Thermoelectric Generators: Waste Heat to Electricity

Thermoelectric generators (TEGs) convert temperature differences directly into electrical voltage using the Seebeck effect. You place one side of the module on a heat source (like an exhaust pipe or hot water pipe) and keep the other side cool, and the device produces a small but steady DC current. This guide explains the physics, the practical steps to set up a working TEG system, and how to avoid the common pitfalls that keep beginners from getting useful power.

What You’ll Need

• A thermoelectric generator module (e.g., TEG1-1263-4.3 or similar, rated for your temperature range)
• A heat source (hot plate, exhaust pipe, wood stove, or hot water line)
• A heat sink with fan or water cooling block (to keep the cold side cool)
• Thermal interface material (thermal paste or graphite pad)
• Clamps, bolts, or a frame to press the module between heat source and heat sink
• A multimeter to measure voltage and current
• A DC-DC boost converter (if you need to charge a battery or run a 5V device)
• Optional: temperature sensors (thermocouple or IR thermometer)

Step-by-Step

1. Choose your TEG module based on temperature. Most common TEGs (like Bi2Te3) work best between 100°C and 300°C on the hot side. If your heat source is hotter, you need a higher-temperature module (e.g., skutterudite or half-Heusler). Check the datasheet for maximum hot-side temperature.
2. Prepare the surfaces. Both the heat source and the heat sink must be flat and clean. Remove any dirt, rust, or old thermal paste. If the surfaces are rough, sand them lightly (e.g., 400 grit) to improve contact.
3. Apply thermal interface material. Spread a thin, even layer of thermal paste (about 0.1 mm) on both sides of the TEG. Alternatively, use a graphite pad. The goal is to fill microscopic gaps—too much paste acts as an insulator.
4. Sandwich the TEG between heat source and heat sink. Place the module with the marked side (usually the side with the wires) facing the heat sink or as per datasheet. Press the heat sink on top. The cold side must be the one with the heat sink; if you reverse it, efficiency drops dramatically.
5. Apply even pressure. Use clamps or bolts to press the assembly together. The recommended pressure is typically 0.5–1 MPa (about 70–150 psi). Too little pressure leaves air gaps; too much can crack the ceramic plates. Use a torque wrench if possible—common values are 0.3–0.5 N·m for small modules.
6. Connect the load. Attach the red wire to the positive terminal of your multimeter (or load) and the black wire to negative. TEGs produce DC, so polarity matters. If you get a negative reading, swap the wires.
7. Heat the hot side gradually. Turn on your heat source. Monitor the temperature with a thermocouple or IR thermometer. Do not exceed the module’s maximum hot-side temperature (often 200°C or 300°C).
8. Cool the cold side. Turn on the fan or water pump. The bigger the temperature difference (ΔT), the more voltage you get. For example, a ΔT of 100°C might give about 4–5 volts open-circuit on a typical 40×40mm module.
9. Measure output. With the multimeter set to DC volts, read the open-circuit voltage. Then connect a known load (like a resistor or a small fan) and measure current. Power = V × I. At maximum power transfer, the load resistance matches the module’s internal resistance (often 1–3 ohms).
10. Boost the voltage if needed. If your TEG produces less than 5V (common when ΔT is small), use a DC-DC boost converter (like a MT3608 or a dedicated TEG booster) to step it up to a usable level. Connect the TEG output to the converter input, and the converter output to your battery or device.

Common Mistakes

• Reversing hot and cold sides. Some modules are symmetric, but many have a specific orientation. Check the datasheet. If you put the heat sink on the wrong side, the module may still work but with poor efficiency.
• Using too much thermal paste. Excess paste creates a thick layer that insulates. Use just enough to fill gaps—a thin, even coat.
• Overheating the module. Exceeding the max temperature can melt the solder inside and destroy the module. Always monitor temperatures.
• Not applying enough pressure. Air gaps are terrible conductors. Without proper clamping, the ΔT across the module is much lower than the ΔT between the source and sink, so you get less voltage.
• Ignoring the cold side. A TEG is only as good as its heat sink. If the cold side heats up, ΔT drops and output collapses. Use a fan or water cooling for any serious power.
• Connecting the load incorrectly. TEGs have low internal resistance; shorting them is okay, but reverse polarity can damage sensitive electronics.

Tips

• Maximize ΔT, not absolute temperature. A TEG with a hot side at 150°C and cold at 30°C (ΔT=120°C) produces more than one with hot at 250°C and cold at 200°C (ΔT=50°C). Focus on cooling.
• Use a dedicated TEG module, not a Peltier cooler. Peltier modules (TEC) are designed for cooling and have different internal resistance and thermal properties. They can generate some power but are much less efficient.
• Match the load resistance. For maximum power, the load resistance should equal the module’s internal resistance at your operating ΔT. You can find this by measuring voltage with two different load resistors and using the formula R_internal = R_load × (V_open / V_load – 1).
• Consider multiple modules. If you need more power, place several TEGs in series (for higher voltage) or parallel (for higher current) on the same heat source. Ensure they are all at the same temperature.
• Use a heat spreader. If your heat source is smaller than the module, use a copper or aluminum plate to spread heat evenly. This prevents hot spots that can crack the ceramic.

Troubleshooting

• No voltage output. Check that the multimeter is on DC volts, the wires are connected, and the module is actually experiencing a temperature difference. If the hot side is warm but the cold side is also warm, ΔT is too small. Increase cooling or heat.
• Very low voltage (e.g., 0.1V). This usually means a small ΔT. Measure the temperature on both sides. If the hot side is 100°C and cold is 90°C, you only have 10°C ΔT. Improve cooling or reduce thermal resistance between the module and heat sink.
• Voltage drops to zero when you connect a load. This is normal if the load resistance is much lower than the module’s internal resistance. Use a higher-resistance load or a boost converter with proper input impedance.
• Module cracks. This happens from uneven pressure or thermal shock. Ensure the surfaces are flat, apply pressure gradually, and heat up slowly. Also, avoid clamping too hard—use a torque wrench.
• Output is unstable. Fluctuations usually come from varying heat source temperature or poor contact. Tighten clamps and ensure the heat sink fan is running steadily.

Frequently Asked Questions

How much power can a typical TEG generate?

A small 40×40mm module can produce about 1–5 watts at a ΔT of 100–200°C. Larger modules or arrays can produce tens of watts, but efficiency is typically 5–8%.

Can I use a Peltier cooler as a TEG?

Yes, but it’s inefficient. Peltier modules are designed for cooling, so their internal resistance is lower and they generate less voltage per degree. You might get a few milliwatts from a small one.

What is the Seebeck effect?

It’s the phenomenon where a temperature difference between two dissimilar conductors or semiconductors creates a voltage difference. TEGs use this to convert heat directly into electricity.

How long do TEGs last?

With proper cooling and staying below maximum temperature, TEGs can last tens of thousands of hours. The main failure is thermal cycling fatigue—repeated heating and cooling can crack solder joints.

Can I connect multiple TEGs in series?

Yes, connecting them in series adds their voltages, which is useful for charging batteries. Ensure they are all at similar temperatures to avoid one module dragging down the others.

Do I need a boost converter?

If your TEG produces less than your load needs (e.g., 3V for a 5V USB device), a boost converter is necessary. It steps up the voltage but also draws more current, so match it to your TEG’s power curve.

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