U.S. patent application number 11/949295 was filed with the patent office on 2009-06-04 for solar thermal energy collector.
Invention is credited to Randy C. Gee, Roland Winston.
Application Number | 20090139515 11/949295 |
Document ID | / |
Family ID | 40674489 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090139515 |
Kind Code |
A1 |
Gee; Randy C. ; et
al. |
June 4, 2009 |
SOLAR THERMAL ENERGY COLLECTOR
Abstract
A solar thermal energy collector includes a receptacle and a
tube positioned within the receptacle and having a closed end. The
tube includes a divider cross-sectionally bifurcating the tube. The
divider is spaced apart from the closed end of the tube to allow
fluid communication between two bifurcated portions of the tube. A
fluid is circulated through the two bifurcated portions of the tube
for transferring of the solar thermal energy.
Inventors: |
Gee; Randy C.; (Arvada,
CO) ; Winston; Roland; (Merced, CA) |
Correspondence
Address: |
FOLEY & LARDNER LLP
P.O. BOX 80278
SAN DIEGO
CA
92138-0278
US
|
Family ID: |
40674489 |
Appl. No.: |
11/949295 |
Filed: |
December 3, 2007 |
Current U.S.
Class: |
126/655 ;
126/643 |
Current CPC
Class: |
F24S 23/80 20180501;
F24S 10/25 20180501; Y02E 10/44 20130101; F24S 10/45 20180501 |
Class at
Publication: |
126/655 ;
126/643 |
International
Class: |
F24J 2/24 20060101
F24J002/24; F24J 2/30 20060101 F24J002/30 |
Claims
1. A solar thermal energy collector, comprising: a receptacle; and
a tube positioned within the receptacle and having a closed end,
the tube including a divider cross-sectionally bifurcating the
tube, the divider being spaced apart from the closed end of the
tube to allow fluid communication between two bifurcated portions
of the tube, wherein a fluid is circulated through the two
bifurcated portions of the tube for transferring of the solar
thermal energy.
2. The collector of claim 1, wherein the fluid for transfer of
solar thermal energy is mineral oil.
3. The collector of claim 1, wherein the fluid for transfer of
solar thermal energy is an antifreeze solution.
4. The collector of claim 1, wherein the tube is coupled to a
manifold and the manifold is coupled to a pump that circulates the
fluid through the manifold and the two bifurcated portions.
5. The collector of claim 4, wherein the manifold is coupled to
additional tubes.
6. The collector of claim 1, wherein the divider is a plate which
cross-sectionally divides the tube into the two bifurcated
portions.
7. The collector of claim 6, wherein the tube has a circular cross
section and the divider forms two bifurcated portions with
semi-circular cross sections.
8. The collector of claim 1, wherein the tube is an integral part
of a manifold.
9. The collector of claim 1, wherein the receptacle is a dewar, the
dewar having an outer wall and an inner wall, the dewar having a
vacuum drawn between the outer wall and the inner wall, and wherein
the dewar is all glass.
10. The collector of claim 9, wherein a region between an outer
surface of the tube and the inner wall of the dewar is filled with
a second fluid to facilitate heat transfer.
11. The collector of claim 9, wherein the second fluid is mineral
oil.
12. The collector of claim 9, wherein the dewar has a thermal
absorption coating on an outer surface of the inner wall.
13. The collector of claim 12 wherein the coating is aluminum
nitride cermets.
14. The collector of claim 1, wherein absent a solar tracker
component and in combination with an external reflector component,
the fluid has a temperature above 280 degrees Fahrenheit when the
fluid exits the receptacle.
15. The collector of claim 1, further comprising an external
reflector for reflecting sun rays onto the receptacle.
16. The collector of claim 15, wherein the external reflector is a
compound parabolic concentrator (CPC).
17. A method for collecting solar thermal energy, comprising:
positioning one or more reflectors external to one or more
receptacles, the reflectors being adapted to direct solar thermal
energy to the one or more receptacles; positioning a manifold
having one or more tubes adapted to fit within the one or more
receptacles, each tube having a closed end and having a divider
cross-sectionally bifurcating the tube, the divider being spaced
apart from the closed end of the tube to allow fluid communication
between two bifurcated portions of the tube; and circulating a
fluid through the two bifurcated portions of the tube for
transferring of the solar thermal energy.
18. The method for collecting solar thermal energy of claim 17,
wherein the fluid is mineral oil.
19. The method for collecting solar thermal energy of claim 17,
wherein the fluid is an antifreeze solution.
20. The method for collecting solar thermal energy of claim 17,
wherein the divider is a plate which cross-sectionally divides the
tube into two bifurcated portions.
21. The method for collecting solar thermal energy of claim 17,
wherein the receptacle is a dewar, the dewar has an outer wall and
an inner wall, the dewar has a vacuum drawn between the outer wall
and the inner wall, and the dewar is all glass.
22. The method of claim 21, wherein a region between an outer
surface of the tube and the inner wall of the dewar is filled with
a second fluid to facilitate heat transfer.
23. The method of claim 21, wherein the dewar has a thermal
absorption coating on an outer surface of the inner wall.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the field of
solar thermal energy. In particular, the present invention relates
to solar thermal energy collectors.
[0002] Solar thermal collectors have been utilized for over 20
years. The designs have varied from flat plate, box, air, integral,
unglazed more commonly to parabolic troughs and dishes and full
power towers. Though they have been commercially available for over
20 years, recent designs of evacuated tubes have become more
efficient and less costly, allowing them to be both commercially
and domestically available as well as more widely utilized. Some
devices contain heat removal inserts that are placed within the
tubes that serve the purpose of transferring the collected energy
to a heat-transfer fluid and are used to transfer heat to a
manifold located at the end of the tubes or in connection with the
inserts.
[0003] Conventional designs are limited in their ability to
transfer heat from the collector. It is desirable to improve the
efficiency with which such heat is transferred.
SUMMARY OF THE INVENTION
[0004] In one aspect, the invention includes a solar thermal energy
collector comprising a receptacle and a tube positioned within the
receptacle and having a closed end. The tube includes a divider
cross-sectionally bifurcating the tube. The divider is spaced apart
from the closed end of the tube to allow fluid communication
between two bifurcated portions of the tube. A fluid is circulated
through the two bifurcated portions of the tube for transferring of
the solar thermal energy.
[0005] In one embodiment, the fluid for transfer of solar thermal
energy is mineral oil. In another embodiment, the fluid for
transfer of solar thermal energy is an antifreeze solution.
[0006] In one embodiment, the tube is coupled to a manifold and the
manifold is coupled to a pump that circulates the fluid through the
manifold and the two bifurcated portions. The manifold may be
coupled to additional tubes.
[0007] In one embodiment, the divider is a plate which
cross-sectionally divides the tube into the two bifurcated
portions. The tube may have a circular cross section, and the
divider may form two bifurcated portions with semi-circular cross
sections.
[0008] In one embodiment, the tube is an integral part of a
manifold.
[0009] In one embodiment, the receptacle is a dewar, the dewar
having an outer wall and an inner wall, the dewar having a vacuum
drawn between the outer wall and the inner wall, and wherein the
dewar is all glass. A region between an outer surface of the tube
and the inner wall of the dewar may be filled with a second fluid
to facilitate heat transfer. The second fluid may be mineral oil.
In one embodiment, the dewar has a thermal absorption coating on an
outer surface of the inner wall. The coating may be aluminum
nitride cermets.
[0010] In one embodiment, absent a solar tracker component and in
combination with an external reflector component, the fluid has a
temperature above 280 degrees Fahrenheit when the fluid exits the
receptacle.
[0011] In one embodiment, the collector further includes an
external reflector for reflecting sun rays onto the receptacle. The
external reflector may be a compound parabolic concentrator
(CPC).
[0012] In another aspect of the invention, a method for collecting
solar thermal energy includes positioning one or more reflectors
external to one or more receptacles, the reflectors being adapted
to direct solar thermal energy to the one or more receptacles;
positioning a manifold having one or more tubes adapted to fit
within the one or more receptacles, each tube having a closed end
and having a divider cross-sectionally bifurcating the tube, the
divider being spaced apart from the closed end of the tube to allow
fluid communication between two bifurcated portions of the tube;
and circulating a fluid through the two bifurcated portions of the
tube for transferring of the solar thermal energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates a solar thermal energy collector
according to an embodiment of the present invention; and
[0014] FIGS. 2A and 2B illustrate cross-sectional views taken along
II-II of FIG. 1 of solar thermal energy collectors according to
embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Embodiments of the present invention provide devices,
methods and systems for collection and/or transferring of solar
thermal energy. In this regard, embodiments of the present
invention may provide inexpensive and efficient manners for
collection of solar thermal energy.
[0016] Referring to FIGS. 1, 2A and 2B, a solar thermal energy
collector according to an embodiment of the present invention is
illustrated. In the illustrated embodiment, a collector 100
includes one or more receptacles 120 coupled to a manifold 110. The
manifold 110 includes an inlet pipe 112 and an outlet pipe 114 for
circulating fluid through the manifold 110 and the collector 100. A
pump 116 is provided to circulate the fluid 110. The dimensions of
the inlet pipe 112, the outlet pipe 114 and the pump 116 may be
selected according to the requirements of the specific
implementation of the collector 100.
[0017] The manifold 110 is coupled to one or more receptacles 120.
The number of receptacles 120 may be selected from any practical
number dependant on the size of the collector system desired.
Further, the manifold may be coupled to a plurality of receptacles
in a serial manner, a parallel manner or any combination
thereof.
[0018] Each receptacle 120 is preferably an all-glass dewar having
a double-wall configuration, as most clearly illustrated in FIGS.
2A and 2B. Of course, in other embodiments, various other types of
receptacles may be used. In one embodiment, the receptacles are
cylindrical borosilicate glass bottles with a closed end, as
exemplarily illustrated in FIG. 1. Each dewar 120 is provided with
an inner wall 122 and an outer wall 124. The region between the
inner wall 122 and the outer wall 124 is evacuated. The vacuum
region results in low heat loss. The level of evacuation of the
region between the inner wall 122 and the outer wall 124 may be
varied to either increase efficiency (e.g., reduce heat loss) or
improve cost-effectiveness. The vacuum space may also incorporate
either a passive or active mechanism to prohibit or mitigate
effects of permeation of space by other gases such as hydrogen or
helium.
[0019] In one embodiment, an outer surface of the inner wall 122
(i.e., the surface facing the vacuum region) is coated with a
thermal absorption coating 126, such as aluminum nitride cermets.
In other embodiments, other commercially available coatings may be
used. The thermal absorption coating 126 facilitates absorption of
solar thermal energy by the receptacle 120.
[0020] Each receptacle 120 is provided with a tube 130 adapted to
fit within the receptacle 120. In one embodiment, on one end, the
tube 130 is inserted into the receptacle 120 and has a closed end
139. The tube 130 is provided with a divider 134 which divides, or
bifurcates, the cross section of the tube 130, as most clearly
illustrated in FIGS. 2A and 2B. In the illustrated embodiment, the
tube 130 has a circular cross section, and the divider 134
bifurcates the tube 130, resulting in two bifurcated portions 136,
138, each having a semi-circular cross section. Of course, in other
embodiments, the cross-sectional shape of the tube 130 or the
bifurcated portions may be different. In preferred embodiments, the
cross-sectional area of the bifurcated portions 136, 138 is
substantially similar to each other. As illustrated in FIG. 1, the
end of the divider 134 is spaced apart from the closed end 139 of
the tube 130. The amount of space between the divider 134 and the
closed end 139 of the tube is sufficient to allow fluid to flow
freely around the divider 134.
[0021] On the other end, the tube 130 is coupled to the manifold
110, which is coupled to a tube corresponding to each of the other
receptacles of the collector 100. The tube 130 may be coupled to
the manifold 110 in a variety of manners including, but not limited
to, welding. In one embodiment, the coupling of the manifold 110
and the tube 130 includes use of screw-type threads formed on the
manifold 110 and the tube 130, similar to those found on
conventional plumbing joints, that may use a thread seal. In a
particular embodiment, as illustrated in FIGS. 1, 2A and 2B, the
tube 130 is an integral part of the manifold 110. In this regard,
the tube 130 may be formed as an integral part of the manifold and
does not include any joints, connections or seals. Thus, once
created, the tube 130 may not easily be removed from the manifold
110. The integral configuration of the tube 130 and the manifold
110 reduces the number of parts required, thereby reducing the time
and effort required for installation and assembly of the collector
100 in the field. Thus, during assembly, the receptacle 120 only
needs to be positioned around the tube 130. A seal (not shown) may
be provided to secure the tube 130 to the receptacle 120. Further,
the integral configuration eliminates a potential leakage point for
fluid flowing through the receptacle, as described below.
[0022] In order to facilitate transfer of heat from the receptacle
120 to the tube 130, a region 132 between the receptacle and the
tube 130 may be filled with a heat transfer fluid. In one
embodiment, this heat transfer fluid is mineral oil. The use of the
fluid reduces heat loss when compared to empty space (e.g., air or
vacuum) therein. In order to retain the heat transfer fluid in the
region 132, a seal (not shown) may be provided between the
receptacle 120 and either the tube 130 or the manifold 110. Such
seals or seal arrangements are well known to those skilled in the
art.
[0023] In accordance with embodiments of the present invention,
assembly and maintenance of the collection 100 is simplified. With
the tube 130 integrally formed (or otherwise pre-assembled) with
the manifold 110, only the receptacle 120 needs to be connected.
Thus, for maintenance purposes, individual receptacles that may
become damaged can be replaced without replacing the entire
collector 100. Further, use of appropriate seals between the
receptacle 120 and the manifold 110 can make such replacement of
receptacles simple, time-efficient and effective. A worker in the
field can accomplish such maintenance without expending substantial
time and effort.
[0024] The receptacle 120 and the manifold 110 are positioned such
that an external reflector 140 concentrates solar thermal energy
(or solar irradiance) onto the receptacle 120. The shape of the
reflector 140 may be selected from a variety of shapes. In some
embodiments, the reflector 140 may operate in conjunction with a
solar tracking component. Preferably, the reflector 140 is adapted
to operate in the absence of such a tracking component. In one
embodiment, the external reflector 140 is a compound parabolic
concentrator (CPC). Such reflectors are well known to those skilled
in the art.
[0025] FIGS. 2A and 2B illustrate two embodiments of an external
reflector 140a, 140b for use with embodiments of the present
invention. Referring first to FIG. 2A, the external reflector 140a
has two concave, parabolic components joined by a central convex,
v-shaped component. Each concave component forms substantially half
of a parabola.
[0026] Referring now to FIG. 2B, the external reflector 140b
includes two concave, parabolic segments joined to each other. In
this embodiment, each concave component forms substantially more
than half of a parabola. In this regard, the two concave segments
join to form an inverted "v" shape.
[0027] Thus, the shape of the reflector 140 directs substantially
all sunlight incident on the reflector 140 within a predetermined
angle of incidence onto the receptacle 120 and, more specifically,
onto the thermal absorption coating 126 on the outer surface of the
inner wall 122 of the dewar 120. In this regard, sunlight is
concentrated efficiently onto the receptacle 120 while minimizing
heat loss. Further, the evacuated, double-wall configuration of the
dewar 120 and the use of the heat transfer fluid in the region 132
between the dewar 120 and the tube 130 facilitate minimizing of the
heat loss. Thus, sufficient efficiency of the collector 100 can be
achieved in the absence of a solar tracking component, thereby
resulting in significant cost reduction. The combination of the
reflector 140, the receptacle 120 and the tube 130 is preferably
configured to have a large acceptance angle. For example, in one
embodiment, an acceptance angle of at least .+-.35 degrees. Thus,
sunlight within at least a 70-degree range is captured, and the
associated solar thermal energy is collected.
[0028] To facilitate collection of solar thermal energy, the
reflector 140 may be configured specifically to capture energy
within the solar spectrum. In this regard, the reflector 140 may be
formed of a material optimized for the solar spectrum of energy. In
some embodiments, the reflector 140 may be coated with a material
for such optimization.
[0029] In one embodiment, a protective cover 150 is positioned
above the receptacles 120. The protective cover 150 may be sized to
cover multiple receptacles 120. Alternatively, a single protective
cover 150 may be positioned above each receptacle 120. The
receptacle is preferably formed of a transparent glazing, such as
soda lime glass, which does not interfere with the transmission of
sunlight to the reflectors 140.
[0030] To further prevent such interference, the protective cover
150 may be provided with an anti-reflective coating. Such
anti-reflective coating ensures that sunlight is transmitted to the
reflectors 140 without substantial reflecting of the sunlight away
from the collector 100. The anti-reflective coating may be applied
to either the inner surface of the protective cover 150 (i.e., the
surface facing the reflector 140 and the receptacle 120) or the
outer surface of the protective cover 150. In one embodiment, a
similar anti-reflective coating may also be applied to a surface of
the receptacle 120. The anti-reflective coating may be formed of
any of a variety of materials. In one embodiment, the
anti-reflective coating includes multi-layer, solgel texturing.
Thus, collection of solar thermal energy is permitted while
providing protection of the collector 100 from debris, for
example.
[0031] In operation, a fluid is circulated through the manifold 110
via the pump 116. The flowrate of the fluid through the manifold
110 may be adjusted for particular conditions and particular
implementations. The fluid circulates through the inlet pipe 112
and into the tube 130 within the receptacle 120. In embodiments in
which the tube is integral with the manifold 110 (and the inlet
pipe 112), no leakage issues are present. The positioning of the
tube 130 within the receptacle 120 forms a circulation path within
the tube 130 and within the receptacle 120. The circulation path
includes the bifurcated portions 136, 138 of the tube 130. Thus, in
one embodiment, the fluid is circulated first from the inlet pipe
112 through one bifurcated portion 136 and then through the second
bifurcated portion 138. In this regard, while the fluid is flowing,
it occupies substantially the entire volume within the tube 130
with one direction of flow occupying the volume in one bifurcated
portion and the opposite direction of flow occupying the other
bifurcated portion. The fluid then exits the tube 130 and the
receptacle 120 to the outlet pipe 114. A seal (not shown) may
prevent leakage of the fluid as it exits the receptacle 120. Those
skilled in the art will understand that the circulation path (inlet
pipe to first region to second region to outlet pipe) may be
reversed in other embodiments, which are also contemplated within
the scope of the present invention.
[0032] Thus, solar thermal energy is directed by the external
reflector 140 onto the receptacle 120. The solar thermal energy is
absorbed by the receptacle 120 and, more specifically, the
absorption coating 126 on the outer surface of the inner wall 122
of the receptacle 120. As noted above, the evacuated region between
the inner wall 122 and the outer wall 124 facilitates reduction in
heat loss, thereby improving efficiency of the collector 100. While
circulating through the two bifurcated regions 136, 138, the fluid
is heated, thereby facilitating transfer of solar thermal energy
from the collector 100. The fluid then carries the thermal energy
out of the tube 130 and the receptacle 120 in the form of heat,
whereby the fluid is heated by the thermal energy as it flows
through the tube 130. The fluid circulated through the collector
100 may be selected from a variety of fluids. In one embodiment,
the fluid is mineral oil. In another embodiment, the fluid is an
antifreeze solution.
[0033] Embodiments of the present invention are capable of heating
the fluid to temperatures of above 280 degrees Fahrenheit without
the use of a solar tracker component. Certain embodiments are
capable of heating the fluid to temperatures of above 300 degrees
Fahrenheit as the fluid exits the receptacle 120. Thus, embodiments
of the present invention can provide efficient collection of solar
thermal energy in a cost-effective manner.
[0034] In one embodiment, the fluid is selected such that the
boiling point of the fluid is higher than the maximum temperature
reached by the fluid within the receptacle 120, typically at the
point at which the fluid exits the receptacle 120. In this regard,
the fluid does not boil while circulating within the receptacle 120
and, therefore, does not exert additional pressure on the walls of
the receptacle 120. Accordingly, the receptacle 120 may be formed
of a greater variety of materials. In a particular embodiment, the
avoidance of additional pressure on the walls allows the receptacle
120 to be formed of glass.
[0035] In various embodiments, the fluid is selected such that the
flash point of the fluid is higher than the maximum temperature
reached by the fluid. In this regard, in the event of a leakage of
fluid in the system (e.g., from the manifold in the region of a
seal), the fluid does not ignite, thereby presenting a fire hazard.
Accordingly, the system is made inherently fire-safe.
[0036] While particular embodiments of the present invention have
been disclosed, it is to be understood that various different
modifications and combinations are possible and are contemplated
within the true spirit and scope of the appended claims. There is
no intention, therefore, of limitations to the exact abstract and
disclosure herein presented.
* * * * *