Abstract:
The present invention concerns an apparatus ( 100, 200 ) for and a method of using solar energy. To provide an alternative apparatus ( 100, 200 ) and an alternative method of using solar energy which structurally requires less complication and expenditure and which is favorable in provision and operation, in accordance with the invention there is proposed an apparatus ( 100, 200 ) comprising a target ( 50 ) and reflectors ( 10, 12, 210 ) for deflecting solar rays on to the target ( 50 ) and a corresponding method, wherein the reflectors ( 10, 12, 210 ) are respectively pivotable about an axis ( 20, 220 ) for tracking in accordance with the azimuth of the sun ( 30 ) in the course of a day, wherein the axis ( 20, 220 ) is a component part of an axis arrangement ( 70, 270 ) which is inclinable for tracking in accordance with the midday height of the sun ( 30 ) in the course of a year. If necessary it is possible to achieve continuous focusing of the system by simple mechanical compensating mechanisms.

Description:
FIELD OF THE INVENTION 
     The present invention concerns an apparatus for and a method of using solar energy. 
     BACKGROUND OF THE INVENTION 
     The sun radiates about a kilowatt of energy on to each square meter of the surface of the earth when incident thereon in perpendicular relationship. A large number of different methods of and apparatuses for using that solar energy radiated by the sun is known. 
     In photovoltaics sunlight is directly converted into electric current. It will be noted however that the costs of that method are very high, at the present time a square meter of photovoltaic solar cells costs about            700.00. The energy efficiency of the method is about 20%.
     An alternative approach involves using energy radiated by the sun for producing heat. Some methods and apparatuses are known in that respect, in which sunlight is concentrated by means of trackable mirrors. 
     The heat to be achieved in that way serves for example for heating an oil or for heating a liquid salt. The oil or salt heats water to produce steam. The steam produced is used to drive a steam turbine for power generation by means of a power generator. That approach is technologically viable but it is found to be comparatively complicated and expensive. 
     A further approach involves the provision of parabolic mirror installations in which a sufficiently large, closed mirror surface is used to track the sun. That tracking operation is effected by pivoting and inclining the parabolic mirror installation so that actuation in respect of two axes is necessary. As a consequence of the large mirror area such an installation is generally high in weight so that it is only with corresponding difficulties that it can be directed towards the sun with an adequate degree of accuracy. The focal point of the system moves with the position of the sun, which causes difficulties in terms of using the focused rays of the sun as thermal energy. An example of such a system is a ‘solar dish’, as is described for example at http://www.solarpaces.org/resources/technologies.html. 
     Simpler tracking can be achieved with trough-type mirror systems as they only have to be moved about one axis. The trough-type mirrors heat a tube which extends in its focal line. A problem arises in terms of technical implementation in that long tube systems have to be adjusted, heated and protected from heat losses, which in turn makes the installations expensive. An example of such a system is the Andasol project (http://ww.solarmillennium.de/). 
     In the so-called ‘solar tower’ concept a large number of mirrors is directed on to a common point at the tip of the ‘solar tower’. In that case in turn each of the mirrors must be individually controlled about two axes, which makes the method expensive in consideration of the accuracy required in that respect (see for example http://www.bmu.de/pressemitteilungen/pressemitteilungen_ab — 22112005/pm/37405.p hp). The price of such an installation is about            1100.00 per square meter of mirror area and thus, with an energy efficiency of about 10%, is even higher than the price for the photovoltaic system.
     A need for tracking of mirror systems for the concentration of sunlight arises out of the fact that, from the point of view of the earth, the sun apparently follows a flat circular orbit around the earth. The plane of that circular orbit can be described in that case by a unit vector which is perpendicular to that plane. As a consequence of the inclination of the axis of the earth with respect to the orbit the direction of that unit vector changes in the course of a year, which manifests itself in the fact that the midday height of the sun, that is to say the apparent height of the sun above the horizon, varies in the course of the year. 
     The known apparatuses for and methods of using solar energy are structurally complicated and expensive and in part costly to provide and operate. 
     SUMMARY OF THE INVENTION 
     Therefore the problem of the present invention is to provide an alternative apparatus for and an alternative method of using solar energy, in which the problems of the known apparatuses and methods are avoided or at least reduced. 
     That problem is solved by an apparatus for using solar energy having the features defined in claim  1 . 
     That problem is also solved by a method of using solar energy having the features defined in claim  13 . 
     Features of advantageous embodiments of the invention are defined in the appendant claims. 
     The apparatus according to the invention firstly includes a target and a number of reflectors for deflection of solar rays on to the target. In that arrangement the reflectors are respectively arranged pivotably about an axis to allow tracking of the reflectors in accordance with the azimuth of the sun in the course of a day, in order therefore to adapt the reflectors to the apparent movement of the sun across the sky in the course of a day. The respective axes are a component part of an axis arrangement which is inclinable for tracking according to the midday height of the sun in the course of a year. That means that the apparatus is adaptable to the change in the apparent path of the sun by virtue of the angle between the axis of the earth and the orbit of the earth around the sun. 
     With the pivotal movement of a mirror or reflector about an axis which like the above-discussed unit vector is perpendicular to the apparent plane of the path of the sun, the solar rays arriving from the sun can be deflected on to the same target over the entire day. In the case of a flat mirror that target represents a surface approximately of the size of the mirror while with a correspondingly curved mirror the rays can also be reduced substantially to a point. The region on to which the solar rays are deflected is usually also referred to as the ‘hot surface’ or ‘hot spot’. 
     If a plurality of reflectors are directed in that way on to a common target the incident solar rays can thus be concentrated in the target region so that here there is an increased intensity of light (power per unit of area). The method and apparatus according to the invention only necessitate tracking of the reflectors in accordance with the azimuth of the sun in the course of the day, that is to say in accordance with the (celestial) direction from which the solar rays are incident, in which case such tracking can be implemented with a pivotal movement of the reflectors about the respective axis. The path of the sun which apparently changes in the course of the year is taken into account by virtue of the fact that the axis about which a reflector is pivoted in the course of the day is adapted by inclination of an axis arrangement accommodating that axis. 
     In a preferred embodiment the axis arrangement is adapted so that the axis can be oriented perpendicularly to a plane of the path of the sun by an inclination. With an axis oriented perpendicularly to the path of the sun the solar rays are deflected upon pivotal movement of the respective reflector substantially in the plane of the path of the sun so that it is possible in that way to achieve particularly simple directing of the solar rays on to the target. 
     In another preferred embodiment of the invention the axis arrangement has a multiplicity of axes and is so adapted that the axes are inclinable transversely relative to a plane parallel to the axes. When the axis arrangement in operation is so directed that the axes are arranged in mutually juxtaposed relationship substantially in the East-West direction, with the reflectors being turned towards the sun, then the axes can be adapted to the change in the apparent plane of the path of the sun in the course of the year by an inclination transversely relative to the plane defined by the axes. 
     In a further embodiment of the invention the axis arrangement has a multiplicity of axes and is so adapted that the axes are inclinable in a plane parallel to the axes. In the morning and in the evening respectively an axis arrangement oriented along the East-West direction as described hereinbefore has a comparatively small effective area in relation to the sun. If now the effective area relative to the sun is to be increased in the evening or morning time or if orientation in the East-West direction is not possible, then with an axis arrangement which allows inclination of the axes in a plane parallel to the axes, it is also possible to provide for orientation of the axis arrangement along a North-South direction in an extreme case, in which respect the inclination of the axes can be adapted to the midday height of the sun or the inclination of the apparent plane of the path of the sun. 
     Advantageously the axis arrangement can be so designed that it allows inclination of the axes both in a plane parallel to the axes and also transversely relative to such a plane. 
     In a further preferred embodiment of the invention at least two reflectors are pivotable about a common axis. A plurality of reflectors can be associated with a common axis so that to pivot those reflectors it is for example necessary only to drive that axis. If a plurality of reflectors are associated with an axis that plurality of reflectors can also be oriented jointly by orientation of the common axis, and that reduces the apparatus complication and expenditure. 
     In accordance with a further advantageous embodiment the apparatus according to the invention has a pivotal drive system for common pivotal movement of a plurality of reflectors about the respective axis, in particular with a first pivotal transmission device, by way of which a predetermined pivotal movement can be effected for each of the plurality of reflectors in dependence on the pivotal drive system. If a plurality of reflectors are pivoted jointly by a pivotal drive system, that reduces the apparatus complication and expenditure and allows control of the pivotal movement of the plurality of reflectors by controlling only the common pivotal drive system. If there is a pivotal transmission device it is also possible by means of the pivotal drive system to drive a plurality of reflectors which are to involve a respectively different pivotal behaviour. It is thus possible for even all reflectors of the apparatus according to the invention to be driven by means of a single pivotal drive system. 
     In a further advantageous embodiment of the invention the apparatus has a pivotal drive device associated with a reflector or an axis for pivoting the reflector or the reflectors associated with the axis. In addition there can advantageously be provided a second pivotal transmission device, by way of which a predetermined pivotal movement can be effected for each of the reflectors in dependence on the pivotal drive device. Instead of a common drive for a multiplicity of reflectors, it is also possible to provide for individual actuation of the pivotal movement of the reflectors by way of respective separate pivotal drive devices. The pivotal drive device can alternatively also be adapted to act on the reflectors of a common axis so that the reflectors of that axis are drivable jointly in co-ordinated relationship. Once again different pivotal movement of the jointly driven reflectors can be implemented by a second pivotal transmission device. 
     In a further embodiment of the present invention a part of the reflectors is tilted with respect to the respective axis. With tilted reflectors the solar rays can be deflected out of the apparent plane of the path of the sun, which makes it possible for a plurality of mutually superposed reflectors to be so co-ordinated that the solar rays deflected thereby are incident on a target which is not in a plane parallel to the plane of the path of the sun, with the reflectors. 
     In a further embodiment of the present invention a part of the reflectors is tiltable with respect to the respective axis. It is advantageous in that respect if a tilt drive system is provided for jointly tilting a plurality of reflectors with respect to their respective axis, in particular if there is also provided a first tilt transmission device, by way of which a predetermined tilting movement can be effected for each of the plurality of reflectors in dependence on the tilt drive system. It is also advantageous to provide a tilt drive device associated with a reflector or an axis for tilting the reflector or the reflectors associated with the axis, in particular if there is also a second tilt transmission device, by way of which a predetermined tilting movement can be effected for each of the reflectors in dependence on the tilt drive device. A particularly preferred embodiment of the invention has a drive for pivoting and tilting a plurality of reflectors, wherein there is provided in particular a transmission device, by way of which a predetermined pivotal and/or tilting movement can be effected for each of the plurality of reflectors in dependence on the drive. 
     In accordance with a further embodiment the target is coupled to the axis arrangement stationarily relative to the axis arrangement so that inclination of the axis arrangement results in a corresponding movement of the target which thus remains in the same relative position with respect to the reflectors. That means that there is no need for separate guidance of the target for adaptation to the altered plane of the path of the sun in the course of the year. 
     Alternatively it can be provided that the target is movable independently of the axis arrangement, in particular by means of a separate target drive. 
     In accordance with a preferred embodiment of the invention the reflectors have mirrors, in particular with flat mirror surfaces. Flat or planar mirrors are particularly simple and convenient in manufacture and do not require any special treatment or machining to be used in the context of the present invention. 
     In a further embodiment of the present invention the reflectors are adapted to focus the deflected solar rays, the reflectors having in particular concave mirror surfaces. 
     While in the case of a flat mirror surface an increase in intensity of the radiation incident at the target is achieved by addition of the radiation deflected by a plurality of reflectors, a further increase in intensity can be achieved with solar rays which are focused by the reflectors. 
     In a further embodiment of the present invention the target is adapted to deflect the solar rays deflected thereonto in a predetermined fashion. There is no need for the solar rays deflected on to the target to be used for energy conversion directly in the target, instead it is for example also possible for a plurality of apparatuses according to the invention to be combined, in which case the respective targets are so adapted that they irradiate a common ‘hot spot’. If in addition for example a desired use presupposes an item of equipment which is too heavy or too bulky or unwieldy to be used directly as the target in the apparatus according to the invention, the deflected solar rays can be directed from the target of the apparatus according to the invention on to that item of equipment without movement of the item of equipment itself being necessary. 
     Advantageously in a further embodiment of the invention the target has at least one reflection element which focuses and/or deflects solar rays arriving from the reflectors to a useful element. For example in addition to or instead of focusing of the solar rays by the reflectors, such an increase in intensity CaO be achieved by focusing also with a suitable reflection element of the target. The useful element can also be arranged separately from the target. 
     In a further preferred embodiment of the invention the target is coupled to a thermal engine, in particular a hot gas turbine or a steam turbine, wherein the medium of the thermal engine is heatable by the deflected solar rays. For example it is possible by means of the deflected solar rays to evaporate water to give steam with which a steam turbine can be driven to generate electric power. It is also possible with the deflection of the solar rays on to the target to heat air or another gas with which a turbine can be driven in suitable fashion. 
     In accordance with a further embodiment of the present invention the target is coupled to a heat storage means, wherein the medium of the heat storage means is heatable by the deflected solar rays. It can be provided in that respect for example that for instance paraffin is heated to a temperature of between 100° C. and 150° C. by means of the deflected solar rays, in which case the thermal energy stored thereby in the paraffin can be taken from the paraffin again at another moment in time. 
     In a further advantageous embodiment the apparatus according to the invention further has the following features. A first reflector of the number of reflectors is provided for deflection of solar rays through a first plane angle out of a plane of the path of the sun and is coupled to a first axis. In this case the first axis is tilted and/or tiltable with respect to an orientation plane of the axis arrangement about a first axis angle, wherein the first reflector is tilted and/or tiltable with respect to the first axis about a first reflector angle. In this case the first axis angle is in opposite relationship to the first reflector angle and the first plane angle. In other words, this in a side view provides for example for deflection of the reflection of a horizontally incident solar ray in the anti-clockwise direction with a tilting movement of the first axis with respect to a vertical orientation plane in the clockwise direction and a corresponding tilting movement of the first reflector with respect to the first axis in the anti-clockwise direction (see also for example  FIG. 17 ). 
     The orientation plane of the axis arrangement is a plane which is determined, preferably also geometrically, by the axis arrangement and which in operation is oriented in a predetermined fashion relative to the plane of the path of the sun. In the case of an apparatus as shown for example in  FIG. 4   a - 4   c ,  5 ,  6  or  16 , the orientation plane is the plane defined by the axes of the apparatus. If the axis arrangement is in the form of a flat carrier structure the orientation plane of that axis arrangement is preferably the plane defined by the carrier structure. 
     A flat mirror oriented perpendicularly to the presumed plane of the path of the sun reflects solar rays incident thereon in parallel relationship with that plane of the path of the sun in the same plane. A correspondingly oriented parabolic mirror for focusing solar rays focuses the solar rays incident thereon in a spot (region) which is also in the path of the sun. Therefore, with mirrors oriented in such a fashion, it is only possible to irradiate targets which are disposed jointly with the mirrors in a plane in parallel relationship with the path of the sun. 
     In an embodiment corresponding to claim  8  or claim  9  a part of the reflectors is tilted or tiltable with respect to the respective axis, the axis preferably being oriented perpendicularly to the plane of the path of the sun. With such tilted or tiltable reflectors, the solar rays can be deflected out of the apparent plane of the path of the sun, which makes it possible to co-ordinate a plurality of mutually superposed reflectors in such a way that the solar rays deflected thereby are incident on a target which is not disposed with the reflectors in a plane parallel to the plane of the path of the sun. It will be noted in this respect however that in this case, with a larger plane angle, that is to say greater deflection of the solar rays out of the plane of the path of the sun, that can involve a difficulty in focusing the reflected solar rays on the target. A solution thereto in accordance with the invention, as described for example hereinbefore, lies in suitable compensation by adaptation of the pivotal and tilting angles of the reflectors. It was now further found that surprisingly, even with a greater plane angle, good simple focusing can be achieved by the above-described tilting movement of the first axis which is associated with the first reflector in relation to the orientation plane of the axis arrangement, for example a plane perpendicular to the plane of the path of the sun, in particular a plane perpendicular to the direction of incidence of the solar rays, and tilting of the reflector with respect to the first axis. 
     The at least one further reflector of the apparatus according to the invention in this embodiment can in turn be arranged like the first reflector, that is to say also coupled to an axis which is tilted with respect to the axis arrangement and can be tilted with respect thereto, or can also be connected to an axis parallel to the orientation plane of the axis arrangement. The one further reflector or the further reflectors or the elements connected thereto of the apparatus can in particular also be designed as is set forth in claims  5  and  8  to  12 . 
     In a further preferred embodiment of the present invention the apparatus has a second reflector as one of the reflectors, which is provided for deflection of solar rays through a second plane angle which differs from the first plane angle out of the plane of the path of the sun and is coupled to a second axis, wherein the second axis is tilted and/or tiltable with respect to the orientation plane of the axis arrangement through a second axis angle, wherein the second reflector is tilted and/or tiltable with respect to the second axis through a second reflector angle, and wherein the second axis angle is in opposite relationship to the second reflector angle and the second plane angle. Thus with the first reflector it is possible to achieve deflection through a first plane angle and with the second reflector a deflection through a second plane angle, whereby for example there are two or correspondingly more ‘levels’ of reflectors which by virtue of an adapted plane angle respectively orient the incident solar rays on to the common target. 
     In accordance with a further embodiment of the invention the reflector angle corresponds to the plane angle and the axis angle corresponds to an oppositely related half of the plane angle. In general the magnitude of the plane angle upon incidence of the solar rays perpendicularly to the orientation plane of the axis arrangement is equal to double the difference between the magnitudes of the axis angle and the reflector angle, as, with the tilting movement of the reflector and the axis, with the reflector unpivoted, there is an angle between reflector and orientation plane, that is equal to that difference. It was found that particularly good results can be achieved with the above-specified arrangement. 
     In a preferred embodiment the axis arrangement is so adapted that the orientation plane can be oriented by an inclination movement perpendicularly to a plane of the path of the sun. An orientation plane which is oriented perpendicularly to the path of the sun makes it possible to provide that the solar rays are particularly easily guided on to the target. 
     In another preferred embodiment of the present invention the axis arrangement has a multiplicity of axes and is so adapted that the axes are inclinable transversely relative to the orientation plane. If the axis arrangement in operation is so oriented that the axes are arranged in mutually juxtaposed relationship substantially in the East-West direction, wherein the reflectors are facing towards the sun, then the axes can be adapted to the change in the apparent plane of the path of the sun in the course of the year by inclination transversely relative to the orientation plane. 
     In a further embodiment of this invention the axis arrangement has a multiplicity of axes and is so adapted that the axes are inclinable parallel relative to the orientation plane. An axis arrangement oriented as previously described along the East-West direction has a comparatively small effective area in relation to the sun in the morning and the evening respectively. If now the effective area in relation to the sun is to be increased in the evening time or morning time or if orientation in the East-West direction is not possible, it is thus possible with an axis arrangement which allows inclination of the axes parallel to the orientation plane also to provide for orientation of the axis arrangement along a North-South direction in the extreme case, in which case the inclination of the axes can be adapted to the midday height of the sun or the inclination of the apparent plane of the path of the sun respectively. 
     Advantageously the axis arrangement can be so designed that it allows inclination of the axes both transversely and also parallel to the orientation plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Individual aspects of the invention are described in greater detail hereinafter with reference to the accompanying drawings in which: 
         FIGS. 1   a  and  1   b  show views of an arrangement for deflecting solar rays on to a target, 
         FIGS. 2   a  and  2   b  show views of a first embodiment of an apparatus according to the invention, 
         FIG. 3  shows a view of a second embodiment of an apparatus according to the invention, 
         FIGS. 4   a ,  4   b  and  4   c  show views of a further aspect of an embodiment of the present invention, 
         FIG. 5  shows a view of an axis arrangement according to an aspect of the present invention, 
         FIG. 6  shows a different view of the axis arrangement of  FIG. 5 , 
         FIGS. 7   a  and  7   b  show views of an apparatus according to the invention in a different orientation, 
         FIG. 8  shows a view of a further embodiment of the present invention, 
         FIGS. 9 to 11  show views of further embodiments of the present invention with concave mirrors, 
         FIGS. 12   a  and  12   b  show views to explain the relationships between incident and reflected light beams, 
         FIG. 13  shows a view of an inclined mirror with associated axis, 
         FIGS. 14   a  and  14   b  show views of a further aspect of the present invention, 
         FIG. 15  shows a view to explain the incidence of light at the morning time and evening time respectively in the case of an axis arrangement oriented towards the South, 
         FIG. 16  shows a view of axis arrangements according to the invention, with axes inclined in the plane defined by the axes, 
         FIG. 17  shows a view of a further aspect of an apparatus according to the invention, 
         FIG. 18  shows a view of a further embodiment of the apparatus according to the invention. 
         FIG. 19  shows a view of a modification of the  FIG. 18  embodiment, 
         FIG. 20  shows a view of a further aspect of an apparatus according to the invention, 
         FIG. 21  shows a view of a modification of the  FIG. 20  aspect, 
         FIG. 22  shows a view of an axis arrangement according to an aspect of the present invention, 
         FIG. 23  shows a modification of the  FIG. 22  axis arrangement, 
         FIGS. 24   a  and  24   b  show views of an apparatus according to the invention in different orientations, and 
         FIG. 25  shows a view of a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the accompanying drawings and the description relating to such drawings mutually corresponding elements are denoted by corresponding references. 
       FIG. 1   a  shows a mirror  10  arranged pivotably about an axis  20  to deflect solar rays  40  from the sun  30  on to a hot spot  50  as the target. The deflected solar rays are denoted by reference  40 ′. 
       FIG. 1   b  shows a situation corresponding to  FIG. 1   a , wherein the sun  30  has assumed a different position relative to the arrangement of mirror  10 , axis  20  and target  50 . 
     In  FIGS. 1   a  and  1   b  the plane of the drawing coincides with the (apparent) path of the sun, wherein the axis  20  around which the mirror  10  is arranged pivotably is perpendicular to the plane of the drawing. 
     The mirror  10  which is rotatable or pivotable about the axis  20  can be moved with a tracking movement during the course of the day in such a way that it always throws the sunlight  40  incident thereon on to the hot surface  50  which is stationary relative to the axis  20 . 
     The two  FIGS. 1   a  and  1   b  show positions of the sun at different times of the day and the corresponding position of the mirror relating thereto. 
       FIG. 2   a  shows a first embodiment of an apparatus  100  according to the invention with an axis  20  and reflectors  10 ,  12  arranged pivotably about the axis  20 . The mirrors  12  are inclined with respect to the axis  20  so that incident solar rays  40  are respectively deflected by the mirrors  10 ,  12  on to the hot surface  50  as deflected rays  40 ′. 
       FIG. 2   b  shows an arrangement similar to that shown in  FIG. 2   a , in which respect however all mirrors  12  are inclined relative to the axis  20  so that the hot surface  50  as the target is arranged outside the beam paths of the incident rays  40 . 
     In  FIGS. 2   a  and  2   b  the plane of the path of the sun is perpendicular to the plane of the drawing and is parallel to the incident rays  40 . Accordingly, as is already the case in  FIG. 1 , the axis  20  is perpendicular to the plane of the path of the sun.  FIGS. 2   a  and  2   b  essentially differ only by virtue of the arrangement of the hot surface  50  relative to the mirrors and the mirrors  12  which are correspondingly tilted differently relative to the axis  20 . The arrangement in  FIG. 2   a  means that, if the sun (not shown in  FIG. 2   a ), the hot surface  50  and the mirror  10  are disposed on a line, the hot surface  50  throws a shadow on to the apparatus  10 . Such shadowing does not occur in the arrangement as shown in  FIG. 2   b.    
       FIG. 3  shows a second embodiment of an apparatus  100  according to the invention, wherein three mirrors  10  are arranged in mutually juxtaposed relationship and are pivotable about respective axes  20 , wherein the mirrors  10  in turn are no arranged that the incident solar rays  40  are deflected on to the hot surface  50 . As is also the case in  FIGS. 1   a  and  1   b , in  FIG. 3  the plane of the path of the sun coincides with the plane of the drawing. 
       FIG. 4   a  shows a further aspect of an embodiment of the present invention. Similarly to the  FIG. 3  arrangement there are three parallel axes  20 , wherein mirrors  10  are respectively arranged pivotably about those axes. In addition there is a pivotal drive system for joint pivotal movement of the mirrors  10  about the respective axis  20 . The pivotal drive system has a bar  62  which is respectively connected by way of levers  64  to the combination of mirror  10  and axis  20  so that displacement of the bar  62 , by way of the levers  64 , causes a corresponding pivotal movement of the mirrors  10  about the axes  20 . The axes  20  with the associated mirrors  10  are thus connected by way of the bar  62  and the levers  64  in such a way that a single motor is sufficient to keep all mirrors  10  suitably oriented in relation to the sun (not shown) in the course of the day so that the reflected light always shines on the hot surface (not shown in  FIG. 4   a ). In the  FIG. 4   a  arrangement all three axes  20  perform rotary movements through the same angle. If the levers  64  are of differing lengths, as shown in  FIG. 4   b , the rotary movements take place through corresponding different angles. A rotary movement for example of the central mirror through an angle ΔΦ 2  therefore involves a rotary movement of the upper mirror through a smaller angle ΔΦ 3 , and the rotary angle ΔΦ 3  is therefore not equal to the rotary angle ΔΦ 2  but is a function of the rotary angle ΔΦ 2 , which can be implemented by suitable suspension for the mirrors. Corresponding suspension arrangements are basically known to the man skilled in the art and in that respect a detailed description of the large number of possible suspension arrangements will not be included here. 
     In a similar manner it is possible for a plurality of mirrors associated with a common axis (see for example mirrors  10 ,  12  in  FIG. 2   a  or  FIG. 2   b ) to be pivoted independently of each other about respective mutually different angles, especially as there is no need for all mirrors associated with a common axis to be pivoted through identical angles. The  FIG. 4   c  arrangement has an additional axis  21  connected by way of a lever  65  to a mirror arrangement similarly to  FIG. 4   a . As a result of the different length of the levers  64 ,  65 , a rotary movement of the axis  21  through an angle φ a  provides a pivotal movement of the mirrors  10  respectively through an angle φ b  which differs from the angle φ a . If a plurality of arrangements as are shown in  FIG. 4   c  are arranged for example in mutually superposed relationship in the form of ‘levels’, so that for each respective one of the axes  20  in  FIG. 4   c  there is an arrangement similar to those in  FIG. 2   a  or  FIG. 2   b , the mirrors of a ‘level’ can be respectively actuated jointly by way of the axis  21 . If in that case levers  65  of respectively different lengths are provided for different ‘levels’, a plurality of mirrors, although associated with an axis (see  FIGS. 2   a  and  2   b ), are pivoted through respectively different angles according to their ‘level’. 
     It will be appreciated that alternatively or supplemental to the lever systems described herein it is also possible to use other structures, for example gear wheels and/or belts. 
       FIG. 5  shows an axis arrangement  70  according to an aspect of the invention having three axes  20  which are arranged in parallel and with each of which there is associated a respective mirror  10  arranged pivotably about the respective axis  20 . The axis arrangement  70  also has a frame  72  in which the axes  20  are arranged. The view in  FIG. 5  corresponds to a view in the longitudinal direction of the axes. 
       FIG. 6  shows the axis arrangement  70  with the axes  20 , the corresponding mirrors  10  and the frame  72  of  FIG. 5 , in a view on to a plane parallel to the axes  20 . The axis arrangement  70  has three axes  20 , with each of which three mirrors  10  are respectively associated so that the axis arrangement  70  has a total of nine mirrors. In the axis arrangement  70  shown in  FIG. 6  the axes  20  are at a right angle to the lower part of the frame  72 . An apparatus according to the invention having such an axis arrangement  70  could be easily set up on flat ground, for reasons of simplicity and thus a cost saving, so that the lower part of the frame  72  is horizontal, as indicated in  FIG. 6 . 
       FIGS. 7   a  and  7   b  each show an apparatus  100  according to the invention with an axis arrangement  70  with a target  50  coupled thereto in different orientations. In  FIGS. 7   a  and  7   b  the coupling between the target  50  and the axis arrangement  70  involves a simple mechanical connection. In the  FIG. 7   a  view the (apparent) plane of the path of the sun is perpendicular to the plane of the drawing, as indicated by the solar ray  40  which is incident on the axis arrangement  70  at a right angle.  FIG. 7   b  shows an axis arrangement which is inclined relative to the view in  FIG. 7   a , with a correspondingly moved target  50  so that the axis arrangement  70  and the target  50  are set to the altered plane of the path of the sun. 
       FIG. 8  shows an embodiment of the present invention with an axis  20  and mirrors  10 ,  12  pivotable about that axis, wherein the axis  20  as a component part of an axis arrangement is so inclined with respect to the horizontal ground  80  that a vector which is perpendicular to the axis  20  (indicated by the arrow in  FIG. 8 ) is directed towards the sun  30 . The mirrors  12  are inclined similarly to  FIGS. 2   a  and  2   b  with respect to the axis  20  so that solar rays reflected by the mirrors  10 ,  12  (these are not shown here) come together in a region between the sun  30  and the axis  20  and are incident on a target (not shown). 
     In the case of an axis arrangement as shown in  FIG. 6  the arrow illustrated in  FIG. 8  corresponds to a normal vector relative to a plane defined by the frame  72  or the axes  20  respectively. In the Northern hemisphere that normal vector would therefore be oriented towards the South when the arrangement  70  involves an East-West orientation. 
     In the above-described embodiments of the present invention the reflectors are formed by flat mirrors  10 . Alternatively or supplemental to flat mirrors it is also possible to use concave mirrors or reflectors which permit higher concentration of the solar radiation and also make it possible to produce a parallel light beam from the reflected solar rays  40 ′, insofar as the concentrated light  40 ′ reflected by the concave mirrors  10  is reflected at a further convex or concave mirror  50 , as shown in  FIGS. 9 and 10 . 
       FIG. 9  shows an arrangement having three concave mirrors  10  arranged pivotably about respective axes  20 . The mirrors  10  are so oriented that incident solar rays (not shown in  FIG. 9 ) are deflected and concentrated towards the target  50 . The target  50  comprises a convex mirror which reflects the reflected solar rays  40 ′ in such a way that they are deflected to provide a parallel light beam. 
     The view in  FIG. 10  substantially corresponds to the view in  FIG. 9 , in which case the target  50  is formed by a concave mirror which also orients in parallel relationship the solar rays  40 ′ deflected by the mirrors  10 . 
     In  FIG. 11  two of the arrangements shown in  FIG. 9  are combined, the targets  50  being so oriented that the solar rays  40 ″ deflected thereby are incident on a common target  50 ′. 
     The different reflectors or mirrors are shown in  FIGS. 9 to 11 , with substantially identical radii of curvature. It will be noted however that different radii of curvature can also be provided for different mirrors when implementing the present invention. 
       FIG. 12   a  shows a mirror  10  with a normal vector  15  which is perpendicular to the mirror surface, and incident and reflected sunlight  40 ,  40 ′. In the  FIG. 12   a  view the plane of the path of the sun is in the plane of the drawing. The projection of the angle between the normal vector  15  and the incident solar ray  20  on to the orbital plane of the sun is denoted by α. The projection of the angle between the normal vector  15  and the reflected solar ray  40 ′ on to the orbital plane of the sun is denoted by α′. 
     As long as the normal vector  15  is parallel to the orbital plane of the sun and the mirror  10  is therefore oriented perpendicularly to the (apparent) orbital plane or plane of the path of the sun, α and α′ are identical and the reflected ray  40 ′ is in the plane of the orbit of the sun. 
       FIG. 12   b  shows an inclination of the mirror  10  relative to the plane of the path of the sun, which is afforded from the incident solar ray  40 . In the  FIG. 12   b  view the plane of the drawing is perpendicular to the plane of the orbit of the sun. The inclination of the mirror corresponds to the angle between the normal vector  15  on the surface of the mirror  10  and the incident solar ray and is denoted in  FIG. 12   b  by β. If the projection of the normal vector  15  on to the plane of the path of the sun and the incident light beam  40  are parallel the angle β between the normal vector  15  and the incident light beam  40  corresponds to the angle β′ between the normal vector and the reflected light beam  40 ′. 
     If the above-described special cases do not apply, then generally there will no longer be any identity between α and α′, and β and β′ respectively, in which case the differences between α and α′ and β and β′ respectively depend on α and β. For example for α=30° and β=15° α and α′ and also β and β′ respectively differ by about 4° from each other. 
     If an apparatus according to the invention only has a multiplicity of mirrors which, as shown for example in  FIG. 6 , are arranged both in mutually juxtaposed relationship and also in superposed relationship, inclination of the mirrors with respect to the respective axis  20  is required in order to hit a common target  50  with the reflected solar rays  40 ′ as shown in  FIGS. 2   a  and  2   b.    
     A mirror  12  inclined in that way is shown in  FIG. 13 , wherein the angle between the inclined mirror  12  and the associated axis  20  is denoted by φ. The solar ray incident from the sun  30  is deflected out of the plane of the path of the sun as a result of the inclination of the mirror  12  and is denoted by reference  40 ′. 
     If in orienting an axis arrangement or the reflectors associated with the axis arrangement the dependency of the direction of reflection on the angles α and β is not included, then in dependence on the geometry of the apparatus according to the invention that can mean that not all solar rays deflected by the reflectors are incident in a common region. In the example of flat mirrors the result of this can be that, although the area irradiated by an individual mirror is not larger than the mirror area, the area illuminated by the arrangement of mirrors is nonetheless larger than the individual mirror area, and the respective individual areas therefore only partially overlap. 
     In an embodiment of this invention the target  50  has a useful element  50 ′, on to which solar rays deflected by the reflectors or mirrors of the apparatus according to the invention are respectively focused or deflected by means of a reflection element  90 . 
     In  FIG. 14   a , arranged beside the useful element  50 ′ are two mirrors  90  which deflect sunlight  40 ′ which is deflected by the reflectors and which is not directed directly on to the useful element  50 ′ so that solar rays  40 ″ which have been deflected again are incident on the useful element.  FIG. 14   b  shows a further embodiment in which there is a focusing mirror  90  which deflects deflected solar rays  40 ′ which go past the useful element  50 ′ so that the solar rays  40 ″ which are deflected again are incident on the useful element  50 ′. 
     In addition it can be provided that the reduction element or elements according to the invention are arranged movably and the position thereof can alter in the course of the day so as to permit optimised deflection on to the useful element. 
     Alternatively or supplemental to the foregoing description it can be provided according to the invention that the dependency of the direction of reflection on the orientation of the reflectors is also taken into consideration in terms of orientation of the reflectors so as to provide for suitable compensation. That can be afforded for example by a suitable transmission device as is shown for example in  FIG. 4   b . Likewise it is possible to provide for compensation of a plane in perpendicular relationship to the plane of the orbit of the sun. With a suitable transmission device, tracking of the reflectors in accordance with the position of the sun in the course of the day for individual mirrors can be such that the areas illuminated by the individual mirrors overlap each other to a relatively great degree or even completely and that therefore provides for better or complete ‘focusing’. If necessary, continual focusing of the system can be achieved by simple mechanical compensating mechanisms. 
     In this respect the movement of the individual mirrors can remain coupled, in which case, as a consequence of the transmission device, individual mirrors however perform different movements. 
       FIG. 15  shows an embodiment of the present invention in which the axis arrangement of the axes  20  with the corresponding mirrors  10  is oriented in the East-West direction so that a normal vector relative to a plane determined by the axes  20  points towards the South. As indicated in  FIG. 15  the sun  30  in the morning and in the evening is at a large angle to the normal vector of the arrangement so that in such a case the apparatus has only a comparatively small effective area, in relation to the incident solar rays  40 . 
       FIG. 16  illustrates axis arrangements suitable for affording the largest possible effective area to the respectively incident solar rays even in the morning and the evening so that it is possible to use more solar energy. In this case the axes  20  are no longer perpendicular on the lower part of the frame  72 , the axes  20  and the frame  72  being of such a configuration that the angle included between them can be adapted to the midday height of the sun, which changes in the course of the year, by an inclination along the frame  72 . 
       FIG. 17  shows a view of a further aspect of an apparatus according to the invention. The flat mirror  210  is pivotably coupled to the axis  220  which in turn is connected to an axis arrangement (not shown). The mirror  210  is tilted with respect to the axis  220  through a reflector angle  218 , that is to say in the anti-clockwise direction in the  FIG. 17  view. The axis  220  is in turn tilted through an axis angle  216  with respect to the orientation plane  212  of the axis arrangement (not shown), with the direction of tilting of the axis  220  with respect to the orientation plane  212  being opposite to the tilting direction of the mirror  210  with respect to the axis  220 , that is to say in the  FIG. 17  view the axis  220  is tilted in the clockwise direction with respect to the orientation plane  212 . In the  FIG. 17  view therefore the mirror  210  is at a tilt angle relative to the orientation plane  212 , which results from the difference in the magnitudes of the reflector angle  218  and the axis angle  216 . In addition  FIG. 17  shows a solar ray  40  which is incident perpendicularly to the orientation plane  212  and which is reflected by the mirror  210 , the reflected solar ray  40 ′ including a plane angle  214  with the incident solar ray  40 , the magnitude of which is twice as large as the tilt angle through which the mirror  210  is tilted with respect to the orientation plane  212  as the plane  212  is oriented perpendicularly to the plane of the path of the sun. That plane is perpendicular to the plane of the paper in the  FIG. 17  view. Even upon a pivotal movement of the mirror  210  about the axis  220  in the course of a day, to adapt the position of the mirror to the (apparent) movement of the sun, the arrangement according to the invention makes it possible very substantially to maintain an orientation of the reflected ray  40 ′ on to the target (not shown). The reflected solar rays  40 ′ are no longer in the plane of the path of the sun so that the target which is thus also no longer arranged in the plane of the path of the sun for the mirror  210  does not throw any shadow on to the mirror  210 , as could happen if the mirror and the target are in a common plane with the sun. 
       FIG. 18  shows an embodiment of the apparatus  200  with respectively three axes  220  and three mirrors  210  arranged pivotably about a respective axis  220 . The mirrors  210  are tilted with respect to the corresponding axis  220  and so arranged or pivoted that incident solar rays  40  are respectively deflected by the mirrors  210  on to the hot surface  50  in the form of deflected rays  40 ′. The tilt or reflector angle of the mirrors  210  with respect to the axes  220  is indicated by the diagrammatic perspective view (dotted line). The axes  220  are in turn tilted with respect to the orientation plane (not shown in  FIG. 18 ) about an axis angle in the direction of incidence of the solar rays  40 , that tilting movement being indicated also by a corresponding perspective view (dotted line). The mirrors  210  are thus also tilted with respect to the orientation plane of the axis arrangement (not shown) whereby the solar rays  40  which are incident in the (supposed) plane of the path of the sun which coincides with the plane of the drawing are deflected out of the plane of the path of the sun. Accordingly the target  50  is also not in the plane of the drawing in  FIG. 18 . 
       FIG. 20  shows a further aspect of an embodiment of this invention. Similarly to the  FIG. 18  arrangement there are three parallel axes  220 , wherein mirrors  210  are respectively arranged pivotably about those axes  220 . In addition there is a pivotal drive system for common pivotal movement of the mirrors  210  about the respective axis  220 . The pivotal drive system has a bar  62  connected by way of respective levers  64  to the combination of mirror  210  and axis  220  so that displacement of the bar  62 , by way of the levers  64 , causes corresponding pivotal movement of the mirrors  210  about the axes  220 . The axes  220  with the associated mirrors  210  are thus connected by way of the bar  62  and the levers  64  so that a single motor is sufficient to keep all mirrors  210  suitably oriented towards the sun (not shown) in the course of the day so that the reflected light always illuminates the hot surface (not shown in  FIG. 20 ). In the  FIG. 20  arrangement all three axes  220  respectively perform rotary movements through the same angle. 
     If the levers  64  are of different lengths the rotary movements take place through corresponding different angles, which can be implemented by suitable suspension means for the mirrors. Corresponding suspension means are basically known to the man skilled in the art and in that respect a detailed description of the large number of possible suspension arrangements will be dispensed with here. 
     It is also possible to provide an additional axis connected by way of a further lever to the mirror arrangement similarly to  FIG. 20 . As a consequence for example of differing lengths for the levers, upon a rotary movement of the axis through an angle φa, that involves a pivotal movement of the mirrors through a respective angle φb which differs from the angle φa. If a plurality of such arrangements are disposed for example in mutually superposed relationship as ‘levels’, then the mirrors of a ‘level’ can be respectively actuated jointly by way of the axis. 
     It will be appreciated that alternatively or supplemental to the lever systems described here it is also possible to use other structures, for example gear wheels and/or belts. 
       FIG. 22  shows an axis arrangement  270  according to an aspect of the invention with three axes  220  which are arranged in parallel and with each of which is associated a respective mirror  210  arranged pivotably about the respective axis  220 . The axis arrangement  270  also has a frame  272  in which the axes  220  are arranged. The view in  FIG. 22  corresponds to a view parallel to the orientation direction of the axis arrangement  270 . In the  FIG. 22  embodiment the carrier structure afforded by the frame  272  also determines the orientation plane (not shown) of the axis arrangement  270 , in which case the orientation plane in the  FIG. 22  view is perpendicular to the plane of the drawing and parallel to the longitudinal direction (viewing from above downwardly) of the view of the frame  272 . It will be appreciated that other arrangements are also possible, in which respect in particular there is no limitation to symmetrical configurations. 
     The aspects or embodiments shown in  FIGS. 19 ,  21  and  23  differ from those in  FIGS. 18 ,  20  and  22  only insofar as the axes  220  are tilted in respective axis tilt planes with respect to the orientation plane (here perpendicular to the incident solar rays), which are not parallel for the illustrated axes  220  of a plane. The axes  220  are here respectively tilted in their own axis tilt plane, in which respect an axis tilt plane is defined in each case by a (hypothetical) untilted axis (which in  FIGS. 19 ,  21  and  23  would be perpendicular to the plane of the drawing) and the tilted axis  220 . In other words it can be said that the respective axes  220  are tilted with respect to the orientation plane (not shown here) with an axis angle which (depending on the respective axis  220 ), in addition to the polar component (that is to say a tilt angle in the axis tilt plane), involves an azimuthal component (that is to say an orientation in the plane of the drawing in  FIGS. 19 ,  21  and  23 , corresponding to a rotation of the axis tilt plane). The azimuthal component is zero in the views in  FIGS. 18 ,  20  and  22 . In the views in  FIGS. 19 ,  21  and  23  the axes  220  are respectively oriented in the azimuth on to the focal point or target  50 . Other orientations, for example with an azimuthal component which is in comparison larger or small, are also possible. 
       FIGS. 24   a  and  24   b  each show an apparatus  200  according to the invention with an axis arrangement  270  with a target  50  coupled thereto in different orientations. In  FIGS. 24   a  and  24   b  the coupling between the target  50  and the axis arrangement  270  is a simple mechanical connection. In the  FIG. 24   a  view the (apparent) plane of the path of the sun is perpendicular to the plane of the drawing, as indicated by the solar ray  40  which is incident on the orientation plane of the axis arrangement  270  at a right angle.  FIG. 24   b  shows an axis arrangement which is inclined with respect to the  FIG. 24   a  view, with a correspondingly moved target  50 , so that the axis arrangement  270  and the target  50  are set to the modified plane of the path of the sun. 
       FIG. 25  shows an embodiment of this invention. The apparatus  200  includes an apparatus with mirrors  10  and axes  20 , similarly to  FIG. 8 , with the axes  20  being oriented perpendicularly to a direction of incidence of the solar rays from the sun  30 . It will be noted however that  FIG. 5  only shows in cross-section one axis  20  with a corresponding mirror  10 . The axis  20  as a component of an axis arrangement is so inclined with respect to the horizontal ground  80  that a vector perpendicular to the axis  20  (the vector is indicated by the arrow in  FIG. 25 ) is oriented towards the sun  30 . The apparatus  200  shown in  FIG. 25  further includes mirrors  210  which are each tilted with respect to a respective corresponding axis  220 , wherein the corresponding axes  220  are in turn respectively tilted with respect to the orientation plane  212  defined by the axis arrangement. The resulting tilting of the mirrors  210  with respect to the orientation plane  212  (and thus also with respect to the mirror  10 ) provides that the solar rays reflected by the mirrors  10 ,  210  converge and are incident on a target (not shown). 
     BY way of example flat mirrors are provided in the embodiments described with reference to  FIGS. 17 to 25 . Other forms of mirrors and kinds of reflectors however are also possible in accordance with the invention, for example corresponding to the structures shown in  FIGS. 9 to 11 . The same applies to the description relating to the configuration of the target, in particular in relation to  FIGS. 9 to 11 ,  14   a  and  14   b.    
     In the accompanying drawings, for the sake of simplification thereof, the axes are respectively arranged centrally in relation to the corresponding reflectors. According to the invention however it is also possible to provide a different arrangement as long as pivotal movement of the reflectors about the respective axis is possible. 
     The present invention provides an apparatus for and a method of utilising solar energy, which allow a construction which is less expensive in comparison with known methods and apparatuses. 
     In an advantageous embodiment the invention provides an apparatus for and a method of using solar energy, in which neither a single one of large mirrors overall has to be moved, nor does a large number of small mirrors each in itself have to be rotated about a respectively different axis or about two axes, but a plurality of mirrors or reflectors are rotated on for example mutually parallel axes (see for example  FIG. 3  or  FIG. 6 ), thereby permitting a construction which is less expensive in comparison with known methods and apparatuses: a square meter of flat mirrors costs about            30.00. The frame in which the axes are held costs about          50.00 per square meter, and to that there are added the axis, some minor parts, a stepping motor with a microprocessor in a sum total of about          100.00 to          150.00 for material costs. Added to that is about          50.00 for assembly. If a square meter of mirror area collects about 500 kilowatt hours per year, in 10 years that gives 5,000 kilowatt hours, thus giving a price of about          0.04 per kilowatt hour which approximately corresponds to the price of energy from oil or gas.
     In an embodiment by way of example of the present invention the rotary or pivot axis of each mirror is not identical to an axis which is perpendicular to the path of the sun and it is also not parallel to that axis. It will be noted however that the mirror is connected by way of the axis to an arrangement defining a plane which is preferably perpendicular to the direction of incidence of the solar rays. The rotary or pivot axis of the mirror tilts through an angle α and the mirror is so mounted on that axis that it forms therewith an angle  2 ·α. In that way the mirror surface faces downwardly or upwardly to a greater degree when the mirror rotates or pivots. The mirror is lowered (or raised) somewhat in the rotary movement (pivotal movement) and thus deflects the light downwardly (or upwardly respectively) to a greater degree. 
     Only two axes are moved by a respective motor: one motor holds the arrangement with the axes to which the mirrors are mounted perpendicularly to the path of the sun in the course of the year, in which case at least some of the axes are themselves not oriented perpendicularly to the path of the sun as they are tilted with respect to the orientation plane of the axis arrangement. A second motor rotates the mirrors about those axes during the day. 
     In the case of a simple tilting movement of mirrors with respect to an axis which is perpendicular to the (apparent) plane of the path of the sun, the problem which arises is that light reflected thereby is in general not at the same angle as the incident light, both in the plane of the sun and also perpendicularly thereto, so that focusing by joint orientation of the mirrors towards a target is found to be difficult. 
     If for example the mirror is to be inclined through 5° so that it deflects the light downwardly through 10°, then in an embodiment the axis of mirror rotation is inclined upwardly through 5° (with respect to a mounting plane), in which case at the same time the angle between that axis and the mirror is set to 10° so that in turn the mirror points downwardly by the required 5° (with respect to the mounting plane). In an embodiment a mirror can be mounted in correspondingly tilted relationship at a flap of a conventional hinge, in which case the other flap of the hinge is fixed to a mounting frame so that the hinge axis is tilted with respect to the mounting frame. 
     In comparison with conventional systems such as parabolic mirror systems (with a three-dimensional mirror curvature), parabolic trough-like systems (with a two-dimensional mirror curvature) and solar towers, the invention affords simplifications in that it is possible to use less expensive flat mirrors, there is no need to move a large and heavy mirror system (as in the case of a parabolic mirror) but only a number of axes which each only bear the weight of the respective mirrors associated therewith while a large part of the holding structure (frame) is not moved in the course of the day, and in addition there is no need to displace a multiplicity of mirrors in two respective axes, as is the case with a solar tower.