Frequency control using C&I energy storage systems
The stability of the grid frequency is a key factor for supply security in modern power grids. With the increasing integration of renewable energies, frequency control is becoming increasingly important and complex. Commercial & Industrial (C&I) energy storage systems are becoming a key tool for ensuring grid stability.
Fundamentals of Frequency Control in the Power Grid
In the European interconnected grid, the grid frequency is set at 50 Hz. This frequency is an indicator of the balance between electricity generation and consumption. If feed-in exceeds consumption, the frequency increases; otherwise, it decreases. Even minor deviations of more than 0.2 Hz can become problematic and trigger protective shutdowns. Larger deviations lead to significant disruptions, even widespread power outages.
Traditionally, frequency stability was primarily ensured by conventional power plants with rotating masses (inertia) and adjustable power. These power plants could adjust their output within certain limits to respond to frequency changes. With the decline of conventional power plants and the increase in renewable energies, which feed in weather-dependent and volatile power, new challenges for frequency control are emerging.
Frequency control occurs in several stages and time ranges: The instantaneous reserve (second range) is provided by the rotational energy of the generators. This is followed by the primary control power (within 30 seconds), the secondary control power (within 5 minutes), and finally the minute reserve. This tiered system ensures that short-term fluctuations can be balanced while simultaneously ensuring sufficient control reserves are available in the long term.
The Role of C&I Energy Storage in Frequency Control
C&I energy storage systems offer unique properties that make them particularly valuable for frequency control. Unlike conventional power plants, they can react almost instantaneously and both absorb and release energy. This bidirectionality, combined with extremely fast response times, makes them ideal tools for modern grid stabilization.
Battery storage systems can activate their full power within milliseconds, making them orders of magnitude faster than conventional power plants. This reaction speed enables them to intervene even at the smallest frequency deviations, thus preventing larger fluctuations. Their ability to provide both positive and negative control power allows them to respond flexibly to over- and underfrequency conditions.
C&I storage systems are typically installed with capacities ranging from 100 kW to several MW, making them ideal for providing control power on an industrial scale. Their modular design also allows for precise adaptation to current needs and easy expandability. Modern systems feature sophisticated power electronics that enable precise control of power output and consumption.
Technical Functionality of Frequency Control with Storage
The technical implementation of frequency control with C&I storage is based on advanced control systems that continuously monitor the grid frequency. Deviations from the setpoint result in an immediate response: If the frequency is under-frequency, energy is fed into the grid; if the frequency is over-frequency, energy is extracted from the grid and stored in the storage.
The control characteristic is typically implemented as a linear function, where the power change is proportional to the frequency deviation. This proportionality ensures stable control without overshoot. The deadbands, i.e., frequency ranges without control activity, can be designed very narrowly, enabling precise frequency control.
Modern battery storage systems feature intelligent management systems that can take into account not only the current frequency but also its rate of change (frequency gradient). This enables predictive control that reacts before major deviations occur. They can also dynamically adapt their operating parameters to the current grid situation to maximize control efficiency.
Integration into higher-level control systems is achieved via standardized interfaces that ensure secure and reliable communication. This enables not only local frequency control but also integration into large-scale control concepts and virtual power plants.
Frequency control using C&I energy storage systems
The stability of the grid frequency is a key factor for supply security in modern power grids. With the increasing integration of renewable energies, frequency control is becoming increasingly important and complex. Commercial & Industrial (C&I) energy storage systems are becoming a key tool for ensuring grid stability.
Fundamentals of frequency control in the power grid
In the European interconnected grid, the grid frequency is set at 50 Hz. This frequency is an indicator of the balance between electricity generation and consumption. If feed-in exceeds consumption, the frequency increases – Conversely, it decreases. Even minor deviations of more than 0.2 Hz can become problematic and trigger protective shutdowns. Larger deviations lead to significant disruptions, including widespread power outages.
Traditionally, frequency stability was primarily ensured by conventional power plants with rotating masses (inertia) and adjustable power. These power plants could adjust their output within certain limits to respond to frequency changes. With the decline of conventional power plants and the increase in renewable energies, which feed in weather-dependent and volatile power, new challenges for frequency control are emerging.
Frequency control occurs in several stages and time ranges: The instantaneous reserve (second range) is provided by the rotational energy of the generators. This is followed by the primary control power (within 30 seconds), the secondary control power (within 5 minutes), and finally the minute reserve. This tiered system ensures that short-term fluctuations can be balanced while simultaneously ensuring sufficient control reserves are available in the long term.
The Role of C&I Energy Storage in Frequency Control
C&I energy storage systems offer unique properties that make them particularly valuable for frequency control. Unlike conventional power plants, they can react almost instantaneously and both absorb and release energy. This bidirectionality, combined with extremely fast response times, makes them ideal tools for modern grid stabilization.
Battery storage systems can activate their full power within milliseconds, making them orders of magnitude faster than conventional power plants. This reaction speed enables them to intervene even at the smallest frequency deviations, thus preventing larger fluctuations. Their ability to provide both positive and negative control power allows them to respond flexibly to over- and underfrequency conditions.
C&I storage systems are typically installed with capacities ranging from 100 kW to several MW, making them ideal for providing control power on an industrial scale. Their modular design also allows for precise adaptation to current needs and easy expandability. Modern systems feature sophisticated power electronics that enable precise control of power output and consumption.
Technical Functionality of Frequency Control with Storage
The technical implementation of frequency control with C&I storage is based on advanced control systems that continuously monitor the grid frequency. Deviations from the setpoint result in an immediate response: If the frequency is underfrequency, energy is fed into the grid; if the frequency is overfrequency, energy is taken from the grid and stored in the storage.
The control characteristic is typically implemented as a linear function, where the power change is proportional to the frequency deviation. This proportionality ensures stable control without overshoot. The deadbands, i.e., frequency ranges without control activity, can be designed very narrowly, enabling precise frequency control.
Modern battery storage systems feature intelligent management systems that can take into account not only the current frequency but also its rate of change (frequency gradient). This enables predictive control that reacts before major deviations occur. They can also dynamically adapt their operating parameters to the current grid situation to maximize control efficiency.
Integration into higher-level control systems is achieved via standardized interfaces that ensure secure and reliable communication. This enables not only local frequency control but also integration into large-scale control concepts and virtual power plants.
Primary Control Power with C&I Storage Systems
Primary control power (PRL), also known as frequency containment reserve (FCR), is a particularly attractive application for C&I storage systems. It serves to immediately stabilize the grid frequency and must be able to be fully activated within 30 seconds. Battery storage systems easily meet the requirement of a fast response time and far exceed conventional providers.
When providing primary control power, the storage system operates symmetrically, meaning it must be able to provide both positive and negative control power in equal amounts. This requires an operating strategy in which the storage system is ideally operated at a state of charge of approximately 50% to maintain sufficient capacity in both directions.
The dimensioning of the storage system for PRL must take into account the maximum required power and the required amount of energy. According to current requirements, the full power must be available for at least 15 minutes. With a PRL power of 1 MW, this means a minimum usable storage capacity of 250 kWh. In practice, however, storage units for this application are dimensioned significantly larger to maintain safety reserves and reduce the number of battery cycles.
Primary control power is marketed through weekly or daily tenders, in which providers offer their power at a specific price. Remuneration is performance-based, meaning that the provision of control power is remunerated, regardless of whether and how often it is actually used. This creates a reliable source of income for storage operators.
Secondary Control Power and Minutes Reserve
In addition to primary control power, C&I storage systems can also provide secondary control power (SRL) and minutes reserve (MRL). These types of control power serve to relieve the primary control system and balance longer-term imbalances. Activation occurs automatically by the transmission system operator via a call signal.
For secondary control power, providers must be able to activate their full capacity within 5 minutes. Minutes reserve must be available within 15 minutes. Battery storage systems easily meet both requirements. In contrast to primary control power, SBP and MBP can be offered asymmetrically, meaning positive and negative control power can be marketed independently of each other.
The remuneration for SBP and MBP consists of a capacity price (for the provision) and a work price (for the energy actually delivered). This two-tier remuneration structure enables a flexible marketing strategy, allowing storage operators to optimize their bids.
One advantage of battery storage systems in this area is their precise controllability, which enables exact compliance with the requested power. This minimizes deviations and associated penalties. In addition, their fast response time allows them to use the entire call period to provide the required amount of energy.
Economic Aspects of Frequency Control with Storage
The provision of control power with C&I storage systems can represent an attractive business model. The revenues from the marketing of control power complement other sources of income such as self-consumption optimization or peak load management, thus improving the economic viability of the storage investment. In many cases, the combination of different applications ("value stacking") is the key to profitable storage use.
Prices for control power are subject to market fluctuations and vary depending on the type of control power, time of day, and season. Historically, the power prices for primary control power have ranged between €1,000 and €3,000 per MW per week, although a price decline has been observed in recent years due to increasing competition. Nevertheless, they still offer interesting revenue potential.
In addition to revenue, the specific costs of providing control power must also be taken into account when calculating profitability. These include increased battery wear due to frequent charging and discharging cycles, energy losses due to battery efficiency, and the costs of prequalification and ongoing participation in the control power market. In addition, a certain amount of storage capacity and power is required, which is then unavailable for other applications.
The payback period for storage systems used primarily for control power is typically between 5 and 8 years, depending on market developments and technical design. With falling battery costs and the increasing importance of frequency stabilization, this outlook is continuously improving.
Regulatory Framework and Market Development
The regulatory framework for the provision of control power has been continuously developed in recent years to facilitate access for new technologies such as battery storage. Product lifecycles have been shortened, minimum bid sizes reduced, and the tendering frequency increased. These changes benefit battery storage systems and promote their integration into the balancing power market.
The European harmonization of balancing power markets is progressing, creating uniform conditions that facilitate cross-border cooperation. At the same time, new products such as Fast Frequency Response (FFR) are being developed that are specifically tailored to the capabilities of storage systems and specifically utilize their advantages.
The prequalification requirements for participation in the balancing power market are demanding, but certainly achievable for modern storage systems. They include technical tests to demonstrate balancing power capability, the implementation of specific communication interfaces, and organizational requirements. Storage manufacturers and integrators now offer standardized solutions that facilitate the prequalification process.
With the ongoing expansion of renewable energies and the decline of conventional power plants, the need for rapidly responding control power sources is growing. This creates favorable long-term market conditions for battery storage, even though short-term price fluctuations may occur. Experts expect increasing differentiation of control power products, which will better address the specific strengths of different technologies.
Primary Control Power with C&I Storage Systems
Primary control power (PRL), also known as Frequency Containment Reserve (FCR), is a particularly attractive application for C&I storage systems. It serves to immediately stabilize the grid frequency and must be able to be fully activated within 30 seconds. Battery storage systems easily meet the requirement of a fast response time and far exceed conventional providers.
When providing primary control power, the storage system operates symmetrically, meaning it must be able to provide both positive and negative control power in equal amounts. This requires an operating strategy in which the storage system is ideally operated at a state of charge of approximately 50% to maintain sufficient capacity in both directions.
The dimensioning of the storage system for PRL must take into account the maximum required power and the required amount of energy. According to current requirements, the full power must be available for at least 15 minutes. With a PRL power of 1 MW, this means a minimum usable storage capacity of 250 kWh. In practice, however, storage units for this application are dimensioned significantly larger to maintain safety reserves and reduce the number of battery cycles.
Primary control power is marketed through weekly or daily tenders, in which providers offer their power at a specific price. Remuneration is performance-based, meaning that the provision of control power is remunerated, regardless of whether and how often it is actually used. This creates a reliable source of income for storage operators.
Secondary Control Power and Minute Reserve
In addition to primary control power, C&I storage systems can also provide secondary control power (SBP) and minute reserve (MRL). These types of control power serve to relieve the primary control system and balance longer-term imbalances. Activation occurs automatically by the transmission system operator via a call signal.
For secondary control power, providers must be able to activate their full capacity within 5 minutes. The minute reserve must be available within 15 minutes. Battery storage systems easily meet both requirements. In contrast to primary control power, SBP and MBP can be offered asymmetrically, meaning positive and negative control power can be marketed independently of each other.
The remuneration for SBP and MBP consists of a capacity price (for the provision) and a work price (for the energy actually delivered). This two-tier remuneration structure enables a flexible marketing strategy, allowing storage operators to optimize their bids.
One advantage of battery storage systems in this area is their precise controllability, which enables exact compliance with the requested power. This minimizes deviations and associated penalties. In addition, their fast response time allows them to use the entire call period to provide the required amount of energy.
Economic Aspects of Frequency Control with Storage
The provision of control power with C&I storage systems can represent an attractive business model. The revenues from the marketing of control power complement other sources of income such as self-consumption optimization or peak load management, thus improving the economic viability of the storage investment. In many cases, the combination of different applications ("value stacking") is the key to profitable storage use.
Prices for control power are subject to market fluctuations and vary depending on the type of control power, time of day, and season. Historically, the power prices for primary control power have ranged between €1,000 and €3,000 per MW per week, although a price decline has been observed in recent years due to increasing competition. Nevertheless, they still offer interesting revenue potential.
In addition to revenue, the specific costs of providing control power must also be taken into account when calculating profitability. These include increased battery wear due to frequent charging and discharging cycles, energy losses due to battery efficiency, and the costs of prequalification and ongoing participation in the control power market. In addition, a certain amount of storage capacity and power is required, which is then unavailable for other applications.
The payback period for storage systems used primarily for control power is typically between 5 and 8 years, depending on market developments and technical design. With falling battery costs and the increasing importance of frequency stabilization, this outlook is continuously improving.
Regulatory Framework and Market Development
The regulatory framework for the provision of control power has been continuously developed in recent years to facilitate access for new technologies such as battery storage. Product lifecycles have been shortened, minimum bid sizes reduced, and the tendering frequency increased. These changes benefit battery storage systems and promote their integration into the balancing power market.
The European harmonization of balancing power markets is progressing, creating uniform conditions that facilitate cross-border cooperation. At the same time, new products such as Fast Frequency Response (FFR) are being developed that are specifically tailored to the capabilities of storage systems and specifically utilize their advantages.
The prequalification requirements for participation in the balancing power market are demanding, but certainly achievable for modern storage systems. They include technical tests to demonstrate balancing power capability, the implementation of specific communication interfaces, and organizational requirements. Storage manufacturers and integrators now offer standardized solutions that facilitate the prequalification process.
With the ongoing expansion of renewable energies and the decline of conventional power plants, the need for rapidly responding control power sources is growing. This creates favorable long-term market conditions for battery storage, even though short-term price fluctuations may occur. Experts expect increasing differentiation of control power products, which will better address the specific strengths of different technologies.
Practical Example: C&I Storage for Frequency Control
A vivid example of the successful use of C&I storage for frequency control is provided by an industrial company that installed a 2 MW / 2.5 MWh lithium-ion storage system. The storage system was primarily designed for peak load management and self-consumption optimization of the company's own PV system, but its dimensions provide sufficient reserves for the provision of control power.
In practice, the storage system is operated to continuously provide 1 MW of primary control power while maintaining a state of charge of 40-60%. The remaining capacity and power are available for operational energy management. An intelligent control system automatically detects potential conflicts between the various applications and prioritizes their resolution, with control power provision being given priority as a system-relevant service.
The revenue from control power marketing amounts to approximately €400,000 per year, which corresponds to approximately 20% of the total investment costs. Combined with the savings from peak load management and self-consumption optimization, this results in a payback period of just under five years. Furthermore, the company makes an active contribution to grid stability and strengthens its image as an innovative and responsible player in the energy transition.
Challenges and Solutions
Despite the many advantages, C&I storage systems also face specific challenges when it comes to frequency control. A key challenge is the limited energy capacity compared to conventional power plants. While battery storage systems are excellent at balancing short-term fluctuations, they reach their limits when faced with longer-lasting imbalances. This problem can be addressed with a clever operating strategy that continuously optimizes the storage system's charge level and detects critical situations early on.
Another challenge is the aging of batteries caused by the frequent cycling required for balancing power. Modern battery management systems address this problem with intelligent control that minimizes cycling stress and maximizes service life. Technological advances in battery cells are also leading to continuous improvements in cycle stability.
Combining different applications in a storage system requires complex control algorithms that detect and resolve potential conflicts. AI-based systems are increasingly being used here, enabling predictive control and optimizing storage operations over different timescales. These systems consider historical data, current market prices, and forecasts to determine the optimal operating strategy.
Finally, precisely meeting control reserve requirements presents a technical challenge, especially when used simultaneously for other applications. Advanced measurement technology and redundant communication systems ensure reliable provision of control reserve even under difficult conditions.
Future Perspectives of Frequency Control with C&I Storage
The future of frequency control with C&I storage will be shaped by technological advances, market developments, and regulatory adjustments. New battery technologies such as solid-state batteries promise higher energy densities, longer service lives, and improved safety characteristics, which will further improve the economic viability and practicality of storage solutions.
The increasing networking of storage systems into virtual power plants will open up new possibilities for coordinated frequency control. This aggregation enables even smaller storage systems to participate in the balancing power market and increases the overall resilience of the system through geographical diversification.
Further digitalization and the use of blockchain technologies could facilitate the direct marketing of system services between storage operators and grid operators and reduce transaction costs. This would enable new business models and promote the decentralized provision of balancing power.
With the ongoing expansion of renewable energies, the need for flexible balancing power sources will continue to grow. C&I storage systems will play a key role in this and contribute to stabilizing the power grid. The integration of forecast models for generation and consumption will improve preventive frequency control and minimize deviations in advance.
Conclusion
C&I energy storage systems have established themselves as valuable tools for frequency control in modern power grids. Their ability to respond to frequency changes with virtually no delay makes them ideal providers of primary control power. By combining them with other applications such as self-consumption optimization or peak load management, an economically attractive overall solution can be realized.
The regulatory framework is increasingly evolving in favor of storage solutions, and technological advances are continuously improving their performance and economic efficiency. As the energy system continues to transform, C&I storage will play an increasingly important role in ensuring grid stability.
Companies that invest in C&I storage systems can not only benefit from the direct economic advantages, but also make an important contribution to the successful implementation of the energy transition. Frequency control with the help of C&I storage thus represents a win-win situation for companies, grid operators, and society as a whole.
Practical Example: C&I Storage for Frequency Control
A vivid example of the successful use of C&I storage for frequency control is provided by an industrial company that installed a 2 MW / 2.5 MWh lithium-ion storage system. The storage system was primarily designed for peak load management and self-consumption optimization of the company's own PV system, but its dimensions provide sufficient reserves for the provision of control power.
In practice, the storage system is operated to continuously provide 1 MW of primary control power while maintaining a state of charge of 40-60%. The remaining capacity and power are available for operational energy management. An intelligent control system automatically detects potential conflicts between the various applications and prioritizes their resolution, with control power provision being given priority as a system-relevant service.
The revenue from control power marketing amounts to approximately €400,000 per year, which corresponds to approximately 20% of the total investment costs. Combined with the savings from peak load management and self-consumption optimization, this results in a payback period of just under five years. Furthermore, the company makes an active contribution to grid stability and strengthens its image as an innovative and responsible player in the energy transition.
Challenges and Solutions
Despite the many advantages, C&I storage systems also face specific challenges when it comes to frequency control. A key challenge is the limited energy capacity compared to conventional power plants. While battery storage systems are excellent at balancing short-term fluctuations, they reach their limits when faced with longer-lasting imbalances. This problem can be addressed with a clever operating strategy that continuously optimizes the storage system's charge level and detects critical situations early on.
Another challenge is the aging of batteries caused by the frequent cycling required for balancing power. Modern battery management systems address this problem with intelligent control that minimizes cycling stress and maximizes service life. Technological advances in battery cells are also leading to continuous improvements in cycle stability.
Combining different applications in a storage system requires complex control algorithms that detect and resolve potential conflicts. AI-based systems are increasingly being used here, enabling predictive control and optimizing storage operations over different timescales. These systems consider historical data, current market prices, and forecasts to determine the optimal operating strategy.
Finally, precisely meeting control reserve requirements presents a technical challenge, especially when used simultaneously for other applications. Advanced measurement technology and redundant communication systems ensure reliable provision of control reserve even under difficult conditions.
Future Perspectives of Frequency Control with C&I Storage
The future of frequency control with C&I storage will be shaped by technological advances, market developments, and regulatory adjustments. New battery technologies such as solid-state batteries promise higher energy densities, longer service lives, and improved safety characteristics, which will further improve the economic viability and practicality of storage solutions.
The increasing networking of storage systems into virtual power plants will open up new possibilities for coordinated frequency control. This aggregation enables even smaller storage systems to participate in the balancing power market and increases the overall resilience of the system through geographical diversification.
Further digitalization and the use of blockchain technologies could facilitate the direct marketing of system services between storage operators and grid operators and reduce transaction costs. This would enable new business models and promote the decentralized provision of balancing power.
With the ongoing expansion of renewable energies, the need for flexible balancing power sources will continue to grow. C&I storage systems will play a key role in this and contribute to stabilizing the power grid. The integration of forecast models for generation and consumption will improve preventive frequency control and minimize deviations in advance.
Conclusion
C&I energy storage systems have established themselves as valuable tools for frequency control in modern power grids. Their ability to respond to frequency changes with virtually no delay makes them ideal providers of primary control power. By combining them with other applications such as self-consumption optimization or peak load management, an economically attractive overall solution can be realized.
The regulatory framework is increasingly evolving in favor of storage solutions, and technological advances are continuously improving their performance and economic efficiency. As the energy system continues to transform, C&I storage will play an increasingly important role in ensuring grid stability.
Companies that invest in C&I storage systems can not only benefit from the direct economic advantages, but also make an important contribution to the successful implementation of the energy transition. Frequency control with the help of C&I storage thus represents a win-win situation for companies, grid operators, and society as a whole.