Selecting the right thermoelectric generator (TEG) hinges on understanding the critical relationship between temperature differential and electrical power output. The core principle is the Seebeck effect: a voltage is generated when a temperature difference (ΔT) is maintained across a TEG module. Crucially, the power output is not linearly proportional to ΔT; it generally increases with the square of the temperature difference. Therefore, a larger ΔT typically yields exponentially greater power.

However, maximizing ΔT is only one facet of selection. The TEG's intrinsic material properties, defined by its figure of merit (ZT), determine its conversion efficiency at a given temperature range. A high-ZT material performs better. System design is paramount. The heat source's temperature and thermal capacity, along with the effectiveness of the hot-side heat exchanger, dictate the maximum achievable hot-side temperature. Conversely, the cold-side heat sink's ability to dissipate heat determines the lowest possible cold-side temperature. The quality of thermal interfaces and mechanical clamping pressure significantly impact the actual ΔT across the semiconductor pellets versus the measured external ΔT.

Furthermore, the electrical load must be matched to the TEG's internal resistance for maximum power transfer. Operating at very high ΔT may induce thermal stresses and degrade materials over time, affecting longevity. In practice, selection involves balancing the desired power output against the available ΔT, system constraints, cost, and reliability. For instance, energy harvesting from waste heat in industrial settings often involves high temperatures but requires robust modules, while wearable or IoT applications leverage small ΔTs at lower temperatures, prioritizing miniaturization. A successful design integrates the TEG as a component within a full thermal system, where optimizing the entire thermal circuit is as important as the generator module itself.