Patent Application
20120154941
This invention is generally in the field of solar energy collection and concentration and relates to an optical system and method for collection and concentration of solar radiation.
The following is a list of references that can be used for better understanding of the background of the invention:
Direct optical electromagnetic (EM) radiation conversion to electricity is possible via the photovoltaic effect, which is a quantum conversion effect. The efficiency of this conversion is dictated inter alia by the energy spectrum of the photon flux irradiating a media bulk.
Concentration of solar energy may be useful for reducing costs and increasing efficiency of the radiation conversion. This is due to the fact that the cost of concentration optics is typically much lower than that saved by using smaller coverage area of photo-voltaic cells.
One of the common problems in the solar energy collection systems is associated with the fact that a solid angle of propagation of the most of the solar radiation varies during the day and seasons as a result of the Sun movement. This problem is typically solved by manually tilting the light collection surface of a passive (stationary mounted) collector or that of its associated light defector with respect to the horizon (i.e. using a stationary mounted tilted light collector or its deflector), or by using an active approach according to which the collector or associated light deflector is mounted for angular displacement for tracking the movement of the Sun. Active solar tracking allows for larger total solid angles of radiation collection, but increases the costs of a solar cell system and requires frequent maintenance of moving parts.
Various techniques have been developed aimed at solving the above problems, i.e. increasing the radiation collection and further conversion. In Ref. [1], the author fabricated simple phase Fresnel lens to be installed on aircrafts, which do not involve long focal lengths and yet have high sensitivity and angular resolution. In Ref. [2], the authors discus energy anamorphic concentrator of a big diffuse light source to achieve extremely high concentration in one lateral direction at the expense of that in the other direction, thus preserving the total (two-dimensional) optical brightness. In Ref. [3], the authors have fabricated and characterized solar fiber-optic mini-dish concentrator. Their prototype was 200 mm in diameter and they have transported concentrated sunlight in a one-millimeter-diameter optical fiber. In Ref [4], a non-imaging optical collecting and concentrating apparatus is described for use in solar power applications that is relatively immune from optical incidence angle and therefore does not need to track the movement of the sun to efficiently collect and concentrate optical energy. In Ref [5], a diffractive structure is used for the redirection and concentration of optical radiation. The structure includes a substrate having a diffractive surface and a coating layer disposed over the diffractive surface, while the coating layer having an index of refraction substantially different from that of the substrate. Also, the use of a holographic planar concentrator for collecting and concentrating optical radiation has been proposed (Ref [6]), as well as solar cell based upon Fresnel zone plate lens for large space based telescope (Ref [7]). Ref [8], similarly to Ref. [4], reports on a passive and non-imaging solar collecting and concentrating apparatus for use in passive lighting and solar power applications.
Some other known techniques are aimed at collecting and concentrating solar radiation with high angular uncertainty. For example:
U.S. Pat. No. 6,299,317 presents a method and apparatus for a passive, fiber-optic day-lighting system collects and transports sunlight as a cost-effective technology solution for day-lighting applications. The system utilizes a low concentration ratio sunlight collection system, in expensive optical fibers, and an inexpensive passive solar thermal tracker. The sun-light collection system uses an array of conical compound parabolic concentrators with concentration ratio in the range of 50-500. The sun-light collection system may also use an array of square or rectangular shaped Fresnel lenses with circular concentric grooves. The array of Fresnel lenses can be formed on a single sheet of plastic, which will minimize the cost of manufacturing and reduce the cost of assembly of individual lenses into an array. The sun-light collection may also use arrays of two concentrators in tandem.
US 2007/0246040 presents a non-imaging optical collecting and concentrating apparatus for use in i.e., optical communications, passive lighting, and solar power applications that is relatively immune from optical incidence angle(s) and therefore does not need to track the movement of the sun to efficiently collect and concentrate optical energy is described. The apparatus includes a tubular support structure having a source-facing entrance and an energy-outputting exit. An interior surface of the structure includes a scattering, reflecting and/or diffractive medium to direct incident energy toward an exit of the tubular structure, such that the rays exiting the tube are more collimated and substantially more parallel to the axis of the tube. The collimated beam is then focused or directed by a lens or similar optical element toward a point where the energy may be collected by a detector, optical fiber, or other collection means.
Another approach in optimization of the conversion efficiency involves minimization of the energy losses associated with a mismatch between the photon energies and the active materials in a photo-voltaic cell, e.g. solar cell. The typical energy which can be converted by the active material is determined typically by the optical band gap (minimum optical absorption energy) of the material that absorbs the radiation. The mismatch between the photon energies and the active materials refers to two parts of the radiation energy split by the optical band gap of the cell. Photons with energy higher than the optical band gap of the absorbing material can be absorbed and their energy be converted to electrical energy. These photons participate in the photovoltaic process, but the energy conversion process suffers from the fact that any excess energy, beyond that of the optical band gap, is lost during the photovoltaic process. On the other hand, photons having energy lower than the optical band gap cannot participate in the photovoltaic process. Consequently, from the photovoltaic point of view, this part of the solar spectrum is lost.
A tandem cell is constructed from a series of several photo-voltaic cells where each of these cells is optimized to a part of the spectrum of the EM radiation. The photo-voltaic cells are positioned one on top of the other, in order of decreasing optical band gap. In one option all cells are connected in series with a common current path and a voltage that is the sum of the voltages of all the cells. In this case current matching and the need for rather sophisticated cell fabrication are the main challenges and reasons for the high cost. Consequently these systems are relevant for systems with fairly high concentrations of radiation, e.g. sunlight, for example by sun tracking concentrators which can concentrated the sunlight by a factor of a thousand (>˜1,000×) or more.
Another suggested solution is the use of spectral splitting of the EM radiation. In this method the incident illumination is optically split into several windows of energy ranges. Each of these spectral components/windows is suitable for cells that are optimized to the specific energy range. The spectral components are typically spilt using a prism which spatially separates the incoming radiation into several energy windows and projects the different components on a series of cells optimized respectively. This approach suffers from the difficulty of spectral splitting illumination over the large areas. Therefore, in this method as well, the system typically requires Sun tracking concentrators.
For example, US 2010/200044 presents a solar energy conversion system. The system comprises at least one waveguide arrangement having at least one light input respectively. The waveguide arrangement comprises a core unit for passing input solar radiation therethrough and a cladding material arrangement interfacing with the core therealong. The cladding material arrangement is configured as an array of spaced-apart solar cells arranged along the core unit and having different optical absorption ranges, such that an interface between the waveguide core and the cladding arrangement spectrally splits the photons of the input solar radiation by causing the photons of different wavelengths, while passing through the core unit, to be successively absorbed and thereby converted into electricity by the successive solar cells of said array.
There is a need in the art for a novel light collection system which provides for collecting external radiation (such as solar radiation) from a relatively large range of solid angle of radiation propagation, and also enabling efficient concentration of the collected radiation into one or more defined locations.
As indicated above, active solar tracking allows for larger total solid angles of radiation collection as compared to the conventional passive approach, but increases the costs of a solar cell system and requires frequent maintenance of moving parts. However, efficient collection of sun light using conventional passive approach is a challenging task.
Assuming that light should be collected and coupled into a photovoltaic cell (directly or via concentrator/director) with a small area but large numerical aperture (NA), a simple solution would be the use of a large area lens. This lens will collect light at its surface area and focus the collected light into a single spatial point (point-like spot). The collection efficiency of the lens is thus defined by its entire surface area and a specific direction of light propagation faced by said surface area, e.g. specific position of the sun. The collected light is focused into the focal point of the lens. The concentrated light forms a spot with small area but with large angular range. This solution fits well for a photo-voltaic cell with small area and large NA. The concentration factor in this configuration equals to the ratio between the area of the surface of the lens and the area of the cell that can match the minimal focal spot. However, such systems assume that the light is coming from a given direction with no angular uncertainty. If the light is coming from another direction, the focal point is shifted and the light is no longer coupled into the cell. Therefore, either the cell or the lens has to follow the changing radiation propagation direction (i.e. follow the position of the Sun).
The main idea of the present invention is aimed at providing a novel radiation collection system defining a passive radiation collecting interface that utilizes anamorphic optics which allows projection and concentration of light collected with a relatively large light collection surface (e.g. defining an effective aperture for light collection) onto an elongated projection region, and allows receiver aperture(s) to extend along said projection region for collecting the concentrated light. The anamorphic optics may include a cylindrical lens (e.g. tapered) or a prism (e.g. tapered prism) that can have a desirably large light collection surface thus enabling coupling/collecting direct (directional) and also diffused light and projection of the same onto the line-like or planar elongated projection region. Also, the invention provides for coupling planar waveguide(s) to the elongated projection region for transporting the radiation to the photo-voltaic (PV) cell(s).
It should be noted that the invention utilizes the principles of anamorphic optics, namely optics that has different optical functions/powers in the horizontal and vertical dimensions of an object being projected/imaged. The anamorphic optical element thus defines a first primary axis which extends in a plane perpendicular to the optical axis of the element and is parallel to the longitudinal axis of the projection region/focal region. A specially designed cylindrical lens, as well as a prismatic structure, of the invention is an example of such anamorphic optical element. Therefore, although the description below refers at times to “cylindrical lens” and “tapered cylindrical lens”, these terms should be interpreted broadly.
It should also be noted that the term anamorphic optical element as used herein relates to an optical element configured to perform certain manipulation/optical function on light along one axis (primary axis), while performing a different manipulation on the light along the other axis (secondary axis). The primary and secondary axes are intersecting axes substantially perpendicular to the optical axis of the anamorphic optical element. An anamorphic optical element can be, for example, a lens with different optical powers along the two different axes, a cylindrical lens having optical power only on a single axis, a prismatic structure, or other forms of optical elements configured with different optical functions along the different axes perpendicular to its optical axis.
The invention is based on the understanding that during a day the Sun is moving along a curved one-dimensional trajectory across the sky with day-night angular range/extent of about 180 degrees about a certain direction/axis (north-south). Practically, only about 100 degrees angular segment from the 180 degrees range is useful for collection of Sun's energy. During the change of seasons, the angular position of this trajectory changes within a total angular range of about 45 degrees about a second direction (east-west). The invention uses this a-priori information in order to design passive light collection optics to perform efficient collection of solar radiation without tracking the Sun's movement in the sky.
Despite the movement of the Sun along these well defined trajectories, the optics of the present invention is capable of collecting and concentrating light/solar energy and directing the light to the same spatial location where a receiver aperture can be position. For example, the receiver aperture may be associated with a light collection surface of a photo-voltaic (PV) conversion element (cell) or with an input facet of one or more waveguides configured for guiding the collected light onto a photo-voltaic (PV) cell.
According to some embodiments of the invention, the waveguide itself can also be used to perform a part of the light concentration operation. This is because waveguides can be configured to concentrate a light beam by converting its cross-sectional area (i.e. to reduce the area) into a wide solid angle (i.e. to output concentrated light with increased solid angle).
The invention can be used with photo-voltaic cells and is therefore described below with reference to this specific application. It should however be understood that the principles of light collection of the invention are not limited to this specific application. The collected radiation can for example be used for other purposes, such as illumination of interior rooms, and many other applications.
Thus, the present invention utilizes prior knowledge of the solid angle defined by the Sun's movement in the sky for providing a passive, highly efficient, system for collecting and concentrating electromagnetic radiation. The collected radiation may be coupled into one or more waveguides for transporting the radiation to one or more PV cells or other locations/receivers or may be directly coupled thereto. By utilizing this a-priori knowledge about the trajectory of the Sun, the passive light collection system of the present invention optimizes the light concentration value by reaching a high factor of concentration and allows approaching the theoretical bound defined by the law of brightness.
It should be noted that according to the invention flexible planar waveguides can be used for guiding the collected light towards a light conversion system (PV cell). Advantageously such planar waveguide(s) can be folded such that its/their output facet matches the dimension of PV cell(s) to which the light is directed. This manipulation of waveguides dimensions can be used to provide high conversion of brightness from area to a solid angle and provide even more efficient conversion of solar radiation to electricity.
The present invention may also be implemented by utilizing existing optical fibers which are used for data communication purposes, in the field of optical communication network. Such optical fibers are widely used for large distance communication and may be used by the system of the present invention for transferring collected energy from a distant collection location (e.g. outside of a city) to photo-voltaic cells arrangement located at a more accessible location (e.g. located within the city).
The technique of the present invention thus utilizes the principles of anamorphic optics and a specific design thereof, which can be accommodated to collect light from multiple directions by a large collection surface and is capable of bringing/concentrating the collected light to a single spatial location. The anamorphic optics used in the invention may be formed with optical diffractive elements (e.g. appropriately patterned light collection surface) for spectral splitting purposes and/or be associated with one or more waveguides as receiver(s) of the collected radiation at the focal elongated region defined by the optics and/or as light guide(s) for guiding the collected radiation to said focal elongated region. For example, the light collection surface of the cylindrical lens/prism and/or the surface of the waveguide(s) may be patterned (spatially engraved, e.g. formed with a grating) to generate spectral splitting of the energy being collected or of the collected energy.
Thus, according to one broad aspect of the present invention, there is provided a system for collecting and concentrating light from a moving light source. The system includes at least one anamorphic optical element, defining an optical axis and a projection region, and having a predetermined effective aperture which defines primary and secondary axes. The effective aperture is configured for collection of optical radiation arriving from a predetermined solid collection angle which defines a first range of angles with respect to a plane spanned by said optical axis and said primary axis. At least a part of said projection region defines at least one receiver aperture. The anamorphic optical element is configured such that light passing through the effective aperture within a predetermined first range of angles is concentrated by a first optical function of said element onto at least part of said projection region. For example, the first range of angle may be a range of about 12 degrees and may extend up to about 45 degrees.
Said anamorphic optical element is configured for collecting and projecting, onto substantially overlapping parts of said elongated region, optical radiation arriving from different angles within a second predetermined range of angles with respect to a plane spanned by the optical axis and the secondary axis. The second range of angles may be of about 110 degrees and may also extend up to about 150 degrees.
The light collection and concentration system can be configured as a passive optical system for collecting and concentrating light from a moving light source. The system is configured for collection of optical radiation arriving from a predetermined solid angle. Light arriving from said solid angle and passing through the effective aperture of the anamorphic optical element is concentrated onto an elongated projection region which may extend parallel to the primary axis of the anamorphic optical element. By arranging the system such that the primary axis is substantially perpendicular to the main direction of movement of the radiation source, the system collects light emitted by said source during most of the propagation of the source.
The first range of collection angles is typically selected in accordance with a known trajectory of radiation source movement during a certain period of time (e.g. to cover seasonal changes in the Sun's position). The second range of collection angles may be selected in accordance with a known trajectory of the radiation source (Sun) during a certain period of time (day-night trajectory). Considering the Sun as the radiation source, the trajectory is defined by the movement of the Sun in the sky during a day, the first axis is substantially parallel to the direction of the propagation of the Sun during a day and the second axis is parallel to the direction of the changes of the trajectory between the different seasons of a year.
Accordingly, the system of the present invention is capable of passive collecting optical radiation from a range of collection angles thus allowing collection of both direct and scattered/diffused optical radiation with increased light collection efficiency. The wide angular range of passive collection is more tolerant to weather conditions since it collects diffusive light in contrast to active systems.
The design of the passive light collecting optics of the present invention takes into account the angularly limited movement of the Sun (i.e. radiation source), and unlike active trackers, the optical system of the present invention collects also the diffused light. In northern countries, where most of the sunlight is diffused, and also in sunny countries, during cloudy days, collection of diffused light to the solar cells will yield production of electricity at high conversion efficiency which is less dependent on the weather conditions.
According to some embodiments of the invention, the system for light collection and concentration may comprise a spectral splitting assembly. The spectral splitting assembly allows directing different spectral ranges of light onto different photo-voltaic cells optimized for the specific spectral ranges. The spectral splitting assembly may be placed on the effective aperture of said anamorphic optical element. Alternatively or additionally, spectral splitting assembly may also be configured as a spectral splitter extending along a surface of one or more of the waveguides to thereby separate light portions of different spectral ranges and allow their output from the waveguide at respectively spaced-apart locations along the waveguide.
The receiver aperture, which extends along at least a part of the projection region, may be associated with one or more light receiving elements. For example, such elements may include one or more waveguides and/or photo-voltaic cell(s) and/or an entry of volume to be illuminated by the collected light. For example, one or more waveguides may be used for guiding the radiation coupled thereto towards one or more different dedicated directions.
In case of more than one receiving elements (e.g. waveguides), the receiver aperture may be a common aperture of all the waveguides. The waveguides may in turn be configured for coupling thereto at least a portion of the collected radiation such that different segments of the first range of angles are coupled into different waveguides. For example, two or more waveguides may be configured and arranged for coupling collected radiation from different segments of said predetermined collection angle, corresponding to main directions of propagation of collected radiation from different trajectories of the radiation source (the different trajectories of the radiation source may be the trajectories of the Sun during different seasons respectively); and/or such two or more waveguide are configured for receiving and guiding different spectral components of the collected radiation. As indicated above, the receiver aperture may be the input aperture of a photovoltaic cell or of other optical instruments or illuminated volume. Also, one or more planar waveguides may be coupled to an elongated projection region for providing efficient optical coupling thereto. The use of flexible waveguides may simplify the orientation of the system of the present invention.
The waveguides can be coupled to the anamorphic optical element at different coupling orientations, the system can collect radiation also when the plane of the source' trajectory of movement changes, e.g. becomes shifted along the “summer-winter” axis. In this case, the collected radiation is coupled to different waveguides. The use of waveguides provides a good tool for transporting collected and concentrated light. Also, an array of specially tapered cylindrical cones can be used to efficiently couple the collected light onto the planar (flexible and/or plastic) waveguides and thus provide the radiation collection system of the invention to be efficient and easy to configure. The waveguides may be combined together to guide the collected radiation into photo-voltaic cells of any possible configuration and position in respect to the collection array.
The one or more waveguides coupled to the receiver aperture may direct the collected light to the same or different locations. Multiple waveguides can guide the radiation coupled thereto towards different locations or towards the same location.
The use of appropriately designed anamorphic optical element allows for collecting radiation regardless to the movement of the radiation source along its trajectory in a way that collected radiation is always concentrated/projected onto a predetermined region (e.g. focal region).
According to some embodiments of the present invention, the anamorphic optical element comprises a cylindrical lens curved at least about said primary axis. The lens concentrates the radiation collected via its external surface onto an elongated focal region parallel to the first axis of the optical element and parallel to the main direction of movement of the radiation source. The cylindrical lens is arranged such that movement of the radiation source along its trajectory results in a corresponding shift of the focal spot along said focal region. In some embodiments, the effective aperture of the cylindrical lens has an elongated shape aligned along the primary axis of the lens. According to some other embodiments of the present invention, the anamorphic optical element is formed as a sealing element of one or more photo-voltaic cells. The anamorphic element has a focal region located downstream of light propagation through the anamorphic element. Such anamorphic element, providing sealing for photo-voltaic cell, may be a cylindrically shaped optical element arranged around a cylindrical photo-voltaic cell. The cylindrically shaped optical element is configured as a cylindrical lens and has a substantially circular light collection surface. In this regards, the receiving element may be located at the center of the cylindrical lens and the system, i.e. sealing optics in the form of cylindrical lens and cylindrical receiving element, is arranged such that light coming from all directions is sufficiently concentrated onto the receiving element.
According to some other embodiments of the present invention, the anamorphic optical element comprises a prismatic structure. The prismatic structure has a facet defining said effective aperture for collection of solar radiation with the predetermined collection angle, and has a top region comprising said projection region. The side walls of the prismatic structure are constructed as waveguides for guiding collected light by total internal reflection from said effective aperture towards the top region of the prismatic structure. The top region of the prismatic structure has a geometry corresponding to said projection region onto which the collected radiation is concentrated.
Generally speaking, the cylindrical lens or prismatic structure has a tapered or cone-like configuration in order to have as large as possible light collection surface. The invention may use an array of specially tapered cylindrical cones which efficiently couple collected light into planar and possibly flexible (e.g. plastic) waveguides or directly illuminate a PV cell or another target. Due to the use of so-designed anamorphic optical element(s), the movement of the light source along its trajectory does not reduce the coupling of the collected light into the planar waveguide. Due to the tapered design of the optical element, light being collected is appropriately converged into a one-dimensional region. An input facet of the waveguide (e.g. planar, flexible) is located along said one-dimensional region allowing coupling of the light coming from different locations of the source. The waveguides used are preferably flexible in order to provide desired freedom in the positioning of its output facet. Combining several planar waveguides as such, and bringing them to the same photo-voltaic cell allows collection of radiation coming from different locations by the same photo-voltaic cell, e.g. different trajectories of the Sun in different seasons along a year.
According to another broad aspect of the invention there is provided a solar radiation system comprising the optical light collection and concentration system described above, and at least one photo-voltaic cell having a light receiving surface extending along at least a part of said receiver aperture.
According to yet another broad aspect of the invention, there is provided a solar radiation system comprising the optical light collection and concentration system described above, and one or more waveguides having one or more input facets respectively extending along one or more parts of said receiver aperture.
According to yet further broad aspect of the present invention, there is provided a method for collecting solar radiation onto one or more photo-voltaic cells, the method comprising:
(a) providing a solid angle of solar radiation propagation in accordance with a first direction corresponding to the trajectory of the Sun during the day and a second direction in which said trajectory varies between seasons, and determining, based on said first and second directions, first and second angular ranges corresponding to the direction of the Sun light propagation during the day and in different seasons.
(b) configuring an anamorphic optical element having an effective light collection aperture with first and second different optical functions associated with primary and secondary axes of the anamorphic optical element, such that said first optical function is operable to collect and concentrate light arriving from different directions within said first angular range and to direct the concentrated light onto substantially the same light projection region, and said second optical function is operable for collecting and concentrating light arriving from different directions with respect to said second angular range ant to project the concentrated light onto substantially overlapping regions at said projection region; and
(c) coupling one or more receiving apertures to said projection region for collecting therefrom concentrated light arriving from any direction within said solid angle.
The invention also provides a method for collecting solar radiation onto one or more photo-voltaic cells, comprising:
(a) providing a solid angle of solar radiation propagation in accordance with a first direction corresponding to the trajectory of the Sun during the day and a second direction in which said trajectory varies between seasons;
(b) providing a system for collecting and concentrating light from a moving light source as described above; and
(c) mounting said system such that its primary and secondary axes are substantially parallel to said first and second directions respectively to thereby optimize a solid angle from which Sun light is collected by said system.
In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
The present invention provides for passive collection of light from a movable/moving light source (e.g. the Sun), namely collection of light propagating from the light source by the same optics (i.e. stationary mounted optics having a given collection angle) to the same concentration region (point), where a receiver aperture (e.g. a photo-voltaic unit/cell) is located. The receiver aperture may be an input port/aperture of one or more receiving elements (waveguides or photo-voltaic cells), or an input optical window of one or more volume/cavities to be illuminated by the collected light.
Reference is made to
The effective aperture 112 (light collection surface 114) is configured for collection of optical radiation R arriving from a predetermined solid collection angle defining a first range of angles FR with respect to a plane spanned by said optical and primary axes OA and PA respectively. For example, the first range of angles FR from which the system is configured for passively collecting light may be selected in accordance with the movement of the light source 200 with respect to/about the primary axis PA.
The anamorphic optical element 110 is configured such that light passing through said effective aperture 112 within the predetermined first range of angles FA is concentrated onto at least a part of the projection region 120. Optionally, the projection region 120 is an elongated region substantially parallel to the primary axis PA. Accordingly, the anamorphic optical element 110 may be configured for collecting and projecting optical radiation arriving from different angles within a second predetermined range of angles SR (e.g. corresponding to the movement of the light source 200 about the secondary axis SA) onto substantially overlapping parts of said elongated projection region 120.
The system 100 of the invention may also be associated with a plurality of waveguides (not shown) arranged at the receiver aperture 122 of the projection region 120. The waveguides may be arranged such that each waveguide is collecting energy form a different propagation direction corresponding to different seasonal period. As the Sun moves along the summer winter trajectory (FR), light propagating within different angular segments during the Sun's movement is concentrated onto projection region 120 and successively collected by at least one of the waveguides. This can be effectively used by providing different waveguides at the receiver aperture for receiving and guiding light components associated with different angular segments of collection depending on the time of year. Since the cost of optical waveguides is very low relative to the cost of a photo-voltaic cell or a lens, the use of multiple waveguides in the system is cost effective as it obviates replicating the optics itself and/or the photo-voltaic cells.
Moreover the invention also provides for efficient passive light collection during the day-night motion of the Sun. The Sun generally moves along a day-night trajectory (SR) with angular extent of about 180 degrees. Efficient collection of the light radiation from the Sun, while it is in different angular poisons with respect to system 100, is achieved according to some embodiments by utilizing one or more planar waveguides (not shown) optically coupled with the elongated projection region 120 of the anamorphic optical element. As the elongated projection region 120 is substantially parallel to the day-night trajectory (SR), optical radiation arriving from different angles during different time intervals of the day (as the Sun is located at different positions along this trajectory) is concentrated and projected onto substantially the same projection region. Namely, during the day-night motion of the Sun the radiation is projected onto substantially overlapping parts of the elongated region. The radiation/light is therefore efficiently collected by one or more planar waveguides coupled thereto.
The solution provided by the present invention realizing an efficient passive collection of light relates to the optical basic law of brightness. The law of brightness conservation is formulated as:
n
2
ΔA·ΔΩ=const (1)
where n is the refractive index of the collecting optics, ΔA is the collection area and ΔΩ is the solid angle (defined by the first and second angular ranges FR and SR) from which the radiation collection is performed. Thus, since the photo-voltaic cell can collect light from a solid angle ΔΩ of 2π Steradians (hemi sphere) while the radiation coming from a distant source (e.g. the Sun) is a-priori limited to a much smaller solid angle (of about π2/8), the area of collection can be reduced accordingly, and in this way a high concentration factor can be obtained.
Following the low of brightness, the maximal concentration of passive collection of solar radiation can be:
where Δφ and Δθ present the angular movement of the Sun in each direction. The exact angles presenting the Sun trajectory differ according to the location relative to the equator, for example, the Sun covers an angle of Δφ=150° (5π/6) along the day and perpendicular shift of about Δθ=45° (π/4) between the summer and winter trajectories. Assuming n=2 (relevant for glass), a concentration factor of about 25 may be obtained (e.g. 25 Suns).
The technique of the present invention is based on the use of the principles of anamorphic optics (which may include a refractive element, and possibly also reflective guiding element and/or optical diffractive element) configured to collect radiation from different directions and concentrate the radiation onto a single spatial location. The radiation is generated by a radiation source moving within a known and limited spatial region along known trajectories. The radiation collection system 100 of the present invention is therefore arranged to collect radiation coming from within the solid angle defined by the Sun's movement during the day and during the seasons and concentrate the collected radiation onto the same location, being the projection region 120, irrespective of the sun's position. At the projection region 120, a photo-voltaic cell or waveguide associated with the same can be placed for collecting the solar radiation. The technique of the present invention also provides for realization of an array of such anamorphic optical elements (specially tapered cylindrical cones or cylindrical lens(es)) which couple collected light into planar (and possibly also flexible and/or plastic) waveguides.
Reference is made to
Such cylindrical tapered lens 110 enables to concentrate light collected with a large solid angle of collection to the elongated planar region 120 which extends along an axis parallel to the primary axis PA of the cylindrical lens 110. The projection region 120 serves as a receiver aperture, namely an input aperture of one or more receiving elements (planar waveguides or photo-voltaic cells), or an input optical window of one or more volume/cavities to be illuminated.
As shown in the present example, the system 100 is associated with three waveguides, generally at 150, having a common receiver aperture at the projection region 120. Projection region 120 is positioned with respect to (e.g. at a facet of) the cylindrical tapered lens 110 such that light incident on the light collection surface 114 from a desired first range of angles (e.g. a range of 45 degrees) is concentrated and projected onto the projection region 120. In the present example, each of the three waveguides is optically coupled to the receiver aperture and is configured to collect light from a different part of the first angular range (e.g. each waveguide is collecting light from an angular range of 15 degrees).
Thus, the taper (lens) 110 is exposed to external radiation by its light collection surface 114 and couples the collected radiation into one or more waveguides 150 which may be flexible and/or planar waveguides. The waveguides 150 transport the collected and concentrated light to one or more locations, where for example light converters (such as a photo-voltaic cell) are placed. Alternatively or additionally, the waveguides transport the collected light to an object/region to be illuminated. Thus, the waveguides 150 having the common receiver aperture are arranged for guiding light components passing therethrough along different paths to spatially separated receiving locations.
The system 100 may include a spectral splitter 140. In some embodiments of the invention, the spectral splitter is located upstream of or integral with the light collection surface 114 so as to be in the vicinity of the effective aperture of the system 112. As exemplified in the figure, this can be implemented by using a diffraction grating 142 placed on top of the light collection surface 114 of the lens 110 in order to spatially separate different spectral components of the solar radiation. This allows utilizing multiple waveguides 150 optically coupled to the projection region 120 to receive different spectral components and guide them to different locations in which wavelength specific PV cells may be accommodated for providing higher conversion efficiency.
The cylindrical optics 110 may be configured such that the primary axis is arranged along the main axis (trajectory) of movement of the light source. This provides that the movement of the light source does not change the position (120) of the light projection region of said optics in space, and therefore does not reduce the coupling of light into waveguide(s) which may be located at the projection region 120 of the system 100. One or more (flexible) waveguides are arranged such that the input facet of the waveguide is located at the projection region 120 to which the light is concentrated and the waveguides can thus transport the received light to remote locations.
The use of plurality of flexible waveguides 150 in the present invention might also be advantageous enabling the system to be modular. By proper arranging the waveguides, almost any configuration of collecting optics and photo-voltaic cells' array (i.e. physical dimensions thereof) can be matched or adjusted. In addition, the system is tolerant to the distance or to the location of the optics with respect to remote photo-voltaic cells array (e.g. the optics can be located on the building's roof while the associated photo-voltaic cells with their electronics may be in the basement).
The use of waveguides 150 allows efficient conservation of the law of brightness (conversion between area and angular span). Optionally, according to some embodiments of the present invention, the waveguides are narrowed at their distal edge by which they are connected to the photo-voltaic cell. This provides that the overall area of the receiver aperture (e.g. by which the waveguides are connected to the anamorphic optical element) is reduced while its numerical aperture is increased to almost 180 degrees (which is the angular span at which the optics can collect radiation). This provides for utilizing the optical waveguides to perform the desired conversion between area and angular span or vice versa.
It should be noted that the waveguides are not necessarily narrowed at their distal edge. In case the waveguides are not narrowed, they can still be arranged in space such that the overall angular span of all the waveguides having a common receiver aperture will reach 180 degrees. In this case, the waveguides configuration may be such that the surface area of the photo-voltaic cell collecting the energy from all the waveguides is smaller than their overall area. For example, this can be achieved when the waveguides illuminating the photo-voltaic cell extend along circumference of a sphere and all of them are directed by their distal ends towards the center of the sphere where the PV cell is located.
Reference is now made to
For example, four waveguides can be coupled to the same tapered cylindrical lens 110 at its receiver aperture and guide the collected light to the same photo-voltaic cell. Each one of these four waveguides would collect light in different segment of the 12 degrees angle out of the 45 degrees angular segment of the movement of the Sun along the summer-winter axis. Thus, when the position of the Sun is varied due to seasonal changes, each time a different waveguide 150 is mainly involved in carrying the collected and concentrated radiation from the same tapered lens 110 to the same photo-voltaic cell.
As indicated above, the invention preferably also utilizes spectral splitting of the collected radiation. Turning back to
According to some embodiments of the invention, spectral splitting is implemented based on a diffractive structure extending along the waveguide (e.g. along its cladding).
It can be seen from the figure that although some mixing of spectral bands still exists, a significant spatial separation between the releasing of red R, green G and blue B wavelengths is obtained. When light, while propagating through the waveguide via the effect of total internal reflection, interacts with the diffractive structure, the condition of total internal reflection becomes destroyed for some wavelengths while being kept for the other(s). As a result, different wavelengths escape at different positions along the waveguide.
According to this embodiment, multiple photo-voltaic cells which are optimized for different spectral ranges are arranged in a spaced-apart fashion at the corresponding different locations along the waveguides at which they are exposed to light components of corresponding wavelengths. This technique provides that the differently spectrally optimized PV cells may be arranged along the same waveguide. Differently from spectral splitting configuration described with respect to
Reference is made to
As shown in
It should be noted that according to the invention prismatic structure illustrated in
Different configurations of the prismatic structure according to an embodiment of the present invention are shown is
The light collector 100A is configured generally similarly to that of
Three-stage light concentration configurations are exemplified in
It should be noted that light conversion system for converting the light to electric power can be located adjacent to the light collection/concentration system of the invention or in remote location. For example, light may be collected from the projection region 120 of the above described prismatic configurations by one or more waveguides and transported thereby to photo-voltaic cell(s) located at some distance from the collection system. Light may also be directly coupled into photo-voltaic cell(s) located near/at the projection region 120.
Reference is now made to
When utilizing cylindrical optics 51 having a fully circular cross-section, the concentration system 50 is insensitive to the position of the Sun (light source), and the concentration factor corresponds only to the square of the refraction index of the material from which the optics cylindrical 51 is made (as is evident from eq. 1). The system 50 can thus be used with a cylindrically structured PV cell which has significant sealing advantages. The system 50 can collect radiation emerging from any possible position of the Sun. A simulations of light rays R1 and R2 originated at different locations (different successive positions of the Sun) and collected by the optics 51 is shown is the figure.
Reference is now made to
Referring now to
Mathematically, denoting the angle along the “summer-winter” axis/trajectory by θS-W, and the angle in the “day-night” axis/trajectory by θD-N, the area reduction Aη (for “day-night” range of 110 degrees) is given by:
and the energy that is being added due to the diffused light equals to:
The combination of these effects provides for an increase in the efficiency of light collection achievable with the system of the present invention.
Thus, the invention provides a simple and effective solution for passive light collection and concentration system. As indicated above, the system defined a receiver aperture where concentrated light can be coupled directly to one or more receiving locations/receiver elements, or via one or more waveguides. In the latter case, the waveguide may be planar and/or flexible thus facilitating connection between remotely located receiver aperture (collector and concentrator) and receiving location/element, also the waveguide may be desirably inexpensive, e.g. plastic waveguide.
Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope defined in and by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2010/000718 | 8/31/2010 | WO | 00 | 2/28/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61272199 | Aug 2009 | US | |
| 61282268 | Jan 2010 | US |
