How Thermoelectric Generators Work
How Thermoelectric Generators Work
Thermoelectric generators (TEG) are solid-state semiconductor devices that convert a temperature difference and heat flow into a useful DC power source. Thermoelectric generator semiconductor devices utilize the Seebeck effect to generate voltage. This generated voltage drives electrical current and produces useful power at a load.
A thermoelectric generator is not the same as a thermoelectric cooler. (also know as TEC, Peltier module, cooling chips, solid-state cooling)
A thermoelectric cooler works in reverse of a thermoelectric generator. When a voltage is applied to thermoelectric cooler, an electrical current is produced. This current induces the Peltier effect. With this effect, heat is moved from the cold side to the hot side. A thermoelectric cooler is also a solid-state semiconductor device. The components are the same as a thermoelectric generator but the design of the components in most cases differ.
While thermoelectric generators are used to produce power, thermoelectric coolers (Peltier coolers) are used for removing or adding heat. Thermoelectric cooling has many applications in cooling, heating, refrigeration, temperature control and thermal management.
The focus of the rest this post is thermoelectric generators.
How does a Thermoelectric Generator utilize the Seebeck Effect?
The basic building block of a thermoelectric generator is a thermocouple. A thermocouple is made up of one p-type semiconductor and one n-type semiconductor. The semiconductors are connected by a metal strip that connects them electrically in series. The semiconductors are also known as thermoelements, dice or pellets.
The Seebeck effect is a direct energy conversion of heat into a voltage potential. The Seebeck effect occurs due to the movement of charge carriers within the semiconductors. In doped n-type semiconductors, charge carriers are electrons and in doped p-type semiconductors, charge carriers are holes. Charge carriers diffuse away from the hot side of the semiconductor. This diffusion leads to a buildup of charge carriers at one end. This buildup of charge creates a voltage potential that is directly proportional to the temperature difference across the semiconductor.
What Semiconductor Materials are used for Thermoelectric Generators?
Three materials are commonly used for thermoelectric generators. These materials are bismuth (Bi2Te3) telluride, lead telluride (PbTe) and Silicon germanium (SiGe). Which material is used depends on the characteristics of the heat source, cold sink and the design of the thermoelectric generator. Many thermoelectric generator materials are currently undergoing research but have not been commercialized.
What is a Thermoelectric Generator Module?
To create a thermoelectric generator module, many p-type and n-type couples are connected electrically in series and / or parallel to create the desired electrical current and voltage. The couples are placed between two parallel ceramic plates. The plates provide structural rigidity, a flat surface for mounting and a dielectric layer to prevent electrical short circuits.
Who discovered the Seebeck Effect? When was the Seebeck Effect Discovered?
Until recently it was thought that Thomas Seebeck discovered what is known today as the Seebeck effect. It is now believed that Alessandro Volta discovered the Seebeck effect 27 years prior to Thomas Seebeck. The discovery happened 224 years prior to this writing.
In 1794, Alessandro Volta did experiments where he formed an iron rod into a u-shape. One end of the rod was heated by dipping it in boiling water. When the unevenly heated rod was electrically connected to a no longer living frog leg, a current was passed through the frog leg and the muscles contracted. This is believed to be the first demonstration of the Seebeck effect.
In 1821, Thomas Seebeck discovered when one of the junctions of two connected dissimilar metals was heated, a close proximity compass needle would rotate. Initially this was called the thermomagnetic effect. Later it was found that a voltage and thus a current was induced by the junction heating. The current produced a magnetic field by Amperes law. This induced voltage due to junction heating became known as the Seebeck effect.
Categories of Thermoelectric Generator Applications
Extreme Environment
Thermoelectric generators are often used for applications where power is needed in an extreme environment. Because thermoelectric generators have no moving parts, they are very reliable. This reliability makes thermoelectric generators a great application for places where it is too far, too expensive or too dangerous for a repair person to travel. Sometimes these extreme applications utilize heat that is generated from a radiological source like Plutonium-238.
Some of these types of applications include spacecraft, mars rovers, Lunar power stations, power generation in Antarctica, flashing light buoy’s, lighthouses and nuclear pacemakers.
Recovering this waste heat makes any conversion process more efficient. This means less fuel is required to generate the same power output or the same amount of fuel will produce more power. Thermoelectric generators have been used to recover and utilize waste heat from automotive exhaust, steel foundries, wood stoves, gas flares, candles, hot water pipes, solar photovoltaic panels and electronics.
Microgeneration for Sensor and Electronics
Microgeneration thermoelectric generator applications can be classified by a heat source that is very small, or the heat source is large with a very small temperature difference between the ambient and the heat source. Or where the thermoelectric generator itself is very small. This leads to microwatt or milliwatt thermoelectric generator power output levels.
Some applications include wireless sensor networks (WSN) for environmental monitoring, low power Internet of Things (IoT) applications, body heat powered wrist watches, body heat powered flashlights and body heat powered medical sensors.
Combined Heat and Power (CHP)
Combined heat and power, or CHP (also known as cogeneration) is the practice of generating power from a heat source and using waste heat from the energy conversion process to provide some type of heating for cooking, space heating or process preheating. This leads to very high energy efficiency since most of the heat that would normally be wasted is utilized for a useful purpose.
Some examples of thermoelectric generator applications include biomass cooking stoves, camping stoves and grills.
Solar Thermal
Solar thermal applications utilize solar energy that is concentrated onto a thermoelectric generator hot side at very high temperatures. The ambient air is used for the heat sink. The high temperature delta improves the energy conversion efficiency of the thermoelectric generator.
How are Thermoelectric Generators Designed?
Thermoelectric generator modules can be bought “off-the-shelf”. These modules are not designed for any specific application. Rather they are a “one-size fits all” product. Theses thermoelectric modules look simple and easy to apply. However, the simple looks can lead to very poor performance and high cost. Without a high level of application knowledge and engineering expertise, theses modules produce very little useful power output.
With some rules of thumb applied and an assembly of cobbled together parts, most hobbyists obtain a small electrical output from a thermoelectric generator. However, for real products and applications, engineered system level solutions are required. Without an engineered solution, many months or years of trial and error usually lead to a product that produces too little power and / or costs too much.
One tool that can be used to verify the design of a thermoelectric generator is modeling and simulation. Recent thermoelectric generator modeling research has significantly improved the accuracy and speed of thermoelectric generator modeling.
Advantages of Improved Modeling and Simulation
Cost Savings
- Lower lifetime product or project cost – continuous prototype Iterations and tests are expensive
- Design problems out now Instead of fix later at very high cost
Huge Time Savings
- Reduced product development cycle
- Design by prototyping and testing is too time consuming
Makes Impossible Possible
- Investigate complex systems and interactions that are not linear or Intuitive
- Many product development tasks are cost and time prohibitive using prototypes and tests
Better Product Design
- More sales, repeat customers and better product reviews
Disadvantages of Improved Modeling and Simulation
- Available thermoelectric generator (TEG) modeling expertise not common
- Higher up-front cost but cost savings overall
- No standard approach. Every project is different
- A simulation cannot solve problems by Itself. Human Interpretation is required
How much Power can a Thermoelectric Generator Produce?
Thermoelectric generators are fully scalable from microwatts to kilowatts and beyond. The amount of power generated depends on the characteristics of the heat source, the cold sink and the design of the thermoelectric generator.
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Very interesting writing kept my interest from beginning to end. My son-inlaw Kevin is a mechanical engineer and I’m sure would be interested. He designs all automotive and aircraft for company’s like ford GM Chrysler Boeing and others.
Thank you, Barbara
Good introduction. I would like to understand the reasons for low efficiency and I would like to understand the temperature ranges and voltages. I would like to consider a natural gas generator for the home that would be replaced with cold fusion when it becomes available.
Thank you, Milo.
As materials get better efficiency will increase. However with the current set of available materials, the main driver of low efficiency is poor thermoelectric generator (TEG) and TEG system design. It is much easier to design a TEG that performs poorly than to design one that has great performance. Most TEG applications need to operate at their maximum efficiency but this is not to say that every application needs to have maximum available energy conversion efficiency when comparing every available energy conversion technology. As per the article, TEGs have many advantages that other energy conversion technologies do not have.
There are different materials to use depending on the application. Contact us for the best options. Contact Us
The voltage available depends on the constraints of the system. Unconstrained systems have unlimited voltage potential. It really depends on the needs of the application.
Thank for writing up this info. My son in 8th grade would like to do a science fair project experiment on thermoelectricity. Do you provide the needed materials on a small scale?
Yes, this is something we can help with. Please note we have a minimum per project fee listed on our contact page.
https://thermoelectricsolutions.com/contact/
This is a lucid explanation for the laymen and scientist. Very good, thanks.
Frying today! This could save the our planet from frying. A lot of waste heat about. … volcanoes, hot springs and above all hot countries could charge batteries. You need a someone with real imagination to make it work commercially.. Its the only variety of fruit a tree cant produce..
Thank you for the information.
Good luck
Jaya.
Jaya, Thank you for the thoughtful comments. Alfred
This is very nice, This is elaborated so properly
Thank you, Sankalp
Very interesting! Can i mention this work and use some images for my study?
Kirill,
Thank you for your interest.
If you would like to mention or work or use our images, please contact us using our contact form. https://thermoelectricsolutions.com/contact/
Let us know where and how you want to use the image(s). We will get back to you with terms of use.
Thank you so much for asking.
Alfred
Is the temperature difference time dependent? Does the temperature have to change very quickly for power to be generated or can the change be gradual?
Karissa,
Thank you for your interest. The temperature difference can be time dependent. Either the hot side can vary with time or the cold side or both. The power output will change depending on the point in time. The temperature changes can be very rapid or gradual.
See this paper regarding transient thermoelectric generators: https://thermoelectricsolutions.com/applied-thermoelectric-solutions-wins-editors-choice-award/
Amazing information! I am doing a project wherein I have a combination of a solar panel and a TEG module. By chance could you tell me what property of the solar panel makes the voltage drop for high temperatures?
Hi Naman, Electrical resistance is an inherent property of the solar panel materials. It can be calculated based on the resistivity of the solar panel materials and their geometry relative to the electrical current flowing through. You can characterize your specific materials by blocking light entry to the panel and measuring the electrical resistance at various temperatures of interest. I hope this helps. If you need more, please contact us through the contact form.
You should reword number 8 on the advantages of thermoelectric generators. Direct energy conversion makes it sound like heat is turned into electrical current. None of the heat is consumed or changed in the process. That is my understanding anyway.
James, Thank you for the comment. Number 8 is correct. Thermoelectrics convert heat directly into electricity. You would be correct if you mean energy is neither created or destroyed. That is true. But energy can be converted from one form to another. In this case, thermal energy is converted directly to electrical energy on a atomic scale.
Check this page for a brief description of the atomic physics:
https://thermoelectricsolutions.com/how-is-heat-transferred-peltier-module/
Note that not all of the heat is turned into electricity. Only a portion. How much of the heat that enters the thermoelectric generator that is converted directly to electricity depends on the efficiency of the thermoelectric generator. The thermal energy conversion efficiency is calculated by dividing the electricity produced in watts by the heat input in watts to the thermoelectric generator.
I have seminar on topic thermoelectric power conversion ,so what should I explain?
Rohan,
What you present depends on the audience and the reason they are attending your seminar.
Perhaps you can use the information contained in this article for your presentation?
Some of the common questions that might help others understand thermoelectric generators are as follows:
How do Thermoelectric Generators Work?
How does a Thermoelectric Generator utilize the Seebeck Effect?
What Semiconductor Materials are used for Thermoelectric Generators?
Who discovered the Seebeck Effect?
When was the Seebeck Effect Discovered?
When was the First Thermoelectric Generator Developed?
What are the Advantages of Thermoelectric Generators?
What are the Disadvantages of Thermoelectric Generators?
What are the Applications of Thermoelectric Generators?
What are the Heat Sources for Thermoelectric Generators?
What are the applications of thermoelectric generators?
Does thermoelectric generator efficiency matter if efficiency is not needed?
How are Thermoelectric Generators Designed?
What are the advantages of Improved Modeling and Simulation?
What are the disadvantages of Improved Modeling and Simulation?
How much Power can a Thermoelectric Generator Produce?
What is the best material for thermoelectric generator?
How can we increase the efficiency of thermoelectric generator?
How long do thermoelectric generators last?
How much voltage can a thermoelectric generator produce?
How much temperature difference is needed for a thermoelectric generator?
Can thermoelectric generator charge battery?
Is thermoelectric generator eco friendly?