A thermoelectric harvester converts temperature differences into electrical energy using the Seebeck effect, enabling power generation from waste heat sources like engine exhausts, industrial processes, cooking stoves, and even body heat. For Indian applications — from powering IoT sensors on factory machinery to charging phones from a cooking chulha — thermoelectric generators (TEGs) offer a unique energy source. This guide covers TEG selection, boost converter circuits, and practical Indian applications.
What Is Thermoelectric Harvesting?
Thermoelectric generators (TEGs) are solid-state devices with no moving parts that directly convert heat flow into electrical current. They are the inverse of Peltier coolers (which use electricity to create a temperature difference). When one face of a TEG module is hot and the other cold, a voltage proportional to the temperature difference appears across the terminals.
The Seebeck Effect Explained
Voltage output: V = S x deltaT
S = Seebeck coefficient of the module (typically 20-50 mV/degC)
deltaT = temperature difference between hot and cold sides
Example: SP1848-27145 TEG module
deltaT = 100degC → V ≈ 4.8V, I ≈ 600mA → P ≈ 2.88W
deltaT = 50degC → V ≈ 2.4V, I ≈ 300mA → P ≈ 0.72W
deltaT = 20degC → V ≈ 1.0V, I ≈ 100mA → P ≈ 0.10WThe key challenge: at low temperature differences (10-30degC), TEG output voltage is below 1V — too low for most electronics. A boost converter is essential to step up to usable 3.3V or 5V.
TEG Module Selection
Common TEG modules available in India:
| Module | Size | Max Power | Cost (India) |
|---|---|---|---|
| SP1848-27145 | 40x40mm | ~3W at 100degC diff | ₹100-200 |
| TEC1-12706 | 40x40mm | ~2W at 100degC diff | ₹150-250 |
| TEG-126T200 | 40x40mm | ~5W at 150degC diff | ₹400-800 |
Note: TEC1-12706 is sold as a Peltier cooler but works as a TEG in reverse. Dedicated TEG modules are optimised for higher deltaT and last longer at elevated temperatures.
Boost Converter for Low-Voltage TEG
LTC3108 Ultra-Low Voltage Boost Converter:
Input: As low as 20mV! (perfect for small deltaT)
Output: 2.35V, 3.3V, 4.1V, or 5V (selectable)
Built-in charge pump and LDO
Designed specifically for thermoelectric harvesting
Alternative: BQ25504 (TI)
Input: 80mV minimum start, 130mV continuous
MPPT tracking for TEG optimisation
Output: Programmable, charges battery or supercapFor simple hobbyist projects, the Zbotic boost module (1.5V to 5V) works when TEG output exceeds 0.7V (approximately 15-20degC difference with SP1848).
Indian Applications
- Chulha (cooking stove) phone charger: TEG between stove surface and aluminium heatsink. 50-80degC difference during cooking generates 1-2W — enough to charge a phone slowly.
- Industrial machine monitoring: TEG on hot machinery (motor housings, boilers, steam pipes) powers IoT sensors without wiring or battery replacement.
- Vehicle exhaust recovery: TEGs on exhaust manifold of trucks/buses can generate 10-50W from waste heat.
- Solar hot water recovery: TEG between hot water pipe and ambient air in solar water heater systems.
FAQ
How efficient are thermoelectric generators?
TEG efficiency is typically 3-8% of the Carnot limit — much lower than mechanical heat engines. However, TEGs harvest energy that would otherwise be completely wasted (exhaust heat, industrial process heat), so even low efficiency is valuable. The zero-maintenance, no-moving-parts nature makes them ideal for remote monitoring.
Can I use a Peltier module as a TEG?
Yes, but with reduced performance. Peltier modules (TEC1-12706) are optimised for cooling, not power generation. They work as TEGs but with lower efficiency and reduced lifespan at high temperatures. For serious applications, invest in dedicated TEG modules designed for higher hot-side temperatures.
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