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Energy Storage for Photovoltaic Plants

From intermittent production to flexible management

A photovoltaic plant produces energy based on solar irradiation and therefore on natural variables such as weather conditions and the day-night cycle. Production peaks during the central hours of the day (between 12:00 and 14:00), while electricity consumption is concentrated mainly in the morning (between 07:00 and 09:00) and evening (between 19:00 and 21:00). This misalignment between production and consumption is structural and tends to widen as renewable energy grows.

Energy storage resolves this issue: it allows excess energy produced during the day to be stored and made available when demand is higher. In this way, production becomes more flexible and better adapted to the needs of the electricity grid.

Production and storage are therefore two complementary activities: when integrated, they significantly increase the value and utility of plants for the energy system.

Partnership opportunities in storage

A rapidly growing sector

The large-scale storage market is evolving rapidly across Europe, driven by several factors:

the growth of non-programmable renewable sources and the consequent increase in demand for flexibility
the significant reduction in storage technology costs over the last decade
the evolution of a regulatory framework favourable to systems capable of responding rapidly to load variations
the development of competitive mechanisms, such as dedicated BESS auctions in several European countries

GDS Sole Italie is developing expertise in this field as a natural extension of its photovoltaic activity, drawing on the know-how built up by the Générale du Solaire group. This experience has been gained particularly in France and Africa, including through the development of mini-grid systems.

Optimising production and market value

The current challenge consists in optimising energy management: deciding when to feed it into the grid, based on demand and market price signals, and participating efficiently in electricity markets and dispatching services.

How it works

Intermittency and the value of energy

The price of electricity on the market is not fixed: it changes every quarter of an hour based on the relationship between supply and demand. When many photovoltaic plants produce simultaneously (typically during the central hours of the day), the supply of energy increases and the price tends to fall. When demand rises and solar production decreases (evening, early night hours), the price tends to rise again. A storage system makes it possible to reinject stored energy during periods of high demand, when the price of electricity is higher.

The role of storage in the electricity system

A storage system can contribute to the grid in two distinct ways:

Spot market arbitrage

Stored energy is fed into the grid during time slots when its value is highest, avoiding the hours of solar overproduction — typically during the central hours of the day — when the spot price tends to fall.

This approach makes it possible to optimise the value of the energy produced, adapting injection to market conditions.

Dispatching services: Mercato per il Servizio di Dispacciamento (MSD)

The electricity grid requires a constant balance between supply and demand. Battery storage systems are particularly well suited to providing this flexibility, thanks to their extremely fast response times.

They can therefore contribute to dispatching services, supporting the stability and security of the electricity system.

How it works

Mercato per il Servizio di Dispacciamento (MSD)

Terna, the national transmission grid operator, purchases through the Dispatching Services Market (MSD) the flexibility needed to keep the grid in real-time balance. Storage systems that meet the technical requirements can participate in these markets and receive remuneration for the availability they provide.

Two project configurations

Storage co-located with the photovoltaic plant

The storage system is installed close to the photovoltaic plant and operates in an integrated manner with it. Excess energy produced during the hours of highest irradiation is stored and subsequently fed into the grid during time slots when energy demand and prices are higher.

This configuration makes it possible to:

maximise the use of energy produced
reduce injections during lower-value hours
increase the overall profitability of the plant

Standalone storage (autonomous BESS)

A standalone plant is an independent storage facility, not paired with a specific production source. It operates autonomously on the energy market, storing and discharging electricity based on market conditions and grid requirements.

This configuration:

offers high operational flexibility
contributes to the stability of the electricity system
fits within a diversified portfolio logic relative to co-located plants

Storage technology

Electrochemical batteries

The main technology currently available at utility scale is electrochemical batteries.

This is the dominant solution in the utility-scale segment, thanks to technical characteristics particularly well suited to the needs of the electricity system:

extremely fast response times (in the order of milliseconds)
predictable life cycles
high scalability, enabling applications across projects of different sizes

Over the last fifteen years, the costs of these technologies have fallen significantly, making them increasingly competitive and financeable at large scale.

GDS Sole Italie's choice

For its storage projects, GDS Sole Italie adopts electrochemical battery systems as its reference technology.

This choice is based on concrete factors:

consolidated industrial maturity
a predictable risk profile for lenders
response times suited to participation in dispatching markets

The specific technology is selected on a case-by-case basis, depending on the technical and economic characteristics of each project.