Frequency Restoration Reserve Research Articles

Revenue stacking of BESSs in wholesale and aFRR markets with delivery guarantees

Battery Energy Storage Systems (BESSs) provide a crucial solution for mitigating the challenges posed by renewable energy intermittency, concurrently driving down energy costs within wholesale markets. To harness their potential, innovative business models are required for optimal BESS operation and revenue maximisation. This paper addresses this need by proposing a novel revenue stacking approach for the participation in Day-Ahead and automatic Frequency Restoration Reserve (aFRR) markets. By considering the uncertainty in the activation of aFRR events, the proposed model provides real-time delivery guarantees for a given reliability level, while maximising the revenues. The model is built over a novel characterisation of the uncertainty and a tight reformulation of the joint chance-constraints that drive energy and capacity guarantees. The effectiveness of the proposed approach is demonstrated through a case study based on real data from the Belgian market, yielding a 17.3% increase in profits over the individual chance-constraints approach.

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.

Load shifting versus manual frequency reserve: Which one is more appealing to thermostatically controlled loads in Denmark?

This paper investigates demand-side flexibility provision in two distinct forms of manual Frequency Restoration Reserve (mFRR) services and load shifting, and explores which one is financially more appealing to Thermostatically Controlled Loads (TCLs) in Denmark. While mFRR is an ancillary service required for the system and being bought by the system operator, load shifting is an individual act of the TCL in response to the variation of hourly electricity prices. Without loss of generalization, we consider a supermarket freezer as a representative TCL, and develop a grey-box model describing its temperature dynamics using real data from a supermarket in Denmark. Taking into account price and activation uncertainties, a stochastic mixed-integer linear program is formulated to maximize the flexibility value from the freezer. Examined on an ex-post simulation based on Danish spot and balancing market prices in 2022, load shifting shows to be almost as profitable as mFRR provision, although it could be more consequential for temperature deviations in the freezer. This indicates the need for regulatory measures by the Danish system operator to make the attraction of ancillary service provision more obvious for TCLs in comparison to the load shifting alternative.

Stochastic economic model predictive control for renewable energy and ancillary services trading with storage

The provision of renewable-based ancillary services (AS) is paramount for the stable operation of power systems featuring high renewable penetration. The combined operation of storage with renewables enables aggregators to increase the reliability of their energy and frequency control AS offers. Existing dispatch strategies for the supply of both energy and AS are usually rule-based or involve tracking a technical reference signal, hence economically suboptimal for aggregators. This study proposes a comprehensive decision framework in which first a stochastic optimization derives bids on energy and AS markets, then stochastic economic model predictive control (SEMPC) optimizes the storage dispatch in order to maximize the profit and minimize the storage degradation, as a function of the predicted renewable production and the expected AS activation. The framework is applied to a real-world case study where storage combined with wind power participates in the energy market, the frequency containment market and the frequency restoration reserve market. The SEMPC-based approach increases market revenue by 15% compared to a standard reference-tracking MPC, and reduces storage degradation by 23%. The stochastic formulation lowers the sensitivity of the economic objectives to renewable energy forecast errors, compared to deterministic approaches.

Incremental Profitability Evaluation of Vehicle-to-Grid-Enabled Automated Frequency Restoration Reserve Services for Semi-Public Charging Infrastructure: A Case Study in Belgium

The current paper defines a framework for the introduction of automated frequency restoration reserve services, enabled by vehicle-to-grid technology, into the business model of an entity owning and operating a network of semi-public Electric Vehicle Supply Equipment. It assesses the profitability of this introduction by performing a case study based on the real-life electric vehicle charging data from the EVSE network located in a hospital parking lot. From the results of the study, it is clearly visible that the introduction of vehicle-to-grid-enabled automated frequency restoration reserve services has a significant positive incremental profitability; however, this is heavily dependent on the plug-in ratio of the charging network, determined by electric vehicle users’ behavior.

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.

The economic impacts of integrating European balancing markets: The case of the newly installed aFRR energy market-coupling platform PICASSO

The coupling of European balancing markets is one of the latest steps towards integrating Europe’s internal electricity market. From mid-2022 onwards, besides imbalance netting, the activation of the automated frequency restoration reserves (aFRR) has also been increasingly integrated between European transmission system operators (TSOs) in the so-called PICASSO framework. The possible benefits of this balancing market integration include cost savings and a reduced use of activation energy.The goal of this paper is to quantify the effects of the joint activation of balancing power in European markets in terms of welfare gains and increases in consumer rents due to lower prices. The paper also aims to demonstrate the reduced use of activation energy under the latest market-coordination framework. For this purpose, the coupling of aFRR markets is modelled by formulating and solving the optimisation problems for economic activation using linear programming. A PICASSO market structure with imbalance netting and cross-border activation of reserves is compared to the non-collaborative reference arrangement and to the existing IGCC set-up with imbalance netting only. A case study of the Belgian, Dutch and German electricity systems is modelled over a full year using historic data from 2021. The study indicates overall welfare gains of €400 million per year, the same order of magnitude as the increase in economic welfare of earlier balancing platforms such as TERRE. In addition, the cross-border effects on activation volumes and prices and their distributional effects are discussed. The results suggest that within the three countries, the primary beneficiaries of PICASSO are balancing service providers in the Netherlands and Belgium, and consumers in Germany.

Limiting imbalance settlement costs from variable renewable energy sources in the Nordics: Internal balancing vs. balancing market participation

Due to the market gate closures in the Nordic energy markets, producers with variable renewable energy (VRE) assets, e.g., PV and wind power plants, must forecast their production prior to delivery, leaving room for significant forecast errors. These forecast errors can lead to imbalances between the contractual market agreements and physical delivery, which have to be financially accounted for through the imbalance settlement. The increasing shares of VREs in the Nordic energy mix and the increasing variability in the price of regulating the imbalances, can lead to potential large revenue losses for the producers.This study investigates how different producer balancing strategies can limit the uncertainty and potential revenue losses in the imbalance settlement. The study focuses on available balancing measures the producers are able to use in the period starting from the last energy market gate closure, i.e., the manual Frequency Restoration Reserve (mFRR, tertiary reserves) balancing market, and throughout the subsequent settlement period. During this settlement period, producers have the option within the Nordic imbalance settlement framework to prevent VRE imbalances by performing internal balancing, i.e., ramping up or down their dispatchable assets which are located in the same bidding area as the VRE assets. However, this study shows both theoretically and quantitatively that such internal balancing is not economically beneficial compared to offering this regulating energy to the mFRR market.

Providing power reserve for secondary grid frequency regulation of offshore wind farms through yaw control

AbstractThe ability to significantly contribute to the frequency regulation and provide valuable ancillary services to the transmission system operator (TSO) is one of the present wind farm (WF) challenges, due to the limitations of wind speed forecasting and insufficient power reserve in certain operating conditions notably. In this work, the feasibility of WFs to participate in frequency restoration reserve (FRR) through yaw control is assessed. To this end, a distributed yaw optimization method is developed to evaluate the power gain achieved by yaw redirection based on wind turbine cooperation and compared with a greedy approach. The method relies on a static wake model whose parameters are estimated in a systematic way from simulation data generated with FAST.Farm. Through a case study based on a scaled version of the Belgian Mermaid offshore WF, it is demonstrated that the requirements of the TSO are fulfilled both in terms of response time and level of power reserve for most wind directions. The assessment is limited to wind speeds below the rated speed of the considered wind turbines.

Optimal Scheduling of Battery Energy Storage Systems for Simultaneous Participation in the Energy and Automatic Frequency Restoration Reserve Markets

Optimal Scheduling of Battery Energy Storage Systems for Simultaneous Participation in the Energy and Automatic Frequency Restoration Reserve Markets

Multimarket Trading Strategy of a Hydropower Producer Considering Active-Time Duration: A Distributional Regression Approach

This article presents a new approach for finding the optimal multimarket trading strategy of cascaded hydropower plants (HPPs) in the sequential electricity markets. These markets are day-ahead energy market, the market for frequency containment reserve in normal mode (FCR-N), and manual frequency restoration reserve markets for both energy production and capacity reserve. The active-time duration (ATD) of an mFRR energy offer is an important required parameter and it is uncertain at the time of day-ahead offer-function submission. Hence, we suggest a distributional regression approach for ATD modeling in an optimal multimarket setup. Also, a modified machine learning approach is proposed to generate price scenarios for the mFRR energy market taking into account uncertain ATD parameters. To illustrate our proposed approach, various numerical experiments are performed. Our numerical results show how proper modeling of ATD parameters can lead to a more realistic multimarket offer-function for cascaded HPPs. Furthermore, the results show how the inclusion of FCR-N and mFRR capacity markets change the optimal day-ahead offer-function.

Multi-Area Frequency Restoration Reserve Sizing

Frequency Restoration Reserves are traditionally sized using deterministic methods. The constant growth in non-dispatchable renewable energy, however, is increasing the importance of probabilistic methods for reserve sizing. In addition, as the geographical scope of reserve sizing expands, overall power imbalance stochasticity is reduced. In this paper, we propose a probabilistic method for shared cross-border frequency restoration reserve commitment and sizing, based on the concept of system generation margin and employing mathematical optimization. The aim is to reduce overall reserve volumes and costs. The cross-border interconnection capacities among countries are taken into account, and the shared uncertainty across interconnections is addressed via a novel robust approach. The method is tested on the cross-border system of south-east Europe that includes 9 countries. 5 different operational scenarios are used and a detailed calculation of the uncertainty distributions in each country is employed. Results show that cross-border shared sizing can significantly reduce overall reserve volumes and costs in a secure way.

Economic evaluation of a power-to-hydrogen system providing frequency regulation reserves: a case study of Denmark

Operating costs are dominant in the hydrogen production of a power-to-hydrogen system. An optimal operational strategy or bidding framework is effective in reducing these costs. However, it is still found that the production cost of hydrogen is high. As the electrolysis unit is characterized by high flexibility, providing ancillary service to the grid becomes a potential pathway for revenue stacking. Recent research has demonstrated the feasibility of providing such a service, but the related economics have not been well evaluated. In this work, we propose a comprehensive operation model to enable participation in the day-head, balancing and reserve markets. Three types of reserves are considered by using different operational constraints. Based on the proposed operation framework, we assess the economic performance of a power-to-hydrogen system in Denmark using plentiful actual market data. The results reveal that providing frequency containment reserve and automatic frequency restoration reserve efficiently raises the operational contribution margins. In parallel, by investing in the cash flows, net present value, and break-even hydrogen prices, we conclude that providing reserves makes the power-to-hydrogen project more profitable in the studied period and region.

A comparative analysis of charging strategies for battery electric buses in wholesale electricity and ancillary services markets

The application of smart charging to battery electric buses can provide opportunities for bus operators to reduce the operational costs of their bus fleet. This research aims to create insight into the impact of different charging strategies for battery electric bus fleets on charging costs and the grid load. It proposes a novel framework to model the charging process of battery electric buses for different charging strategies: charging-on-arrival, peak-shaving, day-ahead market optimization with and without vehicle-to-grid (V2G) functions, including the provision of Frequency Containment Reserves (FCR) and automatic Frequency Restoration Reserves (aFRR) for system balancing in ancillary services markets. Model simulations are conducted to compare the charging costs and grid impact of different charging strategies, using three depots of bus operator Qbuzz in the Netherlands as a case study. Results indicate that the application of smart charging algorithms can considerably reduce charging costs for bus operators. Application of the peak-shaving strategy was found to reduce charging costs by 23–32% compared to the reference case of charging-on-arrival. Charging costs can be further reduced by 6–11% when considering day-ahead market optimization. Participation in ancillary services markets for system balancing is economically attractive for bus operators, particularly in the aFRR market, characterized by a cost reduction potential of 90–¿100% compared to the charging-on-arrival strategy. The grid impact analysis indicates that charging-on-arrival can result in high charging demand peaks, which can be drastically reduced by the application of peak-shaving or day-ahead market optimization charging strategies. However, the provision of aFRR and FCR using the battery electric bus charging process can have a severe impact on the local grid in terms of high peak demand.

Optimal Management of an Energy Community with PV and Battery-Energy-Storage Systems

Most of current prosumer-energy-management approaches are focused on economic optimization by self-consumption maximization. Nevertheless, a lack of energy management strategies (EMS) that tackle different interaction possibilities among community-clustered solar plus battery prosumers has been detected. Furthermore, such active prosumer EMS may include participation in ancillary service markets such as automatic frequency restoration reserves (aFRR) through an optimized battery-energy storage-system (BESS) operation, as well as incorporating community-level energy management. In this study, an optimal EMS that includes aggregated aFRR-market participation of five solar plus battery prosumers participating in an energy community (EC), with the aim of reducing total costs of ownership for each individual prosumer is proposed. For its validation, different scenarios have been analyzed. The results show that the proposed EMS allows a levelized cost of energy (LCOE) reduction for all community members with respect to the base-case scenario. Moreover, the most profitable scenario for all prosumers is still the only PV.

Handling Limitations in the Interzonal Exchange of automatic Frequency Restoration Reserves

In the future, the interzonal exchange of automatic Frequency Restoration Reserves (aFRR), i.e. their exchange between different control areas, is mandatory in Europe. Two control concepts are discussed for its realization: The Control Demand Model (CDM), currently used for existing aFRR cooperations in Europe, and the Control Request Model (CRM), for which only a conceptual definition exists so far without applications. In earlier work, a beneficial implementation of the CRM has been compared with the CDM for operation without active limitations and a stability analysis has been performed. However, the impact of limitations such as transfer capacity limits and finite aFRR availability has not been considered yet. As their impact may be significant, this paper aims at a comparison of both control models in scenarios with active limitations. After a brief recap of both CDM and CRM, we present three possible implementations for interzonal exchange of aFRR with limitations and compare them on the basis of different scenarios.

Assessing flexibility options in electricity market clearing

This work presents a model to co-optimize the energy and reserves markets, taking into account the penetration and participation of various flexibility providers in both markets. In particular, a detailed unit commitment model has been developed based on mixed-integer programming techniques incorporating energy storage systems with both charging and discharging options, electric vehicles with both grid-to-vehicle and vehicle-to-grid modes, and demand response programs for cost-optimal energy and ancillary services scheduling. The balancing services considered include Frequency Containment Reserves (FCR), automatic Frequency Restoration Reserves (aFRR), and manual Frequency Restoration Reserves (mFRR), in both upward and downward directions. The impact of all these flexibility providers on operational and economic aspects has been assessed through an illustrative case study of a power system with high penetration of renewable energy sources, including thermal and hydroelectric power units. The results highlight the superiority of results when considering the participation of all flexibility providers, especially in the ancillary services market, in terms of economic competitiveness, renewable energy curtailment, associated CO2 emissions, and utilization of costly energy resources. The growing share of flexibility providers in both energy management and reserve provision mix highlights the importance of these sources for power mixes with low carbon content. The methodological framework developed can be employed by system operators, market participants, and policymakers to provide price signals and optimize their resources and portfolios.

Stochastic adaptive robust approach for day-ahead energy market bidding strategies in hydro dominated sequential electricity markets

This paper presents a novel methodological approach for the optimal day-ahead energy market bidding behavior of a cascaded hydropower plants (HPPs) portfolio in the sequential electricity markets. The understudy markets are day-ahead energy market and manual frequency restoration reserve (mFRR) markets in both capacity and energy setups. The introduction of the mFRR capacity market ensures transmission system operators (TSOs) about the availability of energy bids in the real-time market, which acts as binding constraints in the mFRR energy markets. As a determining factor, the active-time duration of mFRR energy bids is uncertain at the time of day-ahead bidding, which is modeled as the intervals in our robust optimization, while the electricity prices are considered as the scenarios in the stochastic optimization. Hence, we have proposed a novel stochastic adaptive robust optimization to address the bidding problem in the face of uncertainties accurately. The results show a considerable improvement compared to the conventional fully-stochastic approach in the case study of Swedish cascaded hydropower plants.

Multi-Area Reserve Dimensioning Using Chance-Constrained Optimization

We propose a chance-constrained formulation for the problem of dimensioning frequency restoration reserves on a power transmission network. We cast our problem as a two-stage stochastic mixed integer linear program, and propose a heuristic algorithm for solving the problem. Our model accounts for the simultaneous sizing of both upward and downward reserves, and uncertainty driven by imbalances, contingencies and available transmission capacity. Our core methodology is further adapted in order to minimize inter-zonal flows and in order to split reserve requirements between automatic and manual frequency restoration reserves. We apply our methodology to the problem of sizing reserves in the four load frequency control areas of the Swedish power system. We demonstrate the benefits of our method in terms of decreasing reserve requirements in the absence of reserve sharing, we analyze the spatial allocation of reserves, and we perform various sensitivity analyses.