Converting Electricity Into Heat And Vice Versa

A new University of Wollongong (UOW) study in Australia overcomes a major challenge of thermoelectric materials, which can convert heat into electricity and vice versa,improving conversion efficiency by more than 60%. Current and potential future applications range from low-maintenance, solid-state refrigeration to compact, zero-carbon power generation, which could include small, personal devices powered by the body’s own heat.

The decoupling of electronic (electron-based) and thermal (phonon-based) transport will be a game-changer in this industry,” says the UOW‘s Prof Xiaolin Wang.

Bismuth telluride-based materials (Bi2Te3, Sb2Te3 and their alloys) are the most successful commercially-available thermoelectric materials, with current and future applications falling into two categories: converting electricity into heat, and vice versa:

  • Converting electricity into heat: reliable, low-maintenance solid-state refrigeration (heat pump) with no moving parts, no noise, and no vibration.
  • Converting heat into electricity including fossil-free power generation from a wide range of heat sources or powering micro-devicesfor free‘, using ambient or body temperature.

Heatharvesting‘ takes advantage of the free, plentiful heat sources provided by body heat, automobiles, everyday living, and industrial process. Without the need for batteries or a power supply, thermoelectric materials could be used to power intelligent sensors in remote, inaccessible locations.

An ongoing challenge of thermoelectric materials is the balance of electrical and thermal properties: In most cases, an improvement in a material’s electrical properties (higher electrical conductivity) means a worsening of thermal properties (higher thermal conductivity), and vice versa.

The key is to decouple thermal transport and electrical transport“, says lead author, PhD student Guangsai Yang.


How To ConVert Waste Heat Into Electricity

Thermoelectric materials, capable of transforming heat into electricity, are very promising when converting residual heat into electrical energy, since they allow us to utilize hardly usable or almost lost thermal energy in an efficient way. Researchers at the Institute of Materials Science of Barcelona (ICMAB-CSIC) have created a new thermoelectric material: a paper capable of converting waste heat into electricity. These devices could be used to generate electricity from residual heat to feed sensors in the field of the Internet of Things, Agriculture 4.0 or Industry 4.0.

This device is composed of cellulose, produced in situ in the laboratory by bacteria, with small amounts of a conductor nanomaterial, carbon nanotubes, using a sustainable and environmentally friendly strategy” explains Mariano Campoy-Quiles, researcher at the ICMAB.

“In the near future, they could be used as wearable devices, in medical or sports applications, for example. And if the efficiency of the device was even more optimized, this material could lead to intelligent thermal insulators or to hybrid photovoltaic-thermoelectric power generation systems” predicts Campoy-Quiles. In addition “due to the high flexibility of the cellulose and to the scalability of the process, these devices could be used in applications where the residual heat source has unusual forms or extensive areas, as they could be completely covered with this material” indicates Anna Roig, researcher at the ICMAB.

Since bacterial cellulose can be home made, perhaps we are facing the first step towards a new energy paradigm, where users will be able to make their own electric generators. We are still far away, but this study is a beginning. We have to start somewhere. “Instead of making a material for energy, we cultivate it” explains Mariano Campoy-Quiles, a researcher of this study. “Bacteria, dispersed in an aqueous culture medium containing sugars and carbon nanotubes, produce the nanocellulose fibers that will end up forming the device, in which the carbon nanotubes are embedded” continues Campoy-Quiles.”We obtain a mechanically resistant, flexible and deformable material, thanks to the cellulose fibers, and with a high electrical conductivity, thanks to the carbon nanotubes,” adds Anna Laromaine, researcher at the ICMAB. “The intention is to approach the concept of circular economy, using sustainable materials that are not toxic for the environment, which are used in small amounts, and which can be recycled and reused,“says Roig.

The study has been published in the Energy & Environmental Science journal.