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This paper presents the preliminary design and thermodynamic analysis of hydropower and solar integrated e-fuel production system for a tea factory. In this regard, an integrated hydro-solar e-fuel production system has been developed, which is mainly able to produce e-methanol and green hydrogen. The system contains five main subsystems: i) Proton exchange membrane electrolyzer system, ii) CO 2 capture and storage system, iii) Methanol production system, iv) Photovoltaic system, and v) Penstock hydroelectric power plant. In terms of the general system operating principle, it is important to emphasize that the energy need of the system is supplied by solar power plant during the sunshine duration (the case 1) and provided by hydropower plant in the period when solar energy is not sufficient (the case 2). Considering the required assumptions, in the first step, preliminary design was performed, and in the second step, the energy and exergy analyzes were achieved, and in the final step, the effects of parameters such as CO 2 capture efficiency, methanol reactor conversion ratio, and environmental temperature on the system performance were parametrically investigated. Accordingly, in the case 1, the maximum energy and exergy efficiencies of the integrated e-fuel production system were respectively obtained to be 7.132% and 6.569% while, in the case 2, those were respectively calculated to be 39.44% and 42.36%. Moreover, approximately 235.9 tons of CO 2 emission in operation period of the tea factory considered in this work can be reduced by the integrated hydro-solar e-fuel production system that has a production capacity of 399.8 kg/h for methanol and 37.73 kg/h for hydrogen. It is expected that the integrated system concept may contribute to the researchers, system designers, policy makers, investors, and different enterprises for practical applications. • Hydropower and solar integrated e-fuel production system for a tea factory is proposed. • The preliminary design and thermodynamic analysis have been performed. • Thanks to the developed systems, 235.9 tons of CO 2 emissions can be reduced. • The maximum exergy efficiency of case-1 and case-2 are obtained to be 6.569% and 42.36%, respectively. [ABSTRACT FROM AUTHOR]

Hydropower has played an important role in Europe in recent decades, offering a unique combination of safe, low-cost, and clean power generation. Today, it is still one of the largest renewable energy sources (RES), accounting for about 35 % of RES electricity generation. However, grid stability is threatened by the increasing amount of undispatchable RES. Flexibility and dynamics such as energy storage and rapid response are urgently needed to achieve EU policy goals. In such a context, hydropower can play a key role, not only as a provider of regulated renewable energy but also due to its ability to balance a renewable energy system in the short term and the medium/long term by pumped storage technology. All these aspects underline the new role of hydropower, which aims to strengthen grid stability and power supply resilience and to enable higher penetration of volatile RES. In this context, the aim of this paper is to demonstrate the role of hydropower at the European level as well as the needs and opportunities of modernization to fully exploit its potential. In particular, this study provides, the assessment of the today flexibility offered by hydropower to the power system at the European level by leveraging a database of information collected through the participants to the working groups of the COST Action Pen@Hydropower which includes stakeholders in the hydropower sector of 34 European countries. The study confirms the key role of hydropower in future energy scenarios with 30 % of the flexibility demand at all time scales met by hydropower. Furthermore, the paper presents a review of the digitalization solutions and innovative technologies that support the growth of a new generation of sustainable hydropower together with the modernization opportunities for existing hydropower plants. The results of this work have practical implications for stakeholders in the hydropower sector and policymakers as it provides evidence at the European scale of the role of hydropower technology in balancing the power system and the need to have supportive frameworks and adequate markets to fully exploit the European hydropower potential to achieve the energy transition goals. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the association between hydroelectric energy consumption and CO 2 emissions in the USA from 1980:1 to 2019:8 by using the wavelet transform model. This research revealed that (a) in the short runs (at higher frequencies), hydro energy uses intensified CO 2 emissions for the periods 1990:01–1992:12, 1994:01–1994:12, and 2002:07–2007:11, and (b) during the longer periods (at lower frequencies), however, hydro energy consumption diminished CO 2 emissions for the periods 1983:01–2001:12 and 2011:01–2017:03. The paper explained as well why hydro energy can yield adverse and affirmative contributions to Greenhouse gas emissions by emphasizing the role of energy generation from hydro plants in shorter runs and longer runs in the USA considering all sub-samples of the sample period 1980:1–2019:8. This research eventually suggests some energy policies to enhance the positive environmental influences of hydropower energy production in the USA. [ABSTRACT FROM AUTHOR]

Hydropower plants play an integral role in energy supply and are one of the main renewable energy sources. The efficiency of hydropower reservoir systems is controlled by operating rules that need to be optimized to maximize energy production. Here, a novel optimization algorithm, influential flower pollination algorithm (IFPA), is developed in this paper. IFPA has three enhancements: an efficient exploration mechanism based on an adaptive coefficient, a new exploitation mechanism around the best solution, and a rank-based strategy to smoothly transition from exploration to exploitation. IFPA is tested in two benchmark multi-reservoir systems and a real-world five-reservoir hydropower system in Iran. The results show IFPA outperforms other advanced methods in terms of convergence speed and preciseness to achieve the global solution. The tested algorithms include adaptive guided differential evolution (AGDE), composite DE (CODE), hybridizing sum-local search optimizer (HSLSO), improved teaching learning-based optimization (ITLBO), self-adapting control parameters in DE (jDE), self-adaptive TLBO (SATLBO), and a multi-strategy hybrid of DE and particle swarm optimization (MS-DEPSO). IFPA also achieved better total power production in the real-world case study compared to other algorithms. Overall, IFPA can provide better solutions with less power deficit and shows as a promising method for optimizing hydropower reservoir problems. [ABSTRACT FROM AUTHOR]

As power systems around the world are rapidly evolving to achieve decarbonization objectives, it is crucial that power system planners and operators use appropriate models and tools to analyze and address the associated challenges. This paper provides a detailed overview of the properties of power market models in the context of the clean energy transition. We review common power market model methodologies, their readiness for low- and zero‑carbon grids, and new power market trends. Based on the review, we suggest model improvements and new designs to increase modeling capabilities for future grids. The paper highlights key modeling concepts related to power system flexibility, with a particular focus on hydropower and energy storage, as well as the representation of grid services, price formation, temporal structure, and the importance of uncertainty. We find that a changing resource mix, market restructuring, and growing price uncertainty require more precise modeling techniques to adequately capture the new technology constraints and the dynamics of future power markets. In particular, models must adequately represent resource opportunity costs, multi-horizon flexibility, and energy storage capabilities across the full range of grid services. Moreover, at the system level, it is increasingly important to consider sub-hourly time resolution, enhanced uncertainty representation, and introduce co-optimization for dual market clearing of energy and grid services. Likewise, models should capture interdependencies between multiple energy carriers and demand sectors. • Review methodologies and assumptions commonly used in power market models. • Identify model design features critical to analyzing the clean energy transition. • Survey current state-of-the-art in modeling low-carbon power markets. • Identify key model improvements needed for future deep decarbonization scenarios. • Highlight importance of tailoring tools for specific power market applications. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to estimate hydroelectric turbine runner modal characteristics from experimental measurements coming from asynchronous regimes. This is achieved by investigating resonances generated by the interaction of a structural mode with harmonics of the rotating speed. Resonances are extracted using order tracking and processed with a Fast Bayesian algorithm in an ambient manner to estimate modal parameters and related uncertainties. Since data collection and effective processing of hydropower turbine field measurements is in its early stages, this paper lays some foundations in the treatment of transient regime measurements. A novelty in this approach lies in the use of a probabilistic identification tool in Order Based Modal Analysis (OBMA). A numerical experiment and a study from a hydroelectric Francis turbine field measurements are introduced to illustrate the method. • Operational conditions can significantly alter the modal behavior of turbines. • Data processing can characterize actual resonances from strain field measurements. • Resonances with harmonic excitations occur during asynchronous transient experiments. • Order-tracking can extract resonances, but responses are short-time and non-averaged. • The Fast-Bayesian approach was found effective for identifying modal parameters. [ABSTRACT FROM AUTHOR]

Within the Pacific Northwest region of the United States, there is the unique opportunity to explore alternative energy management solutions of the Columbia River's multi-use hydropower system. As with various European hydropower systems that experience large variability in water runoff, but lack adequate reservoir storage capacity, the Columbia River System is a viable source for renewable hydrogen production. This paper studies the theoretical potential of green hydrogen production from excess hydropower energy from the Columbia River System. The potential surplus hydroelectric energy and hydrogen production potential from surplus energy (during March through July months) are estimated from 11 hydroelectric projects along with the Columbia River System. Results show that the system's total monthly average hydrogen production potential ranges from 2.22 × 106 to 8.96 × 106 kg H 2 with the utilization of surplus energy over a historical 80 water year period (1928–2008). This study concludes that hydrogen production from spilled hydropower energy and its use in the transportation sector is a viable opportunity to lead the country towards a hydrogen economy. [Display omitted] • Hydropower plants are feasible for providing excess and dispatchable electricity to produce green hydrogen. • The scenario for the use of green hydrogen for heavy duty vehicle transportation is presented. • The article supports hydrogen strategies in coordination with renewable energy policies. • The spring through summer runoff period is Ideal for utilizing excess hydropower for hydrogen production. [ABSTRACT FROM AUTHOR]

Kaplan turbines are nowadays used to provide Frequency Containment Reserve (FCR) to the grid due to their fast capacity to regulate their power maintaining high efficiency. However, this continuous power regulation increases the wear and tear of the regulation system considerably. To reduce the amount of movements in the regulation servomotors, and thus their wear and tear, a new technology is being investigated within the frame of the European project XFLEX Hydro. This new technology is based on hybridizing the hydro unit with a small size battery in parallel, this one being in charge of compensating the small frequency fluctuations in the grid by providing or absorbing power. In this paper, the benefits of the implementation of this new technology are evaluated. A Kaplan turbine prototype located in Vogelgrun, France, has been hybridized and different parameters have been monitored while the unit was working in hybrid mode and in normal standalone hydro mode. Wear and tear of the regulation system have been compared for both hybrid and standalone hydro modes. A reduction of about 25% in servomotors mileage and of 50% in fatigue damage have been obtained by hybridizing the unit. • Benefits of hybridizing hydro units with a battery are studied. • A small size battery is installed in parallel with a prototype Kaplan unit. • The battery helps to provide primary frequency control reducing the wear and tear of the hydro unit. • A reduction of wear and tear in the hydro unit regulating systems is obtained. [ABSTRACT FROM AUTHOR]

The need for electric energy storage in the ongoing energy transition with large-scale construction of renewable energy leads to increasing interest for upgrading existing hydropower plants to pumped storage plants. Such upgrading is possible by using existing dams and waterways, and only upgrade the electromechanical equipment. However, this alternative has several technical limitations that must be overcome. The boosterpump concept is a possible solution to overcome these technical limitations. This paper presents the concept and a demonstration on two case-study hydropower plants. A novel electro-mechanical layout and hydraulic design has been developed. The layout, operation, physical dimensions, performance, costs and market analyses are presented. The costs are compared to constructing a new reversible unit in parallel with reuse of the existing dams and waterways. The boosterpump concept is found technically feasible for both Roskrepp HPP and Vinje HPP, and the technology is currently considered to be at TRL 4–5. The cost calculations show that reconstructing with a boosterpump costs 25–35 % less than installing a new reversible unit constructed in parallel. The reconstruction is only found economically feasible for the Roskrepp HPP under the given assumptions and market expectations for these two projects. [ABSTRACT FROM AUTHOR]

Abstract Although hydropower and thermal power constitute the two pillars of China's power supply, the relationship between them has always been a controversial topic. Based on the panel data of China's provincial level covering the period 1991–2015, this paper tried to reveal the relationship between hydropower and thermal power under the framework of autoregressive distributive lag (ARDL) model. Taking the panel unit root and panel cointegration tests as the premise, the PMG estimators implemented under the maximum likelihood method provide unbiased results for this paper. Collectively, In the long run, China's hydropower and thermal power complement each other in ensuring a stable power supply, whereas in the short run, they are competitive to a certain extent, even if factors such as precipitation, grid infrastructure and economic conditions are taken into account. The Granger causality test further reveals the one-way relationship between hydropower and thermal power in short run. That is, thermal power is dominant while hydropower is subordinate and passive, giving an empirical interpretation for the specific phenomenon that discarded water from hydropower plants in China during seasonal water-rich period which has been seriously concerned by policymakers and researchers and appeal for impartial dispatching mechanism. Highlights • Cointegration exists between hydropower and thermal power. • The PMG estimator is employed for panel ECM. • In long run, a 1% increase of thermal power increases 0.5% of hydropower. • The short-term structure exhibits dominant thermal power and subordinate hydropower. [ABSTRACT FROM AUTHOR]

Abstract Due to the massive entrance of new renewable energies such as wind or solar, hydraulic turbines have to work far from its designed point and withstanding multiple transients, such as starts and stops, that shorten the useful life of the machine and cause fatigue damages. The present paper reviews the complex problem of fatigue in Francis turbines particularly focused on the experimental data available for static and dynamic stresses. For this purpose, many researches, which include different Francis turbines covering a wide range of design head and power, have been considered. The experimental stresses characteristics measured with strain gauges installed on the turbine runner and obtained from previous works have been analyzed for the different operating conditions and transient states occurring in the normal life of actual Francis units. The actual computational capabilities and techniques typically used to estimate such stresses have been discussed in detail. Potential future techniques to simplify complex strain measurements on the turbine runner, computational and statistical methods to estimate turbine stresses are reviewed in this paper. Finally, the relative damage of the different operating conditions and useful life estimation of the turbine, based on past strain measurements of the runner, are addressed. Highlights • This paper reviews the complexity of fatigue life estimation of Francis turbines in all the involved steps. • Data and conclusions of different manufacturers and researchers are summarized and compared. • The main characteristics of stresses have been identified and the capabilities of numerical techniques discussed. • Potential future experimental and numerical techniques to simplify actual experimental measurements are shown. • Existing data of relative damages has been compared. Probabilistic fatigue models in hydro turbines have been addressed. [ABSTRACT FROM AUTHOR]

Highlights • Proposing 100% renewable Low Frequency AC system of hydro and wind power plants. • The re-designed hydro generator provides ancillary services on behalf of the wind farm. • The proposed smoothing method adapts both surplus and insufficient wind power generation. • The proposed frequency support methods tackle successive frequency drops at the Grid. • And they are tunable to be Grid Code compliant and avoid major frequency violations. Abstract Wind energy high penetration levels in power systems lead to continuous power imbalance due to the intermittent nature of wind power. This paper proposes and investigates different methods to enable a hybrid generation system to provide frequency support to the grid. The hybrid generation is 100% renewable and composed of a wind farm and hydropower plant (HPP) of comparable generation capacities, and they are interconnected through a Low Frequency AC system (LFAC). The grid–tie is composed of a Voltage-Source Converter based High-Voltage, Direct Current (VSC-HVDC) junction that acts as frequency changer to maintain the grid nominal frequency. The HPP provides two types of ancillary services: wind power smoothing and frequency drops mitigation to avoid the use of thermal generation and battery energy storage. The paper offers different control methods to provide the two AS with improved coordination between the different controls in the hybrid generation system and complying with the common requirements of Grid Codes. The results obtained show that the frequency at the LFAC can tolerate mild drops to provide frequency support to the grid. The controllers' parameters have a clear impact on the frequency response at both systems. Simulation environment is MATLAB and Simulink. [ABSTRACT FROM AUTHOR]

This paper presents a solution to address wear and tear of Run-of-River (RoR) Hydropower Plants (HPPs) providing enhanced Frequency Containment Reserve (FCR). In this respect, the study proposes the integration of a Battery Energy Storage System (BESS) with RoR HPPs controlled by a double-layer Model Predictive Control (MPC). The upper layer MPC acts as a state of energy manager for the BESS, employing a forecast of the required regulating energy for the next hour. The lower-layer MPC optimally allocates the power set-point between the turbine and the BESS. Reduced-scale experiments are performed on a one-of-a-kind testing platform to validate the proposed MPC-based control considering a comparison with different control strategies and different BESS sizes. The results demonstrate superior performance of the proposed framework, compared to simpler techniques like dead-band control or to the standalone RoR scenario, leading to improved FCR provision, reduced servomechanism stress, and extended hydropower asset lifespan. • BESS hybridization of Kaplan turbines is studied to enhance FCR and asset lifetime. • A double-layer MPC is used to optimally control the hybrid system. • Experiments validate the control strategies on a unique reduced-scale model testing platform. • Results show superior FCR provision and reduced wear of the BESS-hybridized Kaplan. [ABSTRACT FROM AUTHOR]

• ES co-production as a concept aims at closing the link between the ecological and social systems. • It can demonstrate the conflicting values and trade-offs in the governance of aquatic ES. • Argument analysis methodology can support ES valuation and management. • It can assist stakeholders to recognize the diversity of arguments related to ES. The co-production of ecosystem services (ES) is an intertwined social-ecological process in which natural and anthropogenic contributions together produce a specific ES. Despite multiple studies in which ES trade-offs have been assessed, few empirical studies on arguments for biodiversity and ES exist, in which ES co-production function as a theoretical framework. In this paper, we study the co-production of aquatic ES and analyse political and legal arguments on biodiversity and ES in a long-standing dispute over hydropower and reservoir construction in the Kemi River basin, Finland. Specifically, we investigate what kinds of representations of ES co-production can be identified from stakeholder argumentation and in legal ruling. Our data consists of 26 semi-structured interviews conducted in 2017 and again 2019 to 2020, 144 news articles, and 4 administrative court resolutions. The results show that the arguments used by the stakeholders aim at maintaining the existing hydrological regime and expanding the use of natural resources, establishing river basin management that considers the multiple uses of river, including recreation, or protecting the last untouched stretches of the river and riparian ecosystems. The analysis also reveals that what is considered a valid and effective argument for specific audiences differs for political and legal audiences. The results of this study show that ES co-production concept set emphasis on the diversity of arguments, including the arguments on biodiversity and sociocultural values, which can contribute to governance and management interactions. [ABSTRACT FROM AUTHOR]

The implementation of hydropower to stabilize electrical grids dictates more frequent off-design operations of these renewable energy resources. Flow instabilities under such conditions reduce the efficiency of hydro turbines. Part-load operation is particularly detrimental since the development of a rotating vortical structure termed rotating vortex rope (RVR) in the draft tube leads to periodic pressure pulsations that jeopardize turbine performance. This paper experimentally explores a novel solution involving the protrusion of flat plates into the turbine draft tube. Three flat plates equally separated by 120° were vertically installed on the draft tube wall. The plates were protruded up to 83% of the draft tube local radius under four different part-load conditions. Their impact was observed through time-resolved pressure measurements in the draft tube and vaneless space, as well as efficiency measurements. The results demonstrated successful RVR mitigation, achieving a maximum 85% reduction in pressure oscillation amplitudes. Protruding flat plates disrupted RVR periodicity and coherence, confining its orbit to the draft tube center. This approach proved particularly effective at lower part-load conditions, enhancing turbine hydraulic efficiency by increasing torque extraction. Reducing the adverse effects under part load, the proposed method appears promising in extending the operational range of hydraulic turbines. [ABSTRACT FROM AUTHOR]

Hydropower, an excellent power source for peak shaving, can respond quickly to load changes, which helps to overcome the anti-peak characteristics of wind and solar power. However, complementary operation with wind and solar power changes the operating boundaries of hydropower stations, making the original operating rules no longer applicable. Considering daily peak-shaving demands, this paper proposes a methodology to develop operating rules for a hydro–wind–solar hybrid system (HWSHS). First, a multi-objective and multi-timescale operation model is developed to ensure energy generation and peak-shaving performance simultaneously. Second, the feasible and reasonable region of available energy-based operating rules is analyzed, and three rule forms are employed to explore the optimal operating rules. Last, NSGA-II is utilized to optimize the rule parameters. A decoupling method is proposed to handle the shape constraints of operating rules, and the multi-timescale simulation method for a HWSHS is developed as the fitness function. In the simulation method, a load reconstruction-based load shedding (LRLS) method is introduced to determine the hourly output of each hydropower station. A forebay elevation check method is performed to obtain the hourly forebay elevation and correct the hourly output. The Beipan HWSHS in Guizhou Province, China, is selected as a case study, and the optimal operating rules are determined. The results also show that (1) the standard operating rules with hedging and packing increase peak-shaving performance by an average of 4.31% and 2.03% compared to the standard operating rules and linear operating rules, respectively; (2) the peak-shaving performance can be significantly increased (6.70%) with a slight decrease (0.37%) in the energy generation through changing the seasonal distribution of water and energy of the cascade hydropower stations; (3) the LRLS method, which makes the interday energy distribution more uniform, increases the peak-shaving performance by an average of 9.17% compared to the traditional load shedding method; (4) the energy generation and peak-shaving performance of the HWSHS are affected by the transmission capacity, and it is necessary to increase the transmission capacity by 25% to 35% of the installed capacity of wind and solar power stations. • A methodology is proposed to develop operating rules considering peak-shaving demands. • A multi-objective and multi-timescale operation model is developed. • The feasible and reasonable region of available energy-based operating rules is analyzed. • A multi-timescale simulation method is designed to simulate the operation of a HWSHS. • The methodology significantly improves the peak-shaving performance. [ABSTRACT FROM AUTHOR]

Hydropower is one of most important considered renewable technologies to provide electricity generation worldwide. Bearing in mind the lack of LCA studies and the development of several hydroelectric projects in Ecuador, the purpose of this paper is to present a complete environmental performance of two hydropower schemes (dam and run-of-river) located in this country, through the life cycle assessment combined with reservoir GHG emissions approach. The run-of-river scheme had better environmental performance than the dam scheme. Very high emissions were found, being 547 Kg CO 2-eq /MWh for dam scheme, which most of those emissions were originated in the reservoir, while the run-of-river scheme only score 2.6 Kg CO 2-eq /MWh. However, comparing with fossil fuel power plants, hydropower dam case still has lower emissions in its entire life cycle. The paper remark that the majority of LCA studies which focus on dam hydropower scheme only consider the emissions of the construction, putting aside the loss of the ecosystem and the emissions caused by the impoundment. Moreover, the analysis also included the impact associated to water uses since reservoirs are usually devoted to several purposes (flood lamination, irrigation, ecological flow, power generation). [ABSTRACT FROM AUTHOR]

This paper focused on the stable operation and control strategy of the hydro-turbine governing system (HTGS) in an isolated-grid operation mode. The stable operation of a hydropower station in isolated-grid operation mode is important for the safe operation of a power system. A regional power grid can be isolated from a main grid due to factors such as natural disasters, grid failures, and human errors. The Lunzua hydropower station in Zambia is often forced to operate as an isolated grid. To ensure its safe and stable operation, we conducted isolated-grid regulation tests in conjunction with field testing of HTGS and determined the parameters of the HTGS for stable operation of the isolated grid. In the field test, we first set the no-load and initial parameters for the isolated-grid mode through the no-load disturbance tests. Through simulated isolated-grid operation tests, we verified and further tuned the initial parameters. Meanwhile, we propose a control strategy for the transition between large-grid and isolated-grid modes. Through operational tests, we determined the parameters for stable operation in isolated-grid mode. During testing, we found that the water flow inertia time constant T w was too large and the inertial time constant T a of the impulsive generator was too small, which resulted in a narrow stability range of proportional–integral–derivative (PID) controller parameters for isolated-grid operation. The governing stability for isolated-grid operation was thus sensitive to the PID parameters. Since the isolated-grid field operation test of the HTGS of the Lunzua hydropower station was completed in August 2016, the generator units have maintained safe and stable operation in large-grid and isolated-grid modes, which validated the isolated-grid operation parameters and control strategy for the transition between large-grid and isolated-grid modes as determined by our test method. The methods of field test and control strategies used for isolated-grid operation have important practical value for the isolated grid operation of hydropower stations. [ABSTRACT FROM AUTHOR]

Hydropower is one environmentally friendly option for meeting these energy demands. Because such technologies do not require a weir or a dam, they may be used with minimal environmental effect. The drag-based Savonius turbine is characterized by working at low-flow speeds which fits well the natural water streams. In spite of its simple and robust design, the Savonius turbine suffers from low efficiency and high static torque fluctuations. In view of this, CFD-based optimization is applied to a Savonius-type hydrokinetic turbine inspired by a couple of swimming Koi fish. The two main design parameters; overlap ratio and gap ratio are used in this paper to define the gap between the blades. The maximum power coefficient can be obtained by employing an evolution strategy optimization technique over the constructed metamodel. The results revealed that the optimal design for the bio-inspired Savonius hydrokinetic turbine corresponds to overlap and gap ratios of 0.2085 and 0.0057, respectively. The optimal configuration generates a maximum power coefficient of 0.2521, which is 17.6% higher than that for a conventional shape at the same tip speed ratio. The new bio-inspired design performs better than the conventional Savonius hydrokinetic turbine for the considered operating range. [Display omitted] [ABSTRACT FROM AUTHOR]

Several studies have shown that the revenue of wind power generators on spot markets (“market value”) diminishes with increasing deployment. This “value drop” is mostly observed in power markets that are dominated by thermal power plants, such as in Germany. This paper assesses the wind market value in power systems where hydroelectric stations with large reservoirs prevail, such as in Sweden. Due to their dispatch flexibility, such hydropower compensates for wind power output variability and thereby mitigates the wind power value drop. The market value of electricity from wind declines with penetration in both types of power systems, but it tends to decline at a slower rate if hydropower is present. This paper presents empirical evidence on the relevance of this effect derived from market data and numerical model results. Our results indicate that when moving from 0% to 30% wind penetration, hydropower mitigates the value drop by a third. As a result, 1 MWh of wind energy is worth 18% more in Sweden than in Germany. Sensitivity analyses indicate high robustness despite large parameter uncertainty: in 80% of all sensitivities, wind energy is valuable 12–29% more in Sweden than in Germany. The benefits of hydropower seem to level off at around 20% wind penetration. This suggests that the hydro flexibility is “exhausted” at this level. Low wind speed wind turbines, carbon pricing, and upgrades of hydropower generation capacity can lever the added value of hydro flexibility further. Not only is wind energy more valuable in the presence of hydropower, hydroelectricity also becomes more valuable if paired with wind power. [ABSTRACT FROM AUTHOR]

Latin America has the largest share of renewable energy for power generation in the world, but has historically been dependent on hydropower, and is vulnerable to long-term phenomena like the El Niño-Southern Oscillation (ENSO). The region is currently experiencing a steady increase in gas-based power generation along with a rapid growth in non-hydro renewables, mainly aimed at improving reliability. But exploiting complementarities between hydropower and other renewables could offer additional benefits. This paper investigates to what extent improved deployment of wind turbines and solar photovoltaic cells (PV), aimed at complementing existing hydropower, could mitigate the impacts of ENSO in Latin America. We use a meteorological reanalysis dataset to model the variations in wind-, solar- and hydropower throughout the entire 20th century and their association with different ENSO phases in the same period. A statistical algorithm is then used to identify locations at national and regional levels offering the maximal level of complementarity. The results show that adding 136 GW of wind- and solar-power with high-complementarity has the potential to cost-effectively compensate the fluctuations of hydropower and reduce the variability of renewable power not only during drought ENSO phases but also outside ENSO events. Benefits include: (i) an increase of up to 5-fold the minimum threshold of renewable power available every month, (ii) a reduction of up to 65% in the variability of renewable power generation, and (iii) reaching a levelized cost of electricity (LCOE) of 0.09–0.23 $/kWh, which is comparable to that of new gas plants. • An improved selection of wind- and solar-power to mitigate impacts of ENSO on hydropower is shown. • A meteorological reanalysis dataset to model variations in wind-, solar- and hydropower is used. • A statistical algorithm is employed to identify locations with maximal complementarity. [ABSTRACT FROM AUTHOR]

This paper studies the potentials of green hydrogen production from hydropower energy and its application in electricity regeneration and replacement of petroleum products from the transportation sector in Nepal. The potential surplus hydroelectric energy, and hydrogen production potential from the surplus energy considering different scenarios, is forecasted for the study period (2022–2030). The results showed that hydrogen production potential ranges from 63,072 tons to 3,153,360 tons with the utilization of surplus energy at 20% and 100% respectively, in 2030. The economic analysis of hydrogen from hydropower projects that electricity is valued based on per kg of hydrogen when the surplus electricity is provided at feasible lower price values compared to the US $1.17. This study concludes that hydrogen production from spilled hydro energy and its use in the transportation sector and independent electricity generation is a niche opportunity to lead the country towards sustainable energy solutions and an economy running on hydrogen. • Methodological study for quantification of excess hydropower and hydrogen production. • Cost projections scenarios from green hydrogen from surplus hydropower electricity. • Identification of role of green hydrogen in multiple end-use areas of developing nation. • Potential replacement of conventional fuel with hydrogen in transportation sector. [ABSTRACT FROM AUTHOR]

Swedish government's target is to have 100% renewable electricity production by 2040. Currently, hydropower contributes the majority of renewable electricity generation of the country. The wind power capacity has increased significantly in the past decade. In this paper, practical data is used to study the possibility of reaching the 100% renewable electricity generation goal by replacing existing thermal generations with wind power generations. It is found that the Swedish electricity generation system can reach 100% renewable by tripling the existing wind power capacity combined with the existing hydropower in the country. Based on current growth rate of wind power installation, the goal could be reached within 20 years. Hourly simulation shows that 100% renewable energy generation system composed by wind power and hydropower satisfy hourly operation requirements. • Sweden can reach 100% renewable generation by tripling existing wind capacity. • Sweden can reach 100% renewable generation goal within 20 years. • Coordinating hydropower and wind power satisfies hourly operation requirement. [ABSTRACT FROM AUTHOR]

Nowadays, one of the major mechanical issues of hydraulic turbines and particularly Francis turbines are the failures produced by fatigue. Due to the massive entrance of new renewable energies such as wind or solar, hydraulic turbines have to withstand off-design conditions and multiple transients, which greatly increase the risk of fatigue failures. Fatigue damage and crack propagation models are based on the static and dynamic stresses on the turbine blades. Therefore, an accurate and realistic determination of these stresses is of paramount importance although it is yet a challenging task. Numerical simulations have still limitations when predicting static and dynamic stresses in the most harmful conditions such as deep part load conditions and transients, which are highly stochastic. The installation of strain gauges on the blades gives accurate stress measurement but it involves long and very expensive measurement campaigns, as the turbine runner is submerged, confined and rotating. In this paper we propose a neural network-based method to determine the magnitude of static and dynamic stresses based on the measurements of stationary sensors, which greatly reduces the complexity and costs of strain gauge testing. Inputs of the neural networks are selected based on previous experience monitoring Francis turbines. The trained network can be implemented in advanced monitoring systems that could continuously evaluate the stress level of the turbine and determine the risk of possible fatigue damage. • Development of a method to predict stresses in a turbine with stationary sensors. • Method uses relevant signal indicators as inputs of an Artificial Neural Network. • The most relevant stationary sensors for the prediction have been determined. • Fatigue assessment of the turbine can be performed. • Complex strain gauge testing in Francis turbines could be simplified. [ABSTRACT FROM AUTHOR]

Hydrogen is considered one of the key pillars of an effective decarbonization strategy of the energy sector; however, the potential of hydrogen as an electricity storage medium is debated. This paper investigates the role of hydrogen as an electricity storage medium in an electricity system with large hydropower resources, focusing on the Swiss electricity sector. Several techno-economic and climate scenarios are considered. Findings suggest that hydrogen storage plays no major role under most conditions, because of the large hydropower resources. More specifically, no hydrogen storage is installed in Switzerland if today's values of net-transfer capacities and low load-shedding costs are assumed. This applies even to hydrogen-favorable climate scenarios (dry years with low precipitation and dam inflows) and economic assumptions (high learning rates for hydrogen technologies). In contrast, hydrogen storage is installed when net-transfer capacities between countries are reduced below 30% of current values and load-shedding costs are above 1,000 EUR/MWh. When installed, hydrogen is deployed in a few large-scale installations near the national borders. [Display omitted] • High-fidelity models of Swiss electricity sector and hydrogen storage technologies. • No significant hydrogen storage is required in Switzerland under most scenarios. • Large hydropower resources reduce the need for hydrogen storage significantly. • Hydrogen storage becomes relevant with reduced electricity net transfer capacities. • Hydrogen storage is used for high self-sufficiency ratios to avoid load-shedding. [ABSTRACT FROM AUTHOR]

The Turgo Impulse turbine provides a unique and novel solution to increasing the capacity of a hydraulic impulse turbine while maintaining the nozzle and spear injector system (as used in Pelton turbines) for flow regulation. This has produced a turbine which operates in the higher flow ranges usually reserved for Francis machines while maintaining a relatively flat efficiency curve, characteristic of impulse machines. Since its invention nearly 100 years ago, the Turgo turbine has been installed in thousands of locations across the globe. The majority of the development of the Turgo turbine design has been through the use of paper based and experimental studies however recent advances in computational fluid dynamics (CFD) tools have allowed the simulation of the complex, highly turbulent, multiphase flows associated with impulse turbines and some work has been done in applying this to the Turgo design. This review looks at the development of the of the Turgo turbine since its invention in 1919 and includes the paper-based analyses, experimental studies and the more recent CFD analyses carried out on the design. [ABSTRACT FROM AUTHOR]

In the Danube River Basin multiple pressures affect the river system as a consequence of river engineering works, altering both the river hydrodynamics and morphodynamics. The main objective of this paper is to identify the effects of hydropower development, flood protection and engineering works for navigation on the Danube and to examine specific impacts of these developments on sediment transport and river morphology. Whereas impoundments are characterised by deposition and an excess of sediment with remobilisation of fine sediments during severe floods, the remaining five free flowing sections of the Danube are experiencing river bed erosion of the order of several centimetres per year. Besides the effect of interruption of the sediment continuum, river bed degradation is caused by an increase in the sediment transport capacity following an increase in slope, a reduction of river bed width due to canalisation, prohibition of bank erosion by riprap or regressive erosion following base level lowering by flood protection measures and sediment dredging. As a consequence, the groundwater table is lowered, side-arms are disconnected, instream structures are lost and habitat quality deteriorates affecting the ecological status of valuable floodplains. The lack of sediments, together with cutting off meanders, leads also to erosion of the bed of main arms in the Danube Delta and coastal erosion. This paper details the causes and effects of river engineering measures and hydromorphological changes for the Danube. It highlights the importance of adopting a basin-wide holistic approach to river management and demonstrates that past management in the basin has been characterised by a lack of integration. To-date insufficient attention has been paid to the wide-ranging impacts of river engineering works throughout the basin: from the basin headwaters to the Danube Delta, on the Black Sea coast. This highlights the importance of new initiatives that seek to advance knowledge exchange and knowledge transfer within the basin to reach the goal of integrated basin management. [ABSTRACT FROM AUTHOR]

In this paper, we examine the ability of a hydropower cascade to balance variability from wind power. We consider a coordinated hydro-wind system that satisfies a single power balance, and we use a real-time control scheme to optimize system operations such that wind and load curtailment is minimized. The control scheme considers system hydraulics (including dynamic tailrace elevations and water travel times) and system constraints. Generation from an individual hydropower plant is modeled using a convex piecewise planar approximation. We give results from a case study involving hydro and wind power in the Pacific Northwest region of the United States. The objective of this paper is to present a framework for evaluating how the regulation of wind generation affects hydropower operations. Our intention is to use this framework in future work to perform a systematic study of balancing capability across different hydraulic conditions, system constraints, and wind generation scenarios. [ABSTRACT FROM AUTHOR]

For evaluating the power quality in primary frequency control for hydroelectric generating units, the power response time is an indicator which is of main concern to the power grid. The aim of this paper is to build a suitable model for conducting reliable simulation and to investigate the general rules for controlling the power response time. Two huge hydropower plants with surge tank from China and Sweden are applied in the simulation of a step test of primary frequency control, and the result is validated with data from full scale measurements. From the analytical aspect, this paper deduces a time domain solution for guide vane opening response and a response time formula, of which the main variables are governor parameters. Then the factors which cause the time difference, between the power response time and the analytical response time of opening, are investigated from aspects of both regulation and water way system. It is demonstrated that the formula can help to predict the power response and supply a flexible guidance of parameter tuning, especially for a hydropower plant without surge tank. [ABSTRACT FROM AUTHOR]

• There exists controversy and potential conflict over transboundary water-sharing and management of rivers in South Asia. • The article provides a comparative view on water and energy cooperation and discusses its implications. • Water diplomacy in the region is impacted by each country's domestic politics and diplomatic approach, India's hegemonic role, and (lack of) functioning regional institutional frameworks. • Water discourses are heavily securitized; energy is perceived as a commodity of exchange. • Energy diplomacy focussing on mutual benefits and shared interests offers a path for cooperation in other sectors such as water. The last decade has witnessed rapid progress in energy cooperation between the countries of the BBIN (Bangladesh, Bhutan, India and Nepal) sub-region. Cooperation has been bilateral, with each of the countries entering into separate energy development and trade agreement with India, broadly similar to the water sector where national governments engage bilaterally on transboundary cooperation and dispute resolution. A more recent wave of electrical grid interconnections and hydro-energy cooperation has emerged with governments increasingly shifting from bilateral to multilateral energy-sharing agreements. This trend holds considerable potential for regional transboundary water governance. Based on documentary and media analysis along with interviews of key BBIN policy-makers, we identify and examine in this paper four factors for future progress: 1) technical cooperation can be extended to information-sharing for policies and institutions to regulate and manage water resources; 2) India must seize the opportunities and benefits of enhanced regional leadership in the region; 3) simultaneous informal discussion and diplomatic negotiation of water, energy and their nexus can provide BBIN countries the opportunity to highlight potential gains of cooperation and interstate interdependencies; and 4) regional cooperation can give a strong impetus to nations for advancing structural reforms, building institutions and capacity, developing a shared knowledge base, bridging infrastructural gaps, attracting private sector participation, and addressing poverty alleviation goals including job creation. [ABSTRACT FROM AUTHOR]

An accurate prediction of hydro-abrasive erosion helps in design, planning and operation strategies of a hydropower plant. In the empirical erosion model from the International Electrotechnical Commission (IEC) 62364 standard, various terms such as flow co-efficient (K f), material factor (K m) and exponent (p) were not provided for Pelton turbines components. The present paper aims to find the values of these terms and to interpret inadequately defined terms like erosion depth (S) and shape factor (K shape) for application of IEC 62364 (2013)# model. From some field and laboratory data, the values of K f and p were obtained for Pelton turbine components using multivariate regression analysis. The obtained values of K f are in the order of 10−6 and 10−12 for various zones of buckets and nozzle assembly respectively whereas p values are in range 1–5. The K m values for 6 different materials, i.e. three types of chrome nickel steels, plasma and high velocity oxygen fuel (HVOF) sprayed coatings and bronze buckets were obtained as 1, 1, 1, 0.6, 0.1 and 2.2, respectively. #IEC 62364 (2013). Hydraulic machines - Guide for dealing with hydro-abrasive erosion in Kaplan, Francis and Pelton turbines. Edition 1.0 (June 2013), International Electro technical Commission, Geneva, Switzerland. Image 1 • Unknown terms of IEC 62364 (2013) standard are found for Pelton turbine components. • Interpretation for inadequately defined terms of IEC 62364 (2013) is provided. • Material factor is found for 6 types of materials including two types of coating. • A sensitivity analysis revealed the effects of various parameters on IEC model. • Practical aspect of measurement with respect to IEC 62364 (2013) is also provided. [ABSTRACT FROM AUTHOR]

Utilization of hydro-power as a renewable energy source is now of prime importance in the world. Hydropower energy is available in abundance as a renewable source. For run-of river, low head reaction type Kaplan turbines mostly used. In this paper, a parametric study has been conducted on a complex geometry of Kaplan blade through static and dynamic computational analysis by varying the blade profile at different angles in the CAD model. Blade geometry surface and design were developed in Creo using the coordinate point system on the blade. Further blade profiles were analyzed to check and compare the output results. Results show that by changing the blade profile geometry, CAD models can be improved using the computational techniques. Consequences obtained were validated with the experimental/operational data and then four different blade profiles were developed. Research consequences showed improvement in the power output of the turbine. • A robust computational model for Kaplan turbine is developed and verified. • Study and research work led to an enhancement of 5.43% in turbine performance. • A method is devised that resulted in markable financial impact on monthly savings. [ABSTRACT FROM AUTHOR]

This paper presents a humanitarian engineering project in Denver, Colorado's Westwood community. This project was a collaboration with Metropolitan State University of Denver, the Mortenson Center in Engineering for Developing Communities at the University of Colorado Boulder and the non-profit community group ReVision International. This paper discusses the implementation of a helpful technology solution for the community that could alleviate an identified problem common for households in Westwood. This paper presents the project through all the steps: community appraisal, analysis, problem identification, strategy planning, implementation and a plan for monitoring and evaluation. The community analysis identified the financial burden of high energy bills on the residents of the community as a pervasive problem that could be alleviated with a simple design, the solar furnace, a box built using recycled aluminum cans, plywood and acrylic plastic that heats the house through the conversion of solar energy into warm air. To demonstrate the technology, students from MSU Denver constructed and tested 4 different solar furnace design units, and implemented a pilot test at Re:Vision's (a local NGO working in Westwood) office. held a focus group with community leaders (“promotoras”) for discussion about the pilot unit, calculated energy and cost savings for the design, and developed a plan to continue the project from pilot stage to community implementation and installed 4 demonstration units on family households. The paper addresses the capacity and risk analysis for this design, the design itself, the implementation plan, the monitoring and evaluation plan which are the natural next steps in the project. [ABSTRACT FROM AUTHOR]

The hydraulic turbine regulating system (HTRS), which is a core part of hydropower station, is essential and significant for the safe and stabilization operation of the hydropower station. The HTRS is a highly nonlinear, strongly coupled non-minimum phase system, which is difficult and significant to design controller to maintain the frequency stability of the HTRS. In this paper, a fixed-time synergetic controller (FTSC) is proposed to make the frequency of the HTRS stable for small and medium-size power stations in an upper bound time. The input/output feedback linearization is implemented to establish the relationship between the frequency of HTRS and the control input. An FTSC is presented based on the Lyapunov stability theory, synergetic control theory, and fixed-time stability theory. Besides, the proposed FTSC can ensure the frequency stability of HTRS in a limited and quantifiable convergence time, which is not dependent on the initial operating condition and thus overcoming the shortcoming of finite-time stability. Finally, comparative simulations between the proposed FTSC, PID, and sliding mode control (SMC) are presented. Meanwhile, the effects of different hydraulic-mechanical parameters are considered. The results validate the effectiveness and the superior performance of the proposed FTSC over existing PID and SMC under various operating conditions. • A FTSC is proposed for stabilization and chattering-free of the HTRS in small and medium power stations. • The Proof for the frequency stability of non-linear HTRS with the proposed FTSC is presented. • The convergence time which is not dependent on initial operating conditions can be evaluated. • Superior performances of the FTSC are presented by comparing with PID control and SMC. [ABSTRACT FROM AUTHOR]

Worldwide electricity generation is featured by the growth of intermittent renewable energies. In this context, hydropower plays a fundamental role because it provides flexibility to the power grid and ensures its stability. The new grid requirements have led hydropower units to working under a wider range of loads and with more start/stop sequences. Pelton turbines are the most suitable for high heads and have a large regulation capacity. In operation, the runner is impinged by high-speed water jets, and, thus, subjected to strong pulsating forces. As a consequence, the structure presents large deformations and high stresses, especially on the buckets. This situation can be much aggravated if the frequency and shape of the excitation is resonant with those of the structure. Therefore, the modal response of the turbine must be thoroughly studied and the most dangerous frequencies avoided. In this paper, a detailed analysis of the modal behavior of Pelton turbines is presented. Four prototypes have been studied for such purpose. The first one has been modeled numerically and analyzed experimentally. Following a systematic investigation, the effect on the modal shapes and the frequencies of the different parts comprising the turbine has been evaluated. The single bucket and the whole runner have been studied. Finally, another turbine installed in the same power plant has been analyzed to determine the effect of the mechanical design on the frequencies. In addition, two prototypes belonging to other power plants have been studied to see the effects of the hydrodynamic design on the modal behavior. [ABSTRACT FROM AUTHOR]

The Winter-Kennedy (WK) method is a popular choice to estimate the relative flow rates, and thus the expected improvement in the efficiency of a low head turbine after its refurbishment. Runner refurbishment is a common way to improve the plant's efficiency. However, a previous experiment on a model turbine reported deviations between the WK coefficients obtained from two different runners ‒ suggesting a deviation between the estimated and actual improvement in the efficiency. Without formal proof, the deviation was attributed to flow changes in the spiral casing. This paper presents a numerical investigation of the effects of a runner change on the WK method. For this purpose, unsteady Reynolds-averaged Navier-Stokes equations (URANS) simulations of a turbine model with two different runners were conducted. The runner's impact on the average flow conditions upstream and its subsequent effect on the WK coefficients were studied. The study shows the dependence of the WK coefficients to the runner ‒ with a maximum deviation on the coefficient up to 0.7%. The larger deviations were observed in regions prone to strong secondary flow. Following a radial and circumferential sensitivity study, a suitable location to minimize the effects of runner change on the WK method is reported. • Runners operated with same specific speed affect the Winter-Kennedy method. • Flow in the semi-spiral casing changes with runner. • Regions prone to strong secondary flows show a higher level of sensitivity. • Radial and circumferential dependence of WK pressure tap studied. [ABSTRACT FROM AUTHOR]

Hydropower is nowadays essential for balancing the electrical grid providing flexibility and fast response. The role of hydraulic turbines has changed from working at their Best Efficiency Point (BEP) to work in the whole operating range when demanded. Francis turbines working at off-design conditions suffer from dynamic problems that affect the useful life of their components, especially of the runner. Reduced scale physical models of Francis turbines are widely used to determine their hydraulic behavior. Most of the hydraulic parameters obtained in model tests are transposable to prototype by using the similarity theories as long as they meet similitude requirements. However, from the mechanical behavior point of view, both model and prototype structures are not always similar and the mechanical behavior of the model is often not considered for transposition. In this paper, a transposition method for the mechanical behavior of Francis turbines models is presented and the results are compared with the real size prototype. The modal behavior of the runner, its stress and fatigue life estimation for different operating conditions are experimentally compared for both model and prototype. Results present the possibilities and limitations of transposing the mechanical parameters from model to prototype. • A Francis turbine runner mechanical behavior is transposed from model to prototype. • Natural frequencies, damping ratios and mode-shapes transposition is studied. • Stress under operating conditions is transposed from model to prototype. • Relative damage between operating conditions is transposed from model to prototype. [ABSTRACT FROM AUTHOR]

Reactive power shortage is one of the current issues that endanger the stability of the power grid systems. Some massive blackouts have been experienced in the past years due to the unbalance of reactive power. One of the solutions to provide the necessary reactive power to the grid is to operate generators as motors and supply or absorb reactive power when needed. Hydraulic turbines are the most suitable machines to perform this task since they can be easily and quickly dewatered to work as motors (Synchronous Condenser (SC) operation). Nowadays, hydraulic turbines are operating as SC for several hours per day, especially in grids like in US or Canada. The change from generating mode to SC and vice versa can be very fast, depending on the grid requirements. However, these fast changes may affect the mechanical behavior of the machine, reducing its useful life-time or increasing vibrations. In this paper, the effect in the mechanical system of SC operation in a Francis turbine prototype is evaluated. Strains in the runner and vibrations in the stationary parts are analyzed in detail in the fast changes between generating to SC and vice versa. • Synchronous condenser operation in a Francis turbine has been studied. • Runner stress and fatigue have been evaluated for this operating condition. • Vibration behavior of the machine is studied during synchronous condenser operation. • Transient events from generating mode to synchronous condenser and vice versa are investigated. [ABSTRACT FROM AUTHOR]

Closed mines can be used as lower reservoirs of Underground Pumped-Storage Hydropower (UPSH) plants. The excavation of ventilation shafts is necessary to allow the exhalation of the trapped air which is displaced during the turbine process. This paper analyzes the influence of air pressure in the lower reservoir due to the energy losses in the ventilation shafts on the overall energy production. Analytical and three-dimensional CFD numerical models (using VOF formulation for two-phase flow) have been developed in order to know the influence of the air pressure on the turbine operation for the first time. The results obtained show that depending on the usual designs of the ventilation system, the pressure inside the reservoir may vary between 0.67 and 42 mH 2 O. The increase in pressure implies a reduction in the available net head and therefore, the stored energy decreases. The reduction in the generation of electricity could reach up to 62 MWh/cycle (12.5% of the available energy) for an installation of a Francis turbine with a flow rate at full load of 55 m3/s and 214 MW of power with a single air duct of 0.5 m in diameter. Economically, this would imply losses of more than 1.12 M€/year. • UPSH allows storing and producing large amounts of energy in underground spaces. • The air pressure inside the underground reservoir influences the energy production. • Analytical and CFD models have been developed to analyze the effect of air pressure. • A properly design of the vent shafts is essential to optimize the energy production. • Energy generation could be reduced up to 12.5% depending on the vent system design. [ABSTRACT FROM AUTHOR]

This paper aims to analyze the effects of biogas and electricity based cooking on energy use and greenhouse gas (GHG) as well as local air pollutant emissions during 2010–2050 in the case of Nepal, which is highly dependent on traditional biomass (mainly fuelwood) for cooking. The country is rich in hydropower resources. A long-term bottom-up energy system model has been developed using Asia-Pacific Integrated Model/Enduse (AIM/Enduse) model for the analysis. The study developed a business as usual (BAU) scenario and three alternative cooking scenarios. Three alternative scenarios, named as "CL", "CM" and "CH" scenarios; consider low, medium and high level of penetrations of electric- and biogas-based cooking options, respectively. The changes in energy use and electricity generation in the BAU and alternative scenarios have been compared. Fuelwood consumption in the residential sector in 2050 when compared to the BAU would decrease by 12.5% in CL, 19.0% in CM and 24.2% in CH scenarios; and liquefied petroleum gas (LPG) consumption would decrease by 12.8% in CL, 16.3% in CM and 19.6% in CH scenarios. The electricity generation requirement in 2050 would increase by 9.4% in CL, 13.9% in CM and 17.0% in CH scenarios. Finally, the assessment of GHG and local pollutant emissions shows the decrease in all gases in CL, CM and CH scenarios when compared to the BAU. • The implications of biogas and electricity based cooking has been assessed in Nepal. • A bottom-up energy system model (AIM/Enduse) has been used for the analysis. • Fuelwood and LPG consumption in residential sector would decrease significantly. • Hydropower generation will have more promising role in Nepal. [ABSTRACT FROM AUTHOR]

As Europe moves towards renewable energy, hydropower stands out as a renewable technology that can provide supply side flexibility through dispatchable electricity production. Several studies have investigated the flexibility hydropower can provide with a particular focus on the Nordic hydropower resources. Of all European countries, Norway has the largest hydropower resources and storage capacity. However, Norway also has a highly electrified heating sector, which means high electricity demand during winter when reservoirs are low. This paper uses EnergyPLAN to analyse how a shift from individual electric heating to district heating affects the flexibility the Norwegian energy system can provide to Europe. The analysis develops a 2015 reference scenario and two scenarios that introduce district heating based on biomass and heat pumps, respectively. Results show that district heating can decrease the maximum load on dammed hydropower facilities, thus freeing up capacity for potential export. Furthermore, the dammed hydropower facilities are able to balance the electricity demands in all hours of the year. However, the shift to district heating also increases forced export to drain reservoirs as domestic electricity demand is reduced. Also, the amount of import the system is able to handle is decreased under the modelled conditions. • A shift from electric heating to district heating frees up generation capacity. • A decrease in electricity demand leads to excess electricity production. • The amount of import the energy system can handle decreases with district heating. [ABSTRACT FROM AUTHOR]

The pursuit of sustainable development has become a prevalent goal in numerous countries. Therefore, renewable energy development is deemed the prime alternative, as it not only curtails CO2 emissions but also stimulates economic prosperity. Hence, there is a need to investigate rational options for renewable energy development. This paper utilises a research framework that combines linear and non-linear modelling. The specific results are as follows. The study's findings reveal that wind, solar and hydro energy can each promote economic growth and lower carbon emissions. Nevertheless, wind energy exhibits the most effective reduction in emissions, followed by solar energy, and lastly, hydro energy. When it comes to promoting economic development, hydro energy proves to be the most effective, followed by wind energy and then solar energy. Additionally, a panel threshold model is utilised to assess further the CO 2 reduction for solar, wind, and hydro energy across a range of economic levels. The results indicate a double threshold effect for wind energy, whereby the effectiveness of CO 2 suppression initially increases and then decreases as the economic level rises. In contrast, the use of solar power displays a sole threshold effect that incentivizes CO 2 emissions at sub-threshold economic levels, yet significantly curbs them beyond it. Similarly, hydro energy also demonstrates a single threshold effect, but lacks statistical significance below the established threshold and actually heightens carbon emissions above it. Our observations can assist in creating sustainable renewable energy development strategies. [Display omitted] • Investigating the impacts of solar, wind, and hydro on economic growth and carbon emission. • Using the linear and nonlinear panel data in 22 countries from 2001 to 2020. • Solar, wind, and hydro contribute to economic growth and carbon emissions reduction. • Countries with a good economy prioritize wind and solar, while others prioritize hydro and wind. [ABSTRACT FROM AUTHOR]

Abstract: Situated at equator level, Central Africa is a wetted area, sunny and not that windy. The region owns important renewable energy potential, namely solar, hydro and biomass. For a number of reasons, this important potential is still suffering from poor development. The main cause of the poor use of renewable energy is the poor commitment and dedication of governments who have not taken the necessary measures to boost enough decentralized and renewable energy. Thermal plants are hence unfortunately heavily used where other alternatives are possible. The purpose of this paper is among other things aiming at showing how solar and hydro energy sources of Central Africa are currently developed and addressing the problems faced. The work also addresses the issue of filling the gap between the abundant solar and hydro resources and its poor development compare to the rest of the world. Based on some case studies in Cameroon, actions to sustain ongoing initiatives and promote their development are suggested. This paper also addresses the problems actually faced and recommends actions for mitigation for a significant improvement of energy infrastructure in remote areas. In such areas, the promotion of renewable energy and energy efficiency are very important for poverty alleviation. From lessons learned, suggestions will be made to help the countries of the region develop a vision aiming at developing adequate clean energy policy to increase the status of solar and microhydro energy sources and, thus, better contribute to fight against climate change. [Copyright &y& Elsevier]

Abstract: The variable electricity output of the RES (renewable energy sources) power plants, such as wind and hydropower, is an important challenge for the electricity system managers. This paper addresses the problem of an electricity system supported mainly on hydro, thermal, and wind power plants. A binary mixed integer non-linear optimization model with hourly time step is described. The model is applied to a system close to the Portuguese electricity case assuming demand forecasts for the year 2020. The main objective of this paper was to analyze the impact that different levels of installed wind power can have in the operation of this electricity system, taking into account the hourly and intra-annual variation of the renewable resources, the demand projections and also the technical restriction of thermal power plants. The results confirmed wind power as strategic technology to reduce both the marginal cost and CO2 emissions. According to the simulations run, wind power will not replace hydropower but a decrease of thermal power production is foreseen as more wind power is added to the system. Large wind power scenarios will particularly affect gas power plants performance, reducing both the load level and the number of operating hours. [Copyright &y& Elsevier]

• The study depicts societal issues associated with the development projects. • A road map developed that focuses on avenues related to establishment of new development projects. • The SEETA model, based on Multi-Criteria Decision Making techniques is proposed. • Model is demonstrated using comparison of fourteen hydropower plants. • The hydropower plants are compared around five main and fifteen sub-criteria. Selecting an appropriate location for a large infrastructure project poses difficult situations. It shall satisfy sustainability indicators and establish harmony among multiple goals of multiple stakeholders. In such a situation, Multi-Criteria Decision Making techniques allow assessing qualitative and quantitative attributes, analysing and removing subjective biases and help in arriving at objective decisions. However, a single Multi-Criteria Decision Making technique may not be an effective tool to generate concrete results as there is no validation of the results. By utilising hybrid Multi-Criteria Decision Making methods, one can incorporate, gauge, and assess the range of social, economic, and environmental impacts precisely and achieve an accurate result by validating results by other methods. Therefore, this paper develops a model called as Social, Economic, Environmental and Technical Assessment model. It combines four fuzzy Multi-Criteria Decision Making techniques viz. Fuzzy Stepwise Weighted Assessment Ratio Analysis, Fuzzy Multi-Objective Optimization by Ratio Analysis, Fuzzy Weighted Aggregated Sum Product Assessment and Fuzzy Technique for Order of Preference by Similarity to Ideal Solution. This paper utilises the case of hydropower plants in India, how the policy and decision-makers can arrive at the selection of the best location for an infrastructure project. According to the assessment value, Teesta Low Dam IV (Darjeeling, West Bengal) is the preferred hydropower plant for all selected methods. The State could bring social justice, ecological stability; achieve economic benefits and sustainability by appropriating this proposed model in other development fields. [ABSTRACT FROM AUTHOR]

Ecosystem valuation methods (EVM) have been developed by economists and offered as information that decision makers may find useful in making choices about ecosystem service levels. This paper examines the use of EVM by the U.S. Federal Energy Regulatory Commission (FERC) when licensing the operation of existing nonfederal hydropower dams. First, we report on the FERC decision to encourage the applicant to engage in a deliberative, decentralized negotiation process with a wide array of stakeholders that allows for, but does not require, EVM analysis as decision making information. Second, we report on 17 major relicensing cases where project operations that have significant impacts on aquatic restoration and recreational opportunities, and find that in no case did the participants request ecosystem valuation studies for comparison with monetary estimates of hydropower benefits. This reliance on a negotiation processes lieu of ecosystem valuation is consistent with the deliberative valuation processes supported by many ecological economists. [ABSTRACT FROM AUTHOR]

The vulnerability of electric potential generation from water resources has been evidenced due to uncertainties of climatic origin and energy planning. Changes in rainfall regimes are multifactorial phenomena difficult to model. Rainfall is the main natural way of restoring the reservoir levels of hydroelectric power plants. The reduction in rainfall levels may increase in the coming years, resulting in a probable change of the energy matrix configuration of the state of Minas Gerais (MG). This could reduce the share of renewable sources increasing dependence on the importance of energy from fossil fuels, which are the immediate primary sources of energy available. Prior examinations have portrayed the depletion of hydroelectricity in Brazil, or its macro-regions, however this work tries to supply a more focused look at the effects on the electricity and social sectors of the state of Minas Gerais. The study developed in this paper aims to investigate the hydrological potential alteration impacts and consequences on the energy matrix of the state, the greenhouse gas emissions and the social reflexes of these changes due to scenarios motivated by climate change. The investigation intends to show the importance of the water-energy-emissions nexus for energy planning and decision-making, in order to evaluate the best options for dealing with adverse and potentially destabilizing conditions. The results of the analyses show that while hydropower demand was 5.24 Mtoe in 2015, in 2030 the supply of hydropower will be 5.81 Mtoe and 4.72 Mtoe, for the conservative and severe scenarios, respectively. In addition, the effect of climate change may require an increase in the share of non-renewable sources in the energy matrix, which could increase CO 2 e emissions from 4.2% to 7.4% by 2030, compared to the levels in 2016. • Reduction in rainfall levels will change the energy matrix configuration of MG state. • Population growth will boost demand for energy. • It is shown the importance of the water-energy-emissions nexus for energy planning and decision-making. • The energy matrix may considerably increase the CO 2 e emissions by 2030, compared with 2016 levels in the MG state. [ABSTRACT FROM AUTHOR]

Abstract Worldwide, the demand for energy has increased significantly in last two decades, leading to an increased use of non-renewable energy resources. The global agenda aims to reduce the carbon intensity of energy in long-term climate change mitigation strategies, and to achieve Sustainable Development Goal 7 (SDG-7) on affordable and clean energy. Use of renewable energy (RE) can contribute to reducing global greenhouse gas (GHG) emissions while providing incremental financial resources to stimulate clean development mechanisms. Hydropower continues to be the leading RE option and has the additional benefits of water storage for agriculture and other uses. Drawing on the position of four Hindu Kush Himalayan (HKH) countries – Bangladesh, India, Nepal and Pakistan – this paper investigates the current status of hydropower generation and related policies, and attempts to identify the key challenges to and opportunities for hydropower development in the region. Collectively, four HKH countries have commercially feasible hydropower potential of nearly 190 GW. However, only one-third of this potential has actually been tapped so far. Nepal and Pakistan have tapped 2% and 12%, respectively, of their hydropower potential. The current hydropower supply has not been able to fulfill the electricity demand in the region, where 26–37% of the rural population is living without access to electricity, and future demand for electricity is likely to increase sharply. There are several economic, social, technical, environmental, ecological and political challenges to hydropower production in the HKH countries. Despite these challenges, hydropower remains an important option for achieving renewable energy goals in the region. To achieve these goals, we suggest capitalizing on emerging opportunities such as large hydropower development using a 'smart approach', micro-hydropower promotion, energy trade, and regional cooperation for collective energy development programs. [ABSTRACT FROM AUTHOR]

Abstract During the last decades, the Asturian Central Coal Basin (ACCB) has been a highly exploited coal mining area by means of underground mining and its network of tunnels extend among more than 30 mines. Parts of this infrastructure will soon become available for alternative uses since most of the coal mining facilities in Spain will fade out in 2018. Increasing penetration of renewable energy sources into the electrical grid, with intermittent and fluctuating supply, leads to excessive frequency variations, so the development of energy storage technologies are required, such as Pumped Storage Hydroelectricity (PSH). Reduced environmental impacts, deep, non-flooded shafts and abundance of water from underground run-off, make coal mines in ACCB suitable for the development of Underground Pumped-Storage Hydropower projects (UPSH). The network of tunnels of a mine facility has an unusual geometry for a water storage system. Although there are numerous studies for the construction of UPSH plants, until now there have been no known projects of this type under operation. Filling and emptying processes during the operation of the turbine-pump are complex due to the presence of two fluids interacting inside the tunnels, water and air. This paper explores the viability of a network of tunnels as an underground water reservoir. Two-phase three-dimensional CFD models have been developed in order to know the flow behavior in the tunnels. The pressure and velocity results that have been obtained in the simulations confirm that the use of underground mines as a lower reservoir of a UPSH is technically possible. Highlights • Underground coal mines can be used as a lower reservoir of a UPSH project plant. • UPSH allows storing and producing large amounts of energy in abandoned mines from the depressed mining regions. • The water is stored in a reservoir in the form of a network of tunnels. • A numerical model has been made to analyze the behavior of the lower reservoir. • Ventilation shafts are necessary to facilitate the exit of the air during the filling of the tunnels. [ABSTRACT FROM AUTHOR]

Abstract The paper presents the recent trends and ideas for flexible operation of Francis turbines using Full-Size Frequency Converter (FSFC) or Doubly-Fed Induction Machine (DFIM) technology for variable-speed operation. This technology allows for the speed of the runner to be adjusted in order to maximize the efficiency and/or reduce dynamic loads of the turbine according to the available head and power generation demands. Continuous speed variation of up to ± 10 % of the design rotational speed can be achieved with the DFIM technology, while for FSFC there is no such limit by the technology itself. For off-design operation of Francis turbines, depending on the variation of the head and the hydraulic design, the hydraulic efficiency gain from variable-speed operation compared to its synchronous-speed representative can go up to 10 %. In addition, turbines operated at variable-speed can have significant improvement in the response times for power output variations, being able to utilize the flywheel effect from the rotating masses (also known as synthetic inertia). This review focuses on the investigations and the achievements done so far and does not tend to enter deeply into each multidisciplinary aspect of the technology itself. Possible further development directions are also disclosed, mainly towards the hydraulic design and optimization of variable-speed Francis turbines. Highlights • Variable-speed turbines can improve off-design efficiency up to 10% for larger head variations. • Variable-speed operation is done by decoupling the stator from the grid or decoupling the rotor magnetic field from the rotor. • Variable-speed operation gives precise, faster and smoother response to load variations. • Both deterministic and stochastic pressure pulsations are dependent on the speed variations. • Design speed of the runner should be a synchronous value due to the need of bypassing the variable-speed equipment. [ABSTRACT FROM AUTHOR]