U.S. patent application number 12/587719 was filed with the patent office on 2011-04-14 for collecting solar radiation using fresnel shifting.
Invention is credited to William James Todd.
Application Number | 20110083664 12/587719 |
Document ID | / |
Family ID | 43853835 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110083664 |
Kind Code |
A1 |
Todd; William James |
April 14, 2011 |
Collecting solar radiation using fresnel shifting
Abstract
Solar energy is concentrated on a target by at least one group
of Fresnel light-shifting devices.
Inventors: |
Todd; William James; (Baton
Rouge, LA) |
Family ID: |
43853835 |
Appl. No.: |
12/587719 |
Filed: |
October 13, 2009 |
Current U.S.
Class: |
126/700 ;
126/714 |
Current CPC
Class: |
Y02E 10/40 20130101;
Y02B 10/20 20130101; F24S 23/31 20180501 |
Class at
Publication: |
126/700 ;
126/714 |
International
Class: |
F24J 2/08 20060101
F24J002/08; F24J 2/00 20060101 F24J002/00 |
Claims
1-3. (canceled)
4. A method for shifting solar radiation onto a solar energy
receptor using a transparent substrate having Fresnel grooves
selected from the category consisting of: at least one group of
Fresnel grooves sufficiently identical within the group such that
parallel waves of solar radiation are altered in direction of
travel to the same extent, as a consequence of passing through that
group, at least one group of Fresnel grooves sufficiently similar
within that group such that parallel waves of solar radiation
passing through said group remain sufficiently parallel to each
other from said group, such that the majority of the solar
radiation waves interact with the solar energy receptor, at least
one group of Fresnel grooves each group focusing parallel rays of
solar radiation passing through that group to form a focal area
outside the domain of the solar radiation shifting group, and
Fresnel grooves focusing parallel rays of solar radiation passing
through the grooves such that a focal line is formed line outside
the domain of the solar radiation focusing grooves.
5. The method of claim 4 wherein solar radiation passing through
the Fresnel substrate is reflected back through the substrate prior
to interacting with the solar energy device.
6. A solar energy concentrating apparatus comprising at least one
group of Fresnel light-shifting devices.
Description
BACKGROUND
[0001] Using solar radiation as an efficient energy resource for
photovoltaics, heating, lighting applications and the like often
requires using the solar radiation in concentrated form. The
present state-of-the-art is to concentrate solar radiation mainly
by using focusing technology to concentrate the solar radiation
prior to use. Focusing is typically accomplished using light
transmission lenses including convex lenses and Fresnel lenses, by
reflective lenses such as various reflective parabolic structures,
or by reflecting solar radiation onto the target using banks of
small mirrors. The mirror-based technologies are difficult to
manufacture and maintain, while the focusing technologies are
limited mainly by constraints of focal lengths.
SUMMARY OF THE INVENTION
[0002] An object of this invention is to enable inexpensive
manufacture of devices to effectively concentrate solar
radiation.
[0003] Another object is to provide devices that are also more
flexible in application than focusing devices.
[0004] These and other objects are realized using the present
invention, which is based upon using groups of Fresnel grooves
designed to shift solar radiation collected from large areas onto
the much smaller solar radiation receptors used to convert the
solar radiation into more useful forms such as electricity, heat,
and more concentrated light for illumination. By using shifting,
most of the limitations of lenses and focusing can be overcome.
[0005] This invention uses a family of Fresnel light shifting
constructs based upon groups of Fresnel grooves to shift solar
radiation onto solar energy receptors or devices. Using groups of
shifting grooves enables solar radiation impacting large areas to
be shifted onto the small areas of solar energy devices,
effectively collecting or concentrating the solar radiation at the
targeted site.
[0006] This shifting method effectively concentrates solar
radiation without the stringent limitations imposed by the various
focusing methods used as the current convention of the art.
[0007] Freeing the design and applications of Fresnel technology
from the constraints imposed by focusing, i.e. freedom from the
theoretical and practical limits of traditional lenses, the
effective concentration of solar radiation can be greatly
facilitated in a cost effective manner. Using the designed Fresnel
shifting groups described below enables projecting shifted solar
radiation to a common area. Indeed, for some arrangements, the
positioning of the solar radiation shifting grooves is effectively
independent of the distance between the solar radiation shifting
grooves and the targeted solar energy device. The principles of
Fresnel shifting as described herein enable collecting solar
radiation efficiently and in amounts related to the need. The solar
radiation collected by shifting can be directed onto any type of
solar energy receptor including non-limiting examples such as
photovoltaics, heat collectors including fluid filled pipes,
cooking containers, or light tubes or fiber optic cables for
transferring light into a structure.
[0008] The manufacture of the shifting devices is also relatively
simple in comparison to most types of lenses and other devices used
to concentrate solar radiation. Because of the flexibility and
simplified design, along with lighter weight, esthetics, varied
geometrical options and diversity in locations, shifting
applications are more cost effective and relevant to many
applications, and often useful even where focusing technologies
would be problematic or impossible.
[0009] Because the science of these shifting constructs or devices
is based principally upon the historical teachings attributed to
Fresnel, as part of the background to understanding this invention
some salient features of Fresnel lenses are shown in FIGS. 1 and
2.
[0010] Lenses, including reflective lenses such as parabolas,
transparent convex lenses, and flat Fresnel lenses are commonly
used to concentrate or focus light for applications to solar
energy, as well as to focus light for use magnification, and other
forms of imaging. Lens focusing properties, based upon the contour
of the refracting surface of a convex lens, have been known for
centuries. According to the principles of the curved lens surface,
the curve is relatively flat at the center of the lens surface,
gradually increasing in bending of the curved surface until near
the edges of the lens circumference, the curve of the lens becomes
quite steep, as diagramed in FIG. 1.
[0011] FIG. 1.1 shows a plano-convex form of such a typical lens.
This type of lens led to the understanding that most of the lens
material could be ground out to form essentially a step-surface
lens, relatively flat, that could mimic the function of the
original plano-convex lens. Fresnel recognized that each groove of
the stepped lens should represent a corresponding curve of the
aspheric surface at that point or line of the original lens, and
that the spacing of the circular patterns of the steps should be
coordinated with the extent of the curvature of the traditional
lens model such that the spacing between the different circles of
steps should decreases proportionally to the distance of the step
from the center. It is important to keep in mind that Fresnel
grooves are designed to mimic the curved surface of the lens. This
innovation of Fresnel greatly improved the functioning of the
stepped type lenses, and for some applications made the
Fresnel-type flat lenses competitive with the convex lenses. A
diagram of a Fresnel lens is provided as FIG. 2, along with two
less common examples.
[0012] Fresnel lenses in varying formats are used in a variety of
ways, especially for magnification, in addition to numerous
applications to focus light as a mechanism to concentrate solar
radiation. Because of lens physics and practical limits of the
refractive index of useful substrates etched with the Fresnel
grooves to construct Fresnel lens, useful sizes of Fresnel lenses
seem typically limited to approximately 12 to 14 inches in
diameter. Fresnel lenses are also known to be very effective at
focusing, forming precise focal points or lines of highly
concentrated solar radiation. This is true because each arrangement
or line of Fresnel grooves is designed to mimic a specific part of
the curve on a convex lens, effectively focusing the light as would
that part of the curve on the lens, (See FIG. 1). Collectively the
Fresnel grooves form a fine point or line of highly concentrated
solar radiation. The heat generated from this concentration is in
the form as "hot spots," creating limitations in some desired
applications wherein the intensely concentrated energy would damage
the target, such as a photovoltaic device, further restricting the
applications of Fresnel lenses with respect to solar energy.
[0013] The principle of this invention is to forego the lens
concept and instead to use Fresnel grooves in sets or groups to
essentially shift solar radiation onto solar energy targets such as
photovoltaic or heat, or other receptors. Because groups of
functionally similar or identical Fresnel grooves cannot, by
definition, mimic the curve of a lens, such groups can not form
such extreme hot spots and can be designed so that the energy
distribution across the surface of a solar radiation receptor is
uniform in intensity. Depending upon the need, this can be
accomplished without focusing as is more preferred, or if desired
with various degrees of focusing as preferred for some applications
where very dense collections of solar radiation are required as
concentrated such as to form a focal line, depending upon the broad
embodiment of this invention.
[0014] Through variations of Fresnel shifting, solar radiation can
be collected and delivered to a solar radiation target or receptor
either evenly across the target in modest amounts or evenly in
intense amounts, or as very high intensity hot spots or intense
areas linear in character such as a near focal point or line.
Because a lens is not used, the size restriction attributed to
Fresnel lenses no longer applies, greatly increasing the area and
therefore the amount of solar radiation that can collected. This
concept also allow different groups or areas of the Fresnel
shifting device to be located along the same plane, as is the
character of the Fresnel lens, or at different planes enabling
additional options for how solar radiation can be collected.
Furthermore, and of particular importance, the parallel shift
design enables the shifted solar radiation to travel in concert
relatively long distances prior to interacting with the solar
energy target.
[0015] With this invention, linear devices can be very long (as can
be Fresnel lenses) but via this invention can also be very wide,
and groups of shifting grooves can be treated independently such
that shifting groups can be at different levels if needed, or
widely separated yet still transfer solar radiation to the same
target. Such is possible by working with groups of Fresnel groves
with the same or related solar radiation shifting characteristics
within each group rather than with a Fresnel lens or section of a
Fresnel lens.
[0016] Although sharp focal areas are possible, they are generally
less preferred for home use because they can constitute a fire
hazard if improperly used. The flexibility of the Fresnel shifting
motif allows incredible variability in design of solar radiation
devices to collect solar radiation by shifting the direction of
solar radiation wave travel. For example, wherein the shifted waves
of solar radiation remain parallel long distances are possible
between the location of solar radiation collecting devices and the
solar radiation targets, therefore high placement of the Fresnel
shifting grooves is feasible. Examples of placement could include
off the edges of builds or on other available structures such as
supports for wind turbines where the necessary electric grid is in
place. Cogeneration of electricity via solar and wind using
established fields of wind generators is cost effective because
some of the structural support needed for solar radiation
collection, and access to an electric grid to transport the
generated electricity are already in place. High placement of
separate groups of shifting grooves would likely limit the
collector geometry to rectangles, the orientation east-to-west, and
the solar radiation target to be long such as a heat pipe to
account for a moving area of solar radiation concentration. Other
arrangements, including circular or even branching such as peddles
of a daisy are possible and can result in concentration of large
amounts of solar radiation within a small area. This freedom of
design is very important to promote applications both for improving
energy efficiencies in "developed" countries as well as in
"developing" countries where even small improvements such as
replacing much of the wood used as fuel to providing safe drinking
water, to even inexpensive ways to generate at least modest amounts
of electricity can have a great impact in the quality of life for
many people.
[0017] By using groups of functionally related Fresnel groves, the
limits imposed by the lens equations, and structural limits in lens
design are no longer valid, liberating the applications of Fresnel
to solar radiation, based principally upon solar radiation shifting
groups of Fresnel grooves rather than the traditional lens
approach. For most, but not all, applications, the solar radiation
shifting grooves are arranged in groups such that the diameter and
length of each Fresnel-based shifting group, are approximately the
same as the solar energy target. Where the direction of light
propagation is extensively altered, where the angle of shifts are
very sharp, the diameter of the shifting groups can be larger than
the diameter of the target yet all the shifted waves can still
contact the target. Fortunately, Fresnel groves, especially in
linear arrays are relatively easy to produce in sheets of various
types of glazing by common methods including but not limited to
etching, extrusion, molding, and imprinting. Such materials are
also acceptably attractive, relatively easy to clean, and cost
effective in comparison to the major competing technologies such as
reflective parabolic troughs or banks of mirrors. The Fresnel
shifting devices can of course be tilted to remain more
perpendicular to the daily path of the sun, or by accepting some
reduction in efficiency orientated more east-to-west along the long
axis, perhaps changing angle of position to be more perpendicular
to the general path as the seasons change, depending upon the
latitude. It should be noted that the transparent Fresnel light
shifting devices can be made much lighter in weight than many of
the other technologies used to collect and concentrate solar
radiation. They are less expensive and easier to maintain under
most circumstances than other technologies such as reflective
parabolas, or banks of mirrors designed to reflect solar radiation
onto a target.
DEFINITIONS
[0018] Targeted solar energy receptor or device includes but is not
limited to photovoltaic devices such as to generate electricity
directly from solar radiation; heat collecting devices such as
pipes or tubes containing liquid or gas fluids, heating solid
surfaces such as for cooking, cooking pans and pots and the like;
light collecting devices such as to transport light into a building
via tubes channels or fiber optics.
[0019] Transparent substrate refers to any glazing or other
material enabling visible and or UV and or infrared light to pass
through.
[0020] Group of Fresnel grooves means three or more grooves of
sufficiently similar character with respect to changing the
direction of light waves to enable the solar radiation shift of
claim one.
[0021] Domain of the solar radiation shifting device or group
refers to the area directly below the group or device, in reference
to the direction of incoming rays of solar radiation striking
perpendicular to said group or device.
[0022] Solar Energy and Solar Radiation for purposes of this
invention mean the broad spectrum of solar radiation including UV,
visible and infrared radiation.
[0023] Fresnel shifting means changing the direction of radiation
as a consequence of passing through glazing containing Fresnel
grooves. For this invention the radiation refers to solar radiation
and is not intended to refer to light such as coming from a light
bulb.
[0024] Fresnel groove and Fresnel facet are interchangeable terms
used to describe the alteration in plane of substrate used to
change the direction of solar radiation travel.
[0025] A single solar radiation shifting device comprises one or
more groups of Fresnel grooves such that the shifted light reaches
the common target of the device. Different groups involved in the
concentration of light at a common target though perhaps separate
and in different locations are functionally and therefore
considered part of the same single solar radiation shifting
device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In the accompanying drawings,
[0027] FIGS. 1a-1f show different types of conventional optical
lenses;
[0028] FIG. 2a is cross-sectional view of a Fresnel lens, showing
lens design variables;
[0029] FIG. 2b is a sectional view of a lift shifting device having
Fresnel grooves on both sides;
[0030] FIG. 2c is a sectional view having facets which shift light
more than once on one surface;
[0031] FIG. 3 is a sectional view showing a group of Fresnel facets
shifting sunlight onto a target;
[0032] FIG. 4 is a diagram showing groups of Fresnel devices
shifting light onto a common target;
[0033] FIG. 5 is a diagram showing Fresnel shifting devices in
combination with a reflector;
[0034] FIG. 6 shows two Fresnel shifting devices in series before a
target;
[0035] FIG. 7 shows a Fresnel shifting device having a focal point
or focal line outside the domain of the shifting group; and
[0036] FIG. 8 is a sectional view of a Fresnel shifting device
above a reflector.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] FIGS. 1a-1f and 2a-2c are included to help explain some of
the features of the historical art relevant to understanding this
invention. FIGS. 3-8 are included as descriptive non-limiting
examples of this invention to promote understanding of the
invention, and to gain insight into some of the ways this invention
can be applied.
[0038] FIGS. 1a-1f are included to provide a basic understanding of
the concept of Fresnel lenses including how a Fresnel groove, or
facet etched into a transparent substrate can result in changing
the direction of waves of light. FIGS. 2a-2c are a general
presentation from the public domain literature on the basic
characteristics of Fresnel grooves or facets that can be
manipulated to control the extent to which the travel direction of
the light waves are modified upon passing through the structure. In
addition to the features mentioned, the refractive index of the
substrate also significantly contributes to the extent of change in
direction. In known applications to solar radiation, these features
are mostly used to create lenses to focus the solar radiation onto
a target of interest. In contrast, this invention uses the lens
principles of Fresnel for non-lens functions, the principle being
to shift the direction of light, without forming the focusing
patterns of any of the known Fresnel types of lenses. The concept
of this invention can be comprehended by understanding FIGS. 3-8 as
teaching aids representative of non-limiting descriptions of this
art.
[0039] In FIG. 3 and in all subsequent figures, unmodified waves of
solar radiation are shown using solid black lines, whereas waves
modified in direction of travel are depicted using lines composed
of dashes and dots. In FIG. 3, a translucent substrate is etched
with a series of uniform Fresnel grooves such that incoming
parallel waves of solar radiation impact the shifting device and
are shifted to the same extent such that upon exiting the device
travel in the shifted direction while maintaining the parallel
character. In this manner when the shifted light waves reach the
target they are uniform and do not form hot spots on the target as
would occur if the light waves had been focused. In this example
the same target also receives solar radiation not altered in
direction. The combined effect is to add more energy evenly
distributed across the target than would otherwise occur. This
configuration would be especially useful to increase the amount of
light impacting photovoltaic panels to increase the amount of
energy that could be produced. With this method, the output of
existing photovoltaic panels could be greatly improved. It is far
less expensive to produce the transparent Fresnel shifting devices
than it is to produce the photovoltaic panels. Depending upon how
much additional energy the type of photovoltaic could efficiently
utilize, many different shifting groups could be used to
collectively shift the total amount of solar radiation desired onto
the photovoltaic; for an example of such an arrangement, refer to
FIG. 4 and modify by replacing the round target shown with a
photovoltaic device of the shape desired.
[0040] FIG. 4 shows one example of how many and different solar
energy shifting groups can work in concert to shift large amounts
of solar radiation onto a target or solar radiation receptor. Note
that this sketch is as a cross-section. The shifting groups could
be arranged for example as long parallel rectangles or even circles
of groups depending upon the need. Long rectangles of shifting
groups might be preferred to heat fluids in pipes or tubes or long
photovoltaics, whereas a circular pattern would be effective to
impact a small area with lots of solar radiation, for a variety of
applications ranging from movement of light such as via a tube or
fiber optic cables, to outdoor cooking Heating of tubes or pipes
containing fluids is of course important for household space and
hot water heating, power to drive steam turbines for electricity
and for moving heat into cooking platform to name a few. Of further
interest, because the shifted light waves remain parallel, they can
travel long distances prior to interacting with the target,
enabling large areas of solar radiation to impact relatively small
targets for functions where lots of solar energy is required in
concentrated form. The shifting groups can be connected in the same
plane, as separate in the same plane as drawn, or they can be in
different planes from each other enabling a wide variety of
designs. The only real requirement is that the shifting groups are
coordinated to reach the receptor to fulfill the objectives at hand
Freeing the geometry from focusing enables one to take advantage of
the local environment depending upon what is available to help
support the shifting groups. Shifting the direction of light
travel, while maintaining the parallel character of the waves, is
also an excellent way to transport energy. Such devices could be
placed where there is sunlight, and transport the light to area
where it is needed, even if the desired area is otherwise shaded.
Shifted solar radiation could also be directed to a solar energy
device located on or near the ground from long distances away such
as from the edge of a building or other tall structures.
[0041] FIG. 4 also reveals much of the strategy of the invention
and stimulates thinking with respect to applications, advantages
and limitations of various designs and arrangements of the groups
of Fresnel shifting grooves. For example, if the shifting groups
are co-joined, the plane of the collector can be kept perpendicular
to the incoming parallel rays of solar radiation by rotating the
shifting platform in an arc and maintaining the solar radiation
target at the center, with or without tilting the receptor.
However, co-joining the shifting groups creates the analogy of a
lens because a fixed distance is now required between the shifting
device and the target, analogous to the focal length of a Fresnel
lens. Because this distance is based upon the number of Fresnel
shifting grooves per group, there is a great deal of flexibility in
the diameter of the shifting device and consequently in the fixed
distance between the shifting groups of the solar radiation device
and the receptor or target. By descriptive analogy the practical
(rather than theoretical) diameter of a point or line of a Fresnel
lens could be, as an instructive example, about 0.01 inch which can
be achieved with about a twelve inch diameter Fresnel lens. For a
non-limiting example of this Fresnel shifting invention, a
practical area of solar radiation concentrated on the solar energy
target might be two inches for a fluid-filled pipe as the target.
Ay analogy of ratio, the 0.01 inch focal diameter is to the two
inch concentration area as the twelve inch lens is to diameter X.
In this equation X is about a two hundred feet in diameter of the
shifting device representing a probable near maximum limit of the
possible diameter to form a two inch area of concentrated solar
radiation. However, the size of the shifting device to reach this
two inch area could also be designed to be much smaller. Of course
the focal length of the lens and the concentration distance between
the shifting device and the target would also be related by about
the same ratio and for a shifting device that large the device
would likely have to be about one hundred feet above the solar
energy receptor, though by decreasing the size of the shifting
device this distance could also be decreased. This example is a bit
extreme as the amount of light that could be brought to an area two
inches in diameter form a two hundred foot in diameter solar
radiation shifting device, assuming nearly one hundred percent
efficiency would be about a 14,000 fold concentration. If the
shifting groups are separate, the limits in size of the shifting
device are effectively restricted only by engineering
considerations including support structures and maintaining
alignment. Of interest, these two different arrangements of groups
of shifting grooves are not mutually exclusive, as the area of a
smaller shifting device could be supplemented by other free
standing shifting groups shifting additional light either directly
onto the target, or onto the fixed shifting device itself.
[0042] FIG. 5 is intended to show that the group shifting
technology of this invention can be used to supplement existing
technology to improve overall function. There are many reflective
parabolic troughs currently in use to concentrate solar radiation
such as to heat fluid-filled pipes. By adding shifting groups, the
amount of energy received by the collecting pipe can be improved
even if many of the shifted light waves miss the collecting pipe.
They could then be reflected back onto the target using the
existing reflecting parabolic trough.
[0043] FIG. 6 is included to demonstrate that several shifting
groups can be used in tandem to shift solar radiation onto a chosen
target. The shifting system to direct solar radiation is very
flexible in application.
[0044] FIG. 7 is a diagrammatical description that Fresnel grooves
can be organized to alter the direction of light to form a focal
line outside the domain of the light shifting group. The figure is
a cross section of a cluster of light shifting grooves orientated
such that light is focused, but unlike a lens, is focused to a line
outside the domain of the shifting device, depicted here by the
cross section of the line indicated by the common point of
intersection. By using many analogous groove clusters in different
positions, a large area of solar radiation can be brought to
intersect at the same line, enabling extensive amounts of solar
radiation to concentrate along the line. This arrangement is not
proposed for home use because the amount of energy concentrated
could be dangerous, including creating a potential a fire hazard.
For comparative descriptions of off axis focusing see Barone,
United States Patent Application number 2005004107.
[0045] FIG. 8 illustrates a reflective surface or mirror in
combination with shifting of light as shown in FIGS. 3-7, greatly
expanding the applicability and flexibility of this invention.
Using a mirror to reflect the shifted solar radiation back through
the same shifting group results both in reflection of the light and
enables a second passage through the shifting group yielding both
the reversal in direction of transmission of the light, and an
increase in the angle of the shift. Because of the reversal in
direction of travel, and increased angle of the shift, additional
amounts of solar radiation could be directed to the solar energy
targets synergistically with shifting devices of FIGS. 4-7 by
placement of the mirror-backed shifting devices beyond the limits
of the primary shifting devices and below the solar radiation
target. An all mirror backed system can be used to concentrate
solar radiation onto the target located above the shifting grooves
adding additional flexibility to applications of the invention.
* * * * *