Imagine: you wake up in the morning, light your wood stove and place the kettle on it to boil. In a few minutes, after your water has boiled and you’ve fixed your tea, you reach down and plug your radio into the stove.
How is this possible? Your stove has no moving parts, yet it can generate electricity from the heat of the fire.
It may sound like science fiction, but thermoelectric generators have existed since the 1800s. Over the past 20 years, these generators have grown popular again in green industrial fields as well as consumer products, and today you can find cooking pots and wood stoves fitted with thermoelectric generators.
But before we look at these products, let’s examine the machine itself: what is a thermoelectric generator?
The science behind the machine
A thermoelectric generator is a simple device that converts heat into electrical energy through the phenomenon known as the Seebeck effect. (Thomas Seebeck, the physicist, discovered the principle in 1821.) No moving parts are needed in a thermoelectric generator because it is the temperature difference that creates the electricity.
Thermoelectric generators are composed of two dissimilar conductors or semiconductors—basically, two different metals connected to form a loop with two junctions. To use the device, a temperature difference is created; for example, heat can be applied to one side. That’s all it takes – when one junction is hot and the other is cold, a circuit is created through which an electric current will flow.
Confused? It’s all in the electrons.
Here’s a quick physics lesson: metals are good conductors of electricity because they contain free electrons. These free electrons act like gases that can quickly move through their solid containers – for example, an electric wire, or each of the two metals within a thermoelectric generator.
Each metal in a thermoelectric generator contains free electrons with different densities, and these electrons diffuse across the junctions and create the current. If you increase the temperature difference, the amount of current will increase as well.
Thermoelectric generators in the 20th century
Thermoelectric generators are not new inventions. There was an initial period of research that spanned the 1800s, and a great hopeful era in the 20th century when researchers believed the thermoelectric generator would replace the internal combustion engine.
By the 1920s, battery-free radios powered by thermoelectricity were widely used in the Soviet Union. The radios came equipped with bi-metal rods, and by placing one rod in the fireplace and one rod outside in the cold, you would produce the electricity required to operate the device. Similar kerosene-powered radios were manufactured by the Soviets and USA during the cold war.
Beyond radio applications, researchers largely found it difficult to create satisfactory consumer solutions that utilized thermoelectric generators. Efficiency had improved but was still low, and by 1970 thermoelectricity fell out of favor.
Rolling into the future
It is said that the history of thermoelectricity is a series of discoveries separated by 20–25 year lulls when nothing much happens. About 20–25 years after the 1970 lull, interest in thermoelectricity revived—driven partly by the increasing desire to conserve resources that swelled in the 1990s.
Since then, researchers have again searched for suitable applications for this device. We expend a lot of waste heat in our world, and the beauty of thermoelectric generators is that they can be used to recover this heat from anywhere. (There’s still the ongoing problem of low efficiency in these generators, but that may be changing with today’s technology.)
One obvious place for thermoelectric solutions is within automobiles, because our cars produce a lot of waste heat. In the near future we will most likely see thermoelectric generators equipped on Volkswagen and BMW models.
BMW has successfully driven a thermoelectric-equipped prototype more than 12,000 km, and Volkswagen has a generator than produces 30% of the car’s electrical requirement and reduces fuel consumption by more than 5%. While there have been several prototypes in the past, these ones look like they’re going to make it all the way to production.
Current thermoelectric applications
If you want to use this technology today, there are a number of products available.
A few different USB-equipped cooking products are for sale now, including this model: PowerPot V. It’s exactly what it looks like – a cooking pot with a fireproof USB cord coming out of the side. To produce electricity, you fill the pot with cold water and put it on the fire. The PowerPot V can charge smartphones, headlamps, GPS units, water purifiers, and more.
Devil Watt Camping Cook Stove
The Devil Watt DW-ST–15W Camping Cook Stove Thermoelectric Generator is similar to but more powerful than the PowerPot V. The Devil Watt device is placed directly on the fire and generates electricity to power a 12V DC device. It also has 5V DC USB output which should charge a variety of USB devices such as smartphones.
The Devil Watt DW-ST–15W Camping Cook Stove Thermoelectric Generator comes with two cables. The first provides 12V DC automotive output as well as the 5V DC USB port, and the second gives 13.8V (for charging batteries).
Thermofor Indigirka wood stove
The Indigirka model by Thermofor contains a built-in thermoelectric generator that kicks in after about 10–15 minutes after ignition. Thermofor states that the stove generates a direct electric current of 12 Volts and up to 60 Watts. “The electricity generated by the stove,” states Thermofor, “is sufficient to power 2 or 3 energy saving bulbs, charge a notebook battery, or that of a cellular or satellite telephone, a radio, DVD player or other portable energy-saving devices.”
DIY – how to make a thermoelectric generator
It’s fairly easy to experiment with thermoelectricity, but remember that you’re working with a low-efficiency device, and the thermoelectric module can be costly.
Here are some links to get you started:
- Backpacking Light
- Generating electricity using a candle and a heat sink
- Smartphone Charger Powered by Fire
(Note that this Backpacking Light and some of the other thermoelectric tutorials online use Peltier cooling modules instead of Seebeck generators. They’re related devices. Research the Peltier effect if you want to know more about this.)
- TEGMART sell a variety of thermoelectric products, including PowerPot, Devil Watt, and a variety of modules and parts.
- TECTEG has a large number of thermoelectric products for sale, including complete power generator systems,and parts for custom designs.
- TEGPro products – TEGPro manufacture the Devil Watt series of thermoelectric systems
- Youtube thermoelectric generator videos
- Glossary Of thermoelectric terms at TECTEG
Practical applications for thermoelectric technology have for a long time laid just beyond our reach, but hopefully advances in physics will bring us some new and easy thermoelectric solutions for our energy needs. Let us know if you do any work with thermoelectricity – we would love to see what you make.
- Thomas Seebeck discovered this phenomenon in 1821. Read more about Seebeck on the Thomas Johann Seebeck Wikipedia page: http://en.wikipedia.org/wiki/Thomas_Johann_Seebeck ↩
- “Electrical conductivity involves a flow or current of free electrons through a solid body. Some materials, such as metals, are good conductors of electricity; these possess free or valence electrons that do not remain permanently associated with the atoms of a solid but instead form an electron “cloud” or gas around the peripheries of the atoms and are free to move through the solid at a rapid rate.” ↩–Encyclopædia Britannica Online, s. v. “materials testing”, accessed January 30, 2014, http://www.britannica.com/EBchecked/topic/369090/materials-testing/80752/Fatigue.
- Batteryless radios: http://en.wikipedia.org/wiki/Batteryless_radio ↩
- See also: http://en.wikipedia.org/wiki/Automotive_Thermoelectric_Generators ↩
- International Thermoelectric Society – Thermoelectric power for automobiles arrives in Europe: http://www.its.org/node/5670 ↩