2023-05-15 06:30:57
One of the challenges of electrical renewable energies is to be able to store electrons to reinject them when needed. Mass storage technology by Carnot battery, developed by the company STOLECT, is the subject of a demonstrator with the SNCF in Rennes.
While electrochemical batteries are often presented as the solution to integrate electrical renewable energies, other technologies are more relevant for longer discharge times. This is the case of electricity storage by thermal conversion, presented by Jean-François Le Romancer, president of STOLECT.
Engineering techniques: What is Carnot’s battery technology?
Jean-Francois Le Romancer: This term “Carnot battery” was proposed by the International Energy Agency to designate the storage of electricity by thermal conversion. This involves using electricity to compress air by heating it up a lot; this sensible heat is stored in two enclosures of refractory materials then extracted once more in the form of hot air expanded in a turbine which turns an alternator and produces electricity. This must be clearly differentiated from thermal storage which restores heat. Here, electricity is the input product and the final product, with a target efficiency of 70%.
With what materials is this sensible heat storage made and under what constraints?
We have tested different types of refractory materials, whether natural or industrially produced, to assess their ability to withstand the temperature range. They must not deteriorate, in particular due to expansion, since the cycling varies between 50 and 600°C. Among the options selected, the cheapest is a basalt extracted in Cantal. The interest of the Carnot battery, unlike an electrochemical battery, is that there is no correlation between the power, which is fixed by the turbomachines, and the stored energy which depends on the size of the enclosures containing the refractory materials. This will eventually make it possible to adapt sites to changing needs: for the same compressor/turbine batch, it will suffice to add enclosures of materials to store and release twice as much electricity. Other advantages are the durability of this technology, estimated at 30 years, and the fact that it has a carbon impact 7 to 30 times lower than electrochemical batteries, depending on the size of the installation.
Where is STOLECT in the development of this technology?
STOLECT was created in 2019 to bring this technology, which had been the subject of initial developments almost ten years earlier: the project had won the global innovation competition in 2014 and had been incubated at Keynergie. After a first prototype, and pre-project studies supported by Investissements d’Avenir and ADEME, we decided to launch a demonstrator. It is being built in Rennes, at SNCF’s Technicentre Maintenance Bretagne, with the support of BPI France, the Smile Smart Grids network of the Brittany and Pays de la Loire regions, as well as a decisive contribution of 2 million euros. from the FEDER fund of the Brittany Region. The installation has a reduced footprint, of approximately 400 m², including the turbomachines (1 MW electric power) and the two cylindrical tanks of refractory materials, each with a diameter of 5 meters and a height of 6 meters. In total, they contain 400 tonnes of materials and can store 5 MWh. By mid-2024, this demonstrator will make it possible to test operating procedures to optimize them and lead us to a larger commercial model (5 MWe and 50 MWh). We have an R&D collaboration with IFPEN, which has carried out dynamic simulations of the behavior of the entire storage system and which will analyze the data from this demonstrator to check its relevance and optimize it.
What market is your electricity storage solution aimed at?
Electrochemical batteries respond in milliseconds and can almost instantly meet the primary reserve needs of the power grid to control the grid frequency. Electricity storage by thermal conversion is positioned in a complementary way: it starts up more slowly, but can meet a need to supply electricity over a period of more than 4 to 6 hours. STOLECT’s solution will therefore be suitable for manufacturers who want to decarbonize their electricity by installing renewable energies and need to supplement them with storage to meet all their consumption needs. This is the case, for example, of the SNCF, which has land reserves and plans to install photovoltaic solar power: with our storage solution, it might have electricity stored during the day all night long. On the scale of an area of activity, we believe that we can really help the massification of renewable energies. This is of course obvious for non-interconnected areas, but might become generalized throughout the territory given the development objectives of renewable energies and the pressure on electricity prices.
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