Maximum Power-Point Theory For Thermoelectric Harvesters.

Thermoelectric generators (TEGs) are resistive dc sources that supply the most power when their resistance drops half the dc voltage. Not all this power reaches the load, however. The energy-harvesting circuit that draws and transfers this power loses some of it in the form of heat. These ohmic losses scale linearly and quadratically with current. From the perspective of the load, linear losses reduce the dc voltage of the source and quadratic losses raise the series resistance. This not only decreases the power delivered to the load but also shifts the maximum power point of the system. Neglecting this shift in maximum power point sacrifices 2.5% to 90% of the maximum achievable power when the added resistance is 10% to 50% of the thermoelectric resistance and the voltage loss is 5% to 23% of the thermoelectric voltage. This paper derives, models, and shows how the maximum power point of the thermoelectric harvester differs from that of the TEG and when that difference is significant.