Bengaluru researchers achieve breakthrough in converting waste heat to power

Bengaluru: A group of researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) in Bengaluru has recently had a breakthrough, successfully reaching an impressive maximum power conversion efficiency of nearly 12% in thermoelectric energy conversion.

This is significantly higher than what a market-based thermoelectric energy converter can produce. On average, a market-based thermoelectric energy converter provides a power conversion efficiency of 6–7%. Among other uses of this research, if one has a hybrid car, such an energy conversion process can be used to charge the electric batteries using the wasted heat from the fuel.

The research group, led by Professor Kanishka Biswas at JNCASR, has been working in the field of thermoelectric energy conversion for the past 15 years, working at the interface of chemistry and physics.

“When you take the example of any energy conversion process, we only end up utilising about 35% of it; 65% goes out in the form of waste heat. This applies to almost any form of energy conversion — from a simple light bulb to fuel conversion in automobiles to even energy conversion at a steel or nuclear power plant,” explained Biswas.

What is the benefit?

What thermoelectricity can do is convert this waste heat into electricity. Thermoelectric conversion directly turns heat differences into electricity, enabling waste-heat recovery and off-grid power, offering sustainable energy by reducing consumption. Thermoelectric systems generate clean electricity without emitting Carbon Monoxide (CO) and Carbon Dioxide (CO₂) and require virtually no maintenance due to the absence of moving parts.

However, for efficient thermoelectric energy conversion, a compound needs to be a bad conductor of heat and a good conductor of electricity. The researchers have achieved this using a Germanium Telluride (GeTe) compound. “For the first time, an extraordinary zT of ~2.7 at 628 K has been achieved in a GeTe-based system by engineering ferroelectric instability,” Biswas told DH. ‘zT’ is the thermoelectric figure of merit, a dimensionless number that indicates how efficiently a material converts heat into electricity — higher zT means better thermoelectric performance.

“This approach induces polar local distortions that strongly scatter heat-carrying phonons, dramatically boosting thermoelectric performance. We used this material to achieve a maximum power conversion efficiency of nearly 12%,” he elaborated. Their work has recently been published in Advanced Materials, a highly regarded journal in materials science.

Biswas also shed light on the wide applications of thermoelectric energy. Capturing and converting this waste heat into usable electricity through thermoelectric materials and devices could transform sectors such as power generation, steel manufacturing, defence, space technology, off-grid cooking like chulahs, and the automobile industry.

“For example, if you’re using a hybrid car with thermoelectric conversion, we can use the waste heat from fuel conversion and use it to charge the electric batteries. In another scenario, in Indian villages, the heat from the wood stove can be used to charge a mobile phone. There are varied applications of thermoelectric energy conversion, especially in the defence sector,” added Biswas.

Additionally, the team has also recently designed a new compound that can aid in the process of efficient thermoelectric energy conversion. It is a quaternary entropy-stabilised material that achieves an exceptional balance of properties required for thermoelectric energy conversion. The compound exhibits ultralow, glass-like thermal conductivity and metal-like electrical conductivity. This work has been recently published in the Journal of the American Chemical Society.