A thermoelectric generator (TEG) converts heat directly into electricity using a simple physical principle: when one side of certain semiconductor materials is hot and the other side is cold, electrons flow from hot to cold, creating a voltage. You can build a working TEG with a few inexpensive components, and the most common DIY version costs under $20 in parts. The output is modest, typically enough to charge a phone or power small electronics, but the process is straightforward and requires no moving parts.
How Thermoelectric Generation Works
In 1821, physicist Thomas Seebeck discovered that joining two different conductive materials and heating one end while cooling the other produces a small electrical voltage. Electrons in the materials flow away from the heat source toward the cooler side, and this movement of charge is usable electricity. Modern thermoelectric modules use pairs of semiconductors (called N-type and P-type) wired together in series inside a flat ceramic plate. The greater the temperature difference between the hot and cold sides, the more voltage the module produces.
The materials used commercially today include bismuth telluride for lower-temperature applications (up to about 250°C on the hot side) and lead telluride or silicon germanium for higher temperatures exceeding 500°C. For a DIY project, you’ll almost certainly be working with bismuth telluride modules, which are cheap and widely available.
Choosing the Right Module
You’ll encounter two types of modules that look nearly identical: dedicated thermoelectric generator modules (like the SP1848-27145SA) and Peltier cooler modules (like the TEC1-12706) repurposed as generators. Both are roughly 40mm × 40mm ceramic squares that cost around $3 to $4 each. The difference in performance is significant.
The SP1848 generator module produces more than double the electrical output of the TEC1-12706 cooler module under identical conditions. In testing at a temperature difference of about 22°C, two SP1848 modules wired in parallel produced around 1,068 millivolts and 106 milliamps. The same setup with TEC1-12706 modules produced only 506 millivolts and about 50 milliamps. Overall, dedicated TEG modules generate roughly 50% more current than repurposed cooler modules.
The SP1848 can handle a maximum temperature difference of 100°C with a hot-side temperature up to 150°C. The TEC1-12706 is rated for a hot-side temperature of only 50 to 57°C, with a maximum temperature difference of 66 to 75°C. If your heat source is a campfire or stove, the dedicated TEG module is the better and safer choice.
Parts You Need
- TEG module(s): SP1848-27145SA or similar dedicated generator module. One module can work, but two or more wired in series will give you higher voltage.
- Heat source: A wood stove, campfire, candle cluster, or any consistent source of heat.
- Heat sink: An aluminum finned heat sink (salvaged from an old computer CPU cooler works well) to keep the cold side cool.
- Thermal paste: Applied between the module faces and the heat conductor/heat sink for efficient heat transfer.
- DC-DC boost converter: A small PFM boost module that steps up the low TEG voltage to a usable 5V.
- Schottky diode (1N5817): Prevents current from flowing backward into the module when you connect a device.
- Capacitor: A buffer capacitor (around 1000µF) across the boost converter output to smooth voltage fluctuations.
- USB connector: A Type-A female USB port for plugging in a charging cable.
Building the Generator Step by Step
Start by creating good thermal contact on both sides of the TEG module. Apply a thin, even layer of thermal paste to both ceramic faces. Mount the hot side against a metal plate or surface that will contact your heat source. A flat piece of aluminum or copper plate works well as a heat spreader. Attach the heat sink to the cold side, again with thermal paste between them. The goal is maximum temperature difference across the module, so the cold side needs to shed heat efficiently.
If you’re using a wood stove, clamp or bolt the assembly so the hot-side plate sits against the stove surface and the finned heat sink faces outward into open air. Some builders add a small fan powered by the TEG itself to actively cool the heat sink, though natural convection works for basic setups. You can also place a container of water or snow against the cold side for a larger temperature gradient.
For the wiring, connect the positive (red) wire from the TEG module to the anode of the Schottky diode. The cathode of the diode connects to the input of the DC-DC boost converter module. Solder the buffer capacitor across the output terminals of the boost converter, then wire the USB connector to those same output terminals, matching positive and ground. Most boost converter boards have a small potentiometer to adjust output voltage. Use a multimeter to set it to 5.0V before connecting any device.
Why You Need a Boost Converter
A single TEG module at a modest temperature difference produces somewhere between 0.5V and 2V, far below the 5V a USB device needs. A boost converter takes this low input voltage and steps it up. Even very efficient converters need a minimum input to function. Most off-the-shelf boost boards for hobbyists require at least 0.9V to 1V input, which a single SP1848 module can reach at a temperature difference of roughly 40 to 50°C.
Advanced boost converters designed for energy harvesting can self-start at inputs as low as 50 millivolts and operate sustainably down to 3.5 millivolts, achieving over 75% efficiency at inputs above 15 millivolts. These are specialized integrated circuits rather than off-the-shelf hobby boards, but they show what’s possible if you want to harvest electricity from very small temperature differences, like body heat. For a stove or campfire project, a standard $2 boost board from an electronics supplier is all you need.
Getting More Power
A single SP1848 module maxes out at about 4.8V open-circuit voltage and 669 milliamps under ideal conditions (a full 100°C temperature difference). In practice, with a wood stove and passive air cooling, you’ll see a temperature difference of 40 to 80°C and a real-world output well below those maximums. That’s enough to slowly charge a phone but not much more.
To increase output, wire multiple modules in series to add their voltages together, or in parallel to add their currents. Four modules in series at a 60°C temperature difference can produce enough voltage to skip the boost converter entirely and feed a 5V regulator directly. Stacking modules also lets you charge devices faster, with total output reaching up to 1,000 milliamps, which is the maximum most smartphones will draw from a USB port.
Consistent contact pressure matters more than most builders expect. Use bolts or clamps to press the module firmly between the hot plate and heat sink. Any air gap kills performance because it disrupts the temperature gradient across the semiconductors.
Temperature Limits and Common Mistakes
Bismuth telluride modules, which include virtually all affordable TEG and Peltier modules, are limited to hot-side temperatures below 250°C. Above that, the semiconductor material degrades and the solder joints inside the module can melt. A wood stove surface typically runs between 150°C and 350°C depending on location, so placement matters. Use the cooler areas of the stove (sides rather than the top near the flue) or add a thicker metal heat spreader to buffer the temperature.
Thermal interface losses are the biggest efficiency killer in homemade setups. Without thermal paste, or with warped surfaces that don’t make full contact, you can lose half your temperature difference before it even reaches the semiconductor elements. Use flat, machined surfaces where possible and always apply fresh thermal compound.
Another common mistake is neglecting the cold side. The module doesn’t care about absolute temperature. It only cares about the difference between its two faces. A blazing hot stove with a poorly cooled heat sink might give you the same output as a warm pot of water with an ice-cooled cold side. Water cooling, whether by running water through a block or simply clamping a water-filled container against the cold side, is the single easiest upgrade to boost performance.
What You Can Realistically Power
A single-module campfire setup with passive air cooling will charge a smartphone slowly, roughly comparable to a low-power USB port. Two to four modules with decent thermal management can charge at normal speed. LED lights, small fans, temperature sensors, and microcontrollers like Arduino boards all run comfortably on TEG power. Some commercial products built on this exact principle, like the PowerPot, generate electricity within seconds of being placed on a fire and deliver a standard 5V USB output.
For anything drawing more than about 5 watts, you’ll need a large array of modules and serious heat management. Thermoelectric generators are inherently low-efficiency devices, converting only about 5 to 8% of the heat energy into electricity under typical conditions. They shine in situations where heat is free and abundant, like waste heat from a stove, exhaust pipe, or industrial process, and where reliability and simplicity matter more than raw power output.