Commonly used terms related to BESS systems: FGR, GRE, FCR, aFRR, mFRR, and the balancing market
A BESS storage system is most often associated with lower electricity costs for a company. However, some projects can be beneficial on a broader scale and help balance the country’s power grid. If you are interested in the specific capabilities of BESS systems, you will encounter the terms FGR, GRE, FCR, aFRR, and mFRR.
How does the balancing market work? To put it very simply, the amount of electricity generated and consumed on the grid must match. If too much or too little electricity is generated, the grid must be balanced. Therefore, Litgrid purchases services from market participants who can respond quickly to imbalances. If a company’s BESS systems meet the technical and market requirements, the BESS owner may gain an additional source of income.
To understand the role of BESS in the balancing market, it is important to distinguish between two groups of terms. FGR and GRE describe the technical operation of the storage system: how the system itself responds to frequency changes, absorbing excess energy or feeding energy back into the grid. Meanwhile, FCR, aFRR, and mFRR balance market products and frequency reserves—in other words, they are services the operator purchases from BESS system owners.
Technical Operation of the Battery System: FGR and GRE
FGR (Frequency Guard Regulation) in BESS projects is designed for rapid response to frequency changes. If grid electricity generation suddenly drops—for example, if a large power plant goes offline—the system frequency may begin to fall. In such a case, a rapidly controllable BESS system could briefly feed power into the grid and help stabilise the situation. The reverse is also important: if too much electricity is generated, the storage system can absorb the excess energy, helping reduce the imbalance.
GRE (Grid Regulation Energy) refers to the amount of energy available to regulate the grid. Simply put, it is the amount of energy the storage system feeds into the grid during a power shortage or stores during a power surplus. For example, if generation is short during a given period, a BESS can be activated as a flexible source to help cover the shortfall.
Balancing Market Reserves: FCR, aFRR, and mFRR
FCR (Frequency Containment Reserve) is a frequency containment reserve. It activates within 30 seconds when the power system’s frequency begins to deviate from its normal level. If grid power generation suddenly drops, FCR quickly stabilises frequency to prevent the situation from worsening. A BESS system, if it meets the technical requirements, can temporarily feed power into the grid and help maintain system stability.
aFRR (Automatic Frequency Restoration Reserve) – automatic frequency restoration reserve. It activates automatically, without human intervention, when the power system’s balance still needs to be restored after the initial response. In the Lithuanian balancing market, aFRR is activated within 5 minutes. For example, if there is a generation shortfall, BESS system resources included in this reserve can help reduce that shortfall.
mFRR (Manual Frequency Restoration Reserve) – manual frequency restoration reserve. It is activated upon the operator’s instruction or in accordance with a set procedure when additional resources are needed to restore balance. In the Lithuanian balancing market, mFRR is activated within 15 minutes. This reserve can be used to manage a longer-lasting imbalance, allowing faster recovery of reserves and readiness for new grid fluctuations.
It is important to understand that a storage system can both reduce electricity costs at a facility and increase revenue by participating in the balancing market. The terms discussed here do not address all relevant business questions. In BESS projects, it is not only the terms of the balancing market that are important. Other acronyms and concepts help explain the cost of a storage system, its technical capabilities, management, and practical business benefits.