Efficient thermoelectric power generation

Abstract

A system and method for efficient thermoelectric power generation by combining natural gas as a thermal source with emitters, such as Silicon Carbide, highly-doped Silicon Carbide semiconductor material as cells, harvesting of electric power through in situ formation of Graphene Carbon, and semiconductor materials. The system is can yield orders of magnitude greater power efficiency over thermoelectric power generation units used in space travel, by practicing the invention, natural gas, such as the 288.7 billion cubic currently wasted by the environmental damaging practice of flaring off, can be converted into useful electricity for transport over low-cost transmission line infrastructure rather than possible future high-cost pipelines. Also, by practicing the invention, households can be provided with standby power, power during natural disasters, such as hurricanes, by converting available natural or propane gas rather relying on generators with single digit efficiency.

Claims

1. A system and method for highly efficient thermoelectric power generation yielding an efficiency of up to 75% and a process for manufacturing such systems by: 1) constructing cells with large length to narrow thickness ratios, such as approaching a 3000:1 aspect ratio; 2) supplying energy incident on the cells by a combustion of natural gas equal to the Earth's opacity spectrum that is filtered out and not available to terrestrial solar cells; 3) using hexagonal crystalline Silicon Carbide semiconductor materials as emitters of a spectrum of energy to create a 1:1 spectral matching as the energy is in turn incident on Silicon Carbide semiconductor material as cells; 4) providing heavy doped cells constructed from the subset of Silicon Carbide crystalline poly types that are hexagonal and arranged in an alternating “p” and “n” configuration; and 5) forming conductive surfaces on the anode hot surface and the cathode cold surface of the Silicon Carbide material cells by sublimation of the silicon to form the hexagonal crystalline carbon, Graphene, with Superconductive conductivity at room temperature at a chirality of 30 degrees, to connect multiple devices in series and in parallel cells that are in turn connected to a terminal to form a power supply.

2. The system, method, and process of claim 1 wherein the Silicon Carbide cells comprise 16 strips cut to form narrow cells from a 0.01-inch thick wafer and long cells with a 3-inch length to achieve a 1:3,000 aspect ratio.

3. The system, method, and process of claim 1 wherein the spectrum incident on the cells, constructed from Silicon Carbide of the same poly type as the emitter, is the infrared spectrum produced by heating of the emitter, to produce congruity of the emission and incident energy spectrums.

4. The system, method, and process of claim 1 wherein the cells are constructed from the subset of Silicon Carbide semiconductor that is crystalline of one of the poly-types that are hexagonal, 2H, 4H, 6H, 8H or 10H and preferably 4H and 6H arranged in an alternating “p” and “n” configuration, Silicon carbide as a semiconductor, which has been heavily doped: p-type by beryllium, boron, aluminum, or gallium and n-type by nitrogen or phosphorus.

5. The system, method, and process of claim 1 wherein conductive surfaces are formed on the anode hot surface, located adjacent to the flame at the bottom of the device, where p-type and n-type cells are electrically connected in parallel, and on the cathode cold surface, located at the top of the device, where p-type and n-type cells are each independently electrically connected in series, are hexagonal crystalline carbon, Graphene, formed by sublimation of the Silicon from Silicon Carbide that exhibits superconductive conductivity at room temperature at a chirality of 30 degrees allowing multiple devices to be electrically connected in series and in parallel cells that are in turn connected to a terminal to form a power supply.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It will be understood that these drawings depict only embodiments of the broader invention disclosed herein and are, therefore, not to be limiting of its scope.

[0029] The invention will be described and explained with additional specificity and detail through reference to the accompanying drawings in which:

[0030] FIG. 1 is a diagram of the geometry of two dissimilar materials required to practice

[0031] Seebeck's Effect to generate electric power directly;

[0032] FIG. 2 is a chart of the Seebeck Effect and associated electric properties of Metal,

[0033] Semiconductor material, and Heavy Doped Semiconductors;

[0034] FIG. 3 is a chart of the Spectrum of Solar Radiation on Earth;

[0035] FIG. 4 is a chart of the Spectrum from the Combustion of a Hydrocarbon;

[0036] FIG. 5 is a chart of the Spectrum of Silicon Carbide Radiated as a function of temperature;

[0037] FIG. 6 is a depiction of characteristics of Hexagonal Crystalline poly types of Silicon

[0038] Carbide in comparison to other indirect materials;

[0039] FIG. 7 is a depiction of the characteristics of poly types commercially available as Silicon

[0040] Carbide wafers; and

[0041] FIG. 8 provides perspective, top plan, and schematic views of an embodiment of the thermoelectric power generation system disclosed herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] The systems and methods for thermoelectric power generation disclosed herein are subject to a wide variety of embodiments. However, to ensure that one skilled in the art will be able to understand and, in appropriate cases, practice the present invention, certain preferred embodiments of the broader invention revealed herein are described below and shown in the accompanying drawing figures.

[0043] By way of further background, thermoelectric power generation dates to 1821 when Thomas Seebeck discovered that electric power is generated when two dissimilar metal rods are connected at hot ends thereof and electrically connected in parallel at cold ends thereof The present invention combines the replacement of solar energy with the energy of natural gas as a thermal source. In one aspect, photovoltaic cells with highly doped Silicon Carbide semiconductor material cells are sized to a highly favorable ratio, such as 1:3,000. Further, a coordination of thermally activated infrared energy spectrum optimizes the spectrum incident on the cells by constructing an emitter from the same poly type of Silicon Carbide as the cell. Harvesting of electric power can be achieved by in situ formation of Graphene Carbon and electric connection by materials that exhibit superconductive at room temperature.

[0044] Maximizing the Seebeck Coefficient. The first unexpected aspect of the present invention is that the merit of materials, such as can be measured by the Seebeck coefficient a in μV per degree Kelvin (also per degree Centigrade), can be the very desirable maximum when using only one semiconductor material and doping material as a p-type and the other n-type.

[0045] FIG. 1 diagrams the geometry of two dissimilar materials required to practice the Seebeck Effect to generate electric power directly. The present invention can utilize, for example, Silicon Carbide as a material with p-type doping to produce one of the dissimilar materials and n-type doping to produce the other dissimilar material. The n-type doping materials can, for example, be Nitrogen or Phosphorus, and p-type doping materials could, for instance, be Beryllium, Boron, Aluminum, or Gallium.

[0046] FIG. 2 shows the Seebeck Effect and associated electric properties of Metal, Semiconductor and Heavy Doped Semiconductors. Exemplary of the metals and metal compounds charted on the right portion of FIG. 2 with low Seebeck coefficients include the compound Lead Telluride that produces a low energy efficiency of seven and eight-tenths percent (7.8%). The present invention can exploit heavy doped semiconductors as charted in the center of FIG. 2 that have peak values of Seebeck coefficient greater than the values associated with either metals or semiconductors without doping. The result is that embodiments of the present invention using heavy doped Silicon Carbide are calculated to achieve 75% efficiency, an order of magnitude increase in power efficiency over that achieved by RTEs used in space.

[0047] Optimizing the Energy Spectrum Incident on the Thermoelectric Cell. A second unexpected aspect of the present invention is that the loss in Solar Spectrum that results from the absorption as it moves through the atmosphere is duplicated by the spectrum from the combustion of hydrocarbons and by impinging this combustion of hydrocarbon energy spectrum onto Silicon Carbide. An energy spectrum is emitted that is efficiently transmitted and received by the thermoelectric cells.

[0048] FIG. 3 shows the Spectrum of Solar Radiation on Earth. The Solar Spectrum that exists outside Earth is attenuated by the following components present in Earth's atmosphere: scattering due to air borne dust and aerosols; infrared absorption due to water vapor, Carbon Dioxide and Carbon Monoxide, and ultraviolet absorption due to ozone. The net effect is that the extraterrestrial spectrum's incident power density of 1,365 watts per square meter (W/m.sup.2) is reduced by 50% to an average incident power density over the surface of Earth of 691 W/m.sup.2 (0.07 W/cm.sup.2).

[0049] FIG. 4 shows the Spectrum from the Combustion of a Hydrocarbon. The table below the Spectrum identifies the peak discharges for the product of combustion. These products of combustion match up to the materials in the Earth's atmosphere that attenuate the solar spectrum. Below the Spectrum is a table that enumerates the materials and their associated characteristics. Among these materials are the primary Carbon compound, Carbon Dioxide (CO.sub.2) and Carbon Monoxide (CO) that occurs at a wavelength of 4.66 um with incident power of 120 W/cm.sup.2/um. By integrating the area under the spectrum curve for CO.sub.2/CO and comparing it to the solar spectrum, it is found that the Emission Power for this CO.sub.2/CO peak is 367 times the emission power for entire solar spectrum (25.7 W/cm.sup.2 versus the Sun's 0.07 W/cm.sup.2).

[0050] FIG. 5 shows the Spectrum of Silicon Carbide Radiated as a function of temperature. In embodiments of the present invention, the material of construction of the emitter and the cells are the same poly type of Silicon Carbide. As shown in FIG. 5, that spectrum emitted is uniform as to temperature over the infrared frequencies and varies in intensity as the temperature increases. Therefore, the spectrum of the Silicon Carbide serving as an emitter, albeit at a higher intensity associated with the higher temperature, with a uniform spectrum so that the spectrum put out by the emitter is equal to a favorable spectrum received by the cells.

[0051] Silicon Carbide Hexagonal Poly Types. A third unexpected aspect of embodiments of the present invention is that five poly types of Silicon Carbide, containing between 20 to 100% hexagonal crystalline, are of the same indirect character as Silicon (Si) and Gallium Arsenide (GaAs). Two of the poly types of Silicon Carbide are commercially available in wafer form at various diameters.

[0052] FIG. 6 shows some characteristics of Hexagonal Crystalline poly types of Silicon Carbide in comparison to other indirect materials. There are five poly types of Silicon Carbide that contain between 20% and 100% hexagonal crystalline structures: 2H, 4H, 6H, 8H and 10H. Of these, the commercially available poly types are 4H and 6 H Silicon Carbide. The characteristics of the poly types of Silicon Carbide 4H and 6H when compared to Silicon (Si) and Gallium Arsenide (GaAs) have superior ability to respond to infrared light with band gap in eV of 3.26 and 3.02 versus 1.12 and 1.43. Among the other more suitable characteristics for the present invention is that the poly types of Silicon Carbide 4H and 6H when compared to Silicon (Si) and Gallium Arsenide (GaAs) demonstrate thermal conductivity in W/cm K of 3.7 and 4.0 versus 1.5 and 0.5.

[0053] FIG. 7 shows the characteristics of poly types of commercially available Silicon Carbide wafers. The single crystalline wafer of Silicon Carbide, poly types 4H and 6H are available in 2, 3 and 4-inch diameter and 250 to 350 pm thickness. The preferred embodiment of the present invention is to use the 6H poly type, 4-inch diameter wafer at 250 μm (0.01 inch) thickness with a band gap of 3.02 eV and a thermal conductivity of 3.7 W/cm K. The desirable dimensional aspect ratio of 1:3,000 can, in certain practices, be obtained by cutting the 0.01-inch thick wafer into 3-inch strips.

[0054] In Situ Formation of the Cell's Conductive Surfaces. A fourth unexpected aspect of embodiments of the present invention is that conductive surfaces of hexagonal pattern Graphene, with superconductive electrical properties at ambient temperatures, can be grown by sublimation of Silicon from Silicon Carbide. In this regard, it is noted that Graphene has an excellent conductivity of 2.35×10.sup.3 Siemens per meter, at 3-degrees angle of chirality.

[0055] The Graphene is grown on the anode hot surface end of the cell and the cathode cold surface end of the Silicon Carbide cell by sublimation of the Silicon to form the hexagonal crystalline Graphene. Graphene, formed by sublimation of Silicon, has the requisite hexagonal crystalline structure onto which is patterned the hexagonal crystalline form of Silicon at locations where the Graphene is formed on the Silicon Carbide.

[0056] In one exemplary embodiment of the present invention, 16 pieces are cut from a heavy doped Silicon Carbide wafer, 0.001 inches thick and a 3-inch long strips of C-terminating 6H-SiC are cut with sufficient width to be a 22.5-degrees cord and are arranged to form a 2-inch diameter circle. The pieces can first be cleaned, such as with Acetone and Methanol, followed by dipping in Hydrofluoric acid. The pieces are then loaded into a Chemical Vapor Deposition (CVD) system. The CVD system can first be purged for two cycles with Hydrogen for 5 minutes at 200 Tone, followed by increasing the temperature to 1,200° C. in the hydrogen atmosphere for 30 minutes to accomplish etching. Finally, the temperature can be increased to 1,700° C. in an Argon atmosphere for thirty (30) minutes to accomplish sublimation of the Silicon. At the end of the Graphene growth cycle, the temperature of the CVD system is reduced to room temperature and purged with Argon before removal of the pieces.

[0057] A Preferred Embodiment. Almost 200 years have passed since heat was first directly converted into electricity by employing the thermoelectric effect. Twenty years thereafter, it was shown that this effect could be reversed to accomplish cooling. Over 100 years have passed since light was first directly converted into electricity by employing the photoelectric effect.

[0058] However, before devices that employ the thermoelectric and photoelectric effect can be competitive with and replace other methods of electric power generation, there must be appropriate materials (M) and best engineering techniques (BET) for utilizing these effects. The present invention provides M and BET solutions in a hybrid system based on both the thermoelectric effect and the photoelectric effect. The systems and methods disclosed herein elevate system efficiencies to multiple times that obtained by previous single-purpose systems that utilize either the thermoelectric effect or the photoelectric effect.

[0059] FIG. 8 shows the elements of a preferred embodiment of the present invention for highly efficient thermoelectric power generation. The high melting point of Silicon Carbide of 2730° C. is compatible with the 1,950° C. flame temperature of Natural Gas. Cells are formed from 16 strips of the 6H poly type of Silicon Carbide formed into a cylinder of 2-inch diameter. The strips are alternately doped as p-type and n-type. The cylinder is heated from the bottom by a Silicon Carbide emitter, such as an emitter of a 1.5-inch diameter and a 0.5-inch height. The 16-strips are electrically connected in series at their lower portions and connected p-type to p-type and n-type to n-type at their upper portions. The 2-inch cylinder is cooled by placing finned heat sinks along its long axis to cover the outer surface. This preferred embodiment of the present invention is designed to obtain a 1:3000 aspect ratio to take advantage of the preferred geometry of long and thin cells for generation of electricity by the Seebeck effect. The highly efficient thermoelectric power generation is calculated to achieve thermal efficiency of up to 75%.

[0060] With certain details and embodiments of the present invention for Highly Efficient Thermoelectric Power Generation disclosed, it will be appreciated by one skilled in the art that numerous changes and additions could be made thereto without deviating from the spirit or scope of the invention. This is particularly true when one bears in mind that the presently preferred embodiments merely exemplify the broader invention revealed herein. Accordingly, it will be clear that those with major features of the invention in mind could craft embodiments that incorporate those major features while not incorporating all the features included in the preferred embodiments.

[0061] Therefore, the claims that will ultimately be employed to protect this invention will define the scope of protection to be afforded to the inventor. Those claims shall be deemed to