The energy system is changing due to variable energy production. This requires new and more storage devices to balance demand and production and additionally to increase flexibility. The aim is to select always the best fitting storage systems with the best fitting operation mode to balance the energy system. The challenge is that there are hardly any, scientific proven, source models for energy storage systems, which are an indispensable prerequisite for operation or structural optimisation and for assessing the value of storage systems. The task is to develop a standardised and scientifically proven approach and methodology to asses various storage devices for various applications: grid connected and grid operated, island grids/ remote areas, industrial sites and residential areas. The results are generic open source models and data sets. These scientifically proven models should be used to find answers to current storage questions (technical, economical and regulatory). The overall aim of this Annex is smart energy conservation and to understand and foster the role of energy storages in the energy system by optimising applications and operation modes and by assessing the benefit to the energy system.