New materials may help conversion of heat into electricity                                                                 


Dr. Ajay Soni, Associate Professor, School of Basic Sciences, IIT Mandi, along with his research scholars (R-L)

In search of new sources of energy, researchers are now working to develop specialized materials that can directly convert heat into electricity. Lot of heat is generated in industry, power plants, home appliances and automobiles. However, most of it goes waste into the environment.

According to estimates, about 70% of energy in the world is wasted as heat and this heat is released into the environment, becoming one of the key players of global warming. The trapping and conversion of waste heat into electricity can serve the dual purpose of energy-self-sufficiency and environmental preservation.

The new work is based on tapping what is called the ‘Seebeck Effect’. It is a phenomenon in which temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the substances. When heat is applied to one of the two conductors or semiconductors, heated electrons flow toward the cooler one. If the pair is connected through an electrical circuit, direct current flows through that circuit.

The voltages produced by the Seebeck effect are very small, usually only a few micro-volts per kelvin of temperature difference at the junction. However, if the temperature difference is large enough, some devices can produce a few milli-volts. Many such devices can be connected in series to increase the output voltage or in parallel to increase the maximum deliverable current. Large arrays of devices can provide useful, small-scale electrical power if a significant temperature difference is maintained across the junctions.

" A typical thermoelectric material must have high thermoelectric power and electrical conductivity, low thermal conductivity and a capability to maintain a temperature gradient."

Many leading automobile firms are developing thermoelectric waste heat recovery systems that promise three to five per cent improvements in fuel economy. Other potential applications for thermoelectric energy harvesting include powering consumer devices and electronics, aviation and even space applications. In India too, several research groups are engaged in research towards developing such devices.

Dr. Ajay Soni, Associate Professor in the School of Basic Sciences at Indian Institute of Technology, Mandi, who has been working in the area, noted, “a typical thermoelectric material must have high thermoelectric power and electrical conductivity, low thermal conductivity and a capability to maintain a temperature gradient. This combination of properties is hard to come by”.

He and his team are working on a range of semiconductors such as bismuth telluride, tin telluride and silver containing crystalline superionic argyrodites, spiking them with various elements in tiny quantities to improve the ‘thermoelectric figure-of-merit,’ which is a metric that indicates the thermoelectric efficiency of the materials system. Ideally, a figure-of-merit value of three to four can convert more than 40% of waste heat to useful electrical energy, but in reality, it has hovered around one, insufficient for practical application.

The research work is funded by Department of Science and Technology – Science and Engineering Research Board (DST-SERB) and Department of Atomic Energy – Board of Research in Nuclear Sciences (DAE-BRNS).
India Science Wire