The energy storage is in one way or another both a natural process (e.g. creation of fossil fuels) and an artificial method for satisfying human energy needs. Conventional fuel storage systems (tanks, underground natural gas storage, etc.) are not mentioned in this presentation. The classification of energy storage systems is quite complex. They can be classified according to the purpose of the system (e.g. production of electric power or heat), according to the form of energy stored, or according to whether these systems are mobile or fixed.
A storage system means a system of electrochemical accumulators for the storage of electrical energy ( BESS : ‘ Battery Energy Storage System ‘) which consists of
- power converters capable of absorbing/injecting active or reactive power,
- batteries connected to the DC side of the inverter,
- electrical equipment for the connection (switches, wiring, protection devices, etc. ) , and
- control and monitoring system.
Storage with pumped savings:
The principle of the method of Pumped savings (pumped hydroelectric energy storage) is simple. It uses excess electricity (during low demand) to transfer water from a lower to a higher water reservoir (man-made or natural) during the night when there is excess electricity. Energy recovery depends on the volume of water and the height. In order for pumped storage to be efficient, a height of at least 100 m is required, while usually the lower reservoir is artificial (excavated).
The method has been applied since 1929 in the USA. and even today it remains essentially the main, almost the only, method of storing electricity.
An advantage of the method is the quick startup and shutdown of the system (within 30 seconds). The main limitation in the development of the method is the high cost of constructing the artificial reservoirs, but there are also geological, geographical and environmental limitations. Today, the possibility of using underground reservoirs is being investigated.