Energy storage systems are components, systems and equipment that store mechanical, chemical, thermal or electrical energy and release it into the power grid as electrical energy when required. They relieve the load on the power grid because they can compensate for voltage fluctuations during short-term and long-term load fluctuations.
Inmechanical energy storage, kinetic energy is stored and retrieved when needed. This principle is used in pumped storage plants, compressed air storage or flywheel mass storage. It always involves buffering energy when there is a surplus of energy, and removing electrical energy when there is a shortage.
In electrochemical energy storage systems, active masses are converted into electrical energy. Batteries, accumulators, quarter storage in the form of battery banks or as high- performance powerbanks are available for electrochemical energy storage, as are lithium-ion accumulators, sodium-sulfur accumulators or lead accumulators as home storage. Furthermore, redox flow batteries.
In addition to the electrochemical energy storage devices, there are also the electrical energy storage devices that have no energy conversion. The incoming stored electricity is injected into the power grid as electrical power when needed without conversion. Electrical energy storage uses supercapacitors, double layer capacitors and superconducting magnetic coils.
Another group of energy storage devices are thermal and chemical energy storage devices. As far as thermal energy storage is concerned, there are heat and cold storage systems that store thermal energy and convert it into electrical energy, including fuel cells that convert power to gas (P2G) or power to heat (P2H) into energy.
Energy storage systems can be classified according to their reaction time or start-up time. According to this classification, there are energy storage systems with very short response times of seconds and minutes for short-term load fluctuations, such as electrical energy storage systems, those with response times of hours, such as thernic energy storage systems, and still others that can compensate for seasonal fluctuations throughout the year, such as pumped storage plants.
Important characteristics of energy storage systems are energy density, power density, and charging and discharging times. As far as energy density is concerned, that of fuel cells is many times higher than that of batteries and supercapacitors, at about 1,000 Wh/kg. While the energy density of capacitors and supercapacitors is much lower than that of rechargeable batteries, their energy can be retrieved in the short term in microseconds and milliseconds. In contrast, the energy of rechargeable batteries can be accessed in minutes and that of fuel cells in hours and days.