A Comprehensive Guide: What Are Primary and Secondary Frequency Regulation in Energy Storage
In Europe (including Northern Europe) and most of Asia, the standard grid frequency is 50 Hz; in parts of North America, it is 60 Hz. Power generation and consumption must be balanced in real time. If the load suddenly increases or renewable energy output suddenly drops, the frequency falls; conversely, if generation exceeds consumption, the frequency rises.
In the past, this was primarily managed by thermal and hydroelectric power plants. However, as the share of renewable energy continues to rise, grid frequency fluctuations have become far more sensitive because wind and solar power lack the rotational inherent in traditional synchronous generators.
Battery Energy storage systems(BESS), on the other hand, offer millisecond response times, precise control, and bidirectional charging/discharging capabilities, making them ideally suited for grid frequency regulation. Electrochemical energy storage, in particular, has become a key player in ancillary services markets across the UK, Australia, the U.S., and Europe. In this blog, we'll break down what primary and secondary frequency regulation entail, technical requirements, and real-world market implementations.
Primary Frequency Response (FCR)
Primary Frequency Response refers to the immediate, autonomous response of localized equipment whenever the grid frequency deviates from its nominal value. For example, if a 50 Hz grid drops to 49.8 Hz, the energy storage Power Conversion System (PCS) detects the localized drop and automatically discharges power into the grid; if the frequency rises, it automatically absorbs power to recharge.
Key characteristics are:
- Trigger mechanism: Local frequency detection, automatic autonomous response.
- Response speed: Milliseconds to several seconds.
- Control target: The frequency deviation itself (arresting the drop/rise).
- Typical requirements: Fast, stable, bidirectional active power regulation.
- BESS advantages: The PCS responds much faster than coal-fired power plants, making it highly suitable for fast frequency response.
In Europe, primary frequency regulation is formally classified as FCR (Frequency Containment Reserve). FCR serves as the first line of response following a frequency disturbance, after which secondary frequency regulation resources take over. In the United Kingdom, similar services are divided into specialized products called Dynamic Containment (DC), Dynamic Moderation (DM), or Dynamic Regulation (DR), all working collectively to maintain system frequency within acceptable operational boundaries.
Secondary Frequency Regulation: AGC and aFRR
Secondary frequency regulation is similar to a grid dispatch center issuing real-time instructions to power plants and distributed assets to continuously adjust their power output via Automatic Generation Control ( AGC) commands.
Rather than considering only local frequency detection, the dispatch authority monitors grid-wide frequency, interconnection line power flows, and regional system balance status. Energy storage systems charge and discharge according to these instructions to restore the frequency back to its exact target value, thereby releasing and resetting the FCR resources for the next potential disturbance.
Taking the Finnish market as an example, the transmission system operator (TSO) Fingrid explicitly differentiates the two: FCR involves grid-connected resources reducing immediate frequency deviations through fast frequency response; while aFRR uses AGC to adjust output in real-time based on centralized dispatch instructions to restore system balance.
Key characteristics are:
- Trigger mechanism: Centralized AGC commands issued by the grid dispatcher or market operator platform.
- Response time: Typically several seconds to several minutes.
- Control targets: Frequency restoration, area control error (ACE), interconnection tier-line power.
- Typical requirements: High tracking accuracy, sustained ramp rates, and sufficient available energy capacity.
- BESS advantages: Exceptional tracking accuracy and the ability to switch instantly between full-scale forward and reverse power modes without mechanical wear.
In Europe, secondary frequency regulation generally corresponds to aFRR (automatic Frequency Restoration Reserve). It systematically takes over from FCR to bring the grid back to its nominal state.
Technical Comparison:Primary vs. Secondary Frequency Regulation
|
Comparison Item |
Primary Frequency Regulation (FCR/ FRR) |
Secondary Regulation (aFRR/ AGC) |
|---|---|---|
|
Common Terms |
Primary Frequency Response,FCR, FFR |
Secondary Regulation, aFRR, AGC |
|
Core Function |
Arrests the rapid frequency deviation immediately |
Restores the frequency to its nominal target value |
|
Control Source |
Localized automatic response by the onsite equipment |
Centralized instructions from the dispatch center or VPP platfor m |
|
Response Speed |
Milliseconds to seconds |
Seconds to minutes |
|
Technical Focus |
PCS rapid response, precise |
AGC tracking, communication, SOC management |
|
Energy Storage Requirements |
High power, fast response, SOC reserve |
Continuous tracking, available capacity, dispatch communication |
|
Revenue Characteristics |
Primarily capacity fees and performance fees |
Primarily mileage fees, capacity fees, and performance assessments |
Which Countries Are Best Suited for Using Energy Storage for Frequency Regulation?
TierⅠ: Mature Merchant Markets (Direct BESS Participation)
|
Country/Region |
Suitability |
Main Services |
Quick Assessment |
|---|---|---|---|
|
United Kingdom |
Very suitable |
Dynamic Containment(DC), Dynamic Regulationt(DR), Balancing Mechanismt(BM) |
Highly mature business models; explicit, stackable frequency service frameworks for merchant assets |
|
Ireland/Northern Ireland |
Very suitable |
DS3 Framework, FFR, System Services |
High penetration of non-synchronous renewable energy; small isolated grid; severe demand for fast frequency response |
|
Australia (NEM) |
Very suitable |
FCAS (Regulation and Contingency markets) |
High participation of ultra-scale BESS; FCAS serves as a core initial merchant revenue stream |
|
United States (PJM) |
Very suitable |
Regulation(RagA/ RagD), Reserve Markets |
Mature market clearings; heavy performance-scoring pay metrics that reward rapid BESS response assets |
|
Texas(ERCOT), U.S. |
Highly suitable |
Reg-Up, Reg-Down, RRS, ECRS |
Highly lucrative historic returns, though rapid battery saturation is driving increased competition and price compression |
|
Germany |
Suitable |
FCR, aFRR |
Highly standardized European cross-border markets; ideal for utility-scale standalone storage and aggregated C&I portfolios |
|
France, Netherlands, Belgium, Austria, Switzerland |
Suitable |
FCR, aFRR |
Part of the European synchronous grid; market rules are gradually being harmonized |
|
Italy |
Suitable |
Fast Reserve, MSD, Capacity Mechanism, Ancillary Services |
Rapid growth in renewable energy; significant room for energy storage participation |
Tier Ⅱ: High Potential & Evolving Markets (Evolving Frameworks)
|
Country/Region |
Suitability |
Assessment |
|
Japan |
Becoming suitable |
Driven forward by emerging balancing markets, newly formed capacity markets, and targeted front-of-the-meter energy storage subsidies |
|
Spain |
Opportunities exist |
High share of solar PV, strong demand for energy storage, but frequency regulation revenue mechanisms are less mature than in the UK or Australia |
|
Poland |
Opportunities exist |
Rising demand for capacity markets and grid flexibility; energy storage is beginning to enter the market |
|
Nordic Countries (Sweden, Finland, Norway, etc.) |
Highly suitable; transitioning to active operations |
Services like FCR-N, FCR-D, aFRR, and mFRR are technically optimal for BESS. Transmission system operators (e.g., Fingrid, Svenska kraftnät) allow independent BESS participation. Day-ahead and intraday spot trading cycles are shrinking, making VPP aggregation and multi-market revenue stacking critical due to finite market capacity |
|
Chile |
Opportunities exist |
Severe curtailment of solar power; energy storage offers opportunities for both peak shaving and ancillary services |
In Northern Europe, Sweden's Svenska kraftnät and Finland's Fingrid have allowed independent energy storage systems to participate in the FCR and aFRR markets, which can be integrated with day-ahead and intraday electricity markets to form a multi-revenue model combining “energy markets, primary frequency regulation, and secondary frequency regulation.” However, it should be noted that the capacity of the Northern European frequency regulation markets is relatively limited, making aggregation and rapid response capabilities key competitive factors for energy storage systems.
TierⅢ:Project-Based & PPA-Driven Markets (No Open Ancillary Markets)
|
Country/Region |
Suitability |
Assessment |
|
Saudi Arabia |
Significant project opportunities, but the frequency regulation market is not yet mature |
Currently focused more on renewable energy storage, long-term PPAs, and capacity guarantees, rather than purely market-based frequency regulation |
|
United Arab Emirates |
Significant project opportunities |
Many large-scale solar-plus-storage projects, but ancillary service market mechanisms are less mature than in Europe, the U.S., and Australia |
|
Oman, Jordan, Egypt |
Primarily project-based |
Energy storage is used more for PV smoothing, peak shaving, diesel replacement, and standby |
|
Some Southeast Asian countries |
Early-stage opportunities |
Weak power grids require frequency regulation from a technical standpoint, but commercial mechanisms are not yet mature |
In markets like the Middle East, energy storage can certainly provide primary and secondary frequency regulation from a technical standpoint, but project revenue generally does not come directly from open ancillary service markets, as it does in the UK, Australia, and PJM; rather, it is incorporated into PPAs, EPC technical specifications, or grid connection standards.
What Impact Does This Have on the Energy Storage System Configuration?
If a project is to perform primary frequency regulation (FFR), focus on the following:
|
System Component |
Key Considerations |
|
PCS |
Response time, overload capacity, frequency sag control, GFM/GFL capability |
|
EMS/PPC |
Frequency control logic, SOC reserve, power allocation |
|
BMS |
Ability to handle frequent, low-power charge/discharge cycles; accurate SOC/SOH |
|
Communication |
Local response priority, coordination with PPC/SCADA |
|
Battery |
High rate of discharge does not necessarily have to be extremely high, but must be able to withstand frequent microcycles |
If the project requires secondary frequency regulation/AGC, focus on the following:
|
System Component |
Key Considerations |
|
EMS/PPC |
AGC command tracking, power ramp rate, response accuracy |
|
SCADA |
Communication with the dispatch center; IEC 60870-5-104, IEC 61850, Modbus, etc. |
|
PCS |
Bidirectional rapid regulation, low-latency execution |
|
Battery System |
SOC management is critical; the battery must not be fully charged or fully discharged immediately upon receiving a command |
|
Contract |
Review performance metrics, mileage compensation, availability rate, and penalties for breach |
Application Analysis: How Pilot Technolog Drives Nordic FCR and VPP Development
As the core value of energy storage assets shifts from simple hardware deployment to software-driven market monetization, the Nordic region (Denmark, Sweden, Finland) has emerged as a key proving ground for advanced ancillary service operations. At Intersolar Europe, Pilot Technology showcased its comprehensive Cloud-Pipe-Edge-Device integrated smart energy solution, specifically designed to address the shrinking day-ahead and intraday electricity trading cycles in the Nordic market.
Pilot Technology's framework accelerates local asset development across Northern Europe through a tightly coupled hardware and software architecture:
- Fast Frequency Response Compliance at the Edge: For primary frequency regulation (such as FCR-D), response speed is paramount. Pilot's self-developed Commercial & Industrial (C&I) BESS features a localized Energy Management System (EMS) embedded with high-speed AI control loops. This enables the hardware to execute the sub-second power adjustments required by Nordic TSOs to stabilize grid deviations.
- Multi-Market Ancillary Stacking via VPP Platforms: Secondary regulation and optimization require macro-level orchestration. Pilot's Virtual Power Plant (VPP) aggregation platform ingests localized load forecasting and spot price algorithms to dynamically generate automated charging and discharging profiles. This allows distributed asset owners to automatically stack returns across multiple markets—participating in Nordic spot electricity trading alongside multi-level ancillary services including FCR-D, aFRR, and mFRR without manual operational intervention.
- Overcoming Local Regulatory Barriers: Nordic countries present unique operational challenges, ranging from specific grid connection approvals to disparate local metering frameworks. Utilizing smart edge computing gateways, Pilot’s solution abstracts these regional technicalities, enabling assets to integrate smoothly with retail energy networks and local aggregator frameworks across Denmark and Sweden.
In practical application—such as Pilot's deployment with Danish energy solutions providers—this unified hardware + VPP strategy bridges the gap between customer-side infrastructure and the wholesale power market. By linking C&I solar-storage assets with smart EV charging systems, the platform manages transformer peak loads to prevent local grid infrastructure overload charges, while simultaneously packaging the latent flexibility of the batteries into revenue-generating ancillary assets for the European grid.
BESS Technical Configuration Requirements
To successfully capture these localized revenue streams, hardware and software architectures must be engineered to specific performance tolerances:
System Configuration for Primary Frequency Regulation (FCR/FFR)
- PCS: Must feature ultra-low latency response times, temporary overload tolerances, frequency sag droop control capabilities, and Grid-Forming (GFM) / Grid-Following (GFL) flexibility.
- EMS / PPC: High-speed processing loops for frequency control logic, maintaining strict real-time SOC operating bands to ensure availability.
- BMS: Must feature micro-cycle calculation capabilities to track rapid, high-frequency, shallow depth-of-discharge (DOD) power fluctuations.
- Battery Cells: Engineered to withstand high-frequency micro-cycling without accelerated capacity fade or thermal accumulation.
System Configuration for Secondary Frequency Regulation (aFRR/AGC)
- EMS / VPP Platform: Continuous AGC command tracking, automated ramp-rate throttling, and multi-market optimization algorithms.
- SCADA/ Telemetry: High-reliability communication interfaces supporting industrial protocols such as IEC 60870-5-104, IEC 61850, and Modbus to maintain constant connectivity with the central grid dispatcher.
- Battery System: Energy capacity becomes highly critical. Large SOC operational buffers are required to sustain prolonged, continuous directional charge or discharge instructions without premature capacity exhaustion.
Conclusion
Primary frequency regulation is universally vital for modern grids saturated with intermittent renewable generation, where BESS assets capitalize on speed and autonomous execution. Secondary frequency regulation relies on sophisticated market frameworks and centralized coordination, where storage assets monetize their accuracy and continuous bi-directional tracking capabilities.
To build a truly bankable asset in advanced arenas like the Nordic region, developers can no longer look at hardware in isolation. Success requires the integration of high-performance BESS equipment, localized edge control compliance, and intelligent VPP orchestration to convert raw technical flexibility into sustainable, multi-market financial returns.
