How thermoelectric generators work

Thermoelectric generators produce electricity by harnessing heat. Thermocouples and thermopiles are the most familiar types, notably so, to those who have ever fixed a hot water tank or furnace when it refused to stay lit.

Thermoelectric generators produce electricity by harnessing heat. Thermocouples and thermopiles are the most familiar types, notably so, to those who have ever fixed a hot water tank or furnace when it refused to stay lit.

A German physicist, Thomas Johann Seebeck, discovered this effect in 1821, when he discovered that a compass needle would deflect when exposed to two dissimilar metals connected at either end.

Today, the metals used are most commonly bismuth telluride (Bi2Te3) or lead telluride (PbTe).

Thermoelectic generation is ideal for producing DC electricity in remote locations for powering communications system, navigation, or well site units. It can be married to photovoltaic arrays as a backup when cloud, fog or darkness reduces insolation. With outputs to 550 watts and up to 48 volts DC for single units, driven by the combustion of propane, or natural gas, these units offer substantial output, but with weights to 680 kg, they are not something that can be put in your pocket.

Electronics are quickly scaling down to where computers, glasses, watches and other devices are becoming part of our daily dress.

The problem with these small-sized semiconductors is how to keep them supplied with energy.

The Korean Advanced Institute of Science and Technology (KAIST) have developed an interesting solution.

Using a glass fabric, they have taken the TE technology on an advanced evolutionary path. Byung Jin Cho and his team have developed a reliable power source that uses the heat of the human body to produce electricity. They have found a way to minimize thermal losses while maximizing energy density without a bulky substrate.

TE generators over the years have evolved from either the previously mentioned inorganic metal thermopile technologies or organic polymers. Polymers are light flexible and ideal for placing next to our skin, but unfortunately they have low power output.

The inorganic TE generators are simply too heavy and awkward to be strapped to an arm.

The researchers accomplished this by making a near-liquid paste of n type Bi2Te3 and p type Sb2Te3, the two different metals required, then using a screen printing technique, applied these pastes to a glass fabric.

Screen printing allows them to arrange the different constituents in a specific pattern. The materials are absorbed into the spaces between the fibres, forming a film of small dots on the surface.

The glass fabric acts as a upper and lower substrate, which allows the two metals to operate, producing a millivolt electrical current strong enough to power electronics.

With a 31C difference between a human body and ambient air temperature, a 10-by-10-cm flexible TE generator made this way can generate 40 millivolts of electrical energy. Although the KAIST prototype was conceived for developing electronic devices that can be worn, like smart glasses, smart watches, pace makers, etc., it has the potential to generate electrical power on larger scale, such as using waste heat from an engine.

It’s an alternative type of energy harvesting developed to power our life.

Lorne Oja is an energy consultant, power engineer and a partner in a company that installs solar panels, wind turbines and energy control products in Central Alberta. He built his first off-grid home in 2003. His column appears every second Friday in the Advocate. Contact him at: lorne@solartechnical.ca.

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