Method and apparatus for the thermoelectric generation of electricity

A thermoelectric generator includes a plurality of thermoelectric junctions embedded in each of a pair of thermally conductive and electrically non-conductive layers, these layers being separated by a thermally and electrically non-conductive layer. The junctions are connected to form a thermopile. An absorbent layer is provided adjacent one of the thermally conductive layers. A liquid such as water is applied to the absorbent layer, so that evaporation of the liquid from the absorbent layer enhances the temperature differential between the two thermally conductive layers.

FIELD OF THE INVENTION 
This invention relates to an improved method and apparatus for generating 
electricity employing a thermoelectric generator, such as a plurality of 
thermoelectric junctions or couples interconnected to form a thermopile. 
BACKGROUND OF THE INVENTION 
In the past, thermoelectric systems have been employed for power 
generation. As an example, U.S. Pat. No. 4,363,938, Wilson, discloses a 
thermoelectric generating panel wherein a plurality of serially connected 
thermocouples are arranged with alternate couples aligned in a pair of 
spaced apart rows, the thermocouples being disposed on a substrate. The 
assembly is enclosed in a chamber through which water is pumped or 
circulated, for example by the power generated by the thermoelectric 
generating panel. The water is intended to maintain the two rows of 
thermocouples at different temperatures. 
The control of the temperature of the junctions in a thermoelectric 
generator by flowing liquids and gases is also disclosed, for example, in 
U.S. Pat. No. 3,138,934, Roane; U.S. Pat. No. 4,284,838, Indech; U.S. Pat. 
No. 4,448,028, Chao et al; U.S. Pat. No. 4,734,139, Shakun et al; U.S. 
Pat. No. 4,275,259, Yamamoto et al; and U.S. Pat. No. 4,420,940, Buffet. 
The requirement in such devices for the circulation of liquids 
necessitates extensive external equipment, and hence limits the 
adaptability of the devices for many applications. The use of circulating 
gases, on the other hand, reduces the efficiency of the devices. 
In these references, Roane, Shakun et al and Chao et al disclose the use of 
thermoelectric devices in vehicles. 
While the provision of evaporative cooling systems, for example for 
vehicular applications, is also well known, for example as disclosed in 
U.S. Pat. No. 3,606,982, Anderson; U.S. Pat. No. 3,738,621, Anderson; and 
U.S. Pat. No. 4,549,406, Ebner et al, these arrangements are not disclosed 
as being adaptable to systems for the thermoelectric generation of 
electricity. 
SUMMARY OF THE INVENTION 
Briefly stated, in accordance with one aspect of my invention, a 
thermoelectric generator is provided, for example (although not 
exclusively) for use in or in combination with a vehicle. The generator is 
comprised of a thermopile panel. The "hot" side of the panel is adapted to 
be directly or indirectly exposed to the sun. The "cold" side of the panel 
has a water-absorbent surface, and water is continually applied to the 
water-absorbent surface. As a result, the "cold" side of the panel is 
cooled by evaporation of the water, to increase the temperature 
differential between the sides of the panel. The electricity generated by 
the panel may be employed, for example, in the movement of the vehicle, 
the powering of other devices on the vehicle, and/or it may be stored in 
batteries of the vehicle.

DETAILED DISCLOSURE OF THE INVENTION 
Referring now to the drawings, therein is illustrated a thermoelectric 
generator panel 10 in accordance with the invention. The term "panel", as 
used herein, is not limited to flat structures, but broadly includes other 
shapes having a pair of opposed surfaces. One surface 11 of the panel is 
comprised of a layer of an electrically non-conductive material that is 
generally thermally conductive. While various ceramic materials have such 
properties, it will be evident that the invention is not limited to 
ceramic materials. 
The layer 11 is spaced from a layer 12 of the same or similar material, by 
an intermediate layer 13 of electrically non-conductive thermally 
non-conductive materials. The layer 13 may be, for example of various 
known mechanically stable thermal insulating materials such as, for 
example, rigid or semirigid epoxy resins. The invention is of course not 
limited to such materials. In general, suitable materials for the layers 
11 and 12 should be as non-conductive to electricity as possible, and have 
as great a thermal conductivity as possible, taking into consideration the 
structural strength, rigidity and other physical requirements of the 
application, and the layer 13 should be as thermally nonconductive and 
electrically nonconductive as possible taken in view of such 
considerations. 
A plurality of rows 20 of metallic or semi conductive thermocouples 21, 
only one row of which is seen in FIG. 1, is embedded in the layer 11, and 
a plurality of rows 30 of metallic or semi conductive thermocouples 32, 
only one row of which is seen in FIG. 1, is embedded in the layer 12. The 
thermocouples 21 of a row 20 are serially connected to the thermocouples 
32 via conductors 33 extending through the layer 13, to form a thermopile. 
Thermocouples 21 and 32 are preferably, although not necessarily, 
alternately connected in the thermopiles, and, for simplicity in 
construction, interconnected rows 20, 30 of thermocouples are also 
preferably generally in a common plane. 
The two ends of the thermopiles are connected to opposite terminals 40, 41, 
and the other thermopiles (not illustrated) in the panel may be connected 
in series or parallel with the illustrated thermopile, in a manner to 
provide an output voltage and current suitable for the given application. 
A series-parallel connection of this type is shown, for example, in FIG. 
2. 
Referring again to FIG. 1, a thin layer 45 of a moisture absorbent material 
is applied against the external surface of the layer 12. The moisture 
absorbent material may be, for example, a porous ceramic or plastic 
material, the material being capable of absorbing liquids such as water, 
so that the water can readily evaporate from the surface of the layer 45, 
especially when air moves across the surface of the layer 45. 
In accordance with the invention, by providing the absorbent layer 45 on 
the thermoelectric generator, the temperature differential can be 
increased between the thermocouple junctions 21 and 32, so that a larger 
voltage will be generated between the terminals 40, 41. In order to 
enhance the voltage, and thus current flowing through a device connected 
between the terminals 40, 41, the layer 11 is advantageously exposed to 
the sun. Such exposure is not necessary, however, especially if air is 
caused to move across the absorbent layer. Evaporation of water from the 
layer 45 effects a cooling of the junctions 32 to maintain a temperature 
difference between the junctions 21, 32, so that a voltage will be 
generated even though the surface of the layer 11 is not exposed to the 
sun. 
Accordingly, as opposed to prior generating arrangements employing solar 
cells, the arrangement of the present invention produces an electric 
current even in the absence of solar exposure. 
FIG. 3 illustrates a motor vehicle having a roof 50, a hood 51, a trunk 52 
and doors 53. In accordance with the invention, panels 54 of the type 
illustrated in FIG. 1 may be mounted to each of these surfaces of the 
vehicle by conventional means, slightly spaced from the respective surface 
of the vehicle to provide an air channel between the vehicle surface and 
the absorbent layer of the respective panel. As will be discussed, water 
or other volatile fluid is caused to flow onto the absorbent layer of the 
panel, so that the water evaporates from the absorbent layer when the air 
is moved in the channels, for example when the vehicle is moving. The 
channels should therefore be oriented to obtain the maximum airflow 
therethrough when the vehicle moves. 
It is therefore apparent that, in accordance with the invention, a large 
portion of the external surface of the vehicle may be covered with 
thermoelectric generator panels, in order to maximize the generation of 
electricity. As discussed above, it is not necessary that the respective 
surfaces of the vehicle be in a position to be exposed to the sun. 
It is further evident that, instead of mounting the panels 54 on the 
external surfaces of the vehicle, the panels may be built into the 
external surfaces of the vehicle, with air channels also being built into 
the vehicle adjacent the layers of absorbent material. 
A system incorporating the thermoelectric generator of the invention is 
illustrated in FIG. 4. In this figure, block 60 denotes a thermoelectric 
generator of the type illustrated in FIG. 1, having an absorbent layer 61. 
The thermoelectric generator is mounted by conventional means to provide 
an air channel 62 between the absorbent layer 61 and a surface 63. The 
surface 63 may be the surface of a vehicle, such as shown in FIG. 3, or 
any other surface across which air may flow. 
The terminals 40, 41 of the thermoelectric generator 60 are connected to a 
controller switch 65, the switch being connected to direct current from 
the thermoelectric generator either to a motor 66 (e.g. the motor of the 
vehicle of FIG. 3) or to a battery 67 (e.g. the battery of the vehicle of 
FIG. 3). The battery 67 is connected to supply operating current to a 
computer 68. A moisture sensor 69 is connected to the computer 68 and is 
mounted in a position to detect the moisture content of the layer 61, 
preferably at the downstream end thereof. 
The system of FIG. 4 further includes a source of water or other volatile 
liquid, such as a tank 70. An outlet of the tank is directed via a valve 
71 to a nozzle 72 positioned to direct liquid from the tank onto the 
upstream end of the absorbent layer 61. The valve is controlled by the 
computer 68. 
In the arrangement of FIG. 4, the tank is advantageously sealed, with the 
air above the liquid being pressured. The air pressure in the tank thus 
can force the liquid from the tank to the nozzle, when the valve 71 is 
open, without the necessity of providing a pump. Alternatively, of course, 
a pump may be provided for the purpose, for example controlled by the 
computer, of the flow from the tank may be a gravity flow. 
When the system of FIG. 4 is employed on a vehicle, movement of the vehicle 
causes air to flow in the direction of the arrow 75, to effect evaporation 
of liquid from the absorbent layer 61. At this time (i.e. when the vehicle 
is moving), the computer 68 controls the controller switch 65 to direct 
current to the motor of the vehicle, for example to constitute or 
supplement motive forces applied to the vehicle. The computer can detect 
movement of the vehicle by any conventional means, such as with a motion 
or speed detector 76. 
When the sensor 76 detects that the vehicle is not moving, the computer 68 
controls the controller switch 65 to direct current to recharge the batter 
67, rather than to energize the motor 66. 
It is of course apparent that the computer may be programmed to control the 
controller switch 65 in any other sequence, as desired. 
The moisture sensor 69 signals the computer of the moisture content of the 
absorbent layer 61. When this layer has a moisture content below a 
predetermined level, the computer controls the opening of the valve 75 to 
direct more liquid to the layer 61, so that the moisture content of the 
layer is maintained above the predetermined level. It is of course 
apparent that the invention is not limited to this technique for 
moistening the absorbent layer 61. 
The thermoelectric generator of the invention may also be advantageously 
employed in other applications. For example, as illustrated in FIG. 5, 
thermoelectric generators 80 may be provided on, or built into, exposed 
surfaces of an airplane 81, such as on the wings 82 and tail surfaces 83. 
The current generated by these thermoelectric generators may be used for 
appliances in the airplane, if desired, although the invention is not 
limited to such use. 
The thermoelectric generator of the invention may also be employed for 
stationary applications, such as in dwellings or commercial buildings. For 
example, as illustrated in FIG. 6, thermoelectric generators 85 of the 
type illustrated in FIG. 1 may be mounted on the roof 86 of a building 87, 
for generating power for use in the building. 
As discussed above, the thermoelectric generator of the invention need not 
be comprised of a flat panel. For example, as illustrated in FIG. 7, the 
thermoelectric generator 90 may be cylindrical, having a thermally 
conductive electrically non-conductive annular outer layer 91 radially 
outwardly spaced from a similar layer 92 by an annular thermally and 
electrically non-conductive layer 93. As in the case of the embodiment of 
FIG. 1, thermocouples 94 are embedded in the layers 91 and 92, and 
interconnected to form a thermopile. An annular absorbent layer 96 is 
provided on the inner surface of the layer 91. The center of the structure 
of FIG. 7 is open, to form a duct 98 for the passage of air. 
The thermoelectric generator of FIG. 7 is advantageously employed in 
locations where it is not generally expected that the generator will be 
exposed to sunlight, for example, under a moving vehicle. 
While a few examples of use of the thermoelectric generator of the 
invention have been discussed, it is apparent that it may also be 
advantageously employ for may other purposes. 
While the invention has been disclosed and described with reference to a 
limited number of embodiments, it will be apparent that variations and 
modification may be made therein, and it is therefore intended in the 
following claims to cover each such variation and modification as falls 
within the true spirit and scope of the invention.