Thermoelectric Generators Basics

In physics, we learn that energy can’t be created or destroyed—it only changes form. This idea, called the Law of Conservation of Energy, drives engineers to find ways to convert energy into forms that are more useful.

A good example of this is thermoelectric generation, which turns heat directly into electricity. This effect, first discovered by Thomas Seebeck and now called the Seebeck Effect, is used in devices called thermoelectric generators (TEGs). These solid-state devices didn’t see much real-world progress until the 20th century, with the first commercial versions appearing in the 1960s. Since then, TEGs have found their way into many different types of applications.

TEG module basics

Thermoelectric generator modules (often called TEGs) work by turning temperature differences into electrical voltage, or the other way around. This behavior, known as the thermoelectric effect, encompasses three related parts: the Seebeck Effect, which generates electricity from a temperature gradient; the Peltier Effect, where heat is absorbed or released when current flows across two different materials; and the Thomson Effect, where heat is produced or absorbed depending on the current’s direction.

A common point of confusion in thermoelectric technology is the difference between thermoelectric generators (TEGs) and thermoelectric coolers (TECs). TEGs harness the Seebeck Effect to generate electricity from heat, while TECs make use of the Peltier Effect to provide cooling or maintain stable temperatures. Both rely on similar semiconductor materials, but their designs differ: TEGs are built for high temperature differences and efficiency in power output, while TECs are optimized for heat transfer using materials like ceramics and copper.

In practice, if the goal is to generate energy from heat, a TEG module is the right choice. For cooling or temperature stabilization, a TEC—or Peltier module—is more effective. Same Sky offers both TEG modules and Peltier modules, making it easier to match the right device to design needs.

In a modern thermoelectric generator (TEG), electricity is produced when a temperature difference exists between its hot and cold sides. Inside the module, multiple pairs of n-type and p-type semiconductors—often made from bismuth telluride—are positioned between two plates (Figure 1). In n-type materials, electrons flow from the hot side toward the cold side, while in p-type materials, the movement is due to holes (the absence of electrons) shifting the same way. Together, these flows create a voltage, and the larger the temperature difference, the greater the output.

TEGs are especially valuable in situations where heat would otherwise be wasted, such as industrial operations, where they help recover lost energy. They also serve in remote or extreme environments. For example, powering space probes by converting the heat from radioactive decay into electricity when sunlight is insufficient.

Figure 1: The general construction of a TEG module. (Image source: Same Sky)

Advantages and disadvantages of TEGs

The key advantage of thermoelectric generator (TEG) modules is their ability to turn waste heat into usable electricity, helping capture energy that would otherwise be lost. This makes them not only practical but also environmentally friendly.

Because TEGs are solid-state devices, they have no moving parts—meaning they’re quiet, durable, and require little to no maintenance. Their compact form factor allows them to fit into tight spaces, and with options available across a range of voltages and currents, they can deliver reliable power without relying on a traditional power grid. This makes TEGs ideal for remote installations or as efficient alternatives to battery-based systems.

Although thermoelectric generators (TEGs) provide a reliable source of electrical power, they do come with design limitations. Their performance depends heavily on having a strong temperature difference, which restricts them to certain applications where heat gradients are available. In addition, TEGs generally operate at relatively low conversion efficiencies—often around 10%—which is modest compared to many other energy generation technologies.

Key TEG selection criteria

When integrating thermoelectric generator (TEG) modules into a system, it’s important to consider key specifications that directly affect performance. The most critical factor in operation is the temperature difference between the hot and cold sides (often called ΔT). While this drives how much power a TEG can generate, it’s not always shown on datasheets. Instead, manufacturers typically list Tmax, the maximum safe operating temperature, which helps define limits but not necessarily the best working conditions.

Other useful specs include open-circuit voltage, matched-load voltage, current, resistance, and power. These values provide insight into how the device will perform under actual thermal and electrical loads. Datasheets, like those from Same Sky, usually present this information in both tables (Figure 2) and performance graphs (Figure 3) to make system-level design easier.

Figure 2: TEG specifications table from a Same Sky datasheet. (Image source: Same Sky)

Performance graphs plot electrical outputs against the hot-side temperature (T_h) and corresponding cold-side conditions. Common graphs include:

• Open-Circuit Voltage vs. T_h – shows the maximum voltage when no load is applied
• Matched Load Resistance vs. T_h – indicates the internal resistance at a given ΔT
• Matched Load Voltage vs. T_h – displays output voltage when the device is under load
• Matched Load Current vs. T_h – shows the current delivered under load
• Matched Load Output Power vs. T_h – represents the usable power generated, which can also be derived from voltage and current using Ohm’s Law

These graphs allow engineers to identify peak performance points, typically at the optimal load resistance, and understand how efficiency varies with different thermal and electrical conditions. By studying these plots, designers can better match a TEG to their application, compare different modules, or troubleshoot performance in a real system.

Figure 3: Typical TEG performance graphs with hot side temperatures plotted on the X-axis, various performance curves for cold side temperatures, and the metric being analyzed on the Y-axis. (Image source: Same Sky)

To choose the right thermoelectric generator (TEG), a designer first identifies the expected hot-side and cold-side temperatures. With these values, the matched load voltage, current, power, and resistance charts on the datasheet can be used to estimate performance. For example, Same Sky’s SPG176-56 module at T_h=200°C and T_c=30°C produces about 5.9 V, 1.553 A, and 9.16 W of power with a resistance near 3.8 Ω. These values can be gathered from each performance graph by drawing a vertical line from T_h=200°C on the X-axis until it intersects with the T_c=30°C curve. From this point, draw a horizontal line over to the Y-axis to gather the expected output. Again, because TEGs follow Ohm’s Law, any combination of the graphs and use of the power formula can get the designer to the expected output from the TEG.

In practice, this process is straightforward under ideal conditions, but designers often need to adjust for less-than-perfect temperature differences or load mismatches using interpolation between the performance curves.

Conclusion

Thermoelectric generators (TEGs) are valuable in applications where remote power is required or where reclaiming energy can boost overall system efficiency. They are generally available in two forms: large TEGs, capable of delivering several watts up to hundreds of watts for industrial purposes, and micro TEGs, which supply from a few watts down to milliwatts for smaller-scale needs. Current uses span a wide range of fields, including consumer devices like wearables, space probes and aerospace systems, industrial waste heat recovery, solar energy conversion, IoT sensors, automotive engines, industrial electronics, HVAC equipment, medical monitoring devices, military systems, scientific instruments, and telecom infrastructure.

With a wide range of power outputs and efficiencies available, TEGs bring value to system design by supporting portability, remote operation, and energy recovery. For selection, Same Sky offers TEG modules in various sizes and output ratings to fit different design requirements.