The first nuclear-heated thermoelectric generator was built in 1954 by
the Atomic Energy Commission’s Mound Laboratory in Miamisburg, Ohio. It
used metal-wire thermocouples. In contrast, the SNAP 3 series
thermocouples shown in Figure 1 are thick lead telluride (PbTe)
semiconductor cylinders about two inches long. In contrast to the
thermocouple wires’ efficiency of less than 1%, SNAP 3 series generators
have overall efficiencies exceeding 5%. This value is still low compared
to the 35-40% obtained in a modern steam power plant, but SNAP 3
generators can operate unattended in remote localities where steam
plants would be totally unacceptable.
Look again at the thermoelements in Figure 1 and the schematic, Figure
5. Underlying the apparent simplicity of the thermoelectric generator
are extensive development efforts. The Figure 1 thermoelectric couple,
for example, shows the fruits of thousands of experimental brazing
tests. It turns out to be uncommonly difficult to fasten thermoelectric
elements to the so-called _hot shoe_ (metal plate) at the bottom. The
joint has to be strong, must withstand high temperatures, and must have
low electrical resistance. We see also that the elements are encased in
mica sleeves to prevent chemical disturbance of the delicate balance of
impurities in the semiconductor by the surrounding gases. A further
complication is the extreme fragility of the elements, and this has yet
to be overcome.
Nuclear thermoelectric generators that provide small amounts of
electrical power have already been launched into space aboard Department
of Defense satellites (Figure 12), installed on land stations in both
polar regions, and placed under the ocean.[6] Propane-fueled
thermoelectric generators, such as shown in Figure 6, are now on the
market for use in camping equipment, in ocean buoys, and in remote spots
where only a few watts of electricity are needed. The Russians have long
manufactured a kerosene lamp with thermoelements placed in its stack for
generating power in wilderness areas.
[Illustration: Figure 6 GENERAL PURPOSE GENERATOR
_Commercially available thermoelectric generators using propane fuel
can provide more than enough electrical power to operate a portable
TV set._
Courtesy Minnesota Mining & Manufacturing Company.]
For the present the role of thermoelectric power appears to be one of
special uses such as those just mentioned. When higher efficiencies are
attained, thermoelectric power may, one day, supplant dynamic conversion
equipment in certain low-power applications regardless of location.