AU2010219369A1

AU2010219369A1 - Tracking unit for a solar collector

Info

Publication number: AU2010219369A1
Application number: AU2010219369A
Authority: AU
Inventors: Klaus Hofbeck; Michael Killermann; Alexander Kist; Hans Poisel; Harry Schilling; Sebastian Schutz
Original assignee: Georg Simon Ohm Hochschule fuer Angewandte Wissenschaften Fachhochschule Nurnberg
Current assignee: Georg Simon Ohm Hochschule fuer Angewandte Wissenschaften Fachhochschule Nurnberg
Priority date: 2009-03-12
Filing date: 2010-03-09
Publication date: 2010-10-14
Also published as: DE102009045033A1; IL207117A0; EP2350539B1; US20100252026A1; EP2350539A2; WO2010102619A2; WO2010102619A3

Description

1 Tracking unit for a solar collector Field of the invention 5 The invention relates to a tracking unit for a solar collector, in particular for harvesting sunlight, which can track the current position of the sun. This allows the angle of incidence of the rays to be perpendicular to the surface of the collector at all times, thus achieving maximum efficiency of the collector. 10 Description of the prior art US 4798444 discloses a solar collector which receives solar radiation from different directions and therefore does not require tracking. US 5581447 discloses a solar collector having a movable biaxial lens system which feeds sunlight into a bundle of optical fibers. 15 Another biaxial lens system for injecting light into a a bundle of optical fibers is disclosed in US 4589400. In this case, a collector head with light collecting elements arranged on a surface tracks the sun biaxially. The disadvantage of this tracking system is that the whole collector surface has to be rotated and/or pivoted. This requires a relatively large structure and a large 20 area for moving the collector head accordingly. Furthermore, large wind loads can occur due to the large surface, which must also be arranged at a great distance from the mounting plane to allow its movement.

2 Description of the invention The object of the present invention is to design a tracking unit for solar collectors, in particular for collectors which feed the sun's rays into bundles of optical fibers, such that it requires less space, has a lower wind load and can be 5 mounted closer to the installation surface. Furthermore, it is designed to track the sun in a more precise manner. This is achieved by an apparatus according to the independent patent claim. Advantageous embodiments of the invention are disclosed in the dependent claims. A tracking unit for solar collectors according to the invention has at least two 10 panels 20a, 20b, 20c, 20d, 20e, which are arranged on a frame 10 and can each be pivoted on a longitudinal axis. The positions of the axes of rotation 21a, 21b, 21c, 21d, 21e of the individual panels are displaced in relation to the adjacent panels by a specified dimension Ax in each case. The movement of the individual panels is achieved by means of a lifting mechanism or a parallel drive, with which 15 the panels can each be pivoted about the same angle. Preferably, the panels have a rectangular, elongated shape, with the longitudinal axis preferably running parallel to the longer edge of the rectangle. Such an arrangement according to the invention results in the entire surface of the solar collector being distributed across several sub-areas, corresponding to 20 the number of panels. This means that it is no longer necessary for the whole surface to track the position of the sun. In fact, only the individual sub-areas need to be moved. This allows the entire configuration to be mounted considerably closer to the installation surface, such as a roof or a wall. Accordingly, the whole arrangement does not project as much, the appearance 25 of the building or other property is compromised less and the wind load is reduced. Such an arrangement, which is relatively flat, can now be mounted in 3 large numbers without any problem on buildings, building roofs or facades, often without the need for additional building permits. In order to allow tracking along a second axis, the frame 10 can be mounted rotatably together with the panels. This means that the arrangement is largely 5 free of the constraints of a mounting angle relative to the mounting surface. In order to make the frame rotatable in a simple manner, it is preferable for it to be attached to a guide ring. This guide ring is provided with a first bearing surface parallel to the frame and/or to the panel arrangement. Furthermore, provision is made for an internal bearing surface arranged at an angle of less 10 than 90 to the first bearing surface. This slanted arrangement means that this internal bearing surface can also bear a (smaller) force perpendicular to the first bearing surface as well as a force arising at a right angle to this. This means that the frame with the panels can be rigidly mounted to the guide ring. If there is an angle of misalignment 51 between this principal orientation 32 of 15 the lens and/or the light collector 30 and the beams of sunlight 50, this must be corrected in order to maintain the optimal degree of efficiency. The exact positioning of the individual lenses in the direction of the sun requires a high level of technical complexity and in particular small tolerances in terms of the mechanics of the individual panels and their suspension. In order to minimise the 20 complexity as much as possible, a further embodiment of the invention provides for a passive micro-adjustment system for the position of the lenses accordingly. To achieve this, radiation from the sun is gathered and expandable material is heated when subjected to the radiation. The material expands in accordance with the radiation, altering the position of the lenses as a result. This means that 25 the lens is positioned optimally in relation to the sun at all times.

4 Description of drawings The invention is described below on the basis of examples of embodiments with reference to the drawing without limiting the general concept of the invention. 5 Fig. 1 shows an apparatus according to the invention Fig. 2 shows a lateral view of the apparatus with vertical panels Fig. 3 shows the arrangement with panels pivoted on an angle to the left Fig. 4 shows the panels pivoted to a high degree Fig. 5 schematically shows the positional and angular relationships of the 10 arrangement according to the invention Fig. 6 shows the positional and angular relationships with pivoting to the left Fig. 7 shows the positional and angular relationships with pivoting to the right Fig. 8 shows the positional and angular relationships for an arrangement without axial displacement 15 Fig. 9 shows a cross-section through the guide ring including the guide rollers running on it Fig. 10 shows a thermally controlled tracking apparatus for the lenses. Fig. 11 shows a thermally controlled tracking apparatus for the lenses in a balanced state 20 Fig. 12 shows a thermally controlled tracking apparatus for the lenses in detail 5 Figure 1 shows an apparatus according to the invention. The solar collector comprises individual panels 20a, 20b, 20c, 20d, 20e. These panels are pivoting mounted in a frame 10. The frame itself is rotatably mounted on the guide ring 11 and can be rotated by means of a drive system 12. The guide ring 11 is 5 mounted rigidly on a mounting surface, such as for instance on the roof of a house, a flat roof or a wall. The individual panels 20a to 20e comprise a plurality of lenses and/or light collectors 30 bundling solar radiation into individual light guiding fibers. An optional solar sensor is mounted rigidly onto the surface of a panel and is moved together with this. It serves to detect the exact position of 10 the sun and therefore to reposition the panels precisely. Provision can also be made for optional solar cells 13 for obtaining electrical energy, for example for driving the tracking system. Figure 2 shows a highly schematic lateral view of the arrangement according to the invention. Once again, the individual panels 20a to 20e can be seen from the 15 side. These are pivoting mounted on rotary axes 21a to 21e. As can clearly be seen here, the rotary axes are arranged at different positions relative to the individual panels. The precise arrangement will be shown later in the Figures 5 to 8. Fig. 3 shows an arrangement corresponding with Fig. 2, whereby the panels are 20 pivoted at a slight angle to the left. It can clearly be seen that there has been a shift in the height of the individual panels as a result of the different arrangements of the rotary axes. Figure 4 shows an approximately 90' rotation of the panels relative to the horizontal. This also produces the maximum offset in height relative to the 25 horizontal. It is obvious that this height offset reduces the mutual shadowing effect of the individual panels. This means that more light can be collected.

6 Fig. 5 shows the size and angular relationships for an arrangement according to the invention. The individual panels 20a to 20e are mounted by means of the rotary axes 21a to 21e. The central axes of the panels 22a to 22e point vertically upward when the panels are arranged horizontally. It is preferable for the 5 distances 24a to 24d of the central axes of the individual panels to be the same size and determined by the size and/or width of the panels. These central distances correspond to the distance of the individual panels less the dimension Ax. In the example of the embodiment shown here, the central axis 22c only runs through the rotational axis 21c in the case of the centre panel 20c. In the case of 10 a panel 20d, the central axis 22d runs at a distance 23d from the rotary axis 21d corresponding to Ax. This distance 23e corresponds to 2 * Ax for the panel 20e. The same applies for the panels 20b and 20a, where in these cases the distances between the central axes and the rotary axes are also Ax (for 20b) and 2 * Ax (for 20a) respectively. 15 Generally, the differences between the central axis and a rotary axis of the adjacent panels differ by Ax. The complete frame 10 for the embodiment according to the invention can be designed to be smaller than an embodiment where the central axes run through the rotary axes as shown in Fig. 8, due to the fact that the rotary axes for the 20 outer panels 20a and 20e are attached on the inner sides. In addition, the panels pivot inward toward the frame 10 so that the distance to the adjacent arrangements can be kept smaller. Fig. 6 shows the previous arrangement with the panels pivoted at an angle 26. In this case, the central axes 22a to 22e of the individual panels are pivoted by the 25 angle 26 relative to the horizontal. Fig. 7 shows an arrangement corresponding to the previous figure, but where the individual panels are pivoted in the opposite direction.

7 Fig. 8 shows an arrangement where the central axes run through the rotary axes. This produces constant distances 27 for the individual rotary axes. These distances between the rotary axes are greater than the distances between the rotary axes in an arrangement according to Fig. 5. As a result, the frame 10 must 5 be designed to be larger. Fig. 9 shows another cross-section through the guide ring 11. In this case, a first roller runs on the first bearing surface 41, which is visible. A second internal bearing surface 42, which forms an angle less than 90* with the first bearing surface 41, serves as a bearing surface for the internal roller 44. The two rollers 10 constitute a roller set and orbit the rotational axis of the entire arrangement 45. The rollers can be rotated around their central axes (shown by the dotted line) and are connected to the frame 10 (not shown here). At least three such roller sets, each consisting of a first roller and a second roller, are borne by the frame 10 on the guide ring 11. As the two bearing surfaces 41 and 42 form an angle 15 that is less than 90*, the internal roller 44 is able to exert a lesser vertical force component in the direction of the first roller 43. The two rollers can be set to be interlocking. This prevents the complete arrangement from slipping upward out of the guide ring. This means that an arrangement of this kind can also be mounted on sloping or vertical wall surfaces. In the case of a vertical wall 20 surface, the first bearing surface 41 would then be parallel to the vertical wall surface and would also be positioned vertically. Fig. 10 shows a thermally controlled tracking apparatus for lenses and/or light collectors 30. The beams of sunlight 50 can only be fed into the light collectors 30 with optimum efficiency when the angle of incidence of the beams of sunlight 25 50 is parallel to the principle orientation of the lens 32. In order to passively minimise the angle 51 of the misalignment, sunlight 50 is transmitted via collimators 53a, 53b onto thermally expanding material 52a, 52b. Corresponding to the heat absorbed by this material, this material expands and changes its 8 thickness, as shown in the drawing, so that the tracking plate 55 bearing the individual lenses 30 is pivoted with respect to the base plate 54. In the example of the misalignment shown here, more light strikes the thermally expanding material 52b than the thermally expanding material 52a. Accordingly, the 5 material 52b will expand more. Fig. 11 shows the example of the embodiment from Fig. 10 with a corrected angle of misalignment 51. In this case, the thermally expanding material 52b has expanded due to the greater solar radiation, while the thermally expanding material 52a has shrunk due to the reduction in solar radiation. Correspondingly, 10 the tracking plate 55 is now pivoted with respect to the base plate 54, so that the lenses 30 are directed optimally toward the sun. Now, the same amount of radiation falls on both the thermally expanding materials 52a, 52b due to the collimators 53a, 53b so that they do not change any further. Fig. 12 once again shows the tracking arrangement for repositioning the lenses in 15 detail. The collimator 53b is pivoted at an angle 56 with respect to the verticals on the tracking plate 55. The sensitivity of the tracking system can be set using this angle and additional canting. Fig. 10 shows a thermally controlled tracking apparatus for the lenses 30.

9 Reference list for drawing 10 Frame 11 Guide ring 12 Drive system 5 13 Solar cells 20a-e) Panel 21a-e) Rotary axis 22a-e) Central axis panel 23a-e) Rotation point / Central axis distance 10 24e-d Distance between central axes 25a-e) Vertical axis of panel 26 Angle of pivot 27 Central axis spacing 30 Lens or light collector 15 31 Solar sensor 32 Principal lens orientation 41 First bearing surface 42 Internal bearing surface 43 First roller 20 44 Internal roller 45 Rotary axis 50 Beams of sunlight 51 Angle of discrepancy 52a,b Thermally expanding material 25 53a,b Collimator 54 Base plate 55 Tracking plate 10 56 Collimator pivot angle

Claims

1. Tracking unit for a solar collector comprising at least one frame (10) with at least two panels (20a, 20b, 20c, 20d, 20e) which can each be pivoted about a rotary axis (21a, 21b, 21c, 21d, 21e), with the positions of the rotary axes 5 of adjacent panels being offset in relation to the central axis (22a, 22b, 22c, 22d, 22e) of the panels by a dimension Ax.

2. Tracking unit in accordance with Claim 1, wherein the rotary axes of the panels are arranged on the mounting (10) on one 10 plane.

3. Tracking unit in accordance with Claim 1, wherein a plurality of panels can be rotated at the same angle by means of a mechanism. 15

4. Tracking unit in accordance with any one of the previous claims, wherein the frame (10) is mounted rotatably on a guide ring (11) mounted rigidly on an installation surface.

5. Tracking unit in accordance with any one of the previous claims, 20 wherein 12 the guide ring (11) is provided with a first bearing surface (41) and an internal bearing surface (42) which is arranged at an angle of less than 90* with respect to said first bearing surface.

6. Tracking unit in accordance with any one of the previous claims, 5 wherein a first roller (43) runs on the first bearing surface (41) and an internal roller (44) runs on the internal bearing surface (42), which are braced against each other.

7. Tracking unit in accordance with any one of the previous claims, 10 wherein provision is made for an apparatus for the passive fine adjustment of at least one light collector (30) arranged on one panel (20a, 20b, 20c, 20d, 20e), with said apparatus correcting the alignment of at least one light collector (30) to the sun by means of thermal expansion of material that 15 expands in response to heat.