The Project

The technology

With decarbonisation, global increase of inflation, rising energy cost, etc., need for energy with low environmental impact have considerably shot up. Among all available technologies, thermoelectric generators (TEG) are solid-state devices converting heat into electricity thanks to Seebeck effect, and made from p- and n-type materials allowing electrons to migrate and generate electric current.

TEGs represent several advantages such as having no moving part, completely silent (unlike internal combustion or stirling engines), low-maintenance, renewable energy source that are simple to install, safe to store, and cost-effective. The global thermoelectric generator market size was valued at 447.1 million € in 2020, and is forecasted to reach 1,365.8 million € by 2030, growing at a Compound Annual Growth Rate (CAGR) of 11.8% from 2021 to 2030, demonstrating a strong interest in this technology for the next years. The main areas targeted by markets include aerospace, transportation, industrial, consumer and healthcare.

The obstacles

Nevertheless, wide-scale applicability of TE devices are still currently limited by their low conversion efficiency, around 5 – 7 % at devices level and around 3 – 5 % at the most at systems level. There are two main reasons to explain these low efficiencies. At materials level, the best known TE material is bismuth telluride (Bi₂Te₃), but this material presents some drawbacks such as a temperature range limitation to below 300 °C, toxicity, scarcity (tellurium is one of the rarest element on Earth). Extensive studies have been performed at the laboratory level to find new materials for higher temperature applications (also more abundant, cheaper, less toxic, etc.) such as skutterudites, Half-Heusler, clathrates, etc. but these materials suffer from serious drawbacks (thermal-mechanical issues, still limited operational temperature range 300 °C – 600 °C, lack of robustness and reliability, etc.) preventing them from serving higher temperature applications in the market. Silicon-germanium (SiGe) alloys have proven to be good TE materials, with the best performances for the high temperature range (700 °C – 1000 °C). SiGe alloys present some other advantages: p- and n-types can be easily obtained by doping, it is an eco-friendly material with
limited cost (for low Ge content), and it has also demonstrated very good robustness and reliability properties, mainly in space applications as a reference material for Radioisotope Thermoelectric Generators (RTG), developed and used by NASA for 60 years in several space missions (Galileo, Cassini, Ulysses, New-Horizon, etc.) to supply on-board
electronic devices and systems. At device level, TEG architecture and manufacturing methods have mostly been based on cumbersome and costly pellet production in flat orthogonal devices, with much effort being put on connection technologies for new and still un-mature materials such as skutterudites and Half-Heusler.

The scope of STARTREC

In the recent past however, there have been a couple of promising advances in a further improvement of the Silicon Germanium based devices, separately made by several parties, among which CEA (Additive Manufacturing) and RGS (Rapid Casting). The main improvements have been concentrated on a significant performance increase by
materials nanostructuring and by advanced architecture designs, potentially improving performance with 50 % – and on advancements in manufacturing technologies – with an impact on scalability, cost effectiveness and integration of devices.

The STARTREC project aims to further advance those advancements and to combine the separate evolutions, and to match them with the requirements of wider scale applications. The end result will be that for 3 high impact use cases the world record material – architecture – manufacturing technology will be selected and demonstrated – hence disclosing applications which can significantly contribute to societal needs.

The main target of the STARTREC project is to develop a new generation of TEG devices based on the optimal combination of nanostructured Si85Ge15 thermoelectric materials with innovative device architectures, leading to double their efficiencies to 10-15% and to demonstrate their high performances at TRL5 for three different and complementary high impact use cases.