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Flexibility Solutions and Innovations for Sustainable Hydropower

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A: Sustainable Energy".

Deadline for manuscript submissions: closed (20 August 2026) | Viewed by 3520

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Editors

Dr. Vassiliki T. Kontargyri

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Guest Editor

1. Department of Electrical and Electronics Engineering, School of Engineering, University of West Attica, 12241 Athens, Greece
2. Department of Digital Industry Technologies, National and Kapodistrian University of Athens, 34400 Psahna, Greece
Interests: power systems; transmission and distribution networks; renewable energy; high voltages; electrical insulation systems; HVDC systems; grounding systems; energy storage systems; microgrids; system flexibility; resilience

Prof. Dr. Theodoros I. Maris

E-Mail Website
Guest Editor

Department of Digital Industry Technologies, National and Kapodistrian University of Athens, 34400 Psahna, Greece
Interests: transient stability analysis; dynamic behavior of power systems; control systems; modern energy infrastructures; distributed energy resources; smart grids; system reliability; flexibility; resilience

Special Issue Information

Dear Colleagues,

The clean energy transition is driving the rapid expansion of renewable energy sources, with solar and wind reshaping power system operations and creating an unprecedented demand for flexibility. Hydropower, as the largest dispatchable renewable source, plays a central role in providing grid stability and ancillary services, while also supporting multifunctional benefits such as water supply, irrigation, drought mitigation, and flood control. However, increasing variability, off-design operations, and emerging climatic risks pose operational and maintenance challenges, highlighting the need for innovative strategies and digital solutions to unlock its full sustainability and flexibility potential. This Special Issue will explore digital solutions, innovative technologies, and operational strategies that can unlock the sustainability and flexibility potential of hydropower.

We invite contributions that address technical, economic, environmental, and social dimensions of this transition, including topics such as the following:

Digitalization for predictive maintenance, efficiency improvement, and safer operation;
Hybridization of hydropower with other renewable energy sources;
Enhancing flexibility and ancillary services provision;
Environmental and social aspects of hydropower operation under changing climatic conditions;
Policy and market frameworks for sustainable and flexible hydropower.

By bringing together diverse perspectives, the Special Issue aims to highlight how hydropower can continue to play a pivotal role in the renewable energy future, while ensuring resilience, sustainability, and alignment with the broader goals of the green and digital transitions.

Dr. Vassiliki T. Kontargyri
Prof. Dr. Theodoros I. Maris
Guest Editors

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Keywords

flexible operation of hydropower plants
control strategies in hydropower systems
optimization techniques for hydropower flexibility
hydraulic and turbine dynamics
pumped hydro energy storage systems
techno-economic assessment
digital twin in hydropower
dynamic operation modeling
data management algorithms
hydropower technologies

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Published Papers (5 papers)

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Research

18 pages, 1066 KB

Open AccessArticle

Impact of Air Temperature Variation on a Wind-Driven Desalination System with Pumped-Hydro Storage: A Case Study of the Regional Unit of Rethymno, Crete, Greece

by Athanasios-Foivos Papathanasiou, Daniil Michail Pitsikalis and Evangelos Baltas

Energies 2026, 19(15), 3507; https://doi.org/10.3390/en19153507 - 25 Jul 2026

Viewed by 273

Abstract

Water scarcity and increasing energy demand are critical challenges that often characterize Mediterranean regions, especially islands such as Crete. A sustainable solution for a combined water and energy supply lies in the domain of hybrid renewable energy systems. This research study evaluates a large-scale wind-driven desalination system with pumped-hydro energy storage for the Regional Unit of Rethymno, Crete, focusing on climate-driven demand and air temperature variation. The proposed system integrates wind energy production, seawater desalination, pumped-hydro storage, and water supply both for domestic and for irrigation purposes. Four scenarios, each with increasing air temperature, are examined in order to assess their effect on water demand and system performance. The analysis evaluates electricity allocation, the production of desalinated water, domestic and irrigation coverage, as well as the economic performance of the system. The results indicate that domestic water demand is almost fully covered in all four scenarios, reaching nearly 99.9%, while irrigation water coverage decreases from 82% under present conditions to 67% under higher-temperature scenarios. Wind-generated electricity is mainly used for water-related processes, with a constant share supplied to the grid. The economic assessment indicates that the system can operate under break-even conditions using realistic water and electricity prices. Full article

(This article belongs to the Special Issue Flexibility Solutions and Innovations for Sustainable Hydropower)

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29 pages, 31532 KB

Open AccessArticle

Reconstruction and CFD Modeling of a Kaplan Turbine for Digital Twin Applications

by Przemysław Szulc, Vassiliki T. Kontargyri, Oleksandr Moloshnyi, Artur Machalski, Aneta Nycz, Janusz Skrzypacz, Magdalena Nemś, Dominik Błoński, Przemysław Janik and Zuzanna Satława

Energies 2026, 19(14), 3341; https://doi.org/10.3390/en19143341 - 15 Jul 2026

Viewed by 401

Abstract

Developing digital twins for legacy hydropower units is difficult when turbine documentation, calibrated performance data, and integrated measurements are incomplete. This study presents a Computational Fluid Dynamics (CFD)-assisted reconstruction workflow for a Kaplan turbine at the Wały Śląskie Hydropower Plant and evaluates its use as a physics-informed foundation for a digital twin. The flow passage was reconstructed from archival documentation, direct measurements, and optical 3D scanning of the runner. A steady-state Reynolds-averaged Navier–Stokes model was then prepared in OpenFOAM v2506 for selected head levels, guide-vane openings, and runner-blade angles. The simulations determined hydraulic performance, flow-field structures, and combinatory characteristics of the double-regulated turbine. The computed hydraulic efficiency reached approximately 85% in the nominal-head range, and the highest-efficiency region formed a broad plateau rather than a sharp optimum. CFD-derived and measurement-derived combinatory trends were consistent, although absolute values remain limited by relative field measurements and uncalibrated Winter–Kennedy flow estimation, a differential-pressure-based method. The CFD results were reduced to compact response surfaces and integrated with reconstructed geometry into an advisory digital twin for operating-point assessment, visualization, documentation, and training. This study establishes a robust workflow for this specific Kaplan turbine case where reverse engineering, integrated with CFD analysis, generates high-fidelity surrogate models for hydropower digital twins, effectively addressing the challenge of incomplete legacy documentation. Full article

(This article belongs to the Special Issue Flexibility Solutions and Innovations for Sustainable Hydropower)

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24 pages, 62397 KB

Open AccessArticle

Slope Stability Evaluation of Earthen Hydraulic Structures at the Dychów Pumped-Storage Power Plant by Electrical Resistivity Tomography and Finite-Element Modelling

by Łukasz Dominik Kaczmarek, Jacek Stasierski, Jacek Kostrzewa, Adam Lubowicki, Kacper Piekarski, Piotr Drużyński, Tadeusz Daszczyński and Maciej Filip Gruszczyński

Energies 2026, 19(14), 3326; https://doi.org/10.3390/en19143326 - 14 Jul 2026

Viewed by 365

Abstract

Pumped-storage hydropower (PSH) remains the main grid-scale energy storage technology in Europe, yet much of the fleet is ageing and requires periodic verification against current geotechnical standards. The Dychów plant (88 MW, western Poland), in service since the 1930s and classified as national critical energy infrastructure, has a documented history of surface mass movements, including a 1997 landslide on the frontal dam. To reassess its condition, two earthen sections were analysed: lateral section of the frontal dam of the upper reservoir and the embankment of the derivation channel. Electrical resistivity tomography (ERT) profiles, measured using a gradient array in 2023 and further detailed in 2024 along the same GNSS-fixed lines, imaged the internal structure of both sections. The resistivity cross-sections, verified against shallow control boreholes and archival geological data, supplied the geometry of the finite-element (FEM) models in ZSoil: the confirmed layer boundaries became the material zones, and piezometric observations set the groundwater boundary conditions. The safety factor SF was then computed with the shear-strength reduction technique for four calculation variants and two groundwater scenarios per section. The resulting SF equals 1.75 for the side section of the frontal dam area and ranges from 1.80 to 2.10 for the channel embankment. A parametric reduction in the friction angle of saturated medium sand gives limit values of φ = 12.3° (dam) and φ = 20.3° (embankment), which are clearly below realistic in situ values. Overall, both structures meet the SF ≥ 1.50 requirement for Class I hydraulic structures. The ERT-to-FEM workflow offers a non-invasive and repeatable tool for the periodic reassessment of ageing PSH infrastructure, which continues to balance variable renewable generation. Full article

(This article belongs to the Special Issue Flexibility Solutions and Innovations for Sustainable Hydropower)

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18 pages, 8946 KB

Open AccessArticle

Joint Scheduling and Coordinating Operation of a Mega Hydropower System Based on Gaussian Radial Basis Functions and the Borg Algorithm in the Upper Yangtze River, China

by Shenglian Guo, Chenglong Li, Bokai Sun, Xiaoya Wang, Peng Li and Le Guo

Energies 2026, 19(10), 2352; https://doi.org/10.3390/en19102352 - 14 May 2026

Viewed by 448

Abstract

A large number of reservoirs (or hydropower plants) have been constructed for flood control and energy production in the past several decades in the Yangtze River basin in China. The conventional scheduling rule curves (Scheme A) were designed in the reservoir construction period and did not consider river flow alternation, which needs to be modified to increase comprehensive benefits in the reservoir operation period. In this study, six large-scale cascade reservoirs or mega hydropower systems constructed and operated by the China Yangtze Three Gorges Corporation were selected for this case study. The current joint scheduling plans of cascade reservoirs (Scheme B) were introduced, and a joint scheduling and multi-objective coordinating operation model (Scheme C) was proposed for this mega hydropower system. The Gaussian radial basis functions (GRBFs) were used to fit operation policies of each reservoir, and the Borg multi-objective evolutionary algorithm was selected to optimize three-objective functions for Scheme C. The observed daily flow data series at main hydrometric stations from 2003 to 2025 were used to simulate and compare different operation scheduling schemes. The results show that the performance of joint scheduling of cascade reservoirs (both Schemes B and C) is much better than the single-reservoir scheduling (Schemes A) with overall benefit; Scheme C-best achieves a comprehensive target of decreasing average annual spillway wastewater by 12.82 billion m³ (or a decrease of 28.5%), increasing average annual power generation by 31.02 billion kWh (or an increase of 10.7%), and improving average annual impoundment efficiency rate by 5.0%. The GRBFs can fit reservoir operation policies well, while the Borg multi-objective evolutionary algorithm can quickly converge with high-precision non-dominated solution sets. The proposed joint scheduling and multi-objective coordinating operation model will provide a scientific basis for achieving maximum benefits in flood protection and hydropower generation for the mega hydropower system. Full article

(This article belongs to the Special Issue Flexibility Solutions and Innovations for Sustainable Hydropower)

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35 pages, 7589 KB

Open AccessArticle

Numerical Study on the Performance of a Gravitational Water Vortex Hydro-Turbine System with a Cylindrical Basin

by Nosare Maika, Mehdi Khatamifar and Wenxian Lin

Energies 2026, 19(5), 1334; https://doi.org/10.3390/en19051334 - 6 Mar 2026

Viewed by 1376

Abstract

Gravitational water vortex power systems are one of the cost-effective systems of extracting low head hydro power. This study investigates numerically a gravitational water vortex power system five-blade turbine rotating in a cylindrical basin for three blade shapes (flat, curved, and vertical twist) and three diameters of the discharge orifice at the basin bottom. The numerical simulations adopted a scaled down model using the Froude number similarity and employed the Volume of Fluid, Moving Reference Frame, and SST

k - ω

turbulence model. The system performance was examined both qualitatively and quantitatively for five turbine rotation speeds over 40–120 revolution/minute (RPM). It was found that blade shape, orifice diameter, and turbine rotation speed have significant effects on system performance. For a specific blade shape and discharge orifice diameter combination, the generated torque and power increases almost linearly at a large rate when the turbine rotation speed is increased from 40 RPM to 80 RPM and then decreases, also essentially linearly, at a much smaller rate from 80 RPM to 120 RPM. The optimal rotation speed was found to be 80 RPM across the speeds considered for all cases. It was also shown that the system with an intermediate diameter ratio performs better for each blade shape and the system with the curved blades performs better than the other two blade shapes. The results further show that for the cases considered, the most favorable operating condition was achieved by using a combination of a five-bladed curved turbine, a medium discharge orifice diameter (

d_{o} / D \approx 0.16

) in a cylindrical basin, and a rotational speed of 80 RPM, yielding relatively the highest efficiency of up to 62%, which are very good outcomes for such low head hydropower systems. Full article

(This article belongs to the Special Issue Flexibility Solutions and Innovations for Sustainable Hydropower)

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