structure of a mirror,

[0056] Fig. 9a, 9b, 9c, 9d four absorber units,

[0057] Fig. 10 the mirror geometry with the resulting angles of incidence,

[0058] Fig. 11 a partial view of an absorber unit,

[0059] Fig. 12a, 12b, 12c the structure of a heat pipe and the assembly of an evaporator unit,

[0060] Fig. 13a, 13b the removal of the heat pipes with heat conducting wings,

[0061] Fig. 14 the structure of a sliding sleeve for expansion compensation in section,

[0062] Fig. 15 the installation of the mirror units in a collector system with two mirrors,

[0063] Fig. 16 the packaging of an absorber unit for transport,

[0064] Fig. 17 a collector system with removed mirrors,

[0065] Fig. 18a, 18b Details of the bayonet closure of an absorber unit,

[0066] Fig. 19a, 19b a cleaning device with three fixed positioned nozzle heads,

[0067] Fig. 20 a cleaning device with two rotatable nozzle heads, Fig. 21 the structure of a rotary distributor of the cleaning device.

[0068] Ways to implement the invention

[0069] Fig. 1 shows the assembly sequence of a mirror unit according to the invention. The central stiffener 1 of the mirror has a quick-release fastener with an annular closure opening 9. The diameter of the annular closure opening 9 is slightly larger than the maximum diameter of an absorber unit 3. A support arm comprises a holding flange 2 with a bolt lock, a connecting flange 11, a support tube 10, and internal piping 8. The mirror or the stiffener 1 as part of the mirror can be guided over the absorber unit 3 or threaded in and out. The holding flange 2 of the support arm and the stiffener 1 form a bayonet lock, which can be opened by rotating the mirror or its stiffener 1 by a slight angle after opening a locking bolt 4. The bayonet lock or the holding flange 2 is sealed, whereby a seal 5 also facilitates the centering of the stiffener 1 on the holding flange 2.The absorber unit 3 can be mounted on the support flange 2 of the support arm. The hydraulic connection is established via two sliding sleeves 6 of the internal piping 8, which are screwed or otherwise connected to the line outlets 7 of the absorber unit 3. When screwed in, the sliding sleeves 6 provide a seal and simultaneously serve as expansion compensators, absorbing the thermal expansion of the internal piping 8 and / or the line outlets 7 that occurs during normal operation of the device. Fig. 2 shows a mirror unit in the assembled state. The absorber unit 3 is attached to the support flange 2 of the support arm. The counter flange 12 of the absorber unit 3, via which counter flange 12 the absorber unit 3 is fastened to the holding flange 2 of the support arm, has blind holes to prevent corrosion due to water penetration at the screw connection points.Alternatively, the absorber unit 3 can also be connected to the support arm or its retaining flange 2 by means of a bayonet lock (see Figs. 18a, 18b). The sliding sleeves 6 are pushed forward, toward the line outlets 7, and screwed to the line outlets 7. The mirror or its stiffener 1 can be installed after the absorber units 3 have been installed. The mirrors are preferably installed last. This allows the collector system to be moved into an installation-friendly position so that the mirrors are facing downwards. Sliding the mirrors with their stiffener 1 over the absorber units 3 and locking them in the bayonet lock is a simple and quick process.

[0070] 3a and 3b show two variants of a central stiffener 1 for the mirrors. In variant 1 (Fig. 3a), the annular closure opening 9 is formed integrally with the mirror stiffener 1, in particular welded; in other words: a closure element 9a forming the closure opening 9 is formed integrally with a stiffening element 1a of the stiffener 1, in particular welded. An upper mirror 14 can be glued to the stiffener 1, for example in such a way that the upper mirror 14 contacts the closure element 9a and / or is also connected, in particular glued, to the closure element 9a. Variant 2 (Fig. 3b) shows a stiffener 1 formed as a die-cast part 13, wherein the annular closure opening 9, which is made of steel, for example, is inserted into the die-cast part 13 during casting and is thereby connected to it. On the die-cast part 13, which here represents the stiffener 1 orTo form the stiffening element 1a, the upper mirror 14 and lower mirror 15 are glued together. The stiffening element 1a or the stiffener 1 can also be formed as a plastic part, in particular as an injection-molded plastic part. A foam lining 16 is provided between the upper mirror 14 and lower mirror 15. These mirrors are very lightweight while being highly rigid. The foam lining 16 also serves as thermal insulation. This is a beneficial effect, as it makes it possible to operate the collector systems without frost protection. To achieve this, heat loss through the pipes and absorber 3 must be minimized. With light bundling, vacuum technology, and insulated mirrors that close together in the resting position, it is easy to prevent freezing. The thermal capacity of the pipe systems and the working fluid should be sufficient in most cases to eliminate the need for additional heating.Should the temperature nevertheless drop to a critical level, warm medium can be buffered, for example from an external storage tank, especially a two-phase storage tank. The heat required for this will be minimal. This definitely creates the possibility of withstanding extremely low temperatures for any length of time, even in areas where undiluted antifreeze would freeze.

[0071] In general, the upper mirror 14 can be attached, in particular glued, to an inner side 55 of the stiffening element 1a and / or the lower mirror 15 can be attached, in particular glued, to an outer side 56 of the (concave) stiffening element 1a.

[0072] Fig. 4a shows the bayonet catch in an exploded view; Fig. 4b in an assembled state. The locking element 9a forms an outer ring of the bayonet catch and has insertion openings 21, a jaw 17, and a locking bolt 4, wherein the locking bolt 4 can be screwed in and out. If the mirror is in the locked position, i.e., the retaining bolt 18 of the retaining flange 2 is at a stop against the jaw 17, the locking bolt 4 is screwed in. In its screwed-in state, the locking bolt 4 prevents the locking element 9a from rotating relative to the retaining flange 2. In the connected state (Fig. 4b), there is a gap 19 of approximately 3.5 mm between the annular locking opening 9 and the retaining flange 2. This is twice the size of a laser cut.This allows both components to be cut out of a single plate, saving material and wasting little waste, while still leaving sufficient material for machining. The retaining bolts 18 are pressed into end-face holes in the retaining flange 2 or are formed integrally with the retaining flange 2. Ideally, the retaining bolts 18 are hardened. In the variant shown, the retaining flange 2 has four through holes 22 for attaching the absorber unit 3 or the counter flange 12. The retaining flange 2 is a welded part of the support arm or can be formed integrally with it. The closure element 9a has a guide recess 20 for receiving the bolts 18, which guide recess 20 is accessible via insertion openings 21 for the bolts 18.

[0073] Fig. 5 shows a section of the support arm with the holding flange 2, on which holding flange 2 the holding bolts 18 are provided as part of the bayonet lock. The holding flange 2 has a seal 23 at least on the front side, which seal 23, in the assembled state, fills the annular gap 19 between the holding flange 2 and the closure element 9a of the stiffener 1. The seal 23 also serves to center the mirror or its stiffener 1 on the holding flange 2. In order to cover the insertion openings 21 of the closure element 9a, the seal 23 has a radially outwardly extending projection to form a sealing lip 24. In the embodiment shown, the projection has a semicircular profile and engages beneath the closure element 9a in its fastened state and / or rests against it. The outer sealing lip 24 is located on the back or underside of the closure opening 9 or.the locking element 9a and prevents dirt and water from penetrating into the guide recess 20 of the bayonet lock via the insertion openings 21.

[0074] Fig. 6a and 6b show a part of the support arm with the connecting flange 11 in two views. The inner piping 8 of the hydraulic piping can be seen, which is connected, preferably welded, to a sealing flange 26 of the support arm. To avoid thermal bridges, the sealing flange 26 is suspended from insulating jaws 27 on the connecting flange 11. Although not shown here, it is understood that the inner piping 8 of the hydraulic pipes can be optimally insulated or foamed. The insulation, which can be seen here on the pipes 8 in the indicated area, is incomplete and is only intended for the high-temperature range in the immediate vicinity of the pipes. The connecting flange is used to attach the support arm to a post oron a tracking unit of a solar or collector system; the sealing flange 26 serves to create a sealing (fluidic) connection between the piping of the support arm and a distribution unit of the solar or collector system (see Fig. 15).

[0075] Fig. 7a and 7b show two mirror variants assembled with the stiffener 1. Variant 1 Fig. 7a shows the stiffener 1 with the upper mirror 14, which can be mounted self-supporting on the stiffener. Variant 1 of the stiffener 1, as shown in Fig. 3, is used here. Variant 2 Fig. 7b shows an assembled mirror with upper mirror 14 and lower mirror 15, whereby upper mirror 14 and lower mirror 15 are in turn fastened to the stiffening element 1a. The stiffener 1 is designed according to variant 2, as shown in Fig. 3. The lower mirror 15 does not have to cover the upper mirror 14 completely, but can be formed by several segments that do not cover the entire mirror circumference. The stiffener 1 or the stiffening element 1a and the foam 16 or another intermediate insert can be seen at the edges of the lower mirror 15.A continuous covering of the lower mirror 14 naturally leads to the desired thermal insulation, as already mentioned above, and is therefore preferred.

[0076] Fig. 8 shows a segmented mirror structure. The segments of the upper and lower mirrors 14, 15 are glued or joined in an overlapping manner. A stiffening element 1a according to variant 1 or variant 2 can be used for this purpose. The advantage is that the costs for the deep-drawing tool for a segment are many times lower than for a solid mirror. Furthermore, the degree of deformation is relatively low (a single pressing is sufficient).

[0077] In general, therefore, an embodiment is preferred in which a mirror with a stiffening element 1a is provided, to which stiffening element 1a either only an upper mirror 14 or an upper mirror 14 and a lower mirror 15 is / are attached, preferably glued, wherein the upper mirror 14 and / or lower mirror 15 are not formed as a full-surface mirror, such as a paraboloid mirror, but rather only in segments. This is independent of other features described in the present application.

[0078] Fig. 9a, 9b, 9c, and 9d show four absorber units 3. These differ in the heating systems used. Variants 1 and 2 have flow heaters with coiled tubing. Variants 3 and 4 have heat pipes. Variant 4 shows the possibility of equipping them with solar cells. The coiled tubing of the absorber unit embodiment shown in Fig. 9b has a larger diameter than the embodiment shown in Fig. 9a, in order to accommodate a higher (steam) volume.

[0079] Fig. 10 shows the mirror geometry of a mirror according to the invention with the resulting angles of incidence and beam paths to the absorber unit 3 arranged centered on the mirror. The division of the radiation shown is chosen such that equal-sized normal radiation areas are covered. This results, as can be seen in the example with the solar cells, in a constant radiation intensity on the solar cells. The angle of incidence on the glass cover is approximately normal in all areas.

[0080] Fig. 11 shows a detail of an absorber unit 3 according to the invention. The key feature is the double-walled support of the glass enclosure with a vacuum annular gap between the inner tube 32 and the outer tube 31. The glass 30 of the glass enclosure of the absorber unit 3 is not subject to thermal stress because it is connected to the outer tube 31 of the tube-in-tube system. The inner tube 32 and the outer tube 31 are welded at the ends, preferably the ends facing away from the glass dome 30.

[0081] Regardless of the heater variant used (see Fig. 9a, 9b, 9c, 9d and the related description), the glass dome 30 can be enclosed on the outer pipe 31 of the pipe-in-pipe system, which forms a vacuum annular gap, whereby the inner pipe 32 can protrude slightly beyond the outer pipe 31 and be connected or welded in a vacuum-tight manner to a welding receptacle 25 of the solar heater. From the welding receptacle 25, the supply and return lines can be led through the inner pipe 32 into the outside space. At the ends of the supply and return lines, i.e. at the line outlet 7, threads are provided for screwing the sliding sleeves 6. The annular gap between the inner pipe 32 and the outer pipe 31 can be sealed in a vacuum-tight manner at the lower pipe ends facing away from the glass dome 30. The welding receptacles of the solar heater form thermal bridges to the outside.Since the heat flow through the double-walled pipe (pipe-in-pipe system with poor thermal conductivity, such as stainless steel) has a long path to the fastening or glass enclosure, whether bayonet fitting or mounting flange, these areas can be considered "cold." The heat flow is minimal. Damage to the glass enclosure due to heat exposure and the associated expansion stresses can be ruled out.

[0082] Fig. 12a shows the structure of a heat pipe according to the invention, and Figs. 12b and 12c show the assembly in the heating system and in the absorber unit 3 of a solar heater, respectively. The heat pipes have a pressure vessel 33, a capillary suction lining 37, a vapor-discharging outer tube 35 with an outlet opening 36, and an inner tube 38 for the condensate supply with a lower outlet 34 and an upper outlet 39. The inner tube 38 and the outer tube 35 are welded. The capillary suction lining 37 has bases with sealed pipe penetrations. The heat pipes are inserted into a distribution unit 40 with, for example, five receptacles 40a and soldered. In order to fully absorb or absorb the incident radiation,In order to be able to direct the radiation onto the rear side of the heat pipes, a reflector 41 can be provided, which reflector 41 can extend parallel to a longitudinal axis of the heat pipes from the distribution unit 40 and can be arranged, for example, in a sleeve-shaped manner in an inner region surrounded by the heat pipes. However, the reflector 41 does not have to have a cylindrical cross-section; any other cross-sections are also conceivable, for example the cross-section of an approximate pentagon as shown in Fig. 12c. The specific shape of the collector 41 can be selected depending on the heating elements 28 used and their geometry such that radiation passing by the heating elements 28 is deflected onto the rear side of the heating elements 28.

[0083] Fig. 13a shows the removal of the heat pipes with heat-conducting fins 42. In order to fully absorb the incoming solar radiation, heat-conducting fins 42 can be provided. These can also be equipped with solar cells. The heat-conducting fins 42 can be pushed or pressed onto the pressure vessels 33; for this purpose, the heat-conducting fins 42 can each have a receiving opening, which is matched to the diameter of the pressure vessels 33 of the heat pipes. The receiving openings of the heat-conducting fins 42 can also be dimensioned such that a press fit on the pressure vessel 33 results, thereby further improving the compressive strength of the heating elements 28, in particular the heat pipes. The heat-conducting fins

[0084] 42 can be dimensioned such that the heat-conducting fins 42 of adjacent heat pipes are in contact with each other when the heat pipes are connected to the distribution unit 40 as intended; alternatively, the heat-conducting fins 42 mounted on the individual heat pipes can also be formed integrally with each other, as shown in Fig. 13b.

[0085] Fig. 14 shows a sectional view of a connection between the inner piping 8 of the support arm and the line outlet 7 of the absorber unit 3 using the sliding sleeve 6 for expansion compensation. This is essentially a stuffing box system. For a sealing sleeve

[0086] 43 of the sliding sleeve 6, a temperature-resistant material with good sliding properties is preferably used. For temperatures below 250°C, Teflon, for example, can be used; for higher temperatures, ceramic materials are used.

[0087] Fig. 15 shows a collector system with two mirrors. In the illustrated assembly state, only the left support arm is equipped with a mirror, while the right support arm is not. For assembly and disassembly, the support arms are positioned so that the mirrors are facing downwards, as shown.

[0088] Fig. 16 shows the packaging of an absorber unit 3 for transport. The two-part design of the packaging, whose housings are preferably made of plastic, in particular polystyrene, expanded polystyrene, and / or extruded polystyrene, and the detachable connection of the two housing parts of this packaging, for example, using adhesive tape, make it possible to reuse the packaging.

[0089] Fig. 17 shows a collector system with removed mirrors and packaged absorber units 3. The packaging serves to protect the glass domes 30 and the heat pipes. The system is designed to accommodate four mirror units and has four support arms for this purpose. As can be seen, surfaces exposed to wind are greatly reduced, particularly with removed mirrors. Figs. 18a and 18b show a bayonet lock via which the support arm is connected to an absorber unit 3. This simplifies the assembly and disassembly of the absorber unit 3. Retaining bolts 44 of the absorber unit 3 are inserted into guide slots 45 in the support arm and locked by twisting. Subsequently, a seal 46, which seal 46 may already be attached to the absorber unit 3 before it is connected to the support arm, is pushed over the retaining bolts 44 or the guide slots 45.An anti-twist device is not provided because the hydraulic connection does not allow any twisting, meaning that once the fluidic connection has been established between the line outlet 7 and the internal piping 8, the absorber unit 3 can no longer be twisted, at least not to such an extent that it would be possible to remove the retaining bolts 44 from the guide slots 45. The variant with the bayonet lock is more cost-effective and more practical than the variant in which the absorber unit 3 is screwed to the retaining flange 2 (see Figs. 1 and 2). Thus, if there is concern that the glass 30 of the absorber unit 3 will break because strong storms are forecast, the absorber unit 3 can be dismantled by one person in a few simple steps after opening both sliding sleeves 6. For this purpose, a part of the support tube 10 located in the area of ​​the sliding sleeves 6 can be formed by a removable cover, which cover can preferably be provided with a seal.

[0090] Fig. 19a and 19b show the installation of a cleaning device with a nozzle unit 47 with three fixed nozzle heads. The nozzle unit 47 must be removed before removing the mirror.

[0091] Fig. 20 shows the installation of another cleaning device with a nozzle unit 47 with two rotatable nozzle heads. Rotation is enabled by a rotary distributor 49. The nozzle units 47 can be quickly mounted and dismounted by loosening a seal, in particular a stuffing box seal 48.

[0092] Fig. 21 shows a detail of the rotary distributor 49. The rotary distributor 49 has an inner ring with a channel 51 and an outer ring 52. The supply line 50 for a cleaning fluid leads into the inner ring 51. The fluid is discharged via nozzles 53 with a bore. The nozzles 53 are guided in the channel and thus position the outer ring 52 on the inner ring 51. A seal is not required, as a precise fit is sufficient. A small gap may even be desirable, since rotation should be smooth and the leakage of the cleaning fluid can serve as lubrication. A mirror unit is preferred in which the mirrors have a central stiffener 1 with an annular quick-release fastener 9a, so that they can be mounted and dismounted purely by twisting the holding flange 2 of the support arm.

[0093] Preferred is a mirror unit in which the holding flange 2 has a seal 5 for the bayonet lock.

[0094] A mirror unit is preferred in which the mirror consists of or comprises an upper mirror 14 and a lower mirror 15.

[0095] A mirror unit is preferred in which a foam or intermediate insert 16 is provided between the upper mirror 14 and the lower mirror 15.

[0096] A mirror unit is preferred in which the upper mirror 14 and / or lower mirror 15 are arranged in segmental overlapping manner.

[0097] A mirror unit is preferred in which the absorber unit 3 has a bayonet lock for connecting the absorber unit to the support arm.

[0098] Preferred is a mirror unit in which the absorber unit 3 has a double-walled holder 29 with an outer tube 31 and an inner tube 32.

[0099] A mirror unit is preferred in which sliding sleeves 6 are provided for the hydraulic connection of the absorber unit 3 to the inner piping 8 of the support arm.

[0100] Preferred is a mirror unit in which the absorber units 3 have heat pipes, the heat pipes comprising a pressure vessel 33, a capillary suction lining 37, a vapor-discharging pipe 35 with an outlet opening 36 and an inner pipe 38 with a lower outlet 34 and / or an upper outlet 39.

[0101] A mirror unit is preferred in which the heat pipes are accommodated in receptacles of a distribution unit 40, in particular inserted and soldered.

[0102] A mirror unit in which a reflector 41 is provided is preferred.

[0103] A mirror unit is preferred in which heat-conducting fins 42 are pushed onto the heat pipes or are attached to them. A mirror unit is preferred in which a cleaning device with a rotary distributor 49 is provided, comprising an inner ring with a channel 51, an outer ring 52, a supply line 50, and nozzles (or bolts) 53 with bores. The nozzles 53 (or bolts 53) merge into line nozzles on which the nozzle units 47 of the cleaning device are mounted.

[0104] List of reference symbols

[0105] 1 stiffening

[0106] 1a stiffening element

[0107] 2 retaining flange

[0108] 3 absorber unit

[0109] 4 locking bolts

[0110] 5 Seal

[0111] 6 sliding sleeve

[0112] 7 Line output

[0113] 8 Internal piping

[0114] 9 Shutter opening

[0115] 9a Closure element

[0116] 10 Support tube

[0117] 11 Connection flange

[0118] 12 Counter flange

[0119] 13 Die-cast part

[0120] 14 Upper mirror

[0121] 15 sub-mirrors

[0122] 16 Foaming

[0123] 17 Cheek

[0124] 18 retaining bolts

[0125] 19 Annular gap

[0126] 20 guide recess

[0127] 21 insertion openings

[0128] 22 through holes

[0129] 23 Seal

[0130] 24 Sealing lip

[0131] 25 welding recording

[0132] 26 Sealing flange insulating jaws

[0133] Heating element

[0134] bracket

[0135] glass (dome)

[0136] outer tube

[0137] inner tube

[0138] Pressure vessel lower outlet outer tube of the heat pipe

[0139] Outlet opening

[0140] Lining inner tube of the heat pipe upper outlet

[0141] Distribution unit a Holder of the distribution unit

[0142] reflector

[0143] Heat-conducting wings

[0144] sealing sleeve

[0145] retaining bolt

[0146] Guide slots

[0147] Sealing

[0148] nozzle unit

[0149] stuffing box seal

[0150] Rotary distributor

[0151] supply line

[0152] Inner ring channel outer ring

[0153] Support

[0154] Recording volume

[0155] inside

[0156] outside

Claims

Claims: Absorber unit (3) for a solar collector or a solar thermal system, wherein the absorber unit (3) comprises at least one heating element (28), which heating element (28) is designed for guiding a heat transfer medium, a translucent enclosure in which the at least one heating element (28), preferably all heating elements (28), is / are arranged, and a holder (29) for the enclosure, wherein the holder (29) comprises an inner tube (32) and an outer tube (31), wherein the enclosure is attached to the outer tube (31), and wherein a supply line and / or a return line for the heat transfer medium is / are guided in the inner tube (32). Absorber unit (3) according to claim 1, characterized in that the enclosure is formed by a glass dome (30).Absorber unit (3) according to claim 1 or 2, characterized in that an annular gap, in particular a vacuum annular gap, is formed between the inner tube (32) and the outer tube (31), which annular gap opens into a receiving volume (54) of the frame, and wherein the inner tube (32) is closed, preferably vacuum-tight, at an end facing the receiving volume (54). Absorber unit (3) according to claim 3, characterized in that a receptacle, in particular a weld receptacle (25), for the heating element (28) closes the inner tube (32) at its end facing the receiving volume (54), preferably vacuum-tight. Absorber unit (3) according to claim 3 or 4, characterized in that the annular gap is closed, preferably vacuum-tight, at an end of the support (29) facing away from the receiving volume (54).Absorber unit (3) according to any one of claims 1 to 5, characterized in that the inner tube (32) is welded to the outer tube (31) at the end of the support (29) facing away from the receiving volume (54). Absorber unit (3) according to any one of claims 3 to 6, characterized in that the inner tube (32) projects beyond the outer tube (31) at its end facing the receiving volume (54). Absorber unit (3) according to any one of claims 1 to 7, characterized in that the heating element (28) is formed by or comprises a heat exchanger. Absorber unit (3) according to any one of claims 1 to 8, characterized in that the heating element (28) is formed by or comprises a flow heater with coiled tubes. Absorber unit (3) according to any one of claims 1 to 9, characterized in that the heating element (28) is formed by or comprises a two-phase thermosiphon. Absorber unit (3) according to any one of claims 1 to 10, characterized in that the heating element (28) is formed by or comprises a heat pipe.Absorber unit (3) according to claim 11, characterized in that the heat pipe comprises a pressure vessel (33), a capillary suction layer or lining (37), an outer pipe (35) for discharging the heat transfer medium from the pressure vessel (33), wherein the outer pipe (35) has an outlet opening (36) opening outside the pressure vessel (33), and an inner pipe (38) for supplying the heat transfer medium to the pressure vessel (33), wherein the inner pipe (38) has a first outlet, in particular a lower outlet (34), and a second outlet, in particular an upper outlet (39), wherein the first outlet and the second outlet open inside the pressure vessel (33).Absorber unit (3) according to claim 11 or 12, characterized in that a distribution unit (40) is provided with several, for example five, receptacles (40a), in or on which receptacles (40a) a heat pipe is attached, wherein the distribution unit (40) establishes a connection between the inner tube (38) and the outer tube (35) of the heat pipes received in or on the receptacles (40a) on the one hand, and the supply line and the return line on the other. Absorber unit (3) according to claim 13, characterized in that the distribution unit (40) forms the receptacle for the heating element (28). Absorber unit (3) according to any one of claims 1 to 14, characterized in that the absorber unit (3) comprises at least one reflector (41), wherein the at least one heating element (28), preferably each heating element (28), is arranged between the reflector and the frame. Absorber unit (3) according to claim 15, characterized in that the reflector (41) is attached to the receptacle for the heater element (28) or to the distributor unit (40) and the reflector extends in the longitudinal direction of the heater element (28). Absorber unit (3) according to any one of claims 1 to 16, characterized in that the at least one heater element (28), preferably all heater elements (28), is connected to or integrally formed with heat-conducting vanes (42) in order to increase the proportion of solar radiation absorbed by the heater element (28). Absorber unit (3) according to claim 17, characterized in that the heat-conducting vanes (42) of adjacent heater elements (28) touch or are integrally formed with each other.Absorber unit (3) according to claim 17 or 18, characterized in that the heat-conducting vanes (42) have solar cells on an outer surface facing the frame, preferably this outer surface being completely covered with solar cells. Absorber unit (3) according to any one of claims 1 to 19, characterized in that a counter flange (12) for screwing the absorber unit (3) to a retaining flange (2) of a support arm of the solar collector or the solar system and / or retaining bolts (44) for engaging in guide slots (45) of a support arm of the solar collector or the solar system and / or guide slots for receiving retaining bolts of a support arm of the solar collector or the solar system are provided on the mounting (29).Absorber unit (3) according to one of claims 1 to 20, characterized in that a line outlet (7) of the supply line and / or the return line has threads for fastening one or more sliding sleeves (6) in order to connect the supply line and / or the return line sealingly to an inner piping (8) of a support arm of the solar collector or the solar system. Mirror unit for a solar collector or a solar system, wherein the mirror unit comprises at least one stiffener (1) with a concave stiffening element (1a), wherein an upper mirror (14) is attached, in particular bonded, to an inner side (55) of the stiffening element (1a) and / or a lower mirror (15) is attached, in particular bonded, to an outer side (56) of the stiffening element (1a), wherein the mirror unit further comprises a closure element (9a), which closure element (9a) with the. TI The stiffening element (1a) is connected to or formed integrally with the mirror unit and forms a closure opening (9), wherein the closure element (9a) has means for detachably fastening the mirror unit to a support arm of the solar collector or the solar array. The mirror unit according to claim 22 is characterized in that the stiffening element (1), in particular the stiffening element (1a), only partially abuts the upper mirror (14) and / or the lower mirror (15). The mirror unit according to claim 22 or 23 is characterized in that a filling, in particular a foam (16), is arranged between the upper mirror (14) and the lower mirror (15).Mirror unit according to any one of claims 22 to 24, characterized in that the closure opening (9), in particular the closure element (9a), is welded to the stiffener (1), in particular the stiffening element (1a), or is connected to the stiffener (1), in particular the stiffening element (1a), by die casting. Mirror unit according to any one of claims 22 to 25, characterized in that the closure element (9a) has a guide recess (20), preferably circumferential, which guide recess (20) is designed to receive one or more bolts (18) of a retaining flange (2) of the support arm and comprises a stop, in particular a jaw (17), for defining a stop position of a bolt (18), and the closure element (9a) further comprises a locking element, in particular a locking bolt (4), for locking the bolt (18) in the stop position. Mirror unit according to claim 26, characterized in that the. The locking element (9a) has insertion openings (21) to allow the bolts (18) to be inserted into the guide recess (20). A mirror unit according to one of claims 22 to 27, characterized in that the lower mirror (15) covers only a section or segment of the rear side of the upper mirror (14) facing the stiffener (1). A solar collector or solar system comprising at least one support arm for receiving a mirror unit and / or an absorber unit (3), wherein the support arm comprises at least one support tube (10), which support tube (10) is connected to a stand or a tracking unit of the solar collector or solar system, and at least one A retaining flange (2) for detachably attaching the mirror unit to the support arm, wherein the retaining flange (2) has at least one radially projecting retaining bolt (18) on one end face. A solar collector or solar system according to claim 29, characterized in that the retaining flange (2) has through holes (22) to allow a screw connection between the support arm and a counter flange (12) of the absorber unit (3). A solar collector or solar system according to claim 29 or 30, characterized in that the support arm has at least one guide slot (45) to allow a bayonet fitting between the support arm and a holder (29) of the absorber unit (3).A solar collector or solar system according to any one of claims 29 to 31, characterized in that the end face of the retaining flange (2) is covered at least partially, preferably over its entire surface, by a seal (5), wherein the retaining bolts (18) penetrate an end-face sealing element (23) of the seal (5). A solar collector or solar system according to claim 32, characterized in that the seal (5) has a projection adjoining the end-face sealing element (23) and extending radially outwards, which projection forms a sealing lip (24) that engages under the retaining bolts (18).A solar collector or solar system according to any one of claims 29 to 33, characterized in that a mirror unit according to any one of claims 22 to 28 is attached to the support arm, wherein the retaining flange (2) is received in the closure opening (9) of the mirror unit and at least one, preferably all, retaining bolts (18) are received in the closure element (9a) of the mirror unit. A solar collector or solar system according to any one of claims 29 to 34, characterized in that an absorber unit (3) according to any one of claims 1 to 21 is attached to the support arm, wherein the counter flange (12) is screwed to the retaining flange (2) and / or wherein at least one of the retaining bolts (44) of the absorber unit (3) engages in a guide slot (45) of the support arm to form a bayonet fitting between the absorber unit (3) and the support arm.Solar collector or solar system according to one of claims 29 to 35, characterized in that a diameter of the closure opening (9) of the mirror unit. The absorber unit (3) is selected such that it can be passed through the closure opening (9). A solar collector or solar system according to one of claims 29 to 35, characterized in that the diameter of the closure opening (9) is larger than the diameter of the enclosing, in particular the glass dome (30).

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