Limitations
Besides low efficiency and high cost, two general problems exist in such devices: high output resistance and adverse thermal characteristics.
- High output resistance - in order to get a significant output voltage a very high Seebeck coefficient is needed (high V/°C). A common approach is to place many thermo-elements in series, causing the effective output resistance of a generator to be very high (>10Ω). Thus power is only efficiently transferred to loads with high resistance; power is otherwise lost across the output resistance. A generator with very high output impedance is effectively a temperature sensor, not a generator. This problem is solved in some commercial devices by putting more elements in parallel and fewer in series.
- Adverse thermal characteristics - because low thermal conductivity is required for a good thermoelectric generator, this can severely dampen the heat dissipation of such a device (i.e. thermoelectric generators serve as poor heat sinks). They are only economical when a high-heat source can be used above 200°C for watts generated and if only small milliwatts are needed then any temperature difference with correct design can be achieved.
Read more about this topic: Thermoelectric Generator
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