WO1983001292A1

WO1983001292A1 - Apparatus for collecting solar energy

Info

Publication number: WO1983001292A1
Application number: PCT/NO1982/000051
Authority: WO
Inventors: Tor Ask
Original assignee: Tor Ask
Priority date: 1981-10-01
Filing date: 1982-09-30
Publication date: 1983-04-14
Also published as: DK242683D0; EP0089976A1; DK242683A

Abstract

An apparatus for collecting solar energy for providing thermic or electrical energy. The apparatus comprises a frame (2, 3) having a reflector means mounted therein in the form of a concave part-cylindrical mirror screen (1) of axis-symmetric cross-sectional shape for concentrating incident solar rays towards a central focal line, a solar energy utilizing means (7) placed in the hot region of the extension of the focal line along the screen (1), a drive means (20; 22) for turning the screen (1) about at least one axis, and a control circuit having a solar sensor means for actuating the drive means, for turning the screen (1) according to the movement of the sun. The solar energy utilizing means is an elongated container of transparent material which is arranged to receive a heating means (40; 43; 45) for direct utilization of the generated thermic energy for baking, roasting or cooking of food products placed in the heating means, or to receive a solar cell means (46) for producing electrical energy under the influence of solar rays concentrated in the container, and the solar sensor means comprises at least one photosensitive element (33) located in the vicinity of the caustic surface created by reflection of the solar rays when incident on the screen (1) parallel to the axis of symmetry of the cross-section of the screen.

Description

The present invention relates to an apparatus for collecting solar engergy for providing thermic or electrical energy, comprising a frame having a reflector means mounted therein in the form of a concave part-cylindri cal mirror screen of axis-symmetric cross-sectional shape for concentrating incident solar rays towards a central focal line, a solar engergy utilizing means placed in the hot region of the extension of the focal line along the screen, a drive means for turning the screen about at least one axis, and a control circuit having a solar sensor means for actuating the drive means, for turning the screen according to the movement of the sun.

From US-PS 4 210 463 there is known a solar energy collecting apparatus comprising a transparent tubular body having end closures sealing each end of the body and providing a fluid-tight cavity within the tube. In this cavity there is placed a rotatable concentrator reflector in the form of a bipartite, part-cylindrical mirror screen, a high temperature energy absorbing unit which is placed in the hot region of the extension of the focal line along the screen, and further a low temperature energy absorbing, unit which is fixedly disposed within the cavity along a part of the periphery of the tubular body, so that it is located in. the path of diffuse solar radiation received directly from the sun or by reflection from the interior of the apparatus or from a reflector disposed outside thereof. Both of said units are arranged for through-flow of the heat-transferring fluid, to be able to utilize the collected thermic energy in this manner. The energy-absorbing unit in the focal line can also be externally covered by photoelectric cells or solar cells for direct conversion of the solar energy to electrical energy. In the patent specification it is stated that the apparatus can be provided with various types of means for turning the tubular body and/or the mirror screen, to track the movement of the sun. As an example it is shown that the two halves of the reflector screen can be rotated about their longitudinal axis by mechanical means comprising weights moved along radial arms by means of a motor arrangement, and suitable braking means actuated intermittently by means of not shown tracking means, to thereby control, the rotation of the screen.

The purpose of the tubular body enclosing the concentrator reflector and the energy absorbing units, is to protect these elements against adverse and detrimental . influence from the surroundings. However, this solution implies a relatively large and bulky apparatus with a reflector screen of the necessary size, and in addition the apparatus is restricted to a permanently installed arrangement of energy-absorbing units within the tubular body. The apparatus is also restricted to sun-tracking rotation about only one axis.

From DE-OS 2 731 246 there is further known a solar energy collecting apparatus comprising a relatively large number of solar energy converting means of which each comprises i. a. a solar cell in which solar energy is converted to electrical energy, an energy concentrator in the form of a dual angle cone shell reflecting the incident solar rays towards the associated, inwards located solar cell, and a heat sink for dissipating heat from the solar cell. The converter means are rigidly connected to each other and form together a solar cell surface which is mounted on a holding means in such a manner that it is independently rotatable about a vertical and a horizontal axis . A plurality of solar sensors are connected in a control circuit for the operation of motors for turning of the solar cell surface about the vertical and the horizontal axis, so that it is positioned in an optimal angle in relation to the sun. The positioning is based on a relatively large number of sensors and the control circuit is relatively complex and comprises a large number of components, such as operational amplifiers, resistors, transistors and relays. This contributes to increased manufacturing costs for the apparatus. The fact that a separate radiation concentrator is used for each solar cell, also contributes to increasing the costs, and it also restricts the flexibility with respect to the arrangement of solar cells . The object of the present invention is to provide an apparatus for collecting solar energy which, by means of a simple and cheap construction, enables efficient, flexible and alternative utilization of concentrated solar energy, and which additionally in a particularly simple manner enables automatic, optimal positioning of the apparatus in dependence of the movement of the sun.

The above-mentioned object is achieved with an apparatus of the introductorily stated type which, according to the invention, is characterized in that the solar energy utilizing means is an elongated container of transparent material which is arranged to receive a heating means for direct utilization of the generated thermic energy for baking, roasting or cooking of food products in the heating means, or to receive a solar cell means for producing electrical energy under the influence of solar rays concentrated in the container, and that the solar sensor means comprises at least one photo-sensitive element located in the vicinity of the caustic surface created by reflection of the solar rays when incident on the screen parallel to the symmetry axis of the cross-section of the screen.

By using a mirror screen of the stated configuratio there is firstly achieved an effective concentration of the solar rays and a very hot zone in the region of the rectilinear extension of the focal line along the screen, and secondly it is achieved that the solar rays after reflection produce a focal surface or so-called "caustic surface" which can be used in connection with a solar sensor means to construct a very simple control circuit which, with a minimum of components, provides for automatic turning of the frame according to the movement of the sun, so that an optimal positioning of the apparatus is achieved. As distinct from the conventional devices , in which the thermic energy is picked up in a heat-transferring fluid, usually water, the high temperature achieved in the focusing system of the apparatus according to the invention can be utilized directly for baking, roasting or cooking of food products in the heating means which can be placed in the solar energy utilizing container. Alternatively, the concentrated light in the hot zone in the region of the focal line can be utilized to produce electrical energy by placing a suitable solar cell assembly in the container. The container can als be adapted for through-flow of a heat transferring fluid, e. g. water, which, in connection with a solar cell assembly in the container, will serve as cooling water at the same time as the thermic energy can be transferred and possibly stored in e. g. a hot water tank. Thus, by means of the invention there is provided a relatively cheap apparatus widening the possibilities of utilization of the solar energy.

The invention will be further described below in connection with exemplary embodiments with reference to the drawings, wherein

Fig. 1 shows a perspective view of a first embodiment of the apparatus according to the invention;

Fig. 2 illustrates the ray path in the reflective mirror of the apparatus and the placing of the energy utilizing container which is shown with a solar cell means placed therein;

Figs. 3a - 3c show examples of heating means for placing in the solar energy utilizing container of the apparatus; Fig. 4 shows a perspective view of a solar cell means;

Fig. 5 shows a section along the line V - V in Fig. 4;

Fig. 6 shows a side view of a second embodiment of the apparatus according to the invention;

Fig. 7 shows a detail at A in Fig. 6 on an enlarged scale;

Fig. 8 shows a section along the line VIII - VIII in Fig. 6; and Fig. 9 shows a circuit diagram of a control circuit for controlling drive motors for optimum tracking and positioning of the apparatus according to the movement of the sun.

The embodiment of the apparatus according to the invention shown in Fig. 1 comprises a reflector means consisting of a concave, part-cylindrical mirror screen 1 which is mounted in a rack or frame together with the other components of the apparatus. The frame is made of metal rods or the like and in all essentials consists of an essentially triangular base frame member 2 and an essentially U-shaped, screen-supporting frame member 3 which, at its upper ends, is pivotally attached to the uper corners of the screen 1 and with its lower web portion is pivotally attached to a length-adjustable rod structure 4 , to thereby be able to adjust the angle of inclination of the screen 1, such as further described below. The rod structure 4 is carried by the base frame member 2 and is attached at one end to a mounting member 5 supported by a supporting rod 6 attached at its ends to the base frame member 2.

In the mounting member 5 there is pivotally journalled a holder for the support of the solar energy utilizing means of the apparatus which consists of an elongated, cylindrical container 7 of transparent material, such as further described below. The holder consists of a bottom rail 8 extending below the reflector screen 1 and which, at its lower end, is journalled in the mounting member 5 and at each end has an upstanding holding member 9 and 10, respectively, for supporting respective ends of the container 7. At its upper end the lower holding member 9 is provided with a notch 11 for the reception of a pipe socket 12 projecting from the container end, whereas the upper holding member 10 at its upper end has a ring 13 wherein the container 7 can be introduced. Thus, in a simple manner the container 7 can be put in place in the apparatus or replaced by another container for further or possibly alternative utilization of -the solar energy.

The reflector screen 1 is made of a suitable, flexible sheet material and is maintained in a suitably curved position by means of pairs of lower and upper suspension stays 14 and 15, respectively, which, at their outer ends, are attached to the ends of screen side edge strips 16 and at their inner ends are e. g. hooked in suitable holes in the holding members 9 and 10.

The base frame member 2 is provided with wheels to be able to turn 360° on the ground. Thus, a wheel pair 17 is rotatably; journalled in the corner of the frame member 2 at the mounting member 5 , and two additional wheels 18 are rotatably journalled on supporting rods 19 at the two remaining corners, the wheels 17 forming an angle of ca. 60° with each of the wheels 18. One of the wheels 18 is driven by a drive motor 20 through a gearing 21 suitably attached to the associated supporting rod 19. The drive motor 20 may be a DC motor for 1,5 - 12 V and provides for turning of the apparatus about a vertical axis which will be located essentially centrally between the wheels 17, so that the apparatus automatically turns after the movement of the sun, such as further described below.

A further drive motor 22, which may also be a DC motor for 1,5 - 12 V, is coupled through a gearing 23 to the length-adjustable rod structure 4 for adjustment of the inclination of the screen 1. The drive motor 22 is reversible to cause extension as well shortening of the rod structure. Such as further described below, the operation of the motor is controlled by the solar sensor means and control circuit of the apparatus, so that the screen is automatically positioned in an optimum angle of inclination in relation to the altitude of the sun.

Such as appears from Fig. 2, the reflector screen 1 has a cross - sectional shape which is symmetric about an axis X - X. The Figure shows the ray path for light rays 24 incident on the screen parallel to the axis of symmetry. The cross-sectional shape causes the rays after reflection to form a focal surface (envelope) or so-called "caustic surface" 25 extending on each side of a centrally located focal line 26. Thus, the focal line is the intersectional line between the caustic sub-surfaces on each side of the symmetry axis X - X of the screen.

In Fig. 2 the curvature of the screen 1 is adapted such that the focal line 26 extends essentially centrally within the container 7 of the apparatus. However, the curvature of the screen may be adjustable, e. g. by means of the suspension stays 14, 15, so that a larger smaller part of the container 7 can be located inside of the caustic surface 25, for the achievement of maximally optimal conditions for the actual solar energy utilization, dependent on whether it is the question of baking, roasting, cooking, fluid heating or irradiation of a solar cell means.

Such as appears from Fig. 2, the container 7 advantageously consists of a pair of coaxial tubes 27, 28 with an intermediate, insulating air layer 29. Advantageously, the innter tube 27 can consist of glass which stands the high temperatures arising within the container, whereas the outer tube can consist of a transparent synthetic material, such as acrylic resin. The container 7 is shown to be closed at its lower end, whereas the upper end is provided with a removable lid 30 as suggested in Fig. 1. Such as shown in Fig. 6, the container at the upper and the lower can be provided with an inlet and an outletRespectively, for a cooling and/or heat-transferring fluid. In Fig. 1, the illustrated lower pipe socket 12 is provided with a valve 31 of the type which is closed in the illustrated condition, but which opens automatically when the end of a tube or the like is introduced into the valve opening.

In accordance with the invention, the solar sensor means for positioning or adjustment of the apparatus in dependence of the movement of the sun comprises at least one photo-sensitive element which is located in the vicinity of the caustic surface (shown in Fig. 2) formed by reflection of the solar rays when incident on the screen 1 parallel to the axis of symmetry X - X of the cross-section. The solar sensor element can be a photocell or solar cell which has its photo~sensitive side turned inwards towards the screen and is coupled to an electronic switch in a control circuit for a drive motor, so that the switch is actuated and the motor is started when the solar cell senses a luminance difference when it is passed by the existing caustic surface. For example, the solar cell can be mounted at a small distance outside said caustic surface, so that the caustic surface moves outwards towards the solar cell during the movement of the sun, and the drive motor is thus started as soon as the solar cell comes into the light boarder area of the caustic surface. By such a utilization of the caustic surface there is achieved a continuous adjustment or "after-carrying" of the screen by means of a control, circuit which in its simplest form may consist of only one solar cell and one electronic switch element (e. g. a transistor).

In Fig. 1 there is shown a number of solar cells forming part of a complete control circuit for controlling the two motors 20 and 22 providing for positioning of the reflector screen 1 in the vertical as well as the horizontal plane (i. e. in azimuth as well as in elevation). A solar cell 32 which, in the illustrated embodiment, is placed at one of the upper corners of the screen 1, causes start of the motor 20 when illuminated. A solar cell 33 is placed on one screen half on the caustic surface shown in Fig. 2 and cooperates with the solar cell 32, so that the motor 20, through an electronic switch, is stopped when the screen is correctly positioned in the vertical plane. Two addition solar cell units 34, 35, each consisting of a pair of cells, are placed at the lower and the upper end, respectively, of the screen 1 (see also Fig. 2), so that the lower cell unit 34 is located in "the shadow" (i. e. outside the ligth zone) when the screen has too small angle of inclination (the sun stands too low), whereas the upper cell unit 35 is located in "the shadow" when the screen has too large angle of inclination (see also the ray path in Fig. 6). Solar cells belonging together in each of the cell pairs 34 and 35 are connected to respective electronic switches and control the operation of the reversible motor 22 so that it is stopped when the screen is correctly positioned in the horizontal plane.

The specific construction and operation of the control circuit will be described in connection with Fig. 9. In Fig. 1 the control circuit is shown in the form of a box 36, and in the Figure there is further suggested a battery 37 for current supply to the drive motors and the control circuit. These elements are only schematically suggested, as itis apparent that the configuration and placing thereof can be varied in the manner found most appropriate. The electrical wiring is also omitted in Fig. 1.

In Fig. 1 a pair of solar cell panels 38 and 39 of conventional type are shown to be attached at each side edge of the screen 1. These solar cell panels are removable, but can in an advantageous manner be used in connection with the apparatus according to the invention, as they then automatically gets an optimum positioning in relation to the sun, which is of essential importance for the efficiency of such solar cell panels.

In Figs.3a - 3c there are shown examples of advantageous heating means which can be placed in the solar energy utilizing container 7 of the apparatus. Fig. 3a shows a longitudinally bipartite cylinder 40 for use in baking of bread or the like in the container. The two halves 41, 42 can e. g. be hinged together. The bread dough can be placed in one half, whereafter the members are placed together and introduced into the container 7 after the dough fills the cylinder after suitable rising. Fig. 3b shows a heat-absorbing element in the form of a chute-shaped, part-cylindrical plate 43 which can be introduced into the container 7 and used for more effective heating of water in the container, or for grilling without water in the container. At its lower end the plate 43 is formed with a collection container 44 for collecting fat or the like delivered from the eatables prepared in grilling Fig. 3c shows a number of tins or stewpans . 45 for roasting, baking or dry cooking of eatables or the like in the container 7. The four tins 45 are intended to fill the container, but.it is apparent that a smaller number of tins can be used or possibly larger tins where one, two or three tins fill the container. All of the means shown in the Figs.3a - 3c consist of a good, heat-conducting material which can possibly be covered by a black, heat-absorbing layer. The diameter of the means is adapted to the diameter of the container 7, so that they essentially fill the container cross-section. Figs. 4 og 5 show a perspective view and a crosssection, respectively, of a solar cell means 46 for placement in the container 7. The means comprises a pair of elongated, spaced parallel plates 47, 48 (insulating material) on the opposite sides of which there is disposed a repsective array of solar cells 49 and 50, respectively, which can have the configuration appearing from Fig. 4. The space between the plates 47 and 48 is utilized for the electrical connections (not shown) of the solar cells,which connections are taken out to external terminals 51 and 52. The plates 47, 48 with the solar cell arrays are surrounded by an insulating enclosure or casing consisting of a pair of glass plates 53, 54 joined along adjacent side edges by means of fluid-tight seals 55, 56 of e. g. silicone. Instead of the illustrated enclosure a corresponding or similar solar array can be insulated from the surroundings by means of an envelope of a suitable plactic material or an insulating film of a suitable lacquer or the like.

A solar cell means 46 of the design according to Figs. 4 and 5 is shown to be placed in the container 7 in Fig. 2. The container is here filled by a liquid 57, e . g. water, serving as a cooling fluid for the solar cells and simultaneously as a heat-transferring fluid in the case of through-flow through the container. The solar cells facing the screen 1 are here irradiated by concentrated sunlight reflected from the screen, and the solar cells facing away from the screen are irradiated by directly incident solar rays 58 which are also concentrated because of the light-refracting effect of the liquid 57. In this manner there is obtained a more effective production of DC current also from the solar cells influenced by direct radiation.

In Fig. 6 there is shown a second embodiment of the apparatus according to the invention. Corresponding members in the embodiments in Figs. 1 and 6 are designated by the same, reference numerals and will not be described again. As distinct from the embodiment in Fig. 1, the base frame member 2 in the embodiment in Fig. 6 is arranged to be turned about a centre of rotation 59 instead of the wheel pair 17 in Fig. 1, one of the two wheels 18 (only one is shown in Fig. 6) being driven by the motor 20 in a manner corresponding to that of the first embodiment. The centre of rotation 59 and the wheels 18 are carried by a supporting plate 60 resting on legs 61 having adjustable height so that the supporting plate can be positioned horizontally on an uneven ground.

By way of the lower valve 31 and an upper coupling member 62 the container 7 is arranged for connection to a system for the supply and through-flow of a suitable liquid, such as water, for cooling purposes or for the transfer of thermic energy for utilization or storing after heating in the container 7. The system includes conduits 63 and suitable pipe couplings for connection to the container 7 through the turning centre 59 and to a tank 64 constituting a heat reservoar. The tank 64 has a e. g. thermostat controlled outlet 65 and an upper inlet 66 for the supply of liquid through a float-controlled valve 67. For the circulation of the liquid in the system, a pump (not shown) which can be controlled by a thermostat, can be inserted at a suitable point in the conduits 63.

A detail A of the turning centre 59 is shown in section in Fig. 7. A liquid-conducting tube 68 is here shown to be surrounded by an inner, insulating sleeve 69 which is in turn surrounded by a tube piece 70 of electrical conducting material. The tube piece 70 is further surround by an outer, insulating sleeve 71. A nut 72 is threaded on to the outer sleeve 71 to rest against the upper side of the base frame member 2 (not depicted in Fig. 7) which is rotatable about the outer sleeve 71. In this manner electric current can pass through the conducting tube piece 70, the necessary electrical leads being connected to the upper and lower end of the tube piece, so that the wiring is not disturbed by turning of the apparatus during operation.

Fig. 8 shows a cross-section of the length-adjustable rod structure 4 for adjustment of the angle of inclination of the screen 1. The rod structure comprises an outer square tube 73 attached at its ends to the mounting member 5. Against the inner sides of the side walls of the tube there are resting a pair of ball bearing rails 74 having a longitudinally extending groove for the reception of a plurality of balls 75 running in longitudinally extending grooves in the outer side surfaces of an inner square tube 76 which is arranged to move back and forth within the outer tube 73 in case of rotation of the reversible motor 22. For this purpose the motor 22 and the gearing 23 are rigidly attached to the inner tube 76 through a mounting member 77 in which the screen-supporing frame member 3 is journalled. Further, the output shaft from the motor and gearing is rigidly connected to a threaded rod 78 extending through a clearance hole in the mounting member .77 and into the inner square tube 76. The threaded rod 78 is in threaded engagement with, a through-hole in a block 79 located within the inner tube 76 and fixed in relation to the outer tube 73 by means of a pair of screws 80 and 81, respectively. The screws are threaded intothe block 79 from the upper side and the lower side of the outer tube 73, the upper side and the lower side of the inner tube 76 being provided with longitudinally extending slots 82 and 83, respectively, so that the inner tube 76 can move freely within the outer tube 73 in case of rotation of the motor shaft and there with the threaded rod 78. The cross-section of the block 79 is adapted to the interior cross-section of the inner tube 76, and the block may e. g. be made of nylon for the achievement of minimum friction between the block and the tube.

The embodiment according to Fig. 1 as well as the embodiment according to Fig. 6 is relatively light of weight and is constructed in such a manner that it can easily be disassembled and the reflector screen be folded so that the apparatus occupies a small space. Thus, the apparatus is also well suited for transport and for storage not requiring much space. The efficiency is optimized in that the reflector screen has a width which is as large as possible in relation to the solar energy utilizing container.

Fig. 9 shows a circuit diagram of the control circuit of the apparatus with associated solar sensor elements, switches and drive motors. As it will appear, the included solar cells are connected in pairs and with opposite polarity so that they counteract each other when both solar cells of a pair are illuminated simultaneously. As shown, the two solar cells 32 and 33 are connected to a first PNP transistor Tl constituting an electronic switch for the motor 20 (Ml) for turning of the reflector screen about the vertical axis. Cells 34a and 35a belonging together from each pair of the solar cell units 34 and 35 are connected to a second PNP transistor T2 constituting an electronic switch for start and stop of the motor 22 (M2) with a first rotational direction, whereas the two other cells 34b and 35b belonging together are connected to a NPN transistor T3 constituting an electronic switch for start and stop of the motor 22 with its other rotational direction. The transistors T1, T2 and T3 receive bias voltage from the battery 37 which is in turn connected to the solar cell means 46 to receive charging current therefrom. As shown, also the conventional solar cell panels 38 and 39 may possibly be connected in the charging circuit for the battery. A diode 84 is connected in the charging circuit to block reverse current from the battery to the solar cells.

The control circuit functions in the following manner: When the solar cell 32 is irradiated by sunlight, it opens the transistor T1 so that the motor 22 starts, the solar cell 33 being supposed to be located in the shadow, so that it is not active. The motor 22 rotates so that the apparatus and the reflector screen is turned in the vertical plane until the solar cell 33 comes into the caustic field of the screen and delivers counter-current to the solar cell 32. Thereby the transistor Tl blocks and interrupts the circuit for the mptor 20, so that the motor stops.

When the reflector screen has arrived at this position, one of the following three alternatives exists, viz. 1) both solar cell units 34 and 35 are illuminated (the screen is correctly positioned), or 2) the unit 34 is illuminated and the unit 35 is in the shadow (the screen is too high in relation to the sun), or 3) the unit 34 is in the shadow and the unit 35 is illuminated (the screen is too low in relation to the sun).

In the case of alternative 1), wherein both solar cell units 34, 35 are illuminated, the system is in balance

(T2 and T3 are blocked) and the reflector screen is stationary. in the case of alternative 2), wherein the solar cells 34a, b are illuminated and the solar cells 35a, b are in the shadow, the cell 34a will open the transistor T2, so that the motor 22 rotates in a direction lowering the screen, the cell 34b simultaneously blocking the transistor T3.

The motor rotates until both cell units 34, 35 are again illuminated and the system is in balance so that the screen is stationary. In the case of alternative 3), wherein the solar cells 34a, b are in the shadow and the solar cells

35a, b are illuminated, the cell 35b will open the transistor

T3, so that the motor 22 rotates in a direction raising the screen, the cell 35a simultaneously blocking the transistor

T2. The motor rotates until both cell units 34, 35 are again illuminated and the system is in balance so that the screen is stationary.

Claims

Patent Claims

1. Apparatus for collecting solar energy for providing thermic or electrical energy, comprising a frame (2, 3) having a reflector means mounted therein in the form of a concave part-cylindrical mirror screen (1) of axis-symmetric cross-sectional shape for concentrating incident solar rays towards a central focal line, a solar energy utilizing means (7) placed in the hot region of the extension of the focal line along the screen (1), a drive means (20? 22) for turning the screen (1) about at least one axis, and a control circuit having a solar sensor means for actuating the drive means, for turning the screen (1) according to the movement of the sun, characterized in that the solar energy utilizing means is an elongated container (7) of transparent material which is arranged to receive a heating means (40; 43; 45) for direct utilization of the generated thermic energy for baking, roasting or cooking of food products placed in the heating means, or to receive a solar cell means (46) for producing electrical energy under the influence of solar rays concentrated in the container, and that the solar sensor means comprises at least one photosensitive element (33) located in the vicinity of the caustic surface created by reflection of the solar rays when incident on the screen (1) parallel to the axis of symmetry of the cross-section of the screen.

2. Apparatus according to claim 1, characterized in that the container (7) consists of a pair of coaxial tubes (27, 28) with an intermediate, insulating air layer (29), the inner.tube (27) consisting of glass and the outer tube (28) consisting of a transparent synthetic material, such as acrylic resin, and the container (7) being closed at one end and being provided with a removable lid (30) at its other end.

3. Apparatus according to claim 1 or 2, characterized in that the heating means consists of a longitudinally bipartite cylinder (40) of a good heat-conducting material.

4. Apparatus according to claim 1 or 2, characterized in that the heating means consists of a chute shaped, part-cylindrical plate (43) of a good heat-conducti material which is provided with a collection container (44) at one end thereof.

5. Apparatus according to claim 1 or 2, characterized in that the solar cell means (46) comprises a pair of spaced, parallel plates (47, 48) on the opposite sides of which there is disposed a respective array of solar cells (49.resp. 50), the plates and solar cells being surrounded by a casing (53, 54) of an insulating, transparent material.

6. Apparatus according to claim 1, 2 or 5 , characte rized in that the container (7) at its ends is provided with an inlet (62) and an outlet (12), respectively, for connection to a system for supply and through-flow of a fluid.

7. Apparatus according to one of the preceding claims, characterized in that the photosensitive element is a solar cell (33) which is connected to an electronic switch .(Tl) in the control circuit for the drive means (20), to actuate the switch and therewith the drive means for the screen (1) when sensing a luminance difference when the cell (33) is passed by the existing caustic surface.

8. Apparatus according to claim 7, characterized in that the solar cell (33) is placed essentially on the caustic surface created by reflection of the light rays when incident on the screen (1) parallel to the axis of symmetry of the cross-section of the screen.

9. Apparatus according to one of the claims 1 - 6, characterized in that the solar sensor means comprises a first pair of solar cells (33, 34) connected to a first transistor (Tl) and arranged to cause start and stop, respectively, of a drive motor (20) for turning of the reflector screen (1) about a vertical axis, and two additional pairs (34, 35) of solar cells placed at the lower and upper ends, respectively, of the screen (1), and of which cells (34a, 35a and 34h, 35b) belonging together from each of the additional pairs (34, 35) are connected to a respective one of two additional transistors (T2, T3) and are arranged to control the operation of a reversible motor (22) for turning of the screen (1) about a horizontal axis, the cells belonging together counteracting each other and causing stop of the motor (22) when both of the additional solar cell pairs (34, 35) are illuminated.