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Inventors
Parise, Ronald J.
Application #
359108
Filed
Jul-22-1999
Published
Dec-19-2000
Current US Class
136/201
136/205
136/206
136/246
International Classes
H01L 035/00
Field of Search
136/201 136/205 136/206 136/243 136/246
Examiners
Gorgos; Kathryn
Attorney, Agent or Firm
Cantor Colburn LLP
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Thermoelectric gen... |
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Focusing device for... |
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Solar cell having... |
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High intensity solar... |
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Solar energy system |
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Multi-purpose solar... |
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Referenced by:
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Citation
Cite This Patent
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Abstract
This invention is a thermoelectric-photovoltaic device for converting electrical energy from both thermal radiation and sunlight. Thermoelectric energy is produced from thermoelectric cells when a temperature difference is present between two different semiconductor materials. Photovoltaic energy is produced from photovoltaic cells when two different semiconductor materials are exposed to sunlight. To achieve increased electrical energy production, one of the semiconductor materials is placed in a cell having a reduced pressure atmosphere to increase the radiative energy thermal exchange with the black sky at night.
Claims
What is claimed is:
1. An electricity generating device for use in an environment having an ambient pressure, using an electricity generating cell comprising:
a first junction surface disposed in contact with a first semiconductor material;
a second junction surface disposed in contact with a second semiconductor material;
a third junction surface disposed in contact with the first semiconductor material and the second semiconductor material;
the first and second junction surfaces disposed within a pressure cell having a pressure less than the ambient pressure; and
the first and second junction surfaces at a temperature different from the third surface junction producing a thermoelectric potential between the first and second junction surfaces.
2. An electricity generating device as set forth in claim 1, further comprising heat augmentation disposed in thermal communication with the third junction surface.
3. An electricity generating device as set forth in claim 1, wherein the first and second junction surfaces are at about the same temperature and the third junction surface at a greater temperature.
4. An electricity generating device as set forth in claim 1, wherein the first and second junction surfaces are at about the same temperature and the third junction surface is at a lesser temperature.
5. An electricity generating device as set forth in claim 1, wherein the first and second junction surfaces are at different temperatures.
6. An electricity generating device as set forth in claim 1, wherein
the electricity generating cell has a thermal resistivity;
the first semiconductor material is disposed in a distance between the first junction surface and the third junction surface; and
the first semiconductor material has a geometry which increases said thermal resistivity as compared to a second electricity generating cell having a first semiconductor material having a straight geometry which spans a substantially equivalent distance.
7. An electricity generating device as set forth in claim 6, wherein said geometry is curved, coiled, snaking, or a combination thereof.
8. An electricity generating device as set forth in claim 6, further comprising at least one first film insulator disposed adjacent to and in contact with said first semiconductor material.
9. An electricity generating device as set forth in claim 8, further comprising at at least one second film insulator disposed adjacent to and in contact with said second semiconductor material.
10. An electricity generating device as set forth in claim 1, further comprising a plurality of first semiconductor materials and a plurality of second semiconductor materials oriented in a cascading arrangement.
11. An electricity generating device as set forth in claim 10, further comprising thermal conductors connecting successive rows of said first semiconductor materials and said second semiconductor materials.
12. An electricity generating device as set forth in claim 11, wherein said thermal conductors are metallic materials or semiconductor materials.
13. An electricity generating device as set forth in claim 1, wherein said first semiconductor material is oriented at a first angle between said first surface junction and said third surface junction, and said second semiconductor material is oriented at a second angle between said second surface junction and said third surface junction; and wherein said first and second angles are 30.degree., 45.degree., 60.degree., 90.degree., or 180.degree..
14. An electricity generating device as set forth in claim 1, wherein said first material has a length and a cross-sectional area, wherein said length is greater than said cross-sectional area.
15. An electricity generating device as set forth in claim 14, wherein a ratio of said length to said cross-sectional area is at least about 4.
16. An electricity generating device as set forth in claim 14, wherein a ratio of said length to said cross-sectional area is at least about 5.
17. An electricity generating device as set forth in claim 14, further comprising a mechanical support disposed between said first surface junction and said third surface junction.
18. An electricity generating device as set forth in claim 17, further comprising a mechanical support disposed between said second surface junction and said third surface junction.
19. An electricity generating device as set forth in claim 1, wherein said first semiconductor material and said second semiconductor material are disposed within said pressure cell.
20. An electricity generating device as set forth in claim 19, wherein said third junction surface is disposed within said pressure cell.
21. An electricity generating device as set forth in claim 20, further comprising first heat augmentation disposed in thermal communication with the third junction surface.
22. An electricity generating device as set forth in claim 21, further comprising second heat augmentation disposed in thermal communication with said pressure cell.
23. An electricity generating device as set forth in claim 19, further comprising
the thermoelectric potential having an electrical current;
the first and second junction surfaces electrically connected such that the current flows to a current flow direction circuitry;
the current flow direction circuitry operable to detect the direction of the current;
the current flow direction circuitry further operable to orient the direction of an output current; and
the current flow circuitry electrically connected to a load.
24. An electricity generating device as set forth in claim 1, further comprising
the thermoelectric potential having an electrical current;
the first and second junction surfaces electrically connected such that the current flows to a current flow direction circuitry;
the current flow direction circuitry operable to detect the direction of the current;
the current flow direction circuitry further operable to orient the direction of an output current; and
the current flow circuitry electrically connected to a load.
25. An electricity generating device as set forth in claim 1, further comprising a mechanical support disposed between said first junction surface and said third junction surface.
26. An electricity generating device as set forth in claim 1, further comprising heat augmentation disposed in thermal communication with said pressure cell.
27. An electricity generating device as set forth in claim 26, wherein said heat augmentation is a finned heat exchanger, fluid heat exchange, baffled heat exchanger, radiation shield, heat transfer composition, or a combination thereof.
28. An electricity generating device as set forth in claim 1, further comprising heat augmentation disposed in thermal communication with the first junction surface.
29. An electricity generating device as set forth in claim 1, further comprising a heat exchanger disposed in heat exchange communication with the second junction surface.
30. An electricity generating device as set forth in claim 1, further comprising a first radiation heat transfer area disposed in thermal communication with said first junction surface.
31. An electricity generating device as set forth in claim 30, wherein said radiation heat transfer area is disposed in thermal communication with said second junction surface.
32. An electricity generating device as set forth in claim 1, further comprising a plurality of electricity generating cells electrically connected together.
33. An electricity generating device as set forth in claim 32, wherein the first and second junction surfaces of said plurality of electricity generating cells is at least partially disposed within a single pressure cell.
34. An electricity generating device as set forth in claim 32, wherein each of the electricity generating cells is at least partially disposed within separate pressure cells.
35. An electricity generating device as set forth in claim 32, wherein the plurality of electricity generating cells are connected in series fashion.
36. An electricity generating device as set forth in claim 32, wherein the plurality of electricity generating cells are connected in parallel fashion.
37. An electricity generating device as set forth in claim 1, further comprising a photovoltaic cell disposed within the electricity generating cell, the photovoltaic cell comprising a third semiconductor material and a fourth semiconductor material, the third and fourth semiconductor materials converting sunlight to electrical energy.
38. An electricity generating device as set forth in claim 37, wherein the fourth semiconductor material is the first semiconductor material.
39. An electricity generating device as set forth in claim 37, wherein the photovoltaic cell includes a light concentrating device for focusing sunlight onto the third and fourth semiconductor materials.
40. An electricity generating device as set forth in claim 37, further comprising a plurality of electricity generating cells and a plurality of photovoltaic cells electrically connected together.
41. An electricity generating device as set forth in claim 40, wherein the first and second junction surfaces of said plurality of electricity generating cells are disposed within a single pressure cell.
42. An electricity generating device as set forth in claim 40, wherein the first and second junction surfaces of each of said plurality of electricity generating cells are disposed within separate pressure cells.
43. An electricity generating device as set forth in claim 40, wherein the plurality of electricity generating cells are connected in series fashion to said plurality of photovoltaic cells.
44. An electricity generating device as set forth in claim 40, wherein the plurality of electricity generating cells are connected in parallel fashion to said plurality of photovoltaic cells.
45. An electricity generating device as set forth in claim 37, wherein the first semiconductor material, second semiconductor material, third semiconductor material, and fourth semiconductor material are chosen based upon the thermal characteristics of that portion of the device.
46. An electricity generating device as set forth in claim 37, wherein the electricity generating cell is connected in series fashion to the photovoltaic cell.
47. An electricity generating device as set forth in claim 37, wherein the electricity generating cell is connected in parallel fashion to the photovoltaic cell.
48. An electricity generating device as set forth in claim 1, wherein at least a portion of said pressure cell is capable of transmitting sunlight to the photovoltaic cell.
49. An electricity generating device as set forth in claim 48, wherein the portion of said pressure cell capable of transmitting sunlight has a reflectivity coating.
50. An electricity generating device as set forth in claim 1, wherein said first material has a length and a cross-sectional area, wherein said length is greater than said cross-sectional area.
51. An electricity generating device as set forth in claim 50, wherein a ratio of said length to said cross-sectional area is at least about 4.
52. An electricity generating device as set forth in claim 50, wherein a ratio of said length to said cross-sectional area is at least about 5.
53. An electricity generating device as set forth in claim 50, further comprising a mechanical support disposed between said first surface junction and said third surface junction.
54. An electricity generating device as set forth in claim 53, further comprising a mechanical support disposed between said second surface junction and said third surface junction.
55. An electricity generating device as set forth in claim 50, further comprising
the thermoelectric potential having an electrical current;
the first and second junction surfaces electrically connected such that the current flows to a current flow direction circuitry;
the current flow direction circuitry operable to detect the direction of the current;
the current flow direction circuitry further operable to orient the direction of an output current; and
the current flow circuitry electrically connected to a load.
56. An electricity generating device as set forth in claim 1, further comprising a photovoltaic cell disposed within the electricity generating cell, the photovoltaic cell comprising a third semiconductor material and a fourth semiconductor material, the third and fourth semiconductor materials converting sunlight to electrical energy.
57. An electricity generating device as set forth in claim 56, wherein the photovoltaic cell includes a light concentrating device for focusing sunlight onto the third and the fourth semiconductor materials.
58. An electricity generating device as set forth in claim 56, wherein the fourth semiconductor material is the first semiconductor material.
59. An electricity generating device as set forth in claim 56, further comprising a plurality of electricity generating cells and a plurality of photovoltaic cells electrically connected together.
60. An electricity generating device as set forth in claim 59, wherein the plurality of electricity generating cells are connected in parallel fashion to said plurality of photovoltaic cells.
61. An electricity generating device as set forth in claim 56, wherein the first semiconductor material, second semiconductor material, third semiconductor material, and fourth semiconductor material are chosen based upon the thermal characteristics of that portion of the device.
62. An electricity generating device as set forth in claim 56, wherein the electricity generating cell is connected in parallel fashion to the photovoltaic cell.
63. An electricity generating device using an electricity generating cell having a thermal resistivity, comprising:
a first junction surface disposed in contact with a first semiconductor material;
a second junction surface disposed in contact with a second semiconductor material;
a third junction surface disposed in contact with the first semiconductor material and the second semiconductor material;
the first and second junction surfaces at a temperature different from the third surface junction producing a thermoelectric potential between the first and second junction surfaces;
the first semiconductor material is disposed in a distance between the first junction surface and the third junction surface; and
the first semiconductor material has a geometry which increases said thermal resistivity as compared to a second electricity generating cell having a first semiconductor material having a straight geometry which spans a substantially equivalent distance.
64. An electricity generating device as set forth in claim 63, wherein the first and second junction surfaces are at about the same temperature and the third junction surface at a greater temperature.
65. An electricity generating device as set forth in claim 63, wherein the first and second junction surfaces are at about the same temperature and the third junction surface is at a lesser temperature.
66. An electricity generating device as set forth in claim 63, wherein the first and second junction surfaces are at different temperatures.
67. An electricity generating device as set forth in claim 63, wherein said geometry is curved, coiled, snaking, or a combination thereof.
68. An electricity generating device as set forth in claim 67, further comprising at least one first film insulator disposed adjacent to and in contact with said first semiconductor material.
69. An electricity generating device as set forth in claim 68, further comprising at least one second film insulator disposed adjacent to and in contact with said second semiconductor material.
70. An electricity generating device as set forth in claim 63, further comprising a plurality of first semiconductor materials and a plurality of second semiconductor materials oriented in a cascading arrangement.
71. An electricity generating device as set forth in claim 70, further comprising thermal conductors connecting successive rows of said first materials and said second materials.
72. An electricity generating device as set forth in claim 71, wherein said thermal conductors are metallic materials or semiconductor materials.
73. An electricity generating device as set forth in claim 63, wherein said first semiconductor material is oriented at a first angle between said first surface junction and said third surface junction, and said second semiconductor material is oriented at a second angle between said second surface junction and said third surface junction; and wherein said first and second angles are 30.degree., 45.degree., 60.degree., 90.degree., or 180.degree..
74. An electricity generating device as set forth in claim 63, further comprising
the thermoelectric potential having an electrical current;
the first and second junction surfaces electrically connected such that the current flows to a current flow direction circuitry;
the current flow direction circuitry operable to detect the direction of the current;
the current flow direction circuitry further operable to orient the direction of an output current; and
the current flow circuitry electrically connected to a load.
75. An electricity generating device as set forth in claim 63, further comprising a mechanical support disposed between said first junction surface and said third junction surface.
76. An electricity generating device as set forth in claim 63, further comprising heat augmentation disposed in thermal communication with said electricity generating cell.
77. An electricity generating device as set forth in claim 76, wherein said heat exchanger is a finned heat exchanger, fluid heat exchange, baffled heat exchanger, radiation shield, heat transfer composition, or a combination thereof.
78. An electricity generating device as set forth in claim 76, further comprising heat augmentation disposed in thermal communication with the first junction surface.
79. An electricity generating device as set forth in claim 78, further comprising heat augmentation disposed in heat exchange communication with the second junction surface.
80. An electricity generating device as set forth in claim 63, further comprising a first radiation heat transfer area disposed in thermal communication with said first junction surface.
81. An electricity generating device as set forth in claim 63, further comprising a second radiation heat transfer area disposed in contact with said second junction surface.
82. An electricity generating device as set forth in claim 63, further comprising a plurality of electricity generating cells electrically connected together.
83. An electricity generating device as set forth in claim 81, wherein the plurality of electricity generating cells are connected in parallel fashion.
84. A method of converting thermal radiation and sunlight into electrical energy utilizing a device having a full sunlight exposure position, a partial sunlight exposure position, and a full shade position, comprising:
forming the device by electrically connecting, in a parallel fashion, at least one electricity generating cell with at least one photovoltaic cell;
producing electrical energy from both the photovoltaic cell and the electricity generating cell in the full sunlight exposure position; and
producing energy from the electricity generating cell in the full shade position.
85. A method of converting thermal radiation and sunlight into electrical energy as set forth in claim 84, further comprising positioning the device in a low orbit about the earth.
86. A method of converting thermal radiation and sunlight into electrical energy as set forth in claim 84, further comprising positioning the device in a terrestrial setting.
87. A method of converting thermal radiation and sunlight into electrical energy as set forth in claim 84, wherein the electricity generating cell comprises a first junction surface disposed in contact with a first semiconductor material, a second junction surface disposed in contact with a second semiconductor material, a third junction surface disposed in contact with the first semiconductor material and the second semiconductor material, the first and second junction surfaces at a temperature different from the third surface junction producing a thermoelectric potential between the first and second junction surfaces, and the first and second junction surfaces are disposed within a pressure cell having a pressure less than the ambient pressure.
88. A method of converting thermal radiation and sunlight into electrical energy as set forth in claim 84, wherein said device is a thermoelectric-photovoltaic array, the array comprising a plurality of electricity generating cells connected electrically, in a parallel fashion, with a plurality of photovoltaic cells.
89. A method of converting thermal radiation and sunlight into electrical energy as set forth in claim 88, further comprising producing electrical energy from a portion of the photovoltaic cells and from the electricity generating cells in the partial sunlight exposure position.
90. A method of converting thermal radiation and sunlight into electrical energy as set forth in claim 84, further comprising orienting the device such that the thermoelectric cell and the photovoltaic cell are in a perpendicular arrangement with the sunlight throughout the orbit.
91. A method of converting thermal radiation into electrical energy, comprising:
utilizing an energy generating device comprising a first junction surface disposed in contact with a first semiconductor material; a second junction surface disposed in contact with a second semiconductor material; a third junction surface disposed in contact with the first semiconductor material and the second semiconductor material; the first and second junction surfaces at a temperature different from the third surface junction producing a thermoelectric potential between the first and second junction surfaces; the first semiconductor material is disposed in a distance between the first junction surface and the third junction surface; and the first semiconductor material has a geometry which increases said thermal resistivity as compared to a second electricity generating cell having a first semiconductor material having a straight geometry which spans a substantially equivalent distance; and
producing electrical energy.
92. A method of converting thermal radiation into electrical energy as set forth in claim 91, further comprising positioning the device in a low orbit about the earth.
93. A method of converting thermal radiation into electrical energy as set forth in claim 91, further comprising positioning the device in a terrestrial setting.
94. A method of converting thermal radiation into electrical energy as set forth in claim 91, wherein said device is a thermoelectric array, the array comprising a plurality of electricity generating cells connected electrically, in a parallel fashion.
95. A method of converting thermal radiation into electrical energy as set forth in claim 91, further comprising using space as a cold sink.
96. A method of converting thermal radiation into electrical energy, comprising:
utilizing an electricity generating cell comprising a first junction surface disposed in contact with a first semiconductor material, a second junction surface disposed in contact with a second semiconductor material, a third junction surface disposed in contact with the first semiconductor material and the second semiconductor material, the first and second junction surfaces at a temperature different from the third surface junction producing a thermoelectric potential between the first and second junction surfaces, and the first and second junction surfaces are disposed within a pressure cell having a pressure less than the ambient pressure; and
producing electrical energy.
97. A method of converting thermal radiation into electrical energy as set forth in claim 96, wherein said device is a thermoelectric array, the array comprising a plurality of electricity generating cells connected electrically, in a parallel fashion.
98. A method of converting thermal radiation into electrical energy as set forth in claim 96, further comprising using space as a cold sink.
Description
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates generally to the use of solar and thermal energy and more particularly to the conversion of solar and thermal energy to electrical energy.
2. Description of the Related Art
The conversion of solar energy to electrical energy through the use of photovoltaic cells is well established in the art. Photovoltaic cells are semiconductor components that convert light into useable electrical energy. A typical photovoltaic cell, commonly referred to as a solar cell, is comprised of an interface between an n-type semiconductor material and a p-type semiconductor material. A thin transparent layer of n-type or p-type material is deposited on a p-type or n-type material respectively to form an active p-n or n-p junction. When the junction is exposed to visible or nearly visible light, in a solar cell application, electron hole pairs, or minority charge carriers, are created at the junction. The minority charge carriers at the n-p interface migrate across the junction in opposite directions producing an electrical potential or an electrical voltage difference. In solar cell applications, electrical contacts, sometimes called ohmic contacts, are connected to the n-type and p-type materials on either side of the junction and an ensuing electric current is obtained.
The prior art has disclosed many variations of the basic p-n junction interface. Many of these variations have been attempts to improve the efficiency and effectiveness of the solar cell at absorbing solar energy. For example, a heterojunction photovoltaic device is comprised of stacked p-n junctions of different materials with band gap energies that match different parts of the solar spectrum. U.S. Pat. No. 4,332,974 discloses a multi layer photovoltaic cell wherein the first p-n layer will absorb energy in a particular band of the spectrum while the remaining energy passes through to the next p-n layer. The next subsequent p-n layer in the stack is comprised of materials that absorb a different band of the spectrum from the preceding layer. Each preceding layer acts as a window to the remaining energy of the spectrum that it does not absorb. With the cells arranged in such a fashion, the amount of solar energy converted to electrical energy is expanded, thus increasing the efficiency of the device.
Another example of a prior art variation of the basic p-n junction is the p-I-n junction. The p-I-n junction is comprised of p-type semiconductor material and n-type semiconductor material separated by an intrinsic-type material semiconductor material. The addition of the intrinsic-type material layer creates a diffusion potential between this layer and the p-type material and the n-type material. The p-I-n device is constructed such that the majority of the incident light energy is absorbed in the intrinsic layer allowing more of the positive and negative charge carriers to diffuse toward their respective p-type and n-type interfaces. This variation on the basic p-n junction enhances the flow of the charge carriers and improves the overall efficiency and effectiveness of the photovoltaic cell.
Typically, the individual interfaces of photovoltaic cells are interconnected to form an array or panel to supply electrical power. Regardless of the type of junction, the photovoltaic cells and the resulting arrays are subsequently interconnected in series/parallel connections to supply the required voltage and current output.
There are many cases of prior art wherein photovoltaic cells are enhanced to increase efficiency of a solar panel. For example, U.S. Pat. Nos. 4,002,499, 4,003,638, 4,088,116, 4,129,115, and 4,312,330 all disclose various methods of concentrating the incident light energy entering a photovoltaic cell. The common theme among the above cited examples is the use of a reflective device to collect sunlight distributed over a larger area and focus it upon a photovoltaic cell thereby increasing the amount of incident light energy.
The use of solar panels to convert light energy into thermal energy is also well known in the art. There are many examples of prior art which utilize light energy to passively heat fluid. For instance, U.S. Pat. No. 5,522,944 discloses the use of interconnected tubes disposed within an array of photovoltaic cells for converting solar energy to thermal energy in a fluid disposed within the tubes.
Likewise, the use of a thermoelectric generator to convert thermal energy into electric energy is well known in the art. Thermoelectric generators are semiconductor or solid state devices which convert thermal energy to electrical energy directly. Unlike photovoltaic cells however they are restricted to a maximum possible thermal efficiency of 1-(T.sub.L /T.sub.H). This relationship is referred to as the Carnot efficiency and is calculated at the operating temperature between the source temperature, T.sub.H, and the sink temperature, T.sub.L.
Thermoelectric generators can be analyzed by using simple thermodynamic relationships at the macroscopic level unlike photovoltaic cells which normally require extensive analysis at the microscopic level. Simple fundamental relationships are utilized in the area of art to aid in understanding the function of the solid state devices employed in thermoelectric generators.
Thermoelectric generators are based on the Seebeck effect which holds that when two dissimilar materials are exposed to a temperature differential an electric current will be generated at their junction. The suitability of the materials for the thermoelectric device depends primarily on a parameter referred to as the figure of merit. The figure of merit is based on the material type evaluated at the perceived operating temperature of the thermoelectric device. The higher the value of the figure of merit in the temperature range of the thermoelectric device the better suited the materials are for a thermoelectric device. It is well known in the art to optimize the figure of merit for candidate materials by optimizing material geometries along with material types. In order to optimize the figure of merit an area ratio between the n-type and the p-type materials is selected such that the following relationships are satisfied: ##EQU1## and
1.sub.n =1.sub.p
where
A.sub.n area of n-type material
A.sub.p area of p-type material
.rho..sub.p, .rho..sub.n electrical resistivity
.lambda..sub.p, .lambda..sub.n thermal conductivity
1.sub.p, 1.sub.n Length of area elements.
With the semiconductor materials selected based on the above equations, the figure of merit, Z, is optimized by satisfying the following relationship:
where ##EQU2## .alpha..sub.p, .alpha..sub.n Seebeck coefficients.
For the optimum figure of merit, Z, the optimum current, I.sub.opt, produced by the thermoelectric generator is calculated by the following equation: ##EQU3## where ##EQU4## and T.sub.H, T.sub.L are the high and low temperatures of the source and the sink, respectively.
and
.chi.=[1+Z((T.sub.H +T.sub.L)/2)].sup.1/2
The open circuit voltage for the thermoelectric generator, .sub.Voc, is calculated by the following equation:
V.sub.oc =(.vertline..alpha..sub.p .vertline.+.vertline..alpha..sub.n .vertline.)(T.sub.H -T.sub.L)
The specific thermal efficiency of the thermoelectric generator for the optimized conditions then becomes: ##EQU5## Note that it is not possible for the thermoelectric generator to have a thermal efficiency greater than the previously stated Camot efficiency and as such T.sub.L /T.sub.H at the operating conditions of the device must be less than one.
An example of a thermoelectric generator is disclosed in U.S. Pat. No. 4,338,560. The thermoelectric generator of the '560 patent discloses a generator that comprises an array of sources and sinks interconnected by n-type and p-type doped material elements. It is disclosed that the sources absorb infrared heat from the earth and the sinks emit excess heat to space.
State of the art photovoltaic cells work well during daylight hours or when there is a sufficient incident light source, while thermoelectric generators tend to work better at night. What is needed is a thermoelectric-photovoltaic cell system with both enhanced terrestrial and space capabilities which employs state of the art design and manufacturing techniques to obtain maximum electrical energy output from the solar cells during daylight and sunlight conditions and from thermoelectric generator cells from temperature differentials.
SUMMARY OF THE INVENTION
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the energy generating device and method of the present invention. The electricity generating device uses an electricity generating cell comprising: a first junction surface disposed in contact with a first semiconductor material; a second junction surface disposed in contact with a second semiconductor material; a third junction surface disposed in contact with the first semiconductor material and the second semiconductor material; the first and second junction surfaces disposed within a pressure cell having a pressure less than the ambient pressure; and the first and second junction surfaces at a temperature different from the third junction surface producing a thermoelectric potential between the first and second junction surfaces.
The method of converting thermal radiation and sunlight into electrical energy of the present invention, comprising: forming the device by electrically connecting, in a parallel fashion, at least one thermoelectric cell with at least one photovoltaic cell; orienting the device such that the thermoelectric cell and the photovoltaic cell are in a perpendicular arrangement with the sunlight throughout the orbit; producing electrical energy from both the photovoltaic cell and the thermoelectric cell in the full sunlight exposure position; and producing energy from the thermoelectric cell in the full shade position.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings wherein like elements are numbered alike in the several Figures:
FIG. 1 is a schematic representation of a thermoelectric-photovoltaic cell of the present invention.
FIG. 2 is a schematic representation of a thermoelectric-photovoltaic cell of the present invention.
FIG. 3 is a cross sectional view of a thermoelectric-photovoltaic cell of the present invention.
FIG. 4 is a cross sectional view of a thermoelectric-photovoltaic cell of the present invention.
FIG. 5 is a cross sectional view of an array incorporating a thermoelectric-photovoltaic cell of the present invention.
FIG. 6 is a plan view of an array panel and support structure incorporating a thermoelectric-photovoltaic cell of the present invention.
FIG. 7 is a cross sectional view of an array panel and support structure incorporating a thermoelectric-photovoltaic cell of the present invention.
FIG. 8 is a perspective illustration of a satellite incorporating a thermoelectric-photovoltaic cell of the present invention.
FIG. 9 is a cross sectional view of a thermoelectric-photovoltaic cell of the present invention.
FIG. 10 is a cross sectional view of a thermoelectric-photovoltaic cell of the present invention.
FIG. 11 is a cross sectional view of a thermoelectric-photovoltaic cell of the present invention.
FIG. 12 is a cross sectional view of a thermoelectric generator of the present invention where the junction surface area is varied to improve performance.
FIG. 13 is an isometric view of a thermoelectric-photovoltaic cell of the present invention where the radiative area is varied as well as the size of the various p-type and n-type materials.
FIG. 14 is a cross sectional view of a cascading thermoelectric generator of the present invention.
FIG. 14A a cross sectional view of a cascading thermoelectric generator of the present invention.
FIG. 15 is a cross sectional view of a thermoelectric generator of the present invention where the geometry and size of the p-type and n-type materials are adjusted to increase thermal resistance and improve power output.
FIG. 16 is a cross sectional view of a thermoelectric generator of the present invention which employs metallic conductors to enable an increase in the length of the p-type and n-type materials.
FIG. 16A is a cross sectional view of section AA from FIG. 16 which illustrates the orientation of the p-type materials with respect to the n-type materials.
FIG. 16B a cross sectional view of a thermoelectric generator of the present invention which illustrates another orientation scheme using a p-type/n-type material arrangement as in FIG. 16A.
FIG. 17 is a cross sectional view of a thermoelectric generator of the present invention employing another geometry which snakes the p-type and n-type materials to increase their length.
FIG. 18 is a cross sectional view of a thermoelectric generator of the present invention employing thin film insulators to enable condensed snaking of the p-type and n-type materials to optimize usage of space.
FIG. 19 is an isometric view of an array incorporating cells of the present invention where the cells are in individual reduced pressure units arranged in an array.
FIG. 20 is a cross sectional view of a thermoelectric-photovoltaic cell of the present invention which illustrates daytime and nighttime operation of the cell.
FIG. 21 is a cross sectional view of a cell of the present invention which employs both internal and external heat transfer augmentation.
FIG. 22 is a cross sectional view of a cell of the present invention employing alternate internal heat transfer augmentation.
DETAILED DESCRIPTION OF THE DRAWINGS
An embodiment of the nighttime solar cell of the present invention is shown schematically in FIG. 1. The nighttime solar cell 1 of the present invention includes a thermoelectric generator 10, current flow circuitry 20, and a current load 21. The generator is comprised of a junction surface 11, a junction surface 12, a reduced pressure cell 13, n-type doped material 14, and p-type doped material 15. The schematic presented in FIG. 1 depicts the operation of the present invention in a nighttime terrestrial embodiment. The junction surface 11 emits thermal energy through radiation heat transfer 16 to the black sky at night. In this embodiment junction surface 11 becomes a cold temperature sink for the thermoelectric generator 10 preferably having an emissivity greater than 0.90, with about 0.96 to about 0.99 especially preferred. The black sky has an effective temperature around zero degrees absolute temperature which allows the cold temperature sink to radiate heat to the black sky via electromagnetic energy. In a terrestrial embodiment of the present invention the junction surface 12 is the hot temperature source as it is exposed to ambient temperature, typically about 200.degree. K to 325.degree. K, with about 220.degree. K to 310.degree. K more common. The temperature difference that exists between the junction surfaces produces an electrical current 17 in the p-type material and the n-type material of the thermoelectric generator.
The present invention utilizes reduced pressure cell 13, 13', 13" (see FIGS. 9, 10, and 11) to take advantage of the extremely low temperatures of the black sky. The reduced pressure cell can encapsulate the junction surface 11, encapsulate the thermoelectric generator 10 except for junction surface 12, or can encapsulate the entire thermoelectric generator, to insulate the junction surface 11 or the thermoelectric generator 10 from the ambient temperatures. The pressure within the reduced pressure cell 13 is a pressure lower than the ambient pressure, with the ideal pressure of the reduced pressure cell 13 being a perfect vacuum. The reduced pressure cell 13 is manufactured from a material suitable to allow junction surfaces 11 to "see" the black sky and exchange energy with it by radiation heat transfer.
In one embodiment, referring to FIGS. 9 and 10, the reduced pressure cell 13' (also known as the vacuum cell or vacuum pod), encapsulates the photovoltaic cell 30 and the majority of the thermoelectric generator 10, leaving junction surface 12 thermally connected to the environment and allowing the establishment of conductive heat transfer with the surroundings. Utilizing the reduced pressure cell 13' in this fashion enables the elimination of the insulation 40 (see FIGS. 3 and 4), thereby reducing the overall system weight and cost, while providing a more effective insulation of the photovoltaic cells and allowing the thermoelectric generator to operate at a higher daytime temperature to improve its performance.
In another embodiment, set forth in FIG. 11, the reduced pressure cell 13" fully encapsulates the thermoelectric generator 10 and photovoltaic cell 30. In this embodiment, junction surface 12 thermally connects to the environment via radiative heat transfer only. This thermal connectivity enables the amount of heat provided to the thermoelectric generator 10 during nighttime usage or removed therefrom during daytime usage, to be controlled, particularly in extreme temperature conditions.
In FIG. 12, the reduced pressure cell 13' (as shown in FIGS. 9 and 10) further comprises an aperture or window 60 (as shown in FIG. 21). This enables the junction surface 11 usage to also serve as a sink during daytime usage. If the thermoelectric generator 10 uses the daytime sky as a sink (normally shielded from the direct rays of the sun) then junction surface 11 is a sink in daylight usage and junction surface 12 is the source. FIG. 21 further illustrates the window which forms the aperture 60 of the reduced pressure cell 13' to exchange radiative energy with a radiative source or sink. The radiative exchange area in the cell prefers line-of-sight contact with the sink (or source) energy exchange external body only, and hopefully no other bodies that will detrimentally influence the energy exchange. The size of the aperture can be larger, smaller, or substantially equivalent to the size of the radiative heat transfer area, with a size which maximizes the effectiveness of the radiative heat transfer area preferred.
To improve the radiative characteristics of the energy exchange, spectral transmitting characteristics of the window with the external body can be chosen accordingly. For example, when deep space is used as a sink, deep space at approximately 4.degree. K is always visible to terrestrial objects in certain band widths. Rain, snow, clouds, etc., notwithstanding, there is always an energy exchange. Window optical properties will be selected to optimize this energy exchange. Coatings may also be applied to the window to augment or improve its energy transmitting capabilities. The internal surface of the window can be coated to maximize transmission from the radiative heat transfer area while minimizing the internal reflectivity. Also, when exclusively using thermoelectric generators and deep space as a sink, the external window surface may be coated with coatings that affect maximum reflectivity of all energy, with minimum transmission inward.
Alternatively, if the daytime usage will be exclusively thermoelectric generator elements that utilize the sun as a thermal source, then maximum transmissivity is desired through the external surface of the window. The optical properties of the window and the surface coatings would preferably effect this result, with radiative energy bandwidths maximized.
In an alternative embodiment employing the thermoelectric generators and the photovoltaic cells in parallel arrangement exposed to the external surroundings of the window, the coatings which maximize the transmissivity of the energy needed to heat the hot junction of the thermoelectric generator elements is preferred. These coatings should also allow the transmittance of the solar radiation that excites the electrons in the photovoltaic cells into the conduction band to increase electron activity and improve electrical power generation.
It should be noted that if the daytime usage will be exclusively employing thermoelectric generator units which will utilize the sun as a thermal source, then maximum transmissivity in the solar thermal range (blocking deep space coating) is desired through the external surface of the window into the pod. The optical properties of the window and the surface coatings would effect this result, with appropriate radiative energy bandwidths maximized.
The appropriate coating to be applied to the interior and/or exterior surface of the window can readily be determined by an artisan, with coatings which would allow transmissivity for the atmosphere of about 8 .mu.m to about 13 .mu.m, preferred.
The electric circuit of an embodiment of the nighttime solar cell is also shown in FIG. 1. During nighttime periods, or periods without incident light, current 17 travels in the direction shown from junction surface 11 to current flow direction circuitry 20 via connection 18. Current flow direction circuitry determines the direction of the incoming current 17, and properly orients the current into outgoing current 19 which is carried via connection 22 where it is stored or consumed by load 21.
Referring next to FIG. 2, there is illustrated a schematic representation of an embodiment of the present invention during daylight operation. In addition to the embodiment previously described the nighttime solar cell illustrated includes a photovoltaic cell 30 comprising concentrating lens 31, n-type doped material 14, and p-type doped material 15. Photovoltaic cell 30 is arranged within thermoelectric generator 10. During daylight operation an embodiment of the present invention produces electrical energy from thermoelectric generator 10 as well as photovoltaic cell 30. Concentrating lens 31 receives solar energy 32 falling between junction surfaces 11 and focuses it upon n-type doped material 14 and p-type doped material 15. Thus configured photovoltaic cell 30 generates current 33, 34 which is carried to load 35, 36 via connections 37, 38.
The operation of a thermoelectric generator during daylight conditions is also illustrated in FIG. 2. During daylight conditions thermoelectric generator 10 functions opposite to that described above for nighttime conditions. Solar energy 32 enters the device and warms junction surfaces 11. The irradiation of solar energy upon junction surface 11 causes the junction surfaces to become the hot junction and the relatively cooler ambient conditions cause junction surface 12 to become the cool junction surface for the thermoelectric generator. In a preferred embodiment, the absorptivity of surface junction 11 is greater than 0.90. In addition, for certain embodiments it is advantageous to select a material for surface junction 11 wherein the emissivity and the absorptivity are nearly equal. Electrical current 17 is generated by the temperature difference between the hot and cold junction surfaces and is opposite in direction to that produced during nighttime operation. Current 17 is carried to current flow direction circuitry 20 wherein its direction is properly oriented into outgoing current 19 and carried to load 21 via connection 22 where it is either stored or consumed.
Alternatively the thermoelectric generator could be solely utilized, even during the day. In this operating mode, during the day, the thermoelectric generator would be shielded from the rays of the sun and allowed to look at deep space. This mode of operation is the same as the nighttime mode of operation, and the current flow direction sensing circuitry is not necessary, but the reduced pressure cell is preferred for improved operation.
Yet another mode of operation would be to expose the radiative heat transfer area to the direct rays of the sun so that it becomes the hot junction for the thermoelectric generators and the ambient environment (or some other sink) becomes the sink temperature for the waste heat. This mode of operation is opposite to the nighttime mode, therefore the current flow direction circuitry is employed.
Although the connections and loads illustrated in FIGS. 1 and 2 are shown as separate they may be combined and interconnected with other such devices as the electrical needs of a particular embodiment dictate. The embodiment shown in FIGS. 1 and 2 may be terrestrial or space based. The important distinguishing characteristic between a terrestrial based application and a space application is the reduced pressure cell. The reduced pressure cell insulates the surface junction of the thermoelectric generator from the earth's ambient surroundings while simultaneously allowing for the surface junction to react radiatively with the sun or the night sky. In space based applications the insulative properties of the reduced pressure cell are not necessary.
Referring now to FIG. 3 there is illustrated another embodiment of the present invention. This embodiment is configured for terrestrial use and includes, in addition to the embodiments previously described, thermally insulative material 40. Thermally insulative material 40 insulates photovoltaic cell 30 from thermoelectric generator 10. With the two devices thermally insulated the performance of the thermoelectric generator is not influenced by any thermal transfer from the photovoltaic cell, and the overall performance of the nighttime solar cell is enhanced. In addition the photovoltaic cell is not influenced by the thermoelectric generator. The embodiment shown in FIG. 3 may also advantageously include a concentrating lens as previously described.
Referring next to FIG. 4 there is illustrated another embodiment of the present invention. In the embodiment illustrated the photovoltaic cell 30 includes n-type 14 and p-type 15 materials connected in series with n-type 14 and p-type 15 materials of the thermoelectric generator 10 to yield a series thermoelectric-photovoltaic device 9. In this particular embodiment the charge carrier collection capability, or the current flow, of the device is greatly improved.
Illustrated in FIG. 5 is still other embodiment of the present invention. The partial array 8 illustrated includes a pair of series thermoelectric-photovoltaic devices, heat transfer fins 41, and encapsulant 42. Heat transfer fins 41 are disposed in heat exchange relationship with junction surfaces 12 and the ambient air. During nighttime operation the heat transfer fins enhance the conduction of heat from the ambient air to the junction surfaces, and during daylight conditions the heat transfer fins improve the transfer of heat from the junction surfaces to the ambient air. Various heat transfer augmentation can be utilized such as forced air, water, another fluid, or a thermal source of waste heat for nighttime operation (e.g., a fluid heat exchanger, baffled heat exchanger, radiation shield, heat transfer composition) and forced air, water, another fluid, or a thermal sink for daytime operation, among others, and combinations thereof. Furthermore, the heat transfer augmentation can be disposed on junction surface 11 and/or 12, external to the cell, or internal to the cell, i.e. in thermal communication with the reduced pressure cell 13, 13', 13", junction surface 11, and/or junction surface 12. Furthermore, the h |