New technology to turn waste heat into electricity

At a time when Russian supplies of natural gas are used as a political weapon, and when Denmark is no longer self-sufficient in energy for the first time since 1996, researchers are working flat out to come up with new energy solutions.

Researchers at DTU have now developed a highly efficient thermoelectric module 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.

DTU’s researchers are working with many aspects of the energy challenge through initiatives including research into fuel cells, solar panels, wind energy and—in particular—establishment of the new Hydrocarbon Research and Technology Centre, which is intended to ensure the best and most appropriate use of resources during the conversion to sustainable energy.

Development of the thermoelectric module commenced in 2010 at DTU Energy Conversion, and tackles the problem from a different angle in that it involves researchers using their knowledge about functional ceramic materials (oxide materials):

“We want to utilize the huge amount of high-temperature waste heat that is to be found in many areas of industry today. For instance, our cars currently use only around 30 per cent of the energy in the fuel, and the same picture is repeated in a number of places in the industry. We have therefore 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 centres on 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 maximized, 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.

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 commercializing the module and implementing it in industry