Frequency Containment Reserve Research Articles

Towards robust state estimation for LFP batteries: Model-in-the-loop analysis with hysteresis modelling and perspectives for other chemistries

The accurate estimation of a battery’s state of charge (SOC) is critical in battery management systems for various applications. Lithium Iron Phosphate (LFP) batteries, preferred for their long cycle life, cost efficiency, and enhanced safety, have emerged as favourable choices for stationary storage. Yet, they still face challenges in precise SOC estimation due to the flatness and hysteresis of their open circuit voltage. Addressing this, our study integrates a hysteresis model into a third-order battery model for BMS controlling a stationary storage system in frequency containment reserve (FCR) application. We analysed three advanced SOC estimation techniques — extended Kalman filter (EKF), dual unscented Kalman filter (DUKF), and particle filter (PF) — with the hysteresis model using a model-in-the-loop (MiL) toolchain. Performance testing under a 48-hour FCR load profile showed EKF with a 4% error, DUKF achieving the best result with a 1.1% error, and PF’s performance varying between 2.9% and 4% depending on particle count. Robustness tests against initialization and current sensor errors under an 8hr profile revealed DUKF maintained a 2% error boundary irrespective of the error introduced, highlighting the hysteresis model’s effectiveness. Broadening the scope, the study also explores extending the method to other lithium-ion chemistries.

Optimal operation of pumped storage power plants with fixed- and variable-speed generators in multiple electricity markets considering overload operation

This work studies the optimal operation of pumped storage power plants with fixed- and variable-speed generators in different electricity markets. This paper extends the state of the art by systematically considering the detailed plant behavior for heterogeneous pumped storage power plants and the possible short-term electrical overload operation. The Day-Ahead, ancillary service, and Intraday markets are studied in the first part by developing a mixed integer nonlinear problem (MINLP). The results demonstrate that variable-speed units, especially if equipped with doubly-fed induction machines (DFIMs), yield the highest profit, particularly in the presence of automatic Frequency Restoration Reserve (aFRR). The proposed optimization of the Intraday market shows that the total profit of the Day-Ahead, Ancillary services, and Intraday markets are the highest in the case of variable-speed units with aFRR, where it might be a drawback offering Frequency Containment Reserve. Finally, a robust optimization-based bidding curve generation strategy is developed in the last step. The strategy allows the plant to operate with high profits under price prediction uncertainties and enables optimal reservoir management. The developed optimization tasks and the bidding curve generation strategy also exhibit shorter computation times than the state-of-the-art strategies.

A comprehensive framework for predicting electric vehicle's participation in ancillary service markets

AbstractElectric vehicles (EVs) have significant potential to offer unused capacity in ancillary service markets, providing unique opportunities for market operators to utilise these resources. EVs have a rapid response and high availability, making them a good fit for the frequency containment reserve (FCR) market. However, EV aggregators (EVAGs) must aggregate capacity blocks due to the limited capacity of individual EVs. An application of a supervised machine learning method named XGBoost is suggested to help EVAGs predict the amount of EV participation in the FCR market. The objective is to forecast yearly involvement using data from only a single week, using the game theory method SHapley Additive exPlanations (SHAP) to minimise extra data. The proposed strategy helps aggregators and uses feature engineering to select EVs with high potential to boost revenue. The proposed framework is effective in predicting EV performance in the DK‐2 market, as shown by multiple analyses.

Local privacy‐friendly verification of customer participation in frequency regulation services using smart meter data

AbstractThe delivery of flexibility from distributed assets guarantees the stable operation of the power system as increasing volumes of renewable energy are deployed. Nevertheless, verifying the adequate provision is challenging when considering behind‐the‐meter resources. A cost‐effective alternative to dedicated metring is using measurements from smart meters. However, flexibility activations must be discerned from the rest of the loads in the household. Furthermore, privacy issues arise since electricity consumption contains personal data. The authors tackle both issues by developing a data‐driven privacy‐friendly verification algorithm for participation in frequency containment reserves (FCRs). Our methodology evaluated three machine learning (ML) classification models, deployed locally, and fed with total consumption measurements and activation set points to verify users' participation. The amount of information that leaves the premises was reduced from low‐granularity power measurements to simple compliance indicators. The models were trained and evaluated using a real dataset of households, where FCR was delivered by behind‐the‐meter batteries, resulting in an accuracy close to 0.90. A proof‐of‐concept setup was employed to test the algorithms under real circumstances. Even with several background loads, an accuracy of up to 0.83 was observed, promising results considering the privacy‐friendly features, use of simple ML models, and embedded deployment.

Improved rule-based power distribution algorithm for hybrid battery storage systems and real-world validation

Large-scale battery energy storage systems (BESS) can serve many applications and are already widely used for grid services. The rapidly growing BESS market and the recent interest in their deployment accentuate the need for safe, reliable, and highly available energy management systems (EMS) for automated control. However, the EMS and their integrated power distribution algorithms (PDA) can still be optimized to adapt various characteristics of the BESS. This study investigates a new version of a PDA with a particular focus on battery aging and system efficiency. The rule-based PDA has been validated on a 6 MW/7.5 MWh BESS system with five battery technologies providing frequency containment reserve to the German power grid. The results underline the PDA's capability to exploit the individual strengths of each battery technology. The PDA sets objectives for the state of charge, energy throughput, and power of the batteries to extend battery life. The distribution of energy throughputs among batteries can be selected in advance through the new implementation of the PDA. At the same time, the inverters are significantly less often activated and used in the optimal efficiency range, increasing the overall system efficiency to approximately 82 %. The optimized switching behavior leads to less frequent power switching between individual battery units and longer phases with more constant power. In addition, the operational efficiency of BESS can be improved by the choice of battery technology and the overall system layout on the hardware side. The improvements on the software side are only possible by increasing the overall power requests through multi-use operation by about 6 % compared to our benchmark test. The results can be used by BESS operators to increase operational profits due to longer battery life and fewer efficiency losses.

On the Potential of Tertiary Espresso Machines to Provide Frequency Containment Reserves Services

On the Potential of Tertiary Espresso Machines to Provide Frequency Containment Reserves Services

An Optimal Wind Farm Operation Strategy for the Provision of Frequency Containment Reserve Incorporating Active Wake Control

This study proposes a novel operation strategy for wind farms' optimal Frequency Containment Reserve (FCR) provision that simultaneously distributes FCR and optimally controls wake formation. The power reserve allocation is dynamically decided at the wind farm supervisory control level, considering the intermittent wind power and direction, grid frequency stochasticity, and the aerodynamic complexity of the wake. A two-stage stochastic programming approach supports decision-making for an optimal contribution to day-ahead energy/FCR markets considering sub-hourly wind power and grid frequency uncertainty. Moreover, a novel method is used to reduce the computational complexity by employing a data-driven surrogate model of wake formation in the optimizer. This surrogate model consists of a neural network trained on the Gauss-Curl-Hybrid wake model in FLORIS. This deep learning approach allows fast estimation of the wake control parameters, i.e., the optimal yaw angles and axial induction factors. Then, a coevolutionary-based multi-objective particle swarm optimization searches for the optimal deloading of the WTs and maximizes the total power production and kinetic energy while minimizing wake. The performance of the proposed algorithm is evaluated on the C-Power wind farm layout in the North Sea. Simulation results demonstrate its effectiveness in improving the wind farm's overall performance for different operational conditions.

Techno-Economic Analysis of a Highly Renewable and Electrified District Heating Network Operating in the Balancing Markets

In pursuit of Finland’s carbon neutrality objective by 2035, integrating renewable energy sources into the power grid is essential. To address the stochastic nature of these resources, additional sources of flexibility are required to maintain grid stability. Meanwhile, district heating network (DHN) operators in Finland are decommissioning fossil fuel-based combined heat and power plants (CHPs) and electrifying heating systems with heat pumps (HPs) and electric boilers. A techno-economic assessment and the optimized operation of DHN-connected HPs and electric boilers in providing ancillary balancing services were explored in this study. The primary goal was to maximize the potential revenue for DHN operators through participation in the day-ahead electricity market and frequency containment reserve (FCR) balancing markets. Three interconnected DHNs in the Helsinki metropolitan area were optimized based on 2019 data and each operator’s decarbonization strategies for 2025. HPs are expected to achieve the highest profit margins in the FCR-D up-regulation market, while electric boilers could generate substantial profits from the FCR-D down-regulation market. In contrast to other balancing markets studied, the FCR-N market exhibited limited profit potential. Sensitivity analysis indicated that spot electricity prices and CO2 emission allowance prices significantly influence the profitability derived from balancing markets.

Flexibility extension in hydropower for the provision of frequency control services within the European energy transition

This paper presents a comprehensive assessment of the large-scale deployment of hydropower on the provision of frequency regulation services, when equipped with the extended flexibility solutions being developed and/or tested within the scope of the XFLEX HYDRO project. The current analysis is performed on the Iberian Peninsula (IP) power grid considering its interconnection to the Continental Europe (CE) system, since this power system zone is expected to have the most severe frequency transient behaviour in future scenarios with increased shares of variable renewable energies. For this purpose, prospective scenarios with increased shares of time variable renewable generation were identified and analysed. To assess the impacts of the hydropower flexibility solutions on frequency dynamics after a major active power loss, extensive time domain simulations were performed of the power system, including reliable reduced order dynamic models for the hydropower flexibility solutions under evaluation. This research assesses the effects of synchronous and synthetic inertia, and of the Frequency Containment Reserve (FCR) and Fast Frequency Response (FFR) services as specified in European grid codes. The main findings highlight the potential of hydropower inertia and of adopting a variable speed technology for enhancing frequency stability, while contribute to better understand the role of hydropower plants in future power systems.

Strategies for electric vehicle bidding in the German frequency containment and restoration reserves market

Germany's transition to renewable energy sources for a sustainable future has introduced variability and instability in the national power grid, thus necessitating innovative solutions to ensure grid stability and reliable energy supply. The integration of electric vehicles (EVs) in the German balancing market, notably within the frequency containment reserve and automatic frequency restoration reserve sectors, is a potential stabilizing force. However, the complexity of this integration, governed by specific rules in the German energy sector, has not been fully explored. To bridge this gap, a robust schedule that maximizes the economic viability and reliability of EV integration by considering critical elements such as uniform product size, alignment with local market product duration, and customer baseline load is proposed in this study. Mixed-integer linear programming is used for the effective integration of EVs in the German balancing market. This framework emphasizes computational efficiency, providing market participants with precise insights into EV behavior and strategies for energy storage optimization. The effectiveness and reliability of the proposed method are substantiated through case studies. The proposed method consistently achieved maximum profit and a significant reduction in the number of failed cases, which underscores its applicability in real-world scenarios.

ANALYSIS OF METHODS OF CHANGING VOLUMES OF ELECTRICITY GENERATION AT SOLAR POWER PLANTS

The article examines the methods of changing electricity generation schedules at solar power plants when operating under the central regulator of the power system. An analysis of the existing regulation methods was carried out, and a new method of controlling the generation of solar power plants under the central regulator of the power system was proposed.
 Background. The increase in the share of solar electricity generation in the energy systems of the countries of the world leads to the need to control and manage the process of electricity production to increase the stability and sustainability of the energy system. A significant price for compensation of imbalances in the energy system is included in the tariffs, which affects the end consumers of electricity.
 Objective: increasing the adequacy of the results of the distribution of deficit frequency containment reserves, frequency restoration reserves to compensate for imbalances that arise when generation is changed at solar power plants. Reducing the cost of compensation for imbalances that occur when changing generation at solar power plants. To solve the goal, it is necessary to analyze the existing methods of compensating power system imbalances that arise as a result of changes in generation at solar power plants and to propose a new technical and mathematical solution for the distribution of deficit reserves of support and frequency restoration.
 Methods: the social engineering approach of forecasting and modeling was used to analyze the processes affecting the method of controlling the generation schedule of the solar power plant.
 Results. A new mathematical and technical solution for compensating the imbalance in the power system in the event of a rapid change in the electricity generation schedule at solar power plants is proposed. For the first time, the given task was solved using a new technical and mathematical solution. Such a technical and mathematical solution can be widely used in the management of the electricity generation schedule at solar power plants in many system operators in different countries of the world, where there is a problem of insufficient for frequency containment and restoration reserves, and the amount of solar electricity generation has a significant share in the total amount of electricity generation energy.
 Conclusions. Existing methods of compensating power system imbalances arising as a result of changes in generation at solar power plants are analyzed and a new technical and mathematical solution for the distribution of deficit reserves of frequency containment reserves and frequency restoration reserves is proposed. The proposed technical and mathematical solution makes it possible to predict an event during which there will be a change in the level of electric energy generation at solar power plants, to transmit information to the central regulator of the energy system, which in turn will give a command to change the schedule of electric energy generation in advance within the insensitivity zone, which will lead to the activation of the frequency restoration reserves and will allow to compensate the existing imbalance at the expense of cheaper reserves and not to activate the frequency containment reserves. Such a mathematical and technical solution will make it possible to significantly increase the stability of the energy system against emerging imbalances and make their compensation cheaper, which in general has a positive effect on the energy security of the state.

Valuing the social cost of carbon: Do economists really care about climate change?

The aim of the article is to analyse the scientific literature of the last decade on the social cost of carbon to identify and discuss the best values representing the external cost of CO2 emis-sions calculated with a damage valuation approach, to use in cost-benefit analysis and in other external costs applications, such as Life Cycle Assessment. The social cost of carbon repre-sents the present value of the global damages of climate change attributable to the emission of an additional ton of carbon dioxide into the atmosphere. The measurement of the social cost of carbon is fundamental in the transition to a net zero emissions economy because it allows bal-ancing the costs of investments needed for decarbonization with their benefits in terms of avoided climate damages. The paper develops and applies a method for identifying the best social cost of carbon estimates, that starts from study reviews conducted within institutional processes (IPCC, OECD, US Government bodies), to then analyse the study reviews made in academic or research contexts and only in the end it delves into selected academic studies that provide original estimates of the social cost of carbon. The method allowed to identify and dis-cuss a robust even if conservative estimate of the social cost of carbon for emissions in the period 2020-2080, recently elaborated by the US Environmental Protection Agency, that can be used worldwide, for example to update the reference external cost values for CO2 emis-sions recommended by the European Commission Handbook on external cost of transport.

Bidding strategy of storage hydropower plants in reserve markets

The increasing share of intermittent sources of energy will increase the need for frequency-control reserves. However, the supply from gas and coal-fired power plants might decrease in the following years. Being the procurement of reserves mostly market-based in Europe, the market design should send price signals to encourage participation in these markets. This pa-per analyses the incentives provided by the French market design for seasonal storage and pumped storage hydropower plants to participate in reserve markets. To that end, a determinis-tic mixed-integer linear optimization model is presented. The objective is to maximize profits in the energy and reserve markets according to 2019 market prices. By optimising the trade-offs between the day-ahead and the reserve markets, the storage hydropower plant increase its profits. The pumped storage hydropower plant sometimes chooses the Frequency Contain-ment Reserve market or the day-ahead market only. The apparition of some hours of FCR par-ticipation with the pumped storage plant is explained by its higher number of generating hours and by the higher volatility of reserve energy prices. These two factors also explain the greater response of the pumped storage plant to the incentive measures on the FCR market.

Optimized siting and sizing of distribution-network-connected battery energy storage system providing flexibility services for system operators

This paper develops a two-stage model to site and size a battery energy storage system in a distribution network. The purpose of the battery energy storage system is to provide local flexibility services for the distribution system operator and frequency containment reserve for normal operation (FCR-N) for the transmission system operator. In the first stage, the priority is to fulfil the flexibility needs of the distribution system operator by managing congestions or interruptions of supply in the local network. Thus, the first stage allocates the battery to ensure reliable electricity supply in the local distribution network. The minimum required size of the battery is also determined in the first stage. The second stage optimally sizes the battery energy storage system to boost the profit by providing frequency containment reserve for normal operation. The first and second stages both solve stochastic optimization problems to design the battery energy storage system. However, the first stage considers worst-case scenarios while the second stage utilizes the most probable scenarios derived from the historical data. To validate the proposed model, real-world data from the years 2021 and 2022 in Finland are employed. The battery placement is conducted for both the IEEE 33-bus system and a Finnish case study. The profitability of the model is compared across different cases for the Finnish case study. Finally, the paper assesses the impacts of cycle aging on the battery's total profit.

Degradation and modeling of large-format commercial lithium-ion cells as a function of chemistry, design, and aging conditions

Demand for large-format (>10 Ah) lithium-ion batteries has increased substantially in recent years, due to the growth of both electric vehicle and stationary energy storage markets. The economics of these applications is sensitive to the lifetime of the batteries, and end-of-life can either be due to energy or power limitations. Despite this, there is little information from cell manufacturers on the sensitivity of cell degradation to environmental conditions or battery use. This work reports accelerated aging test data from four commercial large-format lithium-ion batteries from three manufacturers, with varying design (thickness, casings, …), chemistry (lithium‑iron-phosphate (LFP) or lithium‑nickel‑manganese‑cobalt-oxide positive electrodes (NMC), with graphite (Gr) negative electrodes), and capacity (50 to 250 Amp∙hours). The tested LFP|Gr cell is found to be relatively insensitive to cycling conditions like temperature or voltage window, while NMC|Gr cells have varying sensitivity. Degradation trends are further investigated by training predictive models: simple polynomial trend lines, a semi-empirical reduced-order model, and an empirical reduced-order model identified using machine-learning based on symbolic regression. Calendar and cycle life are simulated over a variety of conditions to directly compare the various batteries. Cell size and thickness are found to substantially impact sensitivity to temperature during cycle aging, while electrode chemistry impacts depth-of-discharge sensitivity. Real-world battery lifetime is evaluated by simulating residential energy storage and commercial frequency containment reserve systems in several U.S. climate regions. Predicted lifetime across cell types varies from 7 years to 20+ years, though all cells are predicted to have at least 10 year life in certain conditions.

Life cycle assessment of electrochemical and mechanical energy storage systems

The effect of the co-location of electrochemical and kinetic energy storage on the cradle-to-gate impacts of the storage system was studied using LCA methodology. The storage system was intended for use in the frequency containment reserve (FCR) application, considering a number of daily charge–discharge cycles in the range of 50–1000. The results show that a significant environmental benefit (up to a 96% decrease in cradle-to-gate global warming potential, from 1.65 ± 0.12 to 0.059 ± 0.004 kg CO2-eq./kWh) can be obtained by the co-location of battery and flywheel storage systems, owing to the ability of the flywheel component to preserve battery lifetime by delivering the frequent charge events required in the FCR application. A moderate saving of 24% in global warming potential (from 1.65 ± 0.12 to 1.26 ± 0.11 kg CO2-eq./kWh) could already be achieved by switching from a battery to flywheel storage system with repeated charge–discharge cycling (200 or more charge events per day). This study highlights the need to consider the intensity of charge–discharge cycling when choosing an environmentally preferable storage technology as well as introducing a methodology for incorporating the number of daily cycles in the analysis.

Environmental and economic analysis of sector-coupling battery energy storage systems used for frequency containment reserve

Battery energy storage systems (BESSs) are advocated as crucial elements for ensuring grid stability in times of increasing infeed of intermittent renewable energy sources (RES) and are therefore paving the way for more sustainable energy systems. Providing frequency containment reserve (FCR) is an attractive business model for capital intensive stationary BESSs, but the current German FCR regulative framework restricts the BESS usage for other applications as capacity shares have to be reserved (FCR energy capacity requirement). Hence, stationary BESSs operating at the FCR market are not fully utilised from an economic and environmental perspective. Linking BESSs with other sectors as potential sinks such as power-to-heat modules or electrolysers, enables unlimited energy infeed and is discussed as potential means to diminish this constraint. Whilst, a couple of studies investigated the economic advantages of such sector-coupling BESSs, their environmental consequences were hardly analysed so far. Based on the life cycle thinking approach, the environmental and economic impacts of FCR provision in Germany by standalone and sector-coupling BESSs (i.e. with power-to-heat unit or electrolyser) were studied in this work. The sector-coupling BESSs were considered regarding different FCR energy capacity requirements (E/P ratios). It was shown that the CAPEX for the sector-coupling unit were primarily critical for the economic performance of BESSs favouring power-to-heat over electrolysers and standalone BESSs. The results of the environmental life cycle assessment indicated to potential benefits due to the reduced battery capacities depending on the varied FCR energy capacity requirement. The environmental implications of the operational stage showed that electrolysers can increase the environmental impacts by up to 10 % due to higher conversion losses compared to power-to-heat units. Finally, it was concluded that future energy system and market designs should foster the implementation of sustainable sector-coupling solutions considering technology-specific economic and environmental characteristics.

Operating strategy optimization considering battery aging for a sector coupling system providing frequency containment reserve

Battery storage systems are increasingly used in the frequency containment reserve (FCR) application. Coupling the battery with a power-to-heat module can further increase the system’s profitability. Different studies optimized the hybrid system’s operation by considering country-specific regulations. However, lithium-ion battery aging has not yet been included. This work analyses the impact of system dimension and operation on net present value, considering battery aging. The operation strategy consists of adjusting the target SoE and using the deadband degree of freedom, which allows to suspend provision of FCR for minor frequency deviations. Battery lifetime is simulated using a semi-empirical aging model describing graphite anode aging mechanisms. The highest NPV is obtained with a battery dimension of 0.5 Wh/W, 90% target SoE, and normal deadband utilization. For the considered NMC battery cells, deadband utilization contributes to battery lifetime extension when operating at high SoE. Without this cell chemistry-specific lifetime gain, a lower target SoE of 60% and a larger system size of 0.6 is economically more advantageous. In a sensitivity analysis, battery aging was detected as the most crucial parameter influencing system profitability at high FCR prices. The results highlight the importance of including reliable battery aging simulations in future FCR operation optimizations.

The role of hydrogen electrolysers in frequency related ancillary services: A case study in the Iberian Peninsula up to 2040

This paper investigates the contribution of hydrogen electrolysers (HEs) for frequency related Ancillary Services (AS), namely Frequency Containment Reserve (FCR), Synthetic Inertia (SI) and Fast Frequency Response (FFR) in future operation scenarios in the Iberian Peninsula (IP) considering low system inertia. The proposed framework for analysis consists of a dynamic model developed in MATLAB/Simulink. Simulations show that an instantaneous inverter based resource (IBR) trip induced by a grid fault may lead to the occurrence of values of Rate of Change of Frequency (RoCoF) close to undesirable thresholds if the FCR is provided solely by the conventional generators. The obtained results illustrate that HEs can outperform conventional generators on the provision of FCR. Furthermore, the FCR is unable to unlock the full potential of fast responding HEs. This suggests the advantage of providing additional AS such as SI or FFR in critical periods. Simulations also show that the benefit of additional AS can be limited in specific conditions, especially depending on the evolution of HEs’ ramping capabilities, but are still a relevant complement to other solutions designed to deal with low inertia in power systems such as synchronous compensators.

Storage System Design for Improved Primary Frequency Control From Hydropower Units

The upcoming modifications to the criteria for providing Frequency Containment Reserves (FCR) in the Nordic synchronous area present severe challenges for some hydropower units. By quantifying the difference between the required FCR power response and the actual response provided by the unit, an additional power response from an energy storage system can be specified to augment the hydropower unit, thus securing its participation in FCR in the future. A practical method to control the storage system, by applying a band-pass filter on the negative frequency deviation, is presented in this paper. The method is verified using a set of field measurements from Swedish hydropower units currently providing FCR. It is found that all tested units are able to satisfy the upcoming criteria with the specified storage systems. The optimality of the method is discussed by comparing the storage system power and energy ratings to the theoretical minimum. Obtained power ratings between 3% and 24% of the FCR power, combined with a short storage system duration of up to 2.5 minutes, indicate that the method presents a possible application for high-power and low-energy storage technologies.