U.S. patent application number 11/455596 was filed with the patent office on 2007-12-20 for integrated solar energy conversion system, method, and apparatus.
This patent application is currently assigned to Lockheed Martin Corporation. Invention is credited to Daniel H. Hecht.
Application Number | 20070289622 11/455596 |
Document ID | / |
Family ID | 38860397 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070289622 |
Kind Code |
A1 |
Hecht; Daniel H. |
December 20, 2007 |
Integrated solar energy conversion system, method, and
apparatus
Abstract
A solar energy conversion package includes a photovoltaic (PV)
cell, a thermionic or thermoelectric conversion unit and a thermal
heating system. Solar radiation is concentrated by a lens or
reflector and directed to the PV cell for electrical power
conversion. A water circulation system maintains the PV cell at
working temperatures. The thermionic or thermoelectric conversion
cell is coupled between these cells in the thermal path to generate
additional power. Additional efficiencies may be gained by
partitioning the solar radiation with prisms or wavelength specific
filters or reflective coatings into discrete spectrum segments
optimized for each conversion unit for maximizing efficiency of
electrical energy conversion and equipment design. Integrating all
three of these conversion techniques produces a synergistic system
that exceeds the performance conventional solar conversion
systems.
Inventors: |
Hecht; Daniel H.; (Ft.
Worth, TX) |
Correspondence
Address: |
BRACEWELL & GIULIANI LLP
P.O. BOX 61389
HOUSTON
TX
77208-1389
US
|
Assignee: |
Lockheed Martin Corporation
|
Family ID: |
38860397 |
Appl. No.: |
11/455596 |
Filed: |
June 19, 2006 |
Current U.S.
Class: |
136/246 ;
136/205; 136/248 |
Current CPC
Class: |
F24S 23/30 20180501;
F24S 23/00 20180501; F24S 23/70 20180501; Y02E 10/44 20130101; F24S
23/10 20180501; H01L 31/0543 20141201; H01L 35/30 20130101; H02S
40/44 20141201; H01L 31/055 20130101; F24S 50/20 20180501; H02S
10/10 20141201; Y02E 10/60 20130101; Y02E 10/52 20130101 |
Class at
Publication: |
136/246 ;
136/248; 136/205 |
International
Class: |
H02N 6/00 20060101
H02N006/00; H01L 35/30 20060101 H01L035/30 |
Claims
1. A solar energy conversion system, comprising: a housing; a cover
lens positioned adjacent the housing for concentrating solar
energy; a package for converting the concentrated solar energy, the
package being positioned adjacent the housing opposite the cover
lens, the package comprising: a photovoltaic (PV) cell for
converting solar energy into electrical power; a thermoelectric
(TE) cell for converting solar energy into electrical power; and a
water circulation system for capturing excess thermal energy for
heating purposes.
2. A solar energy conversion system according to claim 1, wherein
the housing is selected from the group consisting of parabolic,
conical, round, linear, square, and hexagonal reflectors.
3. A solar energy conversion system according to claim 1, wherein
the cover lens is selected from the group consisting of a fresnel
lens and a convex lens, and is positioned adjacent an incoming
solar radiation end of the housing.
4. A solar energy conversion system according to claim 1, wherein
the housing has an aperture located opposite the cover lens, and
the PV cell is located adjacent the aperture and has an efficiency
rating of about 6% to 34% for producing electrical power from solar
energy.
5. A solar energy conversion system according to claim 1, wherein
the water circulation system reduces an operating temperature of
the PV cell to extend a usable life of the PV cell, and the water
circulation system has an efficiency rating of about 25% to 50% for
absorbing heat from solar energy.
6. A solar energy conversion system according to claim 1, wherein
the TE cell has an efficiency rating of about 2% to 25% for
producing electrical power from solar energy.
7. A solar energy conversion system according to claim 1, wherein
the package harnesses over 50% of the solar energy incident on the
package.
8. A solar energy conversion system according to claim 1, wherein
the TE cell is positioned adjacent the PV cell opposite the
housing, and the water circulation system is positioned adjacent
the TE cell opposite the PV cell.
9. A solar energy conversion system according to claim 1, wherein
the TE cell is positioned between the PV cell and the cover lens
within a volume of the housing, the water circulation system is
positioned adjacent the PV cell and continues adjacent the TE cell,
opposite the incident solar energy.
10. A solar energy conversion system according to claim 1, wherein
the housing is positioned between the PV cell and the TE cell for
directing reflected solar energy toward the TE cell, the water
circulation system is positioned adjacent non-irradiated sides of
the PV and TE cells, and an aperture is formed in the housing for
permitting solar energy not absorbed by the TE cell to be directed
toward the PV cell.
11. A solar energy conversion system according to claim 10, wherein
the PV cell is covered with an optical phosphor that shifts
non-optimum wavelengths to optimum wavelengths for greater energy
conversion.
12. A solar energy conversion system according to claim 11, wherein
a secondary reflector collimates solar flux towards a prism to
separate wavelengths and a slotted thermal plane passes PV
efficient wavelengths to the PV cell and absorbs the remaining
wavelengths for conduction to the TE cell.
13. A solar energy conversion system according to claim 12, wherein
a heat pipe conducts thermal energy from a slotted wavelength
separator to the TE cell.
14. A solar energy conversion system according to claim 12, wherein
a stack of wavelength specific filters absorbs non-optimum PV
wavelengths, transfers them to a heat pipe, which conducts thermal
energy to the TE cell.
15. A solar energy conversion system according to claim 12, wherein
a primary fresnel lens concentrates spectral solar radiation to a
secondary concave collimating lens and directs a light beam to the
prism for separation into wavelengths for enhanced solar energy
conversion.
16. A solar energy conversion system according to claim 12, wherein
the TE cell is a heat absorption cell for a system selected from
the group consisting of a thermal-steam powered energy generation
system and a Sterling engine system.
17. A method of converting solar energy into usable energy,
comprising: (a) concentrating solar energy with a housing having a
cover lens onto a package; (b) converting the concentrated solar
energy with the package by: (i) converting a portion of the solar
energy into electrical power with a photovoltaic (PV) cell and with
a thermoelectric (TE) cell; and (ii) capturing excess thermal
energy with a water circulation system for heating purposes.
18. A method according to claim 17, wherein step (a) comprises
providing the housing with a shape selected from the group
consisting of parabolic, conical, round, linear, square, and
hexagonal reflectors; and the cover lens is selected from the group
consisting of a fresnel lens and a convex lens, and is positioned
adjacent an incoming solar radiation end of the housing.
19. A method according to claim 17, wherein step (a) comprises
providing the housing with an aperture located opposite the cover
lens; and further comprising locating the PV cell adjacent the
aperture, the PV cell having an efficiency rating of about 6% to
34% for producing electrical power from solar energy; and the TE
cell having an efficiency rating of about 2% to 25% for producing
electrical power from solar energy.
20. A method according to claim 17, wherein step (b) comprises
reducing a temperature of the PV cell with the water circulation
system to extend a useful life of the PV cell, the water
circulation system having an efficiency rating of about 25% to 50%
for absorbing heat from solar energy, and the package harnessing
over 50% of the solar energy incident on the package.
21. A method according to claim 17, wherein step (b) comprises
positioning the TE cell adjacent the PV cell opposite the housing,
and positioning the water circulation system adjacent the TE cell
opposite the PV cell.
22. A method according to claim 17, wherein step (b) comprises
positioning the TE cell between the PV cell and the cover lens
within a volume of the housing, and positioning the water
circulation system adjacent the PV cell and adjacent the TE cell,
opposite the incident solar energy.
23. A method according to claim 17, wherein step (b) comprises
positioning the housing between the PV cell and the TE cell for
directing reflected solar energy toward the TE cell, positioning
the water circulation system adjacent non-irradiated sides of the
PV and TE cells, and forming an aperture in the housing for
permitting solar energy not absorbed by the TE cell to be directed
toward the PV cell.
24. A method according to claim 23, further comprising covering the
PV cell with an optical phosphor that shifts non-optimum
wavelengths to optimum wavelengths for greater energy conversion,
and collimating solar flux with a secondary reflector towards a
prism to separate wavelengths and a slotted thermal plane passes PV
efficient wavelengths to the PV cell and absorbs the remaining
wavelengths for conduction to the TE cell.
25. A method according to claim 24, further comprising conducting
thermal energy with a heat pipe from a slotted wavelength separator
to the TE cell, and absorbing non-optimum PV wavelengths with a
stack of wavelength specific filters, and transferring them to a
heat pipe that conducts thermal energy to the TE cell.
26. A method according to claim 24, further comprising
concentrating spectral solar radiation with a primary fresnel lens
to a secondary concave collimating lens and directing a light beam
to the prism for separation into wavelengths for enhanced solar
energy conversion; and wherein the TE cell is a heat absorption
cell for a system selected from the group consisting of a
thermal-steam powered energy generation system and a Sterling
engine system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates in general to harnessing solar
energy and, in particular, to an improved system, method, and
apparatus for integrating the conversion of solar energy into a
variety of usable energy forms.
[0003] 2. Description of the Related Art
[0004] In the prior art, solar energy conversion systems attempt to
use a single energy conversion mechanism to achieve an efficiency
that would make them economically feasible. Reaching a sufficiently
high rate of power conversion for broad-based economic viability is
difficult if not impossible at present and has restrained the
growth of the solar energy industry.
[0005] For example, one national solar power program achieved about
34% electric conversion efficiency at 660 suns concentration.
Despite the high conversion compared with the commercial state of
the art, this system's single conversion process only utilized a
portion of the spectrum efficiently. However, that solution also
created very high thermal fluxes and engineering difficulties. In
addition, the extremely high efficiency of that system was limited
to a laboratory bench photovoltaic (PV) prototype.
[0006] More practical models, such as lower complexity, flat panel
solar energy systems are less costly per unit area, but achieve
approximately half or less of the conversion rate of the
concentrated systems. Furthermore, they require much more usable
area to produce the required power. Overall, the lower efficiency
of these expensive types of solar energy conversion modules makes
them economically feasible only in remote locations requiring
extensive infrastructure improvements for standard power
installations. Thus, an improved solar energy conversion system
would be desirable.
SUMMARY OF THE INVENTION
[0007] One embodiment of the present invention comprises a solar
energy conversion package that incorporates two solar energy
conversion methods of photovoltaics (PV) and thermal-steam powered
energy generation or heating. In addition, a thermionic or
thermoelectric conversion unit is also utilized. Although not
usually considered for solar applications, thermionic conversion is
typically used with a nuclear power source for remote power
generation (e.g., spacecraft) or technical instruments. Integrating
all three types of these solar conversion techniques in a
concentrated configuration produces a synergistic system that
exceeds the performance of present solar conversion systems.
[0008] In one embodiment, solar radiation is initially concentrated
by lenses or reflectors to reduce the cost of highly efficient
conversion units (e.g., target concentration of 200:1; range 10:1
to 1000:1). The light is directed to a PV cell with a conversion
efficiency rating of about 14% (e.g., SOTA commercial) to 28.5%
(e.g., SOTA space) to electrical power, while absorbing much of the
excess energy as heat. To maintain the PV cell at an acceptable
temperature for long life, a water circulation system is used to
pull off excess thermal energy. The hot water may be used for hot
water applications, heating, radiant flooring in domestic
applications, and/or low quality heating for commercial
applications.
[0009] The first two conversion units set up the proper boundary
conditions for a thermoelectric (TE) cell, which acts as the third
conversion unit. The TE cell is coupled into the thermal path to
generate power. Commercial TE units offer only about 2% to 7.5%
efficiencies for converting electrical energy to heat. However,
semiconductor based, thermal diode units can produce electrical
energy at about 40% efficiency of the Carnot Cycle potential, which
yields up to about 25% conversion efficiency for the incoming solar
flux. The combination of these three conversion units are
sandwiched in the path of the solar radiation. Each of the three
units produce power from portions of the radiation spectrum that
are poorly utilized by the other devices. Together, they
synergistically yield about 50% or more conversion of the solar
energy spectrum. Theoretical efficiencies are in excess of 60% are
expected as these technologies further develop, with much of the
energy conversion in the preferred form of electrical power.
[0010] The integrated approach of the present invention uses
components within their operating limits and produces more
electrical energy than previously possible while remaining within
engineering parameters to optimize output with respect to the local
solar environment and the needs of the user. In addition, these
very high efficiency units can be readily incorporated into
inherently modular designs at a high economic return on
investment.
[0011] The foregoing and other objects and advantages of the
present invention will be apparent to those skilled in the art, in
view of the following detailed description of the present
invention, taken in conjunction with the appended claims and the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] So that the manner in which the features and advantages of
the present invention, which will become apparent, are attained and
can be understood in more detail, more particular description of
the invention briefly summarized above may be had by reference to
the embodiments thereof that are illustrated in the appended
drawings which form a part of this specification. It is to be
noted, however, that the drawings illustrate only some embodiments
of the invention and therefore are not to be considered limiting of
its scope as the invention may admit to other equally effective
embodiments.
[0013] FIG. 1 is a sectional side view of one embodiment of an
integrated solar energy conversion system constructed in accordance
with the present invention;
[0014] FIG. 2 is a sectional side view of another embodiment of an
integrated solar energy conversion system constructed in accordance
with the present invention;
[0015] FIG. 3 is a sectional side view of still another embodiment
of an integrated solar energy conversion system constructed in
accordance with the present invention;
[0016] FIG. 4 is a sectional side view of yet another embodiment of
an integrated solar energy conversion system constructed in
accordance with the present invention;
[0017] FIG. 5 is a sectional side view of another embodiment of an
integrated solar energy conversion system constructed in accordance
with the present invention; and
[0018] FIG. 6 is a high level flow diagram of one embodiment of a
method in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Referring to FIG. 1, one embodiment of a system and
apparatus for solar energy conversion constructed in accordance
with the present invention is shown. The invention comprises a
housing 11 that controls optical orientation and spacing. Housing
11 may be a conical or parabolic reflective surface, or still other
shapes such as those known in the art (e.g., round, linear, square,
hexagonal, etc. reflectors). Housing 11 has an upper opening 13 and
a lower opening or aperture 15 located opposite the upper opening
13. One or more cover lenses 17 (e.g., a fresnel, convex, etc.
lens) is positioned adjacent the upper opening 13 of the housing 11
for concentrating solar energy toward the lower opening 15 of the
housing 11.
[0020] A package 21 for converting solar energy is positioned
adjacent the lower opening 15 of the housing 11 opposite the cover
lens 17. In one embodiment, the package 21 comprises a photovoltaic
(PV) cell 23 for converting solar energy into electrical power, a
thermionic (TI) or thermoelectric (TE) cell 25 (hereinafter, either
or both are referred to as "TE cell") for converting waste heat
into electrical power via thermionic or thermoelectric conversion,
and a water circulation system 27 to remove excess thermal energy
for various heating purposes. With the development of high
temperature, semiconductor-based PV units, water circulation system
27 also may provide thermal-steam power energy generation.
[0021] In one embodiment, the PV cell 23 is located adjacent the
aperture 15 and has an efficiency rating of about 6% to 34% for
producing electrical power from solar energy. The water circulation
system 27 maintains the PV cell 23 at an acceptable temperature for
long life. In addition, the water circulation system 27 has an
efficiency rating of about 25% to 50% for absorbing heat from solar
energy. The TI or TE cell 25 has an efficiency rating of about 2%
to 25% for producing electrical power from solar energy. Thus,
overall, the package 21 harnesses more than about 50% of the solar
energy incident on the package 21.
[0022] In the embodiment of FIG. 1, the TE cell 25 is positioned
adjacent the PV cell 23 opposite the housing 11, and the water
circulation system 27 is positioned adjacent the TE cell 25
opposite the PV cell 23.
[0023] In one alternate embodiment (FIG. 2), a TE cell 125 is
positioned between a PV cell 123 and a cover lens 117 within a
volume 114 of a housing 111. The water circulation system 127 is
positioned adjacent the PV cell 123 and continues to the
non-irradiated surface of TE cell 125. Improved efficiency is
achieved by treating the irradiated surface of the PV cell 123 with
one or more selective spectrum reflective coatings to allow high
conversion PV wavelengths to pass through to the PV cell 123, and
to reflect less efficient wavelengths to the absorption surface of
the TE cell 125. In one embodiment, the solar radiation heated TE
cells may be coated with high emissivity "blackbody" coatings for
maximum absorption of all incident radiation. Alternatively, large
installations may substitute thermal-steam or closed circuit
Sterling power generation systems for the TE cells at economically
feasible costs.
[0024] In another alternate embodiment (FIG. 3), a reflector 211 is
positioned between a PV cell 223 and a TE cell 225 for directing
reflected solar energy toward the TE cell 225. The water
circulation system 227 is positioned adjacent the PV cell 223,
opposite the reflected solar spectrum and continues adjacent to the
TE cell 225, opposite the reflector 211. An aperture 215 is formed
in the reflector 211 for permitting solar energy reflected from the
surface of the TE cell 225 to be directed toward the PV cell 223.
As discussed above, efficiency is increased by treating the
irradiated surface of the TE cell 225 with selective spectrum
reflecting/absorption coatings directing high PV conversion
wavelengths to the PV cell 123 and absorbing less efficient
wavelengths on the surface of the TE cell.
[0025] Alternatively, an optional optical cover 230 may be provided
for the PV cell 223. Optical cover 230 may be treated with
anti-reflective coatings and also may incorporate phosphors to
shift the wavelength of incident radiation to wavelengths that are
more efficiently converted by the PV cell 223. The inclusion of
phosphor is just in front of the PV cell, rather than elsewhere in
the solar energy path where diffusion would reduce power flux to
the target cells.
[0026] In another alternate embodiment (FIG. 4), linear (e.g.,
trough) reflectors 311, 312 collimate and direct solar radiation
through aperture 315 to a prism 301 that separates the light
spectrum into various wavelengths. A highly thermally conductive
slotted plate with an embedded TE cell 302 passes the high
efficiency photovoltaic wavelengths onto the PV cell 304 and
absorbs the remaining spectrum as thermal energy. The water
circulation system 305 is positioned adjacent the PV cell 304 and
the TE cell 302 opposite incident radiation. This embodiment
precisely partitions the spectrum for greater utilization of the
solar energy by the most efficient device for each wavelength in
the solar spectrum.
[0027] In still other embodiments (FIG. 5), a heat pipe 303
conducts thermal energy from the slotted wavelength separator 302
to the TE cell 302. Alternatively, a stack of wavelength specific
filters may be used to absorb non-optimum PV wavelengths, transfer
them to a heat pipe, which conducts the thermal energy to the TE
cell. In yet another alternative, a primary fresnel lens 314 is
used to concentrate the spectral solar radiation to a secondary
concave collimating lens 313 directing the beam to the prism 301
for separating the into wavelengths for optimum utilization in
energy conversion. In addition, a heat absorption cell for a
thermal-steam powered or sterling engine energy generation system
may be used to replace the TE cell, which would efficiently utilize
the highly concentrated heat source for efficient operation.
[0028] Referring now to FIG. 6, one embodiment of a method of
converting solar energy into usable energy is illustrated. The
method starts as indicated at step 101, and comprises concentrating
solar energy with a housing having a cover lens onto a package
(step 103); converting the concentrated solar energy with the
package by (i) converting a portion of the solar energy into
electrical power with a photovoltaic (PV) cell and with a
thermoelectric (TE) cell (step 105), and (ii) capturing excess
thermal energy with a water circulation system for heating purposes
(step 107), before ending as indicated at step 109.
[0029] The method also may comprise providing the housing with a
shape selected from the group consisting of parabolic, conical,
round, linear, square, and hexagonal reflectors; and the cover lens
is selected from the group consisting of a fresnel lens and a
convex lens, and is positioned adjacent an incoming solar radiation
end of the housing. Alternatively, the method may comprise
providing the housing with an aperture located opposite the cover
lens; and further comprising locating the PV cell adjacent the
aperture, the PV cell having an efficiency rating of about 6% to
34% for producing electrical power from solar energy; and the TE
cell having an efficiency rating of about 2% to 25% for producing
electrical power from solar energy.
[0030] In another embodiment, the method may comprise reducing a
temperature of the PV cell with the water circulation system to
extend a useful life of the PV cell, the water circulation system
having an efficiency rating of about 25% to 50% for absorbing heat
from solar energy, and the package harnessing over 50% of the solar
energy incident on the package; or positioning the TE cell adjacent
the PV cell opposite the housing, and positioning the water
circulation system adjacent the TE cell opposite the PV cell; or
positioning the TE cell between the PV cell and the cover lens
within a volume of the housing, and positioning the water
circulation system adjacent the PV cell and adjacent the TE cell,
opposite the incident solar energy; or positioning the housing
between the PV cell and the TE cell for directing reflected solar
energy toward the TE cell, positioning the water circulation system
adjacent non-irradiated sides of the PV and TI cells, and forming
an aperture in the housing for permitting solar energy not absorbed
by the TE cell to be directed toward the PV cell.
[0031] The method may further comprise covering the PV cell with an
optical phosphor that shifts non-optimum wavelengths to optimum
wavelengths for greater energy conversion, and collimating solar
flux with a secondary reflector towards a prism to separate
wavelengths and a slotted thermal plane passes PV efficient
wavelengths to the PV cell and absorbs the remaining wavelengths
for conduction to the TE cell; or conducting thermal energy with a
heat pipe from a slotted wavelength separator to the TE cell, and
absorbing non-optimum PV wavelengths with a stack of wavelength
specific filters, and transferring them to a heat pipe that
conducts thermal energy to the TE cell; or concentrating spectral
solar radiation with a primary fresnel lens to a secondary concave
collimating lens and directing a light beam to the prism for
separation into wavelengths for enhanced solar energy conversion;
and wherein the TE cell is a heat absorption cell for a system
selected from the group consisting of a thermal-steam powered
energy generation system and a Sterling engine system.
[0032] While the invention has been shown or described in only some
of its forms, it should be apparent to those skilled in the art
that it is not so limited, but is susceptible to various changes
without departing from the scope of the invention. For example,
each embodiment requires the use of a conventional sun tracking
system, including azimuth, elevation, etc., such as those known in
the art.
* * * * *