Innovation trends on high-temperature thermal energy storage to defossilize energy systems

The EU climate neutrality ambitious goals require breakthrough solutions and innovative products in many technological areas. The need of a transition to a more affordable energy system highlights the importance of new cost-competitive energy storage systems, including thermal energy storage (TES) for waste heat recovery, heating and cooling supply or for the increased flexibility of power systems via power to heat to power. This work focusses on technologically mature or close to market TES solutions, overviewing some of the most promising start-ups active in the sector of mid to high temperature TES for industrial heat applications or power to heat to power. It also discusses key elements to transfer these technologies to products available for market uptake. These key challenges include technical issues, such as control mechanisms, increased durability and stability of the employed materials, devices' reliability and fast dynamic performances to provide grid services or enable demand response; but also the development of new business models and novel approaches to produce revenues. Moreover, the review identifies as a key ingredient for the success in scaling up new TES products and manufacturing lines the capability to fast develop demonstration and first of a kind plants that can increase investors' trust.