US20130092155A1

US20130092155A1 - Focal display panel for visual optimization of solar collection

Info

Publication number: US20130092155A1
Application number: US13/273,540
Authority: US
Inventors: Matthew B. McCord; Thomas Matlosz; Michael Forsythe
Original assignee: Florida Power and Light Co
Current assignee: Florida Power and Light Co
Priority date: 2011-10-14
Filing date: 2011-10-14
Publication date: 2013-04-18
Also published as: WO2013055989A3; WO2013055989A2

Abstract

A focal display panel is situated in a parabolic solar energy collection array having reflective surfaces and a tube containing a working fluid to be heated. The panel comprises a target area to display patterns of light and shadow reflected from the array, and provides a visual means for determining the amount, if any, by which the focal point of the parabolic array misses the center of the tube containing the heated working fluid.

Description

BACKGROUND AND FIELD OF ART

Solar power is the conversion of sunlight into electricity, either directly using photovoltaic cells, or indirectly using concentrated solar power. Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam.
One such type of system is the parabolic trough, which uses a curved, mirrored trough which reflects the direct solar radiation onto a tube containing a heat transfer fluid (also called a receiver, absorber or working fluid) running the length of the trough, positioned at the focal point of the reflectors. Mirrors, usually curved mirrors, are positioned along the mirrored trough, and shaped to reflect sunlight onto the tube which contains the working fluid. The working fluid is then heated by the reflected solar energy, and is converted into electricity by any means currently known in the industry for doing so, including boiling water into steam to drive generator turbines.
Because the working fluid tube of a parabolic trough system is suspended at the focal point of the reflectors, and the reflectors are often arranged in linear series extending a significant distance, there is often a set of support elements located at intervals along the length of the trough to keep the tube in position. These supports are often positioned in gaps between the various mirrors which make up the trough.
The trough is parabolic along one axis and linear in the orthogonal axis. For changes in the position of the sun throughout the day, the trough must be tilted and continuously or periodically adjusted along an east to west trajectory, so that the direct radiation remains focused on the receiver. However, seasonal changes in the angle of sunlight parallel to the trough do not require adjustment of the mirrors, since the light is simply concentrated elsewhere on the receiver. Thus the trough design does not require tracking on a second axis.
Concentrating solar power systems, such as parabolic trough systems, use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists, but all have certain shortcomings.
For example, the systems currently in use involve either (1) pre-determined positioning (which is prone to error), (2) the use of expensive devices which help pinpoint the position of the sun, or (3) detailed algorithms and complex equations to calculate the sun's position.
U.S. Pat. No. 7,637,259 to Kuckelhorn describes the use of mirrored collars and a series of algorithms to accomplish this task. U.S. Pat. No. 6,363,928 to Anderson describes a shielded device which receives solar radiation only when directly aligned in parallel with the reflective surface, and which in turn controls the rotation of the reflective surface. U.S. Patent Publication No. 2007/0186921 to Swanepoel describes using sets of “corrector mirrors” in a “box-like structure” in order to focus sunlight without moving the primary mirrors.

SUMMARY OF THE INVENTION

The following disclosure presents a summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify critical or necessary elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention presents, in part, a device for measuring the angle of orientation of mirrors of a solar power system relative to the position of the sun. The present invention further presents methods for using such information to adjust the positioning of the mirrors in order to increase the effectiveness of the system. The invention is described using mirrors forming a parabolic trough as an exemplary embodiment, but one of ordinary skill in the art will recognize that the device and methods of the present invention may be adapted or otherwise implemented in solar power systems having mirrors arrayed in other configurations.
One embodiment of the present invention, as implemented on a parabolic trough system, presents a device comprising a focal display panel and attachment means by which the device may be secured relative to the solar trough. The focal display panel may comprise a target area having a predominantly flat surface oriented such that its plane is orthogonal (or nearly orthogonal) to the axis of the working fluid tube of the parabolic trough system which carries the working fluid. In certain embodiments the device can be attached near the working fluid tube of the parabolic trough system, e.g., to one of the supports which holds the working fluid tube in place, in any manner commonly known to one of ordinary skill in the art, including, without limitation through the use of magnets, bolts, adhesives, welding, etc.
In another embodiment of the invention, a solar energy collection array has reflective surfaces and a tube containing a working fluid, a focal display panel having a target area, a spillage area, and mounting means for securing the focal display panel with respect to the array and tube. The focal display panel forms a cavity extending at least partially around the tube, and the focal display panel is situated to display patterns of light and shadow reflected from the array. A focal area formed by sunlight and shadow reflected from the array is visible on said display panel.
Generally speaking, sunlight reflects off of the mirrored parabolic trough of the parabolic trough system, and onto the target area of the focal display panel, forming a pattern of light that includes a shadow region on the target area. When the mirrored parabolic trough is aligned, the pattern of light that is reflected onto the target area includes a wedge-shaped shadow region that begins at the axis of the working fluid tube, and widens as the shadow region extends away from the axis of the working fluid tube.
When the mirrored parabolic trough is misaligned, the wedge-shaped shadow region becomes laterally skewed such that the apex forming the point of intersection of the sides of the shadow region is laterally spaced away from the axis of the working fluid tube.
In certain embodiments a portion of the device opposite the target area further comprises a spillage area. In such embodiments the spillage area may be bent at an angle relative to the plane of the target area, and may further show patterns of reflected sunlight and shadow that provide additional information regarding orientation of the mirrors.
The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other 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.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further understood, by way of example, with reference to the accompanying drawings, which are not drawn to scale, in which:

FIG. 1 illustrates a perspective view of a parabolic trough system.

FIG. 2 illustrates an exemplary embodiment of the present invention, showing a cross section of a portion of a parabolic trough, looking down the longitudinal axis of the working fluid tube, having a focal display panel attached to the support arm which holds the working fluid tube.

FIG. 3 illustrates the exemplary embodiment shown in FIG. 2, showing the reflection of the incoming sunlight by the parabolic trough onto the focal display panel when the parabolic trough is properly aligned with the incoming sunlight.

FIG. 4 illustrates the exemplary embodiment shown in FIG. 2, showing the reflection of the incoming sunlight by the parabolic trough onto the focal display panel when the parabolic trough is slightly misaligned relative to the incoming sunlight.

FIG. 5 illustrates the exemplary embodiment shown in FIG. 2, showing the reflection of the incoming sunlight by the parabolic trough onto the focal display panel when the parabolic trough is a little more misaligned relative to the incoming sunlight than shown in FIG. 4.

FIG. 6 illustrates an exemplary embodiment in which there is a symmetric gap between the mirrors of the parabolic trough.

FIG. 7 illustrates an exemplary embodiment in which there is an asymmetric gap between the mirrors of the parabolic trough.

FIG. 8 is a perspective view of the focal display panel of this invention mounted about a tube of working fluid.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

FIG. 1 shows a parabolic trough solar energy collector of the kind in which the invention is used. Parabolically shaped mirrors 6 reflect sunlight onto a working fluid tube 3 in which the absorbed energy heats the working fluid. Supports 5 hold the working fluid tube 3 in position. A shadow 20 is cast by the sun onto the mirrored surface. In some parabolic trough solar collectors, the mirrors are spaced apart at the area defined by the shadow 20 and supports 5 may extend therethrough.
FIG. 2 illustrates an exemplary embodiment of the present invention implemented on a parabolic trough system. In FIG. 2 a portion of the cross-section of a mirrored parabolic trough 6 is depicted, wherein the parabolic trough 6 comprises a set of one or more mirrors, preferably curved mirrors, shaped so as to focus incoming sunlight onto the axis of a working fluid tube 3 when the parabolic trough is properly aligned with the incoming sunlight 1. It will be understood by persons of skill in the art that only a portion of cross-section of the mirrored parabolic trough 6 is shown, and that the trough may extend outwards on either side of what is depicted in FIG. 2. Accordingly, the axis of the working fluid tube 3 is the focal point of the mirrored parabolic trough. The working fluid tube is held in place by working fluid tube holders 4 attached to the end of support arms 5. A parabolic trough solar power system may have several mirrored parabolic troughs 6 arranged end to end or in parallel rows, or both, and each such mirrored parabolic trough 6 may contain several such working fluid tube holders 4 and support arms 5 arranged at regular or irregular intervals along the length of the troughs. The mirrored parabolic trough 6 shown in FIG. 2 is oriented such that a base normal 7, i.e., a hypothetical line (or plane) which is normal to the base of the parabolic trough, and which is aligned with the incoming sunlight 1, will orient the trough in order to precisely focus the reflected sunlight onto the working tube 3. Persons of ordinary skill in the art will recognize that alternative arrangements of the support arm are possible, including having the support arm at an angle other than in line with the base normal, the use of two (or more) support arms at each supporting location, or any other arrangement presently known in the art.
The device comprising a focal display panel 10 is shown in FIG. 2, having a target area 11 which is arranged between the working fluid tube 3 and the mirrored parabolic trough 6, and is aligned along the base normal 7. As will be explained in greater detail with respect to FIGS. 3-5, the target area provides a surface upon which reflected sunlight from the mirrored parabolic trough 6 can be visually observed. The target area 11 of the focal display panel 10 is preferably flat, in shape, and its plane is preferably orthogonal to the axis of the working fluid tube 3. In certain preferred embodiments the plane of the target area may be bent or turned slightly to optimize visual observation from an observation post (such as a camera or other light sensor).
The focal display panel 10 may optionally also comprise a spillage area 12 opposite the target area relative to the working fluid tube 3. As explained in greater detail relative to FIGS. 3-5, the spillage area allows the “spilled” reflected light that does not hit the working fluid tube 3 to be visually observed when the mirrored parabolic trough is not properly aligned with the incoming sunlight. In embodiments containing a spillage area 12, it may be advantageous for the spillage area to be bent relative to the plane of the target area of the focal display panel in order to allow the “spilled” light to be more easily visually observed. In certain preferred embodiments, the spillage area 12 is bent relative to the target area 11 such that when viewed along the plane formed by the base normal 7 of the mirrored parabolic trough 6 and the axis of the working fluid tube 3, the target area 11 and the spillage area 12 form an obtuse angle. If the solar installation is situated between certain global latitudes, it may be advantageous to minimize the shadow cast by the spillage area (and thereby maximize the amount of sunlight that can be reflected onto the working fluid tube) by restricting the obtuse angle formed by the target area 11 and the spillage area 12 to no less than 135 degrees. In higher latitudes, it may be advantageous to limit the obtuse angle formed by the target area 11 and the spillage area 12 to no more than 135 degrees. In other embodiments the spillage area may be bent to maximize the amount of light reflected towards an observation post (such as a camera or other light sensor). However one of skill in the art will recognize that the invention can be practiced regardless of what angle is formed by the target area 11 and the spillage area 12, and regardless whether that angle is acute, right, obtuse, or a straight 180 degrees.
In certain embodiments, the focal display panel 10 may also optionally contain a cutout area 13 for attaching the device to the working fluid tube 3. The cutout 13 area may be shaped merely to allow the focal display panel 10 to be positioned properly without having to unmount or disassemble the working fluid tube. Additionally, the cutout may be shaped such that it can secure the focal display panel 10 to the working fluid tube 3, to the working fluid tube holder 4, or so that it otherwise plays a role in securing the focal display panel 10 relative to the working fluid tube 3.
A perspective view of the device having a cutout 13 to allow the device to be fitted around a tube of working fluid 3 is shown in FIG. 8. The spillage area 12 is bent slightly to provide a visual display of light and shadows reflected from the parabolic mirror trough (not shown).
In certain embodiments, the focal display panel 10 may be secured relative to the working fluid tube 3 by securing the focal display panel to the support arm 5 or the working fluid tube holder 4 which holds the working fluid tube 3 in place. For example magnets, bolts, or screws 14 may be used to secure the back of the focal display panel 10 to the support arm 5. Alternatively adhesives may be used to secure the focal display panel 10, or a more elaborate securing structure, such as rings, clamps or a frame that may be welded, soldered or otherwise secured, may be used. A person of skill in the art recognizes that there are a myriad of ways in which the focal display panel 10 may be secured such that the positioning of the target area 11 relative to the working fluid tube 3 and the mirrored parabolic trough 6 (and its base normal 7) can be maintained. It will also be recognized that although a generally rectangular shape has been depicted in the exemplary embodiments, the size and shape of the target area may be varied to fit the needs or desires of the person implementing it.
FIG. 3 illustrates the exemplary embodiment depicted in FIG. 2 in use. As shown in FIG. 3, incoming rays of sunlight 1 are aligned with the base normal 7 of the mirrored parabolic trough 6. The incoming rays 1 are therefore reflected by the mirrored parabolic trough 6, and reflected sunlight 2 is directed towards the focal point of the parabolic trough, along which is superimposed the axis of the working fluid tube 3. When the mirrored parabolic trough is properly aligned, the amount of light that is reflected onto and is observable upon the spillage area should be minimal. A shadow region 15 is visible on the target area 11, directly beneath the axis of the working fluid tube 3. The shadow region 15 is caused at least in part by the absorption/deflection of incoming light by the working fluid tube 3. It may also be due, in part, to shadow caused by the spillage area 12, or, as shown in FIGS. 6 and 7, may result from a gap 18, 18 a between mirrors at the bottom of the mirrored parabolic trough 6. Such gaps 18, 18 a are often found in parabolic trough solar power systems, in order to allow space for the support arms to enter the parabolic trough or in-between different mirrors of the mirrored parabolic trough 6.
Regardless of the cause of the shadow region, if the cause of the shadow region is symmetric relative to the incoming sunlight (i.e. the width of the working fluid tube 3, spillage area 12, or gap 18 in the mirrors is the same on either side of the axis of the working fluid tube when viewed in cross-section), then the shadow region 15 will also be symmetric. For example, in the embodiment shown in FIG. 6, the shadow region 15 is caused by a symmetric gap 18 between the mirrors of the mirrored parabolic trough 6. In such cases it can be visually observed that the mirrored parabolic trough 6 is aligned relative to the incoming sunlight 1 when the shadow region 15 visible on the target area 11 is symmetric across the base normal 7 of the mirrored parabolic trough 6. This evaluation may be done autonomously through the use of commonly known image processing algorithms, whether computationally or through pattern matching. For instance the line 16 bisecting the sides of the observed shadow region 15, may be calculated and compared to the base normal to see if it is in proper alignment. Similarly the image of the currently observable shadow region 15 may be compared to an image of the expected “optimal” shadow region to determine whether they are sufficiently similar to consider the mirrored parabolic trough 6 sufficiently aligned. Alternatively, the apex 17 of the sides of the shadow region can be calculated, and the difference between it and the axis of the working fluid tube 3 can be evaluated. One of skill in the art will recognize that many such algorithms may be used to evaluate the currently observed shadow region 15 and to determine whether the mirrored parabolic trough 6 is focused upon the working fluid tube, and if not, in which direction and by how much it should be moved in order to align it to focus upon the tube. This will become more evident in view of FIGS. 4 and 5.
In cases in which the cause of the shadow region is not symmetric, the shadow region 15 observed on the target area 11 is also not symmetric. For example, in FIG. 7, the shadow region 15 is caused by an asymmetric gap 18 a between the mirrors of the mirrored parabolic trough 6, even though the reflected sunlight is focused upon the working fluid tube. In this situation, it can still be observed whether the mirrored parabolic trough 6 is aligned with the incoming sunlight 1 by using an adaptation of any of the currently known computational or pattern matching algorithms.
For instance, the line 16 a bisecting the sides of the shadow region 15 may be computed, and compared to the bisecting line expected at optimal alignment of the mirrored parabolic trough, given the asymmetry in the shadow region 15. Similarly, the image of the observed shadow region 15 may be compared to images of the shadow region expected at the optimal alignment of the mirrored parabolic trough 6 to determine whether the currently observed shadow region 15 is like or unlike the optimal shadow region. As previously mentioned, the apex 17 of the sides of the shadow region can be calculated, and the difference between it and the axis of the working fluid tube 3 can be evaluated. Persons of skill in the art will recognize that any such algorithm may be adapted to handle the shape of the shadow region at optimal alignment. In so adjusting these algorithms, whether the currently observable shadow region 15 indicates that the mirrored parabolic trough 6 is properly aligned or whether it must be moved and how much it must be moved can also be computed.
As a non-exclusive example of such computations, an observation of the target area can be used to compute the vectors u_leftand u_right, which form the sides of the observed shadow region using any known line detection algorithm (such as a Hough transform, an algorithm using an edge detection algorithm, such as high-pass filters, Canny edge detection, etc.). The vectors can then be normalized by dividing them by their magnitude (u_left′=u_left/∥u_left∥ and u_right′=u_right/∥u_right∥). The sum of the normalized vectors (u_bisect=u_left′+u_right′) bisects the angle formed by the two original vectors, and this vector too can be normalized (u_bisect′=u_bisect/∥u_bisect∥). The arccosine of the dot product of this observed bisecting unit vector u_bisect′ with the bisecting unit vector expected at optimal alignment u_opt′ gives the angle θ between the two vectors (arccos(u_bisect′·u_opt′)=arccos(∥u_bisect′∥ ∥u_opt′∥ cos(θ))=arccos(cos(θ))=θ). The array can then be rotated by θ to improve its alignment. In one embodiment, data needed to perform such calculations can be obtained through graphical imaging of shadows and sunlight on the focal display panel, and appropriate processing can be employed to cause continuous or periodic automatic alignment of the parabolic trough, as may be desired.
FIG. 4 illustrates the exemplary embodiment of FIG. 2 in which the mirrored parabolic trough 6 is slightly misaligned with respect to the direction of the incoming sunlight 1 a. The incoming sunlight 1 a is reflected by the mirrored parabolic trough 6, and the reflected sunlight 2 a is directed towards off-focus points such that the shadow region 15 formed by the reflected sunlight 2 a on the target area 11 of the focal display panel 10 is laterally skewed, and the narrowest point of the shadow region 15 is laterally spaced from the axis of the working fluid tube 3.
As can be seen in FIG. 4, when the mirrored parabolic trough 6 is slightly misaligned relative to the incoming sunlight 1 a, some of the reflected light will miss the working fluid tube 3 completely, and may be reflected by, and visually observable on the spillage area. Additional reflected sunlight 2 a reflected by the portions of the mirrored parabolic trough 6 that are not shown in FIG. 4 may also be visually observable on the spillage area. As the Sun moves across the sky, the mirrored parabolic trough becomes more and more misaligned relative to the incoming sunlight, more light will be reflected onto the spillage area, and less will be reflected onto the working fluid tube.
Accordingly, as explained above, based on a visual observation of the shadow region 15 on the target area 11, the amount of misalignment of the target area can be estimated. If sufficiently detailed information regarding the position and latitude of the installation is known, the degree to which the orientation of the mirrored parabolic trough must be adjusted over time to maintain focus of the reflected sunlight upon the fluid tube can be determined. Once again, any of the known image processing algorithms can be used to accomplish this. These include pattern recognition algorithms which compare the observed shadow region 15 to optimal and sub-optimal shadow regions, and match the observation to the pattern most like it. Alternatively, the line 16, 16 a bisecting the shadow region 15 (shown in FIGS. 6 and 7) could be computed and compared to the base normal in order to compute the degree of misalignment. Also, the lateral spacing or relative positioning of the intersection point, or apex 17 a, of the two sides of the shadow region 15 could be calculated, and the lateral spacing or relative positioning between the intersection point and the axis of the working fluid tube 3 could be used to compute the degree to which the mirrored parabolic trough 6 is misaligned. These methods are meant to be exemplary, not restrictive, and one of skill in the art will recognize that there are many known variations of these and other algorithms which could be implemented to accomplish the task of calculating the degree of misalignment from the visual observation of the 15 region on the target area 11 of the focal display panel 10.
FIG. 5 shows a more severely misaligned mirrored parabolic trough 6 relative to the incoming sunlight 1 b, where the reflected sunlight 2 b misses the working fluid tube altogether. The shadow region 15 on the target area 11 of FIG. 5 is even more laterally skewed than the shadow region 15 on the target area 11 in FIG. 4, with the apex 17 b of the shadow falling well to one side of the axis of the working fluid tube 3.
Additionally, a greater amount of “spilled” light is visible on the optional spillage area 12 as well. Because the spillage area 12 receives more light as the source of incoming sunlight moves until its rays 1, 1 a, 1 b are no longer parallel to base normal 7, a visual observation of the spillage area can be used as an error checking mechanism. There will be some amount of error in calculations based on the visual observation of the focal display panel. This error may be introduced through imprecision in the construction of the parabolic trough system, flaws in the shape of the mirrored parabolic trough, the installation of the focal display panel, or the visual observations recorded of shadow region 15 on the focal display panel 10. By comparing the amount of “spilled” light observed on the spillage area 12, to the degree of misalignment computed from the visual observation of the shadow region 15 on the target area 11, an estimate of the magnitude of the error can be made. If the amount of observed “spilled” light on the spillage area 12 is consistent with the calculation of misalignment of the mirrored parabolic trough 6 computed from the observation of the shadow region 15 on the target area 11, there may be greater degree of confidence that the adjustment computed will properly align the mirrored parabolic trough 6. If the amount of “spilled” light observed on the spillage area 12 is inconsistent with the calculation of misalignment of the mirrored parabolic trough 6 computed from the shadow region 15 observed on the target area 12, then there is a lower level of confidence in the computation, and it may be advantageous to make additional observations after orienting the mirrored parabolic trough 6 to correct for the computed misalignment, or to implement a fuzzy logic algorithm (as such are known to persons of skill in the art) to gradually work towards an optimal solution based on continued observations of the shadow region 15 on the focal display panel's 10 target area 11 and spillage area 12.
Methods of practicing the invention may involve the placing of one or more focal display panels 10 on a parabolic trough solar power system, as described above. In this manner, the target area 11 of the focal display panels will be positioned between the working fluid tube 3 and the mirrored parabolic trough 6 such that the target area lies along the base normal 7 of the mirrored parabolic trough 6. Visual observations of the focal display panel may then be taken by an observation post, such as a camera or some other light sensor. Using the observations taken of the shadow region 15 on the target area 11, the degree of misalignment of the mirrored parabolic trough 6 can be calculated using any of the algorithms described above, or otherwise known to persons of skill in the art. If the optional spillage area 12 is implemented on the focal display panel, it too may be visually observed, and used to error check the calculation of the misalignment of the mirrored parabolic trough as also described above. The mirrored parabolic trough may then be rotated by the calculated amount to bring the system back into proper alignment. Additional visual observations may then be taken in order to determine whether more correction is needed. The visual observations may be taken at regular or irregular intervals throughout the day, or may be taken continuously. The system may change the orientation of the mirrored parabolic trough for every computation or every observation made, regardless of how small the difference is, or a minimum misalignment threshold may be set, and computed misalignments of the mirrored parabolic trough 6 less than the minimum misalignment threshold ignored while computed misalignments of the mirrored parabolic trough 6 larger than the minimum misalignment threshold could be used to activate the orientation of the mirrored parabolic trough 6 to the computed amount. If it is necessary or desirable to minimize the number of adjustments, one embodiment of the invention may require that each adjustment align the trough slightly ahead of the optimal alignment so that solar movement over time will initially bring the system closer to the optimal alignment before passing through the optimal alignment and moving further away from it.
In certain embodiments, the mirrored parabolic trough may be aligned manually, or by a pre-programmed default to the proper orientation such that it is aligned with the rising sun each morning.
Persons of skill in the art will recognize that there are many implementation details and options left to the practitioner, but that would be within the scope of the current invention. It is intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.

Claims

What is claimed is:

1. In a solar energy collection array having reflective surfaces and a tube containing a working fluid, a focal display panel comprising:

a target area, a spillage area, and mounting means for securing said focal display panel with respect to said array and said tube,

said focal display panel forming a cavity extending at least partially around said tube,

said focal display panel being situate to display patterns of light and shadow reflected from said array whereby a focal area formed by sunlight and shadow reflected from said array is visible on said display panel.

2. The focal display panel of claim 1 wherein said target area is predominantly flat, and said spillage area extends beyond said target area in a direction opposite said array.

3. The focal display panel of claim 2 wherein said spillage area is bent at an angle relative to the plane of said target area.

4. The focal display panel of claim 3 wherein the angle of the spillage area relative to the plane of the target area is an obtuse angle.

5. The focal display panel of claim 4 wherein the obtuse angle of the spillage area relative to the plane of the target area is at least 135 degrees.

6. The focal display panel of claim 4 wherein the obtuse angle of the spillage area relative to the plane of the target area is at most 135 degrees.

7. The focal display panel of claim 1 wherein said focal display panel is affixed to supports holding a said tube within said solar energy collection array.

8. The focal display panel of claim 7 wherein said focal display panel is wider than said support structure which holds said tube.

9. The focal display panel of claim 1 wherein, when light reflected from said array is focused upon said tube, said panel displays a shadow region that is symmetric on said target area and when light reflected from said array is not focused upon said tube, said panel displays a shadow region that is not symmetric on said target area.

10. In a solar energy collection array, a method of focusing reflected solar energy in relation to a tube carrying working fluid comprising the steps of:

(a) providing a movable linear array of reflective panels facing inwardly to form a substantially parabolic trough, said linear array being movable to align said substantially parabolic trough with parallel rays of direct sunlight during at least some daylight hours;

(b) suspending a tube carrying working fluid linearly along the focal axis of said substantially parabolically trough;

(c) affixing a focal display panel having a target area about said tube such that said focal display panel extends between said tube and said reflective panels and beyond said tube in a direction away from said reflective panels;

(d) directing said movable array toward incoming direct sunlight;

(e) observing on said focal display panel the position of the apex of a shadow caused by the reflection of sunlight around said tube; and

(f) positioning said movable array to cause said apex of said shadow to fall upon a predetermined position on said focal display panel.

11. The method of claim 10 wherein said predetermined position is based upon at least a determination of the angular velocity of the source of sunlight with respect to said focal axis of said substantially parabolic trough and the frequency and precision with which said movable linear array can be adjusted.

12. The method of claim 10 wherein said predetermined position is based upon at least a determination of the angular velocity of the source of sunlight with respect to said focal axis of said substantially parabolic trough and the length of time said substantially parabolic trough will be stationary between repositioning adjustments.

13. The method of claim 10 further comprising the step of repeating steps (d), (e) and (f) at regular intervals.

14. The method of claim 10 further comprising the step of repeating steps (d), (e) and (f) at predetermined times throughout a day.

15. The method of claim 10 further comprising the step of (e) repeating steps (d), (e) and (f) continuously.

16. The method of claim 10 wherein said focal display panel further comprises a target area and a spillage area.

17. The method of claim 16 wherein said target area of said focal display panel forms a plane, and said spillage area of said focal display panel is bent relative to said plane of said target area such that said spillage area forms an obtuse angle with said plane of said target area.

18. The method of claim 17 further comprising the steps of (g) generating data for computing an angle of difference between the instantaneous position of said substantially parabolic trough and a position that would cause said parabolic trough to focus incoming sunlight on said working fluid tube; (h) determining said angle of difference; and (i) causing said substantially parabolic trough to be moved to a predetermined position relative to said angle of difference.

19. The method of claim 18 further comprising the step of using a fuzzy logic algorithm to orient said substantially parabolic trough whenever said angle of difference exceeds a predetermined amount.

20. A solar energy collector comprising:

An array comprising at least one reflective surface and a working fluid;

a focal display panel comprising a target area and a spillage area, wherein:

the panel indicates a focal area of said array;

the panel forms a cavity extending at least partially around said working fluid,

the panel is situated to display patterns of light and shadow reflected from said array whereby a focal area formed by light and shadow reflected from said array is visible on said panel.