Method of fabricating thermoelectric power generator modules

An improved method of fabricating thermoelectric power generator modules, which are particularly useful in converting solar energy into electrical power and heat, is disclosed. This method involves the formation of an array of longitudinally elongated n- and p-type semiconductor elements tightly contained in a supporting matrix; slicing the supporting matrix containing the semiconductor elements to provide a plurality of matrix plates; and the application of a pattern of electrically conductive pads on opposite surfaces of the matrix plates to connect n- and p-type semiconductor elements, in series, thereby forming a thermoelectric power generator module. This method is simpler, less expensive and more adaptable to large scale production than methods heretofore proposed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to fabrication techniques for thermoelectric power 
generator modules. 
2. Description of the Prior Art 
The need to convert solar radiation into more practical forms of energy, 
such as electrical power and heat, has become apparent recently. This need 
has resulted in a dramatic increase in the amount of research directed to 
more efficient and economical methods of converting solar energy into 
these other energy forms. 
One major area of investigation is that involving the use of photovoltaic 
cells which generate electrical energy directly from sunlight. Typically, 
photovoltaic cells are based on a semiconductor layer having an ohmic 
contact on one side, a rectifying contact on the other side. Despite great 
advances, photovoltaic cells still require near crystal perfection for 
high efficiency operation which means that elaborate procedures must be 
used in producing these devices. Because of this, photovoltaic cells have 
not found wide use in terrestrial applications where cost of production is 
a major factor. 
An alternative technique for generating electrical power from solar energy 
involves the thermoelectric or Seebeck effect. In this technique, a 
thermocouple is formed by connecting a pair of n- and p-type semiconductor 
materials with an electrical conductor at two junctions which are 
maintained at different temperatures. This produces an EMF between the two 
junctions which is a function of the temperature difference and the 
thermoelectric characteristics of the materials forming the thermocouple. 
The EMF can be increased by connecting more than one thermocouple in 
series, in which case the EMF becomes proportional to the number of 
thermocouples connected in series. 
Solar energy can be used to heat one junction of a thermoelectric device to 
a temperature higher than the other. This provides a convenient way to 
convert solar radiation into electrical energy. Some attempts to fabricate 
thermoelectric power generators suitable for use in converting solar 
energy into electrical power are described in issued patents, including: 
Shaffer, U.S. Pat. No. 2,984,696; Stearns, U.S. Pat. No. 3,053,923; and 
Liphis, U.S. Pat. No. 3,088,989. Despite proposals such as those set forth 
in these patents, thermoelectric converters have not been widely accepted 
for use in solar energy conversion because they have suffered from a 
number of problems. Some of the most serious problems relate to the 
difficulty of fabricating arrays of thermoelectric elements because the 
materials required, such as bismuth telluride and lead telluride, have 
oriented or partially oriented crystals which inevitably make them brittle 
and difficult to prepare. For example, great care must be taken during any 
cutting operation required in fabricating thermoelectric power generators 
from such materials because they are so susceptible to damage. 
Furthermore, the difficulty of forming suitable junctions increases with 
the number of junctions to be formed, and many junctions are required if 
practical amounts of power are to be generated from solar energy. 
SUMMARY OF THE INVENTION 
The invention relates to a unique method for forming thermoelectric power 
generator modules. Longitudinally elongated n- and p-type semiconductor 
elements, such as rods or bars, are positioned to form an array in a 
supporting matrix. The supporting matrix can be a block of insulating 
material having holes drilled therein, a stack of insulating sheets 
containing supporting channels, or many other forms of a supporting 
matrix. The important characteristic is that the matrix provide good 
support for the elongated elements and electrical insulation between 
elements. 
After the supporting matrix has been prepared, it is sliced in a direction 
transverse to the longitudinal axis of the elongated semiconductor 
elements. The result is a plurality of matrix plates which each contain 
and support an array of n- and p-type semiconductor elements, but which 
are considerably thinner than the original supporting matrix. 
Subsequently, a pattern of electrically conductive pads is applied on 
opposite surfaces of the matrix plates to electrically connect, in series, 
n- and p-type semiconductor elements within the plate. At this point, each 
plate comprises an individual module suitable for use in a thermoelectric 
power generator. 
Two further coatings are applied to adapt these modules for the conversion 
of solar energy into electrical energy and heat. One surface is coated 
with a layer having high solar radiation absorptivity coupled with low 
solar radiation emissivity. This, of course, will function in normal 
operation as the hot side of a thermoelectric power generator. On the 
opposite, or cold side, a coating is applied which has high solar 
radiation emissivity, which helps to maintain the temperature as low as 
possible on the cold side. 
It can be appreciated that the method for fabricating thermoelectric power 
generator modules of this invention provides many significant advantages 
over methods heretofore used. This method is, for example, relatively 
simple and inexpensive, and yet lends itself to large scale production. 
Additionally, it provides a great deal of flexibility in that the modules 
can be designed in any aesthetically pleasing or functional shape desired. 
The modules produced also offer significant advantages. They have a rugged 
and safe construction, and are thus not subject to damage under normal 
operating environments. Since each unit is a module, there is complete 
independence offered. Modular units can be added, subtracted or 
substituted for other modules at any time. Also, it should be noted that 
thermoelectric power generators function whenever there is a temperature 
difference between their opposite surfaces--they do not depend upon direct 
solar radiation being emitted at any particular time. Thus, they function 
on cloudy days, and for that matter, could even function in the reverse 
direction if the environmental conditions were such that the temperature 
at the hot side becomes cooler than the temperature at the cold side for 
any reason. Most importantly, the thermoelectric power generator modules 
described herein offer relatively high efficiencies in regard to the 
conversion of solar energy into electrical power and heat. dr 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a perspective view illustrating an array of n- and p-type 
longitudinally elongated semiconductor rods positioned in a supporting 
block matrix; 
FIG. 2 is a perspective view of a sheet suitable for stacking to form a 
supporting matrix for elongated semiconductor bars; 
FIG. 3 is a front elevational view of sheets of FIG. 2 stacked to support 
an array of n- and p-type semiconductor bars; 
FIG. 4 is a perspective view illustrating four matrix plates produced by 
slicing the supporting matrix of FIG. 1 in a direction transverse to the 
axes of the semiconductor rods; 
FIG. 5 is a side elevational view of a matrix plate of FIG. 4 having a thin 
uniform conductive coating applied to its opposite surfaces; 
FIG. 6 is a top view of the coated plate of FIG. 5; 
FIG. 7 is a partial perspective view illustrating conductive tabs formed by 
extensions of the uniform conductive coatings to the lateral sides of a 
plate; 
FIG. 8 is a top view illustrating the positioning of a masking grid over 
one surface of a coated plate of FIGS. 5 and 6; 
FIG. 9 is a cross-sectional side view of a plate after a metal coating has 
been applied over the grid shown in FIG. 8; 
FIG. 10 is a top view illustrating electrically conducting pads formed by 
etching away the orginial uniform conductive coating at all areas not 
covered by the metal coating applied over the grid; 
FIG. 11 is an exploded view illustrating an extension of a conductive pad 
to form a conductive terminal on a lateral edge of a thermoelectric plate; 
FIG. 12 is a front elevational view illustrating a thermoelectric plate 
coated on both sides and suitable as a module for converting solar energy 
into electrical energy and heat; 
FIG. 13 is a perspective view of a solar thermoelectric power generator 
module; 
FIG. 14 is a perspective view of a solar thermoelectric power generator; 
FIG. 15 is a schematic illustration of the disassembled elements present in 
the assembled solar thermoelectric power generator of FIG. 14; 
FIG. 16 is a cutaway view illustrating how electrical contact is made 
through the walls of the module of FIG. 14; 
FIG. 17 is a frontal cross-sectional view of the suitable cold reservoir 
for use in a solar thermoelectric power generator; and, 
FIG. 18 is a plan view illustrating an arrangement of three solar 
thermoelectric power generator modules in a system.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIG. 1, block 10 is illustrated as a supporting matrix for supporting an 
array of n-type semiconductor rods 12 and p-type semiconductor rods 14. 
Although block 10 is illustrated as having a square cross section, many 
other shapes also would be suitable. Block 10 is formed from a material 
which has good high temperature properties, is easy to shape, and which 
has relatively low heat and electrical conductivity. Particularly 
preferred materials are asbestos and polytetrafluorethylene, such as that 
sold under the trademark TEFLON by E. I. duPont deNemours and Company, 
although those skilled in the art will know many other suitable materials. 
Semiconductor rods 12 and 14 are inserted into holes which are predrilled 
into block 10. Such holes have a size just large enough to allow the rods 
to be inserted but small enough to insure good contact with the rods. As 
shown, the holes are aligned so as to provide a parallel ralationship 
between the semiconductor rods 12 and 14 in both the horizontal and 
vertical directions. This is not always necessary, but is preferred. 
An example of suitable semiconductor materials is an alloy of bismuth 
telluride and bismuth selenide, which can be suitably doped to provide 
both n- or p-types. Other suitable thermoelectric materials, include, but 
are not limited to, lead telluride, lead sulfide and silicon germanide. 
Semiconductor rods 12 and 14 can be inserted into predrilled holes in block 
10 by heating block 10 to an average temperature to 50.degree.-60.degree. 
C. if block 10 is fabricated from polytetrafluorethylene or other similar 
polymers. The slight expansion of block 10 facilitates rod insertion. 
Typically, semiconductor rods 12 and 14 might have a diameter of about 
2-10 mm and a length of about 10-20 cm. 
An alternative method for preparing a supporting matrix for an array of 
elongated semiconductor elements is illustrated in FIGS. 2 and 3. In this 
method, sheets 20 are formed with recessed channels 22 which are 
rectangularly-shaped, and thus suitable for supporting 
rectangularly-shaped semiconductor rods. Of course, circular recessed 
channels could also be used, or for that matter, many other shapes. Sheets 
20 can be provided with pyramidal extensions 24 on their upper surface and 
matching pyramidal recessions 26 at their lower surface to aid in precise 
fitting and to eliminate lateral motion of the sheets when they are 
stacked as illustrated in FIG. 3. Additionally, enlarged extensions 28 and 
matching recessions 30 can be positioned towards the ends of sheets 20 to 
provide even stronger coupling at the edges of the sheets. As shown in 
FIG. 3, a series of sheets 20 can be stacked one upon the other after the 
insertion of alternating n-type semiconductor elements 32 and p-type 
semiconductor elements 34. 
Sheets 20 can be formed from materials similar to those described for the 
supporting block 10 in FIG. 1. If Teflon.RTM. polytetrafluorethylene is 
used, the sheets can be formed by machining or molding the polymer into an 
appropriate shape. Asbestos sheets could be formed by machining asbestos 
material. 
If desired, stacked sheets 20 can be joined with a temperature resistant 
adhesive or transferred to a frame to add more strength to the array. 
Frames would be formed from materials similar to those used for the sheets 
themselves. 
The method of forming an array illustrated in FIGS. 2 and 3 offers the 
advantages of easier assemblage of semiconductor elements and overcomes 
any problems which might be caused by differences in the coefficient of 
thermal expansion between the longitudinally elongated semiconductor 
elements and support material. Additionally, it offers the possiblity of 
continuous production of sheets for use in this manner. 
FIG. 4 is a perspective view of four matrix slabs or plates 40, 42, 44 and 
46 formed by slicing a supporting matrix, such as block 10 in FIG. 1, in a 
direction transverse to the axis of the longitudinally elongated 
semiconductor elements contained therein. Each matrix plate has a 
thickness chosen to maximize the desired properties of the eventual 
thermal electric power generator to be constructed. Typical thicknesses 
might be, for example, from about 0.5 to about 2 cm. Usually, it is 
preferred that plates 40, 42, 44, and 46 have uniform thicknesses which 
are provided by making parallel cuts into the supporting matrix. It should 
be understood, of course, that an array such as illustrated in FIGS. 2 and 
3, or any other design, could be similarly sliced into matrix plates. 
Slicing might be achieved by using a diamond impregnated slitting saw. The 
supporting matrix provides strong support at all points about the 
elongated semiconductor rods so that slicing does not result in chipping, 
fracture or other damage to these elements. In some cases, the surface 
regions of matrix slabs 40, 42, 44 and 46 might be cleaned and etched in 
an acid bath to repair any slight imperfections caused in the slicing 
operation. Each of the matrix slabs 40, 42, 44 and 46 serves as the 
fundamental unit of a thermoelectric power generator. 
One technique for electrically connecting n- and p-type semiconductor 
elements in series is illustrated in FIGS. 5-11. 
Initially, a uniform thin layer of a conductor is applied on opposite 
surfaces of a matrix plate. As illustrated in FIG. 5, uniform thin 
conducting layer 50 extends across the upper surface of matrix plate 40 
and has a continuous extended portion running down one side to form a 
conductive tab 52. Similarly, a thin uniform conductor layer 54 is applied 
across the bottom surface of matrix slab 40 and continues to form 
conductive tab 56 on the same side of slab 40 as tab 52. 
A plan view is illustrated in FIG. 6 showing the uniform conductive coating 
50 across the top surface of slab 40 with the conductive tabs 52 and 56 
extending onto one side of slab 40. Conductive tabs 52 and 56 are further 
illustrated in the exploded view presented in FIG. 7. The edges of the top 
and bottom surfaces, and the sides of matrix slab 40 are not coated with 
conductive coatings 50 and 54 which can be prevented by masking them with 
tape or the material prior to the coating process. Suitable coatings can 
be applied by a vacuum metallizing process to deposit a thin nickel layer 
or other conducting layer on the upper and lower surfaces of matrix slab 
40. 
The next step is the application of a fine grid of electrically 
non-conducting material as illustrated in FIG. 8. As shown, grid 60 is 
applied which has a pattern of openings therein in the shape of pads for 
each pair of n- and p-type semiconductor terminals. Grid 60 might be 
formed, for example, from Teflon.RTM. polytetrafluoroethylene, poly(methyl 
methacrylate), or other materials. 
After a grid has been applied to both sides of a matrix plate, another 
coating, which can be metal, is applied over the original coatings 50 and 
54 where they are exposed to coating through grid 60. This coating can be 
a metal coating formed by electroplating or otherwise, and this protective 
coating would typically have a thickness of about 0.5 mm to about 2 mm. 
The resulting structure is illustrated in FIG. 9 which shows an additional 
metal coating 62 on both surfaces of matrix plate 40 at all areas not 
covered by grid 60. Semiconductor rods 12 and 14, of course, extend 
through matrix plate 40 and are connected by the metal coatings 50 and 54. 
After the application of metal layer 62, grid 60 is removed from both 
surfaces of matrix slab 40. The portions of metal layers 50 and 54 having 
no protective metal coating thereover are etched with an acid treatment to 
remove them. This might be achieved, for example, by applying a grid 
having the same size and shape as grid 60 and having one side made from a 
porous material impregnated with acid. Etching is quite simple because 
layers 50 and 54 are very thin. Subsequent to etching, the slab is 
subsequently washed. The plate now contains a series of thermocouples 
formed by connecting all n- and p-type semiconductor elements with 
metallic pads 70 as illustrated in FIG. 10. An exploded view of side 
terminal 52 is illustrated in FIG. 11. 
Location of both terminals 52 and 56 on the same lateral edge of matrix 
slab 40 is not essential but does facilitate connection of plates to a 
power generator assembly. 
FIG. 12 illustrates a front elevational view of a thermoelectric plate 40, 
according to this invention, and having further coatings applied to make 
it suitable for converting solar energy to electrical power. On one 
surface, an electrically insulating material having high solar radiation 
absorptivity in the solar spectrum and low infrared radiation emissivity 
in the infrared region is deposited to form solar absorbing layer 82. A 
suitable material, for example, would be "Nickel Black", which is a 
combination of oxides and sulfides of nickel and zinc having an 
absorptance for solar energy, .alpha. equal to 0.94 for .lambda. smaller 
than 3 .mu.m and an emittance .epsilon.=0.11 for .lambda. greater than 3 
.mu.m at a typical temperature for the top face. A typical thickness for 
such a layer would be about 1 mm. 
On the opposite surface of plate 80, coating 84 is applied which is also 
electrically insulating but has high infrared radiation emissivity. For 
example, lamp black or other commercially available materials can be used. 
This helps to insure the coldest possible temperature at the cold surface 
since the total electrical energy generated is proportional to the 
temperature differences between one surface and the other. It is preferred 
to have lower coating 84 be uniformly flat as illustrated in FIG. 11. On 
the other hand, the solar absorbing layer 82 might have a more intricate 
design, such as one having the valleys illustrated, to increase the 
surface area available for solar absorption. 
FIG. 13 shows a perspective view of a thermoelectric power generator plate 
for converting solar energy into electrical energy according to this 
invention. Therein, thermoelectric plate 40 is shown having a solar 
absorbing coating 82 on one surface. As can be seen, coating 82 does not 
extend to the extremities of each side thus leaving an outer edge which is 
helpful in mounting plates into modules. Also shown are electrical 
contacts 52 and 56, on the same lateral side of the solar plate. 
An assembled modular unit for converting solar energy into electrical power 
and heat is illustrated in FIG. 14. As illustrated, solar thermoelectric 
power generating module 100 has a boxlike frame 102 open at the top and 
bottom and formed from four sidewalls (two of which are not shown). As can 
be seen, the lower portions of sidewalls 103 and 104 are thicker than the 
upper portions to provide additional structural strength. Additionally, 
sidewall 104 contains two channels for electrical contacts 106 and 108. 
Electrical contacts 106 and 108 extend through sidewall 104 and make 
electrical contact with a thermoelectric plate. Thus, electrical energy 
generated by a thermoelectric plate can be conducted along contacts 106 
and 108 to a suitable outlet, such as electrical outlet 110. Upper cover 
112 can be attached to the open boxlike structure by screws or other 
fastening means. Upper cover 112 is transparent to the solar spectrum but 
has high emissivity for infrared radiation, and thus serves to allow solar 
radiation to pass to the thermoelectric plate inside module 100 but to 
trap infrared radiation within module 100. Cover 112 also serves as 
protection from the environment. Plate 125 extends along the bottom of 
module 100 and consists of a flat plate with good heat conducting 
characteristics. Plate 125 serves as a holder for a cold reservoir (not 
shown) which has fluid outlet 120 thereby allowing water or other fluid 
which has been heated by passing through the cold reservoir to leave the 
module. A fluid inlet on the other side of module 100 for the entrance of 
cold water is also present but not shown. 
FIGS. 15-18 illustrate, in more detail, the assemblage of the module of 
FIG. 14. 
In FIG. 15, the various elements are illustrated in a disassembled state. 
The basic structural unit is frame 102, which is formed from four 
sidewalls and is open at its top and bottom. Although illustrated as 
having a rectangular shape, any other shape could be used, of course. A 
cold radiator 114 is provided in good thermal contact with metal plate 116 
which in turn is sealed to frame 102 by gasket 124. A base plate 125 is 
placed on the other side of radiator 114 and gasket 126 provides good 
sealing therebetween. Base plate 125 can be attached to frame 102 by 
screws 118 or any other suitable means. Subsequently, electric outlet 110 
is attached. Thermoelectric plate 40 is then introduced into frame 102 so 
that its terminals 52 and 56 are aligned with outer connectors 108 and 
106, respectively. Two protective covers 112 and 127 are then added and 
these are separated from plate 40 and each other by gaskets 129. Cover 112 
is attached directly to frame 102 and serves to cover and seal the module. 
Cover 127 is simply placed over gasket 129 within frame 102. Both covers 
can be formed from transparent plastics having good thermal stability and 
mechanical properties, such as poly(methyl methacrylate). The number of 
covers used in addition to cover 112 is, of course, entirely optional. As 
can be appreciated, plate 40 can be easily removed from the completed 
module by simply removing cover 112. 
FIG. 16 is a partial cutaway view of a section of module 100 illustrating 
the mounting of thermoelectric plate 40 to achieve electrical contact with 
the outer terminals. Therein, thermoelectric plate 40 is supported along 
one of the sidewalls 104 of frame 102 by a ledge 134. Leaf spring 136 
serves as an inner electrical contact to the electrical contact 52 on the 
lateral side of thermoelectric plate 40. Metal pin 140 continues the 
electrical circuit through wall 104 and the head of pin 140 is in contact 
with lead 142 which terminates at electrical outlet 110. 
Of course, other methods for establishing electrical contact with the 
thermoelectric plates in modules could be used. In, for example, a module 
intended for placement in a corrosive area, an alternative contact might 
be provided by simply replacing spring 136 with a pressure contact 
operable by a screw from the exterior of the module. 
FIG. 17 illustrates a cross-sectional frontal view of a suitable cold 
radiator 114. Radiator 114 has a flat conducting plate 116 which would 
normally be designed to have an area approximately the same size as the 
coating on the cold side of the thermoelectric plate. A lower channelled 
member 150 is located beneath flat plate 116 and in thermal contact 
therewith. The cold reservoir could be formed from cast aluminum or other 
metal having good heat transfer properties. In practice, cooling fluid, 
such as cold water, is circulated in the channels provided. Efficient 
cooling is achieved because of the large surface area provided by the 
channelled section 150. 
FIG. 18 illustrates a system for converting solar energy into electrical 
energy and heat which employs three solar thermoelectric generator modules 
160, 162, and 164 according to this invention. The cold water conduit 166, 
warm water conduit 168, and electrical conduit 170 are each connected in 
series to modules 160, 162 and 164. More modules could be added or modules 
could be subtracted or another module could be substituted into this 
system with a minimum of effort. 
Those skilled in the art will recognize many equivalents to the specific 
elements, components, materials, steps, etc. described as preferred 
embodiments herein. Such equivalents are intended to be covered by the 
following claims: