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The pulp and paper industry is under increasing pressure to reduce its energy consumption and carbon footprint. This study examines the feasibility of integrating high-temperature heat pumps (HTHP) into tissue paper production to enhance energy efficiency and decarbonization. Focusing on the energy-intensive drying process, the study uses data from a typical tissue paper mill to simulate and optimize an HTHP system producing four tons per hour of nine-bar saturated steam. It also addresses necessary modifications for HTHP integration applicable across the sector. Various refrigerants were analyzed, achieving a maximum coefficient of performance (COP) of 2.01. Results showed that HTHP can reduce energy consumption and emissions by up to 17% and 40%, respectively, based on the European electricity mix. Although steam production costs increase by 55% compared to fossil fuel-based systems, HTHP is more cost-effective than direct electric resistance heating, which raises costs by 196%. With a CO2 price of EUR 100/t, HTHP offers a 12% cost reduction. However, without public funding, capital expenditures may be unsustainable in many regions, though viable in countries with favorable gas and electricity price differentials. The paper underscores the need for advancements in HTHP technology and cost reductions, emphasizing industry adaptation for seamless HTHP integration. [ABSTRACT FROM AUTHOR]

High-temperature heat pumps are a key technology for enabling the complete integration of renewables into the power grid. Although these systems may come with several variants, Brayton heat pumps are gaining more and more interest because of the higher heat sink temperatures and the potential to leverage already existing components in the industry. Because these systems utilize renewable electricity to supply high-temperature heat, they are particularly suited for industry or energy storage applications, thus prompting the development of various demonstration plants to evaluate their performance and flexibility. Adapting to varying load conditions and swiftly responding to load adjustments represent crucial aspects for advancing such systems. In this context, this study delves into assessing the transient capabilities of Brayton heat pumps during thermal load management. A transient model of an emerging prototype is presented, comprising thermal and volume dynamics of the components. Furthermore, two reference scenarios are examined to assess the transient performance of the system, namely a thermal load alteration due to an abrupt change in the desired heat sink temperature and, secondly, to a sudden variation in the sink mass flow rate. Finally, two control methodologies—motor/compressor speed variation and fluid inventory control—are analyzed in the latter scenario, and a comparative analysis of their effectiveness is discussed. Results indicate that varying the compressor speed allows for a response time in the 8–20 min range for heat sink temperature regulation (first scenario). However, the regulation time is conditioned by the maximum thermal stress sustained by the heat exchangers. In the latter scenario, regulating the compressor speed shows a faster response time than the inventory control (2–5 min vs. 15 min). However, the inventory approach provides higher COPs in part-load conditions and better stability during the transient phase. [ABSTRACT FROM AUTHOR]

The waste heat recovery from the gas turbine (GT) exhaust is typical for increasing performance and reducing CO2 emissions in industrial facilities. Nowadays, numerous already operating gas turbine plants could be retrofitted and upgraded with a bottoming cycle powered by the exhaust gasses. In this case, the standard solution would be to use a water steam Rankine cycle. However, even if this technology usually yields the best efficiency, other alternatives are often preferred on the lower size scale. Organic Rankine cycles (ORCs) are the commercial alternatives to steam Rankine cycles, but many other alternative cycles exist or can be developed, with potential benefits from safety, technical or economic points of view. This study compares several alternative technologies suited to recover gas turbine waste heat, and a detailed cost analysis for each is presented. On this basis, a guideline is proposed for the technology choice considering a wide range of application sizes and temperature levels typical for waste heat recovery from gas turbines. The compared technologies are ORCs, Rankine cycles (RCs) with water and ammonia mixtures at constant composition, supercritical CO2 cycles (sCO2), sCO2 cycles with mixtures of CO2 and other gasses. As it resulted, ORCs can achieve the lowest levelized cost of energy (32 $/MWh-46 $/MWh) if flammable fluids can be employed. Otherwise, Rankine cycles with a constant composition mixture of water and ammonia are a promising alternative, reaching a levelized cost of energy (LCOE) of 36-58 $/MWh. [ABSTRACT FROM AUTHOR]

The growing use of photovoltaic (PV) energy in residential systems presents challenges, notably managing daily and seasonal intermittency. To limit curtailment and maximise self-consumption, decentralised flexibility options are crucial. In this context, Carnot batteries, which combine a heat pump, thermal energy storage, and a heat engine, show promise for integrated heat and power management alongside PV production. However, the economic model (investment costs, electricity pricing system) and control strategy (heat/electricity discharge, seasonal impacts) needed to achieve maximum cost-effectiveness have not yet been identified. This study therefore explores the integration of a Carnot battery in a housing development of 20 dwellings equipped with PV systems. Using a quadratically constrained linear programming model, the designs and operations that minimise the annualised energy cost are identified across different ranges of investment costs. The impact of climatic conditions is assessed by comparing results from Pisa and Brussels. Our findings indicate that, except in scenarios with prohibitively high costs, incorporating a heat engine alongside a heat pump and thermal energy storage is the most cost-effective solution. Parametric analyses reveal that zero feed-in tariffs promote Carnot battery deployment, while non-zero tariffs significantly reduce the installed capacity. Additionally, dynamic (or variable) tariffs generally do not reduce energy costs but do increase the Carnot battery capacity, in order to take advantage of the energy arbitrage mechanism. In conclusion, when heat pumps and thermal storage are necessary to meet heating demand, adding a heat engine to address electricity needs is financially effective. This paves the way for further advancements in residential energy management using Carnot batteries. Future work should confirm and refine these results with more precise models, incorporating non-linearities such as start-up and part-load operations. • Carnot battery for heat and electricity storage in residential applications with PV. • Parametric analyses assess the impact of investment costs on optimum system design. • While climatic conditions affect design, Carnot battery shows interesting potential. • Dynamic tariffs are not advantageous, except for very high levels of fluctuations. • Cost is most sensitive to COP, while rather insensitive to heat engine efficiency. [ABSTRACT FROM AUTHOR]

• A novel reversible Brayton thermo-mechanical storage is proposed and analysed. • Turbomachines operated in similitude allow re-using charge components for discharge. • Multi-objective optimisation is used to analyse efficiency and cost trade-offs. • Cost reduction due to components merging impacts the exchanger cost the most. • Reversible storage has the same efficiency as standard systems but costs 20% less. The surge in non-programmable renewable production expected for the coming years can only be harnessed with a consequential increase in energy storage capacity. Many technologies are being proposed in the search for durable, affordable, and sustainable storage, and thermomechanical technologies are becoming prominent alternatives. Despite the best efforts, thermomechanical storage technologies still suffer from non-competitive capital costs due to using separate (costly) charging and discharging equipment. This paper proposes merging charging and discharging parts to realize a novel reversible thermomechanical storage, cutting the components' number and, consequently, significantly reducing the system's capital cost. To do so, a novel technique is proposed and investigated by focusing on Brayton cycles-based Pumped Thermal Energy Storage, a promising technology for large-scale and long-duration energy storage. This technique allows turbomachines to operate under similitude conditions during charge and discharge phases, thus enabling their use in both phases. Of course, operating the turbomachines in similitude imposes several additional constraints on the system design, components' sizing and operating conditions, the impact of which on the storage cost and performance is discussed in the paper. The analysis encompasses both liquid- and solid-based Brayton Pumped Thermal Energy Storage, assesses the impact of the proposed technique for different storage configurations, and discusses the role of heat exchangers in the realization of reversible storage systems. A techno-economic analysis is performed as a multiobjective optimization problem where performance and cost are pursued as competing objectives. Comparing standard (non-reversible) systems with reversible configurations shows that the latter may achieve an overall plant cost reduction of around 20% in the case of liquid-based systems, whereas reversible solid-based systems show similar costs to their standard counterpart. This occurs because most of the economic gain achieved by reversible configurations comes from reducing the number of heat exchangers, which are absent in solid-based systems. [ABSTRACT FROM AUTHOR]

To integrate large shares of renewable energy sources in electric grids, large-scale and long-duration (4–8+ h) electric energy storage technologies must be used. A promising storage technology of this kind is pumped thermal electricity storage based on Brayton cycles. The paper's novel contribution is in the techno-economic comparison of two alternative configurations of such storage technology. Liquid-based and solid-based pumped thermal electricity storage were studied and compared from the techno-economic point of view. The cost impacts of the operating fluid (air, nitrogen, and argon), power rating, and nominal capacity was assessed. Air was the most suitable operating fluid for both technologies, simplifying the plant management and achieving cost reductions between 1% and 7% compared to argon, according to the considered configuration. Despite a more complex layout and expensive thermal storage materials, liquid-based systems resulted in being the cheapest, especially for large applications. This was due to the fact of their lower operating pressures, which reduce the cost of turbomachines and containers for thermal energy storage materials. The liquid-based systems achieved a cost per kWh that was 50% to 75% lower than for the solid-based systems. Instead, the cost per kW benefited the solid-based systems up to nominal power ratings of 50 MW, while, for larger power ratings, the power conversion apparatus of liquid-based systems was again cheaper. This was due to the impact of the turbomachines on the total cost. The machines can represent approximately 70% of the total cost for solid-based systems, while, for liquid-based, approximately 31%. Since the cost of turbomachines scales poorly with the size compared to other components, solid-based systems are less suitable for large applications. [ABSTRACT FROM AUTHOR]

The growth of renewable energy source requires reliable, durable, and cheap storage technologies. In this field, the pumped thermal energy storage (PTES) is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance, and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e., the inventory control (IC), is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the off-design operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase. [ABSTRACT FROM AUTHOR]

• Brayton Pumped Thermal Energy Storage integrated in urban energy district. • Deep-decarbonization scenarios by integrating PV production. • Mixed Integer Linear programming for day-ahead optimal scheduling. • Multi-energy mode reduces operational costs up to 10 % compared to the electric one. • Multi-energy mode brings to 3–10 % unavoidable thermal curtailment losses. Energy storage systems play a crucial role in supporting the integration of renewable energy sources. In this framework, Brayton Pumped Thermal Energy Storage is an emerging technology thanks to many positive features, including geographical and raw materials independence, long lifetime, and peculiar sector-coupling capabilities. By storing electric energy as thermal exergy, this technology offers the flexibility to discharge energy directly for heating or cooling applications or convert it back into electricity as needed by the grid. This dual functionality fits well with the multi-energy intrinsic nature of urban districts in which electrical and thermal energy carriers are involved. This paper aims then to evaluate the potential economic benefit due to the usage of a Brayton based Pumped Thermal Energy Storage as multi-energy device instead of a solely electric-to-electric. An urban district with thermal and electric requirements is used as a case study to investigate the techno-economic performance of the mentioned storage capacity when coupled to photo-voltaic plants to simulate deep-decarbonization scenarios. The system day-ahead optimization, performed through a Mixed Integer Linear Programming approach, aims to minimize the operational cost computed over a 24-h horizon. The results highlight that operational yearly cost savings are 5–10 % when using the multi-energy storage functionalities compared to the standard electric-to-electric operation. Despite the cost reduction, allowing only direct heating causes unavoidable thermal curtailment losses in the 6–10 % range. However, these losses can be reduced to 3 % by introducing the additional direct cooling functionality, bringing the best performances from the economic and thermodynamic standpoints. [ABSTRACT FROM AUTHOR]

Non-dispatchable Renewable Energy Sources (RES) changed energy production from being centralised and fully dispatchable, to be more decentralised and less predictable. Despite the substantial growth, RES must be increased to fulfil the power production decarbonization targets set by several countries. In several countries, Italy included, RES development must be based on solar PV. Thus, relevant energy quantities will be shifted from day hours to night hours. Such "Load Shifting" is done with energy storage technologies. A few technologies suited for this task are already available, whereas several others have been proposed, but not tested in the practice. In this paper, such storage technologies are reviewed focusing on the performance and costs. Based on the review, current and future storage economic outlooks are assessed by focusing on the Italian scenario. In the paper, the storage operation is optimized at the hourly level to calculate the maximum achievable annual revenue. The optimisation is performed with a linear programming (LP) approach. Since none of the reviewed storage is economically feasible, the energy price modification required to achieve feasibility are estimated. Based on such results, the distance between the current situation and the one favourable to storage is assessed. In this way, the future outlook of each storage technology is discussed. • A review of storage technologies suited for grid-scale applications is presented. • The data from the review are used for an economic feasibility analysis. • The revenue is maximised over a year through a linear programming problem. • The cost over revenue ratio quantifies the required incentive from support schemes. • The energy price modification required to make any storage feasible is discussed. [ABSTRACT FROM AUTHOR]

The great amount of support schemes that initially fueled the fast and often uncontrollable, renewable energy sources (RESs) growth have been strongly reduced or revoked in many countries. Currently, the general trend is to try to equate RESs to traditional power plants. From the energy market point of view, this entails exposing RESs to market competition and mechanics. For example, it could be requested that RESs submit a production schedule in advance and are financially responsible for any deviation from it. This could push the wind farm (WF) operators to make accurate forecasts, thus fostering the electric system resiliency and an efficient use of balancing resources. From the forecasting point of view, this is not a trivial problem since the schedule submission is often due 10-12h before the actual delivery. Since forecast errors are unavoidable, the submitted schedule could turn out to be infeasible, thus forcing the WF to adopt correcting actions, which are generally costly. This study estimates the revenue reduction that would affect a WF operating in the energy market due to forecast errors. To do this in a realistic way, a case study is selected, and realistic forecast scenarios are generated by using a copula approach. Relevant forecast error features, like autocorrelation and dependency on forecasted power level and forecast lead time, are modeled. The revenue reduction due to balancing actions is calculated on an annual basis, by using typical days. These were derived through a clustering procedure based on production data. Losses ranging from 5% to 35% have been found, depending on the days and market prices. A sensitivity analysis to the costs of balancing actions is performed. The effect of different market architectures and different RESs penetration level is considered in the analysis. Finally, the effectiveness of two techniques (i.e., curtailment and batteries) to reduce forecast error impact in highly penalizing market environments is assessed. [ABSTRACT FROM AUTHOR]

• A 25kWh encapsulated LTES is investigated using CFD. • Data from CFD is fed into a scheme to investigate the yearly charging performance. • Performance differs seasonally, with varying temperatures impacting the operation. • Optimization reduces cooling unit heat dissipation and maximizes stored heat. Solar energy's growing role in the green energy landscape underscores the importance of effective energy storage solutions, particularly within concentrated solar power (CSP) systems. Latent thermal energy storage (LTES) and leveraging phase change materials (PCMs) offer promise but face challenges due to low thermal conductivity. This work comprehensively investigates LTES integration into solar-thermal systems, emphasizing medium-temperature applications. It introduces an innovative LTES tank design with encapsulating tubes modeled through computational fluid dynamics (CFD). The system employs a novel hybrid thermal storage approach, enhancing thermal output through a high-temperature heat pump (HTHP) before storage. This approach aligns with future energy systems, emphasizing energy vector integration. The study offers realistic LTES modeling, accounting for natural convection effects, and integrates LTES within solar thermal systems by taking advantage of time dependent CFD results. Real-world solar irradiance data for an Italian city is integrated into the investigation, providing insights into LTES performance and its role in sustainable solar energy solutions. A multi-objective optimization process follows the year-round simulations to maximize the amount of stored heat and minimize the electric input. This approach facilitates better system sizing and performance evaluation, contributing to the advancement of solar thermal technology. [ABSTRACT FROM AUTHOR]

Geothermal resources represent a valuable option to reduce fossil fuel-based power production because they feature an unmatched capacity factor among other renewable energy sources (RES). Geothermal resource availability reduces with the temperature. Therefore, developing cost-effective solutions to exploit low-temperature geothermal energy is mandatory to expand technology utilization. The standard solution for converting low-temperature thermal sources into power is organic rankine cycles (ORCs). ORC basic layout (subcritical) is well-known, but the more advanced alternatives, such as transcritical and two-pressure level cycles, are much less widespread, and it is unclear whether the higher efficiency justifies the higher capital cost. The paper focuses on the exploitation with ORC of geothermal resources (hot water) with a temperature lower than 200 °C and mass flow rates between 200 and 1400 m³/h for a target power production ranging from 3 to 30 MW. The paper compares three ORC layouts, subcritical, transcritical, and two pressure-level, from thermodynamic and economic points of view to map the most cost-effective solutions in the investigated size ranges. The techno-economic comparison considers the impact of the operating conditions and fluid on the machine's expected performance and the heat exchangers' size. As expected, more complicated layouts yield higher conversion efficiencies, with the two pressure-level cycles achieving the highest power output for the same geothermal source conditions. However, the economic analysis showed that the most efficient solutions are not always preferable when considering the cost-efficiency tradeoff. [ABSTRACT FROM AUTHOR]

Climate targets set by international organizations require the implementation of innovative technologies that ensure the decarbonization of energy sector. It may be partially achieved through a large penetration of Renewable Energy Sources. Massive energy storage is essential to handle excess electricity associated to RES and Power-to-Gas represents a promising option to chemically convert electricity surplus into energy carriers that may attend demands substituting fossil fuels. Aiming to avoid the influence of policies and market implications, this study approaches the decarbonization of Spanish system through the analysis of technical potential of RES. Several scenarios with different shares of RES are defined to cover a number of levels of energy demand. First, required wind and photovoltaic power has been estimated together with the required sizes of PtG to completely decarbonize electrical generation and industrial CHP. These scenarios may be reached by installing RES capacities below the technical potential coupled with PtG capacities between 80 and 90 GW. The stored energy amounts to 17% of total primary energy consumption. Secondly, scenarios are modified to consider denuclearization of electrical system. Required installed RES power still does not surpass the technical potential but become extremely high and the economic feasibility should be further analysed. [ABSTRACT FROM AUTHOR]

Electrolytic hydrogen production using renewable sources can play a central role in global decarbonization. However, the direct coupling of electrolyzers with renewable energies can cause frequent shutdowns and high production fluctuations unless adopting electrical storage systems or using electricity from the grid that is generally not completely decarbonized. In this study, a system consisting of a wind turbine, short-term battery storage, and an alkaline electrolyzer was analyzed through annual simulations in MATLAB. A power management strategy sets the electrolyzer and battery operating conditions. Firstly, several battery and electrolyzer sizes were investigated for a given wind site for three scenarios (0%grid , 20%grid , and 100%grid) in which the grid guarantees the electrolyzer operation at a minimum load of 0%, 20%, and 100%, respectively. Secondly, the effect of the wind speed distribution on the system performance was investigated by comparing sixteen different wind sites in the 0%grid scenario. The battery presence always led to a LCOH increase. The 20%grid scenario represented a good compromise between the minimization of specific CO 2 emissions, and the minimization of LCOH (that was always lower compared to the 0%grid scenario and the lowest without battery). The shape parameter of the fitted Weibull wind speed distribution did not affect the system. Instead, a greater scale parameter led to both greater hydrogen production and a lower LCOH. • Direct hydrogen generation from wind energy is investigated. • Scenarios with an increasing absorption from the electrical grid were compared. • Influence of Weibull scale and shape parameters on system performance. • Battery use always increases the levelized cost of hydrogen. • Best results when the electrolyzer minimum load operation is guaranteed by grid. [ABSTRACT FROM AUTHOR]

This paper provides an overview of a novel electric energy storage technology. The Thermally Integrated Pumped Thermal Electricity Storage (TI-PTES) stores electric energy as thermal exergy. Compared to standard PTES, TI-PTES takes advantage of both electric and low-temperature heat inputs. Therefore, TI-PTES is a hybrid technology between storage and electric production from low-temperature heat. TI-PTES belongs to a technology group informally referred to as Carnot Batteries (CBs). As the TI-PTES grows in popularity, several configurations have been proposed, with different claimed performances, but no standard has emerged to date. The study provides an overview of the component and operating fluid selection, and it describes the configurations proposed in the literature. Some issues regarding the performance, the ratio between thermal and electrical inputs, and the actual TI-PTES utilisation in realistic scenarios are discussed. As a result, some guidelines are defined. The configurations that utilise high-temperature thermal reservoirs are more extensively studied, due to their superior thermodynamic performance. However, low-temperature TI-PTES may achieve similar performance and have easier access to latent heat storage in the form of water ice. Finally, to achieve satisfactory performance, TI-PTES must absorb a thermal input several times larger than the electric one. This limits TI-PTES to small-scale applications. [ABSTRACT FROM AUTHOR]

• A pumped thermal electricity storage that exploits waste heat was investigated. • Trade-off between energy ratio, exergy efficiency and density is investigated. • Two configurations, with and without internal regeneration, were compared. • Regenerated configuration performs better and has less-penalizing trade-offs. • Roundtrip energy ratio over 55% can be achieved at cost of low exergy efficiency. In the present paper a multicriteria analysis of a Rankine Pumped Thermal Electricity Storage (PTES) system with low-grade thermal energy integration is performed. The system is composed by an ORC for the discharging phase and a high-temperature heat pump for the charging phase. As previously demonstrated, the low-grade thermal energy can be provided at the heat pump evaporator to boost the PTES performances. As it regards the multi-criteria analysis, a tradeoff is required when electric-to-electric energy ratio η rt , total exergy exploitation efficiency ψ ut and energy density ρ en , are maximized concurrently. By means of multi-objective optimization, theoretical performances of the system are derived in two different layouts, which are differentiated by the presence, or not, of internal regeneration in charge and discharge subsystems. Results showed that regeneration can be very effective, as it relaxes the tradeoff between the objectives, thus yielding better global performances. Pareto fronts are built and explored to characterize the PTES system. Configurations of interest are proposed, and PTES performances are compared with other storage technologies. Theoretical results showed that, by exploiting thermal energy at temperature lower than 80 °C, η rt ≈ 0.55 and ρ en ≈ 15 kWh/m3 can be concurrently achieved. This can be done at the cost of an inefficient exploitation of the thermal source, as ψ ut ≈ 0.05. If higher total exergy utilization efficiency is required, storage density can still be maintained high, but η rt must drop down to 0.4. [ABSTRACT FROM AUTHOR]

Redox Flow Batteries (RFBs) are a versatile and durable type of electrochemical storage and a promising option for large-scale stationary energy storage. Aqueous Organic Redox Flow Batteries (AORFBs) are an innovative category of RFBs that utilize organic species as active molecules in aqueous electrolytes. These species allow for customization of their properties to achieve high technical performance and reduce battery cost. This study presents a comprehensive techno-economic analysis of AORFBs, evaluating their cost metrics and their associated uncertainties. The work modeled both capital cost and Levelized Cost of Storage (LCOS) for RFBs. The model was validated on the Vanadium Redox Flow Battery (VRFB), and it was employed to evaluate the costs for a generic AORFB, using a Monte Carlo technique to incorporate the uncertainty related to the value of critical parameters. Through stochastic analysis, AORFBs are estimated to have an average specific capital cost of 674 €/kWh for 4 h, and 398 €/kWh for 8 h batteries, and probabilities between 16.9% and 29.6% of having lower capital costs compared to VRFBs. AORFBs are estimated to have a current levelized cost, calculated including only the cost of energy lost in the storage due to irreversibility, of about 530 €/MWh for 4 h, and 411 €/MWh for 8 h batteries. The levelized costs of storage, calculated including the total cost of energy charged into the storage, have average values of 663 €/MWh for 4 h, and 543 €/MWh for 8 h batteries. AORFBs have less than 1% probability of having lower LCOS than VRFBs. Current AORFB systems have higher costs compared to state-of-the-art VRFBs, even assuming a low fabrication cost for available organic molecules. This is caused primarily by the AORFBs' low energy and power densities and high degradation rates. To ensure cost competitiveness with VRFBs, it is essential to identify better-performing organic redox pairs, which should exhibit high open circuit voltage (≥ 1.1 V), should maintain reasonable round-trip efficiency (≥ 71%) while operating at a high current density (≥ 55 mA/cm 2 ). Furthermore, new organic species should have low degradation rates (≤ 0.4 %/day). • Redox Flow Batteries' (RFB) capital and levelized cost of storage (LCOS) models. • Cyclic and calendar capacity fade rates included in the levelized cost model. • Stochastic analysis based on available experimental data for organic redox species. • AORFBs exhibit average capital costs of 674 €/kWh for 4 h and 398 €/kWh for 8 h. • AORFBs exhibit average levelized costs of 530 €/MWh for 4 h and 411 €/MWh for 8 h. [ABSTRACT FROM AUTHOR]