Renewable energy systems and storage

Renewable thermal energy is usually available with a time difference between supply and demand. This mismatch can be solved by energy storage. The most appropriate seasonal storage technologies are Underground Thermal Energy Storage (UTES) systems. The most common technologies are ATES, BTES and CTES. It is not possible, for geological or geo-hydrological reasons, to construct all these systems any place but one of them can in most cases be realised. ATES (aquifer) systems are most favourable in large-scale applications. The BTES (borehole) system is the most general system because it finds applications of all scales. CTES (rock cavern) systems are most favourable when loading and unloading powers are extremely high. This paper presents a brief summary of old and new ideas on seasonal storage of renewable thermal energy