Frequency Restoration Reserve Research Articles

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.

Sizing a Battery Energy Storage System for Hybrid Renewable Power Plants Based on Optimal Market Participation Under Different Market Scenarios

This article presents a method for selecting the best battery sizing based on an optimal market participation strategy in a hybrid renewable power plant. The proposed formulation considers different scenarios to ensure the reserve provision compliance and includes two terms. The first one maximizes the day-ahead and automatic frequency restoration reserve (aFRR) market revenues. The second minimizes the battery degradation, accounting for both cycling and calendar ageing effects. The Iberian Electricity Market is selected as the study case, and two different market scenarios are compared: the current market scenario and the upcoming one, in which the upward and downward aFRR band offers are independent. The operation of a set of batteries is simulated until their end of life, and results reveal that energy/power ratios higher than 3 h for the current market scenario, and than 4 h for the upcoming one, are less cost effective. Regarding the best battery energy storage systems sizing, the selection varies considering incomes or profitability criteria. Moreover, keeping the current prices, in the upcoming market scenario hybrid renewable power plants are encouraged to participate more in the downward than in the upward aFRR market.

Multi-market demand response from pump-controlled open canal systems: an economic MPC approach to pump-scheduling

Abstract Participation in demand response (DR) has been explored for many large energy-using assets based on day ahead electricity markets. In this manuscript, we propose the use of multiple electricity spot markets to enable price-based DR for open canal systems in the Netherlands, where many large pumping stations are used for flood mitigation and control of groundwater levels. In the new strategy for pump-scheduling, we combine the day ahead and intraday electricity markets to be used in a hierarchical receding horizon economic Model Predictive Control (MPC). We formulate the decision problem as a Mixed-Integer Quadratic Problem (MIQP), to be solved to near global optimality. A cost-potential analysis was performed for multiple market strategies and the automatic Frequency Restoration Reserves (aFRRs), using actual market and water system data. We show new insights into the trade-off between CO2 emissions and operating cost, the difference between the German and Dutch markets, and temporal changes in market conditions due to renewable energy integration. We observe that the German energy market is rewarding DR more than the Dutch equivalent, due to the higher renewable energy market penetration. The proposed multi-market strategy leads to a cost decrease of 10 and 16% in the Netherlands in 2017 and 2019, respectively. When applying German market scenarios, we found a cost-saving potential of 56 and 50% in 2017 and 2019, respectively. The cost-saving potential for the aFRR market was found to be up to 12% in the Netherlands and 28% in Germany, through a conservative analysis. The results suggest that the proposed control system, optimising costs over the day ahead, intraday and possibly the aFRR markets, is profitable compared to the current strategy in both the current and future electricity market.

Biogas power plant participation in provision of manual frequency restoration reserve

Biogas power plant participation in provision of manual frequency restoration reserve

Battery Energy Storage Participation in Automatic Generation Control of Island Systems, Coordinated with State of Charge Regulation

Efficient storage participation in the secondary frequency regulation of island systems is a prerequisite towards their complete decarbonization. However, energy reserve limitations of storage resources pose challenges to their integration in centralized automatic generation control (AGC). This paper presents a frequency control method, in which battery energy storage systems (BESSs) participate in automatic frequency restoration reserve (aFRR) provision, through their integration in the AGC of an island system. A local state of charge (SOC) controller ensures safe operation of the BESS in case of disturbances, without jeopardizing system security when available energy reserves are diminishing. The aFRR participation factors of regulating units are altered when the storage systems approach their SOC limits, re-allocating their reserves to other load-following units. Restoration of BESS energy reserves is achieved by integrating SOC regulation in the real-time economic dispatch of the system, formulated as a mixed-integer linear programming problem and solved every few minutes to determine the base points of the AGC units. A small autonomous power system, comprising conventional units, renewable energy sources and a BESS, is used as a study case to evaluate the performance of the proposed method, which is compared with alternative approaches to secondary regulation with BESS participation.

Developed Transfer Function Allows Hydro Generators to Enter the Full Range of Ancillary Services Market

As the number of available renewable energy sources has increased annually, there has been a corresponding rise in the levels of pollution created by traditional electricity generation, ultimately contributing to breaking down the stability of the electrical system at large. Therefore, there is an increasing need to integrate the use of nonpolluting electricity sources, such as pumped storage hydropower plants (PSHP), to ensure the stability of the power system and to maintain the frequency of the system from year-to-year. This paper addresses the issue of PSHP being unsuitable for providing Frequency Containment Reserve (FCR) services and proposes real measurements of the aggregation approach to obtain different data arrays. Based on this, the proposed methodology is orientated toward obtaining transfer functions that were developed using the parametric identification models, and the efficiency of these functions was thoroughly investigated. The proposed transfer function in this paper, in combination with battery energy storage system (BESS) technologies, would allow PSHP technologies to occupy a space in the ancillary services market by providing FCR, Frequency Restoration Reserve (FRR), and Replacement Reserve (RR) services. The performance of the function activated in the BESS is positively validated using the Simulink modeling environment.

Control Aspects of the Interzonal Exchange of automatic Frequency Restoration Reserves

This paper compares two control methods for the interzonal exchange of automated Frequency Restoration Reserves (aFRR), i.e. their exchange between different control areas (CA), which is mandated by the EU Commission for the future. The Control Demand Model (CDM) was developed for aFRR-exchange between German CA and is the currently implemented model for the European aFRR exchange. In the CDM, the aFRR demand of the CA is optimized, which has the advantage that there is no intervention in the aFRR control loops and therefore stability is guaranteed to be preserved. However, the activation of aFRR is not optimal, since the optimization result and the actual activation differ dynamically due to the aFRR controller of the respective CA. The Control Request Model (CRM) tries to eliminate this disadvantage by placing the optimizer between the controller and the activation. However, this causes the different aFRR control loops to be partially coupled, meaning that stability might be lost without adequate countermeasures.We describe both the CDM and the CRM, including an adaptation for stable operation for the latter. They are then compared using different scenarios. Finally, a stability analysis is carried out for the CRM.

Monitoring the Compliance of Balancing Reserves Power with the System Operation ⋆ Guideline of Continental Europe

This paper describes an automatic monitoring concept for automatic and manual Frequency Restoration Reserves during operation. There is increasing need for such automatic monitoring due to the increasing share of small decentralized technical units in balancing reserves power provision.For this purpose, an existing procedure for monitoring Frequency Containment Reserves is adapted to automatic and manual Frequency Restoration Reserves. Apart from the requirements for the activation dynamics, these differ from Frequency Containment Reserves by the fact that positive and negative provision may be different. These aspects are taken into account. In order to monitor different balancing reserves power products, the measured active power that is provided to the grid has to be apportioned among the different products. In any case, the power related to the nominal schedule and the balancing reserves power have to be separated. In addition, several kinds of balancing reserves may be provided simultaneously, so that these have to be split as well. This paper proposes to perform the separation of different kinds of balancing reserves based on dynamic models that reflect the provision as good as possible. For the utility, providing this model may be difficult and conflicts of interest may arise. Therefore, we propose to identify the necessary models from measurement data. The paper shows that this procedure can be applied successfully on real measurement data.

The role of district heating systems to provide balancing services in the European Union

European electricity markets ensure the matching between supply and demand at all times. Due to their time-scale operations, the balancing markets are the last resources to achieve so and ensure the grid frequency. The increasing shares of non-dispatchable power capacities intensify the demand for flexibility. District heating systems (DHs) are potential sources of flexibility if interface technologies are in place like CHP or power-to-heat, together with thermal storage. This study assesses the technical potential of DHs to contribute to frequency containment reserves (FCR), automatic and manual frequency restoration reserves (aFRR and mFRR) markets. Through a review of case-studies, we gain insight and derive appropriate assumptions to estimate the potential at country and EU levels. Based on the POTEnCIA Central scenario up to 2050 — a description of the evolution of the EU energy system with the assumption of no further policies introduced beyond 2017 —, we find that the potential is highest for the provision of aFRR, followed by mFRR and FCR. Specifically, the aFRR technical potential is currently 32 GW — 4 times the aFRR contracted in 2019 in the EU — and it only slightly decreases by 2050. Overall, this study highlights the lack of data on current (and future) DHs and their variety in size and composition. A sensitivity analysis is performed by examining different scenarios for DHs deployment. This research emphasizes the large untapped potential to exploit flexibility from DHs, however, the evaluation of the actual potential shall be done on a case-by-case basis.

Manual Frequency Restoration Reserve Activation Clearing Model

The integration of the European markets has started with the successful coupling of spot markets (day-ahead and intra-day) and is expected to continue with the coupling of balancing markets. In this paper, the optimization model for the activation of manual frequency restoration reserve (mFRR) is presented. The model incorporates all order types agreed among the European transmission system operators (TSOs) to be included in the Manually Activated Reserves Initiative (MARI) project. Additionally, the model incorporates the buying curve (demand) of mFRR with the possible tolerance band defined by the TSOs, order clearing constraints and the cross-zonal capacity (CZC) constraints, forming a mixed integer linear programming model. The methodology employs two distinct steps: In the first step, an order conversion process is employed for the markets applying the central-scheduling scheme, and in the second step, the mFRR activation process is executed by solving the presented model. The whole process is tested using a case, including twenty-five European control areas. The attained clearing results indicate that price convergence is achieved among the involved control areas, along with a reduction in the overall balancing costs mainly due to the imbalance netting that is implicitly performed during the joint mFRR balancing energy (BE) clearing process and due to the cross-border exchange of mFRR BE.

Electric water heater flexibility potential and activation impact in system operator perspective – Norwegian scenario case study

Simultaneous activation of demand side flexibility on thermostatically controlled loads will cause adverse impacts later in the form of rebounds. Distribution system operators must know the characterisation of the impact, as they are responsible for voltage quality of power delivery and suffer the loss of lifespan of network components due to overloading. In this paper, characterising parameters for flexibility activation on electric water heaters (EWHs) are proposed and flexibility potentials are computed considering smart activation methods for the Norwegian scenario. The proposed parameters are rebound percentage, delay, ramp rates, second peak distance, activation error, flexible power, and temperature deviation. Four scenarios with different levels of flexible power and activation time are developed in the Norwegian context for quantification of the flexibility potentials and the parameters. The highest average flexible power potential is 53.9% at 8:00 a.m. for a duration of 61 min. EWHs flexibility activation can serve as Frequency Containment Reserves (FCR) at peak demand hours with high ramp-up and ramp-down rates of 48.5% and 23.8% per minute and as Frequency Restoration Reserves (FRR) during non-peak hours.

A mixed-integer distributed approach to prosumers aggregation for providing balancing services

This paper addresses the provision of ancillary services in smart energy systems. A large number of prosumers are aggregated by an Energy Service Provider (ESP) in order to provide a manual Frequency Restoration Reserve (mFRR) service, which consists in offering some degree of flexibility and be willing to provide a power variation over a given time interval upon reception of an explicit manual request by the Transmission System Operator (TSO). The main focus of this paper is to define how the ESP can optimally distribute the requested flexibility effort to the prosumers in the pool, promptly providing the agreed mFRR service upon request of the TSO. In particular, a scalable strategy is proposed, able to account for integer decision variables like on/off commands, while reducing the combinatorial complexity of the problem and preserving privacy of local information via distributed computations. Lead and rebound effects are avoided by maintaining the originally scheduled energy exchange profile before and after the time interval where the TSO request must be satisfied. The simulation results show the effectiveness of the proposed approach in terms of scalability and quality of the obtained feasible solution.

Flexibility Reserve of Self-Consumption Optimized Energy Systems in the Household Sector

Energy generation and consumption in the power grid must be balanced at every single moment. Within the synchronous area of continental Europe, flexible generators and loads can provide Frequency Containment Reserve and Frequency Restoration Reserve marketed through the balancing markets. The Transmission System Operators use these flexibilities to maintain or restore the grid frequency when there are deviations. This paper shows the future flexibility potential of Germany’s household sector, in particular for single-family and twin homes in 2025 and 2030 with the assumption that households primarily optimize their self-consumption. The primary focus is directed to the flexibility potential of Electric Vehicles, Heat Pumps, Photovoltaics and Battery Storage Systems. A total of 10 different household system configurations were considered and combined in a weighted average based on the scenario framework of the German Grid Development Plan. The household generation, consumption and storage units were simulated in a mixed-integer linear programming model to create the time series for the self-consumption optimized households. This solved the unit commitment problem for each of the decentralized households in their individual configurations. Finally, the individual household flexibilities were evaluated and then aggregated to a Germany-wide flexibility profile for single-family and twin homes. The results indicate that the household sector can contribute significantly to system stabilization with an average potential of 30 GW negative and 3 GW positive flexibility in 2025. In 2030, the corresponding flexibilities potentially increase to 90 GW and 30 GW, respectively. This underlines that considerable flexibility reserves could be provided by single-family and twin homes in the future.

A Blockchain-Based Configuration for Balancing the Electricity Grid with Distributed Assets

This paper explores a future perspective to foster the provision of balancing services to the electricity grid by distributed assets. One recent test case, initiated by the Dutch Transmission System Operator (TSO), was to operate an Electric Vehicle (EV) fleet on the automatic Frequency Restoration Reserve (aFRR) market, which entails fast and automated reserves. To achieve that in a decentralised, automated and transparent manner, the role of blockchain technology for this specific application is explored. We propose a novel configuration that can serve as a basis for deploying distributed assets for aFRR markets using blockchain or any alternative Distributed Ledger Technology (DLT). Automation can be achieved via the deployment of smart contracts, which also results in transparency in the system. The blockchain configurations are designed for three phases in the aFRR market, namely: (i) Operational planning and scheduling by a balancing service provider (i.e., formulation and submission of aFRR bid), (ii) Real-time operations (i.e., activation and measurements), and (iii) Verification and settlement (i.e., imbalance correction and financial settlement). The paper concludes that the scalability of distributed assets that can participate in the system, combined with the large transaction times and energy consumption of some consensus mechanisms, could put limitations on the proposed architecture. Future research should address benchmarking studies of other alternatives (e.g., DLTs, such as the ones based on directed acyclic graphs, and non-DLT solutions) with the proposed blockchain solution.

Analysis and improvement of cross-regional cooperation for automatic frequency restoration reserves

Frequency restoration reserves (FRRs) are currently procured and activated by individual transmission system operators (TSOs) in Japan. To enhance the efficiency of the balancing process, a balancing market will be established in 2021, with the introduction of cross-regional cooperation for an automatic FRR (aFRR) being discussed. The cross-regional aFRR cooperation will be conducted through the procedures of the imbalance netting and aFRR sharing. As for the imbalance netting, two methods - i.e., the ACE netting and aFRR demand (aFRR-d) netting - have been used in the US and Europe, respectively. This study examines the merits and demerits of those netting methods through the time-domain simulations using a model comprising two Japanese TSOs’ control areas. Although the ACE netting is more efficiently in reducing frequency fluctuations, the reduction effect in aFRR activations is limited. In contrast, the aFRR-d netting can reduce aFRR activations more efficiently while the time required to restore the frequency can be prolonged. To utilize the merits and compensate for the demerits of the above two netting methods, this paper proposes a combination of those netting methods. The simulation results indicate that the proposed method can reduce the frequency fluctuations as effectively as the ACE netting and can reduce the aFRR activations as effectively as the aFRR-d netting in comparison with the localized aFRR operation.

Advanced Wastewater Treatment to Eliminate Organic Micropollutants in Wastewater Treatment Plants in Combination with Energy-Efficient Electrolysis at WWTP Mainz

To achieve the Paris climate protection goals there is an urgent need for action in the energy sector. Innovative concepts in the fields of short-term flexibility, long-term energy storage and energy conversion are required to defossilize all sectors by 2040. Water management is already involved in this field with biogas production and power generation and partly with using flexibility options. However, further steps are possible. Additionally, from a water management perspective, the elimination of organic micropollutants (OMP) is increasingly important. In this feasibility study a concept is presented, reacting to energy surplus and deficits from the energy grid and thus providing the needed long-term storage in combination with the elimination of OMP in municipal wastewater treatment plants (WWTPs). The concept is based on the operation of an electrolyzer, driven by local power production on the plant (photovoltaic (PV), combined heat and power plant (CHP)-units) as well as renewable energy from the grid (to offer system service: automatic frequency restoration reserve (aFRR)), to produce hydrogen and oxygen. Hydrogen is fed into the local gas grid and oxygen used for micropollutant removal via upgrading it to ozone. The feasibility of such a concept was examined for the WWTP in Mainz (Germany). It has been shown that despite partially unfavorable boundary conditions concerning renewable surplus energy in the grid, implementing electrolysis operated with regenerative energy in combination with micropollutant removal using ozonation and activated carbon filter is a reasonable and sustainable option for both, the climate and water protection.

Evaluation of the Effects of Smart Charging Strategies and Frequency Restoration Reserves Market Participation of an Electric Vehicle

The emergence of electric vehicles offers the opportunity to decarbonize the transportation and mobility sector. With smart charging strategies and the use of electricity generated from renewable sources, electric vehicle owners can reduce their electricity bill as well as reduce their carbon footprint. We investigated smart charging strategies for electric vehicle charging at household and workplace sites with photovoltaic systems. Furthermore, we investigated the participation of an electric vehicle in the provision of positive automatic frequency restoration reserve (aFRR) in Germany from 30 October 2018 to 31 July 2019. We find that the provision of positive aFRR in Germany returns a positive net return. The positive net return is, however, not sufficient to cover the current investment cost for a necessary control unit. For home charging, we find that self-sufficiency rates of up to 48.1% and an electricity cost reduction of 17.6% for one year can be reached with unidirectional smart charging strategies. With bidirectional strategies, self-sufficiency rates of up to 56.7% for home charging and electricity cost reductions of up to 26.1% are reached. We also find that electric vehicle (EV) owners who can charge at their workplace can reduce their electricity cost further. The impact of smart charging strategies on battery aging is also discussed.

Experimental modeling and aggregation strategy for thermoelectric refrigeration units as flexible loads

In the last years, the interest regarding thermoelectric refrigerators has increased thanks to their properties such as the absence of moving parts and toxic or fire-sensitive refrigerants, robustness, and low weight. These devices are also quite flexible and may represent a suitable solution to offer grid services to proper demand response programs. In this article, an aggregation strategy is proposed to fulfil system operator requests on power deviations with limited information exchange between the aggregator and each refrigerator. Downward and upward flexibility in energy consumption can be offered, allowing an aggregated set of loads to provide balancing services such as frequency containment reserve, frequency restoration reserve or replacement reserve to the electrical grid. First, a dynamic model of a thermoelectric refrigerator is built and validated using experimental data collected from a real device under controlled and replicable experimental conditions. A modified temperature controller is proposed and an aggregation strategy with reduced communication requirements is formulated. Then, the aggregation of thermoelectric refrigerators is represented with a linear model to determine that this aggregation can behave as flexible load for reserve provision and demand response applications. It is shown through extensive simulations that a set of refrigerators can operate as in a flexible way by modifying their internal temperature set points, responding in less than 30 s to any power deviation command and sustaining the modified consumption for up to 15 min in the frequency containment and restoration reserves services, and up to 1 h in the replacement reserve service, without overshoots, rebounds, or synchronization problems.

Medium-term scheduling of a hydropower plant participating as a price-maker in the automatic frequency restoration reserve market

This paper presents a novel optimization model for the calculation of the water value of a hydropower plant. The model has a time horizon of 1 year with 1-day decision stages, considers sales of both energy and frequency restoration reserves (FRR) and is solved by stochastic dynamic programming. The novelty of the model is that it considers the producer's price-making ability in the FRR market. The proposed model is used to obtain the water values of an existing hydropower plant. The water values are then used to simulate the day-ahead scheduling of the hydropower plant in a 100-year scenario. The results are compared to those obtained without considering the producer's price-making ability in the FRR market. The profit increase is modest compared to the uncertainty existing in the day-ahead scheduling in all analysed cases. However, the water spillage is significantly lower if the producer's price-making ability in the FRR market is considered when computing the water value. This last result may have important implications for the plant's operation, especially when the reservoir is also used for the purpose of flood control, as the one used as case study in the paper, and many others all over the world.