The invention relates to an optical light-transmission element for a solar energy assembly according to the preamble of claim 1.

Optical light-transmission elements of this kind are for example used in concentrator photovoltaics (CPV). In CPV, small, but highly efficient solar cells are combined with concentrator optics, which focus light onto a solar cell for harvesting the solar energy. The concentrator optics require a perfect alignment of the optics and the solar cell at the module manufacturing process. During use, the CPV modules have to be continuously adjusted to the position of the sun using a tracker mechanism in order to keep the sunlight focused on the solar cell. Any lens-to-cell misalignment, resulting from manufacturing or tracker misalignment that is not compensated by an extra active area of the solar cell reduces the output power of the module.

A solution to control the alignment of the module can be done during manufacture by using the location of the lens center or the focal point of the CPV lenses relative to the cell. A camera looks through the lens and optical recognition software calculates the misalignment.

The initial alignment of the tracker is done by using a similar principle. With a mirror that is fixedly installed in the module, a technician can look by eye onto the cell and adjust the module brackets in a way that the light spots are centered on the solar cells.

Both the alignment during manufacture and the initial tracker alignment are prone to errors. Further, current CPV development envisages the use of a so-called secondary optics (reflective and/or refractive) close to the cell in order to increase and/or homogenize the light flux on the cell. However such secondary optics introduces shading effects that make current alignment procedures difficult or even impossible. Thus there is a need to develop new suitable techniques. Moreover, if the optical light-transmission element uses non-focusing optics, no reference point is available for alignment.

In view of these disadvantages, it is the object of the invention to provide an optical light- transmission element that facilitates alignment both during manufacture and on the tracker.

This object is solved by the subject matters of claim 1 and 12.

According to the invention, the element is divided functionally into two distinctive parts. The harvesting portion is used for harvesting solar energy in that it allows passing or, depending on the configuration, focusing the solar energy onto a solar cell. The harvesting portion may be a non-focusing optical member or a focusing member, e.g. a Fresnel or TIR (total internal reflection) lens. The alignment control portion concentrates solar energy onto a focusing region which is spaced apart from the solar cell and thus can be more readily used for alignment purposes. If the harvesting region comprises focusing optics which result in a focusing region, then the focusing region of the alignment control region may be spaced apart from the focusing region of the harvesting portion, preferably in the plane defined by the focal length of the harvesting portion.

The optical light-transmission element may include an array of harvesting portions that are each associated with a single solar cell. The array may be associated with a single alignment control portion for adjusting the array as a whole and/or with a plurality of alignment control portions for adjusting individual harvesting portions. In particular, an array of harvesting portions which share one alignment control portion may be monolithically connected to each other. If a more individual alignment control is desired, there may be an alignment control portion for each harvesting portion.

Further improvements of the invention are laid down in the dependent claims.

Additional modifications from the embodiments of the independent claims or of any one of the dependent claims are possible. For example, the alignment control portion may be restricted to lie within a circumference of the harvesting portion, wherein the circumference determines the aperture, i.e. in the active area of the harvesting portion. This facilitates assembling several harvesting portions into an array by allowing to seamlessly tile the harvesting portions adjacent to each other. Alternatively or cumulatively, the alignment control portion may be at least partly arranged outside the circumference. If it is desired to utilize the full active area of the lens, the alignment control portion may also be situated completely outside the circumference, e.g. between neighboring harvesting portions in an array and/or outside the circumference of the array.

The active area and/or the alignment control portion may have multi-axial, in particular rotational symmetry to facilitate assembly of the lens area into an array irrespective of the orientation of the light-transmission element. According to another embodiment, the harvesting portion may have a polygonal active area determining its aperture. In such an embodiment, the alignment control portion may be at least partly located at the corners of the polygonal area, either within the active area, or outside of this area, or reaching across the circumference of this area.

For the alignment control portion to work, only a very small area compared to the active are of the harvesting portion may be needed. For example, the alignment control portion may comprise exactly one Fresnel or TIR (total internal reflection) prism of a Fresnel or TIR lens. For an efficient alignment control, it seems certainly not necessary to have more than ten Fresnel or TIR prisms assigned to the alignment control portion. The size of the alignment control portion is determined by the brightness of its focusing region that is needed for proper adjustment procedures.

The alignment control portion may be at least one of an eccentric and a concentric lens with respect to the harvesting portion.

In the following, embodiments of the invention are described exemplarily with reference to the drawings. As laid out above and as stated in the dependent claims, various features which develop the invention further, may be omitted or added depending on the particular application.

Throughout the drawings, the same reference numerals are used for elements which are identical in their construction and/or their function.

In the drawings:

Fig. 1 shows a solar energy assembly using an optical light-transmission element according to the invention in a schematic cut view along the line l-l of Fig. 2;

Fig. 2 shows a schematic plan view of the solar energy assembly of Fig. 1 ;

Fig. 3 shows a schematic plan view of an embodiment of an alignment control portion in an optical light-transmission element according to the invention;

Fig. 4 shows a schematic plan view of another embodiment of alignment control portions tiled together;

Fig. 5 shows a schematic plan view of a full array of the embodiment of alignment control portions tiled together as shown in Fig. 4

Fig. 6 shows a schematic plan view of another embodiment of an alignment control portion located outside the active area;

Fig. 7 shows a schematic plan view of a full array of the embodiment of alignment control portions located outside the active area as shown in Fig. 6.

First, the structure and function of an optical light-transmission element 1 according to the invention and a solar energy assembly 2 comprising the optical light-transmission element 1 are explained with reference to Fig. 1. In addition to the optical light-transmission element 1 , the solar energy assembly 2 may comprise, at its front side 3, which is directed towards the incident light 4 providing the solar energy, a preferably transparent glass plate 5. The optical light-transmission element 1 may be arranged on an inner side 6, opposite the front side 3, of the glass plate 5 e.g. by bonding. It may be manufactured from a transparent resin material.

Further, the solar energy assembly 2 may include a solar cell 7 for harvesting the solar energy of the incident light 4. The solar cell 7 may be arranged on a plate 8 made from heat-conducting material such as metal. The plate 8 may form a heat sink 9 to dissipate thermal energy which could not be converted into usable energy, by the solar cell 7. At a back side 10, which faces away from the incident light 4, of the solar energy assembly, another glass plate 1 1 may be arranged, which may be at least partially translucent.

The solar cell 7 is spaced apart from the optical light-transmission element 1 by a distance 12. The resulting volume 13 may be gas-filled or evacuated.

The optical light-transmission element 1 is functionally divided into two parts. The first part serves as a harvesting portion 14 for allowing to pass and/or directing the incident light 4 onto the solar cell 7. The harvesting portion 14 may be configured as a lens focusing the light onto the solar cell 7, as indicated by the triangle 15. In such a case, the distance 12 may be determined by the focal length of the harvesting portion 14.

Fig. 1 exemplarily shows that the harvesting portion 14 may consist of, or comprise, a Fresnel or TIR (total internal reflection) lens. However it is also possible that the harvesting portion 14 comprises non-focusing optics and the concentration of the incident light 4 onto the solar cell is done by additional elements.

The second part of the optical light-transmission element 1 serves as an alignment control portion 16. The alignment control portion 16 focuses part of the incident light 4 onto a focusing region 17 which is spaced apart from the solar cell 7 or, if the harvesting portion 14 comprises a focusing optics, from a focusing region 18 of the harvesting portion 14. Usually, the solar cell 7 and the focusing region 18 coincide. The alignment control portion 16 may actually comprise several disconnected regions.

Depending on the configuration of the alignment control portion 16, the focusing region 17 may be a single coherent area or may comprise several disconnected areas. In the latter case, each of the disconnected areas which make up the focusing region 17 may be associated with a respective disconnected region of the alignment control portion 16. Alternatively, a subset of the disconnected regions of the alignment control portion 16 may focus on the same area of the focusing region 17. Fig. 2 shows an example of possible locations of the focusing region 17 associated to the alignment control portion 16 in the upper left corner.

The location of the focusing region 17 serves as representation for the location of the solar cell 7. For this, the offset between the focusing region 17 and the solar cell 7 needs to be well- defined. To achieve an accurate offset which is stable over a larger number of product samples, the geometry of the alignment control portion 16 needs to be within tight tolerances, which requires accurate manufacturing.

The amount of energy that the optical harvesting element 1 is capable to collect is determined by the size of an active area 19 through which the incident light 4 passes. This size determines the aperture of the harvesting portion 14. In order not to compromise the energy harvest from the incident light 4, the alignment control portion 16 only occupies a small amount of the active area 19, preferably less than 1/10 of this area, or the alignment control portion 16 can be totally or partly arranged outside the active area 19.

Fig. 1 shows, for explanatory purposes only, that the focusing region 17 of the alignment control portion 16 may be located directly underneath the alignment control portion 16 in the direction of the incident light 4, so that the optical axis 20 of the alignment control portion 16 is parallel to the optical axis (21) of the harvesting portion.

However, the direction of the optical axis 20 of the alignment control portion 16 may, in other embodiments, deviate from the direction of the optical axis 21 of the harvesting portion 14 as is exemplified by the dot-dashed lines 20a and 20b in Fig. 1. This may become necessary if the focusing region 17 of the alignment control portion 14 should be positioned at a specific location e.g. to achieve better visibility.

The focusing region 17 is situated outside the solar cell 7, e.g. either on the back glass pate 1 1 as indicated by the reference numeral 17a, or on the heat sink 9, as indicated by the reference numeral 17b. The focusing region 17a on the back glass plate 1 1 may be viewed from either the edge of front glass plate 5 or from the back side 10, if the glass plate 1 1 has some translucency. The focusing region 17b on the heat sink may be observed by looking into the assembly 2 from the edge of the front side or from the backside using internal mirrors.

By diverting a small portion of the incident light 4 onto the second focusing region 17 by means of the alignment control portion 16, the alignment of the optical light-transmission element 1 with respect to the solar cell 7 is greatly facilitated. The alignment is exact, if the light of the alignment control portion 16 is focusing in a target zone 23, which may be visibly marked. The shape of the target zone 23 may correspond to the shape of the second focusing region 17 to facilitate the alignment process. For example, the second focusing region may be annular having an internal section which is sized to accommodate the solar cell 7. Such an internal section may not be illuminated by the alignment control portion 16 but be still illuminated by the harvesting portion 14. In such an instance, the target zone 23 may be a ring extending around the solar cell 7. Again, alignment is achieved if the second focusing region 17 and the target zone 23 collapse.

For alignment during manufacture a rear assembly comprising the solar cell 7 and at least one of the heat sink 9 and the back plate 1 1 have to be moved relative to the optical light transmission element 1 until the focusing region 17 of the alignment control portion 16 coincides with the target zone 23. At initial tracker alignment, the assembly 2 has to be tilted towards the incident light 4 until the focusing region 17 hits the target zone 23. The alignment control even works if the harvesting portion 14 comprises a non-focusing optics or the focusing region 18 is covered by additional elements, as for instance secondary optics as pointed out above.

Further the focusing region 17 may facilitate for automatic tracking e.g. by placing an array of light-sensitive sensors (not shown) in the target zone 23. Any movement of the focusing region 17 can thus be automatically detected by the sensors and used by a control device to drive a tracker mechanism.

The optical light-transmission element 1 and/or the harvesting portion 14 and/or the alignment control portion 16 comprise optical elements which, in combination, produce the optical effect desired for the light-transmission element 1 , the harvesting portion 14 and/or the alignment control portion 16. If, for example, the light transmission element 1 , the harvesting portion 14 and/or the alignment portion 16 are formed as a Fresnel or TIR lens, the optical elements are one or several prisms 24, which may be ring-shaped or ring sections. The prisms 24 may be precision-cut.

In particular, the alignment control portion 16 may comprise at least one prism 24. For good visibility of the focusing region 17, between 1 and 10 prisms may be necessary.

The alignment control portion 16 or its at least one prism 24 may form a lens which is concentric or eccentric with respect to the lens formed by the harvesting portion 14.

If the alignment control portion 16 comprises at least one prism 24, the slope is preferably larger or equal to 0° and considerably smaller than the angle of the neighboring active prisms 24 of the harvesting portion 14. An angle of 0° leads to an optical axis 20 which is parallel to the direction 22 of the incident light 4. If an angle is larger than 0°, or an optical axis 20a, 20b deviating from the direction of the incident light 22 is used in the alignment control portion 16, it is preferred that a symmetric arrangement of the alignment control portion 16 is used, e.g. by sub-dividing the alignment control portion 16 into symmetrically distributed sub-portions.

Fig. 2 shows a plan view upon the front side 3 of the solar energy assembly 2 of Fig. 1 .

From Fig. 2, it can be seen that the location of the focusing region 17 of an alignment control portion 16 having an inclined optical axis 20a, 20b (Fig. 1) is temperature-dependent. With a change of temperature, the focusing region 17a is displaced from its original location 17a to another location 17'a. Likewise, the focusing region 17b may be displaced upon a temperature change to a location 17'b.

It can be further seen from Fig. 2 that the optical light-transmission element 1 , or its active area 19, respectively, may be of polygonal shape, in particular be rectangular. The alignment control portion 16 may be located at a circumference 25 of the active area 19, for example at corners 26 if the active area 19 is polygonal. In the embodiment shown, the alignment control portion 16 comprises discrete triangular regions that are located in all four corners 26. Variants of this embodiment may include less regions e.g. at only one, two or three corners. All regions focus their light onto the focusing region 17.

In another alternative, the solar energy assembly 2 as shown in Fig. 2 may have more than one focusing region 17 per solar cell 7. This can be accomplished if the alignment control portion 16 focuses the lights onto two or more focusing regions 17. For example, each pair of two diagonally opposing corner regions may have a separate focusing region 17.

Fig. 3 indicates how an alignment control portion 16 in the form of an eccentric lens with respect to the harvesting portion 14 may be formed: the alignment control portion 16 results from the intersection of a ring-shaped, preferably circular focusing lens 27 with the optical light- transmission element 1 . Such intersections giving rise to the alignment control portions 16 may result in equally distributed portions at the corners of the optical light-transmission element 1 . This is the case if the ring-shaped lens 27 is realized by a succession of ring-like or ring-section like Fresnel or TIR prisms 24, following the prisms 24 of the harvesting portion 14 as indicated in Fig. 1 . However, by cutting out the optical light-transmission element 1 from a structure formed of prisms 24, the inner part defining the harvesting portion 14 and the outer part the alignment control portion 16, the center 28 of the lens 27, i.e. the alignment control portion 16, may also be shifted with respect to the geometrical center 29 of the active area 19. Due to the shift of the center 28, some corners 26 are provided with a larger area of the alignment control portion 16 than other corners 26, some corners 26 may even be without an alignment control portion 16. This can be used to increase the active area of the harvesting portion 14 with respect to the optical light-transmission element 1 . Alternatively or additionally to a shift, the optical axis 20 (Fig. 1) of the lens 27 may be inclined with respect to the optical axis 21 of the harvesting portion 14, as was explained above.

The alignment control portion 16 thus results from a modified structure of the optical light- transmission element 1 , e.g. by an abrupt change in the angle of the surface of the element 1 or in the angle of the prisms 24.

By restricting the alignment control portion 16 to the circumference 25 and/or the corners 26, it is ensured that the main portion of the incident light 4 may directly pass through the optical light- transmission element 1 to the solar cell 7 and the aperture of the harvesting portion 14 is not overly compromised.

In a solar energy assembly 2, several solar cells 7 and the corresponding harvesting portion 14 may be combined into an array. In such a case, one harvesting portion 14 may be provided for each solar cell 7. The optical light-transmission element 1 may comprise a single harvesting portion 14, or a plurality of harvesting portions 14 may be combined into a single optical light- transmission element 1 either monolithically or by mounting a plurality of separate harvesting portions 14 together e.g. by using a frame (not shown).

If several optical light-transmission elements 1 are tiled together side-by-side to form an array, the respective alignment control portions 16 may meet at the corners as shown in Fig. 4. The actual number of prisms 24 in each corner 26 varies depending on e.g. the shift of the geometrical center of the alignment control portion 28 as explained in Fig. 3, if an eccentric lens is used.

As a modification to the embodiment shown in Fig. 4, the alignment control portions 16 meeting at the corners 26 may not belong to separate lenses but in combination form a lens which is centered on the tips of the abutting corners. For this, the curvature of the prisms 24 shown in Fig. 4 may be reversed so that concentric circles about the tips of the corners are formed.

In the embodiment of Fig. 4, the structure of the alignment control portion 16 is located in the aperture of the active area 19 in each corner. This may lead to an energy loss. This energy loss may be reduced if the alignment control portion 16 is not arranged symmetrically, but shifted, as shown in Fig. 3, so that some corners do not feature an alignment control portion 16.

Fig. 5 shows a solar energy assembly 2, which comprises a plurality of harvesting regions 14. The harvesting regions 14 are tiled to form an array. Each harvesting portion 14 may be provided with an alignment control portion 16. This can be used for an individual alignment of each solar cell 7 and its associated harvesting portion 14. Each alignment control portion 16 forms an optical element with its own optical axis 20 (Fig. 2) and its own focusing region 17.

Energy loss may be reduced if the alignment control portion 16 is located outside, partially or completely, of the circumference 25 of the active area 19 . Fig. 6 shows such an arrangement. The alignment control portion 16 may be located again at a corner 26 or along another portion of the circumference 25. Instead of being a triangular area, the alignment control portion 16 extends strip-like along the circumference 25 at one or more of the corners 26. The alignment control portion 16 may also form a frame which encircles a single harvesting portion 14 or a plurality of harvesting portions 14.

If, however, several harvesting portions 14 are systematically rigidly combined within tight tolerances, a lesser number of alignment control portions 16 may be sufficient. For example, if a number of harvesting portions 14 is monolithically combined, it may be sufficient that this combination is provided with only one or two alignment control portions 16. Such an embodiment is exemplarily shown in Fig. 7, where the alignment control portion 16 is arranged outside of the combined apertures or outside of the circumference 25 of the array of harvesting portions 14.

As shown exemplarily in Fig. 7, the solar energy assembly 2 may comprise a tracker device 30 which is adapted to move the optical light transmission element 1 or the complete solar energy assembly 2 towards the incident light 4. The latter device may be controlled by the deviation of the location of the focusing region 17 from the target zone 23. For acquiring the deviation, light- sensitive sensors 31 (Fig. 1) may be located at and/or around the target zone 23.

Although the alignment control portion 16 has been shown to be situated at the corners 26 in the above regions, it is also possible that the alignment control portion 16 is located within the active area by modifying the structure provided for the harvesting portion at one or more locations in the active area 19. For example, the alignment control portion 16 may comprise an outer lens 27, which lies within the active area 19, the harvesting portion 14 bordering on the outside and inside perimeter of the lens 27. REFERENCE NUMERALS Optical light-transmission element

Solar energy assembly

Front side

Incident light/solar light

Glass plate

Inner side of glass plate

Solar cell

Plate

Heat sink

Back side

Back glass plate

Distance

Volume

Harvesting portion

Light cone

Alignment control portion

, 17a, 17'a, 17b, 17'b Focusing region of alignment control portion Focusing region of harvesting portion

Active area

, 20a, 20b Optical axis of alignment control portion

Optical axis of harvesting portion

Direction of incident light target zone

Smallest element forming the light transmission element 1 (e.g. Prism) Circumference

Corner

Lens

Geometrical center of alignment control portion 16

Geometrical center of active area 19

Tracker device

Light sensitive sensor