Researchers at the University of Hong Kong (HKU) have developed a thermoelectric generator that can produce electricity use low grade heat.
The Direct Thermal Charging Cell (DTCC) developed by Dr Tony Shien-Ping Feng of the Department of Mechanical Engineering can effectively convert heat to electricity. Low grade heat is abundantly available in industrial processes (80 to 150°C), as well as in the environment through solar (50 to 60°C) and geothermal energy. Over 60% of the world’s primary energy input, whether it is in the industrial process or domestic energy consumption, is wasted as heat. A majority of this loss as waste heat is regarded as low-grade heat.
The DTCC uses asymmetric electrodes: a graphene oxide/platinum (GO/Pt) cathode and a polyaniline (PANI) anode in Fe2+/Fe3+ redox electrolyte. When heated, the cell generates voltage via a thermo-pseudocapacitive effect and then discharges continuously by oxidizing the PANI anode. The energy conversion works continuously under isothermal heating during the entire charge and discharge process and so the system can be self-regenerated when cooled down. The resulting system has a conversion efficiency of 3.5percent, which is higher than most thermoelectric generators, say the researchers.
The low cost, bendable thermoelectric cell measures 1.5 sq.cm and is 1.5 mm thick. It can be used in HVAC (heating, ventilation, and air conditioning) system to recycle low-grade heat from the compressor and condenser into electricity for use in electrical devices. It can be integrated with the window frame to harvest solar thermal energy to power electrochromic windows, or used as portable devices to power cellular phones or medical equipment in the wilderness.
The researchers see the DTCC as a way to harness body heat to power wearable electronic devices or medical devices for monitoring body health conditions like blood sugar levels and blood pressure.
“Efficient low-grade heat recovery can help to reduce greenhouse gas emission but current technologies to convert this heat to electricity is still far from optimum,” said Feng. “DTCC yields a conversion efficiency of over 3.5%, surpassing all existing thermo-electrochemical and thermo-electric systems, which is either too costly or complicated, or too low in efficiency for everyday applications. DTCC is a revolutionary design with great potentials in smart and sustainable energy devices.”
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