WO2002044766A2

WO2002044766A2 - Static concentrator

Info

Publication number: WO2002044766A2
Application number: PCT/DE2001/004430
Authority: WO
Inventors: Niluh Kusani Steigerwald; Max Steigerwald
Original assignee: Niluh Kusani Steigerwald; Max Steigerwald
Priority date: 2000-11-30
Filing date: 2001-11-27
Publication date: 2002-06-06
Also published as: DE10059455A1; WO2002044766A3; AU2002215866A1

Abstract

The invention relates to a concentrator for concentrating incident light on a predetermined area or on a predetermined volume with an entry area and an exit area. In order to provide a static concentrator that is capable of concentrating not only direct radiation but also diffuse radiation with a high level of efficiency, the invention provides that an area-reducing element (3) is connected up from an angle-reducing element (4).

Description

Static concentrator

The present invention relates to a concentrator for concentrating incident light on a predetermined surface or volume with an input surface and an output surface. The entry surface of the concentrator is understood to mean that surface which is intended to receive sunlight, while the exit surface is to be understood to mean the surface which is intended to emit the concentrated sunlight to a predetermined volume or a predetermined surface.

There is a great need for concentrators in particular in photovoltaic technology. Although the price of so-called solar cells has dropped significantly in recent years, solar power is still significantly more expensive than that available from conventional power plants. In principle, solar cells on the market could be exposed to a significantly higher light density. The limit is essentially determined only by the heat development due to energy not converted into electricity. If, for example, a solar cell were loaded with an approximately three times greater light density, approximately three times the amount of electricity could be generated with the same solar cell. The solar power generation costs would then be significantly lower and could compete with conventional power plant electricity.

Static concentrators are already used to increase the light density. The incident direct radiation is concentrated on a solar cell using optics. Both imaging systems (eg classic lenses, Fresnel lenses but also concave mirrors) and non-imaging systems (eg 3D-θ _ιn / θ _0u r concentrators) are already used as optics.

Although optics usually only achieve an efficiency of up to 80-90%, the light density can nevertheless be increased considerably.

However, the known concentrator modules are only able to convert direct sunlight into electrical energy. However, the diffuse fraction of sunlight can be up to 50%, ie with the known concentrators only between 50 and a maximum of 90% of the total solar radiation can be concentrated. For this reason, there are already tracked systems on the market that align the solar cell and concentrator according to the course of the sun. Markt, align the solar cell and concentrator according to the course of the sun. This ensures that the ratio of direct radiation to total radiation is optimized. However, the diffuse radiation cannot be used here either. In addition, the tracked systems are maintenance-intensive due to the necessary moving mechanics.

Arrangements of wedge-shaped optical bodies have already been proposed in order to concentrate diffuse radiation in addition to direct radiation. The wedge-shaped optical body can indeed significantly reduce the opening angle of the incident radiation, but the light emerging at the exit surface or surfaces is not sufficiently "quasi-parallel", so that direct radiation and diffuse radiation, which generally have an opening angle of approximately 180 ° strikes the input surface of the concentrator, is reduced to a significantly smaller opening angle range, the surface onto which the light emerging from the output surface or surfaces of the wedge is imaged, but has not become smaller but larger than the input surface, including the arrangement of several Wedge-shaped elements next to one another cannot be realized, since parts of the light emerging from the exit surfaces of the concentrator can enter the neighboring wedge-shaped elements and are deflected there very unfavorably and are no longer available for concentration.

The present invention is therefore based on the object of providing a static concentrator which is capable of concentrating diffuse radiation with high efficiency in addition to direct radiation.

This object is achieved in that the concentrator has both an angle-reducing element and an area-reducing element, the area-reducing element being connected upstream of the angle-reducing element. In other words, the light incident on the input surface of the concentrator first passes through the area-reducing element and only then through the angle-reducing element before it emerges from the output surface or outputs of the concentrator. For example, the wedge mentioned at the beginning can be used as the angle-reducing element. Of course, there are also other angle-reducing elements, such as a conical optical body, usable. The area-reducing element can be any imaging or non-imaging optics or an optical body that has an input surface that is larger than its output surface. The angle-reducing element can, for example, be a focusing device, e.g. be followed by a lens.

An embodiment is particularly preferred in which the area-reducing element has an optical body, preferably in the form of a truncated cone or a truncated pyramid, the cross section of which tapers in the beam direction. As a result, the light is guided in the optical body until it tapes the area-reducing element on its tapered starting surface. leaves. Since the concentrator is intended for the concentration of sunlight, it will generally be arranged with the input surface facing up and the output surface facing down. Of course, however, the concentrator can also be used advantageously in any other orientation. For example, it is possible to first deflect the sunlight with a deflecting optic, so that the input surface is then no longer arranged at the top and the output surface is no longer arranged at the bottom. If in the following there is nevertheless talk of above and below, above should always be understood in the direction of the entrance surface and below always in the direction of the exit surface.

A particularly expedient embodiment provides that the optical body of the area-reducing element is mirrored in the upper region of its outer surface. The result of this measure is that at least the light rays, which form a large angle with the optical axis in the upper region of the area-reducing element, cannot leave the optical body in the upper area of the area-reducing element on the side. Rather, the light rays are reflected on the lateral surface and directed back into the optical body. Due to the reflection on the mirrored outer surface of the tapered optical body, however, the angle of the reflected light beam with respect to the optical axis is increased. If the angle of the light beam becomes too large, the light will reverse the direction and be reflected back to the entrance surface of the area-reducing element. It is therefore not advantageous to make the tapered optical body of the area-reducing element mirrored on the outer surface even in the lower region without additional measures. The size of the mirrored upper cladding area is therefore preferably dimensioned such that even light that occurs at a large angle to the vertical on the input surface of the area-reducing element is not reflected back by the area-reducing element, but is instead imaged onto a reduced area in the beam direction. However, this has the consequence that light beams can emerge laterally from the area-reducing element in the lower region of the area-reducing element.

For this reason, it is provided in a preferred embodiment that at least one prism or an angle-changing element is arranged on the side walls of the optical body, the refractive index ni of the prism being greater than 1. Since an optical body can also be understood to mean a prism, the optical body is also referred to below as the main body in contrast to the prisms arranged on the side walls of the main body. The at least one additional optical body in the form of a prism refracts the light which may emerge from the side wall of the main body in the lower region of the area-reducing element in such a way that the angle which the refracted light encloses with the optical axis is smaller than the angle of the encloses the optical main body on its side wall leaving light beam with the optical axis. It goes without saying that the angular the element does not necessarily have to be a prism. A grating, in particular an Echellette grating, is also successfully used here.

It goes without saying that the area-reducing element can also have an angle-reducing effect. At the output of the area-reducing element, the radiation intensity can be maximum for rays which form an angle other than zero with the main optical axis. In a special embodiment it can be provided that the deviation (scatter) of some beam angles from the beam angle is reduced with maximum intensity. In other words, the angular expansion of the incident beam is reduced. This in turn can be used to design the angle-reducing part as an angle-transforming part, which refracts light that is incident with the beam angle of the maximum intensity towards the main axis, so that preferably the beams of maximum intensity run parallel to the optical main axis. The ratio of the input area to the output area of this angular transformer is very favorable since it is almost 1. If the angle-reducing effect in the area-reducing element is large enough, the angle-reducing element can also simply be an angle-transforming element.

Preferably not only a prism but a whole row of prisms is arranged on the side wall. These prisms are advantageously arranged periodically from top to bottom on the side wall of the main optical body. Of course, it is also possible to arrange several prisms next to one another in a direction perpendicular to the main optical axis. For example, identical prisms can be arranged periodically. However, it is also possible to arrange prisms with different sizes next to one another. The prisms do not necessarily have to be arranged in an approximately circular manner surrounding the optical main body, but can, for example, also be arranged in a spiral along the outer wall of the optical main body. It is understood that the optical body can also have the refractive index 1, i.e. be made of air. In this case, it only depends on the arrangement of the prisms. The prisms can also be arranged inside the area-reducing body. In this case, however, the refractive index of the prisms must be different from the refractive index of the main optical body.

The prisms can, for example, be formed in one piece with the optical body. In this case, the side walls of the prisms are formed, for example, by preferably non-parallel incisions in the outer wall of the main body.

However, an embodiment is preferred in which the at least one prism is not formed in one piece with the main body. A gap is advantageously provided between the optical main body and the prism. If the gap also does not have a continuous width, the transition from the optically denser to the optically thinner medium, that is to say from the main optical body in air, and the subsequent transition from the optically thinner to the optically thicker medium um, that is, of air into the adjacent prism, to reduce the angle between the light beam emerging from the main optical body and the main optical axis. The at least one prism is preferably arranged such that the tip of the prism is oriented approximately upwards. The tip preferably has a tip angle of less than 90 °.

A particularly expedient embodiment provides that the side walls of the area-reducing element are mirrored, the at least one prism being located between the optical main body and the mirroring. Depending on the application, the mirroring can be done by mirroring at least one outward side of the prism or by providing a separate mirroring, e.g. B. in the form of a reflecting film surrounding the area-reducing element. The mirroring is preferably arranged approximately parallel to the surface of the main body. By arranging the prisms on the outer wall of the optical body, it is now possible to continue the mirroring down to the lower area of the area-reducing element. The prism arrangement ensures that the angles which the light rays make with the main optical axis do not increase any further during reflection on or outside the outer wall of the optical body. The retroreflective effect of a mirrored funnel is avoided.

The mirroring results in a reflection of the light emerging from the main optical body on the mirrored surface. It is therefore not absolutely necessary for the input tip of the prism to face the outer wall of the optical body. Rather, even after the light has emerged from the outer wall of the optical body, it can first be reflected on the mirrored surface and then enter it in the region of the input tip of the prism. It is only essential that the prism is arranged in such a way that the light emerging from the main optical body enters the prism either directly or after reflection essentially in the area of the input tip and not in the area of the surface facing away from the input tip.

A particularly expedient embodiment of the concentrator according to the invention provides that one side of the at least one prism is arranged in such a way that as far as possible all light rays that have entered the prism are totally reflected on the side of the prism facing away from the optical main body, that is to say are deflected downward. For this purpose, the side of the prism facing away from the main body should enclose an angle α with the main optical axis for which a ≥ aresin [(sin (δ _mM ) -] applies, where n _{0 is} the refractive index of the n ι surrounding the side surface

Medium is, ie 1 for air, n ^ is the refractive index of the prism and δ _{max is} the largest angle which the light rays entering the main body facing the main body enclose with the main optical axis. This specially oriented side of this form of management is of crucial importance. The total reflection of the light rays, which enclose a large angle with the main optical axis, means that these light rays are not reflected back to the input surface, but, when they are guided back into the main optical body, always have an angle of less than 90 ° the main optical axis.

Another way of achieving this is realized in another preferred embodiment. Namely, it is also possible to arrange prisms with a mirrored surface on or near the outer wall of the optical body. The prism is advantageously arranged such that a tip, the input tip is oriented essentially upwards, and the mirrored surface, which should be arranged on the side of the prism facing away from the main optical body, is aligned approximately parallel to the main optical axis is. Since the light is always broken away from the refractive edge when light passes through a prism, the combination of the prism with the mirroring ensures that the angle that the light entering the prism makes with the main optical axis is greater than the angle which the light emerging from the prism occupies with the main optical axis.

For some applications it can be advantageous if a second prism is arranged on one side of at least one prism facing away from the input tip, the second prism having a refractive index n ₂ that is smaller than the refractive index n of the at least one prism. It has been shown that under certain circumstances some light rays hit the side of the prism facing away from the input tip so unfavorably that they do not transmit, but are totally reflected. By arranging a second prism with a somewhat lower refractive index, the critical angle of the total reflection is reduced, so that the unfavorably extending light rays from the first prism can reach the second prism. It is essential that at least some light rays from the prism with the refractive index ^ can enter directly into the prism with the refractive index n ₂ . This second prism is preferably arranged so that a tip points substantially downwards. This tip is also advantageously inclined in the direction of the main body. The transition surface between adjacent prisms does not have to be straight. It should be noted at this point that the transition from the prism with a lower refractive index to an underlying prism with a larger refractive index leads to a deterioration in the beam path. However, this is compensated for by the tip angle of the prism below.

For some applications it can be advantageous that the refractive angle φ, that is to say the tip angle φ, is chosen to be so large that the light entering the prism cannot exit at the side surfaces which are adjacent to the input tip. Rather, the light rays that have entered are totally reflected on these side surfaces. In order to be able to use prisms with a smaller refractive angle, it can be advantageous if at least one side surface that borders on the entrance tip is mirrored and applies to the refractive entrance angle:

φ> arcsin -

the refractive index of the prism and n _{0 being} the refractive index of the medium essentially surrounding the prism in the irradiation area. By using such prisms, the light can be guided in the prisms, similar to the light guide in glass fibers. Just as glass fibers can be curved to a certain degree, the prism can also have 'kinks' or 'bending points' so that the light guided in the prism forms a smaller angle with the main optical axis. The bending and bending points are of course not to be understood to mean that local distortions of the material occur here. A bending point could rather arise, for example, by angled at least one side surface of the prism.

Another embodiment is realized by using Echelette gratings for the reflection wall of the main optical body. In contrast to the slit grating, in which the light intensity is distributed over different peaks, the central peak being the one with the greatest intensity, the Echelette grating tries to concentrate the entire light intensity in a diffraction order. For this purpose, the geometry of the echelette grating is chosen such that the desired diffraction maximum of the maximum intensity has an order m, which is different from zero, by inclining the various reflecting grating elements by the so-called blaze angle. The angular width of the diffraction figure of the grating element is equal to the angular distance between two main maxima of the diffraction pattern of the grating.

If the surfaces of a grating plane are a right-angled triangle, a concentration of 70% of the incident light on an order can be obtained.

A particularly expedient embodiment of the concentrator provides that the input surface of the area-reducing element is not flat. This can be achieved, for example, by placing a receiving element upstream of the area-reducing element essentially in the form of optical bodies narrowing in the beam direction. This particular configuration of the input area of the concentrator ensures that the angle of the light beam guided in the main optical body of the area-reducing element to the main axis is optimized. With the surface-reducing element according to the invention, the light falling on the input surface of the concentrator is imaged on the input surface of the angle-reducing element, the surface of the angle-reducing element being significantly smaller than the input surface of the concentrator. This is achieved, for example, by the conical optical main body described, preferably made of solid (plexi) glass, which is surrounded by a special reflection wall which reflects back the rays coming out of the cone. This special reflection wall consists only of a mirrored wall in the upper area of the conical optical body. In the lower area, however, the reflection wall consists of several prisms which are arranged on the outside of the cone wall and which are preferably surrounded by a reflective layer. This "prism wall" ensures that light beams no longer follow the normal reflection law (angle of incidence = angle of reflection) in the lower region of the area-reducing element, but that the angle of reflection is smaller than the angle of incidence. This is achieved through light refraction, total reflection and reflection on mirrored surfaces that work individually or in combination with each other.

There is an output characteristic for this prism wall, which shows the intensity distribution of the output radiation as a function of the angle. These characteristics often have a maximum, i.e. in other words a preferred starting angle. A preferred embodiment therefore provides that the materials of the prism wall are selected so that the maximum is as strong as possible.

In these embodiments, the area-reducing effect is usually somewhat less. In embodiments in which the maximum of the output angle is independent of the point of incidence of the input rays on the prism, the prisms, in particular if they are passed through several times, which is the case with the multiple arrangement on the wall of the main optical body, have a special emission behavior, namely a radiation of the light within a relatively narrow exit angle band or exit angle interval. Although this output angle band initially does not include the direction of the main optical axis, this can be achieved with the aid of the angle transformer described above.

The starting surface of the area-reducing element is in front of an angle-reducing element, for example a wedge. This wedge can be mirrored on one side, but a distance is preferably provided between the mirrored surface and the outside of the wedge, which increases in the direction of incidence. However, an embodiment is particularly preferred in which a prism with a mirrored outer surface is arranged on at least one outer side of the wedge-shaped element, a gap increasing in the beam direction being present between the outer surface of the wedge-shaped element and the prism. In this embodiment, the prism has an end surface at the bottom which can lead into a further angle-reducing element. In a preferred embodiment, inclusions are provided in the wedge-shaped element which have a lower refractive index than the wedge-shaped element. This leads to a further reduction in the angle between the concentrated light rays and the optical axis. An additional prism is preferably also arranged on the outside of the wedge. A preferred concentrator element in the beam direction, ie from top to bottom, therefore consists of the elements input element, area-reducing element, angle-reducing element, focusing device and, if appropriate, solar cell. The concentrator element has a non-homogeneous cross section due to the individual elements. While the input element has a relatively large cross-section, the cross-section in the beam direction is significantly reduced by the area-reducing element before it is slightly expanded again by the angle-reducing element. A plurality of concentrator elements are preferably arranged next to one another. Since the focusing element often has particularly good focusing properties for near-axis rays, that is to say rays in the vicinity of the optical axis, the focusing element, for example a lens, can advantageously also be selected with a diameter larger than the input surface of the receiving element , when adjacent concentrator elements are arranged offset in height. The result of this is that the focusing element is arranged precisely at the height at which the adjacent concentrator element has its area-reducing element, ie has its "constricted" area.

In principle, the cross section of a concentrator element can be arbitrary in supervision. If only one concentrator is used, however, a round cross-sectional shape is usually preferred. If, on the other hand, several concentrators are placed next to each other, other shapes that take full advantage of the available space should be preferred. A hexagonal cross-sectional shape is particularly preferred here, so that the individual concentrator elements can be arranged next to one another in the form of “honeycombs”.

For some applications, it can also be advantageous if several concentrator elements are arranged one behind the other. In principle, any number of levels of concentrator elements can be arranged one behind the other.

A converging lens is preferably attached in the beam direction after the concentrator element and concentrates the beams of the individual elements on a focal surface, which always has a lateral extension.

In this focal surface or focal plane, a further layer of concentrator elements can be inserted or a light beam receiver which transmits its light beams to a light guide in order to convert the light to another location, preferably at the edge of the housing. If a further layer of concentrator elements is inserted, the area-reducing parts are omitted for these concentrator elements. Instead, only a light guide for lateral displacement is required, since the focal surface or plane can be extended to the entire surface in order to be able to use angle-reducing elements with a larger final diameter, which thereby have a smaller scattering angle.

It goes without saying that the light in the focal surface must be converted, but it can also be transmitted. Hollow bodies mirrored on the inside, for example, are suitable for forwarding. If necessary, summing elements can be used which combine the light of individual lines into a common line, since this can reduce the overall length of the lines. Optionally, the light guided in the lines can be refurbished with concentrator elements before the current conversion.

For some applications, it can be advantageous if there is an additional color separation in front of the current transformer, which separates the total light into its spectral colors. This can e.g. B. done by a special coating of an optical body that transmits light at different points of different wavelengths or reflects light of different wavelengths back into the optical body. Alternatively, the color separation could also be carried out using a prism with a large dispersion and a correspondingly small Abbe number. Of course, a staggered embodiment is also possible.

The color separation has the advantage that a color-specific conversion of the light into electricity is possible, so that wavelength-optimized converters can be used which have a considerably higher efficiency. The wavelength-specific converters can also be arranged next to one another by suitable light guidance.

A scattered light collecting element can be arranged in front of the converter or converters, which brings the scattered light onto the focal surface.

The concentrator elements are preferably accommodated in cells, the walls of which are components of the housing. The housing is advantageously designed to be flexible so that the substructures for the housing can be omitted. A simple attachment to the surface, for example with pegs, is sufficient.

Further advantages, features and possible uses of the present invention will become clear from the following description of preferred embodiments and the associated figures.

Show it: FIG. 1 shows a schematic view of a concentrator element,

FIGS. 2 to 5 different embodiments of prism walls,

FIG. 6 shows a preferred embodiment of a prism for a prism wall,

FIGS. 7 and 8 preferred embodiments of an angle-reducing element, FIG. 9 an embodiment of a summing element,

FIG. 10 shows a schematic representation of the beam path through an absolute value converter,

FIG. 11 shows an embodiment of a “zero angle suppression” and

Figure 12 different arrangement options of several concentrator elements side by side.

The present invention and thus also the embodiments shown serve to concentrate daylight, that is to say diffuse and direct radiation, on preferably about 1/20 of the starting surface. This concentration should be done without the help of moving parts if possible. Since the concentrator is to be used for energy generation, large areas are often required. It is therefore advantageous to subdivide the total area into individual cells, each of which contains a concentrator element and whose area is approximately 100 cm ² . The basic structure of a concentrator element 1 is shown in FIG. Here, an area-reducing element 3 is connected upstream of an angle-reducing element 4 in the beam direction, that is to say from top to bottom in FIG. 1. In front of the area-reducing part 3, an input area 2 is connected upstream. The angle-reducing element here consists of a wedge-shaped element 4 with a reflective sheathing 5. Following the wedge-shaped element 4, a collecting lens 7 is attached, which can focus the light emerging from the concentrator onto an area.

One idea on which the invention is based is that the wedge-shaped element 4, which is known per se, can be used for a concentrator if a surface-reducing element 3 is connected upstream of it. The construction of an area-reducing element is described by way of example using some embodiments.

In the embodiments described in FIGS. 2 to 6, the area-reducing element 3 essentially consists of a cone made of an optical material, for example of solid glass. This cone is surrounded by a special reflection wall, which reflects the rays coming out of the cone back into the cone. If the wall of the cone were only mirrored, the angle that the light beam encloses with the main optical axis 6 would be increased with each reflection on a side wall. At some point the angle reaches 90 ° so that the direction of the light is reversed. The special reflection wall, which is arranged at least in the lower area of the cone on the outer wall, is also called prism wall in the following, since it consists of a series of prisms. The prism wall serves to reduce the angle between the light beam and the main optical axis. As a result, this leads to the fact that tial reflection wall does not apply the normal reflection law, in which the angle of incidence is equal to the angle of reflection, but the angle of reflection is smaller than the angle of incidence by a deflection or deflection angle. This deflecting property of the prism wall, which will be described in detail below, works particularly well for light rays which form a relatively large angle with the main optical axis. Therefore, in the preferred embodiment, the special reflection wall is arranged only in the lower region of the cone, while in the upper region the cone is surrounded by a mirrored layer. As already mentioned, the mirrored layer leads to the angle between the light beams and the main optical axis 6 being increased with each reflection on the side wall.

When sunlight enters the cone, the light is refracted towards the main optical axis. This means that the maximum angle that the light rays entering the cone enclose with the main optical axis is not 90 ° but arcsine (1 / n ₁ ), where n- _{\ is} the refractive index of the cone material. If, for example, the cone is made of plexiglass, the maximum angle that the light that has just entered the cone with the main optical axis 6 is 42 °. The fact that the cone is mirrored in the upper region ensures that the maximum angle which the light beams enclose with the main optical axis is increased again. When dimensioning the mirrored area, care must be taken that the maximum angle which the light rays enclose with the main optical axis 6 is increased to a maximum of 90 °. As soon as the maximum angle comes into the range of 90 °, the mirrored surface must end in order to avoid reflections. Now the special reflective wall connects to the bottom.

One way of reducing the angle that light rays enclose with the main optical axis 6 by arranging prisms on the outer wall of the cone is to use the total reflection during the transition from the optically denser to the optically thinner medium. For clarification, a basic structure of a prism wall is shown in FIG. 2 in the left partial image. Here incisions were made in the material. The angle which the incisions enclose with the main optical axis is chosen such that light rays which enclose an angle of approximately 90 ° with the main optical axis 6 are still totally reflected on the underside 13 of the incision. This is illustrated using an exemplary light beam L. This light beam is totally reflected on the underside 13 of the incision, then directed to the reflective layer 5, reflected by it and can then pass through the other incisions almost unhindered. It can be clearly seen that the reflected beam encloses a significantly smaller angle. The arrangement shown makes it possible for a large part of the light rays in the cone to be reflected in the desired manner. The further developments shown in the two other partial images in FIG. 2 are based on the same principle, but have been optimized in order to increase the proportion of light rays reflected in the desired manner. In the optimized embodiment, the incisions are sawtooth-shaped, as shown in the middle partial image of FIG. 2. Further prisms 8 are then inserted into the sawtooth-like incisions. been brought. Here, two transitions from the optically denser to the optically thinner medium 13, 14 are provided, on each of which total reflection occurs for some light rays. The first transition is again the lower incision surface 13. Here, in the example shown, all light rays are reflected which enclose an angle of <78 ° with the main optical axis. Light rays, which enclose an angle between 78 ° and 90 ° with the main optical axis, can leave the cone at the transition 13 and reach the outer prism. However, the upper end 14 of the outer prism is arranged in such a way that these light beams are totally reflected here and are finally mirrored on the side mirrored end 5 of the prism. The upper edge 14 of the prism 8 forms an angle with the main axis, which is chosen such that light rays which form an angle of 90 ° with the main axis are totally reflected at the interface 14 from the optically denser material into the optically thinner material ,

FIG. 3 shows an alternative embodiment of a prism wall, but which is based on the same basic principle as the embodiment shown in FIG. 2. As can be seen in the left partial image of FIG. 3, this embodiment is also based on a cone with incisions. In the optimization, however, the entire incised area is now separated from the actual cone 3, so that its outer surface is largely smooth again. Prisms 8 are arranged, the upper edge 14 of which in turn encloses an angle with the main optical axis, which for the total reflection of light rays forms an angle with the main optical axis of approximately 90 °. close, guaranteed.

In the embodiment shown in FIG. 4, prisms made of a material whose refractive index is smaller than the refractive index of the cone are additionally inserted into the prism wall. The inserted prisms are provided with the reference number 9. These prisms made of material with a low refractive index are used, inter alia, for light rays reflected on the reflected layer 5, which would be totally reflected without the presence of the prism 9 with a refractive index at the upper edge of the incision 16 during the transition from the optically denser to the optically thinner material to safely return to the cone. Because the refractive index of the prism 9 is smaller than the refractive index of the cone 3, but larger than the refractive index of air, the critical angle at which total reflection occurs at the interface 16 is increased, so that those reflected back on the reflected surface 5 Light rays largely pass through prism 9 and are returned to the cone. This prism arrangement is advantageous for light rays that first enter prism 8. However, this arrangement is less advantageous for light beams that do not enter the prism 9 with a lower refractive index via the prism 8, but rather enter the prism 9 directly from the main optical body. Therefore, an improved embodiment provides that the prism is compared to the prism 8 reduced refractive index on the side facing the main body, a surface mirrored on both sides is provided. The optical main body preferably does not run conically in the area of this surface mirrored on both sides, but here has an outer surface which runs essentially parallel to the main optical axis, in order to avoid undesired reflections due to the “funnel effect” mentioned at the outset. It goes without saying that an element which is mirrored on both sides can preferably also be used in the other embodiments in combination with a non-tapering section of the optical main body.

Another embodiment of a prism wall is shown in FIG. Here the light rays are guided in the prisms because their cross-section is constantly increasing. A part of the cone 3 can be seen on the left in the right partial image of FIG. On the right are the pointed prisms. The light rays that leave the cone 3 on its outside enter the prisms 8. Since the prism 8 widens in the beam direction, the light beams are virtually "captured". The light beam can therefore initially not leave the prism and is guided to the end of the prism, similar to the light guiding principle in glass fibers. Due to the curved arrangement of the prism 8, the angle that the light beam encloses with the main optical axis is reduced. At the end of the prism 8, the light rays emerge from the prism and are reflected on the mirror 5. When passing through the prisms 8 in the reverse direction, the light beams are diffracted in the direction of the main optical axis during each pass. As illustrated in the embodiment shown, if the opening angle of the prism body 8 is large enough, the axis of the prism body can be "bent". Several "kinks" 17 can therefore be provided. Similar to the light guiding principle in glass fibers, the light rays cannot leave prism 8.

At this point it should be mentioned that the prisms 8 do not necessarily have to be arranged such that their tip or input tip 15 faces the cone 3. Rather, they could also be facing the mirroring 5, so that the light beams first pass through a plurality of prisms 8 when they emerge from the cone 3 and are thereby "downward", that is to say in the direction of the main optical axis, and only after the reflection are "captured" on the mirror 5 in a prism 8 and then guided in the direction of the cone 3.

FIG. 6 shows a further embodiment of prisms which can be arranged on the outer surface of a cone. The prism 8 has a mirrored outer surface 5. The mirrored outer surface runs essentially parallel to the main optical axis of the cone. By way of example, a light beam L is shown which emerges from the cone 3 and occurs on the first surface of the prism 8. There it is broken to the plumb line and reflected on the mirror 5. When it emerges from the prism 8, it is broken away from the plumb line, so that the reflected light beam encloses a smaller angle with the main optical axis than the light beam L originally emerging from the cone 3. In principle, therefore, a special reflection wall could be realized with the aid of triangular prisms mirrored on one side become. However, these have the disadvantage that when the wall reflected by the mirror 5 strikes the lower surface 16 of the prism 8, the light rays are totally reflected and reverse the direction. Because of this, points the prism 8 shown in FIG. 6 has a further acute-angled prism 9, which is made of a material with a low refractive index. This further prism 9 is preferably arranged so that it points substantially downward with a tip. The tip is advantageously inclined somewhat in the direction of the main optical body, as can be seen in the figure. In a particularly preferred exemplary embodiment, prism 8 consists of polycarbonate with a refractive index of 1.59 and prism 9 of a material with a refractive index of 1.34. This arrangement has the advantage that light rays from the prism 8 can easily penetrate into the additional prism 9, since the critical angle for the total reflection is formed from the ratio of the refractive indices of the adjacent main optical bodies.

FIGS. 7 and 8 show two embodiments of angle-reducing elements. The embodiment shown in FIG. 7 shows an angle-reducing element which essentially consists of a wedge-shaped element 4. Outside of the wedge-shaped element 4, however, a mirroring 5 is provided, on the inside of which a narrow prism 12 is placed. There is a small air gap between the prism 12 and the wedge-shaped element 4. The light beam shown as an example in FIG. 7 is first totally reflected on the radiating side surface of the wedge-shaped element 4. If the back were mirrored, the light beam would be twice the wedge angle after reflection on the emitting side. If the back of the wedge is also open, the light beam can leave the wedge if the angle that the light beam forms with the perpendicular is greater than the total reflection angle. Ideally, the light beam is reflected by the inclined mirror almost parallel to the wedge rear wall, in order to re-enter the prism there with the angle a _R uc _k e _m t _ntt = aresin (1 / n ^. It follows that the largest angle, that can appear on the emitting side surface, is made up of the total reflection angle and the wedge angle, thereby reducing the angular range of the emerging rays.

Another embodiment of the angle-reducing element 4 is shown in FIG. Here, bodies 10 with a different refractive index are introduced into the wedge 4. The angle that the light rays emerging from the wedge enclose with the main optical axis can be reduced by the refraction of light on the embedded parts in front of the exit surface. Overall, this leads to a reduction in the angular range spanned by the emerging light rays, which the emerging light rays enclose with the main optical axis. In other words, the light emerges from the angle-reducing element virtually in parallel. In the embodiment shown in FIG. 8, a further prism 11 is additionally attached directly to the outside of the wedge-shaped element. Although this additional prism 11 leads to the fact that the emerging light beams again enclose a somewhat larger angle with the main optical axis, the angular scatter is reduced at the same time. In other words, the emerging light beams run essentially parallel, if not parallel to the main optical axis. However, this can be compensated for by the surrounding mirror wall. To advance Focusing 7 with a reduced light exit area (see FIG. 12), a conventional element can be used.

FIG. 9 shows a summing element which is preferably used in combination with the concentrator elements. Beams coming from above via the totally reflecting surface 20 and in the figure coming from the right can be guided by transmission on the surface 20 to the relay 21 both in the figure.

FIG. 10 shows the basic structure and the mode of operation of an absolute value converter as it can be used in combination with the concentrator elements.

The absolute value converter 22 essentially consists of a prism with an approximately rhombus-shaped cross section, one side surface of which is mirrored. The light rays coming from the left in the drawing and provided with the reference number 29b are refracted at the two boundary surfaces of the prism. If the effective refractive angle is non-zero, i. H. the two side surfaces (top left and bottom right in FIG. 10) which are traversed by the light rays 29b coming from the left are not parallel, these rays are deflected by a certain amount (depending on the effective refractive angle).

The light rays coming from the right in the drawing (see FIG. 10) and provided with the reference number 29a enter the prism 22 from the top right and are reflected on the mirrored surface 23 (bottom left in FIG. 10), so that they represent the absolute value. Also leave the transducer or the prism 22 on the surface at the bottom right.

While the incident light rays can have an opening angle of 180 °, the emerging light rays are limited to an opening angle of 90 °.

When realizing a static concentrator with absolute value converters, the prisms are preferably formed in a ring. The rings then have a cross section which essentially corresponds to that shown in FIG. 10. The mirrored surface is preferably arranged so that it is attached to the radially outer side of the substantially annular prism.

In this case, the static concentrator consists of several essentially concentrically arranged, approximately ring-shaped absolute value converters. This concentrator can also be combined with optical bodies or concentration bodies for certain applications in order to further increase the concentration factor. Another application of the absolute value converter is the use as an optical adder. For example, the light collected in neighboring concentrators can be diverted using absolute value converters in such a way that neighboring concentrators direct the incident light onto a common (larger) solar cell. This can further reduce the number of solar cells required per area.

FIG. 11 shows an embodiment of a zero-angle suppression. The zero-angle suppression is used to reduce the overall length. For this purpose, inclusions or hollow bodies 24 are introduced in the angle-reducing element in front of the actual wedge, and the rays, which form a small angle with the main optical axis, are broken away from the main optical axis. Since rays that are entering the wedge only have to be increased to the total reflection angle by total reflection on the tapered walls, this can also be achieved beforehand by an inserted optical element. Advantageously, angled cavity prisms 24 are used here, which are arranged with the tip upwards. As a result, the almost vertically incident rays are specifically broken. It is therefore possible to omit the tip of the wedge of the angle-reducing element, which in turn is advantageous in terms of production technology. A cavity prism 24 is understood to be a prism with a smaller refractive index arranged inside an optical body. These prisms preferably consist only of a prism-shaped air inclusion (cavity prism).

Such cavity prisms can also be used successfully in the area-reducing element, but here the tip preferably points downward. At the top, these prisms have a transition to the optical body made of a material with a lower refractive index, so that total reflection can no longer take place there. These prisms support the effect of the prisms on the side.

In addition, a concentration body can be arranged, which can be designed, for example, as a radially symmetrical, externally mirrored concentration prism. The prism has a through opening in its center through which light rays can pass perpendicularly.

Different arrangement possibilities of concentrator elements are shown in FIG. The left part of the figure shows that the individual concentrator elements are arranged side by side. It is striking that the concentrator elements 1 have a maximum cross-sectional width D only in the entrance area. The maximum cross-section is significantly reduced in the area of the area-reducing element. This enables an arrangement as shown on the right in FIG. 9. Here, adjacent concentrator elements are offset in height, so that the focusing device, which is in the form of a lens here, can have a cross section D ₂ which is significantly larger than the maximum cross section D of the receiving element. This is made possible by the fact that the focusing element is arranged in the scaled area of the concentrator element 1.

The concentrator according to the invention makes it possible to concentrate light with an aperture angle of greater than 20 °, preferably greater than 40 °, particularly preferably greater than 100 °

Claims

Patent claims

1. Concentrator for concentrating incident light on a predetermined surface or a predetermined volume with an input surface and an output surface, characterized in that an area-reducing element (3) is connected upstream of an angle-reducing element (4).

2. Concentrator according to claim 1, characterized in that the area-reducing element (3) has an optical main body, preferably in the form of a truncated cone or a truncated pyramid, the cross section of which tapers in the beam direction.

3. Concentrator according to claim 2, characterized in that on the side walls of the optical body (3) at least one prism (8) is arranged, the refractive index ni of the prism being greater than 1.

4. Concentrator according to claim 3, characterized in that the at least one prism (8) is integrally formed with the main optical body (3).

5. Concentrator according to claim 3, characterized in that the at least one prism (8) is arranged such that there is a gap between the optical main body (3) and the prism (8).

6. Concentrator according to one of claims 3 to 5, characterized in that the at least one prism (8) is arranged such that an input tip (15) of the prism (8) with an acute angle φ of less than 90 ° along the optical Path is arranged closer to the entrance of the concentrator than the part of the prism (8) facing away from the tip.

7. Concentrator according to one of claims 3 to 6, characterized in that the side walls of the area-reducing element (3) are mirrored, the at least one prism (8) between the main optical body (3) and mirroring (5).

8. Concentrator according to one of claims 3 to 7, characterized in that the at least one prism is arranged such that one side surface of the prism with the optical

The main axis encloses an angle of a> aresin -, where n _{0 is} the refractive index of the

is the medium surrounding the side surface and - ^ is the refractive index of the prism.

9. Concentrator according to one of claims 6 to 8, characterized in that a second prism (9) is arranged on a side facing away from the input tip of at least one prism (8), the second prism having a refractive index n ₂ which is smaller than that Is the refractive index of the at least one prism and the second prism is preferably arranged such that a tip points approximately downwards.

10. Concentrator according to one of claims 6 to 9, characterized in that approximately applies to the refractive angle φ of at least one prism:

- (^ _max + ^ _B , ι _anz ) = arcsin -,

2

where ni is the refractive index of the prism, n ₀ the refractive index of the medium essentially surrounding the prism in the irradiation area, φ _max the maximum angular deviation of the light emerging from the main optical body from the main optical axis and cpeπ _anz the angular deviation, the same starting angle how has input angle is.

11. Concentrator according to one of claims 6 to 10, characterized in that at least one prism has two side surfaces which together form the entrance angle, one side surface being mirrored and for the refractive entrance angle φ:

φ> arcsin -,

where n- _{\ is} the refractive index of the prism and n _{0 is} the refractive index of the medium essentially surrounding the prism in the irradiation area.

12. Concentrator according to one of claims 1 to 11, characterized in that the input surface of the area-reducing element is not flat.

13. Concentrator according to one of claims 1 to 12, characterized in that the area-reducing element is preceded by a receiving element (2) substantially in the form of optical bodies narrowing in the beam direction.

14. Concentrator according to one of claims 1 to 13, characterized in that the angle-reducing element is a wedge (4) or a conical element.

15. Concentrator according to claim 14, characterized in that the wedge (4) is mirrored on one side.

16. Concentrator according to claim 15, characterized in that the mirroring of the wedge is separated from the wedge and preferably the mirroring is not parallel to the surface of the

Keils runs.

17. A concentrator according to claim 16, characterized in that at least one prism (12) is arranged in front of the mirrored wall (5) of the wedge (4).

18. Concentrator according to one of claims 14 to 17, characterized in that the wedge has enclosed prisms with a reduced refractive index, preferably prism-shaped cavities (10), the tip of which preferably points upwards.