The sun is a renewable energy source, free, available everywhere in large quantities, and which can be converted into heat with excellent efficiency. For thermal applications, however, the main constraint of solar energy lies in the temporal phase shift between availability and needs. Indeed, a conventional solar installation allows, in the best of cases, to meet 60% of the energy needs in domestic hot water and heating. To improve this solar fraction, it is necessary to use an inter-seasonal thermal storage which releases in winter the surplus energy stored in summer. However, the storage applications currently available (in the form of sensitive or latent heat) generally do not meet 100% of our needs unless they are very large.