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Turning Waste Heat into Electricity

Dr Matthew Burton is part of our Thermoelectrics Group, working on energy capture research to allow the widespread use of thermoelectric materials to harness waste heat. Here, he explains why this is important…

How does SPECIFIC’s thermoelectrical research contribute towards the Active Buildings vision?

Put simply thermoelectrics is taking heat energy (thermo) and converting it into electricity (electrics). We research thermoelectric materials to try and make their use more widespread.

Around one-sixth of all UK industrial energy is lost as waste heat and a large portion of domestic energy is also lost as heat, emitted into the atmosphere. Instead of losing that energy, we could harness it, resulting in a significant reduction in industry carbon emissions.

Where does most of the waste heat escape from? Buildings. Unlike a lot of other green energy technologies, thermoelectrics cannot be used in large-scale sites like solar or wind farms. If we are to really harness waste heat, we need to incorporate thermoelectrics into buildings as much as we can. Incorporating them into building designs from the outset would be ideal.

What are the challenges involved with the technology?

Thermoelectrics can currently be found in niche items like mini fridges and stove fans, however, they are not used in widespread waste heat harvesting. This may sound surprising when so much ‘free’ energy is continuously escaping into the atmosphere. The main reason for this is that current manufacturing techniques for thermoelectric generators, such as spark plasma sintering and hot pressing, are costly. In addition, current thermoelectric materials use Tellurium (Te), which is an element as rare on Earth as Platinum, adding to the cost of manufacturing thermoelectric generators.

Why is SPECIFIC’s thermoelectrical research unique to other research being undertaken?

Here at SPECIFIC, we look at cheap methods of manufacturing Earth-abundant thermoelectric materials. We research techniques such as thermal evaporation and electrodeposition, but our main focus is printing. By utilising Earth-abundant materials and cheap manufacturing techniques, we hope to substantially lower the cost of thermoelectric generators.

How do we go from printing, thermal evaporation and electrodeposition to working generators?

These cheap manufacturing techniques often result in less dense materials than the more expensive manufacturing techniques. Whilst we are exploiting this by generating materials that heat can escape through less easily (thus making them more efficient at turning heat into electricity), this causes challenges in making low resistance electrical contacts in working devices. This is something we are actively researching, however, with some promising very initial results.

The Earth-abundant materials are far less studied than their Te counterparts. This can result in issues such as long-term thermal stability, which are not ideal in materials that need to get hot to perform the task being asked of them. However, the more we study them, the more we understand. We are trialling adding in small amounts of iron to increase their thermal stability, as this has been seen to work for other manufacturing techniques.

What is the next step?

Two types of semiconductors are needed to make efficiently functioning thermoelectric generators: a p-type, and a n-type. Last year, we broke the world record efficiency factor for a printed thermoelectric material, however, we were only able to make the p-type. We have been investigating various doping strategies to print the n-type semiconductor too. We are also exploring printing new thermoelectric material groups.

Lockdown has put a hold on all our laboratory work at the moment. We have been using this time to write up our results for publications. This includes work on the electrodeposition of the thermoelectric material Tin Selenide (SnSe), which was recently published here. We are currently writing a comprehensive review paper on printed thermoelectrics, which will help the scientific community understand the biggest hurdles that need to be overcome to progress this technology.

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