Renewable Energy Sources have been growing rapidly over the last few years. The spreading of renewables has become stronger due to the increased air pollution, which is largely believed to be irreversible for the environment. On the other hand, the penetration of renewable energy technologies causes major problems to the stability of the grid. Along with the fluctuations of the renewable energy technologies production, storage is important for power and vo. Renewable Energy Sources have been growing rapidly over the last few years. The spreading of renewables has become stronger due to the increased air pollution, which is largely believed to be irreversible for the environment. On the other hand, the penetration of renewable energy technologies causes major problems to the stability of the grid. Along with the fluctuations of the renewable energy technologies production, storage is important for power and voltage smoothing. Energy storage is also important for energy management, frequency regulation, peak shaving, load leveling, seasonal storage and standby generation during a fault. Thus, storage technologies have gained an increased attention and have become more than a necessity nowadays. This paper presents an up to date comprehensive overview of energy storage technologies. It incorporates characteristics and functionalities of each storage technology, as well as their advantages and disadvantages compared with other storage technologies. Comparison tables with several characteristics of each storage method are included, while different applications of energy storage technologies are described as well. Finally, several hybrid energy storage applications are analyzed and different combinations of energy storage technologies are reviewed.••••Up-to-date representation of the current status of global energy storage capacity.••Comprehensive and updated research of several energy storage technologies.••Comparison tables of all storage technologies by several characteristics.••Overview of grid-scale applications of different energy storage technologies.••Analysis of different hybrid energy storage combinations and applications.CAESCompressed Air Energy StorageCESCryogenic Energy StorageCSPConcentrated Solar PowerDoDDepth-of-DischargeEESElectrical Energy StorageFESEnergy storageRenewable energyComparisonGridApplicationsHybrid storageRenewable Energy Sources (RES) have been growing rapidly over the last few years. The spreading of renewables has become stronger due to the increased air pollution, which is largely believed to be irreversible for the environment. Moreover, the depletion of fossil fuel resources, the increased oil prices and the growth in electricity demand are important factors for the growing attention in RES. In addition to that, buildings in Europe are responsible for the 40% of the total EU energy consumption, and as a result they contribute to greenhouse gas emissions and, possibly, to climate change. Therefore, the reduction of the energy consumption and the use of RES in buildings are believed to have a positive impact on climate and gradual independency on conventional fuels,.On the other hand, the penetration of renewable energy technologies causes major problems to the stability of the electrical grid. This happens because renewable energy production cannot be predicted accurately, as it relies on weather conditions such as sunlight and wind. For instance, when the clouds suddenly appear or the wind stops blowing then the energy production from photovoltaics and wind turbines will be decreased dramatically. Thus, energy storage can allow energy to be stored during high renewable generation or low demand periods, and to be used during low renewable production or high dem.