However, efficiencies remained too low, and the field became somewhat of a scientific backwater. At the same time, the best semiconductor minds turned their attention exclusively to electrical semiconductors which led to the now multi-trillion dollar IT industry.
Though conversion efficiencies restricted the use of thermoelectrics for the mass market, niche applications did emerge for situations where reliability or silence were paramount such as optoelectronic cooling, mini refrigerators and remote power generation, the most well-known example of which are the thermoelectric generators used by NASA to power spacecraft and even planetary vehicles, using a decaying nuclear isotope as a heat source, and capable of operating reliably for decades.
Benefits of Thermoelectrics
As chips are extremely small, applications can consist of a single chip to an array of hundreds or thousands of chips covering many square meters, depending on the amount of power required, and can be made to cover the unique geometry of the heat source.
High Energy Density
Thermoelectric generators produce significantly more electricity per area, volume and weight than comparable technologies – an order of magnitude more than solar devices for example. Power density is a critical factor in many markets, particularly aerospace and portable power.
Minimal Vibrations or Sound
Due to the fact thermoelectric devices are solid state and therefore have no moving parts, they make little or no noise, and are generally vibration-free.
Durable & Reliable
Also as a consequence of having no moving parts, and not vibrating, thermoelectric generators are generally extremely robust which is why NASA uses them as a source of power in space.
Having no moving parts that need replacement is also a significant advantage from a financial perspective and, if the heat source is waste heat, it is essentially free.
If the heat source is indeed waste heat, the additional electricity produced by the thermoelectric system is essentially emissions-free.
Drawbacks of Thermoelectrics
Low Conversion Efficiency
Literature on thermoelectrics often refers to standard efficiencies of around 10% but, in truth, there are very few commercial devices available today that advertise above 5% and in practice, most do not even perform to that level. How thermoelectric efficiency is measured and to what it specifically refers is currently a topic of considerable debate.
By far the most commonly used thermoelectric material is BiTe which can operate up to 250°C. This is fine for cooling applications, which represent most of the current market, but it presents numerous obvious problems when used in a power generation capacity.
Given the relatively low efficiency compared to established technologies, current thermoelectic devices simply do not offer an attractive financial proposition which is why they have been restricted to niche applications where alternatives are not viable.