Abstract:
Inexpensive, lightweight, flexible heating and cooling panels with highly distributed thermoelectric elements are provided. A thermoelectric “string” is described that may be woven or assembled into a variety of insulating panels such as seat cushions, mattresses, pillows, blankets, ceiling tiles, office partitions, under-desk panels, electronic enclosures, building walls, refrigerator walls, and heat conversion panels. The string contains spaced thermoelectric elements which are thermally and electrically connected to lengths of braided, meshed, stranded, foamed, or otherwise expandable and compressible conductor. The elements and a portion of compacted conductor are mounted within the insulating panel On the outsides of the panel, the conductor is expanded to provide a very large surface area of contact with air or other medium for heat absorption on the cold side and for heat dissipation on the hot side.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/101,015, filed May 4, 2011, which claims priority from U.S. Provisional Application Ser. No. 61/403,217, filed Sep. 13, 2010; U.S. Provisional Application Ser. No. 61/417,380, filed Nov. 26, 2010, U.S. Provisional Application Ser. No. 61/433,489, filed Jan. 17, 2011, and from U.S. Provisional Application Ser. No. 61/470,039 filed Mar. 31, 2011, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
     Cooling and Heating  
       [0002]    Thermoelectric modules typically contain densely packed elements spaced apart by 1-3 mm. Up to 256 such elements are connected in an array that is 2×2 inches (5.08×5.08 cm) in area. When these modules are deployed, large and heavy heat sinks and powerful fans are required to dissipate or absorb the heat on each side. The reasons for these dense prior art configurations are well-founded: small elements with low resistance allow larger current I to flow before the resistive heat (I 2 R) generated destroys the thermoelectric cooling (pI1 where p=Peltier coefficient). The use of short elements for maximum cooling capacity results in the hot and cold side circuit boards being close together. This proximity results in the high density. 
         [0003]    To achieve a low density packing of thermoelectric elements, one could space out these elements on the boards laterally, but then the backflow of heat conducted and radiated through the air between the elements limits the overall performance. Some designs require evacuating the module interior to reduce heat backflow due to air conduction, but vacuum cavities require expensive materials and are prone to leaks. Vacuum materials (like glass and Kovar™) are also hard and easily broken when thin enough to limit their own backflow of heat. Broken glass can lead to safety issues when these modules are used in seat cushions, automobiles, and other environments. 
         [0004]    Another problem in spreading out thermoelectric elements is that the rigid connection of elements over large distances causes them to rupture due to sheer stress upon thermal expansion of the hot side relative to the cold side. To solve this problem, other designs have been proposed that use a flexible plastic such as polyimide for the circuit boards, but these materials are too porous to maintain a vacuum. 
         [0005]    Another disadvantage of the prior art design of thermoelectric modules is that the high density of heat moved to the hot side results in a temperature gradient through the heat sink, and this temperature delta subtracts from the overall cooling that the module can achieve. In particular, traditional thermoelectric products are not able to reach true refrigeration temperature because of this temperature gradient. 
         [0006]    Finally, because prior art thermoelectric modules are placed in a solder reflow oven during assembly, only high-temperature materials may be used. Unfortunately, many desired uses of cooling and heating involve close or direct contact with the human body, for which soft materials, such as cushions, cloths, and flexible foam are preferred, but these materials cannot withstand the high temperatures of a solder reflow oven. 
         [0007]    Thermoelectric devices can be as efficient, or even more efficient, than vapor compression cooling systems when the temperature delta is 10 degrees C. or less. For this reason, a strong desire exists to deploy thermoelectric technology for local heating and cooling of occupied spaces and thereby reduce the overall energy consumption needed for personal comfort. The total energy savings of the central A/C or heating system plus the local thermoelectric systems can be 30% or more for such a combination, but the unwieldy implementation of prior-art thermoelectric modules inhibits their use for this purpose. 
         [0008]    Hence, the need exists for a variety of insulating panels to be safely and comfortably improved with thermoelectric capability, such as seat cushions, mattresses, pillows, blankets, ceiling tiles, office/residence walls or partitions, under-desk panels, electronic enclosures, building walls, solar panels, refrigerator walls, freezer walls within refrigerators, or crisper walls within refrigerators. 
       BACKGROUND 
     Power Generation 
       [0009]    Devices that generate electricity from renewable sources all have limitations. The ideal power generation technology supplies power 24 hours per day, is low cost, and uses only energy from renewable sources, such as wind, tidal and wave, sunlight, or geothermal pools. The two most common forms of utility-scale renewable power generation are wind turbines and photovoltaic systems. 
         [0010]    Photovoltaic (PV) technology has the following limitations: (1) high cost, (2) generates power only when the sun is shining brightly which is less than 33% of the time, (3) introduces transients into the electrical grid when clouds suddenly block the sun, and (4) low efficiency without concentration or dangerous temperatures and light levels with concentration. 
         [0011]    Wind turbines have the following limitations: (1) relatively high cost, (2) generates power only when the wind is blowing which is less than 33% of the time on average, (3) introduces transients into the electrical grid when the wind suddenly stops or changes direction, (4) requires very tall and visually unacceptable structures, (5) generates noise, (6) has a random peak capacity time during the day that rarely matches the peak demand time, and (7) has very low land usage at about 4 Kwatts per acre. 
         [0012]    Both PV and wind turbines may be supplemented with large batteries to store energy for periods of time when the renewable source is not available, but such storage is very expensive at about $1000 per Kwatt hour. When combined with battery storage to achieve 100% renewable generation, the cost for a renewable PV or wind turbine plant is around $20 per watt, vs. about $10 per watt for a fossil fuel pant including 10 years of fuel costs. 
         [0013]    Tidal and wave energy installations require high capital startup costs, and like wind turbines, suffer from variable output and may be usually unacceptable structures if erected near shorelines. 
         [0014]    Hence, the need exists for a low-cost electrical power generation capability that can supply power 24 hours per day, 7 days per week, and 365 days per year and only tap renewable energy sources. One preferred embodiment of the invention thermoelectric string and associated panel described herein can accomplish these goals. 
       SUMMARY OF THE INVENTION 
       [0015]    Broadly speaking, this invention makes possible thermoelectric capability for a variety of panel materials and enables local/personal heating and cooling that reduces overall energy consumption. In one aspect this invention provides a thermoelectric string that can be woven or inserted into a variety of such panels, including soft and low-temperature panels. In another aspect, this invention also eliminates the need for a large, bulky, heavy, and expensive heat sinks and fans to dissipate heating and cooling. In one aspect this invention combines hardware that moves electrical current with hardware that dissipates thermal energy, thereby saving cost over embodiments such as U.S. Pat. No. 3,196,524. In another aspect this invention provides a common set of hardware to provide low thermal back flow near the thermoelectric elements and simultaneously provide high thermal conduction to ambient air away from the elements. In one embodiment this invention provides a thermoelectric string that can be routed through small holes in the panel to minimize thermal leakage. In another embodiment this invention eliminates the need for vacuum enclosures such as U.S. Pat. No. 3,225,549 of highly-distributed thermoelectric elements and also eliminate the need for wicking fluids such as U.S. 2010/0107657. In a particularly preferred embodiment this invention provides cooling capability and electricity generation for pennies per watt in manufacturing cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Features and advantages of the present invention will be seen from the following detailed description taken into conjunction with the accompanying drawings wherein like numerals depict like parts, and wherein: 
           [0017]      FIG. 1  is a string showing the thermoelectric elements connected by lengths of braided wire; 
           [0018]      FIGS. 2   a  and  2   b  illustrate a method of assembling the thermoelectric elements on strain reliefs using a standard circuit board manufacturing process; 
           [0019]      FIGS. 3   a ,  3   b ,  3   c  and  3   d  illustrate how the braid of  FIG. 1  is woven into an insulating panel; 
           [0020]      FIGS. 4   a  and  4   b  illustrate how multiple layers of panels as described in  FIGS. 3   a - 3   d  can be cascaded in order to more efficiently achieve a high temperature difference; 
           [0021]      FIG. 5  illustrates how multiple metal materials can serve as an expandable heat sink or heat absorber; 
           [0022]      FIG. 6  illustrates a more exhaustive list of possible expandable metals; 
           [0023]      FIGS. 7   a ,  7   b ,  7   c  and  7   d  illustrate one way that the invention was reduced to practice and cooling performance was measured and compared to the prior art; 
           [0024]      FIG. 8  illustrates, without limitation, many of the applications for the panel of  FIGS. 3   a - 3   d  or  FIGS. 4   a  and  4   b  for heating and cooling functionality, and 
           [0025]      FIG. 9  illustrates one application for the panel of  FIGS. 3   a - 3   d  or  FIGS. 4   a  and  4   b  for generating electricity from a heat storage medium heated by the sun. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    A preferred embodiment of this invention includes a string containing alternating P-type  102  and N-Type  103  thermoelectric elements connected by lengths of braided or stranded wire  101  as shown in  FIG. 1 . The thermoelectric elements preferably comprise metals, although non-metallic conductors such as graphite and carbon may be used. In one embodiment, the alternating elements can be small crystals of, e.g. Bismuth Telluride (N-type)  103  and, e.g. Antimony Bismuth Telluride (P-type)  102 , possibly plated with, e.g. Nickel and/or Tin on the ends to facilitate solder connections  104  or  105 , or can be small thermo-tunneling vacuum tubes. Because the thermoelectric elements or tubes may be fragile, a “strain relief”, made of a stiff material  106  like FR4 combined with copper  107  and solder  104  or  105  bonds prevents a pulling force on the wire from breaking the elements or vacuum tubes. The aggregate diameter of the stranded or braided wire is designed to carry the desired electrical current with minimal resistance. 
         [0027]      FIG. 2  shows how subassemblies of this thermoelectric string might be fabricated using standard circuit board assembly techniques and machinery. A large FR4 circuit board  202  is patterned with the copper pads  107  of the strain reliefs  106  of  FIG. 1 . A packed arrangement is used to assemble the pellets  102  and  103  or tubes  203  and  204  onto the board. An assembly robot can place the thermoelectric elements or tubes and place solder paste  104  at the appropriate joints. The whole assembly is run through an oven to flow the solder and then cooled to harden the solder joints. Once assembly is completed, the strain relief assemblies are cut out along the cut lines  201  to leave the thermoelectric elements mounted on the strain relief  106 . 
         [0028]    The lower portion of  FIG. 2  shows how the invention can also apply to the latest advanced thermo-tunneling devices. Such devices are more efficient, but require packaging in a vacuum tube. These small vacuum tubes can substitute for the thermoelectric elements  102  and  103  of  FIG. 1  and can also benefit greatly from the strain reliefs  106  of  FIG. 1  and  FIG. 2 . Since a useful vacuum package must have a thin glass wall to minimize thermal conduction, it will also likely be very fragile. 
         [0029]    The thermoelectric elements of  FIG. 1  alternate between N-type  103  and P-type  102  in order to move heat in the same direction while the current flows back and forth along the string woven into a panel  301  as shown in  FIG. 3 . One purpose of compacting the wire strands in the string of  FIG. 1  is to be able to route the string through small-diameter holes  302  in the panel. The hole diameter should be small to minimize thermal leakage that compromise the insulating capability of the panel material. Another purpose of compacting the wires near the elements is to minimize the area for heat to backflow from the hot side of the element to the cold side of the element. The string may be woven into the panel  301  in an alternating fashion as illustrated in  FIG. 3   a  and  FIG. 3   b . Or, the N-type and P-type elements may be paired together to allow the string to be pushed though the holes  302  from one side as illustrated in  FIG. 3   c  and  FIG. 3   d . The single sided approach in  FIGS. 3   c  and  3   d  facilitates manufacture of the panel from one side rather than having to work with both sides as in  FIGS. 3   a  and  3   b.    
         [0030]    Another embodiment is when the compacted portions  303  of the string within the panel holes of  FIG. 3  are replaced with solid cylinders made of copper or similar metal and these cylinders are attached to the thermoelectric element on one end and the expanded wire  101  on the other end. This approach would facilitate robotic placement of the cylinders and elements in the holes in an electronic assembly operation. 
         [0031]    Yet another embodiment is to weave or assemble the string into a mold instead of the panel of  FIG. 3 , then injection-mold the panel material into the mold. Upon removal of the mold, a similar configuration to  FIG. 3  is obtained. 
         [0032]    In the embodiment of  FIG. 3 , the thermoelectric elements or tubes are spaced apart over a larger area vs. prior art modules, but the hot and cold sides are also separated by a length much longer than the elements. Since heat backflow conduction is proportional to area/length, scaling both simultaneously maintains a similar overall heat backflow as prior art thermoelectric modules. Since many desirable insulating panels like Styrofoam™, cloth, etc. have thermal conductivities comparable to air, the conduction ability of the invention&#39;s panel is comparable to that of the air cavity in prior art modules. In addition, the presence of the opaque panel blocks heat backflow from radiation almost entirely. 
         [0033]    Once woven or placed, the exterior metal  101  in  FIG. 3  is expanded, if necessary, on the hot and cold sides of the panel in order to maximize the exposure of the metal to air, which in turn maximizes its heat sinking or absorbing capability in either a natural or forced-air convection environment. 
         [0034]    A key element of this invention over the prior art is re-optimizing the heat sinks for natural convection vs. the forced-air convection. With the prior art forced-air convection systems, usually based on a fan, the forced air is moving in one direction only. Hence, the optimal heat sink is a metal plate for spreading the heat and linear metal “fins” for distributing the heat along the direction of the forced air. So, in prior-art forced air systems, the optimal heat sink maximizes the area touching air along the airflow, as represented by the parallel fins commonly used. 
         [0035]    For a natural convection environment, the air flow velocity is much less than with a fan, but the air has the ability to move in all directions. Hence, the optimal heat sink for a natural convection environment is one that maximizes the area touching air in any direction. 
         [0036]    In this preferred embodiment, re-optimizing the heat sink for natural convection brings about the following advantages: (1) better uniformity of the absorption of heat on the cold side and of the dissipation of heat on the hot side, (2) silent operation by eliminating the need for a fan, (3) much less total metal required, (4) more reliable because fans are prone to failure, (5) more efficient because the temperature change across the heat sink can be recovered to provide better additional cooling. 
         [0037]    A typical prior-art thermoelectric module deployment has a heat sink with fins that are typically 2 mm thick. Because two surfaces of the fin are exposed to air, the total cross section perimeter of exposure is 4 mm for each thermoelectric element. In the preferred embodiment of this invention, the aggregate diameter d of the compacted wire is 1 mm. However, when the strands are spaced apart on the hot or cold side as shown in  FIGS. 3   a - 3   d , the total cross section perimeter exposed to air is now Nπ(d/N/ 1/2 ) where N is the number of strands and d is the aggregate diameter. As stranded wire is easily available with 100-400 strands, then total cross section exposed to air for the invention is 31.4-62.8 mm, more than seven times the exposed cross section for prior art devices. Because of this larger cross section of exposure, the heat dissipation and absorption capacity of the invention can be, depending on geometric parameters, sufficient to eliminate the need for a fan as well as a rigid heat sink and rely instead only on natural convection. In addition, the larger amount of area touching air by the use of strands reduces the total amount of metal required for heat dissipation, facilitating lightweight, soft, and wearable panels. 
         [0038]    Furthermore, the number of strands in  FIGS. 3   a - 3   d  may be increased almost arbitrarily while the diameter of each strand is proportionately decreased. As above discussed, more strands leads to increased heat absorption and dissipation by factor N 1/2  with natural convection. Thinner strands also allows for the heat sink of the invention to be soft, lightweight, and flexible in contrast to rigid, hard, and heavy heat sinks of the prior art. Wire braid of tinned copper with 72-400 strands is typically used in the electronics industry, and such braid is designed to be expandable in order to serve as shielding of cables of varying diameter. Each strand in these braids is AWG 36 or about ˜100 microns in diameter. Another type of braid, wick-braided copper, is used to remove solder and its strands are even thinner, making possible a very soft device for dissipating heat and carrying electrical current in a thermoelectric panel when the strands are spread apart. Copper mesh is also readily available with even thinner strands of 44 AWG and spread out in 140 strands per inch when fully expanded. 
         [0039]    Without limitation, the panel  301  in  FIGS. 3   a - 3   d  may be Styrofoam™ (polystyrene foam), natural cloth, synthetic cloth, natural sponge, synthetic sponge, polyurethane, fiberglass, foam glass, building insulation material, wood, paper, cotton, batting, pipe-wrapping insulation, ceiling tile material, memory foam, cushion material, or any other insulating material. 
         [0040]    In some cases, it is desirable to have multi-stage thermoelectric cooling and heating. Higher temperature deltas are achievable. Prior art modules often are stacked with 2 to 4 stages to achieve the very low temperatures needed for sensitive imaging cameras. The same multi-staging is possible with this invention and provides similar benefits, as illustrated in  FIGS. 4   a  and  4   b . Here, two panels  301  are connected thermally in between by thermal connectors  400  that have high thermal conduction and electrical isolation. The thermal connectors may contain copper solder pads  401  and an electrically insulating layer like polyimide  402 . In this configuration, the polyimide layer  402  is so thin that its thermal conduction is high. Without limitation, the electrical insulator could be FR-4, Kapton (polyimide), Teflon (polytetra-fluoroethylene), an insulated metal substrate circuit board, aluminum oxide or any other readily available material. The multi-stage configuration may be applied to the alternating weave as shown in  FIG. 4   a  or to the single-sided weave as shown in  FIG. 4   b . The thermoelectric elements are shown as pellets  102  and  103  but could also be thermo-tunneling tubes  203  and  204  shown in  FIGS. 2   a - 2   b  and  3   a - 3   d.    
         [0041]      FIG. 5  shows several different types of expandable metal conductors that may replace the braid  101  in  FIGS. 1 ,  3   a - 3   d  and  4 . Copper mesh is available in an oriented form  501  or un-oriented form  502  and either provides strands with high contact area to air. Metal tinsel  503  has a thick central wire which is convenient for moving electricity from one thermoelectric element to the other plus many branches of thin copper strands which are convenient for dissipating or absorbing heat to or from the air. Flat braid  504  is also available with or without solder joints on either end. A panel made with one or a combination of these expanded metals  505  becomes a fully functional thermoelectric panel. 
         [0042]      FIG. 6  shows even more possibilities for expanded or expandable metals, including another type of un-oriented copper mesh  601 , copper strands weaved like rope  603 , coaxially grouped strands  604 , copper foam  605 , or loose copper strands  606 . For the metal screen or mesh, the metal may be compacted by rolling tightly or folding tightly in an accordion shape near the thermoelectric elements, and loosening the roll or the folds away from the thermoelectric elements. 
         [0043]    The thermoelectric panels described can also be deployed for generating electricity from heat. When heat is applied to one side, a Seebeck voltage is generated that can be used for electrical power. The heat source can be a selective surface receiving sunlight, a road or highway surface, geothermal heat, engine heat, smokestack heat, body heat, waste heat, and many other possibilities. 
       EXAMPLE 1 
     A Thermoelectric Cooler Using Invention 
       [0044]      FIGS. 7   a - 7   c  illustrate a thermoelectric cooler  701  using the invention. Four thermoelectric panels  505  were built using a string as shown in  FIG. 1  with braid  101  lengths 7 and 11 cm for the cold and hot sides, respectively. The panels were 1-inch (2.54 cm) thick Styrofoam™  301  with 3 mm diameter holes and a pellet spacing of 3 cm. A total of 256 pellets were inserted into the four populated panels. The four thermoelectric panels were combined with two plain Styrofoam™ panels to construct a small cooler. The invention cooler  701  in  FIG. 7   a  did not contain a heat sink or a fan and was powered with 20 watts of electricity. 
         [0045]    The invention prototype of  FIG. 7   a  was compared with a prior art commercial cooler  702  that contains a prior art thermoelectric module  704  also with 256 pellets, a prior art heat sink  706 , and a prior art fan  705 . This commercial cooler was powered as designed with 40 watts of electricity. 
         [0046]      FIG. 7   d  shows the data taken during an experiment to compare the invention cooler with the prior art commercial cooler. The two key measures of performance for such a cooler are (1) the rate of cool-down for a room-temperature cup of water  703  and (2) the minimum temperature reached by the air inside each cooler. The graph  707  in  FIG. 7   d  plots the temperature of on the Y-axis and the elapsed time in minutes on the X-axis. 
         [0047]    The experiment revealed that the cooling-down rate for the cup of water, indicated by the slope of the line  709  and  711  for the invention, was comparable to the cooling-down rate of the prior art commercial cooler, indicated by the slope of  710 . In addition, the minimum temperature of the air inside the box reached 5.5 degrees C. for both the invention cooler as indicated by line  713  and for the prior art cooler  712 . 
         [0048]    The data in  FIG. 7   d  indicates that the invention performs as well as the prior art commercial cooler in cooling. However, the invention only required 20 watts of power vs. 40 watts for the prior art commercial cooler. Hence, the invention achieved the comparable performance with significantly greater efficiency. The greater efficiency is due to the following: (1) not needing the electrical power for a fan, (2) recovering much of the temperature drop across the heat sink, and (3) better distribution of the cooling over the walls of the container. 
         [0049]    The thermoelectric panels of the invention illustrated in  FIG. 3  and  FIGS. 4   a  and  4   b  are generalized insulating panels with the ability to cool or heat one side relative to the other. These generalized panels may be manufactured using a similar process and with similar machines and then deployed in a plurality of applications. Without exception, some of these applications are illustrated in  FIG. 8 . 
         [0050]    In order to save overall energy or achieve greater individual comfort in cooling or heating the human body, one advantageous technique is to allow for local heating or cooling relative, the environment. For example, the thermoelectric panel of the present invention may be placed around the cavity under a desk  805  as illustrated in  FIG. 8  to provide local comfort for an office worker with significant energy savings. Or, the panel could be placed in an office chair  804  in the seat bottom or the seat back or both. In a vehicle, the panels may be placed in the seat bottom or seat back of a car seat  803 . For sleeping, these panels may be placed in an electric blanket  813  combined with a thermostatic controller to maintain a desired under-blanket sleep temperature. The control electronics for the blanket can automatically switch the electrical current in the proper direction when cooling is needed to achieve the set temperature or when heating is needed. Without limitation, such thermostatic control can be applied to any of the applications of the invention including all of those illustrated in  FIG. 8 . 
         [0051]    For individuals that must wear helmets, the body heat confined inside the helmet can be uncomfortable. Or, the helmet may not provide sufficient warmth when worn in cold environments that require head protection. The thermoelectric panel of the present invention may be molded into the proper shape to add cooling and heating capability to helmets of all types, including motorcycle or bicycle  808 , military  810 , or hard hats  809  for construction sites. 
         [0052]    Similarly, the invention panel may be shaped and used to make clothing like vests  816  or, without limitation, other types of clothing such as coats, pants, pant legs, and shirts. 
         [0053]    The thermoelectric panel of the present invention also can be used to cool food and drinks or other objects. These panels can be deployed as the wall, door, back, or top of a wine chiller  806  or a camping cooler  801  and  802 . Because the panel and string can be flexible  812  in  FIG. 8 , it can be wrapped around shaped objects like water pitchers, beer or other mug or bottles, coffee drinks, milk or cream bottles or cartons, etc. 
         [0054]    The thermoelectric panel of the present invention also may be deployed to heat or cool buffet trays  807  shown in  FIG. 8  for self-serve restaurants, cafeterias, or catering services. The prior art uses ice to cool the trays and boiling water to heat them. The supply of ice and hot water must be maintained and the reservoir under the trays must be replenished periodically. The present invention provides benefits over the prior art by heating or cooling the trays electrically and not requiring cold and hot supplies. 
         [0055]    The thermoelectric panel of the present invention also may be deployed in residences and buildings, A portion of a wall or window or floor  815  may be replaced by the panel of the present invention and provide heating or cooling for room. The ceiling tiles  815  in buildings also may be replaced by the panels of the present invention to provide heating and cooling for the space underneath the ceiling. The panel of the present invention also may be employed in combination with central compressor-based air conditioning systems to eliminate the need for forced air that can carry germs and smells from one room to another. In this case, the panels of the present invention would be mounted along plenums with the hot side facing into the plenum. The cool air from the compressor-based HVAC system would carry the heat away from the hot side while the cold side of the panel removes heat from the room. In this case, the room is cooled without forced air. 
         [0056]    In another aspect, the invention, provides renewable electrical power from the sun&#39;s radiation in well-suited climates. A second purpose is to continue providing energy when the sun is not shining and all night long. A third purpose is to improve the land utilization as measured in Kwatts/acre to many times higher than a wind turbine farm. A fourth purpose is to provide peak power capacity at a time of day that better matches the typical peak demand time for electricity. A fifth purpose of this invention is to use inert and non-toxic materials to store the energy of the sun in the form of heat. A sixth purpose is to provide these capabilities at a cost per watt that is a fraction of the cost (including fuel costs) of a traditional power plant and an even smaller fraction of the cost per watt of a PV or wind turbine plant (including battery storage costs). As discussed below, the invention demonstrates better performance over prior art implementations that do not have energy storage such as U.S. Pat. No. 3,088,989, by additionally distributing the thermoelectric elements to match the heat distribution from un-concentrated sunlight and remove the need for metal heat spreaders. 
         [0057]    An embodiment of the invention is illustrated in  FIG. 9 . An insulating material  903  that is largely transparent to the sun&#39;s radiation surrounds heat storage medium  905 . The insulating material  903  also prevents the heat from escaping when the sun  907  is not shining. The insulating material may be, without limitation, bubble wrap, glass or Plexiglas sealing in air or air pockets, or any of the materials used for solar covers for swimming pools. A selective surface layer or coating  904  of the heat storage medium is designed to absorb radiation from the sun and prevent radiative re-emission of absorbed heat. This selective surface layer or coating  904  may be constructed, without limitation, from, e.g. an oxide of copper, aluminum, or iron, from carbon, steel or a combination or alloy of these, black paint, or similar materials used in solar ovens, solar camping showers, or solar rooftop water heaters. The heat storage medium  905  contains a large volume of a material with a high heat capacity. This material could be water, which has a volumetric heat capacity of 4.2 joules/cm 3 /° C. or could be scrap iron which has a heat capacity slightly less than water. The selective surface  904  and the heat storage medium  905  are in good thermal contact. This contact possibly employs a thermal interface material  906  there between that has high thermal conductivity, the ability to mate the surfaces, and the ability to spread the heat. The heat storage medium  905  is thermally connected to the hot side of a distributed thermoelectric panel  902 , again possibly employing a thermal interface material  906 . The distributed thermoelectric panel  902  is an insulating panel with thermoelectric elements inside, as described in  FIGS. 2   a - 2   b  and  FIGS. 3   a - 3   d . The cold side of the thermoelectric panel  902  is thermally connected to ground  901  or floating on a body of water such as an ocean, lake, or pool. 
         [0058]    Without limitation, the power generator illustrated in  FIG. 9  could generate power only when the sun  907  is shining, eliminating the need for storage medium  905 . In this case the selective surface  904  would be adjacent to the thermoelectric panel  902 , possibly with a thermal interface material  906  there between. 
         [0059]    Again without limitation, the power generator of  FIG. 9  could employ a heat source other than sunlight. The water in the storage medium  905  could flow from an active geothermal source, or be heated waste water from a power plant or factory. If the thermoelectric panel  902  were built in the flexible configuration described earlier, then it could be wrapped around pipes carrying hot water or hot gases and generate electricity as illustrated in  FIG. 8 , item  814 . 
       EXAMPLE 2 
     Solar Power Storage and Electricity Generation 
       [0060]    An example power generator in accordance with  FIG. 9  will now be described that is competitive with other power generators such as wind turbines and photovoltaic panels. The heat storage medium  905  is 2 m×2 m×0.3 m and is assumed to reach a peak of 100° C. This temperature does not exceed the boiling point of water, and is a temperature easily reached by insulated solar ovens used to cook food. The cold side  901  temperature is assumed to be room temperature or 20° C. The delta temperature ΔT across the thermoelectric panel  902  is then 80° C. and the average temperature is 60° C. The heat storage medium at a temperature elevated by 80° C. relative to ambient stores 4.0 E+8 joules or 112 Kwatt-hours if the heat capacity of water at 4.2 joules/cm 3 ° C. is assumed. 
         [0061]    The insulating material  903  dimensions are 2 m×2 m×0.05 m, and so the thermal loss through the thickness of the insulator at the ΔT of 80° C. is 147 watts if a typical thermal conductivity of air-pocket insulators of 0.023 watts/m° C. is assumed. 
         [0062]    Thermoelectric elements are readily available with an electrical resistance r of 0.005 ohm, thermal conductance K of 0.009 watts/° C., and Seebeck coefficient S of 300 μV/° C. These values indicate a thermoelectric performance ZT=S 2 T/rK at the average temperature of 60° C. (333 K) of 0.60, which is well within the performance claimed by most manufacturers. 
         [0063]    The distributed thermoelectric panel  902  is 2 m×2 m×0.05 m, and it contains 1333 thermoelectric elements. The elements are spaced apart by 5.5 cm in each lateral direction. The total thermal loss through the elements is 960 watts (1333ΔTK). The total voltage V generated by the elements connected in series is 1333SΔT or 32 volts. The total resistance of the elements, all connected in series, is R  32  1333r=6.7 ohm. Assuming a matched load of 6.7 ohm, then the current flow I is V/2R or 2.4 amps. Hence, a total of 38.4 watts (0.5VI) of power is available to the load by this example embodiment. 
         [0064]    The sun&#39;s  907  radiation is known to be about 1000 watts/m 2 , which indicates that 4000 watts reaches the selective surface  904 . After subtracting the loss through the thermoelectric elements and through the insulating material, 2893 watts (4000-960-147) is absorbed as heat in the heat storage medium  905 . Because 4000 watts are entering the medium for 8 hours of the day and 1145.4 watts (960+147+38.4) are leaving the medium for 24 hours of the day, more energy (net 4.52 Kwatt hours per day) is entering per day than is leaving, allowing for this embodiment to reach and maintain a maximum temperature. The heat builds up in the heat storage medium until it reaches its heat capacity of 112 Kwatt hours. The time required to reach the maximum temperature is about 25 days (112 Kwatt hours/4.52 Kwatt hours per day). 
         [0065]    While this embodiment is less than 1% efficient on an instantaneous basis (38.4 watts generates/4000 watts available from the sun), which is a conservative expectation for a thermoelectric generator at these temperatures, making use of the heat storage allows the thermoelectric device to be about 3% efficient on a daily average basis. 
         [0066]    A feature and advantage of this embodiment is that it reaches its maximum temperature in the mid-afternoon hours as heat builds up in the heat storage medium  905 . Hence, the time of maximum power output of this embodiment better matches the time of peak demand for electricity. Photovoltaic panels have their maximum output at noon, which is two hours earlier than the peak demand. The daily maximum output of wind turbines is unpredictable. 
         [0067]    With this embodiment, 38.4 watts of electrical power generated in a 2 m×2 m area corresponds to 38 Kwatts per acre, which compares very favorably to wind turbines which average about 4 Kwatts per acre. 
         [0068]    Another feature and advantage of the present invention is that the storage medium, water, of this embodiment, is essentially free as the water does not even need to be fresh water. Storing energy as heat is much less costly than storing energy as electricity, and it may be stored without the toxic chemicals found in batteries. 
         [0069]    Various changes may be made in the above, without degrading from the spirit and scope of the present invention.