Abstract:
A solar concentrator assembly is disclosed. The solar concentrator assembly comprises a first reflector facing in a first direction, a second reflector facing in a second direction, the second direction opposite the first direction, and a rotational member having a long axis transverse to the first and second directions, the rotational member disposed between and coupled to each of the first and second reflectors.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the subject matter described herein relate generally to solar concentrators. More particularly, embodiments of the subject matter relate to concentrator component arrangements. 
       BACKGROUND 
       [0002]    Solar concentrators are different from unconcentrated solar panels in a number of ways, including challenges regarding weight distribution. Solar concentrator arrays are frequently mounted to, and have their position adjusted at, a central post or pier. Such concentrator arrays typically have a support structure with a lateral member, such as a crossbeam or strut. The lateral member is typically coupled directly to the post, usually by a positioning mechanism. In turn, several concentrator elements are coupled to the lateral member, and are supported by it. 
         [0003]    As a consequence of the components&#39; position above the lateral member, the center of gravity of the concentrator array is above the post, and, consequently, above the positioning mechanism. When the concentrator array rotates to certain positions, the concentrator array can experience an undesirable moment at the positioning mechanism caused by the position of the center of gravity relative to the positioning mechanism. Traditionally, this is offset by a counterweight, which increases the overall weight of the system and increases cost, among other undesirable effects. 
         [0004]    Additionally, the arrangement of concentrator elements is usually optimized to reduce or eliminate losses to inefficient ground cover, and the associated overall system cost increase. The ratio of concentrator aperture to area of ground covered therefore is preferably increased as high as possible. One way this can be done is with numerous concentrator elements covering the available ground. Dense concentrator elements can present numerous challenges to efficient power conversion. 
       BRIEF SUMMARY 
       [0005]    A solar concentrator assembly is disclosed. The solar concentrator assembly comprises a first reflector facing in a first direction, a second reflector facing in a second direction, the second direction opposite the first direction, and a rotational member having a long axis transverse to the first and second directions, the rotational member disposed between and coupled to each of the first and second reflectors. 
         [0006]    Another embodiment of a solar concentrator assembly is disclosed. The solar concentrator assembly comprises a first plurality of concentrator elements facing in a first direction, and a second plurality of concentrator elements facing in a second direction, the second direction opposite the first direction. 
         [0007]    Still another embodiment of a solar concentrator assembly is disclosed. The solar concentrator assembly comprises a first reflective element facing in a first direction, a second reflective element facing in the first direction, the second reflective element positioned in front of and vertically offset from the first reflective element, a third reflective element facing in a second direction, the second direction opposite the first direction, and a rotational assembly disposed between and coupled to the first and third reflective elements, the rotational assembly adapted to adjust the position of the first, second, and third reflective elements by rotating about a rotational axis, the rotational axis transverse to the first and second directions. 
         [0008]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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. 
           [0010]      FIG. 1  is a side view of an embodiment of a solar concentrator system; 
           [0011]      FIG. 2  is a perspective view of the solar concentrator system of  FIG. 1 ; 
           [0012]      FIG. 3  is a side view of an embodiment of a solar concentrator system in a rotated position; 
           [0013]      FIG. 4  is a side view of an embodiment of a solar concentrator system in a rotated position under wind loading; 
           [0014]      FIG. 5  is a detailed side view of an embodiment of a solar concentrator array; 
           [0015]      FIG. 6  is a side view of a portion of an embodiment of a solar concentrator array; and 
           [0016]      FIG. 7  is a side view of a portion of another embodiment of a solar concentrator array. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    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. 
         [0018]    “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. Thus, although the schematic shown in  FIG. 5  depicts one exemplary arrangement of elements, additional intervening elements, devices, features, or components may be present in an embodiment of the depicted subject matter. 
         [0019]    “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. 
         [0020]    “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. 
         [0021]    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 “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. 
         [0022]    Solar concentrator elements can be arranged to provide nearly complete ground cover. Typical concentrator arrays have a center of gravity offset from a rotational axis of the array. As a result of this offset, when the concentrator array is rotated such that the center of gravity is not directly above the rotational axis, such as during sun tracking, a moment is created about the rotational axis. This moment can increase the difficulty of properly aligning the concentrator array, thereby reducing efficiency. To counter this moment, some concentrator arrays have a counterweight, which adds to system cost and weight, neither of which are desirable. 
         [0023]    Moreover, concentrator arrays typically have successive rows of concentrating elements. Some such arrays have solar receiver elements mounted to concentrator elements 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 variation 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. 
         [0024]    To inhibit these undesirable effects, solar concentrators can be arranged to have the center of gravity of the concentrator array positioned along the axis of rotation of the array. This reduces or eliminates the moment that would be caused by an offset center of gravity. To prevent loss of ground cover that would be caused by positioning a rotational member, such as a torque tube among concentrator elements, the concentrator elements can be arranged such that half face in one direction, the other half in the opposite direction, with the torque tube positioned between. 
         [0025]    Additionally, the concentrator elements can be offset in a vertical direction from each other, rising higher out of a level horizontal plane, the farther they are positioned from the torque tube. This offset can reduce the difference in light travel distance between opposite edges of the concentrator&#39;s reflective surface. Moreover, the angle of light impinging on the solar receiver, relative to the surface of the solar receiver, is adjusted to reduce the angle, and thereby lessen scattering and transmission losses. The vertical offset of the concentrator elements also allows for a reflector design with a smaller angle of light incidence upon the surface, thus reducing optical transmission losses from this element. 
         [0026]      FIGS. 1 and 2  illustrate an embodiment of a solar concentrator array or assembly  100 . The drawings contained herein are for descriptive purposes and may not be to scale. Certain features may be exaggerated for explanation. The solar concentrator assembly  100  comprises a pier or post  102  which supports a crossbeam  104  and torque tube  106 . The crossbeam  104  in turn supports first and second groups of concentrator elements  120 ,  140 . The first group of concentrator elements  120  face in one direction, while the second group of concentrator elements  140  are positioned facing the opposite direction, with the changeover between them occurring at the torque tube  106 . Certain elements are shown, while others are omitted for clarity and descriptive purposes, as will be explained in greater detail below. 
         [0027]    The post  102  can be a single post or one of several supporting the solar concentrator assembly. 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 a metal, such as steel, aluminum, and similar high-strength metals, or alternative material. For example, concrete or ceramic can be used in some embodiments, as desired. 
         [0028]    When groups of concentrator elements are positioned laterally adjacent each other to extend the solar concentrator assembly  100 , multiple posts  102  can be used, spaced appropriately, to support the entire arrangement. Thus, although only one group of concentrator elements is shown facing each direction in  FIGS. 1 and 2 , more groups can be positioned along the torque tube  106 , extending the solar concentrator assembly  100 . Posts  102  can be positioned between every concentrator element group or spaced further apart, as desired. 
         [0029]    The crossbeam  104  is supported by the post  102  and torque tube  106 . As explained in greater detail below, the crossbeam  104  can have a substantially horizontal shape, which can include an upwardly-angled portion for positioning individual concentrator elements. The crossbeam  104  can be one of several crossbeams or cross-pieces which support a given concentrator element group. Thus, although one crossbeam  104  is shown, several lateral members can support a single concentrator element successively along the torque tube  106 . The crossbeam is preferably made from a high-strength metal such as steel, although other materials can be used, as desired. 
         [0030]    The rotational member, or torque tube  106 , can be mounted to, and supported by, the post  102 . The torque tube  106  is preferably mounted by or to a bearing or bushing or other assembly permitting rotation of the torque tube  106  along its long axis. In some embodiments, a motor or other driving device can be situated between the post  102  and torque tube  106  to adjust the position of the torque tube  104 , and correspondingly, the position of the concentrator element groups  120 ,  140 . The torque tube  106  is preferably a hollow tube with a circular cross-section, although other shapes and geometries can be used if preferred, including elliptical or solid shafts. The torque tube  106  has a long axis extending along its length. The long axis extends through the center of the cross-section of the torque tube  106  and the torque tube rotates around it. 
         [0031]    The torque tube  106  can extend through multiple concentrator element groups, including extending substantially entirely along the width of the concentrator elements, either as a unitary piece or by coupling together similar tubes. Thus, although the torque tube  106  is shown with two concentrator element groups  120 ,  140 , there can be other element groups adjacent these, up to an appropriate limit. The torque tube  106  preferably can support the weight of the crossbeam  104  and concentrator element groups  120 ,  140  with minimal elastic or inelastic deforming, thereby inhibiting alignment error into the solar concentrator assembly  100 . The torque tube  106  is preferably rigidly mounted to the crosspieces, including crossbeam  104 , such that rotating the torque tube  106  around its long axis similarly rotates the crosspieces. 
         [0032]    The solar concentrator element groups  120 ,  140 , directly or indirectly, are coupled to and supported by the crossbeam  104  and torque tube  106 . The first concentrator element group  120  is composed of the first, second, and third concentrator elements  122 ,  124 ,  126 . The second concentrator group  140  is composed of fourth, fifth, and sixth concentrator elements  142 ,  144 ,  146 . Each concentrator element  122 ,  124 ,  126 ,  142 ,  144 ,  146  has a front, reflective side and a rear side. The reflective side can be, or can include, a mirror shaped according to the geometric characteristics of the concentrator/receiver combination to provide concentrated sunlight on the solar receiver. The concentrator elements  122 ,  124 ,  126 ,  142 ,  144 ,  146  receive unconcentrated sunlight and reflect it to a solar receiver, while concentrating it to a smaller area than the reflective surface. Preferably, the concentrator elements  122 ,  124 ,  126 ,  142 ,  144 ,  146  have a parabolic shape, as shown, although other shapes can be used. 
         [0033]    For descriptive purposes, certain aspects of the solar concentrator assembly  100  are illustrated not entirely to scale, in a different position, or in a different orientation than they may appear in certain embodiments. For example, concentrator elements  122 ,  142  are illustrated with a greater vertical position than might be the case in some embodiments. Thus, in certain embodiments, the concentrator elements  122 ,  142  may extend substantially entirely over the torque tube  106 , thereby reducing the amount of sunlight which falls between them and increasing the amount captured by the concentrator elements  122 . Similarly, all concentrator elements  122 ,  124 ,  126 ,  142 ,  144 ,  146  can have such different orientations. 
         [0034]    The first concentrator element  122  reflects concentrated sunlight to the first solar receiver  132 . The second concentrator element  124  reflects concentrated sunlight to the second solar receiver  134 . The third concentrator element  126  can also direct concentrated sunlight to a receiver mounted on the crossbeam  104 , although it has been omitted for clarity. Similarly, the fourth and fifth concentrator elements  142 ,  144  can direct concentrated sunlight to the third and fourth solar receivers  152 ,  154 , with the solar receiver corresponding to the sixth concentrator element  146  omitted for clarity. The omitted solar receivers corresponding to the third and sixth concentrator elements  126 ,  146  can be positioned at heights and in orientations necessary to cooperate with certain techniques described herein. Thus, the offset for the omitted receivers can correspond to the offset between the first and second solar receivers  132 ,  134  in a concentrator row. 
         [0035]    Each solar receiver  132 ,  134 ,  152 ,  154  can be mounted to the rear side of a concentrator element, as shown. The solar receivers  132 ,  134 ,  152 ,  154  can comprise a photovoltaic solar cell, diode, interconnect, thermal adhesive, heat spreading device, encapsulant, frame, junction box and/or micro-inverter, and other components as appropriate or desired for efficiently converting received concentrated sunlight to power, including electrical power. In some embodiments, the solar receivers can comprise back-contact, back junction solar cells, while in others, front-contact or other cells can be used. In certain embodiments, the solar receivers  132 ,  134 ,  152 ,  154  can be supported independently from the concentrator elements, such as by a support assembly coupled to the crossbeam  104 . 
         [0036]    Each solar receiver  132 ,  134 ,  152 ,  154  is preferably coupled to a concentrator element in a position such that reflected, concentrated sunlight impinges it at a predetermined angle. It is desirable that the incoming concentrated sunlight impinges at a 90° angle to the surface of the solar receiver  132 ,  134 ,  152 ,  154 . Thus, each solar receiver is preferably mounted in such a position that the surface of each solar receiver  132 ,  134 ,  152 ,  154  is at a right angle, or as nearly a right angle as practicable, to the anticipated angle of impinging concentrated sunlight from each concentrator element  122 ,  124 ,  126 ,  142 ,  144 ,  146 , as will be explained in greater detail below. 
         [0037]    Because the solar concentrator assembly  100  operates most efficiently when the maximum available sunlight is received by the concentrator elements  122 ,  124 ,  126 ,  142 ,  144 ,  146 , the torque tube  106  can be rotated during daily operation to adjust the position of the crossbeam  104  and other cross-pieces. This in turn changes the orientation of the concentrator elements  122 ,  124 ,  126 ,  142 ,  144 ,  146 , which can be positioned to advantageously and desirably receive as much sunlight as possible. 
         [0038]      FIGS. 3 and 4  illustrate another embodiment of a solar concentrator assembly  200 . Unless otherwise noted, the numerical indicators refer to similar elements as in  FIGS. 1 and 2 , except that the number has been incremented by 100. 
         [0039]      FIG. 3  illustrates a solar concentrator assembly  200  in a first, rotated position. As can be seen, the torque tube  206  has been rotated clockwise, which would correspond to tracking the sun to a position to the right of the post  202 . Preferably, the torque tube  206  is rotated by a drive mechanism which is, in turn, operated by a control system. The control system can include a processor, sensors, and other components to track the sun and adjust the orientation of the solar concentrator assembly  200  as desired. 
         [0040]    Thus, the orientation shown in  FIG. 3  is the result of rotating the solar concentrator assembly  200  to follow the course of the sun through the sky. As can be seen, the solar concentrator assembly  200  rotates around the axis of rotation  290  of the torque tube  206 . It is desirable that the center of gravity of the portion of the solar concentrator assembly  200  supported by the torque tube  206  coincide as closely as possible with the axis of rotation  290 . This is accomplished by arrangement of the groups of concentrator elements  220 ,  240  into the assembly shown. 
         [0041]    Specifically, the torque tube  206  is positioned between the first and second groups of concentrator elements  220 ,  240 . Each concentrator element in the first group of concentrator elements  220  faces in a different direction than each concentrator element in the second group of concentrator elements  240 . Thus, the two concentrator elements  222 ,  242  nearest the torque tube  206  have their rear sides both facing the torque tube  206 . Each concentrator element  222 ,  242  also has a reflective front side facing away from the torque tube  206 . Each concentrator elements in the same group of concentrator elements  220 ,  240  have the same orientation. 
         [0042]    This arrangement of concentrator elements permits the torque tube  206  to be positioned above the crossbeam  204 , unlike other concentrator assemblies where the crossbeam  204  is above the torque tube  206 . In such assemblies, the center of gravity is offset from the center of rotation of the torque tube  206 . Such an offset results in a moment about the center of rotation as the center of gravity is acted on by gravity. This moment introduces torque tube twist, which introduces misalignment and undesirable deformation to the assembly. By positioning the first and second groups of concentrator elements  220 ,  240  as shown, the torque tube  206  can be positioned to rotate about its axis  290  which is coincident with the center of gravity of the entire assembly. 
         [0043]    In some embodiments, the axis of rotation  290  is coincident with the center of gravity of the assembly, while in others, the center of gravity is positioned within the torque tube, although it may be slightly offset from the axis of rotation  290 . Preferably, however, any such offset is minimized. 
         [0044]      FIG. 4  illustrates the solar concentrator assembly  200  experiencing wind conditions illustrated by profile U. The force of wind experienced at concentrator element  246  is shown as F 1 . The force of wind experienced at concentrator element  244  is shown as F 2 . Typically, the wind profile U has a higher velocity with increasing altitude from the ground. Thus, the wind force experienced at concentrator element  226  is higher than the wind force experienced at concentrator element  246 . Thus, F 2  is typically higher than F 1 . This relationship continues through F 3 . 
         [0045]    Each force F 1 , F 2 , F 3  is exerted against a respective concentrator element  246 ,  244 ,  242 . Because each concentrator element  246 ,  244 ,  242  is offset from the axis of rotation  290 , a resultant moment M 1  is created about the axis of rotation  290 . In the relationship illustrated, the moment M 1  is clockwise about the axis of rotation  290 . The magnitude of the moment M 1  is determined in part by the velocity of the wind profile U, but also by the apparent cross-section of the concentrator elements  246 ,  244 ,  242  against which the wind forces F 1 , F 2 , F 3  are exerted. As can be seen, the clockwise rotation of the solar concentrator assembly  200  positions the second group of concentrator elements  240  to present a larger cross-section to the wind profile U. 
         [0046]    In addition to the benefit of permitting the torque tube  206  to be positioned above the crossbeam  204  and, therefore, the axis of rotation  290  coincident with the center of gravity, by arranging the concentrator elements as shown, the profile of the first group of concentrator elements  220  is turned into the wind profile U such that only a cross-section of the concentrator elements  222 ,  224 ,  226  is exposed to the wind profile U. The counterforce CF 1  exerted by the wind profile U against the concentrator element  226  contributes to a counter-moment CM 1  which is in the opposite direction to the moment M 1 . Accordingly, the moment M 1  is resisted in part by the forces CF 1 , CF 2 , and CF 3  experienced by concentrator elements  226 ,  224 ,  222 , respectively. 
         [0047]    Most desirably, the counter-moment CM 1  would be equal in magnitude to the moment M 1 , but in the opposite direction, resulting in only drag wind loads being imparted to the torque tube  206 . The arrangement and orientation of concentrator elements as shown contributes to equalizing the magnitudes of M 1  and CM 1 . This is because the higher-elevated first group of concentrator elements  220  experiences higher wind forces CF I , CF 2 , CF 3  because they are higher in the wind profile U. The cross-section presented by the first group of concentrator elements  220  is, however, smaller than that presented by the second group of concentrator elements  220 . The balance between the higher force and smaller cross-section of the first group of concentrator elements  220  and the lower force, but larger cross-section of the second group of concentrator elements  240  minimizes, reduces, and inhibits unequal moments M 1  and CM 1 , thereby reducing the moment experienced by the torque tube  206 . This is another advantage of the arrangement illustrated in  FIGS. 1-4 , in addition to the inhibition of torque tube twist. 
         [0048]      FIG. 5  illustrates a detailed view of a portion of a solar concentrator assembly  300 . Unless otherwise noted, the numerical indicators refer to similar elements as in  FIGS. 1 and 2 , except that the number has been incremented by 200. 
         [0049]    The sun  360  radiates sunlight  362 . The concentrated sunlight  362  is reflected by concentrator element  322  as concentrated sunlight  364  toward the first solar receiver  332 . A top edge of concentrated sunlight  366  travels from the top edge of the concentrator element  322  a certain distance to reach the first solar receiver  332 . A bottom edge of concentrated sunlight  368  travels a different distance from the bottom edge of the concentrator element  322  to reach the first solar receiver  332 . It is desirable that the top edge of concentrated sunlight  366  travel downward as little as possible while covering the distance to the first solar receiver  332 . Similarly, it is desirable that the bottom edge of concentrated sunlight  368  travel to the first solar receiver  332  as vertically as possible, reducing forward travel toward the adjacent concentrator element  324 . The result of these desirable improvements is that the band of focused sunlight impinging on a solar receiver has an even profile, with reduced or eliminated variation in intensity. 
         [0050]    It should be understood that although the top and bottom edges of concentrated sunlight  366 ,  368  are illustrated impinging on substantially entirely the face of the first solar receiver  332 , in practice, the band of concentrated sunlight can be narrower and focused on a solar cell positioned at a desired location on the face. Thus, a narrow band of concentrated sunlight can be reflected to the middle of the first solar receiver  332  and, preferably, to the middle of the solar cell. If the concentrated sunlight band impinges only on a middle portion of the solar cell, small misalignment errors will have a reduced effect on efficiency as the concentrated sunlight will still impinge the solar cell, even if slightly off target. 
         [0051]    The inventors have discovered that offsetting at least some of the concentrator elements  322 ,  324 ,  326  in a vertical direction as they proceed outward from the torque tube  306  permits advantageous geometrical characteristics to the reflector/receiver arrangement over concentrator elements positioned at the same height relative to one another. Thus, the first concentrator element  322  is positioned at a height of h 1 . The second concentrator element  324  is offset vertically to a height of h 2 , which is greater than h 1 . The third concentrator element  326  is offset vertically to a height of h 3 , which is, in turn, greater than h 2 . These heights are measure relative to the reference height of the bottom of the reflector component of concentrator element  322 . 
         [0052]    Angle α is indicative of the angle of constant vertical offset of the concentrator elements from a horizontal axis, as shown. Accordingly, angle α has a value greater than 0°, preferably approximately 5°. Thus, the exact value of the height difference can vary between embodiments so long as a consistent offset is used. In some embodiments, a non-linear offset can be used, such that the value of difference between h 1  and h 2  can be greater than the value of the difference between h 1  and h 0 . For concentrators spaced equally in the horizontal direction, a non-linear arrangement results. 
         [0053]    The solar receivers  332 ,  334  can be have a different orientation when coupled to concentrator elements  322 ,  324 ,  326  offset in a vertical direction than when coupled to concentrator elements without the vertical offset. The different orientation can be solely a rotation about an axis extending through a portion of the receiver, or can be or include a translation in the horizontal or vertical directions, in some embodiments. Preferably, however, a solar receiver does not protrude beyond the overhanging upper portion of the concentrator element to which it is coupled, and therefore does not cast a shadow on a portion of the concentrator element below. 
         [0054]    Additionally, the cross-sectional shape of the concentrator elements  322 ,  324 ,  326  can be altered from a shape used for concentrator elements without a vertical offset. Although both shapes can have a parabolic characteristic, those concentrator elements  322 ,  324 ,  326  vertically offset can have a slope which reflects light collectively more upwardly than a reflective surface of concentrator elements without vertical offset. 
         [0055]    The height difference between the concentrator elements need not display a similar height difference from a horizontal crossbeam  304 . As shown, the crossbeam  304  can have an upward cant substantially the same as angle α, or, in some embodiments, it can be horizontal. Similarly, cross-pieces of the solar concentrator assembly  300  can have a similar shape as the crossbeam  304 , or a different one. 
         [0056]      FIG. 6  illustrates a detailed view of a portion of a solar concentrator assembly  400 . Unless otherwise noted, the numerical indicators refer to similar elements as in  FIGS. 1 and 2 , except that the number has been incremented by 300. 
         [0057]      FIG. 6  illustrates an embodiment in which the two concentrator elements depicted  422 ,  424  are at the same height h 0 , or without vertical offset. Three additional reference lines are added to illustrate principles discovered by the inventors to advantageously increase efficiency of the solar concentrator assembly. First, a lower edge normal  469  is shown extending upwardly in a direction normal to, and from, the lower edge of the reflective side of the first concentrator element  422 . The lower edge of the reflective side of the first concentrator element  422  is preferably in a vertically-extending plane with the upper edge of the second concentrator element  424 . In this way, no sunlight is lost between the concentrator elements  422 ,  424 . The bottom edge of concentrated sunlight  468  forms an angle θ 0  with the lower edge normal  469 . 
         [0058]    The first solar receiver  432  is shown mounted to the rear side of the second concentrator element  424 . A mounting component in addition to a solar panel or cell portion can comprise the solar receiver  432 , as explained above. The solar receiver  432  receives the bottom edge of concentrated sunlight  468  at an angle, which depends on both the tilt of the solar receiver  432  and the parabolic shape of the reflective side of the concentrator element  422 . Preferably, the angle θ 0  is minimized to avoid inefficient sunlight transfer between the concentrator element  422  and the solar receiver  432 . Such inefficiency can occur when concentrated sunlight  464  travels through a glass surface of the solar receiver  432 . Even with anti-reflective coating, some scattering is unavoidable, and should be minimized to reduce the inefficiency of light travel through the surface of the solar receiver  432 . 
         [0059]    The solar receiver  432  has a normal direction  433  which is located at a right angle to the plane of the receiving surface of the solar receiver  432 . The normal direction  433  is preferably directed at the center of sunlight received from the concentrator element  422 . The center of sunlight is not necessarily the geometric center of the parabolic shape of the reflective surface of the concentrator element  422 , but instead is a weighted average of sunlight from the entire reflective surface of the concentrator element  422 . As concentrated sunlight  464  is more directly received from the lower portion of the reflective surface, the value of sunlight from this region is increased relative to, for example, concentrated sunlight  464  received at the solar receiver  432  from near the top edge of concentrated sunlight  466 . Accordingly, the normal direction  433  typically is positioned more towards the bottom edge  468  than the top edge  466  of concentrated sunlight. 
         [0060]    Additionally, light that impinges on the surface of the solar receiver  432  at a smaller angle to the normal direction  433  is more efficient than light which arrives at a larger angle to the normal direction  433 . Thus, light which has a smaller incident angle to the surface of the solar receiver  432  is more desirable. In some embodiments, an anti-reflective coating can be applied to the surface of the solar receiver  432 . One advantage to decreasing the incident angle of concentrated sunlight  464  arriving at the surface of the solar receiver  432  is that anti-reflective coating can be omitted without reducing efficiency, resulting in a cost savings. 
         [0061]    Finally, an upper edge normal  467  extends perpendicularly to the reflective surface at the top edge of the concentrator element  422  as shown. The top edge of concentrated sunlight  466  forms an angle β 0  with the upper edge normal  467 . It is desirable to reduce the angle β 0  for reasons similar to the advantage to reducing angle θ 0 . Moreover, unconcentrated sunlight  462  is reflected by the reflective surface of concentrator element  422  increasingly, that is, with less scattered light, as angle θ 0  decreases. 
         [0062]      FIG. 7  illustrates a detailed view of a portion of a solar concentrator assembly  500 . Unless otherwise noted, the numerical indicators refer to similar elements as in  FIG. 6 , except that the number has been incremented by 100. 
         [0063]    In  FIG. 7 , the second concentrator element  524 , to which the solar receiver  532  is mounted, has been vertically offset to a height h 1 . This vertical offset has an advantageous effect on each of the three characteristics described above with respect to  FIG. 6 .  FIGS. 6 and 7  are not to scale and distances or angles may be exaggerated to values either larger than actual measures or proportions or smaller for descriptive purposes. 
         [0064]    First, the angle θ 1  has been reduced. For reasons presented above, this increases efficiency of the solar receiver  532  by adjusting the angle concentrated sunlight  564  at or near the bottom edge of concentrated sunlight  568  travels through the surface of the solar receiver  532 . Additionally, the reflectance of the mirrored surface of the solar concentrator  522  is increased because the incident angle of unconcentrated sunlight  562  is decreased. 
         [0065]    Second, to continue to direct the normal direction  533  at the weighted average center of concentrated sunlight  564  from the reflective surface of the concentrator element  522 , the angle of the surface of the solar receiver facing concentrator element  522 , and receiving concentrated sunlight  564  therefrom, has been changed downward. Accordingly, the normal direction  533  has also been directed downward relative to the position in  FIG. 6 . Additionally, the shape of the reflective surface of the concentrator element  522  has been adjusted to a different parabolic shape which directs concentrated sunlight  564  in a greater concentration towards the bottom edge  568  than that of  FIG. 6 . This is advantageous for reasons similar to the benefit that results from a smaller angle θ 1 . 
         [0066]    Third, angle β 1  is likewise reduced. This additionally increases the efficiency of the solar concentrator assembly. Similarly to how decreasing angle θ 1  improves the reflectivity of the surface of the concentrator element  522  for sunlight reflected near the lower edge, the decreasing angle β 1  increases the reflectivity of the minor near the upper edge. This increase in reflectivity results in more concentrated sunlight  564  reflected toward the solar receiver  532  from near the upper edge. Moreover, these effects extend across the face of the entire reflective surface of the concentrator element  522 , improving reflectance of the unit as a whole. 
         [0067]    In addition to these three exemplary advantages which result from the vertical offset of the concentrator elements, the solar receiver  532  can be enlarged, as shown in  FIGS. 6 and 7 , while maintaining the same approximate position relative to the surface of the solar concentrator  522 . This is increased size of the solar receiver  532  can enable sizing changes or additional components to be added to the solar receiver  532 . For example, a larger heat sink can be incorporated into the solar receiver  532 . A larger heat sink can reduce the operating temperature of the solar cell included in the solar receiver  532 . By decreasing the operating temperature, the efficiency of the solar cell can be increased, resulting in an overall performance improvement to the system. 
         [0068]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.