Thermo-Electric Energy Harvester for Low-Power Sanitary Applications

The paper presents solutions for self-sufficient energy supply for sanitary applications. The difference in temperature between a hot and cold water pipe is utilized via a thermo-electric generator to feed a DC/DC converter. A sufficiently large voltage can be gained even for moderate temperature differences to power a DC/DC converter capable of stepping-up from low feed voltages in the range of a few millivolts. We could show that even the rather small temperature difference between ambient and cold water pipe temperatures is sufficient. An electronic circuit design is able to convert these voltages in the lower mV-range to necessary levels directly usable for low-power microprocessors and other electronic components. In particular these thermo-electric converters are used successfully for sanitary electronics even allowing to bridge typical idle times by lithium-ion cells. To achieve optimal energy utilization a theoretical model was devised that includes the thermo-electric converter the thermal capacity of the pipes and all thermal resistances involved. The modeling of the thermal section was done using the differential equations solver SPICE in order to allow calculatory efficiency and coupling with electrical loads or step-up converters.