New Technology Turns Waste Heat into Electricity

4 July 2014

The highly efficient thermoelectric module is made of ceramic materials what can withstand high temperatures and convert waste heat from industrial sources into electricity. As such, the new technology may contribute to wringing even more energy out of the sparse resources in the long term:

“We want to utilise the huge amount of high-temperature waste heat that is found in many areas of industry. For instance, our cars currently use only around 30% of the energy in the fuel, and the same picture is repeated in a number of places in the industry. We have developed a thermoelectric oxide module with the capacity to convert this heat into electricity—making use of waste heat that would otherwise literally have vanished into thin air,” relates Professor Nini Pryds from DTU Energy Conversion.

The project has now reached the point where researchers have manufactured a ceramic module and proved in laboratory trials that it is nothing short of the most efficient of its kind in the world—even though there is still some work to be done before it is ready to market.

Materials and design

There are two overarching factors that come into play when attempting to boost the efficiency of the conversion in the module. The first concerns the material properties themselves, while the other is the difference in temperature that can be achieved from one side to the other. The more both can be maximised, the greater the efficiency that can be achieved.

For this reason, the project—which is receiving support from the Danish Council for Strategic Research—is focused both on finding the appropriate materials and on the design of the module itself. The goal for the researchers was originally to achieve an effect density of more than 4.4 kW/m2 , and they have exceeded their aim, as the result was actually an effect density of 6 kW/m2.

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Effect density is an expression of how much electricity (measured in kilowatts) a module measuring 1 m2 can generate. The value achieved makes it realistic to use the modules to collect waste heat from cement production, for example:

“It may look simple on paper, but there are actually all kinds of challenges to overcome. The biggest was probably to develop the materials and then design a thermoelectric element that features low contact resistance between the different parts and materials while still being robust enough to withstand temperatures of up to 1,000 °C. This actually makes huge demands on both the material properties and the design itself,” explains Professor Nini Pryds, who has made use of the knowledge gained through the department’s research into fuel cells, for example.

The project still has over a year left to run and the next step will be to have partners in the project test the new materials. In the medium to long term, the goal is to find a partner with the potential to assist in commercialising the module and implementing it in industry

What is thermal electricity?

Thermoelectricity is based on what is known as the Seebeck effect: if a material with the capacity to conduct electricity is subjected to a difference in temperature, an electric voltage difference arises in this material. This allows the conversion of heat into electricity.

The efficiency depends on factors such as the material properties and the temperature difference between the two sides of the module. The aim is thus to create the biggest possible temperature difference.

Source: Technical University of Denmark

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