Storage, the energy
that’s always there

Storage capacity, from home batteries to utility-scale storage systems, is crucial for the future of the energy transition.

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In the world of electricity, energy and storage have always been related, as demonstrated by Volta’s battery, the first generator of electricity and the precursor to modern batteries. Today, electrical energy storage systems are everywhere: in our pockets with mobile phone batteries, in our cars with lead-acid batteries that start internal combustion engines, or with more modern lithium batteries needed to power electric vehicles. The current push towards a broader adoption of renewable energy sources and the ongoing energy transition hinge significantly on the advancement and proliferation of these energy storage systems.

The importance of lithium batteries in the history of science and technology earned the scientists who made the greatest contribution to their development – John B. Goodenough, M. Stanley Whittingham and Akira Yoshino – the Nobel Prize in 2019. The main feature that has led to their success and use in a wide variety of devices is their ability to restore the flow of electrical energy (and thus the charge and discharge cycle) for an extremely high number of times.

In the field of renewable energy, storage systems come in two main sizes: residential, with battery sizes based on the solar panels used in homes, and utility-scale, with sizing based on the production potential of a wind or solar farm, like the one built by Plenitude in Assemini, near Cagliari, with a storage capacity of 9 MWh, which can also be scaled up.

Other promising electrical storage technologies are currently in advanced stages of development, including flow batteries, which feature circuits for liquid electrolytes. These will soon be part of the storage system connected to the new 6 MW photovoltaic park that Plenitude completed in February 2024 in Ravenna Ponticelle.
Alongside these electrochemical storage systems, there are other types of storage, which are very different from each other in terms of operation, development stages and efficiency, including: mechanical storage, the oldest method, where electrical energy is converted into potential and kinetic energy; electromagnetic storage, which is still under development; chemical storage methods like power-to-gas, which use electrical energy to generate gases; and hydrogen-based systems relying on electrolysis.

Why install a storage system? At a residential level, the reasoning is straightforward: it allows homeowners to use the energy generated by their solar panels even when the sun isn’t shining, such as in the evenings to play videogames or at night for running appliances like the dishwasher. Not only that: those who participate in renewable energy communities, for example, can use their storage system to store generated energy and share it with other participants based on demand.
Looking at the bigger picture, storage systems are also crucial for integrating renewable energy sources (RES) into the national power grid. Since RES are inherently non-programmable, cannot be stored in their primary form, and are tied to their production sites, they pose unique challenges in a grid that must handle a constantly growing and unpredictable demand. The rapid growth in electric vehicle usage exemplifies this challenge. The solution lies in enhancing both the number and capacity of storage systems, paving the way for a more integrated energy network, which includes both small-scale residential storage systems, which are vital for both private homes and energy community projects, as well as large-scale storage connected to renewable production sites, such as wind and photovoltaic parks, directly on-site or virtually through the electricity grid.

According to the Elaborazione Italia Solare on data from Gaudì by Terna as of December 2023, there were 518,947 storage systems connected to the electricity grid in Italy, for a total power of 3.37 GW and a capacity of 6.65 GWh. Most of these are of residential size, primarily used for self-consumption, with 94% of the connected plants having capacities under 20 kW. Lithium-ion technology accounts for 99.5% of the usage. Yet, despite these numbers, this capacity is still insufficient to meet the renewable energy production goals set for the end of the decade, as indicated in the latest Scenario Description Document, presented by Terna and Snam in 2022. In light of a policy scenario aligned with the 2030 Fit-for-55 goals, where RES are to supply 65% of the total electricity demand, it is projected that approximately 71 GWh of utility-scale storage capacity (i.e., systems of 1 MW or greater) will be needed. This capacity is to complement the residential and smaller-scale systems (estimated at 16 GWh) aimed at individual and collective self-consumption.
Large-scale installations are crucial for time-shifting – adjusting production peaks from morning to afternoon and consumption in the evening. Equally important is their role in stabilising the electrical grid and managing excess production and surges in unpredictable demand, like that from electric vehicles. According to Terna data, only 2% of Italian plants had capacities over 500 kWh at the end of 2022. Taking action in this area is essential to incorporate the anticipated power from the “Fit for 55” initiative into the national grid.

In Sardinia, Plenitude has built its first utility-scale storage facility in Italy. Located in Assemini, near Cagliari and operational since June 2023, this facility is situated in the same industrial area as a 23 MW photovoltaic park. This proximity facilitates the sharing of connection infrastructures, which helps to minimise the overall construction costs of the facility. The Assemini facility, equipped with a 15 MW capacity and 9 MWh of energy storage, utilises battery modules based on Lithium Iron Phosphate (LFP) technology and represents one of the first utility scale storage systems integrated into the Italian National Transmission Network.
The utility-scale plant in Assemini is important for its ability to offer Terna the “fast reserve” service for ultra-rapid frequency regulation, aimed at enhancing the stability of the network’s frequency in coordination with existing operations. This system significantly enhances the electrical grid’s security through its rapid activation capabilities, playing a crucial role in increasing the integration of renewable energies into Italy’s energy mix. Plenitude’s involvement in storage, however, extends beyond national borders. In 2022, the company added a facility in Texas, which features a system with a capacity of 200 MW and 200 MWh of storage. This project, even with different market conditions from those in Italy, underscores the strategic importance of electrochemical storage and provides essential stabilisation services to the grid, making it a vital resource in addressing the challenges posed by the growing integration of renewable energy sources.