As power plays an ever more prominent role in modern life, systems need to store and release electricity as it best fits their needs. The main purpose of these systems is to balance power supply and demand, store surplus energy when not needed and discharge electricity into the grid at times like this. With advanced technology, energy storage systems span a number of different technological spectrums, such as batteries (both lithium-ion and flow), flywheel, compressed air and pumped hydro storage. This successful track record includes high efficiency, the capability to expand in size and to discharge and recharge quickly. They are used in a wide range of areas : integration of renewable energy with the grid, peak-clipping, and uninterrupted supplies to remote areas off grid. In this way they have significantly increased the reliability as well as environmental impact of our power infrastructure.