Tracking Concentrator Employing Inverted Off-Axis Optics and Method
Solar concentrators are arranged in an array to define an input aperture such that the solar collector is positionable to face the input aperture of the concentrators skyward. An input axis of rotation extends through the aperture in the skyward direction, and a focus region is smaller than the aperture. Each concentrator includes at least one optical arrangement that is supported for rotation about the input axis for tracking the sun within a predetermined range of positions of the sun using no more than the rotation of the optical arrangement around the input axis. An optical concentrator is described in which a receiving direction extends at an acute angle from an optical axis and in one azimuthal direction outward from the optical axis such that a component of the concentrator is rotatable about the optical axis for alignment to receive input light. A previously unknown inverted off-axis lens is described.
The present application claims priority from U.S. Provisional Patent Application Ser. No. 61/080,554 filed on Jul. 14, 2008, entitled Tracking Concentrator Employing Inverted Off-Axis Optics, which is incorporated herein by reference in its entirety.
BACKGROUNDThe present invention is generally related to collecting and concentrating solar energy and, more particularly, to apparatus and methods for receiving and concentrating light, for example sunlight, for subsequent use as some form of power.
Applicants recognize that in the field of solar energy that one of the greatest challenges to overcome is the diffuse or low density nature of the energy from the sun. Roughly, on the Earth's surface, each kilowatt of energy from the sun is spread over 1 square meter of area. Currently, the most common solar technologies use the sunlight directly to convert the incoming solar radiation into heat or electricity. At an energy density of only 1 kilowatt/m2, (100 milliwatts/cm2), the energy converter often must cover large areas in order to gather and convert a significant amount of energy. Applicants appreciate that the cost of covering a large area with a traditional energy converter can be prohibitive. For example, traditional photovoltaic panels often utilize large areas of expensive semiconductor materials, and solar-thermal converters often utilize large areas of costly metals. In each of these examples, high costs may often render such installations as impractical at least from the standpoint of cost.
One approach to address this problem includes the use of solar concentrators to allow a designer to leverage the energy converter material through the use of relatively low cost reflective or refractive material for focusing solar power to be received by the converter in a more concentrated form as compared to traditional non-concentrating solar collectors. The use of concentrators may reduce the amount of expensive converter material needed in a given application.
It is noted that concentrators may be constructed using refractive material. For example, a Fresnel lens may be used to reduce the amount of material required. A description of Fresnel lenses may be found in “Nonimaging Fresnel Lenses: Design and Performance of Solar Concentrators” by Ralf Leutz and Akio Suzuki; published by Springer and which is incorporated by reference.
Attention is now turned to
As will be described at appropriate points hereinafter, Applicants recognize that while conventional concentrators in some cases may be advantageous from a cost standpoint, at least as compared with systems utilizing non-concentrating collectors, they are not entirely without problems. In some applications, the use of concentrating collectors may introduce specific challenges that are unique to concentrating systems. In other some cases the use of concentration may at least exacerbate problems and/or challenges that may be associated with conventional non-concentrating solar collectors such as PV cells.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of ordinary skill in the art upon a reading of the specification and a study of the drawings.
SUMMARYThe following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools, and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above described problems have been reduced or eliminated, while other embodiments are directed to other improvements.
In general, a solar collector is described. In one embodiment, one or more solar concentrators are arranged in an array such that each of the concentrators is in a fixed position in the array. Each of the concentrators is configured to define (i) an input aperture having an input area such that the solar collector is positionable to face the input aperture of each concentrator in a skyward direction such that the input aperture is oriented to receive sunlight from the sun, (ii) an input axis of rotation that extends through the aperture in the skyward direction, and (iii) a focus region that is substantially smaller than the aperture area. Each of the concentrators includes an optical assembly having at least one optical arrangement that is supported for rotation about the input axis for tracking the sun within a predetermined range of positions of the sun using no more than the rotation of the optical arrangement around the input axis such that the rotation does not change the direction of the aperture from the skyward direction. Furthermore, for any specific one of the positions within the predetermined range of positions, the optical arrangement is rotatably oriented, as at least part of the tracking, at a corresponding rotational orientation as at least part of concentrating the received sunlight within the focus region, for subsequent collection and use as solar energy.
In one feature, the optical arrangement serves as an input arrangement for initially receiving the sunlight, and the optical assembly includes an additional optical arrangement following the input arrangement. The additional arrangement is positioned to accept the sunlight from the input arrangement and is configured for rotation about an additional axis of rotation. The input arrangement and the additional arrangement are configured to cooperate with one another in performing the tracking based at least in part on a predetermined relationship between (i) the rotation of the input arrangement about the input axis of rotation and (ii) rotation of the additional arrangement about the additional axis of rotation to focus the received sunlight into the focus region.
In another feature, the input optical arrangement is configured for bending the received sunlight for acceptance by the additional optical arrangement, and the additional optical arrangement is configured for accepting and redirecting the bent light to cause the focusing.
In one embodiment of an optical concentrator, an optical assembly includes one or more optical arrangements. One of the optical arrangements is an input optical arrangement, and the optical assembly is configured for defining (i) an input aperture having an input area for receiving a plurality of input light rays, (ii) an optical axis passing through a central region within the input aperture, (iii) a focus region having a surface area that is substantially smaller than the input area and is located at an output position along the optical axis offset from the input aperture such that the optical axis passes through the focus region, and (iv) a receiving direction defined as a vector that is characterized by a predetermined acute receiving angle with respect to the optical axis such that the optical axis and the receiving direction define a plane. The receiving direction extends in one azimuthal direction outward from the optical axis in the plane such that at least the input arrangement is rotatable about the optical axis for alignment of the receiving direction to receive a plurality of input light rays that are each at least approximately antiparallel with the vector. The optical assembly is further configured for focusing the plurality of input light rays to converge toward the optical axis until reaching the focus region such that the input light is concentrated at the focus region.
In one feature, the focus region includes a given area and, for at least some of the input light that is characterized by at least a particular amount of misalignment with the receiving direction, that input light is rejected by falling outside of the given area of the focus region.
In an additional feature, the optical assembly includes an additional optical arrangement following the input arrangement, and the input arrangement is configured for bending the received light rays for acceptance by the additional arrangement. In one implementation, the additional arrangement can be a CPC configured to accept the light rays from the input arrangement, and the CPC is configured to cause the focusing. In another implementation, the additional arrangement can be an IOA configured to accept the light rays from the input arrangement, and the IOA is configured to cause the focusing.
In one aspect, an inverted off axis lens includes an optical arrangement having an at least generally planar configuration defining (i) a planar input surface having an input surface area and (ii) an axis of rotation that is at least generally perpendicular thereto. The optical arrangement is configured for defining an acceptance direction as a vector that is characterized by a predetermined acute acceptance angle with respect to the axis of rotation such that the axis of rotation and the acceptance direction define a plane. The acceptance direction extends in one fixed azimuthal direction outward from the axis of rotation in the plane such that the optical arrangement is rotatable about the axis for alignment of the acceptance direction to accept a plurality of input light rays that are each at least approximately antiparallel with the vector. The inverted off axis lens is further configured for transmissively passing the plurality of input light rays through the optical arrangement while focusing the plurality of input light rays to converge toward one another until reaching a focus region that is substantially smaller than the input surface area such that the input light is concentrated at the focus region.
In one embodiment of a solar concentrator, the solar concentrator includes the inverted off axis lens arranged in a series relationship following an input optical arrangement with the input surface of the off axis lens facing towards the input arrangement. The inverted off axis lens and the input arrangement are each configured for selective rotation to cooperate with one another such that the input arrangement initially receives the incoming light rays and bends the incoming light rays to produce intermediate light rays for acceptance by the inverted off-axis lens such that the intermediate light rays are at least approximately oriented antiparallel to the acceptance direction. The inverted off axis lens is aligned for accepting the intermediate light rays such that the intermediate light rays serve as the input light rays for the inverted off axis lens and the inverted off axis lens concentrates the intermediate light rays at the focus region of the inverted off-axis lens.
In one embodiment, the inverted off axis lens is a multi-element inverted off-axis optical assembly including an optical assembly having two or more optical arrangements. One of the optical arrangements is a first arrangement that defines (i) an input aperture having an input area and (ii) an axis of rotation that is at least generally perpendicular thereto. The optical arrangements are configured to cooperate with one another for defining an acceptance direction as a vector that is characterized by a predetermined acute acceptance angle with respect to the axis of rotation such that the axis of rotation and the acceptance direction define a plane. The acceptance direction extends in one azimuthal direction outward from the axis of rotation in the plane, and at least the first arrangement is supported for motion that is limited to rotation about the axis of rotation for alignment of the acceptance direction to accept the plurality of input light rays that are each at least approximately anti parallel with the vector. The optical arrangements are further configured for focusing the plurality of input light rays to converge toward one another until reaching a focus region that is substantially smaller than the input surface area such that the input light is concentrated at the focus region.
In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions.
Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be illustrative rather than limiting.
The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles taught herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features described herein including modifications and equivalents, as defined within the scope of the appended claims. It is noted that the drawings are not to scale and are diagrammatic in nature in a way that is thought to best illustrate features of interest. Descriptive terminology, such as, for example, upper/lower, right/left, clockwise and counter-clockwise and the like may be adopted for purposes of enhancing the reader's understanding, with respect to the various views provided in the figures, and is in no way intended to be limiting.
As described previously in the background section, Applicants recognize that while conventional concentrators in some cases may be advantageous from a cost standpoint, at least as compared with systems utilizing non-concentrating collectors, conventional concentrators are not entirely without problems. In some cases the use of concentrators can exacerbate problems and/or challenges that may be associated with conventional non-concentrating solar collectors such as PV cells. For example, in photovoltaic panels, the efficiency of the PV cells generally decreases with increasing temperature. While this is a common concern in the design of non-concentrating panels heating is of yet greater concern when concentrators are used to increase the incoming light intensity by 10× or 100× or higher, and under these circumstances management of heat-related factors can become a serious challenge. In other cases, the use of concentrating collectors may introduce specific challenges that are commonly associated with concentrating systems. For example, many concentrators require the light to enter with a certain angular accuracy which may require that the concentrator move in order to “track” in relation to a light source such as the sun. Conventional tracking systems can be both costly and complex, and in some cases the cost of a tracking system may substantially undermine cost savings that may otherwise be enabled by the use of concentration.
Applicants describe hereinafter a number of solar collectors including optical concentrators that advantageously utilize internal rotational motion for tracking the light arriving from a movable source and concentrating the light onto a target such as a receiver. The optical concentrators of the present disclosure cause input light to pass through a series of one or more optical arrangements, and typically at least one of the arrangements is supported for rotation. In several examples described hereinafter, at least one of the rotating optical elements can be configured as an inverted off-axis lens arrangement that is configured for rotation as at least part of allowing and/or causing the system to track a moving light source. For example, this disclosure details a number of solar collectors that utilize solar concentrators that are configured to define a receiving direction that is adjustable, for tracking motion of the sun, based on rotational orientation of one or more optical arrangements so that, as the sun changes position, the concentrated light exiting the system can be made to continuously illuminate the receiver.
Turning now to the figures, wherein like components are designated by like reference numbers whenever practical, attention is now directed to
Each of the optical arrangements of optical concentrator 26 can be configured in a relatively flat, thin and generally planar configuration that may be regarded as being analogous to a that of a Fresnel lens, such that the combination of the two arrangements may be implemented in a correspondingly flat and thin shape. Concentrator 26 defines a receiving direction 34 for receiving the incoming rays of sunlight 14 at an input orientation such that the incoming rays of sunlight are anti-parallel therewith, while the bender and the inverted off axis lens arrangement cooperate with one another such that the optical concentrator receives and concentrates the received light onto focus region 41. The bender arrangement and the inverted off axis lens may be closely spaced such that a substantial portion of the intermediate rays of light leaving the bender arrangement will be accepted and concentrated by the inverted off axis lens arrangement. As will be described in detail at appropriate points hereinafter, the optical arrangements including bender arrangement 33 and inverted off-axis lens arrangement 32 can be rotatably oriented relative to one another and with respect to the incoming rays of sunlight, so that the light exiting the bender arrangement enters the inverted off-axis lens at an angle appropriate to cause the inverted off axis lens to accept and concentrate focus the intermediate light rays such that they converge toward one another until reaching focal region 41. As the direction of the incoming rays of sunlight changes, for example as a result of motion of the sun, the two optical elements 32 and 33 can be rotated for tracking the motion of the sun so that a correctly adjusted rotational relationship between them and relative to the incoming rays of sunlight is maintained for concentrated illumination of the focus region.
The embodiment of concentrator 26 illustrated in
Applicants recognize that in many applications, including a number of solar collection applications, the use of a BRIC in a solar PV panel provides a number of sweeping advantages as compared to conventional solar panels. For example, as described above, a concentrator can be configured such that the focusing and concentrating of incoming rays of sunlight allows for the use of a receiver (such as PV cell) having an area that is substantially smaller than the input area of concentrator. As compared to conventional non-concentrating PV cells, the systems and method for tracking the sun and concentrating sunlight, as described above and hereinafter throughout this application, can be employed for reducing the required surface area of relatively expensive PV cells required for a given application and therefore reduce the cost of a solar collector at least as compared to a conventional panel. Furthermore, the relatively flat and thin shape of a BRIC allows it to be incorporated inside a panel enclosure having a relatively low profile as compared to the profiles typically associated with conventional concentrator systems. This may allow a concentrating solar PV system to be packaged in an enclosure having a shape and size that is based on conventional standards, and solar panels constructed in accordance with this disclosure may be compatible with existing installation infrastructures that have been developed, for example, for the conventional panels including non-concentrating solar PV panels.
With ongoing reference to
It is noted, as will be described in greater detail immediately hereinafter, that the optical properties of inverted off-axis lens 32 differs substantially as compared to the optical properties of conventional off-axis lenses.
Attention is now directed to
It is further noted with reference to
As will be described in detail immediately hereinafter, an inverted off-axis lens defines an optical axis and is configured such that a focal region of the inverted off-axis lens is on the optical axis while the incoming light is entering in an off-axis orientation. In particular, an inverted off-axis lens is configured to accept incoming light at an angle relative to the optical axis. Based on designations presented herein and used throughout the remainder of this application, the use of the term “inverted” refers to an inversion of the functional operation of an inverted off-axis lens as compared with a conventional off-axis lens.
Summarizing with respect to the discussion above, a conventional off-axis lens is configured to accept incoming light that is on-axis while the focal region is generally positioned at an off-axis location. By contrast, an inverted off-axis lens is configured to accept incoming light that is incident at a skewed angle with respect to the optical axis, and the focal region is located on the axis.
It is noted that the term ‘Inverted Off-Axis lens’ may be referred to throughout this overall disclosure and in the appended claims by the acronym ‘IOA’. With respect to this nomenclature, it is further noted that the IOA may be an individual lens, consisting of one optical element, or it may be configured as an optical arrangement having two or more optical elements and/or components.
Resuming the discussion, the focal region of an IOA may be positioned along the optical axis such that the incoming light arrives at an angle and is then bent and focused into focus region 41. As described above, and as will be described in greater detail immediately hereinafter, an IOA may be regarded as performing two optical functions: (i) bending the incoming light to direct the light along the optical axis and towards the focal region, and (ii) focusing the light for convergence onto the focal region.
Attention is now directed to
While certain aspects of the immediately following points are to be discussed in further detail hereinafter, it is to be understood that (i) input rays of light 56 entering the IOA in the direction that is at least approximately anti-parallel to the acceptance direction are directed to the focal region, (ii) the acceptance direction 57 is a physical characteristic of the IOA that is structurally defined by the IOA itself, and (iii) any misaligned input rays of light (not shown), entering the IOA in a substantially misaligned direction that is sufficiently skewed with respect to the acceptance direction, will be redirected by the IOA to diverge away from the optical axis such that they pass outside of the focal region, and increased misalignment will generally result in correspondingly increased divergence of the bent light way from the focus region.
With ongoing reference to
It should be appreciated by a person of ordinary skill in the art, having this overall disclosure in hand, that the presence of a unique acceptance direction, in accordance with the immediately foregoing descriptions, implies that there is at least some kind of rotational asymmetry that should be inherently present in the physical structure and/or material properties of the IOA, and in an absence of this form of asymmetry in the structure of the IOA, it is not reasonably possible for the IOA to define a distinct acceptance vector in a manner consistent with the descriptions herein. For example, in one embodiment that will be described in detail at appropriate points hereinafter, the IOA may include prisms that are integrally formed therewith, and the prisms may be oriented in parallel with one another along a reference direction (not show in
While acceptance direction 57 (represented in
It is further noted that the projection 64 (designated in
There are two conditions that can be met in order for input rays 56 to be aligned anti-parallel with acceptance vector 57 thereby causing the IOA to accept the input rays of light for bending and concentrating onto focus region 41, and these two conditions may at times be designated hereinafter and throughout this disclosure according to the following shorthand notation: (i) the IOA is rotatably oriented to be pointed towards the input rays of light, and (ii) the input rays of light enter the IOA at the zenith angle ξ of the IOA. Foreshortening the terminology yet further, for use in subsequent descriptions, input rays of light 56 and IOA 32 may be regarded as being “aligned with one another” at times when these conditions are met, and hereinafter throughout this disclosure a statement that the IOA and the input rays of light are aligned with one another is to be interpreted as stating that these two conditions have been met at least to a reasonable approximation. For purposes of further clarification, it is noted that a statement that the IOA is pointed towards the input rays of light, is only to be interpreted as stating that the first of the two conditions has been met, and under these circumstances, the IOA and the input rays may or may not be aligned with one another. For purposes of descriptive clarity, two examples resulting in misalignment will be discussed immediately hereinafter.
As a first example (not shown) resulting in misalignment, if the IOA were to be rotated away from the appropriate rotational orientation that is illustrated in
As another example resulting in misalignment, if the IOA in
Attention is now turned to
As described above in reference to
As described above in reference to
Attention is now directed to
As described above, concentrator 80 is configured such that rotation of the IOA lens about axis 47 rotates acceptance direction 57 thereby pointing the IOA in varying directions.
During the morning the solar concentrator will function properly only at a particular time of the morning when the morning sun is at a position 86 such that the rays of sunlight 14 are aligned anti-parallel with acceptance direction 57, at which time IOA 32 bends and focuses the rays sunlight toward focal region 41. At other times during the morning, the IOA can be pointed towards the incoming rays of sunlight, but the incoming rays of sunlight at these other times nevertheless do not enter the IOA at the zenith angle ξ of the IOA, and therefore the IOA is misaligned with respect to the incoming rays of sunlight.
Similarly, during the afternoon, the solar concentrator will function properly only at a particular time of the afternoon when the afternoon sun is at a position 86′ such that the incoming rays of sunlight 14 are aligned anti-parallel with acceptance direction 57, at which time IOA 51 bends and focuses the rays sunlight toward focal region 41. At other times during the afternoon, the IOA can be pointed towards the incoming rays of sunlight, but the incoming rays of sunlight at these other times nevertheless do not enter the IAO at the zenith angle ξ of the IOA.
It is noted that single IOA tracker 80 can be used successfully, for continuously tracking the sun throughout a substantial portion of the day, only when utilized with an additional 1- or 2-axis tracking system. One example of such an arrangement, to be described in detail in a subsequent portion of this disclosure, is a solar panel enclosure supporting an array of one or more single-IOA trackers 80 (each tracker has one single IOA) each of which trackers is attached to an external mechanical tracker mechanism. In many conventional applications, a mechanical tracker mechanism may be configured to move a conventional solar panel for continuously pointing the panel such that the panel faces directly towards the sun. In the arrangement under discussion, having an array of single-IOA concentrators, a mechanical tracker may be configured for facing the panel toward the sun within a predetermined tolerance based on the bend angle of the IOA, and the IOA can be rotated to correct for any mechanical misalignment associated with the mechanical tracker.
Having described the basic operating principles of an IOA, and having illustrated the use of a single-IOA solar concentrator having only limited tracking abilities, the description is now directed to optical properties and operating principles relating to an optical arrangement that is configured as a bender. It is first noted that a bender may be considered as being perhaps somewhat analogous to an IOA to the extent that a bender shares certain characteristics that are at least loosely analogous with associated characteristics of an IOA. For example, as one analogous characteristic, a bender receives incoming rays of light and redirects the incoming rays by bending the rays through a given angle and in a given direction with respect the bender and relative to the incoming rays, such that the bender redirects the incoming rays of light in a way that changes depending on the rotational orientation of the bender relative to an orientation of the incoming rays of light. It is noted however that a bender is not configured to cause any focusing of the incoming rays of light. Hence the name “bender”. In this regard, a bender may perhaps be considered as somewhat analogous to a limited special case of a uniquely specified IOA-like device that has an infinite focal length. While this consideration is regarded by Applicants as being more or less a curiosity, the analogy may be nevertheless useful for illustrative and descriptive purposes at least for helping to establish consistent terminology for distinguishing benders from IOA's while putting forth various descriptions relating to cooperation between these two distinct classes of arrangements.
Having introduced a number of general considerations relating to benders, attention is now directed to
It is noted, as described immediately above, that the parallel relationship between the incoming rays of light is maintained during the bending, regardless of the rotational orientation of the bender, at least in part because (i) the incoming rays of light are all parallel with one another, and (ii) the incoming rays of light are all bent in the same way.
It will be appreciated by one of ordinary skill in the art that while the bender may be configured to have a rotationally symmetric overall shape, such as a circular shape as depicted in
As described immediately above, Bender 33 is configured to exhibit different bending performance depending on the orientation of the bender with respect to the incoming rays of light. In this regard, it is useful to establish a bender direction 93 as a reference direction that can be associated with the bender as illustrated in
Since bender direction 93 remains fixed with respect to the bender, it is clear that any rotation of the bender results in a corresponding change of direction of bender direction 93, as illustrated in
Attention is now directed to
In a first orientation wherein the bender is rotated about optical axis 47 so that the bender direction 93 points away from the incoming light, as illustrated in
In a second orientation of the bender wherein the bender is rotatatably oriented about axis 47 such that bender direction 93′ points toward the incoming light, as illustrated in
In a third orientation the bender is rotated by ninety degrees with respect to both of the first and second orientations such that the bender direction (not shown) points out of the plane defined by the figure. With this orientation of the bender the incoming ray of light 14 is redirected to produce an output ray of light 92″ that is bent by a bending angle 104″, between output ray 92″ and axis 105, also having the same angular value as angle 104 but corresponding to a different orientation as compared to both of output rays 92 and 92″. It is noted that magnitudes of the bending angles 104, 104′ and 104″ all have the value β corresponding to the bending angle of the bender.
In a manner that is consistent with the foregoing three examples, rotation of the bender whilst maintaining incoming ray 14 in a fixed direction as illustrated in
With ongoing reference to
Having initially introduced concentrator 26 with reference to
Referring again to
Based on the forgoing descriptions in conjunction with the disclosure taken as a whole, it may be appreciated that for a bender-IOA combination to serve as a concentrator for properly tracking the sun over a predetermined range of positions, such as, for example, a given range of positions corresponding with apparent motion of the sun throughout a given day, the aforementioned cooperation, between a bender arrangement and the IOA, can be reasonably achieved provided that the bender and the IOA are configured at least generally in accordance with the criterion that follow below.
Based in part on the descriptions relating to
It is to be understood that in the context of concentrator 26, output ray 92 of
Considering now
Attention is now turned to
It is noted that as the sun changes position, the orientation of the incoming rays of sunlight changes and therefore the exit cone of the bender shifts and/or changes correspondingly, and the optical source can be tracked during these changes only for as long as the line of intersection is actually present between the two cones, and the tracking is achieved by adjusting the rotational orientations of the bender-IOA combination such that they cooperate with one another for receiving and concentrating the incoming rays of sunlight in the manner set forth above with reference to
For further explanatory purposes, one example illustrative of a special case in which the relationships between various parameters are somewhat simplified as compared to more general cases will now be described. For simplicity, it will be assumed that for a given bender-IOA combination, all focus action is performed by the IOA, and that the bender serves only to bend the light by a particular bending angle β. For additional simplicity, it will be assumed in this example that the bending angle β is equal to the zenith angle ξ defined by the IOA.
Attention is now directed to
Bender 33 and an IOA 32 are configured for rotation around optical axis 47. Furthermore, in the example at hand, the bender and the IOA are specifically matched with one another such that the IOA is configured with an acceptance direction (fixed with respect to the IOA) characterized in part by a acceptance angle ξ (the zenith angle of the acceptance direction relative to the optical axis) having a value equal to the bending angle β of the bender such that ξ=β. Furthermore, the incoming rays of light 14 lie in the bisecting plane and are oriented to enter the system at a receiving angle 2·β, (twice the IOA zenith angle β), relative to the optical axis 47. It is noted that for purposes of illustrative clarity the description with reference to
Bender 33 is configured, based on a particular design configuration that will be presented in detail hereinafter, such that the bending angle may be at least approximately constant regardless of the angle of the arriving light rays. The bender is rotatably oriented to be pointed towards the incoming light such that bender direction 93 of the bender lies in the bisecting plane and the bender receives the incoming rays of sunlight and bends these rays by a bending angle β having a magnitude equal to the zenith angle ξ of IOA 91 thereby producing intermediate rays of light 39 that lie in the bisecting plane and which are tilted with respect to the optical axis by angle β to match the zenith angle (ξ=β for the example at hand) defined by IOA 32.
IOA 32 is positioned and rotatably oriented such that the acceptance direction 57 (represented by vector {right arrow over (A)}) lies in the bisecting plane and is anti-parallel with respect to the intermediate rays of light such that the IOA bends and focuses the intermediate rays of light for concentration at a focal region 41 of the IOA. While the foregoing description with respect to
incoming rays of light that lie in the bisecting plane, it is noted that in view of the disclosure as a whole, based on the operating principles set forth previously with respect to benders and IOA's, a person of ordinary skill in the art will recognize that a plurality of incoming light rays that are each oriented parallel with respect to this particular set of light rays will also be received and focused by concentrator 109 such that they are directed through focus region 41.
Having described the operation of optical concentrator 109 with respect to a particular orientation of incoming rays of light 14, it is to be understood that concentrator 109 may be utilized for receiving and concentrating other rays of light (not shown) that are oriented at different angles. For example, in a case where incoming rays of light 14 are oriented with the entrance angle having a different value that is substantially smaller than 2·β, then one or both of the bender and the IOA will need to be rotated to different orientations in order that they cooperate with one another to bend and focus the incoming rays of light in a manner that is consistent with the operating principles described with reference to
For example, with respect to the embodiment of
With ongoing reference to
The following discussion describes a number of aspects related to determination of the correct orientations for the two IOAs to align the optical system to a given optical source. This discussion again assumes that bend angle 104 of the bender is not a function of input angle or direction, and that bend angle 104 has a value that is equal to the azimuthal angle ξ associated with the acceptance direction of the IOA such that ξ=β. As will be described immediately hereinafter, the operation of a bender may be described mathematically by decomposing a vector representing the incoming ray into three components, as based on a number of definitions that will be described immediately hereinafter.
Attention is now turned to
The directional orientation of incoming ray of light 14 can be represented by a unit input vector 103 (of unit length) pointing in the direction of the incoming ray 14, and based upon the immediately foregoing definitions unit input vector 103 may be mathematically decomposed, in accordance with the aforementioned established conventions, for representation as a 3-vector r including u, v, and z components 126′, 127′ and 128′, respectively, with values ru, rv, and rz, with each value corresponding to an associated projection of vector 103 onto the u-axis, the v-axis, and the z-axis. While 3-vector r is graphically depicted as pointing in opposition to incoming ray of light 14, it is to be understood that this is to be considered as an arbitrary convention defined for purposes of convenience, and that the 3-vector r, defined in this manner, corresponds with the orientation of incoming ray of light 14, and is not intended as corresponding with the direction of the incoming ray of light. In the equations that follow, all orientations will be mathematically represented based on this convention, and will be physically interpreted accordingly. It is further noted that while the bender itself may attenuate the light to some extent, the description at hand relates only to the bending of the light and not to attenuation and/or other modifications. In this regard, it will be appreciated by a person of ordinary skill in the art that that “normalized” vectors (of unit length) are appropriate for use as input as well as output vectors at least insofar as their use is restricted to descriptions relating to the bending, and not to attenuation and/or other modifications to the light. Thus, any incoming ray 103 can be mathematically represented using Cartesian coordinates as 3-vector r (having unit length) that is decomposed into u, v, and z components as follows:
Analytic geometry may be utilized in conjunction with trigonometry and linear algebra in order to mathematically model the effect of passing a ray through the bender. For example, with the incoming ray entering the bender being represented by the 3-vector r of Eq. 1, the orientation of resulting output ray may be described by the 3-vector s, (also having unit length) utilizing the aforedescribed coordinates, as:
The 3-vector s is a unit vector that merely describes the orientation of output ray 93, and is not to be interpreted as representing the physical ray itself. In particular, 3-vector s of Equation 2 corresponds with the orientation of the output ray of light, but is not intended for correspondence with the direction of the output ray of light. A person of ordinary skill in the art will readily appreciate that the foregoing matrix equation implies the v-axis component remains unchanged during the bending such that sv=rv, and therefore the bending action of the IOA may be regarded as being restricted to lie within the u-z plane. Furthermore, in view of this recognition and based on the foregoing mathematical description, it can be appreciated that the U axis corresponds with bender direction 93 in accordance with previous descriptions in reference to
While the bending action may be calculated in Cartesian coordinates in accordance with the foregoing descriptions, a person of ordinary skill in the art will readily appreciate that the performance of the system may also be characterized based on other systems of coordinates, even while the above mathematical technique may be utilized, provided that the appropriate conversions between coordinate systems are properly executed and are performed at an appropriate step of any given overall determination. For example, an orientation of the incoming ray of light 14 may be characterized using a first angle φin (relative to the optical axis) and a second angle δ (relative to the v-axis), as illustrated in
It will be further appreciated by a person of ordinary skill in the art, that these calculations may also be performed as numerical computations by utilizing well known analytical optics techniques. For example, in many cases ray tracing may be employed for simulating the operation of a specific bender, IOA and/or combination thereof.
Based on the analytical techniques described above, in conjunction with well established techniques associated with physical optics, and in view of this disclosure as a whole, a person of ordinary skill in the art will appreciate that a special case of a concentrator 109 described with reference to
In the foregoing discussions, the term ‘focal region’ rather than ‘focal point’ has been used to describe the location of concentration of light rays from a lens. This distinction has been made since the term ‘focal point’ applies to a more traditional imaging optics where collimated light focuses to a point. Instead of being designed with techniques restricted to imaging optics, an IOA can be constructed using analogous methods (such as non-imaging Fresnel concentrating lens techniques), wherein the light rays are directed into a focus region and never converge to a point. One approach to accomplishing this is to directly incorporate a non-imaging Fresnel concentrating lens as part of an optical IOA arrangement. Another general approach is to employ non-imaging optical principles in the design of the IOA. It is noted that a good source on the design of non-imaging lenses can be found in Nonimaging Fresnel Lenses: Design and Performance of Solar Collectors by Leutz and Suzuki, which is incorporated herein by reference. By employing non-imaging optical techniques in the design of an IOA, it is possible to increase the range of directions about the acceptance direction wherein light entering the IOA will still be concentrated and directed into the focus region. In other words, it is possible to exploit the nature of a non-imaging IOA in order to decrease sensitivity to misalignment of the incoming rays of light, such that within a predetermined range of misalignment, the incoming rays of light are nevertheless received and concentrated into the focal region.
As described in the reference by Leutz and Suzuki referred to above, the design of a non-imaging lens involves processing the boundary of the input aperture of the lens and designing the optics so that an input ray of light that is misaligned will still be directed into a particular region. The Leutz and Suzuki references consider only the magnitude of misalignment and thus the range of allowable misalignment is circularly symmetric. Applicants recognize that this is not a requirement, and that by configuring an optical arrangement such that misalignment design values are a function of the direction of the incoming ray, non-imaging optical arrangements can be created that have an asymmetric range of allowable input rays. Applicants further recognize that by utilizing these principles, an IOA can be designed so that the incoming ray distribution can be more oval shaped, which can have the advantage that the sun's path traverses the long axis of the oval, thus requiring less frequent or less accurate movement to track the sun.
For a concentrator comprising a given combination of optical arrangements the design of a given concentrator acceptance range may in many cases be complex, the required analytical techniques are believed to be well described in the Luetz reference, and applicants believe that a person of ordinary skill in the art having this disclosure in hand, will be readily able to implement a number of embodiments based on the descriptions herein. Introducing foreshortened terminology for describing the functioning of a concentrator such as concentrator 26, and variations thereof, a concentrator may be regarded as defining a concentration ratio based on the area of the focal region and the area on the input aperture defined by the concentrator. Furthermore, a concentrator that is configured with a given concentration ratio generally will receive and concentrate rays that are within a given range of misalignment angles. This range of misalignment angles can be considered as defining a “field of view” of the concentrator defined herein as a range of positions of the sun in the sky from which light may be received and concentrated without employing any tracking motion, rotational or otherwise. For example, the field of view of concentrator 26 is that range of positions of the sun in the sky for which concentrator 26 is capable of receiving and concentrating light without performing any rotational adjustments. It is to be understood that the field of view as described above does not account for the question of whether the sun ever actually occupies all the positions in the field of view, and that it is possible to configure a solar concentrator to exhibit a field of view that includes vacant positions that the sun never actually occupies, regardless of the time of day or the time of year. Applicants are aware that even non-imaging optical systems tend to be governed by the well known and fundamental principles of optics that impose theoretical limits with respect to field of view of imaging and non-imaging systems alike. In this regard, a concentrator system having a wide field of view that includes a wide range of vacant positions in the sky may be perhaps be considered as wasting at least a portion of the field of view. Applicants recognize that a wide-field system having circular symmetry may be inherently wasteful in this respect since the sun tends to follow an at least somewhat linear trajectory, and that such a system may be modified to change the shape of the field of view to another shape that more closely matches a given path of the sun in the sky, to account for daily and/or seasonal variation of the position of the sun in the sky.
Concentrators function by taking the light from a given area and focusing the light to a smaller area. A symmetrical circular 10× concentrator may receive sunlight through a circular aperture defined by the concentrator, and may concentrate the received sunlight by bending and focusing the light to a focus region that is 1/10th as large as the input aperture. A solar energy application represents a special case where the light source is continuously moving but the path of the light source is known. These applications typically employ concentrators that take the sun's energy from a near circular area and concentrate it to a smaller circular or square area. This requires that the optics track the sun throughout the day. The greater the concentration, the closer the input light area is to the size of the sun in the sky and therefore the more stringent the tracking requirements. In applications of low concentration, the tracking can be more tolerant since the sun can move through the larger field of view before adjustment of tracking is required.
Attention is now turned to
With ongoing reference to
Attention is now directed to
For example, by modifying a concentrator to provide a field of view that is stretched to match the path of the sun (or other predictable light source) in the manner described immediately above, the need to reposition can be reduced. For example, if IOA 32 of concentrator 26 is modified for producing a field of view having a stretched shape similar to the field of view of
It is to be appreciated that the method of tracking disclosed herein provides a number of remarkable advantages as compared with traditional concentrator systems and associated methods. Perhaps the most significant advantages stem from the simplicity of the drive mechanisms needed to implement this technology. For example, in the context of concentrator 26, a tracking concentrator system, for example including a bender and an IOA, can utilize two sets of moving parts that are independent of one another such that moving the IOA does not move the bender, and vice versa. Furthermore, as described previously in reference to
Applicants recognize that there are yet further advantage associated with configurations that rely solely on rotation for tracking the sun. At least with regard to mechanical considerations, it is noted that rotation is often easier to accomplish than translation, and can therefore be achieved at lower cost. In addition, moving mechanical components that rotate are capable of being balanced. For example, at least with respect to embodiments that are configured such that the rotating optical arrangements (benders and/or IOAs) are inherently balanced, the system may be arranged such that the only torque required by the tracking actuators is the torque required for acceleration and overcoming friction. If the optical tracking application is fairly slow, as it generally is in solar applications, then the torque requirements become minimal. This further reduces the size, complexity, and cost of the implementation.
Applicants further recognize that it may be advantageous to modify a low cost conventional concentrator, at least with the addition of an IOA, in order to improve tracking performance while relaxing certain requirements with respect to the associated tracking mechanism. A person of ordinary skill in the art, having this disclosure in hand, may identify a concentrating system with a simple low cost tracking mechanism, and may then improve the system at least by addition of an IOA such that the modified system includes a fine adjustment, in part resulting from the use of the IOA for improving tracking performance.
Another class of advantages of the IOA-based optical trackers is that the target of the optical system need not move. For example, in an IOA tracking solar photovoltaic (PV) concentrator, the target of the concentrated light, the PV cell, does not move as the system tracks. A stationary optical path is clearly easier, and therefore less expensive, to implement. Additionally, in the solar concentrator example, the stationary PV cell can eliminate the need for moving the conductors that carry the power away from the cell and can significantly simplify the removal of excess heat from the target.
As described in greater detail hereinafter, a solar collector may be configured that utilizes an array of one or more concentrators to redirect and focus the sun's rays on receivers that are configured for absorbing the concentrated light for conversion to a form of power such as electricity or thermal power. Each concentrator may include at least one optical element (IOA or bender) that is supported for rotation as at least part of focusing the sun's rays onto an unmoving target. If more than one optical arrangement (such as an IOA and/or bender) is utilized, then the first optical arrangement to interact with the incoming light may serve as an input arrangement for initially receiving incoming rays of sunlight. In effect, the concentrators act as a solar tracker so that the target, electrical connections and support structure of the assembly need not move and the only moving parts are rotatable optical arrangements in the concentrators, and their associated drive mechanisms and components thereof. Applicants recognize that the panel can be movable (e.g. with an external 1- or 2-axis tracker) and in this case the internal target tracking could be used as a secondary tracker or as an integral part of the whole tracking system. Thus, one approach is to utilize an external mechanical tracker as a coarse (not highly accurate) tracker with an internal BRIC tracker/concentrator acting as a fine tracker utilizing rotation of optical arrangements as described throughout this disclosure. This particular approach may be utilized to relax requirements associated with the external mechanical tracker to allow the tracker to be designed with a lower cost configuration.
Having described the operation of concentrator 26, and having described various details with respect to the operation and characteristics of benders and IOA's. A number of general system level considerations relating to solar concentrators will be presented immediately hereinafter.
One-IOA SystemsOverall concepts relating to two distinct one-IOA designs will be described hereinafter. A first one-IOA embodiment is a 1-dimensional array having one or more IOAs for focusing light onto a linear target. The concentration gain is not as great as compared with a 2-dimensional concentrator (such as concentrator 26). However, Applicants recognize that this first embodiment may provide advantages at least for use with solar-thermal systems where the target may be linear in nature, such as a pipe, though this first embodiment may also be applicable for use with a linear array of PV cells. The IOA itself may include a bender followed by a concentrator. The concentrator may be a 2-dimensional (point-type) concentrator (such as a conventional lens), or a 1-dimensional (line-type) concentrator (such as a cylindrical lens) that is mounted parallel to the 1-dimensional target. Thus, the concentrator may be physically independent of the rotatable IOA, or may be partially combined with the rotatable IOA.
Attention is now directed to
The IOA's are controlled, for example by a drive mechanism (not shown) to rotate and to continuously point towards the incoming rays of sunlight and to direct the exit rays to the target 153. IOA output rays 156 may move up and down the target (left and right in
As one aspect of the operation of concentrator system 150, with the target oriented East-West, then seasonal North-South variation of the sun can be fully corrected. Four examples are worth noting to understand this system. When the sun is in the east with no northern or southern displacement, then the IOA may rotate so that the light is bent toward the target—with no north or south bending since the sun is already on a target-IOA plane. When the sun is in the north and the day and the time are such that sun is positioned along the acceptance direction of the IOA, then the incoming rays of sunlight will bend downward to the target with no east or west component. A similar configuration occurs when the sun is in the south. These last two examples result in the sun's rays entering the target perpendicularly.
Of interest are the cases when the IOA bend angle is less than the sun angle, or when the IOA bend angle is more than the sun angle. In these cases, the sun angle of concern is the angle between the sun's rays and the plane made by the target line-IOA line. With an east-west orientation of the target, the important sun angle is the north-south angle since any east-west angle will not need to be corrected in order for output rays 156 to strike the target, since the sun's rays will be allowed to strike the target with an angle along the target axis (east-west). If the IOA bend angle is less than the sun angle, then the IOA will correct part of the sun's angle, but not all of it and so the rays may strike the target at an angle, but the rays will strike the target at a steeper angle (more perpendicular) than if the IOA were not present. Alternatively, if the IOA bend angle is greater than the sun angle, then the incoming rays of light are focused on the target, but will strike the target at an angle in the opposite direction than if no IOA were present. In fact, there should be a point such that the angle of the sun equals the bend angle and then the rays that fall on the target will be directly below the exit rays from the IOA. For example, if the IOA bend angle is 30 degrees, then the sun's position should be at 30 degrees to have the light rays striking perpendicularly to the target. This 30 degree angle is the total angle made up of the vector sum of the east-west angle and the north-south angle.
As can be seen, the rays will strike the target perpendicularly two times during the day (when the sun is east at the bend angle, and when the sun is west at the bend angle). Thus, if the panel assembly of the IOAs is continuously rotated, then it may be possible for the rays exiting the IOA to strike the target perpendicularly at all times. This in effect becomes a 2-axis tracker with one axis external to the panel that moves the whole panel, and one axis internal to the panel that bends the light to the target. Note: the two axes are not necessarily orthogonal.
IOA with Mechanical Tracker
This second embodiment separates the tracking motion of the panel into two different tracking methods. Traditionally, a solar panel is either fixed (not moving) or is moving so that it is pointed toward the sun—this is generally referred to as “tracking”. (The solar panel has a “direction” which is the perpendicular to the surface of the panel in the direction of the incoming light: thus when the solar panel is pointed toward the sun, the panel is positioned so that the light enters the panel at right angles.) Oftentimes, depending on the configuration of a given solar collector, there may be at least two motivations for tracking the sun: (i) when tracking the sun, the amount of sunlight that enters the panel may be increased as compared to a fixed non-moving panel, and (ii) typical concentrating solar panels often require the sunlight to enter the panel at a constant angle at all times—thus as the sun moves across the sky, the panel can rotate in relation to this movement such that the panel points directly toward the sun. By contrast, a fixed non-moving panel receives less light in the morning and evening due to the shallow angle of the light entering the panel which is commonly called the ‘cosine effect’. This is such a large effect that a number of manufacturers of traditional solar panels presently offer tracking on their panels to recover this lost morning/evening power.
Attention is now directed to
Attention is now turned to
Attention is now directed to
With ongoing reference to
Returning to
If a single optical arrangement (such as a bender or an IOA) can bend the light more than the seasonal variation (+/−23.5°), then the single optical arrangement can correct for the North-South seasonal error while the 1- or 2-axis tracker will correct for the daily sun position. The addition of the optical arrangement allows for the 1- or 2-axis external tracker to be simpler in design and less accurate in its positioning. In the simple case of Spring Equinox when the sun is passing directly over and perpendicular to the panel, at noon, the optical axis of a panel may be tilted east or west (relative to the sun location) by the bend angle so that the input optical arrangements thereon would see the sunlight entering at the bend angle and bend the light so that it is normal to the surface inside the panel and can subsequently be concentrated onto the target. Since the optical arrangement may correct for any light entering at the bend angle and the seasonal variation is less than the bend angle, then there is a panel orientation such that the light will enter the panel at the bend angle so that the optical arrangement can bend the light and concentrate the light onto the target. (Note: at Winter Solstice when the sun is 23.5° below (south) of the normal of the panel, then the 1-axis tracker would point the panel toward the sun direction—in the east-west direction—and the optical arrangement would correct for the low sun entrance angle.) Thus the 1-axis tracker may adjust so that the sun is entering at the angle that is required by the optical arrangement in order to provide the needed corrections with respect to tracking the sun, and a single optical arrangement combined with a 1-axis tracker can be used to orient the sunlight in the panel for use in a solar concentrator. Similarly using an IOA-bender configuration may allow a greater range of sun angle corrections and permit the panel to be oriented perpendicular to the sun without requiring a panel offset to compensate for the IOA bending angle.
As another embodiment of this method, a light bending film could be applied over an entire solar panel that supports a plurality of concentrators, such that light entering all the concentrators in the panel is pre-compensated (or “biased”) with a bend angle. If the panel is mounted so that the seasonal variation is not symmetric, (the winter angle is not equal to the summer angle), then the incoming rays of light could be bent by a fixed angle such that the light in the panel is symmetric with respect to seasonal variation. For example, if the panel is mounted 20° too far northward (e.g. panel tilt of 20° when mounted equatorially), then the seasonal variation will be from 3.5° North to 43.5° South and the optical arrangements (such as benders and/or IOAs) would need to correct for the worst case of 43.5°. If a fixed 20° light bending film is added to the panel, then the light angle may be reduced by 20° resulting in a symmetric north/south variation of +/−23.5°. This simplifies the overall design by reducing the worst case angle correction and balances the system. Note, that due to well known variations of sunlight intensity during the seasons (more intensity during the summer and less intensity during the winter), it may be advantageous to have the panel tilted with a north-south offset to maximize the total amount of energy captured during the year. This is especially true with a one-axis tracker where the only north-south correction is performed by the IOAs and not by a physical movement of the panel.
Dual Optical ArrangementsA bender-IOA embodiment of an optical concentrator may include (i) an input bender, which changes the direction of light rays that pass therethrough and (ii) a lower IOA that accepts rays of light at a given off-axis (off-normal) direction and focuses these rays to a receiver (generally centered) below the lens. The combination of these two rotatable optical arrangements permits the sun's rays to be directed to a single unmoving receiver when the sun is anywhere within a range of receiving directions relative to the concentrator. The extent of this range of receiving directions is a function of the two optical arrangements and is normally made to be as large as possible. The lower IOA has many configurations such as a light bender with a reflective concentrator, a light bender with an embedded refractive concentrator, or a combination with the concentration being accomplished by refraction and/or reflection.
Attention is now directed to
The Lower IOA's 32 and 32′ may be constructed with a circular light bending IOA followed by a square or other shaped concentrator arrangement 187 (represented in
A split cell embodiment may be based on an array of concentrators with receiver locations that are not centered with respect to the concentrators. In particular, when the receivers are located between the concentrators, in a plan view, then it may be possible to concentrate light rays that do not pass through an IOA within the concentrator, but that pass between the IOAs, as will be described immediately hereinafter.
Attention is now turned to
In the following example it may be easier to implement the light bending independently from the concentration. Furthermore, the shape of the receiver does not have to be circular as is described next.
Attention is now directed to
If an IOA is formed by modifying a bender by changing the prism angle of each prism, a line or rectangle can form focus region.
Attention is now directed to
Attention is now directed to
Another option is to configure optical arrangement 210 as an IOA that provides concentration in the second direction. This may avoid additional interfaces and therefore additional optical losses. In this case, the IOA could have a complex configuration attained by convolving the light bending function with the concentrating function. The light exiting the IOA would be redirected refractively or reflectively, providing the same function as the “tents” in the previous examples without adding an additional optical layer.
Another method of 2D concentration is to use upper and the lower surface of the IOA for a combined concentration. One simple method of doing this is to use the same variable angle prism walls as discussed previously with reference to
These methods along with variations of these methods can be used to direct light from a moving source to a single location or multiple locations. Varying levels of concentration can also be achieved. The shape of the illuminated area can also be varied. Furthermore the distance to the focus region can be reduced by focusing the light to multiple points. Using multiple smaller focus regions may also reduce the heat gain at each focus region location which could have a direct benefit for PV applications. All of these have benefits in applications that have limitations in spacing, that have requirements in light concentration, spot size requirements or light location requirements.
Bender-IOA CombinationAttention is now turned to
As a second example that cannot be easily visualized in a single plane, attention is now turned to
To better understand this rotation, referring to
Attention is now directed to
In one orientation, as illustrated in
It is noted that for incoming rays of light that enter from the left and not from the right, then the exiting rays will exit the bender through the sloped wall only, and will not exit the bender through the vertical walls. For a given set of incoming rays of light (parallel with one another and entering with incoming angle θin) the bender produces output rays of light 92 (parallel with one another and exiting the prism array with an output angle θout). It is further noted that output angle θout is related to, but not equal to, the incoming angle θin, and that the bending angle β can be derived, based on the values of θin and θout in conjunction with the geometry illustrated in
A person of ordinary skill in the art will recognize that the amount of bending can be determined, based on well know principles of optics, by the angle of the sloped wall, the refractive index of the bender material, and the application of Snell's Law. With ongoing reference to
In the following three examples, we will consider the angle of (i) the incoming rays of the light 14 entering the bender (ii) internal rays of light 239 passing through the bender and (iii) output rays of light 92 exiting the bender are considered assuming a bender index of refraction n=1.5 and a prism angle Ψ=40° from flat.
For the sun directly overhead and incoming rays of light 14 entering at angle of θin=0° (from optical axis 47), the internal ray angle inside the bender will also be 0° but the ray angle upon exiting the bender (θout) will be −34.6° (to the left). This corresponds, for this particular incoming ray of light, with a bending angle of β=34.6 degrees.
For incoming rays of light entering at (θin) angle of 10° (from optical axis 47), the internal ray angle will be 6.6°, and the rays upon exiting (θout) will be −15.6° (to the left). This example is the situation as depicted in
For incoming rays of light entering at (θin) angle of 22.3° (from optical axis 47), the internal ray angle will be 15°, and the rays upon exiting (θout) will be 0° (relative to the optical axis). This corresponds with a special case wherein the bender bends the incoming rays of light so that they exit the bender parallel to the optical axis, and bending angle β=θin=22.3°.
While the assumption of a constant bending angle has served as a useful approximation for descriptive and illustrative purposes, it is again noted that this is only an approximation, and does not necessarily represent the precise bending performance of a given bender, as illustrated above in the context of a specific embodiment. Nevertheless, this approximation tends to be sufficiently realistic such that it is useful to characterize a given bender as exhibiting a specific “bend angle” even if this number is subject to variation based on the orientation of incoming rays of light, and in the context of this disclosure, a given bender may be specified as having a specific bend angle, even in cases where that bend angle may vary. In order for a specific bend angle to serve as a useful reference, it is helpful to maintain consistency, from one bender to another, as to the definition of bend angle. In view of the foregoing points, the “bend angle” of any given bender, when specified as a single value, is to be associated throughout this disclosure with the special case when output rays are oriented parallel to the optical axis of the bender, for example in the way that is described in the third example set forth immediately above.
For example, while the bender embodiment of the present discussion exhibits variations depending on the orientation of the incoming rays of light, the bender embodiment illustrated in
The following table specifies a number of embodiments that are assumed to utilize the geometry illustrated in
Attention is now turned to
Attention is now drawn to
It is noted that bender 234 and Fresnel lens 235 cooperate with one another to function as an IOA in accordance with previous descriptions in reference to
A specific embodiment of concentrator 26″ will be described immediately hereinafter. This specific embodiment is capable of concentrating the sunlight by at least approximately 10:1, and is capable of tracking the sun within a cone of approximately +/−45 degrees around the optical axis. While the concentrator is tracking the sun and concentrating the light onto the receiver, the concentrator can remain fixed in position and orientation, and the only movement can be restricted to the rotation of the two benders.
It may be useful to refer to
Bender 234 can be chosen to be an acrylic disk with an input area of 120 mm in diameter, and the bend angle can be chosen to be 30°. The larger bend angle for the second bender is chosen to enable the concentrator to target the sun when the sun is near or on the optical axis. During this situation, the sunlight enters the topmost bender nearly normal, which tends to increase the amount of bending that will occur. Increasing the bend angle of the bottommost bender allows it to restore light entering the concentrator nearly parallel to the optical axis to parallel again before entering the Fresnel lens. The bend angle of the bottommost bender should be increased until it approximately matches the increased bend angle of the topmost bender for light entering that bender from normal. As with bender 33, bottom surface 247 of bender 234 is a linear prism array with a pitch of 1 mm and with the vertical walls (
It may be advantageous to place the two benders as close together as manufacturing and operational tolerance allow and still permit rotation for maintaining a small gap 242 between bender 33 and bender 234
The Fresnel lens may have a diameter equal to or larger than that of the bottommost bender in order to not lose (and therefore waste) any further light energy. For example, a non-imaging Fresnel lens, as described in Leutz and Suzuki, may be used as this provides a reasonably efficient configuration. However, a more commonly available imaging Fresnel lens, such as is available from Fresnel Technologies (101 W. Morningside Drive, Fort Worth, Tex. 76110, 817-926-7474, www.fresneltech.com), can be used as well. Lower pitch Fresnel lenses may be preferred as they can have fewer edges and corners which may scatter light and correspondingly reduce efficiency, however as pitch drops—lenses often become thicker. One reasonable choice for this specific embodiment is the Fresnel Technologies Item #18.2 lens that has a pitch of 25/inch and focal length of 6 inches. It is noted that Fresnel lenses are generally not reversible and that this lens is designed to be placed grooved-side up which is the opposite from the depiction of the Fresnel lens in
Still referring to
Attention is now directed to
Furthermore, for reasons of illustrative clarity the forgoing example describes the operation of a concentrator with a single-element IOA that operates analogously with the concentrator of
As described immediately above in reference to
Attention is now directed to
While a number of embodiments described herein utilize a bender as the input arrangement, and an IOA as the additional arrangement, it is again noted that there is no requirement that the arrangements be disposed in this order. However, Applicants recognize that if a given concentrator is modified by re-arranging the order of the arrangements, in many cases, it may be necessary to substantially re-configure the arrangements themselves in order that they cooperate with one another to receive and concentrate the incoming rays of light in a manner that is at least generally consistent with the performance of optical concentrators (for example optical concentrator 26) described herein and throughout this overall disclosure. While substantial modifications of the optical arrangements may be required in conjunction with any particular re-ordering of the optical arrangements, Applicants believe that a person of ordinary skill in the art, having this disclosure in hand, may implement concentrator 244′ in a variety of ways, utilizing a variety of optical arrangements, in accordance with the teachings herein and without adhering to any particular restriction as to ordering of the arrangements. For example, in one embodiment, as described previously, the input arrangement may be a bender, and the additional arrangement may be an IOA. In another embodiment, the input arrangement and the additional arrangement may both be configured as IOAs. It is further noted that there is no requirement that optical arrangements 252 and 255 should consist of only one optical component, ands that one or both of these optical arrangements may include a plurality of optical components.
Prism Wall SlopeReferring again to
Attention is again turned to
If the angle is sufficiently increased, then there will be a shading effect where some of the rays of light are interfered with by part of the bender, and these rays of light may no longer be parallel to the non-interfered rays of light. This shading effect is shown in
Establishing the optimal slope of the prism walls is not a trivial matter and may be different for the bender than for an associated IOA. In the case above, for the 23° entering angle of light, the exit light was normal to the bender. This is the design case for the associated IOA. In this case, the internal ray angle was found to be 15°, thus the vertical wall could be sloped up to this 15° angle with no negative effects. Thus, under normal operation, this part of the associated IOA (between vertical and 15° should never transmit any light rays). This design freedom can be used to improve the prism performance by adjusting the prism corners (from vertical to slope and back to vertical) so that the area of the prism that interacts with the light will be more optimally oriented. In a similar manner, the bender can have its vertical wall modified to improve performance, however there are more trade-offs for the upper bender.
In order to examine the prism wall effects, related aspects of operation of the operation of concentrators are observed. At least within a reasonable approximation, as described previously, a BRIC includes a bender that can be oriented to redirect the incoming light onto an exit cone followed by an IOA that accepts this light and redirects it to the target. In this basic embodiment, the illumination entering the bender is essentially redirected as it travels through the two optical arrangements (the bender and the IOA). In this description, the bender rotates as frequently as needed to keep the sun within its field of view. The IOA rotates in relation to the bender as needed to maintain the light on the target. The amount of rotation required is determined by the sun's movement through the sky in its daily and annual cycle. For an ideal location on earth, the sun's path moves +/−23.5 degrees north to south to north annually and +/−90 degrees as it moves east to west daily.
Attention is now directed to
Here it can be seen that a system, having a bender and an IOA, configured with the bender and the IOA matched with one another such that ξ=β=30°, exhibits a lack of coverage in the morning and the evening (near sunrise and sunset). While the sunlight angle at these times is non-optimum for energy collection, it would still be beneficial to collect this energy since this represents a loss of potential energy conversion on a daily basis.
The IOA in
If the vertical walls are perfectly vertical and top apex 250 and bottom apex 253 are perfectly sharp (not rounded), there will be no optical shading loss—i.e. nearly all of the light entering the bender or IOA will exit the bender or IOA in the preferred direction. However, cases where there is a slight slope to the vertical wall and/or the top apex and/or the bottom apex are not perfectly sharp, some of the incoming light will be redirected in a manner not consistent with the design expectation and will result in “shading” loss. These cases are shown in
Attention is now directed to
Attention is now directed to
It is important to understand that sunlight at shallow angles near sunrise and sunset has less energy potential for a fixed panel design since the shallow angle reduces the amount of energy impinging upon the panel. Therefore it is more important to collect the light in the prime hours, and in the diagram above, this means centering coverage ring 243 horizontally unless there are other special conditions that may modify the theoretical sunlight distribution. The example shown in
Additionally, while the IOA often is associated with a requirement that the light exiting it should normally be centered below it, the bender does not have this requirement. Thus the IOA has a fundamental optimal angle for the vertical wall based on the fact that the light entering the IOA is pre-determined and the light exiting the IOA (in the absence of concentration) must be vertical, this sets the vertical wall angle limits. Referring back to the discussions around
Attention is now directed to
Thus it may be desirable to reduce the noon optimal performance of a system in order to gain performance at other times of the day or year.
Method of Rotation of IOAAs described above, the optical arrangements (for example the bender and the IOA) may be selectively rotated such that a set of two or more optical arrangements in a given concentrator cooperate with one another in order to continuously compensate for the sun's motion for maintaining concentration of the sun's rays on a fixed (stationary) target, and one method of moving a particular optical arrangement is by rotation about the center axis of the arrangement. It is noted that, in all previous descriptions, rotation of the optical arrangements has been described with respect to the optical axis of each of the aforedescribed optical arrangements, and it is to be understood that the optical axis in the foregoing examples has been aligned to be collinear with an axis of rotation such that both the optical axis and the axis of rotation may be considered as equivalent for the descriptive purpose of serving as a reference axis in space. While as few as one concentrator may comprise a solar collector, it is also possible to construct a panel of multiple concentrators containing many optical arrangements wherein groups of optical arrangements can be rotatably controlled together using one or more drive mechanisms. The optical arrangements may be physically supported about their center, suspended by their edges, suspended in a fluid, or in any manner such that they may rotate in a controlled way.
Limits of RotationIn order to consider a number of rotation methods and apparatus that are possible, it may be helpful to consider the requirement of the rotation needed to track the sun. In particular, if the rotation can be limited to less than 360 degrees, then this may simplify the motion and allow other forms of rotation. The amount of rotation required is determined by the sun's movement through the sky in its daily and annual cycle having seasonal variations. For any location on earth, the sun's path moves within a range of +/−23.5 degrees north to south to north annually and it moves +/−90 degrees (nominally) as it moves east to west daily.
Attention is now directed to
The pair of pointing directions 256 and the pair of pointing directions 259 on the same diagram show how there are two distinct solutions for the orientations of the optical arrangements for a light source at any particular point in the range of operation. By evaluating the extremes of +/−23.5° (winter to summer) and the center line (solstice), it can be determined if the range of angles of the optical arrangements can be limited.
Notice that for a given concentrator including a particular bender-IOA combination, it is possible to bend the light from the incoming angle to the target by two different methods. In the context of
It is observed that the bender can be confined to a similar rotational limit if the two optical arrangements are properly paired (with bend angle equal to zenith angle as described above) since their function can be reversed as shown by the two pointing directions illustrated in
In order to confine the rotation to these limited levels, it may require a discontinuity in angle orientation of the optical arrangements sometime during the day to switch the direction of thereof, although this can be accomplished fairly rapidly in comparison to the motion of the sun.
Rotational MethodsTwo methods of rotating the IOA in an array configuration are disclosed. The bender is typically mounted as an array so that all of the benders in an array are rotated, for example by a first drive mechanism, synchronously with one another for maintaining the same orientation as one another. The IOAs may be configured in a separate array that such that all the IOA's are rotated, for example by a second drive mechanism, independently from the bender array, but controlled in a similar manner.
Attention is now turned to
A single drive mechanism can be configured for rotating both the bender and the IOA in a coordinated way to maintain tracking by causing the tilt direction to follow the acceptance direction of the lower IOA. The bender would also be allowed to rotate around its own optical axis. Thus two rotations are still required: (i) the full concentrator rotation of both IOAs about the IOAs optical axis 47′ and (ii) the rotation of the bender about its own tilted axis 47. A filament 264 can serve as at least a part of a drive mechanism to provide rotation of IOA 32 and the bender such that the IOA and the bender are rotatably coupled with one another. The tilt angle can be reduced, but should be larger than zero to gain an advantage in accepting lower angle sunlight and in reducing the effect of the non-vertical walls of the IOA, if a prism array configuration is used.
Attention is now directed to
Attention is now directed to
Attention is now directed to
When we consider the function of the bender, there is a tradeoff between increasing the top angle, which in turn increases the amount of the early morning and late evening sun that is accessible, and shading loss, which increases with increasing top angle.
Attention is now directed to
The filament is moved by a motor 267 which drives the filament in a controlled manner to rotate the benders to the proper angle. At least one motor for each array may be used, or one motor 268 with a shifting transmission to connect the motor to either one of the arrays may be used. The filament may wrap around an output shaft of the motor, and then proceed around each of the benders in the array. Center posts 271 may be used to wrap the filament a half-turn so that the filament changes direction after leaving one lens and before entering the next lens. If a larger array is needed, then additional center posts could be added. Thus if the filament is moving down from the right side of one lens, then it can be guided such that it moves up as it enters the left side of the adjacent lens. While
Attention is now turned to
Attention is now turned to
Attention is now directed to
Bender 33 can utilize an array of prisms with each prism having a width, or pitch, of 1 mm. Each prism indicates a sloped wall that is at an angle of approximately 40 degrees relative to the surface tangent, and a vertical wall that is approximately 90 degrees to the surface tangent. This sloped-wall/vertical-wall pattern repeats over the full surface of the bender.
At least with respect to the example at hand, it may be desirable for the sloped wall angle to be maximized to produce the largest acceptance angle possible given the index of refraction of the material. The maximum angle is calculated when the rays of light enter vertically and are bent as far as possible, which is given by the critical (Total Internal Reflection) angle. This angle is Θ(prism)=arcsin(1/n), where n is the index of refraction. Thus, for an index of refraction of 1.5, the maximum angle is 41.8 degrees. If the prism includes a 90 degree vertical angle, then the prism ramp angle generally should not exceed this and should be less than this angle to allow for tolerance and a larger field of view of the sun. One exemplary design choice is the use of a 40 degree angle, though with a higher index of refraction material, the angle can be different.
The vertical side wall of each prism may also be modified if direct light above the lens is not to be completely concentrated to the target. This may be useful in examples wherein the top lens is tilted with respect to the line connecting the center of the lens to the center of the target. This may also be useful if more of the lower angle performance can be gained at the expense of the near vertical performance, which only occur a few minutes a day for a few days per year.
The pitch (prism width) can be adjusted based upon the sharpness of the corners of the prism (more rounded corners of the prism produce losses so a larger pitch may be preferred) and the volume of material of the prism (a larger pitch require more material which is more costly and will produce more optical aberrations).
By way of example, the bender can be a disk of acrylic with a diameter of 120 mm and maximum thickness of 2 mm with a 3 mm hole centered for support, and the prisms can be integrally formed with the disk. The bender disk rotates about a center hole. The outer rim of the disk can include a slot to accept a filament that provides for rotation. The flat side of the bender can face towards the sun and the prismatic side is facing the target. This bender may be made by standard casting or injection molding techniques. Any suitable dimensions can be used so long as the device functions consistent with these descriptions.
In the example at hand, concentrator 300 immediately follows the IOA. The concentrator can be configured such that that it causes a focus region spot size of 30 mm at the design distance of 12 cm. In one embodiment, the IOA and the concentrator are integrated into one optical element which removes two optical interfaces. This IOA will have a complex surface related to the convolution of the light bending prisms and the concentrating Fresnel and should be numerically modeled for optimal efficiency. The examples described herein are in no way intended to be limiting, and it is to be understood that there are innumerable solutions to this lens shape, that are considered to enable overall performance, as described. The IOA may be fabricated using a variety of well-known manufacturing techniques, including but not limited to injection molding and the like. It is to be understood that the concentrator need not be integrally fabricated with the rotating IOA refractive element, and that in another embodiment, the concentrator may be a compound parabolic concentrator (CPC) or similar reflective concentrator that can be arranged as a separate and distinct component from the rotating IOA refractive element. Additionally, the IOA could be completely reflective where the reflective element bends the light and concentrates the light; thus the system could comprise one refractive IOA bender and one reflective IOA as the complete optical system.
In the example at hand, the bender can be rotated about its axis by filament 264 and the IOA may be rotated about its axis by filament 264′. A PV solar cell 303 of 30 mm diameter can be fixedly centered under the concentrator so that it may be fully illuminated. The PV solar cell can be attached to a metal backing plate (not shown) which may serve as a heat sink for the thermal energy added by the concentrated solar radiation. Note, that as compared to a standard non-concentrating solar panel, this BRIC method has nearly the same solar density and thermal density, thus the thermal penalty for a BRIC panel should be no greater than that of a standard solar panel without concentration.
This design has a theoretical concentration of 16 as the sun's rays are captured over a 120 mm diameter area and concentrated over a 30 mm diameter area resulting in a 4× reduction in diameter and a 16× reduction in area. However, due to an approximate 4% reflective loss on each lens interface, (6 optical interfaces), the lens efficiency is approximately 78%, and a protective cover layer (not shown) is typically about 90% efficient, resulting in a concentration factor of about 11. All values are for demonstration only and any suitable values may be used so long as the device functions consistent with these overall descriptions.
Control circuitry (not shown) may be configured to direct the filaments 264 and 264′ to move causing the bender and the IOA to rotate in such a manner that the sun's rays are illuminating focus region 41 for reception by PV cell 303 at least at times when the rays are within the range of receiving angles of the concentrator.
Variations with respect to
Attention is now directed to
In one embodiment, bender 33 and bender 234 may be configured to cooperate with one another such that output rays 92′ exiting bender 234 may be collimated (parallel with one another) in an orientation that is at least approximately parallel with optical axis 47. With regard to this embodiment, Applicants believe that a person of ordinary skill in the art will recognize that there are a variety of well known techniques for utilizing parabolic reflective surface for collecting and concentrating collimated light. For example, reflector 206″ may be configured as a concentric parabolic concentrator (CPC) according to well known techniques. These techniques are discussed in “Nonimaging Optics” by Roland Winston, Juan C. Minano, and Pablo Benitez; published by Elsevier Academic Press and which is incorporated herein by reference. While an example utilizing collimated output rays 92′ has been presented herein for purposes of descriptive clarity, it is to be appreciated that there is no requirement that output rays 92′ should be collimated and/or parallel with optical axis 47, and a person of ordinary skill in the art, having this overall disclosure in hand, may readily implement a variety of configurations in which reflector 206″ can be configured to collect output rays 92′ that have been received and bent by bender 234 and are neither collimated nor parallel with optical axis 47. However, it is to be appreciated, based on well known principles of optics, that a given reflector 206″, in order to collect and concentrate the light as described herein, may require that output rays 92′ fall within some predetermined range of angles relative to optical axis 47.
With ongoing reference to
While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.
Claims
1. A solar collector comprising:
- one or more solar concentrators arranged in an array such that each of said concentrators is in a fixed position with a fixed alignment in said array and each of said concentrators is configured to define (i) an input aperture having an input area such that the solar collector is positionable to face the input aperture of each concentrator in a skyward direction such that said input aperture is oriented to receive sunlight from the sun, (ii) an input axis of rotation that extends through said aperture in said skyward direction, and (iii) a focus region that is substantially smaller than said aperture area, and each of said concentrators includes an optical assembly having at least one optical arrangement that is supported for rotation about said input axis for tracking the sun within a predetermined range of positions of said sun using no more than said rotation of the optical arrangement around the input axis such that said rotation does not change the direction of the aperture from said skyward direction,
- wherein for any specific one of said positions within said predetermined range of positions, said optical arrangement is rotatably oriented, as at least part of said tracking, at a corresponding rotational orientation as at least part of concentrating the received sunlight within said focus region, for subsequent collection and use as solar energy.
2. The solar collector of claim 1 wherein for said specific one of said positions of said sun, a rotational misalignment caused by rotating the optical arrangement away from said corresponding rotational orientation causes at least some of said received sunlight to be directed outside of said focus region.
3. The solar collector of claim 1 wherein said optical arrangement serves as an input arrangement for initially receiving the sunlight, and said optical assembly includes an additional optical arrangement following said input arrangement to accept the sunlight from the input arrangement and configured for rotation about an additional axis of rotation, and said input arrangement and said additional arrangement are configured to cooperate with one another in performing said tracking based at least in part on a predetermined relationship between (i) said rotation of said input arrangement about said input axis of rotation and (ii) rotation of said additional arrangement about said additional axis of rotation to focus the received sunlight into the focus region.
4. The solar collector of claim 3 wherein said additional axis of rotation and said input axis of rotation are at least approximately parallel with one another.
5. The solar collector of claim 3 wherein said additional axis of rotation and said input axis of rotation are collinear with one another.
6. The solar collector of claim 3 wherein said input optical arrangement is configured for bending the received sunlight for acceptance by said additional optical arrangement, and said additional optical arrangement is configured for accepting and redirecting the bent light to cause said focusing.
7. The solar collector of claim 3 including a group of two or more of said solar concentrators and a drive mechanism rotatably couples all of said input arrangements in said group to collectively rotate all of said input arrangements while maintaining, during said tracking, at least approximately the same rotational orientation for all of the input arrangements as at least part of causing the optical assemblies in the group to track the sun in a synchronized way.
8. The solar collector of claim 7 wherein said drive mechanism is further configured for rotatably coupling all of said additional arrangements in said group to collectively rotate all of said additional arrangements while maintaining, during said tracking, at least approximately the same rotational orientation for all of the additional arrangements as at least part of causing the optical assemblies in the group to track the sun in said synchronized way.
9. The solar collector of claim 8 wherein said additional arrangement and said input arrangement of each concentrator are rotatably coupled with one another through said drive arrangement such that a first amount of rotation of one of said input arrangement or said additional arrangement causes a second amount of rotation in the other one of the input arrangement or the additional arrangement, and the predetermined relationship is maintained throughout said tracking at least in part as a result of said coupling.
10. The solar collector of claim 3 wherein said optical assembly is configured to define a receiving direction as a vector that is characterized by a predetermined acute receiving angle with respect to the input axis such that the input axis and the receiving direction define a plane, and which receiving direction extends in one azimuthal direction outward from the input axis in said plane, such that said receiving direction is adjustable, based on a coordinated rotation of said input arrangement and of said additional arrangement, for performing said tracking of said sun.
11. The solar collector of claim 10 wherein said input optical arrangement is configured for bending the received sunlight for acceptance by said additional optical arrangement, and said additional optical arrangement is configured for accepting and redirecting the bent light to cause said focusing.
12. The solar collector of claim 3 wherein said input arrangement defines an at least generally planar configuration, and said input arrangement includes a planar input surface that defines said input aperture.
13. The solar collector of claim 12 wherein said input arrangement is configured for bending the received light rays.
14. The solar collector of claim 13 wherein said additional arrangement is a CPC following said input arrangement to accept the light rays from the input arrangement, and the CPC is configured to cause said focusing.
15. The solar collector of claim 14 wherein said CPC is a reflective CPC configured for performing said focusing by reflecting the light rays received from the input arrangement to the focus region.
16. The solar collector of claim 13 wherein said optical assembly includes an IOA following said input arrangement to accept the light rays from the input arrangement, and the IOA is configured to cause said focusing.
17. The solar collector of claim 1 wherein said optical arrangement serves as an input arrangement for initially receiving the sunlight, and said optical assembly includes an additional optical arrangement following said input arrangement to accept the sunlight from the input arrangement and configured for rotation about an additional axis of rotation, and said input arrangement and said additional arrangement are configured to cooperate in performing said tracking based at least in part on said rotation of said input arrangement about said input axis of rotation.
18. The solar collector of claim 17 wherein said optical assembly is configured to define a receiving direction as a vector that is characterized by a predetermined acute acceptance angle with respect to the input axis such that the input axis and the receiving direction define a plane, and which receiving direction extends in one azimuthal direction outward from the input axis in said plane, such that said receiving direction is rotatably adjustable, based at least in part on said rotation of said input arrangement.
19. The solar collector of claim 18 wherein said input optical arrangement is configured for bending the received sunlight for acceptance by said additional optical arrangement, and said additional optical arrangement is configured for accepting and redirecting the bent light to cause said focusing.
20. The solar collector of claim 17 wherein said input arrangement defines an at least generally planar configuration, and said input arrangement includes a planar input surface that defines said input aperture.
21. The solar collector of claim 20 wherein said input arrangement is configured for bending the received light rays for acceptance by said additional arrangement.
22. The solar collector of claim 21 wherein said additional arrangement is a CPC following said input arrangement to accept the light rays from the input arrangement, and the CPC is configured to cause said focusing.
23. The solar collector of claim 22 wherein said CPC is a reflective CPC configured for performing said focusing by reflecting the light rays accepted from the input arrangement to the focus region.
24. An optical concentrator comprising
- an optical assembly having one or more optical arrangements including an input optical arrangement, and said optical assembly is configured for
- defining (i) an input aperture having an input area for receiving a plurality of input light rays, (ii) an optical axis passing through a central region within said input aperture, (iii) a focus region having a surface area that is substantially smaller than the input area and is located at an output position along said optical axis offset from the input aperture such that said optical axis passes through said focus region, and (iv) a receiving direction defined as a vector that is characterized by a predetermined acute receiving position with respect to said optical axis such that the optical axis and the receiving direction define a plane, and which receiving direction extends in one azimuthal direction outward from the optical axis in said plane such that at least the input arrangement is rotatable about the optical axis for alignment of the receiving direction to receive a plurality of input light rays that are each at least approximately antiparallel with said vector, and
- thereafter, focusing the plurality of input light rays to converge toward said optical axis until reaching said focus region such that the input light is concentrated at the focus region.
25. The optical concentrator claim 24 wherein said focus region includes a given area and for at least some of said input light that is characterized by at least a particular amount of misalignment with the receiving direction, that input light is rejected by falling outside of the given area of the focus region.
26. The optical concentrator of claim 24 wherein said input arrangement defines an at least generally planar configuration, and said input arrangement includes a planar input surface that defines said aperture.
27. The optical concentrator of claim 26 wherein said optical assembly includes an additional optical arrangement following said input arrangement, and said input arrangement is configured for bending the received light rays for acceptance by said additional arrangement.
28. The optical concentrator of claim 27 wherein said additional arrangement is a CPC configured to accept the light rays from the input arrangement, and the CPC is configured to cause said focusing.
29. The optical concentrator of claim 27 wherein said CPC is a reflective CPC configured for performing said focusing by reflecting the light rays received from the input arrangement to the focus region.
30. The optical concentrator of claim 27 wherein said additional arrangement is an IOA configured to accept the light rays from the input arrangement, and the IOA is configured to cause said focusing.
31. The optical concentrator of claim 30 wherein said IOA is configured for selective rotation about said optical axis, and said input arrangement and said IOA are configured to cooperate with one another in performing said receiving and said focusing based at least in part on (i) said rotation of said input arrangement about said optical axis and (ii) said rotation of said IOA.
32. An inverted off-axis lens, comprising:
- an optical arrangement having an at least generally planar configuration defining (i) a planar input surface having an input surface area and (ii) an axis of rotation that is at least generally perpendicular thereto; and
- said optical arrangement is configured for
- defining an acceptance direction as a vector that is characterized by a predetermined acute acceptance angle with respect to said axis of rotation such that the axis of rotation and the acceptance direction define a plane, and which acceptance direction extends in one fixed azimuthal direction outward from the axis rotation in said plane such that the optical arrangement is rotatable about the axis for alignment of the acceptance direction to accept a plurality of input light rays that are each at least approximately antiparallel with said vector, and
- thereafter, transmissively passing the plurality of input light rays through said optical arrangement while focusing the plurality of input light rays to converge toward one another until reaching a focus region that is substantially smaller than the input surface area such that the input light is concentrated at the focus region.
33. The inverted off-axis lens of claim 32 wherein said focus region includes a given area and for at least some of said input light that is characterized by at least a particular amount of misalignment with the acceptance direction, that input light is rejected by falling outside of the given area of the focus region.
34. The inverted off axis lens of claim 32 wherein said focal region is located along said axis of rotation offset from the input surface area such that said axis of rotation passes through said focal region.
35. The inverted off axis lens of claim 32 wherein said optical arrangement further defines an output surface that is at least generally parallel with said input surface and spaced therefrom by a thickness, and at least part of said thickness refracts said plurality of input light rays to cause the focusing of the light rays.
36. The inverted off axis lens of claim 32 wherein said optical arrangement is integrally formed of an optical material.
37. The inverted off axis lens of claim 36 wherein said optical arrangement includes a plurality of optical prisms to accept and focus said input light rays.
38. The inverted off axis lens of claim 35 wherein said optical arrangement includes a plurality of optical prisms that are configured to cooperate with one another to accept and the focus said input light rays, and the prisms are integrally formed of an optical material.
39. The inverted off axis lens of claim 38 wherein at least a subset of said plurality of prisms is integrally formed with said input surface.
40. The inverted off axis lens of claim 38 wherein at least a subset of said plurality of prisms is integrally formed with said output surface.
41. The inverted off axis lens of claim 38 wherein a first subset of said plurality of prisms is integrally formed with said input surface, and a second subset of said plurality of prisms is integrally formed with said output surface,
42. The inverted off axis lens of claim 41 wherein said first and second subsets of prisms are cooperatively configured to cooperate with one another for accepting and focusing said input light rays, and wherein said first subset of prisms is configured for bending the input light rays for acceptance by said second set of prisms, and said second subset of prisms is configured to cause said focusing of said input light rays.
43. A solar concentrator for collecting and concentrating a plurality of mutually parallel incoming rays of sunlight, said solar concentrator including the inverted off axis lens of claim 32 arranged in a series relationship following an input optical arrangement with the input surface of the off axis lens facing towards the input arrangement, and the inverted off axis lens and the input arrangement are each configured for selective rotation to cooperate with one another such that
- the input arrangement initially receives said incoming light rays and bends the incoming light rays to produce intermediate light rays for acceptance by said inverted off-axis lens such that the intermediate light rays are at least approximately oriented antiparallel to said acceptance direction, and
- said inverted off axis lens is aligned for accepting said intermediate light rays such that said intermediate light rays serve as said input light rays for said inverted off axis lens and the inverted off axis lens concentrates the intermediate light rays at said focus region of said inverted off-axis lens.
44. The solar concentrator of claim 43 wherein said input arrangement is aligned with said axis of rotation, and said inverted off axis lens and said input arrangement are configured to cooperate with one another to define a receiving direction as a vector that is characterized by a predetermined acute acceptance angle with respect to the axis of rotation such that the axis of rotation and the receiving direction define a plane, and which receiving direction extends in one azimuthal direction outward from the axis of rotation in said plane, such that said receiving direction is rotatably adjustable, based on a coordinated rotation of said input arrangement and of said additional arrangement.
45. The solar concentrator of claim 43 wherein said input arrangement is concentrically aligned on said axis of rotation of said inverted off axis lens such that said selective rotation of said input arrangement revolves around said axis of rotation.
46. The solar concentrator of claim 45 wherein said input arrangement includes an input axis of rotation that is skewed with respect to said axis of rotation of said inverted off axis lens such that said input arrangement is tiltable toward the sun.
47. The solar collector of claim 44 including a receiver following said inverted off-axis lens, said receiver having a receiving surface facing towards the off axis lens and aligned such that the receiving surface at least partially overlaps said focus region, and said receiver is configured such that at least some of the concentrated input light is absorbed by said receiver and converted into a form of energy.
48. The solar collector of claim 47 wherein said receiver is configured for converting the absorbed input light into electrical energy as said form of energy.
49. The solar collector of claim 48 wherein the receiver is configured for converting the absorbed light into thermal energy as said form of energy.
50. The solar collector of claim 49 wherein said receiver is in thermal communication with a fluid and said receiver is configured such that at least a portion of said thermal energy is transferred to said fluid.
51. The solar collector of claim 50 wherein said receiver is configured for passing a liquid therethrough, and at least some of said thermal power is transferred to said liquid for subsequent use outside of said receiver.
52. A multi-element inverted off-axis optical assembly, comprising:
- an optical assembly having two or more optical arrangements including a first arrangement that defines (i) an input aperture having an input area and (ii) an axis of rotation that is at least generally perpendicular thereto; and
- said optical arrangements are configured to cooperate with one another for
- defining an acceptance direction as a vector that is characterized by a predetermined acute acceptance angle with respect to said axis of rotation such that the axis of rotation and the acceptance direction define a plane, and which acceptance direction extends in one azimuthal direction outward from the axis of rotation in said plane, and at least said first arrangement is supported for motion that is limited to rotation about said axis of rotation for alignment of the acceptance direction to accept said plurality of input light rays that are each at least approximately antiparallel with said vector, and
- thereafter, focusing the plurality of input light rays to converge toward one another until reaching a focus region that is substantially smaller than the input surface area such that the input light is concentrated at the focus region.
53. The multi-element inverted off axis optical assembly of claim 52 wherein said first arrangement is positioned for initially accepting said plurality of input light rays and said optical assembly includes a second optical arrangement following said first arrangement to collect the light rays from the first arrangement, and said first arrangement and said second arrangement are configured to cooperate in performing said accepting and said focusing based at least in part on said rotation of said first arrangement about said axis of rotation.
54. The multi-element inverted off axis optical assembly of claim 53 wherein said second optical arrangement is rotatably fixed such that the second optical arrangement is not rotatable.
55. The multi element inverted off axis optical assembly of claim 53 wherein said first arrangement and said second arrangement are fixedly attached to one another for simultaneous rotation such that said first arrangement and said second optical arrangement co-rotate together with one another as part of said alignment of said acceptance direction.
56. The multi element inverted off axis optical assembly of claim 53 wherein said first optical arrangement is configured for bending the received input light rays for acceptance by said second optical arrangement, and said second optical arrangement is configured for collecting and redirecting the bent light to cause said focusing.
57. The multi-element inverted off axis optical assembly of claim 53 wherein said second arrangement is a CPC.
58. A solar concentrator for collecting and concentrating a plurality of mutually parallel incoming light rays, said solar concentrator including the multi-element inverted off axis optical assembly of claim 52 arranged in a series relationship following an input arrangement that is aligned on said optical axis of said inverted off axis optical assembly with the input arrangement with the input surface of the off axis optical assembly facing towards the input arrangement, and the inverted off axis optical assembly and the input arrangement are each configured for selective rotation to cooperate with one another such that
- the input arrangement initially receives said incoming light rays and bends the incoming light rays to produce intermediate light rays for acceptance by said inverted off-axis optical assembly such that the intermediate light rays are at least approximately oriented antiparallel to said acceptance direction, and
- said intermediate light rays serve as said input light rays for said inverted off axis optical assembly such that the inverted off axis optical assembly concentrates the intermediate light rays at said focus region of said inverted off-axis optical assembly.
59. The solar collector of claim 58 including a receiver having a receiving surface facing towards the off axis optical assembly and aligned such that the receiving surface at least partially overlaps said focus region, and said receiver is configured such that at least some of the concentrated input light is absorbed by said receiver and converted into power.
60. A method for solar collection, said method comprising:
- arranging one or more solar concentrators in an array to position each of said concentrators in a fixed location with a fixed alignment in said array and configuring each of said concentrators for defining (i) an input aperture having an input area such that the solar collector is positionable to face the input aperture of each concentrator in a skyward direction with said input aperture oriented to receive sunlight from the sun, (ii) an input axis of rotation that extends through said aperture in said skyward direction, and (iii) a focus region that is substantially smaller than said input aperture;
- configuring each of said concentrators with an optical assembly having at least one optical arrangement and supporting said optical arrangement for rotation about said input axis for tracking the sun within a predetermined range of positions of said sun using no more than said rotation of the optical arrangement around the input axis such that said rotation does not change the direction of the aperture from said skyward direction; and
- for any specific one of said positions within said predetermined range of positions, rotatably orienting said optical arrangement, as at least part of said tracking, to a corresponding rotational orientation as at least part of concentrating the received sunlight within said focus region, for subsequent collection and use as solar energy.
61. A method for focusing collimated light, said method comprising:
- configuring an optical IOA arrangement for defining (i) a planar IOA input surface having an input surface area and (ii) an axis of rotation that is at least generally perpendicular thereto; and
- further configuring said optical IOA arrangement for
- defining an acceptance direction as a vector that is characterized by a predetermined acute acceptance angle with respect to said axis of rotation such that the axis of rotation and the acceptance direction define a plane, and which acceptance direction extends in one fixed azimuthal direction outward from the axis rotation in said plane such that the optical arrangement is rotatable about the axis for alignment of the acceptance direction for accepting a plurality of input light rays, as said collimated light, that are each at least approximately antiparallel with said vector, such that said plurality of input light rays transmissively pass through said optical IOA arrangement and are concentrated by focusing the plurality of input light rays to converge toward one another until reaching a focus region that is substantially smaller than the input surface area.
62. A method for concentrating a plurality of mutually parallel rays of sunlight, said method comprising:
- providing an input optical arrangement for initially receiving a plurality of incoming rays of sunlight;
- positioning the optical IOA arrangement of claim 61 in a series relationship following the input arrangement with the input surface of the optical IOA arrangement facing towards the input optical arrangement;
- supporting the optical IOA arrangement and the input arrangement for selective rotation to cooperate with one another such that the input optical arrangement re-directs the incoming rays of sunlight to produce a set of intermediate rays of sunlight, for acceptance by said optical IOA arrangement, such that said intermediate rays of light are at least approximately oriented anti-parallel to said acceptance direction of said optical IOA arrangement; and
- accepting said intermediate light rays with said optical IOA arrangement such that said intermediate light rays serve as said input light rays for said optical IOA arrangement and (ii) concentrating the intermediate light rays at said focus region of said inverted off-axis lens.
Type: Application
Filed: Jul 13, 2009
Publication Date: Jan 14, 2010
Inventors: Robert Owen Campbell (Boulder, CO), Michael George Machado (Boulder, CO)
Application Number: 12/502,085
International Classification: F24J 2/38 (20060101);