BESS
FAQ
Key terms
- BESS — Battery Energy Storage System
- MW / MWh — units of power (MW) and energy storage capacity (MWh)
- BMS — Battery Management System
- EMS — Energy Management System
- Capacity market— a mechanism that remunerates available dispatchable capacity in the power system
- Balancing (ancillary) services — services that support the stability of the power grid, including FCR, aFRR and mFRR
- FCR / aFRR / mFRR — frequency regulation services activated within several seconds (FCR), from 30 seconds to 15 minutes (aFRR), and within 15 minutes (mFRR), helping maintain grid frequency at the required level
- Price arbitrage — charging the battery when electricity prices are low and supplying electricity to the grid when prices are high
- Cable pooling — sharing a single grid connection between renewable energy installations and/or energy storage systems
- Curtailment / redispatch— temporary reduction of electricity generation by the system operator
- IPP — Independent Power Producer (an independent electricity producer that owns the installation)
- RES — renewable energy sources
- ESG — Environmental, Social, Governance
- CSRD — Corporate Sustainability Reporting Directive
BESS technology basics
1. What is BESS and how does an energy storage system work?
BESS (Battery Energy Storage System) is a large-scale battery system that stores electricity when there is a surplus and supplies it to the grid when demand increases. It acts as a buffer for the power system: charging during periods of low prices and surplus generation, and discharging during periods of peak demand or high prices.
BMS (Battery Management System) monitors the condition and safety of individual battery cells, including temperature, voltage and state of charge. EMS (Energy Management System) controls when and how much energy the system draws from or supplies to the grid, optimising its operation based on market signals and grid requirements.
Volta Polska develops and operates large-scale energy storage systems, providing services on the energy and flexibility markets, supporting grid security and facilitating the integration of renewable energy sources
2. What is the difference between a standalone BESS and a storage system added to a cPPA or SaaS (+BESS)?
Standalone BESS is a standalone, large-scale energy storage installation connected directly to the electricity grid. It is not physically linked to a specific renewable energy installation — it charges using surplus electricity available in the system, regardless of its source, and supplies electricity when the grid needs it. It participates directly in the energy and flexibility markets as an independent, flexible asset.
+BESS is an energy storage system added as a module to a cPPA or Solar as a Service. In this model, the storage system increases flexibility and improves the delivery profile under a specific customer contract — for example, by shifting the use of electricity generated by an on-site PV installation or better matching electricity deliveries from a renewable energy plant with the customer’s consumption profile.
Both models use the same energy storage technology, but differ in terms of grid connection, application and business model. A standalone BESS primarily creates value in energy and ancillary services markets, while +BESS supports the delivery of a specific contract.
3. Why has energy storage become so important in Poland?
The growth of solar and wind power in Poland is changing how the electricity grid operates. During the sunniest hours, photovoltaic generation can be so high that market prices fall sharply — sometimes reaching negative values. As more solar capacity is installed, the value of electricity generated around midday decreases because it is produced when its market value is at its lowest.
Energy storage allows this surplus to be captured and supplied to the grid when it is actually needed — in the evening or during other periods of higher demand. This increases the flexibility of the power system, improves the utilisation of renewable energy and increases the economic value of renewable energy investments as a whole.
4. How is BESS different from cPPA and SaaS — when do I need energy storage?
cPPA and SaaS are models for purchasing renewable electricity — respectively from a renewable energy plant located outside the customer’s site and from a PV installation located at the customer’s site. BESS is not a source of energy, but a flexibility tool: it does not generate electricity, but shifts it over time.
| cPPA / SaaS | BESS | |
|---|---|---|
| Role | Supply of renewable electricity | Flexibility and supply stabilisation |
| Source of value | Sale/supply of electricity from renewable sources | Shifting energy over time, ancillary services |
| Typical customer | Company purchasing renewable electricity | Company with a cPPA/SaaS contract looking to improve its delivery profile, or an investor |
In practice, BESS most often serves as an addition to a cPPA or SaaS agreement, increasing the flexibility of already contracted energy supplies, or as a standalone investment participating directly in energy markets, regardless of whether a company already has a renewable energy contract.
Value and revenue model
5. What are the revenue sources for Volta's standalone BESS?
A standalone BESS creates value through several complementary revenue streams:
- Capacity market — remuneration for maintaining available dispatchable capacity, ready to be activated at the request of the system operator.
- Balancing (ancillary) services — energy storage systems are well suited to fast frequency regulation (FCR) and aFRR (automatic Frequency Restoration Reserve) services thanks to their very fast response times.
- Price arbitrage — charging the battery during periods of low electricity prices (e.g. around midday, when solar generation is high) and supplying electricity to the grid during periods of high prices.
Combining these revenue streams can reduce dependence on a single market mechanism. The exact revenue structure depends on the current capacity market rules, the system operator’s (PSE) qualification requirements and electricity price volatility, which is why Volta Polska assesses the revenue model individually for each project.
6. What are the benefits of adding BESS to a cPPA or SaaS contract?
Under a cPPA, an energy storage system can increase flexibility and improve the delivery profile — allowing the timing of electricity supplied from a renewable energy plant to be better matched with the customer’s actual consumption profile, while reducing exposure to market price volatility during periods when electricity from the renewable energy plant itself is unavailable.
Under SaaS, energy storage allows a company to make better use of electricity generated on-site — for example, by shifting its consumption to hours when, without a storage system, it would need to draw electricity from the grid and pay for it, thereby increasing the effective self-consumption of the installation.
As with cPPA and SaaS, Volta Polska finances and is responsible for the implementation and operation of the storage system. Adding a +BESS module to a contract does not require the customer to make capital investments or assume the technical risks associated with operating the storage system.
Project development and operation
7. What does the construction and commissioning process for a BESS project look like?
Volta Polska has started construction of its first standalone BESS in Poland. The Połaniec project will have a power of 6 MW and a storage capacity of 15 MWh. The storage system will be directly connected to the electricity grid, with commissioning planned for early 2027.
The process includes a technical and economic assessment of the location and grid connection conditions, obtaining the necessary permits and grid connection conditions from the network operator, construction of the installation, as well as testing and certification before the system is authorised to provide services on the energy and capacity markets.
8. Who is responsible for the safety and operation of the storage system?
The BMS plays a key role in the safety of the storage system, monitoring the condition of each battery module in real time — including temperature, voltage and state of charge — and protecting the installation against overload and overheating. The EMS is responsible for optimising the operation of the storage system based on market signals and grid requirements.
Volta Polska is responsible for project implementation and long-term operation — from commissioning through the ongoing technical and commercial management of the installation, based on the internal operational standards already applied to the Volta Group’s photovoltaic installations.
9. What is the planned scale of Volta's BESS portfolio in Poland?
The Volta Polska target is to reach more than 250 MW of installed energy storage capacity within three years of commissioning the first project, planned for early 2027. The portfolio will include both standalone installations and storage systems added to cPPA and SaaS contracts in the +BESS model.
10. Can BESS be added to a cPPA or SaaS agreement after the contract has been signed?
Yes, a +BESS module can be added to an existing contract structure if the customer’s consumption profile and the technical conditions at the site allow it. Volta Polska assesses each case individually, taking into account the customer’s electricity consumption profile, available space (in the case of on-site installations) and grid connection conditions. Details of integrating the storage system with an existing contract are discussed during free consultations.
ESG and renewable energy integration
11. How does BESS support the integration of renewable energy into the power system?
Energy storage systems act as a buffer, balancing fluctuations between generation and demand. During periods of surplus renewable generation — typically around midday on sunny days — BESS stores excess electricity and supplies it to the system when demand increases. This can reduce the need to curtail renewable energy generation and allow a greater share of generated renewable electricity to be used instead of being curtailed due to insufficient demand at a given time.
Energy storage therefore supports the integration of renewable energy sources into the power system, improving grid frequency stability and supporting the security of its operation.
12. How does BESS reduce curtailment of renewable energy installations?
Energy storage can reduce the need for redispatching (curtailment), which means the forced reduction of renewable energy generation by the system operator when the grid is unable to absorb all the electricity being generated.
Instead of curtailing generation, BESS can absorb part of this electricity and supply it to the system later, when demand is higher.
13. How does energy storage fit into ESG strategies and CSRD reporting?
A storage system added to a cPPA or SaaS agreement (+BESS) can improve the delivery profile of renewable electricity by reducing the periods when the customer needs to rely on electricity from the national energy mix. This may be relevant to Scope 2 emissions reporting under the market-based method, particularly in the context of the growing role of hourly matching in GHG Protocol reporting.
A standalone BESS supports ESG objectives primarily by increasing the flexibility of the power system and facilitating the integration of greater amounts of renewable energy. Its impact is systemic and does not directly translate into an individual company’s Scope 3 result.
14. What experience does Volta Group have in energy storage?
Volta Group brings nearly ten years of experience in energy storage. The Group has been developing energy storage projects since 2018, including large-scale projects in Corsica and Mayotte, where energy storage plays a key role in integrating renewable energy sources and supporting the stability of local power systems.
Volta Group applies the knowledge and experience gained from these projects to energy storage development in France and Poland — developing, financing, implementing and operating projects while maintaining control over each stage of their lifecycle. More information about the group is available on the Volta Groupe website.