U.S. patent application number 12/278353 was filed with the patent office on 2009-07-02 for electromagnetic radiation collection device.
This patent application is currently assigned to SUNDAY SOLAR TECHNOLOGIES PARTY LTD.. Invention is credited to Garry Chambers, Alastair McIndoe Hodges.
Application Number | 20090165782 12/278353 |
Document ID | / |
Family ID | 38344893 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090165782 |
Kind Code |
A1 |
Hodges; Alastair McIndoe ;
et al. |
July 2, 2009 |
ELECTROMAGNETIC RADIATION COLLECTION DEVICE
Abstract
An electromagnetic radiation collector includes a channeling
area having an entry end for receiving the electromagnetic
radiation, an exit end, and at least one reflective wall between
the entry end and the exit end; and a radiation collection element
near the exit end of the channeling area, the radiation collection
element being adapted to collect the electromagnetic radiation.
Inventors: |
Hodges; Alastair McIndoe;
(Victoria, AU) ; Chambers; Garry; (Victoria,
AU) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
Assignee: |
SUNDAY SOLAR TECHNOLOGIES PARTY
LTD.
Sydney
AU
|
Family ID: |
38344893 |
Appl. No.: |
12/278353 |
Filed: |
June 2, 2006 |
PCT Filed: |
June 2, 2006 |
PCT NO: |
PCT/IB06/01533 |
371 Date: |
December 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60765726 |
Feb 7, 2006 |
|
|
|
60774676 |
Feb 21, 2006 |
|
|
|
Current U.S.
Class: |
126/684 |
Current CPC
Class: |
F24S 2023/88 20180501;
H01L 2224/18 20130101; F24S 50/20 20180501; F24S 2030/136 20180501;
F24S 2023/872 20180501; H01L 2224/48227 20130101; Y02E 10/40
20130101; F24S 2030/16 20180501; H01L 31/0547 20141201; H01L
2224/73267 20130101; F24S 2030/131 20180501; Y02E 10/47 20130101;
Y02E 10/52 20130101; H01L 24/97 20130101; H01L 2224/48472 20130101;
F24S 30/425 20180501; F24S 2023/878 20180501; F24S 23/70 20180501;
H01L 2224/48472 20130101; H01L 2224/48227 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
126/684 |
International
Class: |
F24J 2/10 20060101
F24J002/10 |
Claims
1. An electromagnetic radiation collector, comprising: a channeling
area having an entry end for receiving the electromagnetic
radiation, an exit end, and at least one reflective wall between
the entry end and the exit end; and a radiation collection element
near the exit end of the channeling area, the radiation collection
element being adapted to collect the electromagnetic radiation.
2. The collector of claim 1, comprising a plurality of the
channeling areas and a plurality of the radiation collection
elements.
3. The collector of claim 2, wherein the entry ends of the
plurality of channeling areas are adjacent to each other.
4. The collector of claim 2, wherein each of the channeling areas
is formed by a first surface for reflecting the electromagnetic
radiation, and a second surface opposite the first surface.
5. The collector of claim 4, wherein the first surface of each of
the channeling areas is parabolic and the focal area of each
parabolic first surface is one of the plurality of radiation
collection elements.
6. The collector of claim 5, wherein the radiation collection
elements are photovoltaic cells.
7. The collector of claim 5, wherein the radiation collection
elements are pipes for containing a fluid that is for absorbing the
radiation.
8. The collector of claim 5, wherein the first surfaces are movable
relative to the radiation collection elements.
9. The collector of claim 8, wherein the first surfaces can rotate
about their corresponding radiation collection element.
10. The collector of claim 5, wherein the radiation collection
elements are sized to be only slightly larger in the surface area
they cover than the surface area covered by the radiation reflected
onto the radiation collection elements by the first surfaces.
11. The collector of claim 6, wherein the plurality of photovoltaic
cells are electrically connected to each other.
12. The collector of claim 11, wherein an upper surface of a first
photovoltaic cell of the plurality of photovoltaic cells is
electrically connected to a lower surface of a second photovoltaic
cell of the plurality of photovoltaic cells.
13. The collector of claim 12, further comprising a lower surface
connector electrically connected to the lower surface of the second
photovoltaic cell; an upper surface connector electrically
connected to the upper surface of the first photovoltaic cell and
electrically connected to the lower surface connector.
14. The collector of claim 13, wherein the upper surface connector
comprises a wire.
15. The collector of claim 14, further comprising a first bead that
electrically connects the upper surface connector to the upper
surface of the first photovoltaic cell.
16. The collector of claim 15, further comprising a second bead
that electrically connects the upper surface connector to the lower
surface connector.
17. The collector of claim 14, wherein the wire is round in cross
section.
18. The collector of claim 14, wherein the wire is trapezoidal in
cross section.
19. The collector of claim 1, wherein the channeling area is in the
form of a slot and further comprising a reflective wall at each end
of the slot.
20. The collector of claim 19, wherein the plane of each of the
reflective walls is normal to a lengthwise axis of the slot.
21. The collector of claim 20, wherein each of the reflective walls
is planar and the plane of each of the reflective walls is normal
to a plane of the radiation collection element.
22. A control mechanism for a radiation collector where the
radiation collector is adjustable to track a moving radiation
source and where the control mechanism comprises a first sensor to
monitor the ambient radiation conditions and a second sensor to
monitor the output of the radiation collector.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to electromagnetic
radiation collection.
[0003] 2. Related Art
[0004] The collection and concentration of electromagnetic (EM)
radiation is well known. Radio waves are typically collected and
concentrated using parabolic dishes. Solar radiation is collected
and concentrated using parabolic mirrors or lenses. The former
devices suffer from requiring a relatively high
height-to-collection area ratio and the latter being expensive,
heavy and fragile. Both these types of device also suffer from the
requirement to track the source in order to function properly.
BRIEF SUMMARY OF THE INVENTION
[0005] The invention seeks to overcome at least some of the
deficiencies in the prior art by providing an EM radiation
collection device which can cover a large area, have a low profile,
have no requirement to track the source and be constructed so as to
be relatively light and inexpensive.
[0006] There is a pressing need to be able to generate energy from
renewable energy sources. Solar energy is one such resource which
has potential to be exploited. Conventional devices for collecting
radiant energy to generate energy in a useful form suffer from a
high capital cost and/or the inability to generate high enough
temperatures to be useful for many applications. The invention
seeks to overcome these deficiencies in the prior art by providing
a radiant energy concentration device that can gather energy from a
relatively large area and concentrate it onto a small target area.
The device is relatively inexpensive to produce, can be light in
construction and has the potential to generate high target
temperatures or, in the case of conversion to electricity by
photovoltaic cells, require only a small area of cells, thus saving
cost.
[0007] The invention is directed to a device that can cover
relatively large collections areas at relatively low cost, does not
necessarily require materials of particular refractive index and
can be made of light construction.
[0008] The invention is capable of being less massive and having a
lower profile than prior art concentration devices. It is also
capable of having high concentration factors. It is suitable in any
application where it is desired to collect and concentrate EM
radiation, with particular utility in the collection and
concentration of solar radiation. In the case of solar radiation, a
device in accordance with the invention can be used in conjunction
with photovoltaic cells or to heat a fluid to harness the solar
energy for a desired purpose. In the case of radio frequency
radiation, the subject device could be used to collect, focus and
tune the radiation.
[0009] An example of a device in accordance with the invention is
an electromagnetic radiation collector that includes a channeling
area having an entry end for receiving the electromagnetic
radiation, an exit end, and at least one reflective wall between
the entry end and the exit end; and a radiation collection element
near the exit end of the channeling area, the radiation collection
element being adapted to collect the electromagnetic radiation.
[0010] Another example of a device in accordance with the invention
is a control mechanism for a radiation collector where the
radiation collector is adjustable to track a moving radiation
source and where the control mechanism comprises a first sensor to
monitor the ambient radiation conditions and a second sensor to
monitor the output of the radiation collector.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing and other features and advantages of the
invention will be apparent from the following, more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings wherein like reference
numbers generally indicate identical, functionally similar, and/or
structurally similar elements.
[0012] FIG. 1 shows an example of a channeling area;
[0013] FIG. 2 shows an example of a device having multiple
channeling areas;
[0014] FIG. 3 shows a cross-sectional view of an array of
channeling areas;
[0015] FIG. 4 shows a cross-sectional view of a different array of
channeling areas;
[0016] FIG. 5 shows a first embodiment of the invention;
[0017] FIG. 6 is a cut-away view of the embodiment shown in FIG.
5;
[0018] FIG. 7 shows a second embodiment of the invention;
[0019] FIG. 8 shows a side view of the embodiment shown in FIG.
7;
[0020] FIG. 9 shows an alternate embodiment related to the
embodiment shown in FIGS. 7 and 8;
[0021] FIG. 10 shows a third embodiment of the invention;
[0022] FIG. 11 shows an alternate embodiment related to the
embodiment shown in FIG. 10; and
[0023] FIG. 12 shows a fourth embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] An exemplary embodiment of the invention is shown in the
drawings and described herein.
[0025] An example of a device in accordance with the invention has
an assembly of channeling areas wherein the EM radiation can be
internally reflected within the channeling areas. In one
embodiment, the channeling areas are constructed such that at least
some of the EM radiation that enters a broad end of the channeling
areas will be steered within the channeling areas to exit a narrow
end of the channeling areas. The broad ends of the channeling areas
are assembled to form a surface that is herein termed the
collection surface. EM radiation falls on the collection surface
and enters the broad ends of the channeling areas. The EM radiation
is reflected from the walls of the channeling areas so as to be
directed to exit from the narrow end of the channeling areas. This
is achieved by ensuring that at each reflection point the angle of
incidence of the EM radiation to the reflecting surface is less
than 90.degree.. A method for ensuring that this is the case for a
wide arc of angles of the EM radiation incident on the collection
surface is to shape the channeling areas such that they are much
longer than they are broad at their broad end. This provides, in
some embodiments, a small angle of taper of the walls of the
channeling area thus fulfilling the reflection angle requirements
for a broader range of incident EM radiation angles. The ratio of
length of the channeling area to the breadth of its broad end
should desirably be between 2 and 1000, more preferably between 5
and 100, and most preferably between 10 and 50. FIG. 1 shows an
example of a single channeling area and a typical path 20 that EM
radiation might take within the area.
[0026] The channeling areas can be made of solid material that is
capable of transmitting the EM radiation that is to be collected
and concentrated and with walls that reflect the EM radiation back
into the channeling area. In another embodiment of the invention,
the channeling areas are formed as cavities, where the walls of the
cavities are capable of reflecting the EM radiation back into the
cavity.
[0027] In one embodiment of the invention, the narrow ends of an
assembly of channeling areas are gathered together into an area
that is smaller than the area of the broad ends of assembled
channeling areas. In such an example, the EM radiation collected
over the broad ends area is concentrated into the narrow ends area.
An example of this embodiment is shown in FIG. 2.
[0028] In some embodiments of the invention, the channeling areas
are tapered in only one dimension, that is they take the form of
tapered slots. In other embodiments, the channeling areas are
tapered in two dimensions so that they take the form of tapered
rods, where the rods can be of any cross-sectional shape that is
suitable for packing together at high density. Examples of such
shapes are circles, squares, rectangles, triangles and other
multi-sided polygons.
[0029] When the channeling areas take the form of tapered rods, to
aid in accommodating the curvature or the rods, maintain a high
packing density for the broad ends of the channeling areas and
enhance the strength of an assembly of the channeling areas, the
channeling areas can be assembled such that each channeling area is
staggered relative to its neighbors. In a particular embodiment of
this aspect of the invention, rows of channeling areas are
assembled such that the channeling areas in each row are offset
from the row in front such that the narrow end of each channeling
area is between the narrow ends of the neighboring channeling areas
in the rows immediately in front of and behind the subject row. By
assembling the channeling areas in this way it is possible for the
narrow end of each channeling area to curve into the space between
the neighboring channeling areas in the row in front of it. This
allows the channeling areas to be curved while maintaining high
packing density of the broad ends of the channeling areas.
[0030] It is desirable to maintain a high packing density of the
broad ends of the channeling areas at the collecting surface so
that the highest fraction of the EM radiation incident on the
collecting surface enters a channeling area and is not reflected
back.
[0031] In one embodiment of the invention, the channeling areas are
circular in cross-section and the broad ends are assembled in a
packing arrangement as is shown in FIG. 3, where a top view of the
assembled rows of the broad ends of the circular channeling areas
are shown offset from one another. Triangles are superimposed on
the view to show the relationship of the centers of the circular
ends. This arrangement increases packing density and allows space
for the channeling areas to be curved as disclosed above. With this
arrangement, a maximum fraction of .pi./2 3 (approx. 90%) of the
incident radiation is collected. In a particular embodiment of this
aspect of the invention, channeling areas with a square or
rectangular cross-section are used. A top view of this arrangement
is shown in FIG. 4. With this shape of channeling area, the broad
ends of the channeling areas can be packed such that close to 100%
of the incident radiation enters the channeling areas and is thus
collected. Note that in the embodiment shown in FIG. 4 it is
possible, but not necessary, for the channeling areas to be of
rectangular cross-section down their full length. For example, the
channeling areas may be square or rectangular at the collecting
surface but then transition to a circular area as we move down the
channeling area toward its tip.
[0032] Devices in accordance with the invention are useful in
applications where EM radiation concentration devices have been
used in the prior art, in particular solar radiation and radio
frequency radiation. Examples of such uses particularly relevant to
the collection and concentration of solar radiation are to heat
fluid circulating though a tube or pipe, to generate electricity
directly using photovoltaic cells or to produce hydrogen from
water. Note that the invention has particular utility in the
application of producing electricity using photovoltaic cells as it
allows the light to be collected from an extended area using the
relatively inexpensive device of the invention and concentrate it
on to a relatively small area of the relatively expensive
photovoltaic cells. This potentially allows electricity to be
generated at lower capital cost. Also, this device addresses
deficiencies in the conventional art when attempting to use a
concentrator with photovoltaic cells. Apart from expense and
weight, the conventional devices suffer from relatively low
concentration factors of typically less than 10 and the problem of
the photovoltaic cells overheating and becoming less efficient.
[0033] A low profile collector and concentrator is desirable in
applications for radio frequency (RF) radiation. In these
applications, the device could be used to focus the RF radiation
onto an RF receiver. Also, by careful choice of the dimensions of
the channeling areas, the subject device could be used to tune the
collected RF radiation to a frequency that can be received more
easily by a receiver. For example, the device can be used to tune
the RF radiation to a higher frequency, which requires a smaller
and more easily implemented receiver.
[0034] The subject devices can be made by any suitable method. The
channeling areas can be solid elements transmissive of light and
made from materials such as polymers or glass. For these solid
elements, the walls of the elements can be coated with a reflective
material or the refractive index of the material can be such that
in most cases the incident angle of the EM to be reflected to the
wall of the element exceeds the critical angle so that total
internal reflection occurs. This embodiment has potential
advantages in ease of fabrication but can also tend to be heavy.
This embodiment could be constructed by manufacturing many elements
and assembling them into arrays as disclosed above.
[0035] A particular embodiment is one where the channeling areas
are cavities formed in a monolithic block made of metal or polymer
material. This may be somewhat harder to fabricate but will be
lighter. A method of manufacturing this embodiment is to form an
assembly of curved elements, for example tapered elements, from a
malleable material such as copper or nickel. The assembly can be
one of individual elements or of rows of elements formed into combs
where each tapered element is a "tooth" of the comb. Each comb
forms a row or portion of a row of the elements and the "teeth" of
the combs of successive rows in the assembly are staggered to give
the arrangements shown in FIG. 3 or 4. Before being assembled into
an array, the elements can be straight or already curved. If the
elements are straight, a bar can be passed over the assembly of the
narrow ends of the elements as a convenient method of introducing
the desired curvature. The assembled elements can be held in their
assembly by being clamped into a frame or other similar device. The
curved assembled elements, in conjunction with side walls and, if
applicable, a top and/or base, can then be used as a mold for the
final monolithic shape. The shape with the desired assembly of
cavities can be molded by any applicable method. It may be cast by
pouring polymer into the mold and letting it set or by injection
molding techniques. In this process it is desirable to first coat
the mold with a suitable release agent to facilitate removal of the
mold elements from the cast shape. After the cast shape is set the
mold elements can be removed. This can most easily be achieved by
first removing the cast shape from the mold side walls, top and/or
base then unclamping the assembly of elements and removing them
separately or in groups as is most convenient and practical. Note
that in most cases the elements will need to be straightened
somewhat to be withdrawn from the cavities so it is desirable that
the material from which the tapered elements are made be malleable
so that in can undergo the straightening process without breaking
or distorting the shape of the cavity from which it is being
withdrawn. This process results in a cast shape that contains an
assembly of densely packed curved, light guiding cavities, wherein
the broad ends of the cavities all open onto one face of the shape
and the narrow ends of the cavities all open on to a different face
of the shape.
[0036] If the shape is not cast from an intrinsically reflective
material such as metal or metal filled polymer, then the external
faces of the shape and/or the walls of the cavities can to be
coated with a reflective layer. For polymer material this is most
easily achieved with an electroless metal deposition process such
as electroless chrome or nickel deposition. A further transparent
coating could be applied over the reflective coating if desired to
protect the reflective coating.
[0037] An alternative embodiment for creating an assembly of
channeling areas for collecting the EM radiation is to use a series
of mirrors that focus the light into a series of spots or strips.
In the case of a strip, the optimal mirror shape is parabolic in
the plane of the strip and normal to it. In the case of spots, the
mirror is optimally a parabolic dish. According to this embodiment,
the channeling areas are formed by the space between the adjacent
mirrors where, rather than the adjacent mirrors forming a tapering
space, the tapering space is defined by the tapering shape of the
radiation beam reflected from the rear wall of the channel. Also,
the exit to the channel according to this embodiment is the strip
or spot which is the focal point of the rear mirror. Therefore, in
this embodiment it is not necessary for the walls of the channel to
taper in order for the radiation beam to be tapered. This has
advantages in flexibility of design and in minimizing the number of
reflections that the radiation undergoes before exiting the
channel. The strips or spots that form the exit to the channel are
arranged to be at the focal line or point of the mirror such that
EM radiation reflected off the mirror is substantially concentrated
onto them. To allow for different angles of EM radiation incident
on the mirrors, the mirrors can be rotated about their focal line
or point such that the focus of the light remains co-incident with
the strips or spots. A control mechanism can perform the rotation
whereby a signal, which could be the output from an EM radiation
target or from a separate sensor, is monitored and the rotation of
the mirrors performed so as to maximize the amount of EM radiation
impacting the target. A particularly preferred embodiment of sensor
configuration is where the output of a separate sensor can be used
in combination with the output of the radiation target, or a sensor
that correlates to the output of the radiation target, to achieve
the control. According to this embodiment a separate sensor is
configured to respond to the ambient conditions with the target
sensor output responding to the focusing configuration of the
mirrors. In the example of when PV cells form the target to
generate electricity from solar radiation, a separate light
sensitive sensor would be mounted away from the mirrors such that
it monitored the ambient incident radiation on to the panel. This
sensor would for example detect a change in the radiation level due
to a cloud or other object passing between the sun and the panel.
The target sensor on the other hand would monitor the output of the
light impinging on to the target PV cells. So, the control
mechanism would monitor both the ambient and the target sensor and
if the output of the two sensors varied in a similar way over time,
then the control system would take no action as it would assume
that the change in output of the target was due to a change in the
ambient conditions. If, on the other hand, the target sensor output
changed in a different way to the ambient sensor output then the
control system would move appropriately to maximize the output of
the target sensor.
[0038] The mirrors may have a rear reflecting surface that reflects
EM radiation onto one of the focusing mirrors.
[0039] An assembly of parabolic louvers that can be made to rotate
about their focal line have been described above. The focal line of
each louver impinges upon a receiving area in which one or more
receiving elements are placed. The receiving elements can be in the
form of openings into a concentration chamber, as disclosed in
co-pending application PCT/IB2005/003838, herein incorporated in
its entirety by reference. Alternatively, the receiving elements
may be adapted to directly convert the incident radiation. The
receiving elements may be adapted to convert the radiation into
electrical energy, for example photovoltaic cells could be placed
in the receiving areas. Alternatively the receiving elements maybe
adapted to collect the thermal energy, thus transferring heat to a
fluid medium whereby the energy can be utilized elsewhere. In the
embodiment where PV cells are used as the receiving elements it is
desirable to be able to cool the PV cells for their efficient
operation. According to the current invention, cooling can be
provided by having heat dissipation areas between the areas of PV
cells. Since these in-between areas are shaded from the incident EM
radiation by the parabolic louvers they can readily be adapted to
radiate heat efficiently, for example by coating them with a
radiating coating such as a black coating. In an alternative
embodiment, a fluid layer can be placed in a space below the plate
containing the PV cells and in thermal contact with the back of the
PV cells. The fluid can be permanently contained within the space
and allowed to circulate within the space, such that the fluid aids
in the transfer of heat from the PV cells to the heat dissipation
areas. In a further embodiment the fluid can be allowed to, or made
to, flow though the space beneath the PV cells wherein the heat is
dissipated external to the plate containing the PV cells.
Preferably, the PV cells could be connected in series to a
sufficient extent to obtain the output voltage that is desired.
[0040] An advantage of particular embodiments of the present
invention is that there is space between the lines of PV cells.
This allows room for the rows of cells to be connected in the
desired fashion. For example each row of cells, or a portion of
each row of cells under a particular focal line can form a series
element. An electrically conductive connection band can be placed
in the spaces between each row of PV cells wherein the connection
band extended beneath one row of PV cells to effect electrical
connection to the underside of that row of cells and a series of
thin connection bands extended across the upper surface of the
second row of PV cells and out to make connection with the
connection band between the two rows of PV cells. Alternative
methods for forming an electrical connection to the upper surface
of the PV cells are discussed later in this disclosure. Preferably
at least the lower connection bands would be made of material of
high electrical and thermal conductivity, for example copper or
aluminum. The bands can be a single band made of one material or
can be a composite band made of one or more materials. For example,
the portion of the band that extends under the row of PV cells can
be made of aluminum and the portion of the band between the rows of
PV cells can be made of copper or another suitable material.
Preferably the bands of material can be deposited. The width of the
band that is allowed by the space between the rows of PV cells
allows a relatively thin film of connection band to have a
relatively large surface area and cross-sectional area. The latter
allows for low electrical resistive losses and the former allows
for efficient heat dissipation of the heat generated by the EM
radiation impinging upon the PV cells. The bands that extend across
the top of the cells can be of any suitable material and in general
would be of thin width so as to cover a minimum area of the PV
cells.
[0041] In the case of the collection of thermal energy, a conduit
containing a fluid to be heated could be placed at the focal line
of each parabolic louver. Preferably this conduit is adapted such
that it receives energy on one surface from absorption of the
concentrated EM radiation and its other surfaces are insulated to
minimize heat loss. There could be multiple conduits or could be
one or more conduits that extend to pass under two or more
parabolic louver focal lines. The conduits would be made of
thermally conductive material such as copper. Since it is desired
to have thermally insulating areas between the conduits, unlike the
prior art, there is no need to have a plate such as a copper plate
extend between the conduits. This reduces the cost and weight of
the device. The thermally insulating areas can be filled with air
or with insulating materials such as, for example, foams.
[0042] The profile of the reflective surface of the louvers is
preferably parabolic in shape. The profile of the parabola can be
defined by the equations below. In these equations the focal point
of EM radiation reflected from the parabolic profile is defined to
be at the x, y point (0, 0). Also where x.sub.o and y.sub.o are
defined to be the x and y coordinates respectively of the upper tip
of the parabolic profile when the profile is rotated such that EM
radiation normal to the x-coordinate is focused on the focal point
(0, 0). The profile is then defined by the equation:
y = tan .alpha. 0 2 x 0 x 2 - x 0 2 tan .alpha. 0 ##EQU00001##
Where .alpha. 0 = - .pi. 2 - .alpha. tan ( y 0 x 0 ) 2
##EQU00001.2##
[0043] It is to be understood that due to manufacturing
imperfection and changes over time and temperature, the louver
profile will only ever approximately conform to the profile give by
the equations above. The degree of conformance of the profile to
the equation above will determine the width of the focal line that
results in practice in the device. The louvers can be manufactured
by any method that results in a reflective surface with a profile
along its length that reflects an acceptable portion of the
incident radiation on to a focal line of the desired width. An
acceptable portion of the radiation is determined by considerations
of the overall cost of producing electrical or thermal energy from
a specified area. This includes considerations of cost of
manufacture of the device, its useful life, the efficiency of the
energy conversion process and the capabilities of competitive
technologies. The desired width of the focal line is decided upon
by a combination of factors balancing cost, practicality of
manufacture, device longevity and ability to dissipate heat. These
factors taken together will determine the optimum width of the
focal line for a particular manufacturing method and cost
structure. For example, to reduce the cost of the PV cells, an
expensive component of the system, it is desirable to reduce their
area, however, past a certain point the cost of producing a
reflector capable of the fineness of focus required and the ability
to dissipate heat from the PV cells for their efficient operation
becomes compromised, thus creating an optimum width.
[0044] The louvers can be constructed of metal plates which are
bent to conform to the desired profile. The plates can be
intrinsically reflective or polished or coated and polished to form
a suitably reflective surface. These metal plates could be mounted
in suitable mounts to hold the plate at the right location and to
allow them to rotate about their focal lines. Alternatively, the
louvers can be cast from metal, preferably with the mounting means
integral, with the reflective surface being polished or coated and
polished after the casting. In yet another alternative, the louver,
preferably with integral mounting means, could be cast or molded
from plastic and subsequently metal plated to yield at least the
front parabolic surface reflective. Optionally, the part could then
be post coated with a clear layer to protect the reflective surface
from environmental degradation.
[0045] FIG. 5 depicts one embodiment of the current invention. FIG.
5 depicts a partially assembled device 100 to illustrate the
various components. Reference number 110 denotes the front
parabolic reflective surface of an exemplary louver 105. Pins 150
locate the louver in side block 120 (only one side shown) such that
the focal line of the louver is coincident with the target area
140. Pins 160 locate in tie rods 130 to link the louvers together.
Pins 150 and 160 are free to rotate in the location holes in side
blocks 120 and tie rods 130, such that when tie rods 130 are moved
upward and forward in unison the louvers are rotated about the
centre of the pins 150. Note that the centre of the pins 150 are
coincident with the focal line of the corresponding louver such
that the louver rotates about its focal line. This insures that for
any angle of incident light in the desired range the louvers can be
rotated such that the focal line remains coincident with the target
area 140.
[0046] FIG. 6 depicts a further cut-away illustration of the
current invention showing how incident radiation is reflected
towards the target area. The arrows in FIG. 6 show exemplary
radiation paths. Note that the louvers are spaced such that
radiation that is not captured by one louver is captured by the
louver in front of or behind it, thereby maximizing the collection
efficiency.
Example 1
[0047] Louvers were designed with a parabolic reflector shape
according to equation (1) where x.sub.o and y.sub.o were -37 mm and
40 mm respectively, with a louver pivot point separation of 22 mm.
End mounting clamps were constructed with the computed shape by
wire cutting the shapes out of aluminum. The mount clamps were made
in two pieces with the concave parabolic shape cut into the front
of the rear half of the clamp and the corresponding convex
parabolic shape formed as the rear surface of the front portion of
the clamp. 0.2 mm thick brass sheet was nickel plated and polished
to give a highly reflective surface and the plate cut into widths
corresponding to that needed for a louver. The plated brass sheet
was clamped at either end between the two halves of the mounting
clamps. Steel pins were used to mount the mounting clamps to side
plates, where the pins were located in holes coincident with the
focal line of the louver. Pins in the upper end of the mounting
clamps were mounted in holes in a tie rod, as shown in FIG. 5. Ten
louvers with a length of 200 mm were assembled in this way.
Example 2
[0048] Louvers manufactured by injection molding were fabricated.
The parabolic shape was computed according to equation 1 with
x.sub.o and y.sub.o as -35 mm and 60 mm respectively, with a louver
separation of 20 mm and the base of the louver being 7.15 mm above
the focal plane of the louvers. The dimensions were chosen such
that the louvers could be rotated to be able to accommodate
incident radiation angles from 20 degrees to 115 degrees, measured
from the x-coordinate, without the base of the louvers having to
impact the focal plane. End mounts with integral pins were designed
to be molded with the louver shape in one piece. The mold was
constructed to give a mirror smooth finish on the front parabolic
surface. The louver was injection molded from an ABS/polycarbonate
blend Bayblend.RTM. T 45 PG (Bayer MaterialScience) and then
metallized to form the reflective coating.
[0049] In one embodiment of the invention, narrow strips of PV
cells are placed at the focal lines to receive the concentrated
radiation to convert it to electricity. To gather the current
generated from the PV cells, it is necessary to make electronic
connection to the upper and lower surface of the PV cells. It is
also often desirable to connect a number of the strips of PV cells
in series to generate a higher voltage and decrease the current
that needs to be carried for a particular power output.
[0050] According to the present invention, the lower connection to
a strip of PV cells is made by a conductive plate on which the PV
cell sits. The plate can be made from any material with
sufficiently low electrical resistance. Non-exclusive examples of
suitable materials are aluminum, copper, tin and copper covered
with a layer of tin.
[0051] If it is desired that two or more PV cell strips are to be
connected in parallel then the lower connection plate is common to
those strips of cells or individual plates are brought into
electrical connection by other means such as by separate wires.
[0052] If it is desired that the strips of PV cells be connected in
series then there is a separate lower connection plate for each
strip of PV cells. The connection plate would extend beyond the
edge of the strip of PV cells to allow other electrical connections
and to act as a heat dissipation device to cool the PV cells when
in operation.
[0053] According to the present invention, the electrical
connection to the upper surface of the PV cell strip is made by an
electrically conductive layer placed in contact with the upper
surface of the PV cell. In a preferred embodiment, the upper
surface connector is a continuous strip that runs the length of the
PV cell strip, overlapping and in electrical contact with the upper
surface of the PV cell strip along one lengthwise edge of the
connector strip, in the area of the PV cell strip that is in shadow
in operation. For the embodiment where the PV cells are to be
connected in series the other lengthwise edge of the connector
strip overlaps and is in electrical contact with the extension of
the lower connection plate of the next strip of PV cells. The
connector strip in this embodiment thus makes a bridging electrical
connection between the top surface of one strip of PV cells and the
lower surface of the next strip of PV cells.
[0054] Suitable materials for the upper connector strip are any
materials that call form a layer and have sufficiently low
electrical resistance. Non-exclusive examples of such materials are
metals, metals coated with electrically conductive adhesive, metals
coated with a non-conductive adhesive but where the metal is
textured such that areas of the metal penetrate through the
non-conductive adhesive, conductive inks, unsupported conductive
adhesives and solder. Non-exclusive examples of suitable metals are
aluminum, copper, tin, tin coated copper or silver. Non-exclusive
examples of suitable conductive adhesives are pressure sensitive
adhesives filled with silver or carbon such as ARclad@90038
(Adhesives Research Inc, Glenn Rock, USA) and silver doped epoxy.
An example of a suitable conductive tape with a conductive adhesive
is 1181 Tape Copper Foil with Conductive Adhesive (3M Corporation).
An example of a suitable conductive tape coated with a
non-conductive adhesive is 1245 Tape Embossed Copper Foil (3M
Corporation) where the embossed features on the foil penetrate
through the non-conductive adhesive layer. Examples of suitable
conductive inks are carbon or silver filled inks. Note that the
upper surface connector must only be capable of forming a
continuous electron conduction path from the PV cell to the next
lower connector plate with acceptably low electrical resistance. It
need not be a continuous connection path along the length of the PV
cell strip, as long as the overall resistance of the connection of
the upper surface of the PV cell with the lower connection plate of
the next strip of PV cell is desirably low. For example, the
connection could be a series of wires or dots bridging the gap to
achieve the electrical connection. However, a continuous connection
layer down the length of the PV cell strip is usually preferred as
in general it will lower the electrical resistance of the
connection and will aid in heat transfer away from the PV cell to
cool it for more efficient operation.
[0055] An additional advantage of the present invention is that
there is a small distance between any area of the upper surface of
the PV cell exposed to the concentrated sunlight and the current
collector. The width of the PV cell strip exposed to the
concentrated sunlight is small, at best equivalent to the width of
the focal line from the parabolic louver mirror. A typical width is
less than 5 mm and more preferably less than or equal to 2 mm. So
the current collected by the upper surface connector only has to
travel a short distance through the PV cell before entering the low
resistance connector. This reduces resistive losses in the device
without the need to have any of the sunlight blocked from the PV
cell by the upper surface connector.
[0056] Optionally, after the array of connections has been
constructed as illustrated above, part or all of the array could be
overlaid with a layer of transparent material (as is known in the
art) to protect the device from water ingress, corrosion and
mechanical damage. As a further option, the transparent protective
layer need not cover all of the array, but only cover the PV cells.
The upper surface connector and the lower surface connector could
be covered with a layer to protect against corrosion and to aid the
radiation of heat, for example a black paint or other thin polymer
layer. Preferably there would be a good seal between the
transparent coating and the heat radiating coating to prevent the
ingress of moisture into the device.
[0057] FIGS. 7 and 8 give a top view and cross-sectional view
respectively showing three strips of PV cells connected in series
in one embodiment of the present invention.
[0058] If it is desired to connect the strips of PV cells in
parallel then the upper surface connector layer from one strip of
PV cells is connected to the upper surface connector layer of the
next strip of PV cells. One embodiment of the connection method for
parallel connection is shown in FIG. 9.
[0059] In FIGS. 7, 8 and 9, 210 denotes the lower surface
connectors, 220 denotes the PV cell strips and 230 denotes the
upper surface connectors. In operation, light is concentrated onto
the areas pointed out by 220. In FIG. 8, 240 denotes a support base
which is electrically non-conductive or at least electrically
insulated from 210 and 230. In FIG. 9, 250 denotes side connection
bars. These bars 250 serve to connect the strips of upper surface
connector together in parallel fashion. In this configuration the
lower surface connector is a continuous plate, connecting the lower
surfaces of the strips of PV cells in parallel fashion.
[0060] To connect an external circuit to the array of PV cells
shown in FIGS. 7 and 8, one connection would be made to the lower
surface connector 210 at one end of the array and the other
connection to 260, the plate connected to the upper surface of the
last strip of PV cell. Optionally, the second connection could be
made directly to the last upper surface connector in the array, in
which case 260 is not necessary. To connect an external circuit to
the parallel array shown in FIG. 9, one connection would be made at
any suitable location or locations on 210 and the other connection
at any suitable location or locations on one or both bars 250. The
bars 250 are made of a material with low electrical resistivity.
They could be made from the same material as the upper surface
connectors 230 or they could be made for example from copper wire
or timed copper wire that is soldered to each upper surface
connector strip 230.
[0061] According to another embodiment, a solid electrically
conductive wire or ribbon is laid abutting one edge of the strip of
PV cell(s). The wire or ribbon is of suitable cross-section such
that it overlaps at least a portion of the adjacent conductive pad
to which it is desired to connect the top surface of the PV
cell(s). A bead of solder or conductive ink (can then be applied to
form an electrically conductive bridge between the top surface of
the PV cell(s) and the conductive wire or ribbon. Optionally, an
additional bead of solder or conductive ink can be applied to form
a conductive bridge between the conductive wire or ribbon and the
conductive pad. In the absence of this second bead, the fact that
the conductive wire or ribbon overlaps and rests against the
conductive pad can be used to provide sufficient electrical
connection. A cross-sectional schematic illustrating this aspect of
the invention using a wire of substantially circular cross-section
is given in FIG. 10 and the situation when using a ribbon of
substantially trapezoidal cross-section is given in FIG. 11.
[0062] In FIGS. 10 and 11, the lower surface of the PV cell 320 is
placed in contact with a conductive pad 310, which is formed on an
electrically insulating substrate 340. A wire 330 (of circular
cross-section in FIG. 1 and of trapezoidal cross-section in FIG. 2)
is placed so as to abut one side of 320 and to also overlap a
portion of a second conductive pad 315. A bead of conductive
bridging material 350 increases the area of electrical connection
between wire 330 and the top surface of the PV cell 320. A second,
optional bead of conductive material 360 can be formed between 330
and 315 to increase the robustness of the connection if
necessary.
[0063] It is to be understood that this aspect is not restricted to
any particular cross-section of wire or ribbon but that any
cross-section that allows bridging between the top surface of the
PV cell(s) and the adjacent conductive pad is within the scope of
this invention. Examples of other suitable cross-sectional shapes
are, oval, triangular, square, rectangular, rhomboid, among
others.
[0064] Suitable materials from which the wire or ribbon can be
constructed are any materials with suitably low electrical
resistance through the cross-section of the wire or ribbon.
Examples of suitable materials are copper, aluminum, steel,
stainless steel, brass and bronze.
[0065] The bead forming the bridge between the conductive wire or
ribbon and the top surface of the PV cells(s) can be made of any
material and applied by any method that is capable of laying down
the bead within a pre-defined area of the top surface of the PV
cell(s) and bridging any gap between the edge of that surface and
the adjacent edge of the wire or ribbon. For example, a bead of
liquid solder can be applied. Alternatively, a length of solid
solder can be laid against the wire and ribbon, such that it
overlaps a pre-defined portion of the top surface of the PV cell(s)
and the solder subsequently melted using heating methods. In
another example, a bead or layer of conductive ink can be applied
from a dispensing device such as a nozzle or a printing screen,
whereupon the ink is dried or cured to form the finished
bridge.
[0066] Another aspect disclosed here is to include reflective side
walls as part of the solar concentration module to improve light
capture when the incident radiation is not normal to the focal
lines of the louvers. When radiation hits the parabolic mirror at
an angle other than normal to its length, the radiation will be
reflected at the same angle to the other side of the normal angle.
In other words the reflected radiation will travel sideways as well
as forward, when looking from the front of the louver. Therefore,
if nothing is done, a portion of the reflected light will not hit
the receiving section on the focal line of the mirror, but rather
travel past the end of the receiving section. There would also be a
commensurate portion of the receiving section at the other end of
the louver that would receive no concentrated radiation. Therefore,
in this situation, a portion of the radiation falling on the louver
will not be focused on to a receiving area.
[0067] According to this aspect of the current invention, this
situation can be avoided by installing additional reflective walls
normal to the focal plane of the parabolic mirrors and normal to
the axis running along the length of the parabolic mirrors. If this
is done, the radiation that would otherwise be lost is reflected
back and focused on to a portion of the receiving section for the
parabolic mirror.
[0068] This aspect of the invention is illustrated in FIG. 12. FIG.
12 depicts a cross-section view of the solar panel 400 when viewed
from the front. The reflective side walls 410 and 420 and the focal
plane 430 of the parabolic mirrors (not shown) containing the
receiving sections, are shown. The radiation 440, is the reflected
radiation from radiation incident on the leftmost portion of the
parabolic louver. Radiation incident to the left of this radiation
will be blocked by the side wall 410, creating a shadowed area 460.
The radiation 450, is the reflected radiation from radiation
incident on the rightmost portion of the parabolic louver. The
dotted lines depict the path of this radiation if the sidewall 420
was not present. As is illustrated, the radiation 450 will be
reflected back on to a portion of the radiation receiving area 470.
Thus, this radiation will be captured by the radiation receiver.
Further, if the side wall 420 is normal to the focal plane 430 and
normal to the axis running along the length of the parabolic
mirror, then the length of the ray reflected off 420 to reach the
focal plane and the absolute angle of the light ray to 420 is the
same as if the radiation were to carry on and be focused on the
focal plane past the end of the receiving area (depicted by the
dotted lines). Therefore, the radiation 450 reflected from the side
wall 420 will be focused onto a portion of the receiving section,
and thus be correctly captured. So, according to this aspect of the
invention, although a shadowed area 460 is created when radiation
incident on the parabolic louver is not normal to the axis running
long the length of the louver, a commensurate amount of extra
radiation is reflected by side wall 420 on to receiving area 470,
resulting in no net loss of radiation. This allows the panel to
efficiently concentrate radiation from a wide range of angles
without the need to rotate the panel to face the source of
radiation, for example the sun.
[0069] The side walls can be made of any suitable material with an
internal face that is reflective for the radiation that is being
concentrated. Examples are polished aluminum sheet, polished
aluminum sheet covered with a transparent coating, nickel coated
steel, bright chrome coated steel, nickel coated brass or bronze,
bright chrome coated brass or bronze, transparent plastic or glass
coated on the back surface with a reflective coating and a back
side protective layer applied, plastic with a front surface
reflective coating with an optional transparent over-coat to afford
protection for the reflective coating or other methods for creating
a planar reflective surface.
[0070] It is to be appreciated that FIG. 12 is merely illustrative
and that this aspect of the invention works equally well for
radiation traveling in from the right side of 400, where 470 would
become the shadowed area and 460 the area receiving the extra
radiation reflected off 410.
[0071] The invention is not limited to the above-described
exemplary embodiments. It will be apparent, based on this
disclosure, to one of ordinary skill in the art that many changes
and modifications can be made to the invention without departing
from the spirit and scope thereof.
* * * * *