The present invention relates to a solar apparatus for collecting solar radiation and concentrating it to a receiver such as a photovoltaic cell or thermovoltaic cell.
Solar cells have great potential to meet the world's energy needs with zero carbon emissions, but they currently have a long pay-back period, and there is a great need to reduce the cost of power generation. The apparatus in accordance with the present invention aims to reduce the cost of solar panel manufacture by reducing the quantity of active solar cells per unit area compared to a conventional flat panel. This is achieved by concentrating the light from the sun into a smaller area than it would normally illuminate. There are many known ways to achieve this. Some methods require a mechanism for the solar panel or cell to track the sun and are able to deliver high concentration values. Other concentrating methods have been designed to work with solar panels that do not track the sun, but the resulting concentration factor that can be achieved is much lower. It is the aim of the apparatus in accordance with the invention to deliver a modest concentration factor through the use of an optical waveguide to concentrate the solar radiation, thus replacing expensive active solar cell material with a low cost optical waveguide.
The simplest type of optical waveguide concentrator is described in U.S. Pat. No. 4,074,704 (Gellert, 1978) and U.S. Pat. No. 4,344,417 (Malecek, 1982), which illustrate many designs of a wedge concentrator. Light is incident to a large surface of the wedge and collected at a smaller surface. The ratio of the areas of the surfaces gives the basic concentration factor of the device. Several designs are described including solid wedges or hollow ones designed to be filled with a fluid such as water. The radiation collected at the output face can be used to power a photovoltaic device or be used to heat water thermal solar device. The other surface of the wedge redirects the light by total internal reflection (TIR) or by a reflector placed on the outside of the surface. Designs are described which include smaller prisms (refracting devices) at the input face to increase the acceptance angle or concentration factor.
WO 2008/131561 A1 (Morgan, Morgan Solar, Inc.) is similar in nature in that it uses an optical wedge-shaped waveguide to concentrate light at an input face to an exit face. The invention requires the use of optical elements formed between a light input surface and a first light output surface, and an optical waveguide coupled to the first light output surface and having a second output surface.
U.S. Pat. No. 5,646,397 (Wenham, Unisearch Limited, 1997) describes a more advanced type of solar wedge concentrator which incorporates a flat reflector and a curved reflector. The solar cell is placed at the input surface and collects light that enters through the input surface and is reflected from the flat and curved surfaces onto the back of the solar cell. The flat reflector has facets to increase the acceptance angle of the device. Two wedges are used placed adjacent but with one rotated 180° with respect to the other. In this way light incident on the device is collected in one or other concentrator as it deviates from the normal to the devices.
U.S. Pat. No. 6,294,723 (Uematsu, Hitachi, Ltd. 2001) describes an improved version of this device in which wedge concentrators of a very similar design are linked together. However the wedge concentrators are designed to have an asymmetric collection efficiency with respect to the normal to the light incident face. In this way the wedge concentrators can be optimized to work with a particular insolation angle range (the range of angles over which the sun will move during the course of a specified time period—for a year the sun will change it's zenithal inclination by about 46°). However, the invention requires the use of bi-facial solar cells to work well. If light is collected simply from the side of the cell that faces the reflecting surfaces of the prism then some light is lost or blocked at the incident surface. Using a bi-facial solar cell overcomes this problem, but at the expense of increased cost or lower overall efficiency.
A first aspect of the present invention provides a solar concentration apparatus comprising: an optical waveguide with a light input face and a light output face which is substantially parallel to the light input face but displaced such that the two surfaces are not co-planar, the light output face being smaller than the light input face; the optical waveguide comprising at least one part that is shaped in a uniform wedge; the optical waveguide further comprising a light turning element; and a solar receiving device. As used herein, a uniform wedge is defined as a wedge that has the same cross-section throughout its depth (meaning the orthogonal direction to the cross-section).
The solar receiving device may be a photovoltaic cell, thermovoltaic cell or other thermal solar device.
The solar receiving device may be attached directly to the light output face such that it is optically coupled to the light output face.
The light turning element may be a single reflective surface using total internal reflection or reflector on the exterior of the wedge concentrator. The reflective surface may be flat or curved. Such a curved reflective surface may comprise one or more radii of curvature. Alternatively the light turning element may comprise several surfaces for reflecting the light.
The solar concentration apparatus is designed to be positioned so as to receive and concentrate all light incident upon it during the day without the need to track the sun. In such a case the sun will traverse in a plane substantially perpendicular to the wedge cross-section. The solar concentration apparatus is also designed to be positioned so as to receive and concentrate the majority of light incident upon it during the year without the need to track the sun. In such a case the acceptance angle of the waveguide concentrator is designed to be less than or equal to 46° As used herein, an acceptance angle is defined as the angle within which light entering the device through the input face is guided/delivered to the output face (e.g., light incident on the input face at angles outside this angle range will not exit the device through the output face).
According to another aspect of this invention an array of waveguide solar concentrators may be formed together such that they are tiled with the thin end of one wedge concentrator lying adjacent to or overlapping the light turning element portion of an adjacent concentrator, such that there is no loss of aperture at the light input surfaces allowing 100% collection of all incident solar radiation. The solar receiving devices are arranged to be co-planar. The solar receiving devices can be attached directly to the output faces of the waveguide concentrator elements, or may be formed on a separate substrate and the waveguide concentrator assembly fixed on top of the array.
According to another aspect of this invention, the waveguide concentrator is designed to have a single light input face, but with many light output faces. The total area of the light output faces is less than the light input face. Each light output face is associated with a wedge shaped portion of the waveguide concentrator. One surface of each wedge shaped portion is designed to reflect incident light. Each light output face is also associated with at least one light turning element formed as part of the waveguide. All the light output faces are arranged to lie co-planar and parallel to the light input face. Each light output face is coupled to a solar receiving device.
The solar receiving devices may be attached directly to the waveguide concentrator, and may be optically coupled to the light output faces.
The solar receiving devices may be formed on a separate substrate. The waveguide concentrator may be designed to be placed directly onto the solar receiving devices and positioned so that the active areas of the solar receiving devices are designed to align with, and be optically coupled to, the light output faces.
According to another aspect of the invention, the waveguide concentrator is made from a single sheet of glass.
According to another aspect of the invention, the waveguide concentrator is made from a single sheet of plastic.
According to another aspect of the invention, the waveguide concentrator incorporates a UV blocking filter to prolong the lifetime of the concentrator material.
According to another aspect of the invention, the waveguide concentrator is used as the front cover glass of a solar panel which serves a dual function of providing concentration of solar radiation as well as providing a barrier between the active solar receivers and the environment.
According to another aspect of the invention the solar concentration apparatus may be formed as at least part of a roof tile. Several such solar concentration apparatus may be easily combined to form a roof comprised of overlapping tiles. It is thus possible to provide a solar apparatus for collecting solar radiation and use it to generate power in a very cost effective manner compared to conventional solar panels such as photovoltaic modules. Compared to existing art the apparatus in accordance with the present invention provides a means of concentrating all of the incident solar radiation without loss of efficiency due to limited fill factor. In addition, a large area non-tracked solar concentrator can easily and cheaply be fabricated using discrete areas of active solar receiving device and a single waveguide concentrator. In addition, the active solar receiving devices may be fabricated to lie co-planar, for example on a separate glass substrate, thus leading to a simple and cheap method of manufacturing an array of solar receiving devices.
According to one aspect of the invention, a waveguide concentrator includes: a wedge-shape optical waveguide including a light input face for receiving light and at least one light output face for outputting light, the light input face being on one side of the optical waveguide and the at least one light output face being on an opposite side of the optical waveguide, the light input face and at least one light output face being substantially parallel to each other and offset perpendicularly, wherein a surface area of the light input face is greater than a surface area of the at least one light output face; and at least one turning element coupling the light input face and the at least one light output face, the at least one turning element configured to turn light through an angle relative to a propagation direction of light in the waveguide.
According to one aspect of the invention, an angle of the light input face relative to the at least one light output face is less than 20 degrees.
According to one aspect of the invention, the wedge-shape optical wave guide includes a reflective surface on at least one side.
According to one aspect of the invention, the at least one light turning element is configured such that at least some light incident on the light input face directly impinges on the at least one light output face without being reflected in the waveguide.
According to one aspect of the invention, the at least one turning element is formed integral with the light input face and the at least one light output face.
According to one aspect of the invention, the at least one turning element comprises a single reflective surface.
According to one aspect of the invention, the reflective surface comprises a holographic element configured to redirect light propagating in the waveguide concentrator to the light output face.
According to one aspect of the invention, the reflective surface comprises a curved reflective surface.
According to one aspect of the invention, the curved reflective surface comprises at least two different radii.
According to one aspect of the invention, the reflective surface comprises both a curved reflective surface and planar reflective surface.
According to one aspect of the invention, the reflective surface comprises at least one planar surface.
According to one aspect of the invention, the at least one planar surface comprises a plurality of planar surfaces that are arranged at different inclinations relative to the light input face.
According to one aspect of the invention, the waveguide is configured to have an acceptance angle that is less than or equal to 46 degrees.
According to one aspect of the invention, the at least one light output face comprises a plurality of light output faces.
According to one aspect of the invention, a combined surface area of the plurality of light output faces is less than a surface area of the light input face.
According to one aspect of the invention, the waveguide comprises a plurality of wedge-shape portions, and each of the plurality of light output faces corresponds to a respective one of the plurality of wedge-shape portions.
According to one aspect of the invention, the waveguide comprises a plurality of turning elements, and each of the plurality of light output faces corresponds to a respective one of the plurality of turning elements.
According to one aspect of the invention, the waveguide concentrator comprises an ultra-violet blocking filter.
According to one aspect of the invention, the input face exhibits greater than 95 percent aperture ratio.
According to one aspect of the invention, a solar concentrator includes: the waveguide concentrator according to any one of the embodiments described herein; and a solar receiving device optically coupled to the light output face.
According to one aspect of the invention, the solar receiving device is at least one of a photovoltaic cell or a thermovoltaic cell.
According to one aspect of the invention, the solar receiving device and the waveguide concentrator are formed on separate substrates.
According to one aspect of the invention, the solar concentrator is integrated within building materials.
According to one aspect of the invention, the solar receiving device is directly coupled to the light output face.
According to one aspect of the invention, the solar receiving devices are electrically coupled to one another.
According to one aspect of the invention, a solar concentrator array includes a plurality of solar concentrators as set forth in any one of the embodiments described herein, wherein a waveguide of a first solar concentrator of the plurality of solar concentrators and a waveguide of a second solar concentrator of the plurality of solar concentrators are arranged relative to each other such that at least a portion of a light input face of the first solar concentrator is adjacent to a light turning element of the second solar concentrator.
According to one aspect of the invention, respective light input faces of the first and second waveguide concentrators are co-planar.
According to one aspect of the invention, at least part of the light turning element has an inclination to a plane of the light input face that is equal to or greater then an angle formed between the light input face and a side wall of the waveguide that is opposite the light turning device.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
Embodiments of the invention will be further described, by way of example, with reference to the accompanying drawings, in which:
The present invention will now be described with reference to the drawings in which like reference numerals are used to refer to like elements.
a shows a cross-section of a solar concentration apparatus 4, comprising a waveguide concentrator 14 and a solar receiver 16. The waveguide concentrator comprises a light input face 6 for receiving incident radiation 2, a light output face 8 which is substantially parallel to the light input face 6 but displaced from each other in a direction perpendicular to the light output face (e.g., they are not co-planar with one another), a wedge portion 10 which tapers to a point 9 with a wedge angle 7, and at least one light turning element 12. As used herein, “substantially parallel” is defined as two faces or planes having an angle less than 20° and, more preferably, less than 10° relative to each other.
Incident radiation 2 illuminates the waveguide concentrator 14 as shown in
The wedge portion 10 may have flat surfaces as depicted
The solar concentrator apparatus is designed to work for a range of solar insolation. The solar concentrator apparatus is designed to be arranged such that the sun tracks in a plane which is orthogonal to the cross-section shown in
The light turning element 12 shown in
The
The waveguide concentrator 14 may be made of a solid material such as glass or plastic as shown in
A small solar concentration apparatus was fabricated to prove the principles herein described, and to compare the measured performance to theoretical prediction from ray tracing software. A waveguide concentrator 14 as shown in
The solar concentration apparatus 4 shown in
There is a further advantage of forming solar concentration apparatus in this way if the solar receiving devices 16 are kept co-planar. The solar receiving devices 16 may be formed together on a single large substrate 22. Once fabrication of the solar receiving devices is complete then the waveguide concentrators 14 may be placed on top of the solar receiving devices. In this way it is possible to simply and cheaply make a large area solar concentration apparatus.
In order to further simplify fabrication of a large area version of the solar concentration apparatus described hereinbefore it is possible to make a version of the wedge concentrator which has a single light input face 6 but many light output faces 8. Such a design is shown in
The waveguide concentrator may be used in a solar concentration apparatus as shown in
The waveguide concentrator of this embodiment may be used to form the front protective cover plate of a solar panel.
If the waveguide concentrator is fabricated from plastic then it is advisable to use a highly UV resistant plastic to reduce degradation problems. Alternatively a protective film 24 may be applied to the waveguide concentrator as shown in
In describing specific embodiments in this invention, certain desirable features have been omitted for clarity. For example, no electrical or thermal connections between solar receiving units have been described, nor loads nor electrical converters have been described, but it is obvious to any ordinary person that such features would be required in order for the solar concentrating apparatus to function. In order to rectify this, an example is shown in
The solar concentration apparatus hereinbefore described is primarily intended to be formed into a stand-alone apparatus that could be installed in a number of situations and applications. Such examples would be on rooftops or walls of houses or industrial buildings. The apparatus could be used as a portable power supply for example for powering devices in a motor home. The apparatus may also by used to power mobile electronic devices such as mobile phones and laptop computers if the solar waveguide is made at the appropriate scale.
The apparatus may also be used in building integrated photovoltaic systems. For example, the solar concentration apparatus may easily be used as roof tiles as illustrated in
It is the intention that the invention is not limited to the specific embodiments and examples given above, and that others will be obvious to anyone skilled in the art.