Storage systems: connection diagrams

A storage system is defined as a set of devices capable of absorbing and releasing electrical energy that can generally be identified in the batteries, in the BMS (battery management system) and in the converter, which can be configured in different ways.

In practice, the different configurations that a storage system can have and the method of connection to the grid are identified as follows:

Connection to the energy network

AC side: It is a connection scheme that keeps the configuration of the existing photovoltaic system unchanged, which is why it is also called Retrofit.

The storage system inverter and the photovoltaic inverter are two distinct machines; the power of the accumulator is added to the power of the photovoltaic.

This scheme is also adopted for new systems, especially if they are of high power.

DC side storage system: In this system configuration, the inverter that manages the storage and production of energy from the photovoltaic is a single machine; the power that is supplied is at most equal to that of the only inverter present.

From a theoretical point of view, the efficiency of this connection scheme is slightly greater than that for the AC side connection.

Characteristics of the inverters

Hybrid inverter

In common parlance, an inverter is defined as a hybrid that is able to convert both the power developed by the photovoltaic system and that available in the battery, even independently of each other.

In most of the products on the market there is a dedicated input for each of the energy sources. Hybrid inverters can be configured on connection AC or DC side.

Battery Inverter

They are those products intended exclusively for the conversion of battery energy. They can only be connected in the figuration of the AC side system.

Bidirectional inverter

They are defined as bidirectional in the context of storage inverters, those devices that are also able to draw energy from the grid to recharge the batteries.

This function, which may not seem economically advantageous, may instead prove necessary to ensure a long life of the battery avoiding deep discharges (for example in the event of a photovoltaic failure).

It can also be used to ensure a certain stored energy and then make it available at times of greatest demand (peak shaving) or when it is economically more convenient.

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