Light-concentrating lens assembly for a solar energy recovery system

A light-concentrating lens assembly for a solar energy system, the assembly comprising a plurality of concentrically arranged paraboloid mirror reflectors, a conical light guide extending below the plurality of paraboloid mirror reflectors, an inner central cone disposed along a central axis of the concentrically arranged paraboloid mirror reflectors, and a compound paraboloid concentrator disposed beneath the inner central cone.

TECHNICAL FIELD

The present technology relates generally to solar energy and, in particular, to lenses and concentrators for solar energy systems.

BACKGROUND

Solar concentrators are devices that augment the efficiency of solar power by concentrating sun rays using parabolic mirrors or a fresnel lens. A good review of solar concentrators is presented by Ari Rabl in “Comparison of Solar Concentrators”,Solar Energy, Vol. 18, pp. 93-111.

With the increasing importance of solar energy, further improvements and enhancements in solar concentrator technology remain highly desirable.

SUMMARY

An inventive aspect of the disclosure is a light-concentrating lens assembly for a solar energy system, the assembly comprising a plurality of concentrically arranged paraboloid mirror reflectors, a conical light guide extending below the plurality of paraboloid mirror reflectors, an inner central cone disposed along a central axis of the concentrically arranged paraboloid mirror reflectors, and a compound paraboloid concentrator disposed beneath the inner central cone.

Another inventive aspect of the disclosure is a light-concentrating lens assembly for a solar energy system, the assembly comprising two concentrically arranged spherical and conical mirrors, a central lens to collect flux, a central reflective cone disposed along a central axis of the concentrically arranged spherical and conical mirrors to redirect flux from the mirrors, a compound paraboloid concentrator (CPC) disposed beneath the central reflective cone, and a small negative lens having a diameter substantially equal to an exit aperture of the CPC. Although the light-concentrating lens assembly illustrated in the figures and described herein may have a central lens55on top and a small negative lens57beneath and within the central reflective cone54, the small negative lens57may be omitted or, alternatively, both the small negative lens57and the central lens55may be omitted.

Other aspects of the present invention are described below in relation to the accompanying drawings.

DETAILED DESCRIPTION

FIGS. 1-5depict a light-concentrating lens assembly for a solar energy system in accordance with an embodiment of the present invention. The light-concentrating lens assembly may be used with any suitable solar energy system including a hybrid solar energy system.

In general, the light-concentrating lens assembly, which is generally designated by reference numeral10, comprises a plurality of concentrically arranged paraboloid mirror reflectors12, a conical light guide14extending below the plurality of paraboloid mirror reflectors, a reflective inner central cone16disposed along a central axis18of the concentrically arranged paraboloid mirror reflectors, and a compound paraboloid concentrator20disposed beneath the inner central cone. The compound paraboloid concentrator (CPC) is also known as a Winston cone. The Winston cone is described and illustrated in U.S. Pat. No. 3,923,381, U.S. Pat. No. 4,003,638 and U.S. Pat. No. 4,002,499, which are all hereby incorporated by reference. The publication by Ari Rabl in “Comparison of Solar Concentrators”,Solar Energy, Vol. 18, pp. 93-111 is also hereby incorporated by reference.

In the embodiment illustrated in the figures, the conical light guide14has a reflective coating and extends from a bottom22of a most radially outward reflector to an upper periphery24of the compound paraboloid concentrator.

In the embodiment illustrated in the figures, the light-concentrating lens assembly10includes a top glass plate26disposed on top of the plurality of concentrically arranged paraboloid mirror reflectors. This glass plate26may be coated with a reflective coating on the underside to fully capture all light that passes initially through the glass plate. In one specific embodiment, a thickness of the top glass plate is substantially equal to a thickness of each reflector. The thickness of the top glass plate may vary in a range equal to 90-110% of a thickness of each reflector. Persons of ordinary skill will recognize that other glass thicknesses may be employed. The top glass plate may be replaced with other suitable materials that permit incident light to enter the lens assembly.

In the embodiment illustrated in the figures, a gap G between successive paraboloid mirror reflectors is greater than a thickness t of each of the paraboloid mirrors reflectors. The ratio of the gap (G) between successive paraboloid mirror reflectors to the thickness (t) of each of the paraboloid mirror reflectors (G/t) may be between 1 and 2. The reflectors in the illustrated embodiment are equidistantly spaced (i.e. the gap between successive reflectors is constant). However, in other embodiments, the gap may be variable.

In the embodiment illustrated in the figures, the reflective inner cone16is longer than the compound paraboloid concentrator20. The reflective inner cone16, as shown by way of example, has a base diameter (D) equal to that of the compound paraboloid concentrator. As further illustrated, the compound paraboloid concentrator has a length equal to its base diameter. The base (upper surface) of the cone16may support a structure such as a pyramidal or conical structure which may have a reflective surface to reflect rays into the lens assembly. The central zone above the cone16may also be used to house circuitry.

In a specific embodiment, as illustrated in the figures, the inner cone has a length (L) to base diameter (D) ratio (L/D) of 8 to 5.

A ratio of a base diameter (D) of the inner cone to a diameter (d) of the top glass plate (D/d) ranges between 1:7 and 1:8. In the embodiment specifically illustrated, the ratio of the base diameter (D) of the inner cone to the diameter (d) of the top glass plate (D/d) is 1 to 7.6.

As shown inFIG. 5, each reflector12has a lens profile characterized by a lower curved lens portion28having an upwardly facing convex surface30and a downwardly facing concave surface32and an upper curved upper lens portion34having a radially outward convex surface36and a radially inward concave surface38. Specifically, the upper curved lens portion34may terminate in an upper circular edge40as shown in the figures. A spacing (S) between each successive upper circular edge may be equal to three times a thickness of each reflector or this spacing between each successive upper circular edge may range from two to four times a thickness of each reflector. It is further noted that the spacing (S) is greater than the gap (G). It is further noted in the illustrated embodiment that there is a flattened face42that is substantially parallel to the axis18.

In the specific embodiment illustrated in the figures, the inner central cone16has a highly reflective coating to ensure that all light that passes through the reflectors12into the light guide14travels into the CPC20.

The concentrator assembly (or lens assembly)10may work in conjunction with a heat exchanger for dissipating some of the heat produced by the concentrated solar energy. The heat exchanger, which may be placed below assembly10, for example below the exit aperture of the Winston cone, increases the efficiency of the concentrator assembly by keeping the temperature of the assembly within a desired temperature range. This concentrator may thus be used with a solar energy recovery system. This concentrator may be particularly useful in conjunction with a hybrid solar energy recovery system. Such a system comprises a frame, a heat exchanger plate disposed above the frame, and a dual-purpose solar energy recovery plate mounted to the frame. The dual-purpose plate has a plurality of light-concentrating lenses for concentrating incident solar radiation onto the heat exchanger plate to recover thermal energy and a plurality of photovoltaic cells for generating an electric current in response to solar radiation incident on the photovoltaic cells.

The specific dimensions of the light-concentrating lens assembly shown in the figures relate to one specific design. As will be appreciated by those skilled in optics, these dimensions may be varied to achieve different size and/or performance requirements.

FIGS. 6-8depict a further embodiment of the light-concentrating lens assembly. This lens assembly includes two spherical and conical mirrors and one central lens to collect flux, namely an outer mirror (or reflective ring)50and an inner mirror (or reflective ring)52. The lens assembly also includes one central reflective cone54to redirect (reflect) flux from the mirrors50,52. The lens assembly further includes an optional large lens (Zeonex lens)55at the front of the cone54and an optional small negative lens at the end of the cone to fill the exit aperture of the reflective cone54as best shown inFIG. 8. In other words, the small negative lens has a diameter substantially equal to the diameter of the exit aperture of the cone. Behind the cone54is a compound parabolic concentrator (CPC) or Winston cone56. In the illustrated embodiment ofFIG. 8, the outer diameter (OD) of the large (outer) mirror=104.4 mm, the exit diameter of CPC=5.0 mm, and the theoretical concentration=563×. As will be appreciated these dimensions are merely to illustrate the precise geometry of one specific embodiment and shall not be construed as the limiting the invention. In other words, the inventive concept may be applied to a lens assembly having different dimensions from those presented inFIG. 8. The two outer rings are concave and are mirrored only on the inside surface. In this particular embodiment, the cone that holds the zeonex lens and the negative lens is mirrored only the outside but not on the inside. This geometry guides the reflected light from the two spherical mirrors into the Winston cone. Additional spherical rings (additional spherical mirrors) may be added in other embodiments which may require increasing the diameter and length of the Winston cone and the length of the inside central reflective cone which is predicted to increase the amount of solar energy recovered. However, it is believed that the diameter of the zeonex lens cannot be substantially changed (in particular, increased) without degrading the overall system efficiency. As will be appreciated by those skilled in optics, the central cone54could have a reflective mirror geometry on its inside to guide light into the CPC56without the inclusion of a large zeonex lens55or the small negative lens57on or within the central reflective cone54. In other variations of this embodiment, the large zeonex lens55could be included as illustrated inFIGS. 7-9without the small negative lens57.

This novel lens assembly does not necessarily need a specific focal point for it to work as it will produce a ray or beam of concentrated solar radiance from the end aperture (e.g. 5 mm aperture) of the Winston cone. However, the distance away from the beam has to be such that it will direct the energy to the collecting receiver within a relatively short distance from the tip (to ensure efficient energy capture).

This lens assembly may be used not only in a hybrid solar hydronic panel but in other solar or optical systems. The lens assembly is scalable to any dimension with a theoretically infinite number of mirrored rings.

The lens may be used to produce and concentrate solar energy for thermal or flux purposes for any number of applications. Other applications can also utilize its concentrated heat and/or concentrated photovoltaic directional capacity.

FIG. 9depicts a ray trace showing that the lens assembly ofFIGS. 6-8has a 99.5% collection efficiency.

FIGS. 10-13depict yet another embodiment of the lens assembly10which is an improved design over the others presented herein. As shown by way of example in these figures, the lens assembly has an outer mirrored ring50and an inner mirrored ring52, a reflective cone54with an optional large lens55at the input aperture of the cone. The cone54has an optional small negative lens57at its exit aperture as shown inFIG. 11. Light is collected (by both reflection and refraction) by a compound parabolic concentrator (CPC)56aligned with the rings and cone along a central axis of the lens assembly. Accordingly, in one embodiment, the lens assembly has two concentrically arranged spherical and conical mirrors, a central reflective cone disposed along a central axis of the concentrically arranged spherical and conical mirrors to redirect flux from the mirrors and a compound paraboloid concentrator (CPC) disposed beneath the central reflective cone. Note in this embodiment that there is no large lens55and no small lens57. In this embodiment, the central reflective cone may optionally have a highly reflective inner coating. In another embodiment, the lens assembly further includes a large central lens55at an inlet of the cone. In yet another embodiment, the lens assembly further comprises a small negative lens57at an outlet of the cone. In this latter embodiment, the central reflective cone may have a highly reflective outer coating.

This highly compact form is achieved by utilizing a catodioptric concentric ring reflector design and by concentrating the collected energy using the compound parabolic concentrator (CPC), also known as a Winston Cone. The non-imaging characteristics eliminate the need to precisely position the concentrator photovoltaic (CPV) cell relative to the lens assembly. Additional focal independence is enabled by utilizing an afocal lensed system which outputs the light collected from the central area of the input aperture to match the CPC exit aperture size.

The lens assembly10is capable of providing a 555× optical concentration at +/−0.5 degree input with up to 99.9% optical efficiency (collection efficiency) as illustrated in theFIG. 9ray trace ofFIGS. 6-7. In the specific lens assembly illustrated inFIGS. 10-13, the diameter is 106 mm and the exit aperture of the Winston cone is 4.5 mm. The overall depth of the illustrated lens assembly is 82.4 mm giving an equivalent focal ratio of 0.81. These dimensions are provided to illustrated one specific implementation and are not intended to be limiting. Persons of ordinary skill in the art will recognize that variations in these dimensions may still provide substantially similar results and performance.

The lens assembly10ofFIGS. 10-13includes an outer housing58,60,64. In the illustrated embodiment, the front portion of the outer housing has a square collar58with bevelled and rounded corners. The width and height of the square collar58of the housing is 110 mm in the illustrated embodiment although this dimension may be varied. The main body60of the housing has a stepped cylindrical shape as shown with a large diameter portion60followed by a smaller diameter portion64which retains the Winston cone56. In the illustrated embodiment, the lens assembly includes a tri-arm holder62for holding the inner (central) ring52and a tri-arm holder68for holding the central cone54. A rear cover plate66that includes the smaller diameter portion64of the housing may be fastened to the main cylindrical body60of the housing by threaded fasteners as shown or by any other suitable mechanical fastening means such as clips, pins, press-fit, interference-fit or snap-fit interconnections, adhesives, welding, soldering, or any suitable combination thereof. The rear cover plate66therefore defines an annular abutment surface63for being seated or installed in a holder, receptacle or socket as will be described in greater detail below. In the illustrated embodiment, the lens assembly further includes an internal retainer68which retains the cone54, inner ring50, and outer ring52.FIG. 13illustrates how the lens55is concentric to the CPC56and how the rings50,52are concentric as well. As will be appreciated by those skilled and experienced in manufacturing, slight modifications and improvements in the lens assembly's10outer casing58,60,63,64,66and internal tri-arm holders62and68design may occur for improved cost containment and lens and production efficiencies.

A variant of the embodiment illustrated inFIGS. 6 to 8has a 122 mm diameter three-ring reflector design that can provide 735× concentration at +/−1-0.5 degrees with 99.9% design optical efficiency. The overall depth increases to 91 mm, giving an equivalent focal ratio of 0.75. It is noted that the design may be scaled up to collect increasing amounts of solar energy by utilizing additional ring structures. While there is no theoretical upper limit in the extending the input aperture size, the cost of adding and aligning additional rings becomes counterproductive. More importantly, the parts have non-zero wall thicknesses, which means that as the number of rings increases the optical efficiency may decrease.

In the embodiments illustrated, a depth of the lens assembly is less than a width of the lens assembly. As shown for example inFIG. 11, the depth (measured from the input plane of the inner ring to the exit aperture of the CPC) is less than the width or diameter of the housing (less than an outer diameter of the outer ring).

The lens assembly10may be integrated into a solar energy system having a heat exchanger, which is herein referred to as a hybrid solar energy recovery system since it generates electric power by photovoltaic cells and also directly heats water or other fluid in a heat exchanger. The heat exchanger also functions to cool the CPV cells to improve their performance.

One such heat exchanger is partially depicted by way of example inFIG. 14. The heat exchanger coil, loop or conduit70has an intake pipe and an outlet pipe. Although five parallel segments or passes are illustrated inFIG. 14, the number of segments or passes may be varied. On each segment or pass, there is a flattened portion72for receiving eight photovoltaic (CPV) cells74mounted or supported by the flattened portion72of the heat exchanger although a different number may be used. This provides for a total of forty CPV cells74in this particular embodiment. The number of CPV cells per pass, the number of passes and the total number of CPV cells may vary in other variants. Above each CPV cell is a respective lens assembly10for concentrating light on the respective CPV cell, for a total of forty lens assemblies in this particular embodiment.

FIG. 15shows how two lens assemblies10are mounted in alignment with two CPV cells74which in this embodiment are Advanced Quantum Dot Enhanced High Efficiency Concentrator Photovoltaic (CPV) cells along the first pass of the loop/coil. These lens assemblies10may be mounted flush (by virtue of the square collar58) with its neighbouring or adjacent lens assembly or assemblies as shown inFIG. 15.

As shown by way of example inFIG. 16, each lens assembly10is mounted in a spaced-apart arrangement relative to its respective CPV cell74. There is a gap or space between the exit aperture of the Winston cone56and the CPV cell74as shown inFIG. 16. The CPV cell74may be mounted on a very conductive adhesive compound or on a pedestal, support bracket, holder or mounting fixture73which is mounted to the flattened portion72of the heat exchanger conduit70.

As shown inFIG. 16, the housing of the lens assembly suspends securely just above the CPV cell74held in place from a mounting bracket or array assembly holder (which is not illustrated inFIG. 16) which results in a space80that permits concentrated light exiting the CPC56to fully and completely (“uninhibitedly”) discharge upon the CPV cell74to thereby augment the light energy delivered to the CPV cell. In other words, there is free space80between the heat exchanger unit, the CPV's and the lens assembly. The CPV cells are connected via wires or other electrical conductors, either in series or parallel, to a power storage device such as a battery, capacitor or equivalent energy storing means and/or directly to a power-consuming device such as an appliance, light, motor, etc., and/or delivered back to the electrical grid.

FIG. 17depicts a solar panel (or panel assembly)100which incorporates a variant of the heat exchanger shown inFIG. 14. The solar panel100includes a lens plate102and a base plate or frame104. The frame104has pivot mounts106for rotating the panel about a first axis, e.g. a generally horizontal axis. A post, shaft or axle108permits rotation about a second axis, e.g. a generally vertical axis. However, the panel may be installed in different orientations. The lens plate has a transparent pane or window to allow light to reach the heat exchanger and CPV cells74which are disposed along the flattened portion74of the conduit of the heat exchanger. It is to be noted that the light-concentrating lens assemblies10are not illustrated inFIG. 17and that a fully functioning solar panel100would require the light-concentrating lens assemblies10to be installed. Water or other heat-transferring fluid enters the heat exchanger at inlet110and leaves via outlet112.

FIG. 18shows the rear of the panel. The pivot mounts106attached to the back cover or frame104rotationally receive a U-shaped pivot arm subassembly107driven by a motor109to provide pitch. The motor may also rotate the panel about the axle108to provide yaw. The pitch and yaw enable the panel to track the arcuate path of the sun to maintain the panel perpendicular to the sun to optimize collection efficiency.

The heat exchanger as shown inFIG. 19has a conduit70, flattened portion72and a plurality of CPV's74disposed along the flattened portion of the conduit although other arrangements or configurations are possible.

The lens plate102as shown inFIG. 20has a generally rectangular frame-like structure surrounding a central or inner rectangular opening that houses the window or pane103which may be made of glass or other transparent or translucent material.

The back cover or frame104has two pivot mounts106that are spaced-apart to receive the U-shaped pivot arm subassembly. The pivot mounts may be, or may include, journals, bushings, bearings, sockets or any other suitable rotational housing.

This new technology has been described in terms of specific implementations and configurations which are intended to be exemplary only. Persons of ordinary skill in the art will appreciate that many obvious variations, refinements and modifications may be made without departing from the inventive concepts presented in this application. The scope of the exclusive right sought by the Applicant(s) is therefore intended to be limited solely by the appended claims.