Energy storage systems: the future of photovoltaics

Photovoltaics is the energy of the future: the figures show this, with almost 1.8 million active installations in Italy at the end of 2024. Choosing photovoltaics for your home or business therefore means contributing to national energy production in a sustainable, renewable way. Of course, the sun is an inexhaustible natural source, but it is not always able to provide sunlight; for example, during the night or on cloudy days. 

Modern photovoltaic systems with a Battery Energy Storage System, however, allow the user to have a continuous supply of solar energy. This innovative system to store the energy produced but not immediately used allows it to be reused at a later date, in a continuous exchange between the photovoltaic installation and the grid. Let's find out how it works.

What is a Battery Energy Storage System?

Photovoltaic storage translates as Battery Energy Storage System (BESS), which immediately identifies a system based on battery-based electricity storage. The battery pack consists of cells of different electrochemical composition connected in series or in parallel, depending on the required capacity and voltage. The system then acts as an accumulator for the excess electricity produced by the photovoltaic panels, and its performance is monitored by the Battery Management System (BMS).  

The battery pack can be installed on solar, photovoltaic or thermodynamic systems or on systems powered by another renewable source according to the guidelines of the GSE (Gestore dei Servizi Energetici - Energy Services Manager). 

The GSE defines the main ways in which a storage system can be installed on a photovoltaic system. These are distinguished by the position of the batteries in relation to the inverter and the direction of the energy flows:

• Unidirectional production-side (DC) system: the batteries are installed between the photovoltaic panels and the inverter. In this configuration, the energy produced by the panels (in direct current, DC) goes first to the batteries and then to the inverter, which converts it into alternating current (AC) for everyday use. It is called “unidirectional” because the batteries can only be charged by the energy produced by the photovoltaic system.

• Bidirectional production-side (DC) system: again, the batteries are located between the panels and the inverter, so always on the DC side. The difference is that, in addition to receiving energy from the panels, the batteries can also be charged from the grid, making the system more flexible.

• Bidirectional system on the post-production side (AC): here the batteries are installed after the inverter, so they work with alternating current. In this case, energy can come either from photovoltaic panels or from the electricity grid. This solution is ideal for those who want to add a storage system to an existing photovoltaic installation without having to replace the inverter.

Why install a photovoltaic storage system?

Opting for a photovoltaic system with storage provides incentives for self-production and self-consumption of sustainable energy, reducing dependence on the national grid. Conventional photovoltaic systems are advantageous if the energy produced is used immediately, as in the case of an apartment building with many homes. Installations with storage systems, on the other hand, offer more realistic conditions for the average consumption habits of users, exploiting the energy stored over the course of the day during the evening and night hours, when the whole family is usually at home. For the same consumption, a photovoltaic storage system saves on the energy component of the bill due to greater energy independence, which is especially useful for isolated homes far from the grid.

Purchase costs and incentives 

But how much does a photovoltaic storage system cost? With an additional component to consider, the cost of installing a system with storage increases compared to a conventional photovoltaic system without. However, it is an investment that guarantees significant savings on bills in the long run, and is influenced by a number of factors:

• Storage capacity: the higher the battery pack energy storage capacity, expressed in kWh, the higher the cost.

• Chemical composition: battery cells can have different electrochemical compositions, which influence their cost. Lithium cells, for example, are the most popular because of the optimal performance they provide, but they are also the most expensive.

• Longevity and efficiency: the cost of a storage system is also influenced by the durability of the batteries, i.e. the number of charge and discharge cycles they can sustain before they discharge. 

In Italy, state and regional incentives and concessions are available for the installation of photovoltaic systems with storage, such as the 50% Renovation Bonus on a maximum expenditure of €96,000 for renovation work on the main residence*. 

* In the event that the same expenses are incurred by the holders of the right of ownership or right in rem of enjoyment over the property unit used as the main residence (L. 30 December 2024, no. 207, Art. 1, co. 55(b), no. 1). A main residence is defined as the dwelling in which the natural person, who owns it by way of ownership or other right in rem, or their family members usually reside

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