Thermoelectric (TE) materials are semiconductor materials that can convert waste heat to electrical energy or utilizing electrical energy can cause a cooling/heating effect. The efficiency of any TE material is determined by the figure of merit-ZT, which is defined as ZT = S2cT/k, where S is Seebeck coefficient, c is the electrical conductivity, k is the thermal conductivity, and T is the absolute temperature. Since S, c, and k are all interdependent material properties, increasing ZT is not a straight-forward matter of material choice, but involves smart design of material interfaces. In the case of cooling, heat has to be pumped via electron (n-type TE) and hole (p-type TE) carriers from the cold to the warm end. In order to increase the performance efficiency of such a pumping, the thermal conductivity of both types of TE, which is responsible for the reverse heat conduction from the warm to cold end, should be reduced. In this project, the key strategy is to use Nanotechnology to improve ZT of promising TE materials in the bulk form. Therefore, this project will allow further steps of processing materials into module/devices which can be actually tested in industry. Based on the identified interesting applications and materials, the current module/device technology will also be developed during the project. As a result, novelty exists in the Material concept, Module/device concept, and Application concept, which constitutes this project a comprehensive effort in the field of TEs. Due to the absence of a module utilizing skutterudite materials (which is mainly for energy generation), achievement of the project objectives will represent a significant step in the industrialization of thermoelectric energy generators. The main objective of this project is to further develop bulk NS TE materials with even higher TE performance (ZT greater than 1.5-3), which can be processed into TE modules/devices and actually demonstrated for interesting applications. Bulk NS skutterudites and their nanocomposites display a maximum ZT in the temperature range 200-600 °C, which makes them well suited for the generation of electricity from waste heat. The potential applications for waste heat recovery mainly include car exhaust pipes, industrial materials processing. Appropriately modified conventional TE modules will be fabricated using the new bulk material and subjected to rigorous laboratory testing in order to characterize their TE performance. For applications to car exhaust a target yield of 0.5 W/cm2 is expected to ensure the technological viability of such devices. Due to the availability of commercial modules in the market, the main focus of the project efforts will be guided towards skutterudite module development.
Nevertheless improvements material properties of bulk NS bismuth telluride will be investigated in this project. Conventional TE module/device technology can be directly used for NS bulk bismuth telluride. The NEXTEC project proposes to develop new TE generators with high efficiency which may allow introduction of a new generation of economically viable, simple and robust renewable energy devices for geothermal and thermosolar sectors. In addition, at this moment the European Commission is aware that the share of renewable energy is growing too slowly. In these conditions, the development of the energy efficiency technologies like the ones proposed by the NEXTEC project, rise in importance as they contribute to a cleaner energy, may prove cheaper than the development of new renewable energy technologies, and offer the time necessary for advance of the alternative sources. The main advantage of the new TE modules developed during NEXTEC is that they can be used as efficient energy harvesters with high thermal to electrical conversion yield in a wide range of applications where enormous thermal losses occur: automotive, aerospace, most of industrial/transformation processes. This technology will ensure an enhancement of the energetic efficiency in all the selected applications. Moreover, achieving highly efficient thermoelectric modules will allow reaching coefficient of performance better than those of actual technologies.
Benefits in energy consuming of cooling applications (domestic and industrial) will be obtained. The improvements foreseen by the project could have an important share at speeding the market spread and the industry integration of these devices.