This technology therefore promises to save 1

Move effectively heat to electricity without gas, photovoltaic battery-free turbine or without mechanism is no longer a fantasy. The new researchers marotte will smile the most sceptical, but it deserves to take a few million euros. In any case is what decided several French laboratories and some inspired business. It was time to take this train, running for a few years. The Japanese bought the first tickets, banging of tens of millions of dollars. Since little, the US DoE have followed them suit.

In reality, the adventure began long ago. As in many of the inventions of the 20th century, the fundamentals have posed the brilliant nineteenth-century. In this case, the German physicist Thomas Johann Seebeck discovered in 1821 that his compass moves in a metal room with an end had been heated. It will be understood later than in certain materials subjected to a temperature difference, electrons react from hot spot to the cold point, the definition of an electric current.

Very attractive, this effect has been more than a century to materialize in applications. Antoine Maignan, Director of the laboratory of Crystallography and materials to Caen (Crismat) science, explains that it is very difficult to find an ideal material for the thermal power. It must have three qualities of which the first two are at odds.

Its electrical resistivity must be weak to facilitate the transport of electrons. But its thermal conductivity must also be small to not alter the difference in temperature across the material. It corresponds to the modes of vibration of the atoms. Finally, it must have the highest possible "figure of merit", a measure of the Seebeck effect. Pure metals, for example, a high resistivity, good conductivity thermal but know a figure of merit deplorable. Semiconductors such as Silicon offers a high Seebeck effect but a high resistivity. The thermal power is therefore a science of the compromise. As the ideal material must also power withstand extreme temperatures, up to 1,500 C thermal differences where the Seebeck effect is greatest.

For several decades, researchers have managed to find some materials that can perform some confidential applications. Nasa including equipped with its first interplanetary probes by taking advantage of the huge difference in temperature between the interplanetary space and the heat emitted from the decay of a radioactive source. An approach, for example, was to boost semiconductor to reduce resistivity.

Since 2000, the research is relaunched in the study of the Seebeck effect (and its counterpart, the Peletier effect), motivated by his intimate understanding of the matter. Antoine Maignan laboratory took his job very well known on the high critical temperature superconductors for carving thermoelectric oxides. "Oxides are interesting because they already incorporate oxygen and therefore remain chemically very stable up to 1,500 C, where the gas is corrosive," explains Antoine Maignan.

But unlike metals, in which electrons have little interaction, these oxides have a power relationship strong. The Crismat thus reinforced its teams with physicists to model quantum behaviour of electrons. Its chemists then design appropriate molecular structures. In their Toolkit, tip, such as the creation of local disorders in the matter, they have to reduce thermal conductivity without too encumbering the resistivity.

CO2 savings

Other teams, especially in the United States, rely on the intermetallic alloys but this sector requires very toxic products. A sector is also developing thermocouples in film for the production of low currents. CEA Grenoble is working in particular on this close technology of nanotechnology. It already gives rise to commercial products such as watches powered by heat from the skin or pacemakers. The materials have therefore made great progress since 2000. Their merit factor was multiplied by 5, explains Sylvie the Crismat Hébert. Dozens of patents were filed and the phase of industrialization has even started.

The space industry is currently enjoying the State of the art of this technology. Not constrained by costs, it relied on a cocktail of very sophisticated materials able to convert 18 of the heat into electricity. Most laboratories are working on economic solutions. Current performance then levelled off at 6, for the moment and the objective is to reach 10 by 2015. The automotive industry is the first sector of mass to be seized of the subject. Its engineers have a simple reasoning: only half of the energy consumed by a vehicle is used, the rest is essentially lost to heat. Flue gas temperatures up to 1000 C, display engine to the tailpipe. This is precisely that manufacturers hope graft thermocouples. Toshiba just announced a prototype generating 1 kW per vehicle. Toyota is committed to objective to collect enough electricity to remove the generator of the cars, or 16 of the total energy consumed. This technology therefore promises to save 1.6 million tonnes of CO2 per year.

Infinite opportunities

Researchers do not have cried victory. They must still improve performance but also reduce costs while succeeding in the integration of the thermocouple in the exhaust system. Expansion of the material constraints may for example problem.

If the technology matures, the opportunities are endless. The energy sector also follows this technology that could to boost yields. In the gas cogeneration plants, turbines lose much heat. The steel industry could improve the economy of the production of aluminum, a die by its high temperatures. The Japan already leads a program to equip 2,200 incinerators. An equivalent success for the Peletier effect would also revolutionize the air conditioning. IBM already incorporates this technology to cool some chips.

At Toyota, General Electric, to the Department of Energy or to the Agency for Naval Research, R & D French may seem slight. For Antoine Maignan, it has the merit to organize quickly. A platform of 6 laboratories pioneers was created and a group of 23 teams have formed a network. Next step: convince Brussels to open a specific row in its framework programme for research and development.