Battery Energy Storage Systems (BESS) are key players in the energy transition: they enable electricity to be stored and thus, on the one hand, they compensate for the non-programmability of new renewable sources (the Sun and the wind) and, on the other hand, they promote grid stability. This is a very fast-growing sector: according to data from the International Energy Agency (IEA), the installed capacity of BESS worldwide increased from 1 GW in 2013 to 85 GW in 2023. And even more spectacular expansion is expected in the future. But what does a BESS plant look like? And how is it built? The main elements in a BESS plant BESS plants differ from each other in size and battery technology, but essentially they all have the same modular structure: that is, they are composed of the same elements that can be added to increase the overall power output of the plant according to market needs. This great scalability is one of the strengths of BESS, compared to other energy storage systems (such as gravitational energy storage systems, compressed air systems, and flywheels). The structure of a BESS plant is conceptually quite simple, with a small number of basic components: Batteries: these are the basic units that make up a BESS. They are the cells where, through electrochemical reactions, the charging and discharging of electricity takes place. The cells are assembled into modules; the modules in turn are joined together to form larger components, called racks; a group of racks is called a container. The container is typically about 6 meters in length, 2.5 meters in width, and 3 meters in height. It is the fundamental element in a BESS. The inverter is the instrument used for transforming the alternating current (AC) supplied by the grid into the direct current (DC) used in order to charge the batteries, and vice versa to convert the direct current from the batteries back into the suitable alternating current for the grid in the discharge phase. Each inverter is connected to one or more containers. Auxiliary systems are used for the cooling, control and safety of the system. The transformer is used in order to raise the voltage before switching to the substation. A group of containers, equipped with a (single) transformer and the auxiliary systems, is called an island. An island is therefore technically a self-sufficient BESS plant, although plants often consist of several islands. All islands are then connected to a single substation where the voltage is further raised to the high voltage of the grid. The steps in the construction of a BESS plant As with all types of plant, the first phase concerns the permitting process. In the case of BESS, it’s quite streamlined because they are containers that take up little space, involve no emissions and have no particular environmental impact. Once the administrative formalities have been completed, the suitability of the land needs to be checked; again, the procedure is simpler than that required for large-scale plants, or for those with a more complex configuration. This is followed by the opening of the construction site, with digging for the laying of the foundations, the arrival of the containers and the cranes to move them. This is followed by the installation of the containers and then the wiring of the inverters, the implementation of the safety devices and the substation. Finally, the connection to the grid is made: at that point all that is missing is the official opening of the plant and its entry into operation.
