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Due to the inherent uncertainty and intermittence of wind power, and the geographical mismatch between the wind power bases and the load demand, the problem of wind curtailment is becoming increasingly serious in China. To promote the consumption of wind power, this paper studies the short-term operation of a wind farm-pumped storage hydropower plant (WF-PSHP) hybrid system which transmits power to multiple cross-regional power grids through ultra-high-voltage (UHV) transmission lines. In this study, the forecasted error distribution of wind power is fitted using kernel density estimation. An optimization model that considers the peak shaving demands of receiving-end power grids (REPGs) is then established to determine the daily operation of the WF-PSHP system. The hydraulic constraints of the PSHP and individual unit operation constraints are also taken into account to make the model more accurate. To improve the solving efficiency, the original stochastic model is transformed into a deterministic mixed-integer linear programming (MILP) problem through several deterministic conversion and linearization techniques. The real-world case studies demonstrate that the integrated transmission of the WF and PSHP can reduce the peak-valley difference of the REPGs while absorbing large-scale wind power on different typical days in summer and winter.

Fluctuation in hydro-electricity production is primarily attributed to natural and human-induced flow variations. Reduced electricity generation because of unavailability of flow inflicts significant upward pressure on the sources and prices. Despite studies on the impact of externalities on river flow variation, there is a distinct research gap on the responsiveness of hydropower plants to change in flow. This study has introduced a novel concept of flow elasticity of power ( e ) to assess the resilience of hydropower projects to flow variation. The theoretical aspect has been established for run-of-river (ROR) and storage-type (ST) cases separately and validated at two projects, one of each type, located in the Budhigandaki Basin in central Nepal. Responsiveness of hydro-projects to the topographical parameters are also dealt with here. For ROR systems, wide-ranging values of e indicate varying levels of resilience to power generation and loss of resources. For ST projects, the response differs according to emptying, filling and ROR-equivalent phases. Furthermore, strong topographical implications on power production and its elasticity are evident. This concept of e sets out a significant research contribution in the hydropower sector and demonstrates its possibility of direct application in projects in ‘priori’ as well as ‘posteriori’ while planning/designing and updating stages, respectively. The e coefficient scientifically informs the planners and developers on the sensitivity of the powerplants to hydrological variations and topography ultimately benefitting the existing global challenge to minimize the loss of precious resources for sustainable hydropower development.

Cascade hydropower plants which have good regulation performance and are managed by the dispatching center of regional power grids are usually required to simultaneously shave the peak load for multiple provincial power grids, which is an important way of relieving the growing peak shaving pressure on power grids in central and eastern China. This paper establishes an optimization model for the short-term generation scheduling of cascade hydropower plants in regional power grids. In this model, minimizing the peak-valley load difference of multiple power grids is adopted as the objective function. In addition to conventional hydraulic constraints, the operation constraints of individual hydropower units, electrical constraints and head effect on the power generation are all considered to obtain precise scheduling. The original nonlinear and non-convex model is converted into a standard mixed-integer linear programming (MILP) formulation through several linearization strategies. The results for the real-world case study indicate that: 1) the proposed model is computationally efficient with a calculation time of 326 s; 2) the peak-valley differences of the Shanghai Power Grid and Zhejiang Power Grid decreased by 9.71% and 2.29%, respectively; 3) compared with actual operation, the proposed model shows better performance in peak shaving for multiple provincial power grids.

Low-head hydropower bears tremendous potential as a renewable energy source, especially in the context of the progressing global warming. In locations with a low head, for economic and environmental reasons, a small hydropower plant with a waterwheel and an asynchronous generator may provide the best solution for sustainable electricity production. The purpose of this study is to demonstrate a new type of low-speed radial piston pump intended to be part of the hydrostatic transmission of such a small hydropower plant. The advantage of the transmission is the possibility of stepless, automatic change of the gear ratio during operation. First, we describe a mathematical model of the proposed pump and subsequently demonstrate a test stand equipped with its prototype with three suction-pressure units. The pump flow rate characteristics calculated using the theoretical model were compared with those obtained from experiments, resulting in the determination and characterization of the pump's efficiency. Supplementary experiments with a hydraulic accumulator installed as part of the investigated system, demonstrated the possibility of flow rate pulsation dampening. The experimental results showed the validity of the developed mathematical model. In conclusion, the correct operation of the pump was corroborated, and its potential application confirmed by the efficiency results.

As the worldwide energy crisis worsens, renewable energy sources have undeniably opened new horizons for our society. It will offer an efficient solution to this severe energy crisis, environmental issues and fulfilling human energy needs. Therefore, six main criteria, social, economic, quality of energy, political, technical, environmental, and sixteen sub-criteria have been employed, and an assessment model is developed for prioritizing the most pertinent renewable energy sources for electricity generation in developing countries in which four major resources, solar energy, wind energy, hydropower, and biomass energy, are considered and their electricity generation potential. Furthermore, the integrated method with the analytical hierarchy process and VIekriterijumsko KOmpromisno Rangiranje are acquired for a comprehensive assessment. The results demonstrate that the economic criterion had the highest weight of (0.353) compared to the technical criterion, which took place second with a weight of (0.244) followed by environmental (0.205) and quality of energy with a weight (0.098), respectively. The political and social criteria have the lowest weights of (0.057) and (0.043). From the review, renewable resources seem to have sufficient potential to develop a sustainable electricity system. Likewise, the model priorities these resources, revealing that hydropower is the best renewable energy source option, followed by wind energy. Biomass energy and solar energy ranked third and fourth. The assessment performed in this study can help decision-makers in Pakistan to frame long-term energy policy directing for sustainability.

The changing energy mix under the integration of wind and solar power widens the load peak-valley difference of the power grid and poses great challenges in power grid operation, especially for peak shaving. Hydropower has a crucial role to play in enabling the integration of more variable renewables. To explore a reasonable approach for the changing roles of hydropower and the development of wind and solar power in response to energy transition, a long-term typical daily aggregate model is developed for hydro-wind-solar power with peak shaving operation. Scenarios of integrated wind and solar power proportions under increasing penetrations are simulated by incrementally increasing the installed wind and solar power capacity. The model is converted to a mixed integer linear programming formulation. Groups of numerical experiments divided by influencing factors are used to analyze the complementary influence and optimization mechanisms. The results demonstrate that (1) the proposed model decouples hydro-wind-solar sources at temporal scales and conducts peak shaving effectively. (2) Different scales of wind and solar power have notable impacts on both long-term and short-term hydropower operation. (3) Developing wind and solar power in reasonable proportions could effectively utilize the complementarity and reduce hydropower output fluctuations on different time scales.

The objective of the current research is to develop a novel analytical approach for the performance evaluation and optimization of a run-of-river hydropower facility. Two types of turbines, Kaplan and Francis are considered and the analysis is validated on the basis of a new hydrological model through adopting a case study approach. In the second step of the study, a sensitivity analysis was conducted to determine the optimum energy production values of the designed hydropower system. The results of the analysis have demonstrated a high energy efficiency for both Kaplan and Francis turbines. The Francis turbine has particularly outperformed the Kaplan turbine in terms of productivity and technical performance. Optimization of the energy production for each turbine concluded that with a fixed water height ranging from a minimum of 5 m up to maximum of 20 m, the highest levels of the energy production are observed when the water speed and the net head reach larger values.

This study employs the econometrics test of endogenous structural breaks to separately investigate the changes in trends of the share of hydropower and non-hydro renewable power in electricity production for China using two separate sub-panels of data spanning from 1971 to 2015 and 1990–2015. To identify structural changes in each renewable power generation series, we apply the Bai and Perron procedure for determining structural breaks to estimate shifting-mean autoregressions and use the low frequency Fourier-type Lagrange Multiplier test to approximate the time series in a non-linear form. Through these tests, our empirical results reveal that the series under investigation are characteristic of segmented trend stationary processes around four or one structural breaks, among which, there are two upward shifts in the 45-year series of hydroelectricity generation occurring in 1978 and 2008, respectively. Meanwhile, one upward shift is identified in the 26-years series of non-hydro renewable generation occurring in 2005. The patterns in the timing of structural changes are suggestive of the causal effects from the recent regulatory shocks and policy change. In the present study, we conduct an innovative attempt to reveal the relevance of renewable energy and policy changes, which may also provide some empirical value in investigating the effect of policy series on renewable energy in other countries.

Energy efficiency interventions in Water Supply Systems (WSSs) need a precise evaluation of the available water flow rates for energy recovery interventions; however, flow meters are generally too costly for being installed in all the gravity adduction pipelines of a WSS. This paper presents a methodology for predicting flow rates in gravity adduction pipelines based on the electricity bill consumption. In this study, the predicted average flow rate is 0.0300 m3∗s−1, being 1.64% lower than the real one. A Pelton turbine has been chosen as energy recovery unit for supplying electricity to a pumping station of a preloading tank where the water is treated to make it drinkable. An energy saving of 475.26 (MW∗h)∗year−1 is achieved, which can be also expressed as 88.87 saved Tonnes of Oil Equivalent (TOE) and 204.36 ktCO2 not released into the atmosphere. The gross economic saving due to the installation of the Pelton turbine is equal to 94.29 k€∗year−1 and it can be further increased up to 116.51 k€∗year−1 if the energy efficiency certificates issued by the Italian Authorities are considered. The Payback Period (PBP) of the intervention corresponds to 3 years, and a Net Present Value (NPV) after twenty years is approximately 1.4 M€.

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 Tw was too large and the inertial time constant Ta 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.

Extreme weather lasting for 5–15 days not only brings large inflows in the medium-term but also causes sharp fluctuations in the daytime load of the power grid which imposes considerable challenges to the modeling and solving of medium-term power grid scheduling. The complex nonlinear constraints and water delay times of cascade hydropower plants significantly increase the difficulty of finding solutions. Hence, this study first advocates an accurate optimization model for determining the medium-term peak shaving operation of cascade hydropower plants considering the water delay time. The objective is to minimize the variance of the remaining load and maximize energy production that aims to regulate the load fluctuation and enhance hydropower efficiency. Then, to describe the water delay time of cascade hydropower plants, a piecewise delay time method (PDTM) is proposed based on the water balance equation. Finally, cascade comprehensive benefits (CCB) are established to alleviate the deviations from the scheduling plan and actual plan affected by the lag time. The developed model is implemented on the eleven cascade hydropower plants of the Lancang River in China. Simulation results demonstrate that the model is able to provide more realistic and executable generation scheduling while obtaining larger hydropower generation benefits and good peak shaving performance.

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.

Private sector actors are taking on an increasingly prominent role in energy transitions, including in hydropower development and finance. Yet, there is little empirical research on the topic. This study covers private sector views on accelerating hydropower investment in Nepal, using Q methodology. Three main viewpoints were identified among 17 interviewed hydropower developers, planners, and investors based in Nepal: 1) Efforts need to be focused on reforming hydropower policies and administration at the national level; 2) Funds for hydropower development need to be increased and sought from a diversity of domestic and foreign private sources; 3) Nepal needs to integrate its energy grid with its South Asian neighbours, starting with India. Areas of strong disagreement include the role of political stability in enabling hydropower development, as well as modes of engagement with Indian, Chinese, and Western partners. Areas of consensus include the need to smoothen land acquisition procedures as well as discomfort with the state-owned Nepal Electricity Authority’s perceived monopolistic status in the sector. Overall, this study contributes to debates on private sector involvement in hydropower development with a nuanced empirical assessment of views which contain clear visions for an independent and domestically driven future of the country’s hydropower sector. Postprint

In the last few decades, the energy demand is increasing globally which, given the present dependency of the energy generation on fossil fuels, results in a continuous increase in CO2 emissions. In an isolated electric grid system like in the SIDS, the majority of the electricity is produced by fossil fuels, therefore most of the SIDS nations are now focusing on Variable Renewable Energy sources (VREs). VREs such as wind and solar are hardly predictable and bring instabilities in the electric power system if not buffered by a storage system. Here we investigate the possibility of using Seawater Pump Storage Hydropower Systems (S-PSHS) as a renewable energy storage solution in an isolated electric grid. For this, the island of Curacao (one of the SIDS nations) is used as proof of the concept. For detecting potential locations for the S-PSHS sites on the island, GIS application was developed. The application of this conceptual proposed solution in similar systems is straightforward and it can be easily upscaled in other geographies. The concept of using seawater for the pumped hydro project is not common in practice and it is anticipated to have technical, environmental and financial challenges which are discussed in this paper.

Power system operations are unavoidably influenced by forecast uncertainties. The forecast uncertainty's effect on operations was quantified in individual systems, however, was seldom investigated in a hybrid system. This study aims to quantify the effect of forecast uncertainties on the hybrid hydro–photovoltaic system operation. First, the operation model is built considering streamflow and photovoltaic forecast uncertainties with long- and short-time scales. Second, total release uncertainty is determined from the sum of squares for releases under different forecast scenarios. Finally, a variance partitioning method is used to divide the total release uncertainty into the uncertainties induced by individual forecast errors. Longyangxia hybrid hydro–photovoltaic power plant from China was selected as a case study. Results provide following insights: (1) long-term inflow forecast uncertainty accounts for 98.89% of the contribution to the long-term release uncertainty, while photovoltaic uncertainty accounts for 1.11%; (2) long-term inflow forecast uncertainty still dominates the short-term release uncertainty, with the contribution of 62.06%; and (3) the total release uncertainty decreases in long-term hybrid operation compared with the reservoir operation, indicating the complementary relationship between long-term hydropower and photovoltaic power. These implications highlight the importance of improving forecast accuracies for varied energy sources at different time scales.

This study investigates the impact of monetary policy on renewable energy generation in Iran. It examines three types of renewable energy generation: total renewable energy generation; solid biomass and biogas energy generation; and the hydropower, solar, and wind group energy generation. The study uses the Kalman filter and vector autoregression (VAR) models to examine annual data from 1984 to 2016. The Kalman filter model showed that the money supply parameter moved with a steady trend, except for a sharp point during the Iran-Iraq War. A sharp point can be found for real interest rate parameter as well, although the time of global crisis and sanctions also affects this coefficient. The VAR model results indicate that only a shock to money supply can affect all the three renewable energy generation types.

The pursuit of Best Management Practices (BMPs) for pressurized water systems has intensified interest in Pumps As Turbines (PATs), given that PAT use enables coupling of pressure regulation with small-scale hydropower generation. Installing PATs instead of micro-turbines provides for several advantages, such as cheaper procurement and maintenance costs, and importantly, the ability to select the most reliable model from among a wide variety of devices available in the market. Nevertheless, the current state of knowledge regarding PAT performance leaves out critical aspects that remain to be adequately addressed, especially for some models, such as centrifugal vertical axis multi-stage pumps running in reverse mode, despite such devices having attractive features that offer particularly advantageous benefits when high head in the system is exploitable. In contributing key experimental findings on four vertical multi-stage (single-, two-, three-, and four-stage) PATs, this paper thus extends the performance related knowledge about vertical multi-stage PATs: prior models from the literature are demonstrated to reliably predict performance, with the contribution additionally consisting in assessing performance dependence on number of pump stages. The results showed both head and power to be highly correlated with the variable number of stages, especially for predicting PAT characteristics at the Best Efficiency Point (BEP) for multi-stage models. However, the single-stage model exhibited slightly lower performance values.

This paper describes the procedure for an extensive survey of hydropower potential locations to be employed at the originating hydropower development planning stage in a basin. The approach utilized spatial tools such as Arc-Hydro, Remote Sensing (RS), and GIS to characterize the Osse Sub-basin (OSB) and Natural Resources Conservation Service - Curve Number (NRCS-CN) hydrological model to compute the stream Peak discharge Qp. This method permits identification of Small Hydropower (SHP) potential locations by considering obtained catchment parameters along the drainage network in a run-of-river project that satisfies the requirement of establishing hydropower plants, which is difficult to achieve in traditional survey study. Results indicate 18 out of 148 points examined in OSB can produce between 677.485 kW and 7622.877 kW clean energy at 92% flow exceedance annually, preventing between 555.8 and 6543.0 tCO2/yr emission from polluting the environment if developed against GHG emission sources. The calculated project cost range is £ 937,167.48–4,048,733.99. This study establishes first clean development mechanism (CDM) procedure in Nigeria to help future activation of SHP resources by identifying SHP promising project sites that can earn saleable certified emission reduction (CER) credits in the optimization model named SHP Resource Assessment and Sustainability Analysis (SHPRASA).

Energy consumption in Pakistan has increased considerably over the last two decades particularly due to industrialization, urbanization, and population growth. To keep pace with the economic growth, the growing energy demands have been fulfilled at the cost of switching from abundant, cheap, and environmentally friendly domestic hydropower to expensive, imported, and higher GHG emitting petroleum products, thus leaving Pakistan at the mercy of global oil crises and environmental degradations. While employing the trans-log production framework, this study has investigated the potential inter-fuel and inter-factor substitution among energy vs. non-energy factors in calculating substitution elasticities between pairs of labour, capital, petroleum, coal, natural gas, and hydroelectricity in order to design policy for Pakistan on how to ensure secure energy and environmental protection. Using the time-series data covering the period 1980–2017, the ridge regression technique was adopted to calculate parameter estimates. The findings show that labour-energy and capital-energy are substitutes, thus signifying the need for greater focus on technological progress and skilled employment creation to save energy and mitigate CO2 emissions. The gradual removal of energy subsidies is suggested to discourage inefficient energy use and stimulate capital-intensive production approaches. The findings also advocate the significance of a diversified energy-mix consisted of hydroelectricity and natural gas.

Globally, demand for electricity has seen a steady increase, with nations striving to meet the demand. However, Nigeria is abysmally struggling to meet the increasing demand with the meagre per capita electricity consumption of 151 kWh, which is lower than the average of per capita electricity in Africa. Presently, the grid-tied electricity installed capacity in Nigeria, estimated at 13,435 MW is primarily generated by fossil and hydro-power plants at approximate distribution of 82.3% and 17.7%, respectively. This work presents single capsule that shows a holistic narrative of the energy access sector in view of energy penetration, sustainability, technology advancement and energy policy evolution. From available records, renewable energy sources in Nigeria are equitably distributed throughout the country, unlike the fossil reserves that are mostly concentrated in the south-south geopolitical zone. Also, there are huge potentials buried within untapped renewable energy in the country, namely wind, small-scale hydropower, geothermal, tidal and biomass energy. Furthermore, cutting edge power generation technologies that incorporate fuel cell, gas-, steam-, and low grade-turbine with carbon capture and fired by dual fuel of natural gas and biomass is promising for both energy access and climate action. The Federal Government of Nigeria's friendly energy policies, coupled with political will to excite implementation are panacea to significantly drive energy access for sustainable socio-economic development.

This article explores the transition to renewable energy for all purposes in developing countries. Ethiopia is chosen as a case study and is an exemplary of developing countries with comparable climatic and socioeconomic conditions. The techno-economic analysis of the transition is performed with the LUT Energy System Transition model, while the socio-economic aspects are examined in terms of greenhouse gas emissions reduction, improved energy services and job creation. Six scenarios were developed, which examine various policy constraints, such as greenhouse gas emission cost. The Best Policy Scenarios cost less than the Current Policy Scenarios and generate more job. The results of this research show that it is least costing, least greenhouse gas emitting and most job-rich to gradually transition Ethiopia's energy system into one that is dominated by solar PV, complemented by wind energy and hydropower. The modelling outcome reveals that it is not only technically and economically possible to defossilise the Ethiopian energy system, but it is the least cost option with greatest societal welfare. This is a first of its kind study for the Ethiopian energy system from a long-term perspective. Publishers version

In recent decades global warming has turned into an international concern. Anthropogenic Greenhouse gases (GHG) are produced through burning fossil fuel leading to an increase in the global warming effect; thus, GHG reduction contributes to mitigating climate change. Utilizing renewable energies, increasing efficiency of and capacity factor (CF) of existing power plants, and recycling waste energy in various industries are convenient solutions to improve the energy systems performance to reduce fossil fuel consumption, leading to GHG emission. So, there is a substantial need for planning and evaluating the energy systems in which various technologies are used, technically and economically. Theis study's main objectives are utilizing the capacity of renewable energies such as biomass, wind, solar, hydropower, and enhancement of CF and efficiency of the power plants in the Mazandaran region in the south of the Caspian Sea. The energy system considered for the region is modeled and analyzed by six scenarios in this paper. The results indicated that the share of renewable energies in electricity production could be increased from 5.4% to 47.7%. The results of cost analysis show that by applying the sixth scenario, which is integrated policies of increasing RER share and improvement of efficiency and capacity factor. The trends of total annual cost, CO2 emission, and fossil fuel consumption are reduced compared to the business as usual (BAU) scenario. The average cost saved by this scenario is about 220 MUSD/year. The average amount of fossil fuels and CO2 emission save are 11 TWh/year and 2.438 Mt/year between 2020 and 2030, respectively.

Energy losses in the region between the runner and outlet section of a conventional hydraulic turbine have been the subject of investigation for a long time. In this paper as well, elbow draft tube losses are determined for the relevant wide range on-cam operating modes of the Kaplan turbine using a contemporary approach. The research considers the impact of swirl flow parameters, defined for the referent inlet of the draft tube, on the hydraulic losses. According to the methodology and obtained numerical results, a new formula for the calculation of draft tube losses is proposed. In the process of a hydropower plant refurbishment, the presented approach may enable more efficient and economically justified consideration of the performance improvement of the entire double regulated hydraulic turbine, especially in the case of keeping the existing elbow draft tube.

Wind power generation faces intermittency challenges, typically requiring reserve power sources to maintain reliability of the electricity grid. This study proposes that hydropower turbines installed at low-head dams can provide reserve power generation to support wind power, avoiding the externalities associated with fossil-fuel plants and conventional hydropower. Low-head dams in the United States are used for flood control, securing municipal water supplies, and providing reservoir pools for recreation. As a case study, we estimated hydropower potential at 12 low-head dams along a 150-km reach of the Fox River (Northeastern Illinois, USA) using a calibrated river flow model. We analyzed the model's output to assess power generation capacity and reliability as a source of baseload power and as a component in a coupled wind-hydropower system. The modeled system performed reliably over a five-year time period despite significant long-term fluctuations in streamflow, offsetting the short-term variability of wind power. However, combining the low-head hydropower system with wind power limited the output of the system to the minimum generated by the low-head hydropower. The low-head hydropower system's small capacity and high break-even price suggest that it is better suited for local applications rather than grid-scale operations, especially if permitting regulations are considered.

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 Nino-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.

Hydrokinetic energy conversion refers to the conversion of kinetic energy in moving water to electricity. It offers an alternative to conventional hydropower, with benefits of modularity and scalability, in addition to being environmentally and socially less impactful. This study aims to determine the theoretical global riverine hydrokinetic resource. We use a 35 year modelled daily discharge data set and vectorised representation of rivers, with near-global coverage and suitable spatiotemporal resolution, to determine the mean annual energy yield of 2.94 million river reaches. The mean global resource (excluding Greenland) is estimated to be 58 400 ± 109 TWh yr−1 (6.660 ± 0.012 TW). Consideration of global spatial distribution, by river reach, illustrates regional variation and shows a tendency for potential to be concentrated along major rivers and in areas of significant elevation change. China, Russia and Brazil are found to be the countries with the greatest potential. After normalisation by total river length, Bhutan, Nepal and Tajikistan also show great potential. Hydrokinetic energy conversion can benefit isolated communities currently without access to electricity. We consider how the specific advantages of this particular technology have the potential to be combined with and complement other established forms of renewable energy technology, providing the means to support the reduction of energy poverty.

A new model, REVUB-Light, an extended modelling approach for the recently developed “Renewable Energy Variability Upscaling and Balancing” (REVUB) model, is highlighted in this study for its relatively simple and effective parameterization for power balance optimization simulations, considering high Intermittent Renewable Energy integration. We demonstrate the effective use of the REVUB-Light model, considering a study for Suriname. The results for different cases are compared to those of the REVUB model, previously used for similar assessments for Suriname. Following distinct optimization procedures, our results confirm the REVUB model findings, i.e., a highly complementary role for wind energy, with up to 20–30% feed-in potential, based on the assumed (currently most probable) hydrological and wind regimes. The REVUB-Light model is validated based on actual operational data, enabling assessments of the potential real world response, and the benefits of flexible (optimized) operational regimes, underlining its potential for renewable energy modelling. It is further shown that Suriname has potential for (near) 100% renewable energy supply, for the mid-term horizon (2030), if additional hydropower potential is developed in combination with hydro-supported wind energy. Overall, the parsimonious approach of REVUB-Light proves to be a reliable modelling tool, and facilitates general usability by “non-experts” such as policymakers.

China has proposed the Renewable Portfolio Standard (RPS) policy to advance the stable development of renewable energy. The RPS requires each province to achieve a stated minimum share of renewable energy power in the total provincial power generation. However, there is an obvious mismatch between the actual capability of generating renewable power and the assigned responsibility for the share of renewable energy power based on the RPS in some provinces. Therefore, this study aims to optimize the renewable power dispatching strategy across provinces for satisfying the RPS requirements in China and to assess the corresponding pressure for each province. A renewable energy power dispatching model is developed, and an economically feasible strategy for dispatching renewable energy power in Chinese provinces in 2020–2022 was obtained. The results indicate that it is necessary to dispatch 395.2 and 140.4 TWh of hydropower and non-hydropower nationwide, respectively, in 2022 to fulfill the RPS target when the COVID-19 is effectively controlled worldwide. If COVID-19 cannot be effectively controlled, 376.6 and 127.8 TWh of hydropower and non-hydropower must be dispatched nationwide to fill the gap. Beijing, Tianjin, Shanghai, and Zhejiang are faced with a relatively high pressure under the RPS target. Finally, a path for each province to achieve its RPS target is proposed.

Positive displacement hydraulic turbine (PDT) is a new class of turbine, capable of effectively generating micro and Pico hydro power for low specific speed applications. This type of turbine is not very popular and hence, it is interesting to research on it. With the rising concerns of environmental pollution, climate change and global warming, emphasis is laid to harness power from renewable energy sources. Micro and Pico hydro turbines are actively researched to generate clean power in addition to the existing conventional turbines. PDT was designed and developed to replace the pressure differential control valves in the hot water supply system and utilize the surplus differential head to generate power and make the system energy efficient. In the present work, experimental studies were conducted on the developed PDT at the designed rotational speed with water at 15, 50 and 110 °C and various differential heads ranging from low to high. The performance data showed the effect of fluid properties on the performance of the PDT due to the change in the temperature of the working fluid. Also, empirical co-relation was developed based on dependent variables using Buckingham π-theorem to predict the flowrate through the PDT at various heads and temperatures. This could help engineers, in future, for designing a new turbine for harnessing micro and Pico hydropower for any application.

Million miles of gravity-fed drinking water and sewage pipelines around the world, especially in rural and urban areas in mountain ranges, have introduced a new renewable energy sources (RES), i.e., in-pipe hydropower systems (IHS). Output power of this technology, similar to other types of RES, suffers from intermittency, while it is still more predictable in comparison to other technologies of RESs. Besides, energy storage systems (ESS) are introduced as a pivotal technology for dealing with the intermittent and non-dispatchable characteristics of IHS through spatio-temporal arbitrage. This paper aims to develop a stochastic mixed-integer linear programming (MILP) formulation that simultaneously determines the optimal location and size of ESS and IHS in a microgrid (MG) considering the correlation between prevailing uncertainties. In this regard, the proposed optimization problem minimizes the expected social cost of MG considering the AC power flow equations and operation constraints. Finally, the efficiency and applicability of the proposed model are illustrated using numerical simulations on the IEEE 33-bus distribution test system.

This paper enables a screening of existing irrigation dams in order to assess and rank potential sites for small hydropower development by using a Geographic Information System (GIS)-fuzzy logic multi-criteria scoring technique. The following criteria are evaluated: dam characteristics (reservoir normal level, reservoir capacity, dam purpose, dam ageing), and grid connection spatial characteristics. The proposed method estimates the suitability degree of each criterion separately and then aggregates them into a Site Suitability Index (SSI). Existing irrigation dams in Turkey are assessed in order to be utilized for hydropower development. The overall score of each candidate site is obtained and, their performance is compared for different strategies. One of the most suitable dams, Karadere, was chosen as a case study. By using the daily continuous monitored data, we showed that flow and head is highly variable during the irrigation season. Accordingly, we evaluated an innovative compact medium-head hydro turbine that can capture those fluctuations with its operational flexibility and minimal civil works. Moreover, an optimal path methodology was applied to find the best grid connection route from the dam to its nearest substation considering the site land use characteristics in order to minimize land expropriation.

Optimizing the hydro unit commitment (HUC) has the potential to increase water use efficiency. However, the large number of variables, along with some nonlinear and non-concave constraints, present a huge challenge to the efficient solution of the HUC problem. For hydropower stations including multiple power plants that have different hydraulic heads, the problem is even more difficult. In this paper, we address this complex HUC problem using a two-layer nested optimization method. First, the total load demand is allocated to each power plant using a novel distribution rate. Thus, in the outer layer, a cuckoo search algorithm optimizes the distribution rate and each unit’s on/off status, while in the inner layer, the load demand of each plant is allocated to online units through dynamic programming. China’s Gezhouba Hydropower Station is selected for a case study. It is shown that: (1) the optimized water consumption is, on average, 1.71% lower than that of actual operations; (2) the optimized status of units vary smoothly with fewer startup/shutdown events; and (3) the optimization performance in non-flood seasons is better than that in flood seasons. These findings verify that the two-layer nested optimization method is an effective means of solving HUC problems for hydropower stations including multiple hydro plants with different hydraulic heads.

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.

Renewable Energy Resources (RERs) are becoming increasingly significant for energy generation and will have vital for the future of humans, earth, and other living things. Due to the negative environmental impacts of fossil fuels, the authorities have taken RERs into account further. As a result, the present study extended a novel model using the Level Based Weight Assessment (LBWA) model based on in Interval Rough Number (IRN) extension of the Combinative Distance-Based Assessment (CODAS) method to cope with uncertain domain-based RER selection. A survey method using literature review and interview has been conducted to find and select appropriate perspectives and criteria; in this regard, the selected criteria were classified based on four groups, including socio-political, environmental, economic, and technical. Five sources of renewable energy, including solar energy, biomass energy, wind energy, hydropower energy, and geothermal energy, are evaluated in Turkey. The results of the extended IRN CODAS approach demonstrated that hydropower energy had the first rank among other sources, followed by solar energy, geothermal energy, biomass energy, and wind energy. In the application of the suggested model, the most suitable RER alternative is determined for Turkey. The results of this study showed the effectiveness, efficiency, and capability of the proposed methodology in the assessment of RERs.

This paper investigates the multi-frequency dynamic performance of hydropower plant (HPP) under coupling effect of power grid and turbine regulating system with surge tank. Firstly, a model of grid-connected HPP with surge tank is established and verified. Dynamic performance of grid-connected HPP with surge tank is evaluated by analyzing stability and dynamic response. Then, the number of frequencies of dynamic response is identified. The generation mechanism of multi-frequency dynamic response is revealed. Finally, the influence of system parameters on multi-frequency dynamic performance is studied. Guidance for actual applications of the obtained law and mechanism is proposed. The results indicate that the dynamic response of grid-connected HPP with surge tank has a feature of multi-frequency. There are three frequencies for the dynamic response corresponding to three subwaves i.e. mass oscillation, water hammer oscillation and grid disturbance oscillation. Low-frequency mass oscillation is induced by water flow and level oscillation in subsystem of headrace tunnel and surge tank. Medium-frequency water hammer oscillation is induced by natural hydraulic oscillation in subsystem of penstock, turbine, governor and generator. High-frequency grid disturbance oscillation is induced by power grid. The coupling effect among penstock, turbine unit and power grid on water hammer oscillation is strong.

Hydropower plants are one of the most convenient option for power generation, as they generate energy exploiting a renewable source, they have relatively low operating and maintenance costs, and they may be used to provide ancillary services, exploiting the large reservoirs of available water. The recent advances in Information and Communication Technologies (ICT) and in machine learning methodologies are seen as fundamental enablers to upgrade and modernize the current operation of most hydropower plants, in terms of condition monitoring, early diagnostics and eventually predictive maintenance. While very few works, or running technologies, have been documented so far for the hydro case, in this paper we propose a novel Key Performance Indicator (KPI) that we have recently developed and tested on operating hydropower plants. In particular, we show that after more than one year of operation it has been able to identify several faults, and to support the operation and maintenance tasks of plant operators. Also, we show that the proposed KPI outperforms conventional multivariable process control charts, like the Hotelling t 2 index.

Africa is characterised by a very high solar potential, with a yearly sum of solar irradiation exceeding 2000 kWh/m2. Many African countries are heavily dependent on hydropower, however, increasingly frequent droughts have been severely affecting hydropower generation in the last few decades. The installation of floating photovoltaics (FPV) in existing hydropower reservoirs, would provide solar electricity to help compensate hydropower production during dry periods and reduce evaporation losses while helping to sustainably satisfy the current and future energy needs of the fast-growing African population. This study provides a comprehensive analysis of the potential of FPV installation in Africa, by using highly accurate water surface data of the largest 146 hydropower reservoirs in the continent. In addition to the electricity production, evaporation savings and the potential extra hydroelectricity generated by these water savings are also estimated at reservoir level for four different cases and two types of floating structures. The results indicate that with a total coverage of less than 1%, the installed power capacity of existing hydropower plants can double and electricity output grow by 58%, producing an additional 46.04 TWh annually. In this case, the water savings could reach 743 million m3/year, increasing the annual hydroelectricity generation by 170.64 GWh.

With the construction of cascaded hydropower stations and high-voltage direct current transmission systems, hydro-dominated power systems are being developed all over the world. Regulation stability of sending terminals is an important guarantee for utilizing clean energy. However, the potential hydropower-induced frequency oscillations in these systems might limit the hydropower delivery quality. There is a need for comprehensive understanding and systematic tools to support decision-making processes in frequency regulation. This paper studies this issue from three aspects: modelling adaptability, quantitative analysis and coordinated optimization. Firstly, four models of hydropower governor system in two regulation modes are conducted to analyze the effect of model simplification on stability. The refined eighth-order model of hydraulic damping is derived. Secondly, the oscillation characteristics are quantified by applying a new method of stability margin. The operating boundary is proposed to guide the high-quality operation. Finally, a novel multi-objective optimization strategy is proposed to coordinate the stability-tracking conflict. The reliability and effectiveness are demonstrated in the isolated operation mode and the islanded operation mode. This work can be applied by power producers and grid operators to a better understanding of oscillation features, and supply insights and method on how to improve the regulation quality of hydro-dominated system.

This paper presents an overview of current electricity generation and consumption patterns in the Arctic. Based on published data and new data collection this paper provides an overview of the installed capacity per energy source. A more detailed view of electricity systems is also presented, showing how different types of resources can be used and combined within Arctic communities. The paper briefly discusses which aspects of transmission systems are of special interest under the harsh climatic conditions of the Arctic. A description is given of the various electricity generation technologies that have been proven to be effective for use in Arctic environment, and those that are currently in use, including diesel, hydropower, photovoltaic, and wind power, in addition to discussion of different back-up options. Furthermore, for a more holistic view concerning such energy systems the socio-economic dimension is addressed with a focus on energy security, through an investigation of energy availability and affordability in the Arctic. The availability of energy in the harsh Arctic environments can be crucial for survival and affordability, and can have a huge impact among low-income communities.

The increasing peak-valley differences pose a major threat to safe operation of the thermal-dominant power grid in China. Cascade hydropower stations, especially for one-reservoir and multi-cascade hydropower stations (OMHS), as the second largest power supply in China form an important part of peak shaving operation. However, nonconvex and nonlinear constraints have made it deeply difficult to perform the daily peak shaving operation (DPSO) of OMHS. In this paper, an improved DPSO model of OMHS considering water delay time is formulated and solved. Firstly, the confluence coefficient method (CCM) is developed to accurately describe the water delay time of OMHS. Secondly, to reduce the errors and water spillage, aggregation of nonlinear constraints, selection of the linearized area and periodic hypothesis are performed. Finally, an MIQP model integrated CCM is established by considering one-reservoir and six-cascade hydropower stations from the Hongshui River of China as a case study. The optimization results demonstrate that the proposed model can accurately simulate real-world system, and the optimized peak-valley differences on typical days in dry season and wet season reduce by 25% and 33%, respectively. Moreover, the CCM can produce more realistic and executable generation scheduling than the state-of-the-art description method of water delay time.

Despite the considerable contribution of hydropower for meeting electricity demand and meanwhile achieving free carbon emission, the rationality of hydropower exploitation needs to be reassessed in the context of hydropower curtailment being severe in some hydro-dominant areas. In this paper, a two-stage fuzzy-stochastic chance-constrained interval (TFCI) regional energy system optimization model under multiple complexities is developed for systematically assessing the rationality of existing hydropower exploitation plan, and reflecting the tradeoff between system cost and reliability for Sichuan territory where the exploitable hydropower resources rank first in China. Results showed that the degree of hydropower overcapacity would become far more severe under the real existing energy structure planning. Instead of continuously boosting hydropower exploitation, proper limitation on hydropower installed capacity expansion to make other renewable energy obtain deserved promotion can effectively reduce system cost and improve the utilization efficiency of all the renewable technologies. The highest utilization efficiency of hydropower, wind power and solar power could achieve [90%, 100%], [100%, 100%], and [100%, 100%], respectively. The obtained results also indicated that greater uncertainty about system cost may have to be faced if policymakers aim to lower risk and enhance system reliability. Suggestions are provided for eliminating the irrationality of hydropower in Sichuan and other similar hydro-dominant regions based on above mentioned conclusions.

Ladder hydropower systems can improve hydropower stability by dispatching the load among each station. However, the impact to ecosystem brought by the stations is obvious. In order to study the ecological and economic performance of ladder hydropower systems, this paper conducts an emergy evaluation on the ladder hydropower system of the Lancang River in Yunnan Province, China. Based on the input and output data of each station, the emergy indices under separate and combined operation modes are calculated. The ecological service losses show that the impact of hydropower stations on environment is mainly reflected in the sediment loss, followed by soil erosion and non-endangered biodiversity loss. The results of other emergy indices for the separate operation mode show good sustainability of the hydropower stations. As for the combined operation mode, the sustainability index of the system will finally be 8.88, which means a good utilization efficiency and sustainability. The fair price of the system is 0.205 yuan/kWh when the seven stations are operated, which is higher than the grid connected hydroelectricity price in Yunnan province, demonstrating that the system is unprofitable. Considering the results of economic and emergy analysis, a better economic benefit and sustainability could be achieved when Jinghong and Gongguoqiao hydropower stations are cancelled.

Agriculture is one of the most energy intensive activities within the European Union. The common absence of electric infrastructure in these rural settings has led to the need for in situ generation in many cases. The existing excess pressures in large pressurised irrigation networks makes the generation of micro hydropower here a possible alternative renewable energy source. Pump-as-turbines have been proposed as a cost-effective technology for such purposes, taking advantage of the excess pressure in pipe networks to produce energy. This paper presents a methodology for the design of a plant for micro hydropower generation in an agricultural farm and outlines the predicted benefits of the installation. These predicted benefits were also compared with the measured performance of the plant for the 2019 irrigation season. The main aim of the plant was to replace a diesel generator that supplied energy to the farm. The excess pressure found in the pipe network varied between 0m and almost 60m. The nominal power of the pump-as-turbine was selected to supply the maximum energy requirements of the farm. The predicted operation time of the plant was estimated at up to 3199 h concentrated between April and September. An annual savings of approximately €2950 and 11 t eCO2 were also estimated. The measured results showed an actual operation time of 2443 h between May and September, as in April the monitoring system was not operational. For this operation time, the savings were €2258 and 8.4 t eCO2. Considering the April theoretical irrigation time obtained, the savings raised up to approximately €2434 and 9.1 teCO2. The return on investment of the installation was computed to be recovered in less than ten years.

Wind variability and hydro-wind complementarity should be both considered in the planning of electrical power systems. In such cases, the spatio-temporal dependence between streamflow and wind speed regimes needs to be asses to balance the electricity generation. Medium-term hydrothermal scheduling problems (MTHS) are used to define operation policies for electrical power systems under 5–10 years horizon. MTHS uses stochastic optimization techniques fed by synthetic streamflow scenarios. To set better operation policies, such scenarios should well represent statistical features of historical data. With the rapid growth in the installed capacity of wind power, operators are encouraged to consider novel approaches to represent the dependence of hydrometeorological variables. This study integrates wind variability and hydro-wind complementarity in the medium-term planning of electrical power systems employing joint simulation of periodic streamflow and wind speed time series. The generated scenarios are used as input to derive monthly operational policies via Implicit Stochastic Optimization. A hydropower plant and a wind farm, both located in the Northeast region of Brazil were selected as a case study. Results show that considering wind variability and hydro-wind complementarity can significantly reduce energy deficits in power systems and increase the flexibility in the operation of water reservoirs.

A comprehensive optimization model was developed to identify the optimal set of non-storage based small hydropower projects (SHP) along a given river reach. The model was based on a greedy genetic algorithm that maximizes net annual benefit. For each project, the model determines intake location, penstock diameter and length, and turbine number and capacity. The novel features in the model include: 1) bi-level optimization that produces robust results, 2) improved search for SHP intake locations, 3) inclusion of turbine number as an explicit optimization variable, and 4) nested optimization modules and parallelized execution. Model performance was assessed through application to the Mamquam River in Canada and the Guder River in Ethiopia. For the Mamquam River, the model identified seven feasible projects. The model provided suggestions for further improvement of one of the two existing SHPs on the river through shifting the intake 1.2 km upstream of the existing intake to provide a greater net benefit. No SHPs have been constructed on the Guder River yet; however, the model suggested 19 potential SHPs that could provide 62% higher annual net benefit compared to the results of a previous model recently applied to the same study area.

The optimization of hydropower multi-reservoir systems is one of the most challenging reservoir management problems due to the complex dynamic nonlinear influencing variables such as reservoir active storage volume, released water discharge rate, and water pressure head available for hydropower generation. To optimize such a complex problem in an efficient way, the development of a high-precision meta-heuristic algorithm are of essential significance. This paper develops an adaptive differential evolution with particle swarm optimization (A-DEPSO) algorithm to derive optimal operating rules for multi-reservoir systems with the purpose of hydropower production. A-DEPSO algorithm uses novel mutation and crossover mechanisms to improve global and local search capabilities, respectively. The application of the proposed method is verified to solve a complex four-reservoir hydropower generation system, located in the southwest of Iran. The results achieved indicate that the A-DEPSO reduced the value of the objective function by an average of 57% compared with other well-known optimizers in the literature. Furthermore, the total power generated from the four-reservoir system using the proposed method increased by an average of 11% compared to the other methods. Finally, the results obtained in this study confirm that the A-DEPSO can be used efficiently to solve complex multi-reservoir hydropower generation systems.

As energy system will increasingly become renewable, they will face new challenges that mainly arise due to the varying output by many renewable energy technologies. An issue that is especially prominent for countries with high shares of hydropower in their electricity generation is the varying yearly output of these technologies. This work aims to propose a techno-economically optimized energy system for such a country, using Portugal as example. For this purpose the current situation is analyzed and an energy demand model for 2050 created. The energy system is optimized for years with different outputs of hydropower to analyze the system’s behavior using the simulation tool EnergyPLAN. As the tool does not possess inherent optimization capabilities it was coupled with the gray wolf optimization algorithm using Matlab. Subsequently, a system is proposed that is able to cover Portugal’s expected energy demand under all circumstances. The future system will rely strongly on wind and solar power as they are expected to cover around 75% of Portugal’s electricity demand. Furthermore, the analysis showed that Portugal needs to build up electrolyzer capacities of 4.2 GW and SynGas capacities of 2.4 GW as the SynGas will be used to balance supply in demand, especially in years with lower hydropower output. The system’s cost will be between 22 and 35% cheaper than the created reference model. Furthermore, the primary energy demand is expected to decrease from 253 TWh to around 150 TWh while the electricity demand rises from 49 TWh to around 110 TWh.

This study provides a meta-analysis of renewable landscape energies in Iran. In order to do this effectively, we identify and estimate the amount of wind, solar, geothermal, biomass and tidal energy in Iran, identifying the potential for exchanging RE with neighboring countries, and methods for utilizing these energies in architectural design and landscape design. Data used are collecting from local and world databases and presented for analysis using descriptive and inferential statistics. The results show that the level of achievements of the stated goals is generally low. The plurality of RE documents and offices, lack of operational programs and sub-optimal use of private sector capacity are the main weaknesses. It is further concluded that if conditions were more conducive to private sector participation and appropriate operational and action plans were adopted, Iran could supply solar energy to Azerbaijan, wind energy to Turkmenistan and Afghanistan, and can supply Iraq with hydropower. Ultimately it is proposed that the adoption of a comprehensive and integrated RE policy which minimizes the number of policy documents and concentrates RE management in a small number of offices is an important factor in facilitating the success of renewable energies in Iran.

Water column separation (WCS), the breaking of continuous water flow by a vapor cavity, is extremely dangerous because the rejoining of the separated water columns would lead to tremendous pressure rises. Therefore, the turbine draft-tube pressure after the load rejection in hydropower stations should be controlled to prevent such an unbearable load of turbine units. To understand the forming, growing and collapsing processes of WCS in pump-turbines during the load rejection transients with guide-vane closing, a model pumped-storage system was simulated by the one-dimensional and three-dimensional coupled computational fluid dynamics model, in which the water conveyance system and pump-turbine were treated as one-dimensional and three-dimensional domains, respectively. The entire processes of the breaking and rejoining of water flow in the pump-turbine, as well as the variations in the pressure field and hydraulic forces on the runner, were analyzed. The main finding is that the collision of the separated water liquids and the collapses of the cavities occur separately with a time difference, which induces two high-amplitude mono-pulses in both the axial and radial forces on the runner. These two successive hydraulic impacts are extremely destructive and should be considered with greater emphasis when evaluates the risk of WCS.

The present work is carried out to study the performance of a Savonius rotor for small-scale hydropower generation. It has been observed that some of the irrigation channels available in the rural areas are having enough bed slope to generate kinetic energy, which can be harnessed through a Savonius rotor. An in-house fabricated scale-down model of the Savonius rotor is tested at an inclination of the re-circulating indoor multipurpose tilting flume at 0°, 0.5°, 1.0°, 1.5° and 2.0° to determine performance under controlled conditions. It is observed that at the tip speed ratio of 0.92 and channel inclination of 0.5° compared to 0° inclination, the coefficient of power and coefficient of torque improved to 40% and 10%, respectively. Furthermore, it is found that the torque and power developed by the turbine are maximum at a bed slope of 2.0° owing to the maximum available energy.