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This paper presents the results of experimental research focused on wave energy harvesting and its conversion to power Internet of Things (IoT) devices. The harvesting and conversion process was performed using a wave energy converter (WEC) consisting of a lead zirconate titanate piezoelectric ceramic perovskite material and a prototype power electronic circuit. The designed WEC was considered as a power supply for an end node device (END) of an IoT network. The END consisted of a long-range radio module and an electronic paper display. A set of physical experiments were carried out, and the results confirmed that an energy surplus was supplied by WEC compared to the energy consumed by the END. Hence, the proposed scheme was experimentally validated as a convenient solution that could enable the autonomous operation of an IoT device. The use case presented here for the proposed WEC was analysed for selected sea areas on the basis of wave statistics. The novelty of this paper arises from an investigation that confirms that WECs can significantly contribute to the development of wireless and mobile IoT communication powered by freely available sea wave energy. [ABSTRACT FROM AUTHOR]

This paper examines the intersection of regional geopolitics and the governance of transboundary rivers using the case studies of multipurpose reservoirs in Himalayan South Asia. It uncovers the various ways Indian hydrocracy uses its institutional and technical expertise to strengthen India's centrality in Nepal's water and hydropower sectors. The practices of security undertaken by the hydrocrats are classified as structural, institutional, and statutory acts. By focusing on practices of an epistemic community like hydrocrats, this paper addresses longstanding weaknesses of the securitisation theory of being elitist and ignoring the agency of mid-level bureaucrats. It also highlights the constructivist nature of international politics. The findings contribute empirically to securitisation theory's 'Paris School' of thought. [ABSTRACT FROM AUTHOR]

Hydropower and photovoltaic power are widely used as clean energy sources around the world. Hydro-Photovoltaic complementary is precisely the use of the regulation performance of hydropower stations and the peak regulation performance of PV electric fields to improve the system's power generation efficiency. The Yalong River basin as one of China's clean energy bases, is rich in water and light resources. And now its midstream Yangfanggou hydropower station has just been completed, and the relevant PV electric field is in the construction planning stage. It is worth studying how to effectively utilize its hydropower and PV output resources. Therefore, Yangfanggou hydropower station and its PV electric field are taken as the research objects in this paper. The possibility of hydro-photovoltaic complementarity is analyzed within the year and day respectively. Then, a short-term scheduling model of hydrophotovoltaic complementarity is constructed according to the principle, and its operation mode and effect are optimized using the genetic algorithm NSGA-II. The results indicate that the annual power generation of the system is increased by about 1.4 billion kWh from the original hydropower through the hydrophotovoltaic complementary, and the annual guaranteed output is also increased with a large increase degree at the same time. [ABSTRACT FROM AUTHOR]

This paper addresses the critical need to determine the stable operating limit of modular multilevel converter-based high voltage direct current (MMC-HVDC) systems, particularly concerning the integration of extensive renewable energy sources. To achieve this, the steady-state mathematical model and state-space model of bundled hydropower and photovoltaic integration through MMCHVDC systems are established. A novel methodology considering steady-state and small-signal stability constraints is proposed to compute the stable operating region of the system. The quantitative assessment reveals that diminishing AC system short-circuit capacities amplify restrictions from small-signal stability constraints, thereby reducing the system's stable operating region. Eigenvalue and participation factor analyses shed light on the pivotal factors affecting smallsignal stability in weak AC systems. To expand the system's stable operating region, a supplementary frequency damping control strategy is proposed. The theoretical analysis and calculation results are validated by building a simulation model for the bundled hydropower and photovoltaic integration through MMCHVDC systems in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

This paper presents the results of the design process focused on the development of the energy subsystem (ES) of a wave energy converter (WEC). The ES is an important electrical part that significantly affects the energy reliability and energy efficiency of the entire WEC device. The designed ES was intended for compact WECs powering IoT network devices working in the distributed grid. The developed ES is an electronic circuit consisting of three cooperating subsystems used for energy conversion, energy storage, and energy management. The energy conversion subsystem was implemented as a set of single-phase bridge rectifiers. The energy storage subsystem was a battery-less implementation based on the capacitors. The energy management subsystem was implemented as a supervisory circuit and boost converter assembly. The designed ES was verified using the physical experiment method. The model experiment reflected the operation of the designed ES with a piezoelectric PZT-based WEC. The experimental results showed a 41.5% surplus of the energy supplied by ES over the energy demanded by the considered load at a duty cycle of ca. 6 min—37.2 mJ over 26.3 mJ, respectively. The obtained results have been evaluated and discussed. The results confirmed the designed ES as a convenient solution, which makes a significant contribution to the compact WECs that can be applied among others to a distributed grid of autonomous IoT network devices powered by free and renewable energy of sea waves. Finally, it will also enable sustainable development of mobile and wireless communication in those maritime areas where other forms of renewable energy may not be available. [ABSTRACT FROM AUTHOR]

Renewable energy mini-grids are considered a cost-effective way to provide electricity for a large proportion of the population in developing countries who do not have access to it. Compared with standalone home systems and national grid systems, mini-grids can potentially offer a better service. They can be deployed faster, making them essential for sustainable development, especially in rural and semi-urban areas of developing countries. However, mini-grids often face challenges regarding their resilience, and many fail to survive beyond their pilot phases. This paper aims to identify the factors contributing to the success of mini-grids and to identify common themes that can help existing and future mini-grid developments become more resilient and influence policy decision making. To achieve this goal, we developed a database of the status of mini-grids in Malawi, with the energy generation resource(s) of their installed capacity, enabling factors, and challenges. We undertook a more detailed investigation of two hydro mini-grid systems—Bondo and Chipopoma. We collected qualitative and quantitative data through literature reviews, site visits, interviews, and observations. The study identified 19 mini-grids with a combined installed capacity of 26 MW. Of these, seven had been abandoned, and one was under development. Several factors that affect successful mini-grid efficacy in Malawi were identified, including financial resourcefulness, technical resourcefulness, policies and regulations, community engagement and capacity building, cross-sector linkages, and institutional organisational frameworks. These factors need to be integrated into decision making by all stakeholders to ensure the enhancement of resilience and the sustainable development of mini-grids. [ABSTRACT FROM AUTHOR]

Hydropower plants (HPPs) create barriers across rivers and fragment aquatic ecosystems, river reaches and habitats. The reservoirs they create slow the flowing water and convert the riverine into lacustrine ecosystems. The barriers created by HPPs interrupt the seasonal migrations of many fish species, while the reservoirs drive away fish species that are dependent on flowing water habitats. This paper assesses the distribution of fish species in the 3S rivers—Sekong, Sesan and Sre Pok, in Cambodia, Laos and Viet Nam—using IUCN Red List-assessed species distribution by HydroBasin Level 8 from the freshwater reports of the Integrated Biodiversity Assessment Tool (IBAT) and their connectivity with the Mekong. There are currently 61 commissioned dams in the 3S basins and a further 2 under construction, 23 of which are larger than the 30 MW installed capacity. A further 24 HPPs are proposed or planned in these basins. The changes in connectivity caused by the dams are measured by adapting the River Class Connectivity Index (RCICLASS); the original connectivity of the 3S basin taking into account the two major waterfalls in the Sesan and Sre Pok rivers was estimated at 80.9%. With existing dams, the connectivity has been reduced to 23.5%, and with all planned dams, it is reduced further to 10.9%. The resulting re-distribution of fish species occurring throughout the 3S basins is explored, by focusing on migratory guilds and threatened and endemic fish species. With all dams built, it is predicted that the total numbers of species in HydroBasins above the dams will be reduced by 40–50%. The Threatened Species Index is estimated to fall from over 30 near the confluence of the three rivers to less than 10 above the lowest dams on the 3S rivers. The analysis demonstrates how widely available global and regional datasets can be used to assess the impacts of dams on fish biodiversity in this region. [ABSTRACT FROM AUTHOR]

The economic operation of hydropower stations has the potential to increase water use efficiency. However, there are some challenges, such as the fixed and unchangeable flow characteristic curve of the hydraulic turbines, and the large number of variables in optimal load distribution, which limit the progress of research. In this paper, we propose a new optimal method of the economic operation of hydropower stations based on improved Long Short-Term Memory neural network (I-LSTM) and Random Forest (RF) algorithm. Firstly, in order to accurately estimate the water consumption, the LSTM model's hyperparameters are optimized using improved particle swarm optimization, and the I-LSTM method is proposed to fit the flow characteristic curve of the hydraulic turbines. Secondly, the Random Forest machine learning algorithm is introduced to establish a load-distribution model with its powerful feature extraction and learning ability. To improve the accuracy of the load-distribution model, we use the K-means algorithm to cluster the historical data and optimize the parameters of the Random Forest model. A Hydropower Station in China is selected for a case study. It is shown that (1) the I-LSTM method fits the operating characteristics under various working conditions and actual operating characteristics of hydraulic turbines, ensuring that they are closest to the actual operating state; (2) the I-LSTM method is compared with Support Vector Machine (SVM), Extreme Learning Machine (ELM) and Long Short-Term Memory neural network (LSTM). The prediction results of SVM have a large error, but compared with ELM and LSTM, MSE is reduced by about 46% and 38% respectively. MAE is reduced by about 25% and 21%, respectively. RMSE is reduced by about 27% and 24%, respectively; (3) the RF algorithm performs better than the traditional dynamic programming algorithm in load distribution. With the passage of time and the increase in training samples, the prediction accuracy of the Random Forest model has steadily improved, which helps to achieve optimal operation of the units, reducing their average total water consumption by 1.24%. This study provides strong support for the application of intelligent low-consumption optimization strategies in hydropower fields, which can bring higher economic benefits and resource savings to renewable energy production. [ABSTRACT FROM AUTHOR]

Tajikistan holds the eighth position globally in terms of hydropower potential, estimated at 527 terawatt-hours (TWh), with a technically exploitable capacity of 317 TWh. Only 4–6 percent of this immense potential is currently utilized. In this paper, employing a combination of the Johansen cointegration test, vector autoregression, and the Granger-causality test on annual data from 1993 to 2021, we examine the causality relationship between electricity production and key macroeconomic variables, including gross domestic product (GDP), GDP per capita, exports, imports, final consumption, capital investment, and employment, in Tajikistan. The empirical findings reveal a positive unidirectional causality from electricity production to exports and imports. A positive bidirectional or feedback causality is found between electricity production and variables such as GDP, GDP per capita, final consumption, and employment. No causality relationship between electricity production and variables such as trade openness and capital investment is observed. The exploration of complex causal relationships between electricity production and key macroeconomic variables in Tajikistan, as revealed in this study, offers a modest yet meaningful addition to academic discourse. It presents insights that may inform policymakers and stakeholders, albeit with a recognition of the limitations inherent in the findings. These insights could potentially guide the formulation of sustainable development strategies and shed light on the underutilized potential of the country's hydropower resources. [ABSTRACT FROM AUTHOR]

Hydropower as a renewable source can help many countries achieve their sustainable energy and climate goals, but large projects are challenging to finance because of their costs and risks. To fully realize the climate benefits of such projects, sponsors have recently fashioned complex financing arrangements that structure and allocate risks to reduce financing costs. This paper focuses on the blended financing approach adopted for the Nachtigal Hydropower Plant (NHP) in Cameroon. The purpose of the paper is to present a detailed systems analysis of Nachtigal's financial arrangement to address the question of why the complex financing approach worked in practice. We accomplish this by creating a "financial simulator"—a computational model for evaluating risks and incentives embedded within the financing structure under different contract architectures and risk–event scenarios. Our simulator is a dynamic value–risk calculator that can be easily updated to study other climate-oriented projects that involve complex financial arrangements. We evaluated three aspects of the financing/contractual arrangements that made Nachtigal "bankable:" (i) guarantees that covered nonpayments, (ii) financial options on locally sourced loans; and (iii) an interest rate swap. We found: (i) the guarantees recovered project value threatened by four specific risks often associated with large hydropower investments (cost overruns, schedule delays, offtake risk, and low flow due to climate change); (ii) the mechanism significantly lowered interest rate charges; and (iii) private finance was mobilized—especially due to the options. The financial safeguards employed increased the likelihood of capturing the long-run sustainability benefits from NHP. [ABSTRACT FROM AUTHOR]

Although the movement of people from rural to urban areas has caused the increased use of energy, the abundance of water resources can be made into a form of renewable energy known as hydroelectricity. As European countries are ranked as the first users and exporters of hydropower, the production of renewable energy in developed countries such as the Nordic region has caused great impacts on economic growth and human development. The importance of this paper is to investigate the relationship between hydroelectricity and the Human Development Index by depending on some variables such as urbanization, rule of law, corruption, trade openness, and GDP per capita from 2002 to 2021 in Nordic countries. The results were estimated depending on impulse response function after conducting the Vector autoregressive model (VAR) model and Granger causality test. Results showed a negative impact from hydro plants in the short run but a significant positive impact in the long run in Nordic countries. The long-term sustainment of Human Development Index (HDI) is due to policies limiting the immigration of labor as well as protection of energy use. Water batteries are gaining popularity across Europe and their implementation is near mandatory. [ABSTRACT FROM AUTHOR]

Water system management models represent different purposes, such as water supply, flood control, recreation, and hydropower. When building large-scale system models to represent these diverse objectives, their most appropriate time steps for each purpose often do not coincide. A monthly time step is usually sufficient for water supply modeling, but it can be too coarse for flood control, hydropower, and energy operations, where hourly time steps are preferred. Large-scale water management and planning models mostly employ monthly time steps, but using monthly average energy prices underestimates hydropower revenue and overestimates pumping energy cost because these plants tend to operate during times with above- or below-average energy prices within any month. The approach developed here uses hourly varying prices depending on the percent of monthly operating hours. This paper examines an approach that approximately incorporates hourly energy price variations for hydropower and pumping into large-scale monthly time-step water system model operations without affecting water delivery results. Results from including hourly varying energy prices in a large-scale monthly water supply model of California (CALVIN) are presented. CALVIN is a hydroeconomic linear programming optimization model that allocates water to agricultural and urban users with an objective to minimize total scarcity costs, operating costs, and hydropower revenue loss. Thirteen hydropower plants are modeled with hourly varying prices, and their revenue increased by 25 to 58% compared to revenue calculated with monthly average constant energy prices. Hydropower revenue improvements are greater in critically dry years. For pumping plants modeled with hourly varying prices, the energy use cost decreased by 10 to 59%. This study improves system representation and results for large-scale modeling. [ABSTRACT FROM AUTHOR]

Despite the reliability and flexibility of hydropower, the operation of hydroelectric power plants may have significant impacts on the downstream river system, including its water stage, sediment transport, and water temperature, ultimately affecting the ecology. To address these challenges, there is a need to identify water scheduling patterns that improve both hydropower economics and the environment relative to current operations. This paper presents a new methodology to explore promising operational criteria/rules that can achieve such improvements. Typical environmental impact statements and relicensing processes generally perform detailed site-specific analyses of a few alternatives that focus on reservoir water release operating rules and their associated environmental impacts. In contrast, the methodology presented in this article uses a widely applicable approach that explores a much larger solution space. This large set of potential alternatives can be represented in a multidimensional space for which one axis represents the economic value and the other axis quantify individual environmental impacts (e.g., sediment transport and fish growth), and they are explored via two approaches: a Monte Carlo simulation that identifies "win–win" alternatives and a multi-objective optimization problem that identifies Pareto-optimal alternatives. [ABSTRACT FROM AUTHOR]

The Pelton turbine has been widely regarded as the most efficient hydro turbine for high-head applications. However, the Pelton turbine buckets, especially the area commonly referred to as the 'splitter', are highly susceptible to erosion, drastically reducing efficiency over prolonged periods of time. This paper demonstrates a novel turbine idea that has been validated through both computational and experimental methods. This turbine addresses the issues associated with the erosion of the splitter through a redesign of the Pelton turbine to remove the need for a splitter and therefore potentially reducing downtime due to maintenance. The computational fluid dynamics (CFD) simulation results show that the turbine is capable of efficiencies greater than 82% with room for further improvement. The practical experimental results also show efficiencies within 6% of an optimized Pelton turbine. The results from this study indicate that through further optimization this turbine design could provide a means to produce power outputs similar to conventional Pelton turbines, with the added benefit of lower maintenance costs. [ABSTRACT FROM AUTHOR]

To make clear the influence of renewable energy on ultra-low-frequency oscillation (ULFO) in a hydro-dominant system via an high voltage direct current (HVDC) transmission system, this paper studies the damping characteristics when wind power is integrated into the sending power system. The damping torque method is applied for the mechanism study and risk evaluation of ULFO. The study of the inner cause and outer performance proves that ULFO belongs to frequency oscillation rather than conventional power oscillation. According to the theoretical analysis, the suggested control mode is identified to reduce the risk of ULFO. Moreover, a robust controller is designed for wind units based on mixed H2/H∞ robust control theory, and the control method makes use of the fast response ability of the converter without compromising the primary frequency regulation ability. Finally, a simulation model of a hydro-dominant sending power system with wind integration is established in PSCAD Version 4.6 software. The simulations verify the proposed control can suppress ULFO effectively. [ABSTRACT FROM AUTHOR]

Kaplan turbines, as one of the well-known hydraulic turbines, are generally utilized worldwide for low-head and high-flow conditions. Any failure in each of the turbine components can result in long-term downtime and high repair costs. In a particular case, if other parts are damaged due to the impact of the broken blades (e.g., the main shaft of the turbine), the whole power plant may be shut down. On the other hand, further research on the primary causes of failures in turbines can help improve the present failure evaluation methodologies in power plants. Hence, the main objective of this paper is to present the major causes of Kaplan turbine failures to prevent excessive damage to the equipment and provide practical solutions for them. In general, turbines are mainly subjected to both Internal Object Damage (IOD) and Foreign Object Damage (FOD). Accordingly, this paper presents a state-of-the-art review of Kaplan turbine failures related to material and physical defects, deficiencies in design, deficits in manufacturing and assembly processes, corrosion failures, fatigue failure, cavitation wear, types of cavitation in hydro turbines, hydro-abrasive problems, and hydro-erosion problems. Eventually, the authors have attempted to discuss practical hints (e.g., nanostructured coatings) to prevent damages and improve the performance of Kaplan turbines. [ABSTRACT FROM AUTHOR]

As ecological civilization construction receives growing attention in China, the eco‐friendliness of the power supply structure is becoming increasingly important. Thermal power and hydropower are the two major power sources in China. Hydropower has both positive and negative effects on the ecosystem. However, there are few studies on the comprehensive impact of hydropower on the ecosystem. Therefore, the main innovation of this article is to integrally and comprehensively study the impact of hydropower to propose recommendations for hydropower development. The study of hydropower's effects on the overall ecosystem including resources, the environment, and economic society reflects the integrity, and the simultaneous study of hydropower's positive and negative effects reflects the comprehensiveness. First, this paper constructs a system dynamics (SD) model that can analyze the impact of replacing thermal power with hydropower on the ecosystem and proposes an improved coupling coordination degree (CCD) model. Then, this paper takes the province of Fujian as an example for SD scenario simulation and proposes recommendations for each indicator in the ecology subsystem. Finally, this paper performs CCD analysis on subsystems of the ecology subsystem in different policy scenarios and provides suggestions for future hydropower development in Fujian. Results show that hydropower technology improvement and efficiency increase (HTIEI) is more conducive to the development of the overall ecosystem. The scientificity of the current hydropower policy in Fujian is proven through theoretical analysis, and further hydropower development proposals are proposed. This paper provides a basis for the formulation of power generation policies and promotes ecological civilization construction for Fujian. The proposed methods in this paper can also provide tools for policy research on clean energy power generation. [ABSTRACT FROM AUTHOR]

Leakages in water distribution systems (WDSs) profoundly affect their operations, elevating water production demand and treatment and pumping costs. Moreover, they strain the energy system by increasing power requirements at pumping stations. In regions heavily reliant on hydropower, such as Brazil, there is a nuanced implication: diminishing reservoir water levels due to increased WDS flow withdrawal. This not only immediately affects hydropower generation by reducing available head but, over time, may lead to interruptions in hydropower generation. This paper investigates the water–energy nexus, specifically focusing on WDS leakages in Brazil. It begins with an overview of the current situation and future outlook, considering evolving policies to enhance WDS efficiency and also the evaluation of different climate change scenarios. A more in-depth case study explores a reservoir utilized for both energy and water production. In this context, leakage management assumes critical importance, given the various water uses within the reservoir that impact the available energy and water resources. Overall, this study offers a comprehensive perspective on the water–energy nexus within WDSs, underscoring the critical importance of leakage control and its direct and indirect consequences, particularly on energy generation capacity, the environment, and the economy. [ABSTRACT FROM AUTHOR]

All long-term hydropower planning problems require a forecast of the inflow during the planning period. However, it is challenging to accurately forecast inflows for a year or more. Therefore, it is common to use stochastic models considering the uncertainties of the inflow. This paper compares deterministic and stochastic models in a weekly rolling horizon framework considering inflow uncertainty. The stochastic model is tested in both a risk-neutral and a risk-averse version. The rolling horizon framework helps make periodic decisions and update the information in each rolling week, which minimizes the errors in prolonged forecasts. The models aim to utilize the water stored in the rainy season throughout the year with minimum load shedding while storing as much water as possible at the end of the planning horizon. The Conditional Value at Risk ( C V a R ) risk measure is used to develop the risk-averse stochastic model. Three different risk measures are investigated to choose the risk measure that yields the best outcome in the risk-averse problem, and the two best measures are compared to a deterministic and risk-neutral model in a weekly rolling horizon framework. The results show that the risk-neutral and best risk-averse models perform almost equally and are better than the deterministic model. Hence, using a stochastic model would be an improvement to the actual planning performed in the Ethiopian and other African countries' power systems. [ABSTRACT FROM AUTHOR]

Since the early 1970s, as part of India's developmentalist agenda, a number of hydropower dams have been built in Manipur, the country's north-eastern-most State bordering Myanmar. However, none of the mega-dams built in the State have proven to be effective and fully functional today. Civil Society Organisations (CSOs) have been vocal in their opposition to mega-dams due to their negative effects on the environment and the livelihood security of local populations. Based on secondary data, historical antecedents, personal field information, and observable facts, this paper indicates that the Indian state's developmentalist approach begun in Manipur is roughly analogous to the western development model initiated during the cold war period. Despite overwhelming proof of Manipur's mega-dam failure, the Centre refuses to admit it and ignores CSO demands, and the failed mega-dams are unlikely to be decommissioned due to the Centre's clandestine objective. The hanger-on approach of several CSO leaders and local political figures who are subservient to the Centre's high command has gradually delegitimised and politicised genuine dam campaigns in Manipur. [ABSTRACT FROM AUTHOR]

In today's intrinsically connected world, the Water–Food–Energy–Climate Nexus (WFEC Nexus) concept provides a starting point for informed and transparent decision-making based on the trade-offs and synergies between different sectors, including aquatic ecosystems, food security, energy production, and climate neutrality. The WFEC Nexus approach is particularly applicable in regions requiring transboundary water management, such as Central Asia. Unfortunately, this region with unevenly distributed water resources—consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan—is characterized by data scarcity, which limits informed decision-making. However, open-source geodata is becoming increasingly available. This paper aims to fill Central Asia's WFEC Nexus data gap by providing an overview of key data. We collected geodata through an integrated survey of stakeholders and researchers, stakeholder consultation, and literature screening. Sixty unique datasets were identified, belonging to one of six thematic categories: (1) climate, (2) hydrology, (3) geography and topography, (4) geomorphology, (5) ecology, and (6) anthropogenic uses. For each dataset, a succinct description, including a link to the online source, is provided. We also provide possible applications of using the presented datasets, demonstrating how they can assist in conducting various studies linked to the WFEC Nexus in Central Asia and worldwide. [ABSTRACT FROM AUTHOR]

Planet Earth is simultaneously approaching a number of ecological and resource limits. The resulting uncertainties will heavily impact future energy choices, both the level of primary energy used globally and the shares of fossil, renewable and nuclear fuels in the energy mix. This paper reviews the possible futures for the various types of renewable energy. To be viable, all potential energy sources must be assessed on their energy return on energy invested (energy return). Given that renewable energy RE growth is considered important for sustainability reasons, renewable energy must be assessed on its ecologically sustainable or 'green' energy return, which includes the energy costs of ecosystem maintenance as input energy costs. The green energy return is accordingly much lower than the conventional value, so that ecologically sustainable renewable energy is unlikely to deliver anything near existing global energy use. The paper further argues that such constraints on renewable energy growth rates mean it cannot be a timely response to global climate change. The paper concludes that energy reductions will be essential, mainly in high energy use countries. [ABSTRACT FROM AUTHOR]

The energy crisis is affecting a number of countries, but particularly those that are heavily dependent on the traditional energy generation formula (e.g., Poland), as well as those neighbouring the territory of the ongoing war in Ukraine, i.e., Poland, Lithuania, Latvia and Estonia. With this in mind, the authors of this study decided to explore the issue of water energy as a source of green (cheap and environmentally safe) energy in these countries. The main objective of the paper is to review the available literature, which is needed to identify the role hydropower plays in energy security and energy transition in these energy markets. This paper is based on a review and critical appraisal of the available literature and studies together with an inference. The structure of the paper consists of an introduction, the main part of the review and conclusions. The geopolitical location and socio-economic conditions of the adopted set of countries, form the basis of the review of the existing literature on the theme explored and the substantive inference. The main findings of this review indicate that the literature is most strongly focused on the overall assessment of the energy transition of the adopted countries for review, where the hydropower thread is most often taken up as one source of renewable energy supply. Hydropower, due to its relatively low share in the energy systems of the adopted set of countries, is, according to the authors, insufficiently explored. The most significant gap relates to the aspect of the potential for hydropower development in these areas, considering both the construction of new hydropower plants and opportunities signalled in the literature for the modernisation or restoration of existing ones. In this respect, the need for analyses (studies and simulations) of hydropower development, considering the economic benefits associated with their development juxtaposed with the safety dimension of this course of action for the environment (analysis and assessment of environmental costs) is indicated, which is the main recommendation of the review. [ABSTRACT FROM AUTHOR]

Double-regulated Kaplan turbines with adjustable guide vanes and runner blades offer a high degree of flexibility and good efficiency for a wide range of operating points. However, this also leads to a complex geometry and flow guidance with, for example, vortices of different sizes and strengths. The flow in a draft tube is especially challenging to simulate mainly due to flow phenomena, like swirl, separation and strong adverse pressure gradients, and a strong dependency on the upstream flow conditions. Standard simulation approaches with RANS turbulence models, a coarse mesh and large time step size often fail to correctly predict performance and can even lead to wrong tendencies in the overall behavior. To reveal occurring flow phenomena and physical effects, a scale-resolving hybrid RANS-LES simulation on a block structured mesh of about 400 million hexahedral elements of a double-regulated five-blade model Kaplan turbine is carried out. In this paper, first, the results of the ongoing simulation are presented. The major part of the simulation domain is running in LES mode and seems to be properly resolved. The validation of the simulation results with the experimental data shows mean deviations of less than 0.8% in the global results, i.e., total head and power, and a good visual agreement with the three-dimensional PIV measurements of the velocity in the cone and both diffuser channels of the draft tube. In particular, the trend of total head and the results for the draft tube differ significantly between the scale-resolving simulation and a standard RANS simulation. The standard RANS simulation exhibits a highly unsteady behavior of flow, which is not observed in the experiments or scale-resolving simulation. [ABSTRACT FROM AUTHOR]

The structural dynamic response of hydraulic turbines needs to be continuously monitored to predict incipient failures and avoid catastrophic breakdowns. Current methods based on traditional off-board vibration sensors mounted on fixed components do not permit inferring loads induced on rotating parts with enough accuracy. Therefore, the present paper assesses the performance of fiber Bragg grating sensors to measure the vibrations induced on a rotating shaft–disc assembly partially submerged in water resembling a hydraulic turbine rotor. An innovative mounting procedure for installing the sensors is developed and tested, which consists of machining a thin groove along a shaft line to embed a fiber-optic array that can pass through the bearings. At the top of the shaft, a rotary joint is used to extract, in real time, the signals to the interrogator. The shaft strain distribution is measured with high spatial resolution at different rotating speeds in air and water. From this, the natural frequencies, damping ratios, and their associated mode shapes are quantified at different operating conditions. Additionally, the change induced in the modes of vibration by the rotation effects is well captured. All in all, these results validate the suitability of this new fiber-optic technology for such applications and its overall better performance in terms of sensitivity and spatial resolution relative to traditional equipment. The next steps will consist of testing this new sensing technology in actual full-scale hydraulic turbines. [ABSTRACT FROM AUTHOR]

Hydropower is one of the most sustainable and desirable renewable energy sources. Gravitational water vortex hydro turbine (GWVHT) systems are one of the most suitable and sustainable renewable power generation devices for remote and rural areas, particularly in developing countries, owing to their small scales and low costs. There are various GWVHT systems with different configurations and various operating conditions. The main components of a GWVHT system include the inlet and outlet channels, a basin, and a turbine on which there are a number of blades attached. This paper presents a comprehensive review regarding the progress and development of various GWVHT systems, covering broad aspects of GWVHT systems, particularly various types of basins, inlet and outlet channels, turbines with blades which have different shapes, orientations, sizes, numbers, etc. The nature of the previous studies is summarised. The fundamentals of the vortex dynamics involved and the quantitative analysis of the performance of GWVHT systems are also described. The turbulence models and multiphase models used in some leading numerical simulation studies have been reviewed. As a case study, the implementation of a GWVHT system in PNG is presented. Based on the review of previous studies regarding GWVHT systems, the major issues and challenges are summarised, and some key topics are recommended for future research work on the performance of GWVHT systems. [ABSTRACT FROM AUTHOR]

In this paper, an hourly dispatch model was developed to analyze the system balancing and wind power curtailment challenges in the future of the Ethiopian electric power grid system. The developed model was validated using historical data and was used for the analysis of the grid system in 2030 with different scenarios. The model was used to examine the impacts of transmission capacity, regulation reserve requirement, and daily minimum generation of hydropower for irrigation with three cases of wind annual energy share of 14.5%, 17.8%, and 25.2%. Thus, the curtailment was found to be below 0.2%, 1.1%, and 9.8% for each case, respectively. The cost of wind energy increases in proportion to the percentage of curtailment and the increase in transmission line capacity. Reducing the minimum hydropower generation results in smaller wind power curtailment and better generation–consumption balancing. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of the development of the alternative energy market between 2010 and 2022 in seven Central European countries, namely Poland, the Czech Republic, Slovakia, Romania, Lithuania, Hungary, and Bulgaria. Analyzing changes in electricity generation from hydro, solar, wind and bioresources makes it possible to comprehensively assess trends in the development of alternative energy. The countries of Central and Eastern Europe are economically and climatically similar to Ukraine, so studying the development of their renewable energy is of scientific value for the drafting of both Ukrainian and European energy strategies in the context of the transforming global energy system. Additionally, the article discusses the impact of renewable energy development on the labor market, outlining potential challenges and threats to regional labor markets. Research conclusions confirm the practical development and effective implementation of RES in the European energy system, even in countries that do not take the lead in generating energy from renewable sources, i.e., in Central Europe. [ABSTRACT FROM AUTHOR]

The increasing penetration of wind energy in electric power systems leads to a great demand for flexible resources to regulate power fluctuations. This paper focuses on investigating the impacts of the operational flexibility of hydropower generation systems on reducing wind curtailment and load shedding in a hybrid hydro–wind power system. Considering timescale variabilities of wind power, the upward and downward regulation capabilities of hydro flexibility under sub-hour and hour dispatch scales are estimated. Based on developed flexible indicators, the ultimate access ratio of wind power penetration into the power system is obtained by using the estimated probability of insufficient regulation reserves. All these analyses are carried out under the wet and dry periods to better understand their differences with the hydro flexibility. The method and obtained results provide important guidance for the stable and high-efficiency operation of hybrid power systems. [ABSTRACT FROM AUTHOR]

Perspectives on the Environmental Implications of Sustainable Hydropower gathers scientific papers from three of the worlds most important hydropower producers to discuss aspects of sustainable hydropower and the means by which it can be studied and achieved. The papers examine the application and use of new technologies and protocols for studying hydropower, adaptive management and the implications and use of long-term data sets for minimizing hydropower impacts on fish populations. The papers include a cross section of biological and hydrological experts. The implicit among country comparisons highlight a number of common hydropower themes, particularly the need to expand from single species studies to include broader consideration of the ecosystem, the importance of maintaining habitat, trait and species diversity and the need for consistently collected long-term data sets. [ABSTRACT FROM AUTHOR]

When less water is available, hydropower turbines are less efficient, or have to stop altogether. This reality is often neglected in recent work on the planning and operations of hydropower systems, despite widespread expected increases in drought intensity, frequency and duration. This paper is the first to integrate variable‐efficiency turbines into a hydropower plant design framework that accounts for design optimization as well as deep uncertainty in climatic and socio‐economic variables. Specifically, this framework focuses on leveraging multi‐objective robust decision making for the financially robust design of run‐of‐river hydropower plants, whose output is highly sensitive to flow variability. Application to five plants in Türkiye challenges two key design assumptions, use of net present value as a design objective and use of identical turbines. Instead, maximizing the benefit‐cost ratio yields plants with better financial viability over a range of plausible futures. They tend to have smaller capacity, and feature a small turbine that is well‐adapted to low‐flow periods. Another key insight is that socio‐economic uncertainties have as much or even more impact on robustness than climate conditions. In fact, these uncertainties have the potential to make many small hydropower projects too risky to build. Our findings are of considerable practical relevance at a time where 140 GW of unexploited small hydropower potential could help power the energy transition. They also highlight the need for similar research in reservoir‐based plants, considering over 3,000 such plants planned or in construction worldwide. Key Points: Traditional approaches to hydropower planning need to be revisited to account for the impact of a variable climate on turbine efficiencyMaximizing the benefit cost ratio rather than the net present value promotes smaller designs, better adapted to a drought‐prone worldSocio‐economic and climatic factors are both crucial to design financial robustness [ABSTRACT FROM AUTHOR]

Hydropower is the most prevalent source of renewable energy production worldwide. As the global demand for robust and ecologically sustainable energy production increases, developing and enhancing the current energy production processes is essential. In the past decade, machine learning has contributed significantly to various fields, and hydropower is no exception. All three horizons of hydropower models could benefit from machine learning: short-term, medium-term, and long-term. Currently, dynamic programming is used in the majority of hydropower scheduling models. In this paper, we review the present state of the hydropower scheduling problem as well as the development of machine learning as a type of optimization problem and prediction tool. To the best of our knowledge, this is the first survey article that provides a comprehensive overview of machine learning and artificial intelligence applications in the hydroelectric power industry for scheduling, optimization, and prediction. [ABSTRACT FROM AUTHOR]

Since its appearance in the first century BC, the water wheel has developed with increasing pre-industrial activities, and has been at the origin of the industrial revolution for metallurgy, textile mills, and paper mills. Since the nineteenth century, the water wheel has become highly efficient. The reaction turbine appeared by 1825, and continued to undergo technological development. The impulsion turbine appeared for high chutes, by 1880. Other turbines for low-head chutes were further designed. Turbine development was associated, after 1890, with the use of hydropower to generate electricity, both for industrial activities, and for the benefits of cities. A model “one city + one plant” was followed in the twentieth century by more complex and efficient schemes when electrical interconnection developed, together with pumped plants for energy storage. [ABSTRACT FROM AUTHOR]

Hydropower plays an essential role in Europe's energy transition and can serve as an important factor in the stability of the electricity system. This is even more crucial in areas that rely strongly on renewable energy production, for instance, solar and wind power, as for example the Peloponnese and the Ionian islands in Greece. To safeguard hydropower's contribution to total energy production, an accurate prediction of the annual precipitation is required. Valuable tools to obtain accurate predictions of future observations are firstly a series of sophisticated data preprocessing techniques and secondly the use of advanced machine learning algorithms. In the present paper, a complete procedure is proposed to obtain accurate predictions of meteorological data, such as precipitation. This procedure is applied to the Greek automated weather stations network, operated by the National Observatory of Athens, in the Peloponnese and the Ionian islands in Greece. The proposed prediction algorithm successfully identified the climatic zones based on their different geographic and climatic characteristics for most meteorological stations, resulting in realistic precipitation predictions. For some stations, the algorithm underestimated the annual total precipitation, a weakness also reported by other research works. [ABSTRACT FROM AUTHOR]

This paper examines progress and limitations in the transition from current dependence on carbon-based energy toward clean, renewable, and socially just energy in the Hindu Kush Himalaya and the Andes. Focusing on electricity production from sustainable hydropower, solar, and wind energy, the assessment does not cover biomass energy, although this is recognized to be an important energy source in these regions. Using meta-analysis methods, a set of 68 peer-reviewed publications was reviewed to systematically address 2 research questions: (1) Which electricity generation options in mountains can address local demands and adaptation needs while supporting broader decarbonization efforts? (2) What technical innovations, policy, and governance mechanisms can aid this transition? Considering governance, finance, individual and collective action, and science and technology dimensions of the transition challenge, recommendations for policymakers, mountain communities, and practitioners are made. These include setting up clear and effective policy measures, programs, and incentives to support energy transition plans and help mountain communities and energy practitioners to fully embrace the transition. Strong political commitment supported by international cooperation for a transition agenda centered on mountain people will enable community participation, stimulate technological innovation, and establish mechanisms to monitor and enforce social and environmental impact remediation. [ABSTRACT FROM AUTHOR]

The increasing presence of non-programmable renewable energy plants increases the intermittency of the electricity supply and thus threatens the adequacy of a power system. Hydropower can solve this problem due to its flexibility. This paper applies statistical approaches to assess water availability in the context of hydropower generation and adequacy analysis on a seasonal basis for one site in Sicily and the other in Sardinia, where major hydroelectric plants are present. First, an empirical relationship between soil moisture content (SMC) and potential evapotranspiration (ET0) is evaluated through linear regression analysis. Then, precipitation trends over the last twenty years are analyzed to determine any effects of global warming on water availability. Finally, Monte Carlo algorithms are used for the stochastic generation of hourly precipitation, direct runoff profiles, and daily SMC profiles. Strong positive and negative correlations between ET0 and SMC (p < 0.05), and R2 ≥ 0.5 are found for both sites, except for summer, and R2 ≥ 0.5 is obtained. The cumulative pH-historical precipitation shows changes in seasonal trends, with evidence of a decrease at the annual level. The algorithms used to synthetically generate hourly precipitation and direct runoff profiles, as well as daily SMC profiles, effectively simulate the statistical variability of the historical profiles of these physical quantities. [ABSTRACT FROM AUTHOR]

In a hydropower system, inflow is an uncertain stochastic process that depends on the meteorology of the reservoir's location. To properly utilize the stored water in reservoirs, it is necessary to have a good forecast or a historical inflow record. In the absence of these two pieces of information, which is the case in Ethiopia and most African countries, the derivation of the synthetic historical inflow series with the appropriate time resolution will be a solution. This paper presents a method of developing synthetic historical inflow time series and techniques to identify the stochastic process that mimics the behavior of the time series and generates inflow scenarios. The methodology was applied to the Ethiopian power system. The time series were analyzed using statistical methods, and the stochastic process that mimics the inflow patterns in Ethiopia was identified. The Monte Carlo simulation was used to generate sample realizations of random scenarios from the identified stochastic process. Then, three cases of inflow scenarios were tested in a deterministic simulation model of the Ethiopian hydropower system and compared with the actual operation. The results show that the generated inflow scenarios give a realistic output of generation scheduling and reasonable reservoir content based on the actual operation. [ABSTRACT FROM AUTHOR]

Hydropower, as a flexible energy source, has sparked renewed interest in the ongoing decarbonisation of the society. Simultaneously, a wider transformation of the socio-ecological system towards more sustainable practices of energy production is required. Our paper draws from the sustainable transformation theory and the concepts of transformability, hydro-social cycle, and aquatic regime to study a system of water governance and regulation in Finland. Our case study data consists of 16 semi-structured interviews and 207 news articles from Yle national broadcast company. We studied the policy frames to reveal how the water governance actors understand, view and make sense of future river use and restoration, and how they utilise the frames for strategic purposes. Results demonstrate that the future river use and restoration were framed by four modes of thinking: 1) hydropower as a 'cultural trauma', 2) restoring rivers and dam removal after hydropower construction and operation to improve ecological flows in rivers, 3) improving the social acceptance of hydropower and dam removal, and 4) improving the efficiency of the hydropower regime as a flexible source of power. Our paper shows that to enable pathways for socio-ecological-technical transformations of aquatic ecosystems further scientific scrutiny should be focused on reconciliation of the interest of river restoration, recreational uses of aquatic environments and the flexible energy function of hydropower in energy transition. Removal of migration barriers and small-scale hydropower plants and building fishways and bypasses are part of this transformation. Furthermore, the river regulation needed to give impoundment facilities the flexibility, causes changes in water levels which may be a potential source of conflict between riparian residents and hydropower operators. Therefore, more emphasis should be placed on water governance that recognises the local dynamics and interactions within the social-ecological systems. [ABSTRACT FROM AUTHOR]

In the wake of the enthusiasm for green energy, previously contested energy and mining projects can be framed as part of a green transition. When state authorities decide to forego the standard procedural protections and the processes and forums for deliberation and local influence, it contributes to constructing green sacrifice zones. This paper compares two Swedish energy policy processes. The first is occurred during World War II and the hydropower expansion of the 1940s and 1950s. The second takes place today when wind power is expanding to increase renewable energy production. In Sweden, policymaking seems to be back to square one in the green transition, leaving out both important knowledge of the past and contemporary voices of the ongoing and probable consequences. In certain issues, such as how the recognition of the Indigenous status of the Sámi actually affects the legislative process and how to address the Indigenous rights of the Sámi, policymaking is particularly slow to adapt. The green transition industry is already affecting the Sámi, as the construction of the Nordic welfare society has done during the last century, and still does. It deepens an ongoing colonial wave that started in the 1300s. By showing how the Swedish legislative process, historically as well as currently, has neglected to involve Sámi representatives, this study points to the importance and obligation of Swedish policymaking to engage Sámi representatives in an early phase to avoid further sacrifice zones in Sápmi. [ABSTRACT FROM AUTHOR]

This paper presents research concerning dewatered areas in the littoral zones of the Kaunas hydropower plant (HPP) reservoir in Lithuania. It is a multipurpose reservoir that is primarily used by two large hydropower plants for power generation. As a result of the peaking operation regime of the Kaunas HPP, the large quantity of water that is subtracted and released into the reservoir by the Kruonis pumped storage hydropower plant (PSP), and the reservoir morphology, i.e., the shallow, gently sloping littoral zone, significant dewatered areas can appear during drawdown operations. This is especially dangerous during the fish spawning period. Therefore, reservoir operation rules are in force that limit the operation of HPPs and secure other reservoir stakeholder needs. There is a lack of knowledge concerning fish spawning locations, how they change, and what areas are dewatered at different stages of HPP operation. This knowledge is crucial for decision-making and efficient reservoir storage management in order to simultaneously increase power generation and protect the environment. Current assessments of the spawning sites are mostly based on studies that were carried out in the 1990s. Surveying fish spawning sites is typically a difficult task that is usually carried out by performing manual bathymetric measurements due to the limitations of sonar in such conditions. A detailed survey of a small (approximately 5 ha) area containing several potential spawning sites was carried out using Unmanned Aerial Vehicles (UAV) equipped with multispectral and conventional RGB cameras. The captured images were processed using photogrammetry and analyzed using various techniques, including machine learning. In order to highlight water and track changes, various indices were calculated and assessed, such as the Normalized Difference Water Index (NDWI), Normalized Difference Vegetation Index (NDVI), Visible Atmospherically Resistant Index (VARI), and Normalized Green-Red Difference Index (NGRDI). High-resolution multispectral images were used to analyze the spectral footprint of aquatic macrophytes, and the possibility of using the results of this study to identify and map potential spawning sites over the entire reservoir (approximately 63.5 km2) was evaluated. The aim of the study was to investigate and implement modern surveying techniques to improve usage of reservoir storage during hydropower plant drawdown operations. The experimental results show that thresholding of the NGRDI and supervised classification of the NDWI were the best-performing methods for the shoreline detection in the fish spawning sites. [ABSTRACT FROM AUTHOR]

Despite consistent maintenance and monitoring equipment installed in pumped storage hydropower (PSH) facilities, many shafts and electrical component failures are reported, possibly resulting from undetected sources. These sources include undetectable vibrations or, in certain conditions, high-frequency mechanical or electrical harmonics. This paper presents a direct method for plotting Campbell diagrams of large motors supplied by variable frequency drives (VFDs) for torsional analysis purposes in PSH systems. These diagrams display the precise locations where torsional stress components induced by VFDs can interfere with shaft resonance modes. The method simplifies the determination of the magnitude of stimulus forces in the motor airgap that may threaten the shaft. The method has been successfully applied to two-level, three-level neutral-point clamped, and seven-level cascaded H-bridge multilevel inverters, which are commonly used industrially available VFD topologies for pumped PSH plants. The paper also discusses the theoretical motor-pump voltage, current, and torque spectra when driven by a cascaded H-bridge multilevel converter operating with bypassed and faulty cells. The accuracy of the theoretical developments is supported by selected simulations results at different operating points and different fault conditions. Hybrid experimental-numerical VFD-induced harmonic stress analysis is also performed to demonstrate the relevance of the proposed study.

This paper presents a method to quantitatively assess the impact of ice-affected hydraulics on hydropower operations using the widely used Hydrologic Engineering Center River Analysis System (HEC-RAS) hydraulic model. The model was used to identify historical periods where downstream river ice growth reduced the net head on a US Army Corps of Engineers dam on the Pend Oreille River in Idaho, USA. The model was used to create curves of projected stage impacts based on border-ice and continuous bank-to-bank ice formation scenarios. The temperature modelling capabilities in HEC-RAS were used to hindcast ice formation periods on the river that were validated with shore-based webcam data. These results provide a framework that can be applied to other rivers with hydropower generation, particularly sites where an open-water HEC-RAS model exists. [ABSTRACT FROM AUTHOR]

This paper presents research on the dewatering areas during drawdown operations in the Kaunas Hydropower Plant (HPP) reservoir situated in the lowland area of Lithuania. It is a multipurpose reservoir primarily used for power generation by two large hydropower plants. Because of the HPP peaking operation and the reservoir morphology—a shallow, gently sloping littoral zone—significant dewatered areas can occur (during drawdown operations). This is especially dangerous during the fish spawning period. Therefore, reservoir operation rules are in force that limit operation of the HPPs and secure other reservoir stakeholder needs. There is a lack of knowledge about the fish spawning locations, how they are changing, and what areas are dewatered at different stages of HPP operation. This knowledge is crucial for decision making and efficient water resources management in order to increase power generation and protect the environment at the same time. A detailed survey of an area containing several potential spawning grounds (about 5 ha) was conducted to track changes in the dewatering areas. The aim of the study is to investigate different surveying methods, gather knowledge about potential fish spawning sites, and investigate the dewatered areas that occur during water level (WL) fluctuations. The methodology and insights of this study can be used in similar lowland countries to assist in improving the usage of water resources while increasing power generation. [ABSTRACT FROM AUTHOR]