U.S. patent application number 10/621933 was filed with the patent office on 2005-01-20 for solar energy collector.
Invention is credited to Johnson, Neldon P..
Application Number | 20050011513 10/621933 |
Document ID | / |
Family ID | 34063100 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011513 |
Kind Code |
A1 |
Johnson, Neldon P. |
January 20, 2005 |
Solar energy collector
Abstract
A solar energy collector comprised of Fresnel lenses attached by
support frames to a solar tracking drive. Each of the Fresnel
lenses is continuously alined with the sun during a desired period
of operation and are maintained at a focus distance from energy
absorbers by the support frames and the solar tracking drive. The
energy absorbers may be absorption conduit.
Inventors: |
Johnson, Neldon P.; (Salem,
UT) |
Correspondence
Address: |
J. David Nelson
NELSON, SNUFFER, DAHLE & POULSEN, P.C.
10885 South State Street
Sandy
UT
84070
US
|
Family ID: |
34063100 |
Appl. No.: |
10/621933 |
Filed: |
July 17, 2003 |
Current U.S.
Class: |
126/698 ;
126/600; 126/652 |
Current CPC
Class: |
F24S 2030/136 20180501;
Y02E 10/40 20130101; Y02E 10/47 20130101; F24S 20/20 20180501; F24S
30/455 20180501; F24S 23/31 20180501 |
Class at
Publication: |
126/698 ;
126/652; 126/600 |
International
Class: |
F24J 002/08 |
Claims
What is claimed is:
1. Apparatus for solar energy collection comprising: a) one or more
Fresnel lenses, each Fresnel lens having a focal axis; b) one or
more energy absorbers, each energy absorber having one or more
internal absorption ducts for transferring solar energy absorbed by
the energy absorber to an absorption liquid; c) one or more support
frames, each support frame securing a respective Fresnel lens in a
respective focus position for focusing solar energy passing the
Fresnel lens on an absorption zone of an energy absorber; and d)
one or more solar tracking drives affixed to the support frames for
maintaining alinement of the focal axis of each of the Fresnel
lenses with the sun and maintaining each of the Fresnel lenses in a
respective focus position during a desired period of operation.
2. Apparatus as recited in claim 1 wherein the energy absorbers are
absorption conduits.
3. Apparatus as recited in claim 1 further comprising an absorption
liquid circulating system connected to the absorption ducts in each
energy absorber.
4. Apparatus as recited in claim 2 wherein each absorption zone is
comprised of an energy assimilator of high thermal conductivity
material affixed to the absorption conduit.
5. Apparatus as recited in claim 4 wherein each energy assimilator
is spherically shaped.
6. Apparatus as recited in claim 1 wherein the absorption zone of
each energy absorber is encapsulated in an energy retaining capsule
of material with a high solar radiation transmission rate and a low
thermal conductivity rate.
7. Apparatus as recited in claim 6 wherein the energy retaining
capsule is comprised of transparent material.
8. Apparatus as recited in claim 6 wherein the energy retaining
capsule is spherically shaped.
9. Apparatus as recited in claim 7 wherein the transparent material
is a borsilicate glass.
10. Apparatus as recited in claim 3 wherein the absorption liquid
circulating system comprises an absorption liquid conduit system
and one or more absorption liquid pumps.
11. Apparatus as recited in claim 3 wherein the absorption liquid
is an oil.
12. Apparatus as recited in claim 3 further comprising an energy
transfer system connected to the absorption liquid circulating
system.
13. Apparatus as recited in claim 12 wherein the transfer liquid is
water.
14. Apparatus as recited in claim 12 wherein the energy transfer
system comprises an energy exchanger, a transfer liquid conduit
system and one or more transfer liquid pumps, the energy exchanger
being connected to the absorption liquid circulating system.
15. Apparatus as recited in claim 1 wherein the solar tracking
drive comprises longitudinal pivot means, lateral pivot means and
tracking control means.
16. Apparatus as recited in claim 1 wherein one or more of the
Fresnel lenses have an elongated focus for an elongated absorption
zone on the energy absorbers.
17. Apparatus as recited in claim 1 wherein one or more Fresnel
lenses have longitudinal grooves with a linear distributed focus
for a linear elongated absorption zone on the energy absorbers.
18. Apparatus as recited in claim 1 wherein one or more Fresnel
lenses have oval grooves with a distributed focus for the
absorption zones on the energy absorbers.
19. Apparatus as recited in claim 1 wherein the energy absorbers
have absorption surfaces which are displaced radially from the
focal point of the respective lenses for a distributed focus on the
absorption zones of the energy absorbers.
20. Apparatus as recited in claim 2 wherein the absorption conduits
comprise one or more pipes.
21. Apparatus as recited in claim 1 further comprising an energy
retaining capsule with a high solar energy transmission rate and a
low thermal conductivity rate encapsulating each absorption
zone.
22. Apparatus as recited in claim 21 wherein the energy retaining
capsule is spherical in shape.
23. Apparatus as recited in claim 21 wherein the capsule is made of
borsilicate glass.
24. Apparatus as recited in claim 2 further comprising a respective
energy retaining capsule encapsulating each absorption zone on each
absorption conduit.
25. Apparatus as recited in claim 24 wherein the energy retaining
capsule comprises a conduit coating with a high solar energy
transmission rate and a low thermal conductivity rate.
26. Apparatus as recited in claim 25 wherein the conduit coating is
made of borsilicate glass.
27. Apparatus as recited in claim 25 wherein the conduit coating is
ceramic.
28. Apparatus as recited in claim 1 further comprising a respective
absorption fin mounted in an interior absorption duct of one or
more energy absorbers in the absorption zone.
29. Apparatus as recited in claim 1 wherein one or more of the
energy absorbers comprise an energy assimilator affixed on an
absorption liquid conduit.
30. Apparatus as recited in claim 29 wherein the absorption liquid
conduits comprise one or more pipes.
31. Apparatus as recited in claim 30 further comprising an energy
retaining capsule with a high solar energy transmission rate and a
low thermal conductivity rate encapsulating each absorption
zone.
32. Apparatus as recited in claim 31 wherein the energy retaining
capsule is spherical in shape.
33. Apparatus as recited in claim 31 wherein the energy retaining
capsule is hemispherical in shape.
34. Apparatus as recited in claim 31 wherein the energy retaining
capsule is made of borsilicate glass.
35. Apparatus as recited in claim 1 further comprising a respective
absorption fin mounted in an interior absorption duct of one or
more energy absorbers at the absorption zone.
36. Apparatus as recited in claim 1 further comprising one or more
secondary lenses affixed by a secondary lens frame to the support
frame.
37. Apparatus as recited in claim 14 further comprising: a) steam
turbine, the steam turbine having an output shaft; and b) rotary
generator affixed to the output shaft of the steam turbine.
38. Apparatus for solar energy collection comprising: a) one or
more Fresnel lenses for concentrating incident solar energy, each
Fresnel lens having a focal axis; b) absorption means for absorbing
solar energy concentrated by the Fresnel lenses and transferring
the absorbed solar energy to an absorption liquid; c) support means
for supporting each Fresnel lens in a respective focus position for
focusing solar energy passing the Fresnel lens on the absorption
means; and d) solar tracking means affixed to the support means for
maintaining alinement of the focal axis of each of the Fresnel
lenses with the sun and maintaining each of the Fresnel lenses in a
respective focus position during a desired period of operation.
Description
FIELD OF THE INVENTION
[0001] This invention is in the field of solar energy systems and
in particular in the field of solar energy collectors which use
lenses to concentrate solar radiation for use in heat exchange
applications.
BACKGROUND OF THE INVENTION
[0002] The use of lenses to concentrate solar radiation on an
absorbing device is known in the art. Solar concentrators utilizing
Fresnel lenses have also been disclosed in the prior art. U.S. Pat.
No. 5,915,376 to McLean discloses a solar heat collecting apparatus
comprised of glass domes consisting of Fresnel lenses. Solar
radiation entering the solar heat collecting apparatus is absorbed
by an absorber plate, and transferred to a remote storage system by
conventional heat transfer means.
[0003] U.S. Pat. No. 6,384,320 to Chen discloses a compound
parabolic concentrator (CPC) which is mounted under a Fresnel lens
that concentrates the intensity of solar radiation to five to ten
times above normal level. The focused solar radiation is further
concentrated twenty to fifty times by the CPC collector. The
intensified solar radiation is focused onto the top of a stainless
steel heat pipe or heat exchanger.
[0004] The use of Fresnel lenses for concentrating solar energy is
disclosed in U.S. Pat. No. 6,399,874 to Olah, U.S. Pat. No.
6,299,317 to Gorthala, and U.S. Pat. Nos. 5,959,787 and 6,091,020
to Fairbanks. The devices disclosed in these patents provide for
concentrating solar energy for photovoltaic cells.
[0005] It is an object of the present invention to provide a
simplified, economical and efficient solar collector for heat
transfer applications.
[0006] It is a further object of the present invention to provide a
solar collector using a pipe for an energy absorber.
[0007] It is a further object of the present invention to provide a
solar collector that is flexible as to the intensity, distribution
and geometry of concentration of solar radiation on an energy
absorber.
[0008] It is a further object of the present invention to provide a
solar collector that incorporates an energy absorber with enhanced
energy absorption efficiency.
[0009] It is a further object of the present invention to provide a
solar collector that uses a pipe with an energy retaining capsule
encapsulating the absorption zone as an energy absorber.
[0010] It is a further object of the present invention to provide a
solar collector with a simple and economical solar tracking
drive.
[0011] It is a further object of the present invention to provide a
solar collector that is readily incorporated into a solar collector
installation that is flexible as to size and geometry.
[0012] It is a further object of the present invention to provide a
simple, economical and efficient solar collector installation.
[0013] It is a further object of the present invention to provide a
solar collector installation that is simple and economical to
operate and maintain.
[0014] It is a further object of the present invention to provide a
solar collector installation that utilizes pipes as energy
absorbers.
[0015] It is a further object of the present invention that
provides a solar collector and energy extraction installation that
is simple and economical to construct, operate and maintain.
SUMMARY OF THE INVENTION
[0016] The solar energy collector of the present invention uses one
or more Fresnel lenses. Typically the Fresnel lens used for the
present invention is a extruded or molded from a thin, lightweight
plastic sheet with concentric grooves formed in one side of the
lens. The grooves act as individual refracting surfaces, like small
prisms when viewed in cross section, bending parallel rays in a
very close approximation to a common focal length. Because the lens
is thin, very little energy is lost by absorption.
[0017] For a preferred embodiment, the Fresnel lenses are mounted
on a support frame above an absorption conduit which is typically a
metal pipe. If the Fresnel lenses are designed for a point focus or
a distributed focus on an absorption zone, the absorption conduit
may have an energy absorber mounted on the conduit in the
absorption zone which is enclosed in an energy retaining capsule
with a high solar radiation transmission rate and a low thermal
conductivity rate, thereby providing for transmission of the
focused incident solar radiation to the absorption zone of the
energy absorber while minimizing the loss of energy from the energy
absorber to the surrounding air. An in-line or attached spherical
energy absorber with a spherical energy retaining capsule or a
hemispherical energy absorber with a hemispherical energy retaining
capsule may be used. Alternatively, a spherical or hemispherical
energy retaining capsule can simply be used to encapsulate an
absorption zone on the absorption conduit. For a linear absorption
zone, a cylindrical capsule is preferred on the absorption conduit.
The absorbed energy is transferred to an absorption liquid flowing
through the absorption conduit.
[0018] An absorption fin can also be incorporated inside the energy
absorber which extends into the absorption duct and is in contact
with the absorption zone, thereby assisting in the transfer of
energy to the absorption liquid which flows through the energy
absorber. The absorption fin would normally be made of high thermal
conductivity material thereby rapidly transferring the energy of
the incident solar radiation from the absorption zone to the
absorption liquid. A preferred material for the absorption zone and
absorption fins is tungsten due to its high thermal conductivity
rate, its high melting point and its glass to metal sealing
capabilities.
[0019] Each Fresnel lenses is mounted on a support frame which is
attached to a solar tracking drive. The solar tracking drive
continually aligns each Fresnel lenses with the sun, during a
desired period of operation, thereby providing for continual point
focus or distributed focus of the incident solar radiation on an
absorption zone of the energy absorber. The absorption conduit, or
other energy absorber, can be positioned so that the Fresnel lens
top surface is separated from the absorption conduit top surface by
a distance which is equal to the focal length of the lens, thereby
providing for the incident solar radiation to be focused at a
single point in the absorption zone of the energy absorber or can
be positioned such that incident solar radiation is distributed on
a larger area of the absorption zone. If the incident solar
radiation is focused on a single point in the absorption zone of
the energy absorber, substantially higher temperatures will be
experienced at the focal point. Having the focal point coincident
with the center of the energy absorber, rather than a point on the
surface of the energy absorber, results in distribution of the
energy and therefore substantially reduced temperatures. The focus
of the incident solar radiation can be varied between the center of
the absorption conduit and a point on the surface of the absorption
conduit thereby varying the distribution of the focused solar
radiation and thereby the maximum temperature experienced in the
absorption zone.
[0020] Rather than a circular pattern of grooves, the Fresnel
lenses may have longitudinal grooves which result in the incident
solar radiation having a line focus rather than a single focal
point. This offers an advantage of distributing the focused
incident solar radiation over a larger area, thereby reducing the
temperature of the absorption zone. The expanded absorption zone
for embodiments utilizing a Fresnel lens with longitudinal grooves
can be encapsulated in an energy retaining capsule with a high
solar radiation transmission rate and low thermal conductivity rate
such as glass. Other portions of the absorption conduit which do
not receive focused incident solar radiation can be insulated or
merely be covered with the energy retaining capsule material to
reduce energy loss to the surrounding air. Similarly, Fresnel
lenses with oval grooves may be used to provide for distribution of
energy on the absorption zone as the lens will distribute the
concentrated radiation on an expanded area rather than a single
focus point. Further distribution of the energy can be
accomplished, regardless of the pattern of grooving on the Fresnel
lens, by positioning the Fresnel lenses so that the energy
absorbers have absorption surfaces which are displaced radially
from the focal point or focal line of the respective lenses. The
extent of the distribution can be selected based upon the desired
range of surface temperatures for the absorption zone.
[0021] The Fresnel lens itself is preferably constructed of an
optically clear material. These materials include but are not
limited to acrylic, glass, rigid vinyl, polycarbonate,
polyethylene, polyester blends including PET and PETG respectively,
poly IR, polystyrene, polyurethane, polypropylene,
polyacrylonitrile, Kevlar, Nomex, rubber, germanium, silicon, zinc
sulfide, quartz and other such materials. The inventor's preferred
materials are polyester (PET or PETG) or a blend thereof.
[0022] A Fresnel lens can be formed or manufactured in a number of
ways from the substrate materials identified above. This includes
but is not limited to press thermalforming, roll thermalforming,
casting, emboss extruding, injection molding, milling, lathing, or
UV curing. Emboss extrusion is the preferred method of creating
Fresnel lenses. Extruding allows for the creation of an
inexpensive, thin, flat plastic sheet with an embossed Fresnel
image imprinted on one side of the lens. The preferred materials,
namely polyester (PET or PETG) can be utilized with or without
protective additives. Protective additives may include ultraviolet
light and antioxidant additives, both of which reduce yellowing and
clouding of the Fresnel lens. These additives can be introduced
into the resin prior to the extrusion process or during the
extrusion process in a step referred to a co-extruding. A
protective co-extruded cap layer is preferred, promoting longevity
of the Fresnel lens.
[0023] Each Fresnel lens is secured in a focal position for
focusing solar radiation passing the Fresnel lens on the absorption
zone on the energy absorber by a support frame. A preferred
embodiment consists of a lens retainer to which the perimeter of
the lens is attached and secured on its perimeter and a pair of
pivot brackets. A preferred embodiment of the solar tracking drive
is comprised of a base frame, a base drive, a pivot rail, pivot
bar, a pivot drive, a pivot drive plate, anchor pedestals and base
bearings. Each of the support frames is pivotally attached to the
base frame by base pivot bearings which pivotally attach the bottom
of the pivot bracket, thereby providing for longitudinal pivoting
of the support frames respectively. The longitudinal pivoting of
the support frames is controlled by the pivot drive which varies
the position of the pivot bar, which is pivotally attached to the
pivot rail by a pivot bar bearing. The pivot rail is pivotally
attached to the top of one of side of each of the solar collector
support structures by top bearings.
[0024] Lateral pivoting of the solar collector support structures
is accomplished by lateral rotation of the base frame which is
controlled by the base drive and facilitated by base bearings. The
number of anchor pedestals and base bearings can be varied as
needed to provide for adequate support and reliability. By
controlling the lateral pivoting and the longitudinal pivoting of
the support frames the axis of each of the Fresnel lenses can be
maintained in alignment with the sun during a desired period of
operation thereby maintaining the focus of the incident solar
radiation on the desired absorption zones of each of the energy
absorbers. The base drive and the pivot drive can each be
controlled by a sensor which continually adjusts the alignment of
the axis of the Fresnel lenses to match the position of the sun in
the sky during a desired period of operation. This allows the
Fresnel lenses to be aligned with the incident solar radiation for
the time of day and season of the year.
[0025] Depending upon the material used for the Fresnel lens and
the thickness of the lens, the lens may be rigid or somewhat
flexible. Because the solar collector will generally be used in an
exterior, unprotected environment, the support frame and the solar
tracking drive must be able to withstand wind loading, moisture and
temperature variations. Further, because of the wind and other
environmental conditions to which the lens will be subjected, it
must be securely attached to the lens retainer. This can be
accomplished by many attachment means known in the art
including.
[0026] The Fresnel lens support frame as well as the solar tracking
drive components, can be constructed from a variety of materials
including, but not limited to, steel, aluminum or plastic. A
preferred material for the support frames and the solar tracking
drive is steel. A non-corrosive coating such as galvanizing, paint
or powder coating, would be needed.
[0027] The base drive and the pivot drive, which comprise the drive
means of preferred embodiments of the solar tracking drive, can be
comprised of any of common drive mechanisms known in the art. These
drive means will generally be composed of a combination of electric
motors and gears. Chains and belts may also be used. The solar
tracking can be accomplished through simple programming to a vary
the longitudinal angle and the lateral angle based on the
orientation of the solar collector, the longitude and latitude of
the installation, the time of day, and the day of the year.
Alternatively, a sensor can be used to continually align the axis
of the Fresnel lenses with the incident solar radiation during a
desired period or operation.
[0028] Many variations of geometry and grooving of the Fresnel lens
may be used. As discussed above, longitudinal grooving will provide
for distributed focus of the incident solar radiation on a
absorption conduit. If a spot focus is desired, then the grooving
will be circular. A rectangular or square lens is more practical
and economical to manufacture and utilize and is more efficient for
a normal application, since the grooving provides for the
concentration of solar radiation incident to the corners of the
lens on the absorption zone as well. One of the main advantages of
the present invention is economy. One preferred embodiment
utilizing rectangular lenses with longitudinal grooving, providing
for a distributed focus on an absorption conduit, and a solar
tracking drive which is actuated by a sensor can be very economical
and very effective compared to other solar energy collection
systems known in the art. Preferably, the longitudinal axis of the
solar collector installation will be aligned in an east/west
direction and the lateral axis will be aligned in a north/south
direction.
[0029] One or more absorption liquid pumps typically circulate the
absorption liquid through absorption liquid lines to the absorption
conduit and back to an energy transfer device which can be one or
more of a number of energy exchange devices which are known in the
art. A variety of absorption liquids may be used for circulating
through the absorption conduits, which include but are not limited
to water, oil or salt. Absorption liquids preferred by the present
inventor are heat transfer oil for lower temperatures and molten
salt for higher temperature absorption liquid applications. Salt
materials which work well for high temperature applications include
sodium nitrate, sodium nitrite or potassium nitrate. Heat transfer
oil can be synthetic, organic or a combination of synthetic and
organic oil.
[0030] A preferred embodiment of an energy transfer system
comprises the energy transfer device, transfer liquid circulation
lines and transfer liquid pumps. Transfer liquid is circulated
through the transfer liquid circulation lines by the transfer
liquid pumps to the energy transfer device and back to an energy
extraction device such as a steam turbine engine. Again, any number
of liquids may be used for the transfer liquid but to eliminate the
necessity of another heat exchange process at the energy extraction
device, water is preferred. The steam turbine engine illustrated in
FIG. 10 is disclosed in U.S. Pat. No. 6,533,539 to Johnson, the
inventor of the present invention and provides for the flashing of
heated water or other liquids from peripheral nozzles. The energy
extracted by the energy extraction device, such as the steam
turbine illustrated, can be used to drive a generator or other
energy conversion device. Make up water can be supplied through a
make up water line which is controlled by an automated valve or
pump connected to a make up water supply.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a longitudinal vertical cross section of an
embodiment of a solar energy collector of the present
invention.
[0032] FIG. 2 is a plan view of a Fresnel lens with longitudinal
grooves for a solar collector with a linear absorption zone.
[0033] FIG. 3 is a side perspective view of a solar energy
collector installation of the present invention with an absorption
conduit having a spherical energy absorber in a spherical energy
retaining capsule.
[0034] FIG. 4 is a side perspective view of a multiple solar energy
collector installation of the present invention with support
frames, absorption conduit, and solar tracking drive.
[0035] FIG. 5 is a perspective detail of an embodiment of a solar
tracking drive of the present invention.
[0036] FIG. 6 is a perspective detail of an embodiment of a solar
energy collector installation of the present invention with
secondary lens, secondary lens frame and an in-line half spherical
energy absorber with a half spherical energy retaining capsule.
[0037] FIG. 7 is a cutaway detail of an in-line half spherical
energy absorber of the present invention with a half spherical
energy retaining capsule.
[0038] FIG. 8 is a plan view cross section of an in-line half
spherical energy absorber of the present invention with absorption
fins and a half spherical energy retaining capsule.
[0039] FIG. 9 is a vertical cross section of an in-line half
spherical energy absorber of the present invention with absorption
fins and a half spherical energy retaining capsule.
[0040] FIG. 10 is an isometric illustration of an embodiment of the
solar energy collector installation, energy exchange system, and
turbine engine of the present invention.
DETAILED DESCRIPTION
[0041] Referring first to FIG. 1 a cross section of a Fresnel lens
3 and energy absorber 5 components of a solar energy collector 1 of
the present invention. The energy absorber as shown is an
absorption conduit 7 which has an internal absorption fin 9
extending into an absorption duct 10, which for an absorption
conduit is merely the internal barrel of the pipe. The Fresnel lens
axis 11 is aligned with the incident solar radiation 13. This
results in the incident solar radiation being focused to a focal
point 15 as is illustrated by the incident rays 17 and the focused
rays 19. The energy absorber, which for the embodiment shown in
FIG. 1, is an absorption conduit, will have an absorption zone 21
on the top surface of the absorption conduit. The absorption
conduit will preferably be positioned so that the center 23 of the
absorption conduit is aligned with the Fresnel lens axis. The
absorption conduit, or other energy absorber, can be positioned so
that the Fresnel lens top surface 25 is separated from the
absorption conduit top surface 27 by a distance 29 which is equal
to the focal length of the lens as shown in FIG. 1, thereby
providing for the incident solar radiation to be focused at a
single point in the absorption zone of the energy absorber or can
be positioned such that incident solar radiation is distributed on
a larger area of the absorption zone. If the incident solar
radiation is focused on a single point in the absorption zone of
the energy absorber, substantially higher temperatures will be
experienced at the focal point. Having the focal point coincident
with the center of the energy absorber, rather than a point on the
surface of the energy absorber, results in substantially reduced
temperatures. Of course the focus of the incident solar radiation
can be varied between the center of the absorption conduit and a
point on the surface of the absorption conduit thereby varying the
distribution of the focused solar radiation and thereby the maximum
temperature experienced in the absorption zone. An absorption fin 9
can also be incorporated inside the energy absorber which extends
into the absorption duct 10 as shown FIG. 1 and shown in FIGS. 8
and 9 is in contact with the absorption zone, thereby assisting in
the transfer of energy to the absorption liquid 33 which flows
through the energy absorber. The absorption fin would normally be
made of high thermal conductivity material thereby rapidly
transferring the energy of the incident solar radiation from the
absorption zone to the absorption liquid. An energy retaining
capsule 35 can be used to encapsulate the absorption zone. The
energy retaining capsule will be constructed of material with a
high solar radiation transmission rate and a low thermal
conductivity rate thereby providing for transmission of the focused
incident solar radiation to the absorption zone of the energy
absorber while minimizing the loss of energy from the energy
absorber to the surrounding air 37.
[0042] Each groove 38 of the Fresnel lens is a small piece of an
aspherical surface 39. The tilt 41 of each surface is varied with
distance 42 from the center 43 of the lens to provide for focus of
the incident solar radiation at the focal point of the lens. The
cross section shown in FIG. 1 could be illustrative of a Fresnel
lens with circular grooves which will provide for focusing of the
incident solar radiation to a single focal point or could be
illustrative of a Fresnel lens with longitudinal grooves as shown
in FIG. 2.
[0043] The Fresnel lens of FIG. 2 with longitudinal grooves 44
results in the incident solar radiation being focused in a line
rather than a single focal point. This offers an advantage of
distributing the focused incident solar radiation over a larger
area, thereby reducing the temperature of the absorption zone. The
expanded absorption zone for embodiments utilizing a Fresnel lens
with longitudinal grooves can be encapsulated in an energy
retaining capsule with a high solar radiation transmission rate and
low thermal conductivity rate such as glass. Similarly, a Fresnel
lens with oval grooves provides for distributed focus and
distribution of the concentrated energy on the energy absorber.
Also, if the Fresnel lens is positioned so that the energy
absorbers have absorption surfaces which are displaced radially
from the focal point or focal line of the respective lenses, the
larger absorption zone may be encapsulated. Other portions of the
absorption conduit which do not receive focused incident solar
radiation can be insulated or merely be covered with the energy
retaining capsule material to reduce energy loss to the surrounding
air.
[0044] A cement coating can be placed on the absorption zone to
increase the absorption rate of the focused incident solar
radiation. Alternatively, an energy assimilator of high thermal
conductivity material can be placed on the absorption conduit or
other energy absorber. Further the energy assimilator can be
thermally connected to an absorption fin extending into the
absorption duct, thereby increasing the energy transfer rate to the
absorption liquid.
[0045] Material selection for the absorption zone of the energy
absorber or energy assimilator placed on the energy absorber in the
absorption zone will be selected based upon anticipated maximum
temperatures and desired absorption and thermal conductivity rates.
Materials that can be used include stainless steel, carbon steel,
tungsten, titanium, molybdenum, rhenium, niobium, platinum, copper
and other metals and non-metallic materials. A preferred material
for the absorption zone and absorption fins is tungsten due to its
high thermal conductivity rate, its high melting point and its
glass to metal sealing capabilities.
[0046] The energy retaining capsule 35, whether it is spherically
shaped as indicated on FIG. 1 and FIG. 3, hemispherically shaped as
indicated on FIG. 6 or tubularly shaped for an absorption conduit,
the capsule can be made from a number of materials including soda
lime glass, borsilicate glass or quartz. Borsilicate glass is a
preferred material because of its inherent impact strength and its
lower thermal conductivity rate. While a spherical or hemispherical
shape is preferred for a point focus due to a higher solar
radiation transmission rate and a higher absorption rate, other
shapes can be used, depending upon the energy distribution desired
on the absorption zone. For a linear absorption zone, a cylindrical
capsule is preferred on the absorption conduit.
[0047] It is preferred for the retaining capsule material to be
bonded or hermetically sealed to the absorption zone or to the
absorption conduit. This generally increases energy retention by
the absorption conduit or other form of energy absorber.
Alternatively a space may be provided between the energy absorber
and the energy retaining capsule, whether the energy retaining
capsule is spherically shaped, hemispherically shaped or
cylindrically shaped, which may be air evacuated, thereby providing
a vacuum space separating the energy retaining capsule from the
energy absorber, thereby further enhancing the energy retention of
the energy retaining capsule.
[0048] The Fresnel lens itself is preferably constructed of an
optically clear material. These materials include but are not
limited to acrylic, glass, rigid vinyl, polycarbonate,
polyethylene, polyester blends including PET and PETG respectively,
poly IR, polystyrene, polyurethane, polypropylene,
polyacrylonitrile, Kevlar, Nomex, rubber, germanium, silicon, zinc
sulfide, quartz and other such materials. The inventor's preferred
materials are polyester (PET or PETG) or a blend thereof.
[0049] A Fresnel lens can be formed or manufactured in a number of
ways from the substrate materials identified above. This includes
but is not limited to press thermalforming, roll thermalforming,
casting, emboss extruding, injection molding, milling, lathing, or
UV curing. Emboss extrusion is the preferred method of creating
Fresnel lenses. Extruding allows for the creation of an
inexpensive, thin, flat plastic sheet with an embossed Fresnel
image imprinted on one side of the lens. The preferred materials,
namely polyester (PET or PETG) can be utilized with or without
protective additives. Protective additives may include ultraviolet
light and antioxidant additives, both of which reduce yellowing and
clouding of the Fresnel lens. These additives can be introduced
into the resin prior to the extrusion process or during the
extrusion process in a step referred to a co-extruding. A
protective co-extruded cap layer is preferred, promoting longevity
of the Fresnel lens.
[0050] Referring now to FIG. 3 and FIG. 4, a preferred embodiment
of a solar energy collection apparatus of the present invention is
shown. Referring to FIG. 3 the Fresnel lens 3 is secured in a focal
position 45 for focusing solar radiation passing the Fresnel lens
on the absorption zone on the energy absorber by a support frame
47. For this embodiment the support frame consists of a lens
retainer 49 to which the perimeter 51 of the lens is attached and
secured on its perimeter and a pair of pivot brackets 53.
[0051] Referring to FIG. 4 and FIG. 5, a preferred embodiment of
the solar tracking drive is comprised of a longitudinal pivot
means, a lateral pivot means and a tracking control means. A
preferred embodiment of the lateral pivot means comprises a base
frame 55, a base drive 57, anchor pedestals 67 and base bearings
69. Lateral pivoting 83 of the solar collector support structures
is accomplished by lateral rotation 85 of the base frame 55 through
a lateral angle which is controlled by the base drive 57 and
facilitated by base bearings 69. The number of anchor pedestals and
base bearings can be varied as needed to provide for adequate
support and reliability.
[0052] A preferred embodiment of the longitudinal pivot means
comprises a pivot rail 59, pivot bar 61, a pivot drive 63, a pivot
drive plate 65, base pivot bearings 71, pivot bar bearing 77, and
top bearings 81. Each of the support frames is pivotally attached
to the base frame by the base pivot bearings 71 which pivotally
attach the bottom 73 of the pivot bracket, thereby providing for
longitudinal pivoting 75 of the support frames respectively through
a longitudinal angle. The longitudinal pivoting of the support
frames is controlled by the pivot drive 63 which varies the
position of the pivot bar 61, which is pivotally attached to the
pivot rail by a pivot bar bearing 77. The pivot rail is pivotally
attached to the top of one of side 79 of each of the solar
collector support structures by top bearings 81.
[0053] A tracking control means controls the lateral pivoting 83
and the longitudinal pivoting 75 of the support frames so that the
axis 11 of each of the Fresnel lenses is maintained in alignment
with the sun during a desired period of operation thereby
maintaining the focus of the incident solar radiation on the
desired absorption zones of each of the energy absorbers. For a
preferred embodiment, the tracking control means consists of a
sensor which controls the base drive and the pivot drive, thereby
continually adjusting the alignment of the axis of the Fresnel
lenses to match the position of the sun in the sky during a desired
period of operation. An alternative embodiment of the tracking
control means is a simple computer which controls the base drive
and the pivot drive and continually positions the support frames,
during a desired period of operation, based upon the physical
orientation of the solar collector installation, the date, the time
of day, and the longitude and latitude of the installation. This
allows the Fresnel lenses to be continually aligned with the
incident solar radiation.
[0054] Referring to FIG. 4, preferably, the longitudinal axis 109
of the solar collector installation will be aligned in an east/west
direction and the lateral axis 111 will be aligned in a north/south
direction.
[0055] Referring now to FIG. 6 and also FIG. 7, an in-line energy
absorber 87 which has a hemispherical absorption zone which is
encapsulated by a hemispherical shaped energy capturing capsule 89.
The energy absorber is affixed in line in the absorption conduit 7
with the connection to the conduit 90, typically by flanged or
mechanical joint connections. For some embodiments an optional
secondary lens 91 is affixed between the Fresnel lens and the
energy absorber by a secondary lens frame 93 which is affixed to
the opposing pivot brackets 53 of the Fresnel lens support
frame.
[0056] Referring now to FIG. 8 and FIG. 9, an embodiment of a
hemispherical shaped energy absorber 87 with absorption fins 9
inserted in the flow path 97 of the absorption is shown. The
absorption fins facilitate the transfer of energy from the energy
absorber to the absorption liquid 33. The energy absorber is
encapsulated by an energy capturing capsule 101 of one of the
preferred materials described above.
[0057] Depending upon the material used for the Fresnel lens and
the thickness of the lens, the lens may be rigid or somewhat
flexible. Because the solar collector will generally be used in an
exterior, unprotected environment, the support frame 47 and the
solar tracking drive must be able to withstand wind loading,
moisture and temperature variations. Further, because of the wind
and other environmental conditions to which the lens will be
subjected, it must be securely attached to the lens retainer 49.
This can be accomplished by many attachment means known in the art
including, but not limited to, springs, wire, bungee cords, plastic
strips or ties, glue, screws, clamps or slidable inserts. A
preferred attachment means is springs. Springs allow for thermal
expansion, wind loads, hail stones or any other type of contraction
or expansion that the Fresnel lens may encounter. Referring to FIG.
2, spring receptacles 103, which, in the case of a lens formed by
extrusion, may be extruded out during the extrusion process or they
may be punched or drilled in the perimeter 105 of the lens. Spring
grommets 107 may be inserted into the spring receptacles if needed
for added strength and durability. One end of the spring is
inserted in the spring receptacle and the other end is attached to
the lens retainer or other point on the support frame.
[0058] Referring to FIGS. 3, 4 and 5, pivot bearings can be any
variations known in the art. Pivot bearings can be manufactured
from a number of types of commonly used material including, but not
limited to, steel, graphite, plastic or ceramic. A preferred pivot
bearing is a steel metal sleeve bearing. The base bearings 69 can
also be steel metal sleeve bearings or a ceramic pipe, tube or
sleeve bearing can be used as a heat barrier. Base frame bearings
can be used as a thermal barrier between the support frame and the
absorption conduit.
[0059] The Fresnel lens support frame 47 as well as the solar
tracking drive components, can be constructed from a variety of
materials including, but not limited to, steel, aluminum or
plastic. A preferred material for the support frames and the solar
tracking drive is steel. A non-corrosive coating such as
galvanizing, paint or powder coating, would be needed.
[0060] Referring to FIG. 5, the base drive 57 and the pivot drive
63, which comprise the drive means of the solar tracking drive can
be comprised of any of common drive mechanisms known in the art.
These drive means may be comprised of a combination of electric
motors and gears or may be pneumatically or hydraulically actuated.
If the base drive and the pivot drive are pneumatically or
hydraulically actuated, solar tracking will ordinarily be
accomplished through the use of pneumatic or hydraulic cylinders.
Chains and belts may also be used with electric motor drives.
[0061] The solar tracking can be accomplished through simple
programming to a varied longitudinal angle 75 and the lateral angle
83 based on the longitude and latitude of the installation, the
time of day, and the day of the year. Alternatively, the sensor can
be used to continually align the axis of the Fresnel lenses with
the incident solar radiation during a desired period or
operation.
[0062] Many variations of geometry and grooving of the Fresnel lens
may be used. As discussed above, longitudinal grooving as shown in
FIG. 2 will provide for distributed focus of the incident solar
radiation on a absorption conduit. If spot focus is desired so the
solar energy can be concentrated to energy absorbers such as shown
in FIGS. 6, 7, 8 and 9, then the grooving will be circular. A
rectangular or square lens is more practical and economical to
manufacture and utilize and is more efficient for a normal
application, since the grooving provides for the concentration of
solar radiation incident to the corners of the lens on the
absorption zone as well.
[0063] One of the main advantages of the present invention is
economy. One preferred embodiment utilizing rectangular lenses with
longitudinal grooving, providing for a distributed focus on an
absorption conduit, and a solar tracking drive which is actuated by
a sensor can be very economical and very effective compared to
other solar energy collection systems known in the art.
[0064] Referring now to FIG. 10, a schematic of an energy
production system 113 utilizing the solar energy collector 1 of the
present invention shown. The incident solar radiation 17 focused on
the absorption conduit 7 by one or more solar collectors, each
utilizing a Fresnel lens 3 and a support frame (not shown) and
being positioned by a solar tracking drive (not shown). One or more
absorption liquid pumps 115 circulate the absorption liquid 33
through absorption liquids lines 117 to the absorption conduit and
back to an energy transfer device 119 which can be one or more of a
number of energy exchange devices which are known in the art.
[0065] A variety of absorption liquids may be used for circulating
through the absorption conduits, which include but are not limited
to water, oil or salt. Absorption liquids preferred by the present
inventor are heat transfer oil for lower temperatures and molten
salt for higher temperature absorption liquid applications. Salt
materials which work well for high temperature applications include
sodium nitrate, sodium nitrite or potassium nitrate. Heat transfer
oil can be synthetic, organic or a combination of synthetic and
organic oil.
[0066] Transfer liquid 121 is circulated through transfer liquid
circulation lines 123 by transfer liquid pumps 125 through the
energy transfer device 119 and back to an energy extraction device
127 such as the steam turbine engine 129 illustrated in FIG. 10.
Again, any number of liquids may be used for the transfer liquid
but to eliminate the necessity of another heat exchange process at
the energy extraction device, water is preferred. A preferred steam
turbine engine for incorporation with the solar collector
installation of the present invention as illustrated in FIG. 10 is
disclosed in U.S. Pat. No. 6,533,539 to Johnson, the inventor of
the present invention and provides for the flashing of heated water
or other liquids from peripheral nozzles. The energy extracted by
the energy extraction device, such as the steam turbine
illustrated, can be used to drive a generator or other energy
conversion device. Make up water 131 can be supplied through a make
up water line 133 which is controlled by an automated valve or pump
135 connected to a make up water supply 137.
[0067] Other objects, features and advantages of the present
invention will become apparent from the preceding detailed
description considered in connection with the accompanying
drawings. It is to be understood, however, that the drawings are
designed as an illustration only and not as a definition of the
limits of the invention. Therefore, the foregoing is intended to be
merely illustrative of the invention and the invention is limited
only by the following claims.
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