Abstract:
A thermoelectric power generator includes a thermoelectric pile in a chamber. A window admits light and/or heat radiation such as solar radiation into the chamber, which is absorbed in a radiation absorbing body in thermal contact with a first side of the thermoelectric pile, whereby the temperature of the first side is raised. A second side of the thermoelectric pile is in thermal contact with the wall of the chamber, which is a heat sink to maintain the second side at a lower temperature. The temperature difference produces a voltage difference at electrical contacts to the thermoelectric pile, which is capable of powering electrical devices.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    This invention generally relates to energy conversion systems and methods and, more particularly, to a solar powered thermoelectric generator. 
         [0003]    2. Related Art 
         [0004]    In many industrial processes a considerable quantity of heat energy is generated that is discarded as an unused byproduct. Conventional methods for removing or eliminating this heat may be through evaporation or heat exchange, eventually to the environment. Discarded heat energy is a cost of production that contributes to production cost inefficiency and may be measured as a direct cost of energy. It would be desirable to recapture and use such wasted energy. 
         [0005]    Solar cells are a conventional source of electrical power in numerous applications, particularly where the cost of energy delivery or power requirement does not justify the investment in infrastructure. An example is a source of electrical power derived from sunlight in an at-sea application, where standard power generation is not available and power requirements may not justify conventional generation methods (i.e., oil or coal fired power generators). However, solar cells are responsive to a limited portion of the visible and near- infrared spectrum, whereas the solar spectrum reaching the surface of the earth is considerably broader. 
         [0006]    Therefore, there is a need for power generation from solar and other radiation sources that takes more advantage of an available radiation spectrum that is independent of fossil or other conventional energy sources. 
       SUMMARY 
       [0007]    The present invention applies the well-known principles of operation of thermoelectric devices to conversion of light and/or heat radiation energy for useful production of electrical power in a thermoelectric power generator (TPG). 
         [0008]    In one embodiment, a thermoelectric power generator includes a chamber having a thermoelectric pile contained within, where one surface of the pile is in physical and thermal contact with the inner surface of the chamber wall. A radiation absorbing body is in physical and thermal contact with an opposing surface of the thermoelectric pile. An optically transparent window enclosing the chamber on at least one face of the chamber admits radiation toward the radiation absorbing body, heating one side of the pile, thereby causing the pile to produce an electromotive force. Electrical wires connected to opposing terminals of the thermoelectric pile connect provide voltage and current to power the external device. 
         [0009]    In a second embodiment, the heat absorbing body of the thermoelectric power generator described may further include an internal cavity to hold a first heat absorbing fluid. 
         [0010]    In a third embodiment, the chamber wall of the thermoelectric power generator may further include an internal cavity in the chamber wall to hold a second heat absorbing fluid. 
         [0011]    In a fourth embodiment, either or both of the fluids may be circulated through access ports between their respective cavities and the exterior of the thermoelectric generator. 
         [0012]    In a fifth embodiment, the circulating fluids may be provided by external sources to maintain a temperature difference between opposing sides of the thermoelectric pile, thereby causing the thermoelectric generator to produce electrical power with or without radiation energy incident on the heat absorbing body. 
         [0013]    In a sixth embodiment, a thermoelectric generator includes a flotation device coupled to the generator to enable the generator to float on water. The thermoelectric generator further includes a weight coupled to the bottom portion of the chamber wall of the generator, and may be configured to conduct heat from the chamber wall to the water. 
         [0014]    In a seventh embodiment, a method of converting light radiation and heat to electricity includes a thermoelectric pile in a chamber receiving light radiation energy through a window on a radiation absorbing body in physical and thermal contact with one side of a thermoelectric pile and/or receiving heat energy from a fluid circulated to an internal cavity of the heat absorbing body. The thermoelectric pile, being in physical and thermal contact with the chamber wall, which is maintained at a lower temperature, generates an electromotive force to power an external device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates one example of a Seebeck Effect thermoelectric couple. 
           [0016]      FIG. 2  illustrates one example of a Seebeck Effect thermoelectric pile. 
           [0017]      FIG. 3A  is an exemplary graph illustrating the transmission characteristics of quartz (SiO 2 ). 
           [0018]      FIG. 3   b  is an exemplary graph illustrating the transmission characteristics of potassium bromide (KBr). 
           [0019]      FIG. 4  illustrates one embodiment of a thermoelectric power generator, in accordance with the present disclosure. 
           [0020]      FIG. 5  illustrates a second embodiment of a thermoelectric power generator, in accordance with the present disclosure. 
           [0021]      FIG. 6  illustrates a third embodiment of a thermoelectric power generator, in accordance with the present disclosure. 
           [0022]      FIG. 7  illustrates a fourth embodiment of a thermoelectric power generator, in accordance with the present disclosure. 
       
    
    
       [0023]    Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
       DETAILED DESCRIPTION 
       [0024]    The concept of thermoelectric generation is well known.  FIG. 1  illustrates a typical Seebeck Effect thermoelectric couple. A thermoelectric device  100  for electrical power generation usually involves using conventional thermoelectric couples  101 , i.e., pairs of P and N doped semiconductor “pellets”  110  and  120 , respectively, of materials such as, for example, bismuth/telluride. 
         [0025]    The performance of thermoelectric couple  101  is based on well known thermoelectric generation principles, commonly known as the Seebeck effect, which involves producing a current in a closed circuit of two dissimilar materials, i.e., N doped pellets  110  and P doped pellets  120 , forming two junctions, where one junction is held at a higher temperature (hot junction  130 ) than the other junction (cold junction  140 ). 
         [0026]    The elevated temperature at hot junction  130  drives electrons in N doped pellet  120  toward cold junction  140  and drives “holes” in P doped pellet  110  in the same direction, i.e., toward cold junction  140 . Since “holes” moving in one direction is equivalent to electrons moving in the opposite direction, the induced direction of charge movement, i.e., current, around a closed circuit is the same. Thus, a net voltage difference develops at the two terminals (+ and −) of couple  101 , which may be applied to an external load  150 . 
         [0027]    Thermopiles are generally rated to produce a maximum current at a given voltage for a known temperature difference T 2 -T 1 . Terminal wires connected to the thermopile may be connected to provide an effective amount of voltage and current to electrical load  150  at its stated ratings, which may be, for example, a motor, lamp or other direct current (DC) electrical load, a battery for charging and storing electrical energy, or a converter for generation of alternating current (AC) to supply devices so adapted to operate. Other types of electrical load  150  may also be employed. 
         [0028]    A corresponding Peltier effect is the inverse of the Seebeck effect. The Peltier effect involves the heating or cooling of the thermocouple junctions by a driving current from an external source. 
         [0029]      FIG. 2  shows a thermoelectric pile  200 , which comprises a plurality of couples  101  connected electrically in series and thermally in parallel. Connecting couples  101  in series electrically results in producing a larger net additive voltage. Connecting them in parallel contact between a temperature differential assures a uniformity and maximum thermal differential across each couple  101 , resulting in the largest voltage difference per couple  101 . In combining the couples into thermopiles  200 , a greater variety of sizes, shapes, operating currents, operating voltages, and ranges of voltage and current generating capacity becomes available between the two terminals (+ and −). 
         [0030]    In various embodiments presented below, the heat source for the thermoelectric generation may be any heat source, including any generated, excess, wasted, and/or recyclable heat source, and including solar energy. It may be advantageous to contain thermopile  200  in a chamber with a window for admitting light and heat radiation to be absorbed by hot junction  130 . A window material may be chosen for its efficient transparency to a broad range of light wave radiation. For example, FIG.  3 A is a graph of a transmission efficiency of quartz (SiO 2 ), which is effective over wavelengths from approximately 200 nanometers to approximately 3 micrometers. Potassium bromide (KBr) transmission, shown in  FIG. 3B , is effective from approximately 250 nanometers to approximately 25 micrometers. Numerous other materials exhibit similar transparency over a useful range of wavelengths. 
         [0031]      FIG. 4  illustrates an embodiment of a thermoelectric power generator  400  according to the present disclosure. The radiation source, for example, may be the sun. In one embodiment, thermoelectric pile  200  is mounted in a chamber  401  including a window  410  to permit sunlight or other radiation  405  to pass through. In one embodiment, the transparency of the window spans as broad a wavelength spectrum as possible to admit a maximum amount of energy to pass, but typically includes the range from ultraviolet to infrared. 
         [0032]    A portion of thermopile  200  facing window  410  through which radiation  405  enters is in intimate contact with a heat absorbing body  420  composed of or coated with a material that efficiently absorbs radiation  405 . The absorbed energy in heating body  420  establishes an elevated temperature on the contacting portion of thermopile  200 . 
         [0033]    The opposing side of thermopile  200  is in intimate physical contact with a bottom wall  402  of chamber  401  to enable thermal contact. The bottom and sides walls of chamber  401  are preferably highly thermally conductive and in intimate physical and thermal contact with each other or they may comprise a unitary structure, and which serve substantially as a heat sink at a lower temperature than heat absorbing body  420 . Chamber  401  may be configured to serve as a passive heat sink, whereby the outer walls  402  of chamber  401  are in intimate contact with other structures and materials adapted to passively or actively conduct heat away or otherwise maintain a temperature that is lower than that of absorbing body  420 . 
         [0034]    For example, in a space-borne application, chamber  401  may be attached to radiative fins (not shown) that are shielded and facing away from direct exposure to the sun. The fins may then substantially radiate any accumulated energy to the vacuum of space, maintaining a thermodynamic equilibrium with the surrounding space, i.e., at a lower temperature. In an ambient application, a similar structure would establish equilibrium with the atmospheric temperature through radiative and conductive heat transfer using, for example, fins or similar structures adapted for efficient heat rejection. 
         [0035]    Chamber  401  may be evacuated with a vacuum pump (not shown) to reduce convective transfer of heat from absorbing body  420  to chamber walls  402 , thereby maintaining the maximum thermal differential between absorbing body  420  and heat sinking chamber walls  402 . This, in turn, provides a maximum thermal differential between the two opposing sides of thermopile  200 , and consequently, a maximum voltage difference generation. In a space-borne application, this is particularly beneficial, since no energy need be expended to produce a relative vacuum in the chamber, thereby being totally passive. 
         [0036]      FIG. 5  illustrates another embodiment of a thermoelectric power generator  500 , wherein fluids  504  heated in absorbing body  420  may be circulated out of chamber  401  for one or more purposes, as will now be described. Excess heat generated by other processes, such as manufacturing, may be circulated to pass through heat absorbing body  420  via fluids  504  to elevate or maintain its temperature. Thus, heat energy from other sources that may otherwise be wasted, may be recycled to assist or provide for thermoelectric power generation. Reciprocally, since it may be advantageous to maintain the temperature differential across thermopile  200  at a fixed value, and at a fixed absolute temperature, circulation of fluid  504  may be used to remove excess heat in order to limit the maximum temperature of heat absorbing body  420 . 
         [0037]    Furthermore, a cold fluid  506  at a lower temperature (i.e., heat sink fluid) may be circulated out of the body of chamber  401  to maintain cold junction  140  at a selected temperature lower than hot junction  130 . For example, both hot fluid  504  and cold fluid  506  may be circulated to mediate and maintain a stable temperature differential between heat absorbing body  420  and heat sink/chamber wall  402 , thus assuring a constant voltage potential difference, since this differential is directly dependent on temperature differential. Alternatively, or in combination with this mediating function, the fluid  504  and cold fluid  506  may be coupled to an external system whereby excess heat generated in thermoelectric power generator  500  is used to perform additional non-electrical work such as, for example, environmental heating or cooling, that would otherwise be wasted in overheating generator  500 . Thus, additional work may be extracted from generator  500  in addition to electrical power. 
         [0038]      FIG. 6  illustrates an embodiment of a thermoelectric power generator  600  in which a heat absorbing body  620  may further include fins or a complex surface facing a window  610  to increase the surface area exposed to radiation  405 , thereby making it a more efficient absorber. Additionally, the surface fins or other structures may be configured to improve the omni-directional efficiency for absorption of radiation. Absorbing body  620  may further include an inner chamber  625  filled with a fluid or it may be, alternatively, a substantially solid body. In either case, heat absorbing body  620  may comprise one or more materials (solid and/or fluid) with a large thermal capacity, whereby the large thermal mass enables large heat storage—in effect a thermal heat battery, in analogy to an electric battery—resulting in a more stable temperature and consequently more stable voltage and power output by generator  600 . The large thermal mass of absorbing body  620  may, by analogy to an electric battery, provide continued power generation by generator  600  when radiation  405  is absent or insufficient. 
         [0039]    Window  610  may be of various shapes such as, for example, a bell jar, to accommodate the more complex structure of absorbing body  620 , thereby requiring a variation in the detailed shape of chamber  601  and the chamber walls  602  which serve a heat sink function for cold junction  140 . As described before, generator  600  may be coupled to a vacuum pump to evacuate chamber  601  to minimize thermal convective loss of heat energy from heat absorbing body through any path other than thermoelectric pile  200 . Chamber wall  602  may provide the heat sinking function, as described earlier, and may be in intimate contact with additional external heat transfer and rejection structures (not shown), as described earlier. Chamber wall  602  may also include a fluid circulating system to remove excess heat, as described earlier, to maintain a stable temperature differential between opposing sides of thermoelectric pile  200 , thereby maintaining stable voltage and power characteristics. 
         [0040]      FIG. 7  illustrates another embodiment of a thermoelectric power generator  700 , which may be configured for supplying power in a water-borne application. Here, the water, which may be ocean, lake, river, or any body of water, is in contact with chamber wall  702 . Generator  700  may further include a floatation device  703  to insure buoyancy of generator  700 . Chamber wall  702  may further include an additional weight  704  that simultaneously may provide vertical orientation control by establishing a center-of-gravity of generator  700  below a mid-line  703   a  of floatation device  703 . Weight  704  may also be adapted to provide additional surface area and thermal mass for conducting excess heat to the water from cold junction  140 , in order to maintain the thermal differential across thermoelectric pile  200  for electrical operational stability. Chamber  701  may be evacuated, as previously described, to increase thermodynamic efficiency. 
         [0041]    The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. For example, it will thus be obvious to those skilled in the art that various changes and modifications may be made without departing from this invention in its broader aspects. Therefore, the appended claims encompass all such changes and modifications as fall within the true spirit and scope of this invention.