What is Thermoelectric Generator : Working & Its Uses

In the year 1821, a famous scientist named Johann Seebeck revived the concept thermal gradient which is developed in between two various conductors and this can generate electricity. In relation to the thermoelectric effect, there is a concept called as temperature gradient in the conducting substance which produces heat and this outcome in charge carrier’s diffusion. This heat flow in between the hot and cool substances developed voltage difference. So, this scenario has discovered the device thermoelectric generator, and today, our article is on its working, advantages, limitations, and related concepts.

What is Thermoelectric Generator?

Thermoelectric is the name which is the combination of words electric and thermo. So the name signifies that thermal corresponds to heat energy and electricity corresponds to electrical energy. And thermoelectric generators are the devices that are implemented in the conversion of the temperature difference that is generated between the two sections into the electrical form of energy. This is the basic thermoelectric generator definition.

These devices are dependent on the thermoelectric effects which involve interface that happens between heat flow and the electricity through solid components.

Construction

Thermoelectric generators are the devices that are solid-state heat components constructed of two essential junctions which are p-type and n-type. The P-type junction has an increased concentration of +ve charge and the n-type junction has an increased concentration of -ve charged elements.

The p-type components are doped in the condition to have more positive charged carriers or holes thus providing a positive Seebeck coefficient. In a similar way, n-type components are doped to have more negative charged carriers thus providing a negative type of Seeback coefficient.

With the passage of the electrical connection between the two junctions, every positively charged carrier moves to the n-junction, and similarly negatively charged carrier moves to the p-junction. In the thermoelectric generator construction, the most implemented element is lead telluride.

It is the component that is constructed of tellurium and lead which have minimal amounts of either sodium or bismuth. In addition to this, the other elements that are used in this device construction are bismuth sulphide, tin telluride, bismuth telluride, indium arsenide, germanium telluride, and many others. With these materials, thermoelectric generator design can be done.

Thermoelectric Generator Working Principle

The thermoelectric generator working is dependent on the Seeback effect. In this effect, a loop that is formed in between the two various metals generates an emf when the metal junctions are maintained at various temperature levels. As because of this scenario, these are also termed as Seeback power generators. The thermoelectric generator block diagram is shown as:

A thermoelectric generator is generally included with a heat source that is maintained at high values of temperature and a heat sink is also included. Here, the heat sink temperature has to be less than that of the heat source. The change in temperature values for the heat source and heat sink allows the flowing current across the load section.

In this kind of energy transformation, there exist no transitional energy conversions dissimilar to the other types of energy conversion. As because of this, it is termed as direct energy transformation. The generated power because of this Seeback effect is of single-phase DC type and is represented as I²R_L where RL corresponds to resistance value at load.

The output voltage and power values can be increased in two ways. One is by increasing the temperature variation that rises in between hot and cold edges and the other is to form a series connection with thermoelectric power generators.

The voltage of this TEG device is given by V = αΔ T,

Where ‘α’ corresponds to the Seeback coefficient and ‘Δ’ is the temperature variation in between the two junctions. With this, the current flow is given by

I = (V/R+R_L)

From this, the voltage equation is

V = αΔT/R+R_L

From this, the power flow across the load section is

P at load = (αΔT/R+R_L)²(R_L)

The power rating is more when R reaches to R_L, then

Pmax = (αΔT)²/(4R)

There will be current flow till the time when there is heat supply to the hot edge and removal of heat from the cold edge. And the developed current is in DC form and it can be transformed into AC type through inverters. The voltage values can be more augmented through the implementation of transformers.

This kind of energy conversion can also be reversible where the energy flow path can be changed back. When both the DC power and load are removed from the edges, then heat can be simply withdrawn from thermoelectric generators. So, this is the thermoelectric generator theory behind working.

Thermoelectric Generator Efficiency Equation

The efficiency of this device is represented as the proportion of generated power at the resistor at load section to the heat flow across the load resistor. This ratio is represented as

Efficiency = (Generated power at RL)/(Heat flow ‘Q’)

= (I²R_L)/Q

Efficiency = (αΔT/R+R_L)²(R_L)/Q

This is how the efficiency of the thermoelectric generator can be calculated.

Thermoelectric Generator Types

Based on the TEG device size, kind of heat source and source for heat sink, power ability and application purpose, TEG’s are mainly classified as three types and those are:

• Fossil fuel generators
• Nuclear fueled generators
• Solar source generators

Fossil Fuel Generators

This type of generator is designed to make use of kerosene, natural gas, butane, wood, propane, and jet fuels as heat sources. For commercial applications, the output power ranges from 10-100 watts. These kinds of thermoelectric generators are employed in remote locations like in navigational assistances, information collection, in communication networks and in cathodic safety thus avoids electrolysis from destroying metallic pipes and marine systems.

Nuclear Fueled Generators

The decomposed components of the radioactive isotopes might be utilized to offer increased temperature heat source for the TEG devices. As these devices are correspondingly sensible to nuclear emission and the heat source element can be used for a long period, these nuclear fueled thermoelectric generators are applied in remote applications.

Solar Source Generators

Solar thermoelectric generators have been employed with few achievements to provide power minimal size of irrigation pumps in remote locations and underdeveloped areas. Solar thermoelectric generators are constructed to supply electric power for orbiting spacecraft.

Advantages and Disadvantages of Thermoelectric Generators

The advantages of the thermoelectric generator are:

• As all the components used in this TEG device are solid-state, they have enhanced reliability
• The extreme range of fuel sources
• TEG devices are constructed to deliver power ranging not minimal to that of mW and greater than KW which means they have huge scalability
• These are direct energy transformation devices
• Silently operated
• Minimal size
• These can function even at extreme and zero range of gravitational forces

The disadvantages of thermoelectric generator are:

• These are a bit expensive when compared to other kinds of generators
• These have minimal efficiency
• Minimal thermal properties
• These devices need more output resistance

Thermoelectric Generator Applications

• For enhancing the fuel performance of cars, the TEG device is mostly employed. These generators make use of heat that is generated at the time of vehicle operation
• Seebeck Power Generation is utilized to provide power for the spacecraft.
• Thermoelectric generators to implemented provide power for the remote stations such as weather systems, relay networks, and others

So, this is all about the detailed concept of thermoelectric generators. On the whole, as generators have huge prominence, they are widely used in many applications across many domains. Apart from these related concepts, the other concept to be clearly known here is what is thermoelectric generator temperature difference?