Abstract:
A solar collector assembly ( 10 ) comprising a pipe ( 18 ) exposed to solar energy adapted to accommodate a fluid flow in such a way that the solar energy is transferred to the fluid, a heat pipe or any other energy guiding system or absorber; a reflector assembly ( 12 ) with a curved reflector ( 14 ) for focusing solar radiation in the range of the pipe ( 18 ), and an actuator ( 90,64, 80 ) for moving the reflector assembly ( 12 ) in a way that the solar radiation is reflected in the direction of the pipe ( 12 ), is characterized in that means ( 30, 32 ) are provided for releasably fixing the reflector assembly ( 12 ) to the pipe ( 18 ), and the actuator ( 90, 64, 80 ) is fixed at the reflector assembly ( 12 ) or in the reflector assembly ( 12 ).

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application is filed herewith for the U.S. National Stage under 35 U.S.C. §371 and claims priority to PCT application PCT/EP2014/064556, with an international filing date of Jul. 8, 2014. The contents of this application are incorporated in their entirety herein. 
     
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       TECHNICAL FIELD 
       [0003]    The invention relates to a solar collector assembly comprising 
         [0004]    (a) a pipe exposed to solar energy adapted to accommodate a fluid flow in such a way that the solar energy is transferred to the fluid, a heat pipe or any other energy guiding system or absorber; 
         [0005]    (b) a reflector assembly with a curved reflector for focusing solar radiation in the range of the pipe, and 
         [0006]    (c) an actuator for moving the reflector assembly in a way that the solar radiation is reflected in the direction of the pipe. 
         [0007]    Furthermore, the invention relates to a method for operating such an assembly. 
         [0008]    If the reflector used in the assembly has a parabolic cross-section the reflector has the effect of a cylinder lens. The solar radiation incident on the earth surface with practically parallel rays is focused in a line. Therefore, the reflector is moved according to the solar movement. A pipe is positioned in the focal line. A fluid such as, for example, water or oil, flows through the pipe. In such a way the incident solar energy is transferred to the fluid. The hot fluid is available for further use, i.e. for heating, the generation of electric energy or as energy for processes. 
         [0009]    In order to make optimal use of the incident solar energy a precise shape of the reflector and a good movement following to the solar movement is important. 
       BACKGROUND OF THE INVENTION 
       [0010]    DE 10 2011 056 790 A1 describes a parabola trough collector. Solar radiation is collected with such a collector and reflected towards an absorber pipe. A heat carrier medium circulates in the absorber pipe. The parabola troughs are provided with a carrier structure carrying mirror elements which are moved according to the solar movement. The parabola troughs are held on pylons. One of the respective pylons is provided with a belt drive thereby forming a driving pylon engaging at an end of the parabola trough. For maintaining the parabolic cross section over the entire length the reflector is pre-formed in such a way that the parabola is formed only after the impact of the twisting. 
         [0011]    Known parabola trough collectors are relatively large. They require many efforts for installation. Furthermore, it is difficult to maintain a precise shape over the entire length of the parabola trough. 
         [0012]    The working life time of known solar collectors is essentially determined by the environmental conditions which the collectors are exposed to. Overheating will excessively strain the components. Strong winds cause forces and vibrations which may damage mechanical components with the course of the time. Condensation of water vapor at the reflector or its cover will cause absorption or reflection of solar radiation and thereby reduce the usable energy. 
         [0013]    US 2009/0314283 A1 discloses solar collectors where light is focused on a pipe by means of elongated mirrors. Furthermore, engines are provided to move the assembly after the solar position. The document discloses the movement of the assembly according to the position of the sun. Measures to protect the assembly from environmental impact are limited to a transparent cover and sealings in connections. 
         [0014]    WO 2010/142666 A2 discloses solar collectors where light is focused on a pipe by means of reflectors. The pipe is held in holders which are arranged in periodic distances along the reflector. Furthermore, a movement is disclosed in accordance with the solar position. 
         [0015]    WO 2013/028522 A3 discloses solar collectors where light is focused on a pipe with reflectors. The reflector sits in a frame which is rotatably mounted on pylons. An engine causes a movement. The pipe is fixed to the frame with fixings. The frame is rotated by means of the engine. Furthermore, sensors are disclosed for controlling the movement in addition to or instead of a stored algorithm. 
         [0016]    WO 2012/128877 A2 discloses a large, open solar collector assembly arranged in a glass house. The reflectors as well as the pipes are suspended from a structure which is formed by the roof of the glass house or the like. A rotating connection is used for this purpose. The weight is held by the roof. The reflectors have several portions and are mounted at the point of use. For this purpose fixing elements and adjustable cables are provided. The positions of the reflectors suspended at cables can be adjusted by pulling the cables by means of a pulley. 
         [0017]    WO 2011/141737 A2 describes a reflector assembly with an actuator. The reflector rotates about a focal axis with the pipe. The reflection assembly is rotatably held by a fixed frame through a bearing and the pipe is guided through a pin ring and a worm gear without having any contact thereto. It is a disadvantage of the assembly that the pipe must be opened at least once to insert the pin ring and the worm gear. An installation and pre-adjustment as a whole is not possible with this assembly. 
         [0018]    WO 2007/146183 A2 discloses a closed reflector assembly where the reflector is arranged inside a housing with a track-shaped housing bottom. Supports are mounted at the track holding the pipe. The sun is tracked by the assembly with a belt at the track. The force is transmitted on the track or rotatably born end faces of the reflector assembly. In the same way WO 2009/146215 A2 and WO 2012/025849 A2 disclose assemblies where the sun is tracked by a reflector with a belt. 
       BRIEF SUMMARY OF THE INVENTION 
       [0019]    It is an object of the invention, to provide a device of the above mentioned kind which is particularly economical and has a long life time with best possible functionality. 
         [0020]    According to an aspect of the invention this object is achieved with an assembly of the above mentioned kind in that 
         [0021]    (d) means are provided for releasably fixing the reflector assembly to the pipe, and 
         [0022]    (e) the actuator is fixed at the reflector assembly or in the reflector assembly. 
         [0023]    Thereby, the actuator, the control means and the power supply form a module which can be fully assembled by the manufacturer. The pipe or the absorber must not be opened or removed. At the point of use only a pipe with a fluid flow must be provided where the reflector assembly is mounted in one piece. The installation at the point of use only requires little expertise, is less faulty and can be carried out much quicker than the assembly of an installation with several components. Any kind of heat pipe or other energy containing medium can be used as a pipe. Preferably, the actuator is positioned with a gearing at one of the end faces of the reflector assembly. 
         [0024]    Preferably, the means for fixing the reflector assembly to the pipe comprise: 
         [0025]    (a) a first clamping element; 
         [0026]    (b) a second clamping element for connecting with the first clamping element, wherein the reflector assembly is rotatably mounted. 
         [0027]    The first clamping element may be provided with an integrated socket for the bearing. 
         [0028]    In particular, the first and the second clamping element may have a semicircular cross section and each may have an annular groove for receiving a bearing element for rotatably mounting the reflector assembly about the pipe. The bearing elements are then shaped as half shell bearings which can be fixed to a closed energy transmitting system, such as a pipe. The reflector assembly is applied to the pipe with one of the clamping elements. The assembly is then screwed thereto with the other, complementing clamping element or releasably fixed in any other way, such as, for example, with latching devices or a bayonet coupling. All other functionalities are realized already at the components of the assembly whereby no further adjustments or installations are required. 
         [0029]    With such an assembly the reflector assembly is rotatably mounted on the pipe by means of a slide bearing. Comparing to a ball bearing this has the advantage that practically no sand can enter the bearing surfaces of the slide bearing which is advantageous for solar collectors used in the desert. The at least two pipe bearing shells of the slide bearing surround the pipe and are torque proof connected thereto. Preferably, the slide bearings i.e. their bearing shells, are made of from ceramic material, from PTFE or another heat resistant material. PTFE is sufficiently heat resistant and suitable for absorber temperatures of 200° C. or even higher and provides little friction at the gliding PTFE/PTFE-surfaces of the slide bearing. 
         [0030]    Preferably it is provided that means for releasably fixing the reflector assembly to the pipe are provided at each end of the reflector assembly, such means being connected by a shaft in such a way that the force exerted by the actuator on the reflector assembly is partly transferred to the other end of the reflector assembly by the shaft. With such a modification of the invention only one actuator is necessary. The transmission of the power, however, is not effected by the reflector but through an additional shaft. The shaft extends parallel to the pipe. In such a way an undesired distortion of the reflector is avoided. 
         [0031]    The reflector assembly can operate fully independent. If solar cells are used for the energy supply of the actuator no further cables and connection works must be carried out. The solar cells can be chosen particularly small if a low voltage direct current engine and a gearing are used. The required power which the actuator normally does not have can be generated with a gearing with a suitable transmission ratio. The energy supply of the actuator and the control unit can be effected by an electro thermal converter within the solar collector. Preferably, a storage, such as, for example, an accumulator, is provided enabling the proper function of the actuator and the control unit even in darkness or with unfavorable weather conditions. 
         [0032]    For the tracking a sun position sensor and/or a sun rising/sun dawning sensor and a control unit can be provided for controlling the actuator using the data of the sun position sensor. 
         [0033]    Using the read sensor data the probable position of the sun is calculated and tracked. Thereby, the system is less sensitive regarding disturbance by other light sources. The determination of the time of the day and the day in the year is possible. 
         [0034]    In a particularly preferred modification of the invention a temperature sensor is provided for sensing the temperature at each end of the reflector assembly. The temperature sensors can be fixed to the rotational bearings of the clamping elements. The inlet temperature at the inlet of the pipe and the outlet temperature at the outlet of the pipe is measured thereby. With such temperatures it can be determined if there is a risk of overheating. If this is the case the reflector can be moved from the focus. Thereby, less solar energy is reflected to the pipe where the temperature is decreased and overheating can be avoided. Alternatively or additionally, the fluid flow through the pipe can be increased or decreased in order to effect a temperature change. In a simpler modification of the invention a temperature sensor is provided only on the outlet side. 
         [0035]    In a particularly advantageous modification of the invention provides 
         [0036]    (a) a converter provided at a first end of the reflector assembly the converter having a light source for converting temperature data of a temperature sensor a this end into an optical signal, 
         [0037]    (b) a detector provided at the opposite, second end of the reflector assembly for receiving such optical signal, and 
         [0038]    (c) a converter with a sender for transmitting the temperature data of the first and second temperature sensor to a control means. 
         [0039]    With such a modification of the invention no cables and no connecting of electrical or other connections is necessary. The temperature signal is transmitted in the form of an optical signal. The optical transmission is wireless and effected through the air. Such a transmission path is insensitive. After converting to a suitable electric signal the temperature can be sent to the control unit via cable or wireless, for example by infrared signals or Bluetooth. The control unit can adjust the flow volume of the fluid in the pipe or activate the actuator of the reflector assembly. 
         [0040]    In a particularly preferred embodiment of the invention the reflector assembly is provided with one or more reinforcements extending parallel and/or ribs lateral to the pipe. The ribs are curved in accordance with the profile line of the reflector. Such a reinforcing framework of stiff material, such as aluminum or the like, will improve the shape stability of the reflector. The longitudinal reinforcements can be formed by sectional strips with T-shaped or H-shaped cross sections. The T-shaped profiles are mounted to the reflector edges with the plane top surface of the T-shaped profile. The reflector keeps its shape due to the reinforcing frame during use and during transport, storage and installation. 
         [0041]    Preferably, an acceleration sensor is provided at the reflector assembly. The acceleration sensor is exposed to the gravitational force. From the gravitational force caused by the movement of the reflector assembly the exact position can be calculated. The acceleration sensor can be one-dimensional, two-dimensional or three-dimensional. Together with the date and the geographical position the result can be used for tracking the sun with the reflector assembly. Alternatively, a detector is provided. 
         [0042]    In addition, from the signals of the acceleration sensor vibrations can be detected. Such vibrations occur, for example, with wind and can have high frequencies. The vibrations are not desired and affect the life time of the assembly. If vibrations are detected having frequencies and/or amplitudes exceeding a selected threshold the reflector assembly is moved by the actuator until the vibrations assume a minimum. In such a way the assembly is treated with care and the life time is increased. 
         [0043]    Strong wind can exert large forces on the reflector assembly which may damage the installation. In order to avoid such damages the angular momentum required for a rotational movement of the reflector assembly is determined. This can be effected in such a way that the current required for the actuation of the motor is detected. If the angular momentum exceeds a threshold the “storm case” is assumed. The sun is then not tracked anymore by the reflector assembly but skewed into the wind. This is carried out in such a way that the reflector assembly is moved into the position where the movement requires the smallest angular momentum, i.e. where the smallest current is needed for the movement. 
         [0044]    In addition wind breaker formations can be provided at the outside. Thereby, airfoil effects at the solar collector are avoided which may cause breakdowns or damages of the solar collector. 
         [0045]    Preferably, it is provided that the reflector assembly surrounds a closed space with the reflector and a transparent cover and the space is provided with a diaphragm bordering to the outside, the diaphragm adapted to be permeable for nitrogen molecules, oxygen molecules and other small gas molecules and impermeable for water molecules. 
         [0046]    The cover protects the reflector and the mechanical components of dirt and environmental effects. Additionally, the cover can be coated with an optical anti-reflex coating for solar radiation. Furthermore, a non-stick coating for dirt-repelling can be provided on the cover. One embodiment of the invention provides that the cover is a glass plate. In addition to protecting the reflector surface from dirt the closed space also forms a heat buffer enabling the leveling temperature variations. 
         [0047]    It is a problem where water remains causes interfering condenser water due to temperature and pressure variations. It is expensive to apply a vacuum and pressure variations will cause leaks. The use of a waterproof diaphragm enables the pressure compensation with gases such as nitrogen and oxygen which are always comprised in the air. A hygroscopic material can be enclosed in the closed space for removing water remains. Since no further water can enter through the diaphragm a small amount of such material is sufficient to provide dry air which prevents condensation. 
         [0048]    A valve diaphragm comprises, for example, a hygroscopic range at its inside surface which is transparent for air, while the remaining range of the valve diaphragm is hydrophobic which is transparent for air. The hygroscopic range can be provided in the form of a hygroscopic coating of the hydrophobic diaphragm material. Such a valve diaphragm enables a pressure compensation between the collector space and the environment due to its transparency for O2 and N2 on one side and the drying of the atmosphere inside the collector space. This, in turn, enables the use of thinner glass plates as a cover and prevents the formation of condenser water or ice, for example during a day/night cycle or during a summer/winter-temperature cycle. 
         [0049]    For further prevention of dirt and damages due to the weather it is provided that the assembly is tilted downwards during the night, i.e. that the reflector is positioned above the pipe with its outside. Rain, particles, leaves and the like from above will then not hit the light inlet side but the insensitive outside of the assembly. 
         [0050]    A method for operating an assembly according to the present invention, comprising the steps of: 
         [0051]    (a) determining the position of the sun; 
         [0052]    (b) adjusting the reflector assembly; and 
         [0053]    (c) flowing a fluid through the pipe for absorption of solar heat; 
         [0000]    provides that 
         [0054]    (d) the temperature in the range of the pipe is determined; and 
         [0055]    (e) the reflector assembly is adjusted in such a way that the determined temperature is lower than a selected threshold. 
         [0000]    Furthermore, it can be provided that 
         [0056]    (d) the reflector assembly is moved, 
         [0057]    (e) the inertia of the reflector assembly is determined during such movement, and 
         [0058]    (f) the reflector assembly is moved into a position where the forces acting on the reflector assembly are a minimum if the inertia exceeds a selected threshold. 
         [0059]    The assembly can be used in large numbers with solar collectors assembled with a fluid flow in series or parallel. 
         [0060]    A preferred method for operating an assembly according to the present invention, as described above comprises the steps of: 
         [0061]    (a) determining the position of the sun; 
         [0062]    (b) adjusting the reflector assembly; and 
         [0063]    (c) flowing a fluid through the pipe for absorption of solar heat. 
         [0000]    The method is characterized in that 
         [0064]    (d) the temperature in the range of the pipe is determined; and 
         [0065]    (e) the reflector assembly is adjusted in such a way that the determined temperature is lower than a selected threshold. 
         [0066]    In a further modification of the method it is provided that 
         [0067]    (d) the reflector assembly is moved, 
         [0068]    (e) the inertia of the reflector assembly is determined during such movement, and 
         [0069]    (f) the reflector assembly is moved into a position where the forces acting on the reflector assembly are a minimum if the inertia exceeds a selected threshold. 
         [0070]    Using an analogue or digital set of rules, it can be further provided that the position of the sun is determined with the acceleration sensor and photo sensors and the exact time of the day and the exact day of the year is calculated. 
         [0071]    Using a temperature control it is advantageous if each solar collector is pre-adjusted by the manufacturer and/or manually adjusted at the point of use to a well-defined target temperature which may not be exceeded at the inlet and outlet of the pipe. 
         [0072]    Using a radio receiver in the control means the reflector assembly can prophylactically externally be transferred into an emergency operation mode upon exceeding too high vibrations or too high rotational forces where the solar collector is downwardly directed with the cover. 
         [0073]    An acceleration sensor can be used in the control unit for measuring vibrations in particular caused by wind while the reflector assembly is rotated upon exceeding too high vibrations to a position where such vibrations are minimized or compensated. 
         [0074]    Using a radio sender in the control means, it is enabled that all available data of the reflector assembly can be emitted at any time. 
         [0075]    Further modifications of the invention are subject matter of the sub-claims. A preferred embodiment is described below in greater detail with reference to the accompanying drawings. 
         [0076]    BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0077]      FIG. 1  is a perspective view of the installed solar collector; 
         [0078]      FIG. 2  shows the solar collector of  FIG. 1  without cover; 
         [0079]      FIG. 3  is a perspective view of installed clamping elements for fixing the solar collector to a pipe in greater detail; 
         [0080]      FIG. 4  is a cross sectional view of the assembly shown in  FIG. 3 ; 
         [0081]      FIG. 5  is an exploded view of the assembly in  FIG. 3 ; and 
         [0082]      FIG. 6  is a perspective view of the connection of the slide bearing to the reflector assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0083]      FIG. 1  shows a solar collector generally designated with numeral  10 . The solar collector  10  is a portion of a solar power station consisting of many of such solar collectors  10 . A reflector assembly designated with numeral  12  is provided with a reflector  14  coated with aluminum on its inside and a plane cover  16  of transparent glass. The cover  16  is coated with an anti-reflex layer and a non-stick coating. The reflector  14  is curved and has a parabolic cross section. Parallel solar radiation which is incident on the cover  16  under a perpendicular angle will be focused in one focal line. In such a way the entire incident radiation is focused in one line. A pipe  18  is installed in the range of the focal line. The pipe  18  of the present embodiment consists of copper which is a good heat conductor and in the present embodiment water flows through the pipe. A controllable circulation pump (not shown) is provided for this purpose. The solar radiation is absorbed at the pipe  18  which forms an absorber and the thermal energy is transferred. The thermal energy is flowed away by the water flowing through the pipe  18  for further use in common ways. In areas where there is a risk of freezing a fluid is used which will not freeze even at lower temperatures. 
         [0084]    The reflector is provided with plates  20  and  22  at its end faces. The reflector assembly  12  forms a closed space with the reflector  14 , plates  20 ,  22  and cover  16 . The closed space surrounded by the reflector assembly  12  is sealed against the environment with suitable sealings (not shown). A hydrophobic diaphragm  24  is inserted into an opening in the plate  20  at the end face of the reflector assembly, such as by OXYPHEN AG, Giessereistrasse 1, 8620 Wetzikon in Switzerland. The diaphragm  24  is transparent for small molecules, in particular for oxygen molecules O2 and nitrogen molecules N2. Larger water molecules H2O are allowed to pass only towards the outside in the direction of the environment. Therefore, no water can enter the inside of the reflector assembly  12 . A pressure compensation can be achieved by the hydrophobic diaphragm  24 . Sealings and components of the reflector assembly  12  are not stressed. A vacuum is not necessary. Accordingly, the glass cover  16  may be thin. In addition to the hydrophobic diaphragm  24  hygrophilous material in the form of salt is used in the inside. The salt binds all water which might be present in the inside. 
         [0085]    The dried air in the inside of the reflector assembly  12  allows for no water condensation at the cover or plate whereby the radiation is passed unaffected to the pipe independently of the weather—and temperature conditions. 
         [0086]    The solar collector of the present embodiment is about 2 m long. The reflector  14  is thin in order to avoid excessive weight which would render transport and installation difficult. In order to maintain the stability of the shape of the reflector  14  the reflector is held in a frame of bent ribs  26  and longitudinal reinforcements  28 . The longitudinal reinforcements  28  are T-shaped and are connected to the ribs  26  and the plates  20 ,  22  of the reflector. 
         [0087]    The reflector assembly  12  is rotatably connected to the pipe  18 . For this purpose, two slide bearings  30  and  32  are provided which are shown in  FIGS. 3 to 6  in greater detail.  FIG. 3  is a perspective view and shows a section of the pipe  18  with installed slide bearing  30 . The slide bearing  30  comprises a lower clamping element  34  and an upper clamping element  36 . This can be well seen in the exploded view in  FIG. 5 . The clamping elements  34  and  36  are half-shell shaped. They form a U-shaped trough  38  which abuts the pipe  18  when it is installed. A sealing  88  is provided between the clamping elements  34  and the pipe. The clamping element  34  is provided with four bore holes  40  at each corner. Screws  44  extend through the bore holes  40  which are screwed into threaded bore holes  42  in the upper clamping element  36 . In such a way the clamping elements  34  and  36  are tightly connected to the pipe  18  without the need to open it. 
         [0088]    The clamping elements  34  and  36  each are provided with a wide annular groove  46  and  48 . A first bearing element  50  is accommodated in the annular groove  46  of the slide bearing  30 . A second, complementary bearing element  52  of the slide bearing  30  is accommodated in the annular groove  48 . An inner portion  54  of the bearing element  50  is movably guided in a receptacle  56 . An inner portion  58  of the bearing element  52  is movably guided in a receptacle  60 . The slide bearing  32  is identical to the slide bearing  30 . In such a way the plates  22  and  20  of the reflector assembly  12  are rotatably guided about the longitudinal axis of the pipe  18 . 
         [0089]    A cogwheel  62  is fixed to the slide bearing  32 . The cogwheel  62  is moved by a gear  64 . Such gear transmits the driving power of a motor  90  to the slide bearing  32  present above. Furthermore, a shaft  66  is driven by the motor  90 . The shaft  66  extends along the entire length of the solar collector  10 . At the opposite end the shaft  66  ends in a gear  80  engaging in a cogwheel  68 . The cogwheel  68  is connected to the slide bearing  30 . In such a way the power of the motor  90  is exerted on the slide bearing  30  as well as on the slide bearing  32 . The motor  90  is supplied with energy by solar cells  82 . Additionally, accumulators  70  are provided which ensure the energy supply even in the night or with unfavorable light conditions. 
         [0090]    By activating the motor  90  the movement of the sun is tracked by the reflector assembly  12 . An acceleration sensor  84 , such as, for example, LIS3DH by STMicroelectronics, is fixed to the plate  20 . The acceleration sensor provides data relating to the position of the reflector assembly to a control unit  72 . The control unit calculates the position of the sun from the actual time, the date and the geo-position and controls the motor  90  in such a way that the reflector assembly  12  assumes an optimum position where the entire solar radiation is focused in one focal line. The use of an acceleration sensor has the advantage over an optical tracking that the optimum position is found even if the light conditions, such as with clouded sky, do not allow for an unambiguous determination of the solar proceeding. The detection of the light intensity serves to unambiguously determine the solar proceeding over the day and the year. Two photo detectors or photo sensors  86  are used for this purpose. 
         [0091]    Furthermore, the acceleration sensor  84  detects if and how much vibrations occur. With strong vibrations, which, for example, exceed 63 Hertz, the assembly is moved into a position where the vibrations are minimized. 
         [0092]    Furthermore, the current necessary for the rotational movement during the movement is detected. A large current is necessary for a movement to overcome a high wind resistance (storm). If the wind resistance exceeds a threshold the assembly is protected. 
         [0093]    For this purpose the assembly is moved into a position where the smallest current is required for a rotational movement by the step motor. In other words: the assembly is moved into a position with the smallest wind resistance. In such a way the assembly is protected against damages by storm. 
         [0094]    In order to avoid dirt the reflector assembly  12  is continuously moved forward during the night even after sunset until the glass plate is at the bottom side. Only upon sunrise the reflector assembly  12  is moved back into its operating position. 
         [0095]    Temperature sensors  74  and  76  are fixed to the clamping elements of the slide bearings  30  and  32 . The temperature sensors  74  and  76  detect the temperature at the pipe  18 . For example, the outlet temperature is detected with temperature sensor  74  and the inlet temperature is detected with the temperature sensor  76  if the fluid flows in the direction of arrow  78  through the pipe  18 . If one or both temperatures exceed a maximum threshold, such as, for example, 300° C. the reflector assembly  12  is moved whereby less solar radiation is passed to the pipe. Additionally, it can be provided that the pumping power of the circulation pump is increased. Thereby, overheating and damaging of components is avoided. 
         [0096]    The temperature sensor  74  is provided with a converter. The converter converts the temperature signal to an optical laser signal. The laser signal is emitted parallel to the pipe axis to a detector (not shown) on the opposite side of the reflector assembly. The detector detects the optical signal, converts the signal to an electric signal and a sender transmits it wireless to the control unit  72 . 
         [0097]    The entire reflector assembly  12  is pre-adjusted during manufacturing. Only the clamping elements  34  and  36  surrounding a mock pipe installed during manufacturing must be released from each other for installation at the point of use. At the point of installation of the solar collector the above components are again mounted by screwing. Further installation works or adjustment works are not necessary. Thereby, the installation can also be carried out by untrained persons. Qualified personnel is necessary only in the factory and does not need to travel to worldwide distributed installation locations. The assembly can, therefore, be particularly economically produced and installed. Due to the use of suitable sensors overheating and storm damages are avoided. Therefore, the assembly has a particularly long life time. 
         [0098]    The solar collector was described above in great detail with indications regarding diameters, component designations, fixing methods, sensors and materials. Such indications only serve to illustrate the invention and shall not limit the scope of the invention. Further modifications are possible without deviating from the general idea of the invention the scope of which is defined exclusively by the wording of the claims.