Patent application title: TROUGH COLLECTOR FOR A SOLAR POWER PLANT
Andrea Pedretti (Bellinzona, CH)
AIRLIGHT ENERGY HOLDING SA
IPC8 Class: AF24J214FI
Class name: Solar heat collector with means to reposition solar collector for optimum radiation exposure gearing
Publication date: 2011-05-05
Patent application number: 20110100355
The invention relates to a trough collector (1) for a solar power plant,
comprising a mount (34) carrying a supporting structure (30), means
disposed on the supporting structure (30) for providing heat originating
from incident solar radiation, and a pivot device (40) that is fixed to
the supporting structure (30) and is used to pivot the supporting
structure (30) with respect to the mount (34), wherein the centroidal
axis (36) of the supporting structure (30) equipped with the means for
providing the heat is located outside the pivot axis of the supporting
structure (30), and wherein the pivot device (40) is configured such that
the centroidal axis (39) of the fully equipped supporting structure (30)
is located in the region of a fixed pivot axis (35). In this way, a
cost-effective, and zero-backlash pivot drive for the trough collector is
1. A trough collector for a solar power plant comprising: an arrangement
for supplying heat originating from solar radiation, which is tiltable
for alignment with respect to a position of the sun; means for tiltable
mounting of the arrangement wherein a tilt axis of the arrangement is
arranged substantially in a fixed position and lies in an area of a line
of gravity (39, 89) of the tiltable arrangement; a circular-arc-shaped
section above which the arrangement rests operationally for a rolling
motion on stationary pedestals; wherein a centre of curvature of the
circular-arc-shaped section lies in the area of the line of gravity of
the trough solar collector; and wherein the rotation axis of the trough
solar collector is arranged in a fixed position and coincides with its
line of gravity.
2. The trough collector according to claim 1, wherein: the means comprise at least one stationary pedestal with respect to a subsurface on which the arrangement rests for a rolling motion; wherein a single pedestal is located vertically under the line of gravity; and a plurality of pedestals are arranged under said line and symmetrically to said line.
4. The trough collector according to claim 1, wherein: the arrangement comprises longitudinal supports between which a concentrator is located; and wherein at least one bearing rim is connected at one end to respectively one longitudinal support in such a manner that the longitudinal supports and the concentrator are rollable about the rotation axis by means of a movement of the at least one bearing rim.
5. The trough collector according to claim 4, wherein: the supporting structure of the arrangement for supplying heat in which the concentrator is located has a modular structure; and wherein the modules have substantially the same structure, comprising two opposed longitudinal supports for receiving the concentrator and a bearing rim which is located perpendicularly to this and wherein each bearing rim is assigned at least one pedestal.
8. The trough collector according to claim 5, wherein the rotation axis lies underneath the operationally spanned concentrator.
11. The trough collector according to claim 1, wherein the means for supplying heat comprise a pressure cell which contains the concentrator and wherein the pressure cell is clamped between longitudinal supports which are components of the arrangement for supplying heat.
12. The trough collector according to claim 1, wherein the line of gravity of the completely equipped arrangement runs at a distance from the rotation axis, at the most so far that the tilting forces of a predetermined wind action acting on the supporting structure hold the arrangement in equilibrium with respect to the tilt axis.
13. The trough collector according to claim 1, wherein the arrangement comprises means to change the forces acting thereon as a result of a wind action.
 The present invention relates to a trough collector for a solar
power plant according to the preamble of claim 1.
 For some time, solar thermal power plants have already been producing power on an industrial scale at prices which, compared to photovoltaic methods, are close to the commercial prices now usual for power produced in the conventional manner.
 In solar thermal power plants the sun's radiation is reflected by collectors with the aid of a concentrator and is specifically focussed onto a location at which high temperatures are thereby produced. The concentrated heat can be removed and used for operating thermal machines such as turbines which in turn drive power-generating generators.
 Three basic forms of solar thermal power plants are in use today: dish Stirling systems, solar tower power plant systems and parabolic trough systems.
 Parabolic trough systems have a large number of collectors which have long concentrators having small transverse dimensions and therefore do not have a focal point but a focal line, which fundamentally distinguishes these in their design from the dish Stirling and solar tower power plants. The trough collectors today have a length of 20 m to 150 m whilst the width can reach 3 m, 5 m or more. An absorber line for the concentrated heat (up to around 400° C.) runs in the focal line, which transports this to the power plant. A fluid such as, for example, thermal oil or superheated water vapour which circulates in the absorber lines can be considered as transport medium.
 Although a trough collector is preferably configured as a parabolic trough collector, trough collectors with spherical or only approximately parabolically configured concentrators are frequently used since an exactly parabolic concentrator having the aforesaid dimensions can only be produced at great expense, which is therefore barely economically reasonable.
 The 9 SEGS trough power plants in Southern California together produce a power of about 350 MW; an additional power plant in Nevada should presently be going onto the grid and deliver over 60 MW. Another example of a trough power plant is the Andasol 1 under construction in Andalusia having a concentrator area of 510,000 m2 and 50 MW power, where the temperature in the absorber lines should reach about 400° C. The pipeline system for circulating the heat-transporting fluid in such power plants can reach a length of up to 100 km or more if the concepts for future large plants are implemented. The costs for Andasol 1 are estimated at several hundred million Euro.
 According to rough calculations, it can be noted that an increasingly large proportion of the overall costs, today for example, 65% or more in such a solar power plant, are attributed to the trough collectors and the pipeline system for the heat-transporting fluid.
 The trough collectors of the said type are configured as tiltable so that in North-South alignment, they can track the daily position of the sun or in West-East alignment they can track the seasonal position of the sun (but with likewise daily but smaller variation in the position of the sun). In this case, an exact alignment to the current position of the sun is crucial for a high efficiency of the power plant. An error in the alignment of 3.5 mrad, i.e. 0.2°, is today considered to be the limit of what is reasonably tolerable; at the same time, it is to be expected that in view of the advancing technology, the requirements will become more stringent.
 In view of the high weight of the collector in particular with large dimensions (see above), the tilting drive is frequently complex to manufacture.
 It is known that the supporting structure for the parabolically or spherically configured trough concentrator must encompass this from behind in the manner of a bracket in order to keep its front reflecting surfaces facing the sun completely free. This rapidly leads to complex structures for the mounting and movement of the concentrators which are then additionally cost-intensive when the use of light-weight construction is sometimes essential.
 In this case, it is not only necessary to optimise between high weight and precision of movement but it should also be taken into account that the collector is not impermissibly warped due to movement or alignment or also due to the action of wind. In such structures, warping as such may indeed usually be unproblematical constructively but then has negative effects on the efficiency since the warpage is added to the error in the alignment.
 Optimally, a collector would continuously track the position of the sun but frequently for simplicity, the collector is realigned in a stepwise manner.
 For the alignment according to the daily position of the sun (in accordance with a North-South alignment of the collector), for example, this means that the collector is realigned when the position of the sun has changed twice by 3.5 mrad=0.4° (in a specific alignment the sun initially lags behind by the permissible error, is then positioned precisely above the collector and then advances by the permissible error). This would mean that the collector would need to be realigned every 69.12 seconds in the required accuracy. It is self-evident that the aligning movement must be exact i.e. correction movements are undesirable after the alignment has been made.
 When the collector is in a West-East alignment, the position of the sun also varies by more than the permissible amount of error over the day so that the collector must be realigned many times a day.
 It is therefore the object of the present invention to provide an improved trough collector for the alignment movement.
 In order to achieve this object, the trough collector according to the invention has the features of claim 1.
 Since the line of gravity of the tiltable arrangement 2 lies in the area of the now fixed tilt axis despite the fundamentally asymmetrical construction (the structure encompasses the concentrator from behind), the retention forces for securing the respective position of the arrangement 2 are constant over the entire tilting range which allows a simplified tilting drive to be provided. In addition, the forces required for the alignment movement itself are now reduced to the friction and therefore constant, which opens up the way towards a continuous alignment movement. This has a positive effect on the efficiency of the collector which can thus be optimally aligned continuously and no longer intermittently to the sun.
 In a preferred embodiment, the mounting of the arrangement is located symmetrically to its line of gravity. As a result, the retention forces for securing the respective tilting position of the arrangement 2 are reduced to a minimum, i.e. the weight of the arrangement 2, and are constant. The arrangement 2 is located at rest in every position so that over the entire tilting range, retention forces for securing the respective position are not necessary. Lower requirements for the design of the arrangement itself and for the tilting drive are the consequence, which can be designed accordingly simply for the necessarily precise movement.
 In addition to the constructive simplification of the supporting structure, an improved efficiency is achieved overall due to the possible continuously effected alignment to the sun.
 Since in a further embodiment of the trough collector according to the invention, counterweights acting on the arrangement 2 can also be used to bring the position of the line of gravity into the range of the tilt axis due to the changed mass distribution, conventional designs, modified according to the invention, can be used. Retrofitting is therefore also possible which can lead to a considerable cost advantage in existing power plants. In another modified embodiment, dead weights can be saved if the mass of the tilting drive is arranged in such a manner that it fulfils the function of a counterweight.
 The invention is described in detail hereinafter with reference to the figures.
 In the figures:
 FIG. 1 shows schematically a trough collector of the known type
 FIG. 2 shows a cross-section through the trough collector of FIG. 1
 FIG. 3 shows a view of a first embodiment of the trough collector according to the invention,
 FIG. 4 shows a view of a second embodiment of the trough collector according to the invention,
 FIG. 5 shows the section AA through the supporting structure from FIG. 3.
 FIG. 1 shows a view of a trough collector 1 known from the prior art, comprising an arrangement 2 for supplying heat originating from solar radiation and a mounting 3 on which the arrangement 2 rests. Such collectors 1 can have the aforesaid dimensions (e.g. a length of 150 m) or even exceed these, with such large dimensions the weight of the arrangement 2 is easily between 10 and 20 tonnes.
 The arrangement 2 comprises a frame 4 for a pressure cell 5 which for its part consists at least partially of a flexible membrane 6 whose cushion-like curvature is indicated by the auxiliary lines 7. The frame 4 (including the mounting 3) is preferably made of concrete, which brings with it advantages in regard to cost-effective manufacture on site, in particular in inaccessible areas.
 The structure of the pressure cell 5 clamped in the arrangement 2 is explained in detail, for example, in FIG. 2; the heat obtained from the sunlight is removed via a conventional line network, not shown to avoid overburdening the figure, from the collector 1 and used for power generation in the solar power plant.
 The mounting 3, here consisting of supports 8 and feet 9, bears the arrangement 2, a tilting device 10 being partially fixed on said arrangement, said tilting device here comprising a tilting bracket 11 by which means the frame 4, i.e. the arrangement 2, can be tilted with respect to the mounting 3 until this is aligned according to the position of the sun.
 Such an arrangement is known to the person skilled in the art, for example, from WO 2008/0037108 or from the afore-mentioned solar power plants, in particular with regard to the tilting drives of the prior art.
 The arrangement shown in FIG. 1 is an example from the prior art; the application of the present invention is not restricted to a trough collector of the type shown (here: a pressure cell equipped with a secondary concentrator). Any suitable framework for receiving the concentrator which can also consist of metal can likewise be provided.
 FIG. 2 shows a cross-section through the trough collector 1 from FIG. 1 as is presented in detail in the Swiss Patent Application CH 2008/0462.
 The pressure cell 5 is clamped in the frame 4 and consists at least partially of a flexible membrane, i.e. here of a membrane 21 transparent for solar radiation 20 and a membrane 23 covered with a reflecting layer 22, which together form the concentrator 24 of the trough collector 1. The solar radiation 20 is reflected via a secondary concentrator 25 to an absorber line 26 which removes the heat of the solar radiation 20 in a known fashion.
 The pressure cell 5, in particular with the concentrator 24, the secondary concentrator 25 and the absorber line 26 pertain to the arrangement for supplying heat originating from the solar radiation.
 However, it is self-evident that the said arrangement 2 for supplying heat originating from the solar radiation comprises everything which serves the said purpose in the specific case, whether this be conventional concentrators of metal inserted in the frame 4, various constructions for suspending the concentrator, various systems for the absorber lines or other such elements such as are built in the respective trough collector for a specified solar power plant. Apart from parts of the mounting, this comprises that equipment which co-determines the position of the centre of gravity or the line of gravity of the tiltable part, i.e. the arrangement 2 of the trough collector 1.
 It is apparent from the Figure that the tilting drive 12 (consisting, for example, of driven rollers 13 which pull the tilting bracket 11 through between them) is suitable for tilting the concentrator 24 horizontally/approximately vertically between the positions. In such a conventional design the centre of gravity of the arrangement 2 provided with the means for supplying heat lies outside the instantaneous tilt axis of the arrangement 2 (or depending on the geometry of the tilting device 10, lies only randomly thereon in an individual tilt position). It follows that, depending on the tilt position, the tilting drive 12 is held variably but continuously under load by the combined weight of the supporting structure 2 and the means for supplying heat and must be designed with appropriate complexity.
 FIG. 3 shows a cross-section through a trough collector 70 configured according to the invention according to a first embodiment. Shown is an arrangement 71 for supplying heat originating from the solar radiation and means 72 for the tiltable mounting of the arrangement 71.
 To avoid overburdening the Figure, a pressure cell 5 comprising the concentrator 24, the secondary concentrator 25 and the absorber tube 26 is merely indicated schematically. The pressure cell is disposed between longitudinal supports 75, 76 and is spanned by these, said longitudinal supports 75, 76 in turn rest on transverse struts 77, 78 which go over into a bearing rim 79 having a circular-arc-shaped section 79' which for its part rests on pedestals 80, 81.
 The bearing rim 79 is thus connected to respectively one longitudinal support 75, 76 at the ends in such a manner that the longitudinal supports 75, 76 and therefore the concentrator 24 are tiltable about the tilt axis 88 by means of a movement of the bearing rim 79.
 The circular-arc-shaped section 79' is disposed perpendicularly to the tilt axis 84 of the arrangement 2 and projecting downwards. The pedestals 80, 81 are suitably configured, here with rollers 82, 83, so that the bearing rim 79 can be turned in the pedestals 80, whereby the arrangement 2 as a whole is operationally tiltable with respect to the stationary pedestals 80, 81. To avoid overburdening the Figure, a tilting drive is omitted; this can consist of a motor which acts via a pinion on a sprocket wheel located on the section 79'. The pedestals 80, 81 in turn are anchored on a foundation 85, that is are stationary with respect to the subsurface 86. The height of the foundation 85 is matched to the desired tilting range of the collector 70: the minimum height h is determined in such a manner that the longitudinal supports 75, 76 (or the elements of the arrangement 2 located the furthest outwards) at maximum tilt still have the desired distance from the subsurface 86.
 As a result of the geometry of the arrangement 2 shown, in particular the circular-arc shaped section 79' of the bearing rim 79, a fixed tilt axis 88 of the arrangement 2 is obtained, which runs through the centre of curvature 85 of the circular-arc-shaped section 79'.
 The line of gravity 89 of the elongate arrangement 2 is given by its mass distribution which in turn depends on the design of the various components of the arrangement (pressure cell 5, longitudinal supports 75, 76, transverse struts 77, 78 etc.) and in particular on the length of the radius of curvature 90. The length of the radius of curvature 90 can now be determined by the person skilled in the art in conjunction with the said elements in such a manner that the tilt axis 88 lies in the range of the line of gravity 89.
 Although the said parameters all influence each other, according to the basic principle, it is the case that the position of the tilt axis 88 is specifically determined such that it lies in the range in which the line of gravity 89 lies on the basis of the general constructive requirements. The tilt axis 88 tracks the line of gravity 88.
 In other words, in this embodiment it is possible according to the invention to optimally design the arrangement 2 in the specific case according to its function without needing to take account of the location of the line of gravity 89. Then by suitable dimensioning of the bearing rim 79, the tilt axis 88 can be simply placed in the area of the line of gravity 89.
 The use of the bearing rim 79 makes it possible to arrange the tilt axis 88 favourably in the area of the pressure cell 5 which in conventional designs, can only be achieved with considerable constructive effort or is not possible at all on account of the bearings to be located in the tilt axis.
 The result is a construction which is optimized in regard to complexity, costs and weight and at the same time, can be aligned highly precisely.
 Tilt axis 88 and line of gravity 89 preferably coincide so that the advantages according to the invention are optimally realised (e.g. constant retention forces for the arrangement 2, forces for the aligning movement reduced to the friction). If tilt axis 88 and line of gravity 89 do not coincide, this can occur for the reasons described in connection with FIG. 5 (action of wind, other boundary conditions). Then, as described in connection with FIG. 5, the person skilled in the art then determines the distance range of tilt axis 88 and line of gravity 89, e.g. as a result of wind loading or other locally occurring factors.
 As can be seen from the Figure, the pedestals 80, 81 are configured symmetrically with respect to a vertical plane 91 indicated by a dot-dash line, running through the line of gravity 89. They lie below the line of gravity 89 and symmetrically with respect to this. A possible single pedestal would be located vertically below the line of gravity 89, a plurality of pedestals below this and symmetrical to this. Thus, the retention forces for the arrangement 2 are reduced to their weight; moments due to eccentric mounting no longer occur.
 As mentioned above, trough collectors can have a considerable length. Within the scope of the present invention, the supporting structure of the arrangement (but not necessarily the pressure cell 5) therefore has a modular structure. The modules preferably have this same basic structure each having respectively two longitudinal supports of, for example, 10 m length and a bearing rim located perpendicularly thereto, which then has at least one pedestal. Accordingly, the weight of each module is mounted via its bearing rim which allows the supporting structure of the arrangement 2 to be simplified since it can be supported at the desired locations by means of a bearing rim, it need not have a high stiffness with respect to the weight of the trough collector 70. Even if the end-side modules must be modified compared with the inner modules by the very nature of the matter, all the modules advantageously have substantially the same basic structure.
 FIG. 4 shows a view of another preferred embodiment of a trough collector 100 according to the invention. Shown is an arrangement for supplying heat originating from solar radiation comprising a two-part frame 31, 31' in which, for example, a pressure cell 5 (FIG. 2) can be clamped or a conventional metal concentrator can be attached. Such a pressure cell or such a concentrator and the further respective means for supplying heat are omitted to avoid overburdening the Figure; these are fundamentally of a conventional nature and can be defined by the person skilled in the art for the specific application.
 The supporting frame 31, 31' rests on a number of transverse struts 32 which pertain to the supporting structure 30 and whose concave shape is specifically determined to accommodate a parabolic or spherical concentrator or a pressure cell 5. The transverse struts 32 for their part are mounted on supports 34 by means of pivot bearings 33 thereon. All the pivot bearings 33 are therefore stationary and determine a common fixed tilt axis 35 indicated by the dot-dash line. This lies below the concentrator depending on the design.
 Each transverse strut 32 together with the parts of the supporting frame 31, 31' assigned to it has a centre of gravity 37. It is apparent that the line of gravity 36 indicated by the dotted line cannot coincide with the tilt axis 35 thanks to the necessarily concave configuration of the transverse struts 32 but must lie above the pivot bearing 33. This applies all the more if the means for supplying heat as prescribed are disposed on the arrangement 30.
 The arrangement 30 is only completely equipped when the parts of the tilting device 40 assigned to it (FIG. 5) are likewise located thereon. Due to their weight, these then also influence the position of the line of gravity, in the present case due to the encapsulation 38 for a chain 44 (FIG. 4).
 In other words, it is the case here that the encapsulation 38 serves as a counterweight for balancing out the arrangement 30 in such a manner that its line of gravity 36 lies in the area of the tilt axis 35 and preferably coincides with this.
 Thus, in contrast to the first preferred embodiment according to FIG. 3, the line of gravity 36 is brought into the area of the tilt axis 35; the line of gravity 36 tracks the tilt axis 35. This principle can also be used for retrofitting existing structures and achieves advantages according to the invention.
 FIG. 5 shows the tilting device 40 for the arrangement 30 in detail, by means of a section through a transverse strut 32 with the related encapsulation 38. The transverse strut 32, the supporting frame 31, 31' and the encapsulation 38 are constructed in a box shape and their walls 41, 41' shown cutaway in the Figure (from the supporting frame 31, 31'), 42 (of the transverse strut 32) and 43 (of the encapsulation 37) are shown hatched. Also shown is a tilt member of the tilting device 40, preferably configured as chain 44, which acts with both its ends 45, 45' via fastening points 46, 46' located laterally of the tilt axis 36 on the supporting structure 30 or is fixed thereon and can thereby tilt these with respect to the pivot bearing 33. The chain 44 runs on an arcuately running supporting surface 47 and is tensioned by a tensioning wheel 48. Two drive wheels 49, 50 are tensioned with respect to one another in the direction of the indicated arrows 51, 52 with the consequence that the tilt position of the supporting structure 2 is defined free from play over the entire tilt region. The wheels 48, 49, 50 are mounted in the support 34 and therefore do not pertain to the parts of the tilting device 40 disposed on the arrangement 30. Alternatively to using a chain 44, a sprocket wheel, for example, is also possible which is then driven by a gear wheel fixed in the support 34.
 The tilting of the arrangement 30 is effected by means of a synchronous drive of the two drive wheels 49, 50, likewise provided in the support 34 (i.e. generally on the mounting of the supporting structure 30), in the clockwise or anticlockwise direction, wherein the pre-tensioning according to the arrows 51, 52 is preferably retained. A drive motor for the drive wheels 49, 50 as well as a pre-tensioning device (arrows 51, 52) are omitted to avoid overburdening the Figure and could be determined by the person skilled in the art for the specific case according to the prior art.
 The encapsulation 38 encloses the chain 44 and protects this from weathering and contamination, likewise in part the other elements of the tilting device 40 insofar as these are not protected by the support 34. In principle, the encapsulation 38 has a slot 53 on its concave outer side which allows the tilting of the encapsulation 38 with respect to the drive wheels 49, 50. The slot 53 can easily be closed by conventional means which leave free an opening for the wheels 49, 50 which is displaceable according to the tilt position.
 In principle, tilting is possible until a fastening point 46, 46' impacts against a drive wheel 49, 50. If the supporting structure 30 is to be tilted on one side substantially as far as the vertical, the drive wheels 49, 50 can be accordingly displaced in the support 34 towards the other side.
 It is now possible to determine and arrange the mass of the encapsulation 37 with little effort and minimal costs in such a manner that the line of gravity 39 of the completely equipped arrangement 30 coincides with the tilt axis 35 or lies in the area of the fixed tilt axis 35.
 Naturally, the play-free drive indicated above can also be used as such (i.e. disregarding the mass distribution over the encapsulation) in the embodiment according to FIG. 3.
 As mentioned above, the arrangement 30 is completely equipped when all means for supplying heat and in addition all the elements of the tilting device 40 to be arranged thereon are arranged operationally thereon.
 The mass of the encapsulation 38 is dependent on its material and the distribution of the material. As has likewise been mentioned above, in the preferred exemplary embodiment shown, the supporting structure 30 is made of concrete, likewise the encapsulation 38, the walls whereof are now made with such a thickness that the line of gravity 39 of the completely equipped supporting structure 30 coincides with the tilt axis 35. However, the person skilled in the art can not only appropriately select the wall thickness but also modify the geometry of the encapsulation 38 such that whilst maintaining the prescribed function of the tilting device 40, the desired mass distribution results. It is further possible to use materials having different weight. In other words, it is the case that with regard to the specific configuration of the trough collector, the person skilled in the art designs the tilting device 40, in particular its encapsulation 38, with regard to the position of the line of gravity 39.
 The line of gravity 39 can now coincide with the tilt axis 35 in the sense of the optimal solution or "only" be arranged in the area of the tilt axis 35. This is understood as a slight displacement to the extent that the advantages according to the invention are certainly effective but nevertheless, a comparatively small, intentional continuous stressing of the tilting device 40 remains. Thus, for example, in order to keep the tilting device 40 free from play under unilateral loading (in the case of using a rack as a tilting member) or in order to trigger one tilting direction of the supporting structure 2, 30 substantially via the drive and the other tilting direction substantially via its weight. Or in general, if the person skilled in the art achieves the advantages according to the invention with respect to a different constructive optimisation but nevertheless avoids the geometrically precise overlap of the line of gravity 39 of the completely equipped supporting structure 2, 30 and the tilt axis 35.
 Another reason for arranging the line of gravity 39 in the area of the tilt axis 35 but not making it coincide therewith can be seen from the forces forming on the supporting structure in the event of wind action. In principle, it can certainly be assumed that such forces rarely occur because of the symmetrical shape of the completely equipped supporting structure. On the one hand, however, the tilt axis 35 will frequently lie somewhat eccentrically to the supporting structure and on the other hand, the specific configuration of the supporting structure, the deformability of the pressure chamber 5 consisting of a flexible membrane etc. can lead to a (possibly instantaneous) flow pattern which results in considerable resultant force on the completely equipped supporting structure. In this respect, the person skilled in the art can define a predetermined wind action, whether this be as a maximum real storm strength or a maximum permissible standard value and derive from this the resulting force (possibly approximately) acting on the supporting structure. The line of gravity 39 of the completely equipped supporting structure 2, 30 can then be located at a distance from the tilt axis 35, at the most so far that the supporting structure 2, 30 is held in equilibrium under the tilting forces produced as a result of the resulting force of the predetermined wind action. In other words it is then the case that with wind action, the supporting structure "hangs" somewhat unilaterally in the mounting and is balanced out under a predetermined wind action. Depending on the design in the specific case, the person skilled in the art can also select the distance between the line of gravity 39 and the tilt axis 35 in a range from zero as far as the described maximum distance.
 In a further embodiment, the supporting structure is additionally provided with means which change the forces acting thereon due to the wind action. As a result, the forces produced by the wind action can be reduced or influenced in their direction which alone or in conjunction with the measures described above results in improved design of the supporting structure. Such means can be configured as spoilers located on the supporting structure or as wind deflectors of any kind or can be formed on the supporting structure or moulded thereon (thus, for example, by fluid-dynamically determined shaping of frame parts or other surfaces). These are preferably arranged movably so that they can also develop their effect when winds act from various directions.
 This reasoning also all applies to the embodiment shown in FIG. 3.
 The arrangement shown makes it possible to achieve a play-free tilting drive for continuous tilting of the concentrator or for tilting in discrete steps, in which case only the adhesive friction in the pivot bearings needs to be overcome and thus a simple and cost-effective, but at the same time high-precision drive, is available.
Patent applications by Andrea Pedretti, Bellinzona CH