Patent Application
20170063294
Embodiments of the subject matter described herein relates generally to solar concentrators. For example, embodiments of the subject matter relate to concentrating reflectors used for concentrated photovoltaic solar systems.
Concentrated solar power systems are different from unconcentrated solar power systems in a number of ways. Firstly, unconcentrated solar power systems are exposed to direct focused or diffused sunlight which generally strikes individual solar modules with a high degree of uniformity. Concentrated solar power systems, on the other hand, include curved reflectors designed to concentrate direct focused sunlight onto a smaller solar receiver. Additionally, many systems are designed so that the curved concentrator redirect the sunlight in a direction skewed relative to the direction of incident light from the sun, making the optical geometry more complicated.
Additionally, because concentrated solar power systems concentrate the sunlight directed at the solar receivers, the receivers of a concentrated solar power system must be designed to withstand higher temperatures and greater amounts of solar irradiation.
The solar cells used in both concentrated and unconcentrated solar modules are essentially the same, albeit tuned for different maximum levels of irradiation exposure. However, both types of solar cells experience decreased or impaired performance when irradiated in a non-uniform manner. For example, solar modules designed for nonconcentrated systems can be completely shut down when a single solar module is partially shaded.
On the other hand, solar receivers for concentrated solar systems are desirably fine tuned based on the predicted magnitude of irradiation, and more particularly, the maximum predicted irradiation intensity, anywhere on the exposed surface of the receiver.
Thus, if a solar receiver for a concentrated solar system is exposed to a non-uniform concentrated irradiation, for example, which may impact a limited portion of the receiver, the entire receiver, including the solar cells, would be designed to withstand that maximum predicted irradiation intensity. Such predicted maximum irradiation intensity also affects the design of thermal management devices, such as heat sinks and active cooling devices designed for cooling the solar cells so as to withstand the predicted maximum irradiation intensity.
An aspect of at least one of the embodiments disclosed herein includes the realization that certain non-uniformities which inherently result from certain concentrator-receiver geometries, can be combined in a way so as to offset each other so as to provide more uniform irradiation of an associated receiver.
For example, with some concentrator-receiver pair designs, one edge, such as a lower edge of the concentrating reflector, is closer to the receiver than an upper edge. Thus, when light is reflected onto the receiver, in a converging beam, the intensity of the light received at the receiver from the bottom edge of the reflector is more intense than the light received at the receiver reflected by the top edge of the reflector. The resulting irradiation intensity profile is therefore decreasing in the vertical direction along the height of the receiver. An example of such an irradiation intensity profile illustrated in
On the other hand, if the curvature of the concentrating reflector is designed to create a focal point before striking the receiver, the resulting intensity profile is inverted, for example, increasing in intensity in the height direction, in the example described above. Thus, if a concentrating reflector is configured with two different curvatures, providing two beams having different characteristics, e.g., different focal points, the different intensity profiles generated by these two different curves can be combined, resulting in a more uniform intensity profile.
Thus, in accordance with an embodiment, a concentrated solar power unit can comprise a paired sunlight concentrating reflector and photovoltaic receiver, arranged such that incoming sunlight from the sun is reflected by the first sunlight concentrating reflector, onto the first photovoltaic receiver. The sunlight concentrating reflector can have a reflective side facing a sunlight sensitive side of the photovoltaic receiver, the sunlight sensitive side of the photovoltaic receiver comprising a receiver lower edge, a receiver upper edge, and a light sensitive portion disposed between the received upper edge and the receiver lower edge, the sunlight concentrating reflector comprising a concentrator lower edge and a concentrator upper edge. The reflective side of the sunlight concentrating reflector can comprise a first lower portion extending between the concentrator lower edge and an intermediate point on the reflective side and a first upper portion extending between the intermediate point and the concentrator upper edge. The first lower portion of the reflective side can have a first curvature configured to reflect the incoming sunlight into a first lower beam projecting a first band of reflected sunlight extending over substantially an entire height of the light sensitive portion of the first photovoltaic receiver. The first upper portion of the reflective side can have a second curvature configured to reflect the incoming sunlight into a first upper beam projecting a second band of reflected sunlight overlapping the first band of reflected sunlight. One of the first lower beam and the first upper beam has a first focal point between the reflective side and the sunlight sensitive portion and the other of the first lower beam and the first upper beam has a second focal point that is not between the reflective side and the sunlight sensitive portion.
In accordance with another embodiment, a concentrating reflector can comprise a concave, reflective surface extending along a longitudinal direction having first and second longitudinal ends and extending in a transverse direction between upper and lower edges. The reflective surface comprising at least a first portion having a first curvature, a second portion having a second curvature, and an intermediate portion disposed between the first and second portions. The first portion of the reflective surface extending between the lower edge and the intermediate portion, the second portion of the reflective surface extending between the upper edge and the intermediate portion. The first and second curvatures being configured to reflect first and second reflected beams of light, respectively, which are substantially coincident at a plane spaced from the reflective surface, forming a planar band of light comprising a superposition of the first and second beams. The first reflected beam of light has a first focal point and the second reflected beam of light has a second focal point, the second focal point spaced closer to the reflective surface than the first focal point, the plane being disposed between the first and second focal points.
In accordance with yet another embodiment, a concentrated solar power unit can comprise a photovoltaic receiver and a sunlight concentrating reflector having a reflective side facing toward a light sensitive portion of the photovoltaic receiver, the reflective side comprising a lower portion extending between a lower edge of the reflective side and an intermediate point on the reflective side, and an upper portion extending between the intermediate point and an upper edge of the reflective side. The lower portion reflecting sunlight into a lower beam projecting a first band of reflected sunlight onto a light sensitive portion of the photovoltaic receiver. The upper portion of the reflective side reflecting sunlight into an upper beam projecting a second band of reflected sunlight overlapping the first band of reflected sunlight. One of the lower beam and the upper beam has a first focal point between the reflective side and the sunlight sensitive portion and the other of the first lower beam and the first upper beam has a second focal point that is not between the reflective side and the sunlight sensitive portion.
In accordance with yet another embodiment, a concentrated solar power unit can comprise a photovoltaic receiver having a light sensitive portion and means for directing first and second beams of reflected sunlight, respectively, the first and second beams of impinging on the light sensitive side of the photovoltaic receiver with first and second different, non-uniform, irradiation intensity profiles, and summing the first and second beams of light so as to produce a resulting irradiation intensity profile that is more uniform than both of first and second different, non-uniform, irradiation intensity profiles.
In accordance with yet another embodiment, a concentrated solar power system can comprise an array of paired sunlight concentrating reflectors and photovoltaic receivers, the array including at least a plurality of first sunlight concentrating reflectors and a plurality of first photovoltaic receivers. Each of the first sunlight concentrating reflectors and each of the first photovoltaic receivers can be arranged such that incoming sunlight from the sun is reflected by the first sunlight concentrating reflectors, along a reflected direction skewed relative to the incoming sunlight, onto the first photovoltaic receivers. Each of the first sunlight concentrating receivers having a reflective side facing toward a sunlight sensitive side of respective first photovoltaic receivers, the sunlight sensitive side of the first photovoltaic receivers comprising a receiver lower edge and a receiver upper edge, the first sunlight concentrating reflectors comprising a concentrator lower edge and a concentrator upper edge, wherein the first photovoltaic receivers are fixed in an orientation such that a lower spacing between the receiver lower edges and the concentrator lower edges is smaller than an upper spacing between the receiver upper edges and the concentrator upper edges. The reflective sides of each of the first sunlight concentrating reflectors comprising a first lower portion extending between the concentrator lower edge and an intermediate point on the reflective side and a first upper portion extending between the intermediate point and the concentrator upper edge. Each of the first lower portions of the reflective sides having a first curvature configured to reflect and concentrate the incoming sunlight into a first concentrated beam projecting a first band of reflected sunlight extending substantially an entire height of the light sensitive side of a respective one of the first photovoltaic receivers between the receiver upper and receiver lower edges and with a first focal point further from the reflective surface than the light sensitive surface. The first upper portion of each of the reflective sides comprises a second curvature configured to reflect and concentrate the incoming direct sunlight into a second concentrated beam projecting a second band of reflected sunlight overlapping the first band of reflected sunlight with a second focal point disposed between the reflective surface and the light sensitive surface.
A more complete understanding of the subject matter may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.
The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration. Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
“Coupled”—the following description refers to elements or nodes or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically.
“Adjust”—Some elements, components, and/or features are described as being adjustable or adjusted. As used herein, unless expressly stated otherwise, “adjust” means to position, modify, alter, or dispose an element or component or portion thereof as suitable to the circumstance and embodiment. In certain cases, the element or component, or portion thereof, can remain in an unchanged position, state, and/or condition as a result of adjustment, if appropriate or desirable for the embodiment under the circumstances. In some cases, the element or component can be altered, changed, or modified to a new position, state, and/or condition as a result of adjustment, if appropriate or desired.
“Inhibit”—As used herein, inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, and/or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.
“Concave”—As used herein, concave is used to indicate a surface that is indented or recessed in any shape, including curved, notched, conical, or other mathematically-defined curvatures, as well as series of flat or curved surfaces that together form a recess, or other similar shapes.
In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “height”, “width”, “longitudinal”, “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, and “side” describe the orientation and/or location of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second”, and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.
The description set forth below discloses embodiments in the context of concentrated, photovoltaic solar power systems because they have particular advantages in that context. However, embodiments disclosed herein can be used in other contexts as well, such as concentrated thermal solar systems, other energy systems, and other optical systems.
Concentrator arrays typically have successive rows of concentrating elements. Some such arrays have solar receiver elements mounted to concentrating reflectors to conserve space and preserve ground cover. A level array of such concentrator/receiver pairs introduces undesirable paths for concentrated light to travel. For example, the light travel distance from a concentrator reflective surface to a receiver element may be different for light reflected from opposite sides of the reflective surface. This difference can introduce undesirable characteristics, such as intensity variations over the surface of the receiver and during slight misalignment. Additionally, an edge can reflect light to the solar receiver at an undesirably steep angle, which can reduce the optical transmission efficiency of the system. Steep angles of incidence occurring at the reflective surface also reduce optical transmission efficiency.
Solar energy collection systems can be in the form of concentrated or nonconcentrated systems. Additionally, nonconcentrated systems can include sun tracking systems or can be installed in fixed orientations relative to the sun. However, known concentrating systems are required to be moved for sun tracking purposes due to the optics employed for concentrating sunlight onto photovoltaic receivers or thermal receivers.
With reference to
In the description set forth below, the solar energy collection system 10 is described in the context of a plurality of concentrating solar energy units, comprising a paired concentrating reflector and a photovoltaic receiver. Pluralities of these pairs are supported on common, pivotally adjustable, sun tracking support systems. Each of the units can include wiring for connecting the various photovoltaic receivers to each other and to other units.
The solar energy collection system 10 of
With reference to
The concentrator assembly 100 can comprise a pier or a post 102 which supports a crossbeam 104 and a torque tube 106. The crossbeam 104, in turn, supports the plurality of paired concentrating reflectors and receivers noted above, which can be referred to as first and second groups 120, 140 of concentrator-receiver pairs. As illustrated in
The post 102 can be a single post of one of several supporting the solar concentrator assembly 100. The post 102 is preferably anchored within a foundation in the ground to support it. The post 102 can be a solid or hollow member of sufficient size and cross-sectional characteristics to support the solar concentrator assembly 100. The post 102 can be formed of metal, such as steel, aluminum, and similar high strength metals, or alternative materials. For example, concrete or ceramic can be used in some embodiments, as desired.
The crossbeam 104 is supported by the post 102 and the torque tube 106. The crossbeam 104 can have a substantially horizontal shape when the assembly 100 is oriented at a “noon” position. Additionally, the crossbeam 104 can include an upwardly angled portion for positioning individual concentrator units at different vertical heights, relative to the rotational axis 190 of the torque tube 106. The torque tube 106 can be supported by a bearing or bushing (not shown) or other assembly permitting rotation of the torque tube 106 about its long axis, i.e., rotational axis 190. In some embodiments, a motor (not shown) or other driving device can be situated between the post 102 and the torque tube 106. A controller (not shown) can be used to drive the motor, and thus drive the torque tube 106 through a sun tracking motion.
With continued reference to
In the embodiment of
The concentrators 322, 324, 326, are each configured to generate two beams of light, generating different irradiation intensity profiles on the corresponding receivers 332, 334, 336 such that the beams of light are superimposed such that their irradiation are summed at the surface of the receivers 324, 326, 336. Additionally, the concentrator-receiver pairs are mounted at different heights H2, H3, H4, relative to the crossbeam 104 such that the lower edges of the reflectors 322, 324, 326 follow along an angle α relative to horizontal in the orientation illustrated in
With continued reference to
Although the top and bottom edges of the beams of light are illustrated as impinging on substantially entirely the face of the receiver 336, the bands of sunlight projected onto the light sensitive side of the receiver 336 can be narrower and focused on a solar cell positioned at a desired location on the light sensitive side of the receiver 336. Thus, a narrower band of concentrated sunlight can be produced in a precise geometry, as closely as possible on the solar cells within the receiver 336 so as to not waste reflected light on nonfunctional portions of the receiver 336.
Because the lower edge of the concentrating reflector 326 is positioned furthest from the receiver 336, the resulting beam of light bounded by boundaries 368, 364 varies in intensity, projecting a band of light on the receiver 336 that varies in intensity with the lowest intensity at the lower edge of the receiver 336 and the highest intensity at the upper edge of the receiver 336. However, because the beam of light generated by the upper portion 372 of the concentrating reflector 326 converges to a focal point 374 between the reflector 326 and the receiver 336, the intensity profile of the reflected light projected onto the receiver 336 is inverted, with the highest intensity at the lower edge of the receiver 336 and the lowest intensity at the upper edge of the receiver 336. Similar intensity profiles are described below with reference to
With reference to
As shown in
It should also be noted that the sunlight reflected onto the receiver 432 also varies in accordance with an effective intensity affected by the angle of incident of light on the receiver 432. This is because some photovoltaic receivers 432 receive sunlight in a highly efficient manner when sunlight is perpendicular to the light sensitive side of the receiver, and less efficiently when the light impinges on the light sensitive side of the receiver 432 at a non-normal angle. For example, an upper edge normal line 467 extends perpendicularly to the reflective surface at the top edge of the concentrator 422. The top edge of concentrated sunlight 466 forms an angle β0 with the upper edge normal 467. It is desirable to reduce the angle β0. Various parameters and the effects thereof are disclosed in U.S. Patent Publication number 2012/0031393, the entire contents of which are hereby incorporated by reference.
As shown in
With reference to
In the graphs of
As shown in
On the other hand, the intensity profile generated by the upper portion 372 of the reflector 326 is inverted relative to the profile of
Thus, as shown in
The geometry of various embodiments of concentrating reflectors is illustrated in
With reference to
With reference to
The beam 680 is a converging beam, and a plane 682 can be defined within the beam 680. In this context, the beam 680 converges to a focal point 675 at a position further from the concentrating reflector 626 than the plane 682. The curvature of the concentrating reflector 626 can be defined by a high order polynomial, such as a 20, 30, 40, or higher order polynomials, conic sections, other mathematical functions or shapes using known techniques. The concentrating reflector 626, and more specifically, the reflective surface 684 can be manufactured so as to follow any desired geometric shape, which can be defined by a mathematical function, such as the high order polynomial noted above. Such manufacturing techniques are well known, and include a sag bending technique.
With reference to
As such, the beam 680 illustrated in
With reference to
With reference to
With reference to
As shown in
As such, as illustrated in
Optionally, the intermediate portion 790 can be configured to produce a beam 792 that impinges on a portion of the upper edge of the light sensitive portion 735 or onto the nonsensitive encapsulant surrounding the solar cell 735.
As such, the light sensitive portion 735 of the receiver 732 is in essentially the same shape and orientation as the plane 682 of
As such, the beam 780 projects a band of light onto the light sensitive portion 735 that has the strongest intensity at the lower edge 741 of the light sensitive portion 735 and the weakest intensity at the upper edge 743 of the light sensitive portion 735. On the other hand, because the beam of light 786 has a focal point 774 disposed between the receiver 732 and the concentrating reflector 726, the beam 786 produces a band of light on the light sensitive portion 735 that is the weakest at the lower edge 741 of the receiver and the strongest at the upper edge 743. As such, the beam 780 would produce an irradiation intensity profile similar to
Thus, with the beams 780, 786 producing superimposed bands of light on the light sensitive portion 735, the summed irradiation can produce an irradiation intensity profile similar to that of
In the embodiments of
As shown in
As illustrated in
As illustrated in
In the assembly 900, the beams 980, 989 do not include focal points between the receiver 932 and the concentrating reflector 926. Rather, the beams 980, 989 produce focal points (not shown) that are disposed further from the reflector 926 and the receiver 932. On the other hand, the beams 987 and 986 produce focal points 974, 977, both of which are disposed between the receiver 932 and the concentrator 926. As such, the beam 980 can produce a resulting intensity profile like that of
Similarly, the beam 987 produces a focal point 977, and thus can produce an intensity profile like that of
Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure.
The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features.
