arXiv subjects

Enrica Raheli

Publications and source records attributed to Enrica Raheli.

5 recordsLinked to original sources

arXiv2026

Towards European Hydrogen Market Design: Perspectives from Transmission System Operators

Despite hydrogen being central to Europe's decarbonisation strategy, only a small share of renewable hydrogen projects reached final investment decision. A key barrier is uncertainty about how future hydrogen markets will be designed and operated, particularly under Renewable Fuels of Non-Biological Origin requirements. This study investigates the extent to which future hydrogen market design can be adapted from existing natural gas markets, and the challenges it must address. The analysis was based on a survey targeting European gas transmission system operators, structured around five components: market design principles, trading frameworks, capacity allocation, tariffs, and balancing. The survey produced two outputs: an assessment of mechanism transferability and an identification of challenges for early hydrogen market development. Core market design principles and trading frameworks are broadly transferable from natural gas markets, as entry-exit systems and virtual trading points. Capacity allocation requires targeted adaptation to improve coupling with electricity markets. Tariffs require adaptation through intertemporal cost allocation, distributing infrastructure costs over time to protect early adopters. Balancing regimes should be revisited to reflect hydrogen's physical characteristics and different linepack flexibility usages. Key challenges for early hydrogen markets include: temporal mismatches between variable renewable supply and expected relatively stable industrial demand, limited operational flexibility due to scarce storage and reduced pipeline linepack, fragmented regional hydrogen clusters, and regulatory uncertainty affecting long-term investment decisions. These findings provide empirical input to the hydrogen network code led by the European Network of Hydrogen Network Operators and offer guidance to policymakers designing hydrogen market frameworks.

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arXiv2024

Flexibility of Integrated Power and Gas Systems: Gas Flow Modeling and Solution Choices Matter

Due to their slow gas flow dynamics, natural gas pipelines function as short-term storage, the so-called linepack. By efficiently utilizing linepack, the natural gas system can provide flexibility to the power system through the flexible operation of gas-fired power plants. This requires accurately representing the gas flow physics governed by partial differential equations. Although several modeling and solution choices have been proposed in the literature, their impact on the flexibility provision of gas networks to power systems has not been thoroughly analyzed and compared. This paper bridges this gap by first developing a unified framework. We harmonize existing approaches and demonstrate their derivation from and application to the partial differential equations. Secondly, based on the proposed framework, we numerically analyze the implications of various modeling and solution choices on the flexibility provision from gas networks to power systems. One key conclusion is that relaxation-based approaches allow charging and discharging the linepack at physically infeasible high rates, ultimately overestimating the flexibility.

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arXiv2023

A Conic Model for Electrolyzer Scheduling

The hydrogen production curve of the electrolyzer describes the non-linear and non-convex relationship between its power consumption and hydrogen production. An accurate representation of this curve is essential for the optimal scheduling of the electrolyzer. The current state-of-the-art approach is based on piece-wise linear approximation, which requires binary variables and does not scale well for large-scale problems. To overcome this barrier, we propose two models, both built upon convex relaxations of the hydrogen production curve. The first one is a linear relaxation of the piece-wise linear approximation, while the second one is a conic relaxation of a quadratic approximation. Both relaxations are exact under prevalent operating conditions. We prove this mathematically for the conic relaxation. Using a realistic case study, we show that the conic model, in comparison to the other models, provides a satisfactory trade-off between computational complexity and solution accuracy for large-scale problems.

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arXiv2023

Electrolyzer Scheduling for Nordic FCR Services

The cost competitiveness of green hydrogen production via electrolysis presents a significant challenge for its large-scale adoption. One potential solution to make electrolyzers profitable is to diversify their products and participate in various markets, generating additional revenue streams. Electrolyzers can be utilized as flexible loads and participate in various frequency-supporting ancillary service markets by adjusting their operating set points. This paper develops a mixed-integer linear model, deriving an optimal scheduling strategy for an electrolyzer providing Frequency Containment Reserve (FCR) services in the Nordic synchronous region. Depending on the hydrogen price and demand, results show that the provision of various FCR services, particularly those for critical frequency conditions (FCR-D), could significantly increase the profit of the electrolyzer.

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arXiv2023

Optimization of Hybrid Power Plants: When Is a Detailed Electrolyzer Model Necessary?

Hybrid power plants comprising renewable power sources and electrolyzers are envisioned to play a key role in accelerating the transition towards decarbonization. It is common in the current literature to use simplified operational models for electrolyzers. It is still an open question whether this is a good practice, and if not, when a more detailed operational model is necessary. This paper answers it by assessing the impact of adding different levels of electrolyzer details, i.e., physics and operational constraints, to the optimal dispatch problem of a hybrid power plant in the day-ahead time stage. Our focus lies on the number of operating states (on, off, standby) as well as the number of linearization segments used for approximating the non-linear hydrogen production curve. For that, we develop several mixed-integer linear models, each representing a different level of operational details. We conduct a thorough comparative ex-post performance analysis under different price conditions, wind farm capacities, and minimum hydrogen demand requirements, and discuss under which operational circumstances a detailed model is necessary. In particular, we provide a case under which a simplified model, compared to a detailed one, results in a decrease in profit of 1.8% and hydrogen production of 13.5% over a year. The key lesson learned is that a detailed model potentially earns a higher profit in circumstances under which the electrolyzer operates with partial loading. This could be the case for a certain range of electricity and hydrogen prices, or limited wind power availability. The detailed model also provides a better estimation of true hydrogen production, facilitating the logistics required.

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