Thermoelectric materials have, like solar cells, a high potential to help solving the global problem of the renewable energy supply. Those materials are able to generate power from waste heat (heat flow caused by temperature gradient) and therefore can recycle energy. The waste heat is generated everywhere: in computer centers as well as in households. A large part of the heat cannot be utilized using traditional energy generation processes. The thermoelectrics can operate even with small heat fluxes and temperature gradients. They do not feature movable parts or circulating liquids, they are quiet, easy to install and maintain. The research in the Solar House is focusing on the optimization of the characteristics of thermoelectric materials. In particular, the Seebeck-coefficient, the electric conductivity and the thermal conductivity can be measured. The sustainability of the fabrication processes plays an important role in the research as well.

SolarTEG

The doctoral project "Elektrisch leitfähige Polymere zur Umwandlung von Abwärme in Strom an nanostrukturierten Solarzellen” (Electrically conductive polymers for the conversion of waste heat into electricity on nanostructured solar cells, SolarTEG) is commencing at the TH Lübeck. Its aim is to develop, build, and test a novel solar-thermoelectric cell under real conditions. Sustainable thermoelectric materials based on conductive polymers coupled with nanostructured silicon-based solar cells are used. Conventional thermoelectrics are often based on toxic, environmentally harmful and expensive materials. The idea is to replace them in the project by sustainable conductive polymers. Nanostructured silicon-based solar cells are used as they are more efficient than conventional solar cells. The entire project aims at increasing the efficiency of energy generation and recycling. Solar cells cannot convert the entire absorbed sun energy into electricity. A large part of the energy heats the cell and is wasted. The increased cell temperature can additionally deteriorate its efficiency. The thermoelectrics can be used to harvest the wasted heat and ultimately lead to an increased combined solar cell-TEG system efficiency.
Snyder, G., Toberer, E. Complex thermoelectric materials. Nature Mater 7, 105–114 (2008).
Left: N. Buczek (neé Geyer), "Nanostructuration of silicon by means of metal assisted chemical etching", Ph.D. dissertation, Martin Luther University Halle-Wittenberg, 2011. Z. Huang, N. Geyer, P. Werner, J. de Boor, and U. Gösele, "Metal-assisted chemical etching of silicon: A review", Advanced Materials, vol. 23, p. 285, 2011. Right: N. Nandihalli, C.-J.- Liu, T. Mori, „ Polymer based thermoelectric nanocomposite materials and devices: Fabrication and characteristics”, Nano Energy, vol. 78, p. 4, 2020. G. Prunet, F. Pawula, G. Fleury, E. Cloutet, A. J. Robinson, G. Hadziioannou, A. Pakdel, “A review on conductive polymers and their hybrids for flexible and wearable thermoelectric applications”, Materials Today Physics, vol. 18, p. 4, 2021.

Innovations for the SDE

n a preliminary study a prototype of a solar-thermoelectric cell is developed, built, and tested in the Solar House. Materials already available on the market, a conventional silicon solar cell and a conventional thermoelectric module are used. The influence of biological cooling based on moss is also being investigated. The effects of this clever coupling of state-of-the- art materials will be investigated in different scenarios. The scenario that shows the greatest effect, specifically the highest increase in efficiency, will be presented as a prototype at the Solar Decathlon. This will provide a glimpse into the future of energy generation in sustainable buildings.