Small-scale Hydropower Generation Research Articles

Numerical studies on the performance of Savonius turbines for hydropower application by varying the frontal cross-sectional area

The Savonius turbine is a drag-based device that utilizes hydrokinetic energy in irrigation channels for small-scale hydropower generation. Since it is a drag-type device, the turbine blade frontal cross-sectional area influences the performance of the turbine blade. In this paper, the influence of taper on the turbine blade bottom, top, and middle sides on the Savonius turbine performance was computed numerically using the sliding mesh technique with a 0.5 m/s water inlet velocity. In this study, the effect of various blades with varying cross-sectional areas has been analyzed numerically using the sliding mesh technique, and the results were compared with the semicircular blade profile. The variation of torque coefficient with respect to rotor blade rotation was plotted, and pressure and velocity variation were analyzed to investigate the performance parameters. The results showed that the top small, middle high, and bottom small blade profiles performed better than the semicircular, inverted taper and top high, middle small, and bottom high blade profiles. It is observed that the maximum torque coefficient at a TSR of 0.7 is 0.35, and the maximum power coefficient at a TSR of 0.9 is 0.253.

Design and Optimization of an Alkaline Electrolysis System for Small-Scale Hydropower Integration

Alkaline electrolysis systems are currently considered to be suitable for large-scale hydrogen production. Previous research has primarily focused on integrating renewable energy sources such as solar and wind into water electrolysis systems. However, intermittent issues stemming from the sporadic nature of renewable energy sources have led to the introduction of energy storage systems (ESSs) to address these intermittent challenges. Extensive research has been conducted on the efficiency and operational aspects of these systems. In contrast to other renewable energy sources, hydropower offers the advantages of stable output and high utilization, making it a promising solution for overcoming intermittent issues. In this study, we propose the design of an optimized alkaline electrolysis system tailored for small-scale hydropower generation. This approach allowed us to confirm the efficiency of a small-scale hydropower-based hydrogen production facility and the analysis of hydrogen production costs under diverse scenarios. Notably, the optimal selling price per kilogram of hydrogen was determined to be USD 15.6 when the operational time exceeded 20 h, albeit indicating a challenging market supply. Under the consideration of various scenarios and government subsidies, this study revealed that a USD 10/kgH2 subsidy or 24 h of continuous operation achieved break-even points in the sixth and eighth years, respectively. Ultimately, the findings underscore the necessity for essential measures, including government backing and technological advancements in small-scale hydropower facilities, to enhance the economic viability of the green hydrogen market in South Korea.

Investigation of a helical Savonius turbine with a deflector system

The growing demand for renewable energy sources to meet electricity needs has underscored the importance of exploring new resources of renewable energy. Among the various alternatives, Helical Savonius rotors have emerged as one of the most widely used technologies for small-scale hydropower generation. Numerous studies have been conducted to investigate these types of rotors, particularly to enhance their power output. Despite existing research, there is still a need for modifications and proposals for new configurations of Savonius rotors. This paper presents a numerical study of a Savonius rotor equipped with a new design of a deflector. The results indicate that the highest power coefficient achieved is 0.1247 at a tip-speed ratio of 0.7 in the absence of a deflector system. The geometric parameters of the deflector are varied to identify the configuration that generates the highest power output. With the implementation of an optimal configuration for the new deflector system, the maximum power coefficient is improved to 0.168 at a tip-speed ratio of 0.7. Otherwise, the maximum power coefficient could be enhanced by 34% compared to the same configuration without a deflector. This significant improvement highlights the potential of the proposed design system.

Experimental Study on the Effects of Turbine Blades Types on the Performance of Centrifugal Pump as Pico-Hydropower Generation

Turbines are rotary mechanical devices used to extract energy from rivers with waterfall and convert them into electricity for rural areas. However, many small turbines installed in rural areas are expensive and dependent on the types of blades to provide the required energy. Therefore, this study aims to determine the effects of backward, inclined, and forward blades of turbines on the centrifugal pump's performance as pico-hydro power. This study was carried out in Riau Province due to the low flow of water, with varying turbine blades for small-scale hydropower generation. Rust-resistant and lightweight materials were selected for the manufacture of the turbine and to keep it from damaging. The turbine was tested in a laboratory to determine the characteristics and maximum power output from rivers and waterfall. The result showed that the turbine produces a maximum electrical power of approximately 1000 Watts using the backward blades due to its ability to support and save water resources.

Energy performance evaluation of an axial-flow pump as turbine under conventional and reverse operating modes based on an energy loss intensity model

As a low-cost scheme for small-scale hydropower generation, pump as turbines (PATs) are used at different hydrosites around the world. Nevertheless, a big number of recently conducted studies on PAT performance have mainly focused on the centrifugal type, despite the fact that the axial-flow type has a comparatively large flow capacity, thus disposing of higher power density. Therefore, this article seeks to investigate the flow dynamics of an axial-flow PAT and associated energy loss characteristics, under both pump and turbine operating modes. It adopts the numerical simulation method and uses entropy production theory to propose an energy loss intensity model in the cylindrical coordinate system, which quantitatively gives the spatial variation pattern for energy losses in pump and turbine operating modes. In addition, the correlation between energy loss and flow instability is deeply analyzed, where the energy characteristics in pump and turbine modes are quantitatively evaluated. It is shown that the energy loss within the impeller and the guide vane flow fields, for both operating modes, is mainly because of the turbulent entropy production. The proportion of direct entropy production and wall entropy production is found to be relatively small. The velocity gradient, flow vorticity, turbulence intensity, and energy losses within the flow passages of the axial-flow PAT have been closely related. However, owing to the difference in PAT operating modes, there is a significant difference in the location of energy losses. The unstable flow phenomena, such as the impact at the blade inlet, flow deviation at the blade outlet, flow separation, back-flow, and vortex, are the main reasons for entropy production. This study serves as a reference for the design, optimization, and application of axial-flow PATs.

Effective grid connection approach for an overshot waterwheel

Interest in very small-scale hydropower generation has increased over the past few years. These pico-hydro systems range from a few watts to several kW. The exploitation of low head sites does not require expensive civil works and is environmentally sustainable. Pico-hydro systems are attractive not only for remote areas where the grid is not available, but also for grid connection. This is especially relevant in existing infrastructures, used for other activities but which can also be used for energy generation. Waterwheels are emerging with enormous potential in this context. Low speeds and variations in head and water flow are a constraint to their connection to the grid. This study shows that they can be effectively connected to the grid using competitive and widely available technology for other renewable sources, such as photovoltaics. This paper presents an innovative approach for an effective grid connection of a pico-hydro system based on an overshot waterwheel. For this purpose, a permanent magnet synchronous generator and a photovoltaic inverter are used. The compatibility between them is analysed in detail and the analysis is valid for other hydro turbines. The 2 m diameter waterwheel has been installed on an existing infrastructure of an aquaculture centre. With a flow rate of about 13 l/s, it injects an average power of 126 W into a microgrid with a global efficiency of 50%.

An Operative Framework for the Optimal Selection of Centrifugal Pumps As Turbines (PATs) in Water Distribution Networks (WDNs)

The current significant increase in energy consumption has resulted in the need to develop and implement effective approaches for defining alternative and sustainable solutions to couple primary resources with supporting methods of energy generation. In the field of effective water distribution network (WDN) management, the suitability of combining pressure regulation with small-scale hydropower generation is attracting even more interest, given that it can possibly reduce water leakages, as well as produce attractive rates of renewable energy. Specifically, pumps as turbines (PATs) are widely considered a viable solution because they combine hydraulic benefits with affordable investment and management costs. Nevertheless, despite several approaches available in the literature for the optimal selection and management of PATs, choosing the most suitable device to be installed in the network is still a challenge, especially when electrical regulation is arranged to modulate the PAT rotational speed and optimize the produced energy. Several approaches in the literature provide interesting solutions for assessing the effectiveness of electrical regulation when a PAT is installed within a water network. However, most of them require specific knowledge of the PAT mechanical features or huge computational efforts and do not support swift PAT selection. To overcome this lack of tools, in this work, an operative framework for the preliminary assessment of the main features (the head drop and the produced power at the best efficiency point (BEP), the impeller diameter and the rotational speed) of a PAT is proposed, aimed at both maximizing the daily produced energy and performing challenging economic selection. Then, it is assessed by estimations of the corresponding payback period (PP) and the net present value (NPV).

Performance enhancement of vertical axis hydrokinetic turbine using novel blade profile

Savonius hydrokinetic turbine is a promising technology for small-scale hydropower generation. The savonius turbine has a simple design and good starting characteristics but suffers from poor performance. In this study, a novel blade profile has been proposed to improve the performance of the conventional savonius turbine rotor. The new blade profile is based on a S1048 airfoil section. The geometry of S1048 airfoil section blades is composed of straight and curved segments. The long straight edge provides larger moment arm and gap flow while the curved segment decreases the effect of negative torque on the rotor. Unsteady RANS CFD simulations have been performed to evaluate and compare the performance of the proposed blade profile. It is shown that the maximum power coefficient of the conventional design can be improved by 14% at a tip speed ratio of 1, by using the new blade profile. The performance of the proposed design has also been evaluated by augmenting an upstream curtain arrangement with the turbine. As a result, an additional 13% increase in the power coefficient was realized when compared with the conventional augmented rotor.

Optimization of the Efficiency of a Michell-Banki Turbine through the Variation of its Geometrical Parameters using a PSO Algorithm

Small-scale hydropower generation can satisfy the needs of communities located near natural sources of flowing water. The operating conditions of a Michell–Banki Turbine (MBT) are relatively easier to meet than those of other types of turbine, making it useful in places where other devices are not suitable. Moreover, MBT efficiency is almost invariable with respect to flow rate conditions. Nevertheless, such efficiency commonly ranges between 70% and 85%, which is lower than that of other water turbines like Turgo, Pelton, or Francis turbine. The objective of this work is to determine the maximum theoretical efficiency of an MBT and its associated geometrical parameters by implementing Particle Swarm Optimization. The results show a higher effectiveness of the mathematical formulation compared with other cases from literature and show the performance of the optimization method proposed in this study in terms of solution and processing time. Finally, a maximum MBT efficiency of 93.3% was achieved.

Optimization of the Efficiency of a Michell–Banki Turbine Through the Variation of Its Geometrical Parameters Using a PSO Algorith

Small-scale hydropower generation can satisfy the needs of communities located near natural sources of flowing water. The operating conditions of a Michell–Banki Turbine (MBT) are relatively easier to meet than those of other types of turbine, making it useful in places where other devices are not suitable. Moreover, MBT efficiency is almost invariable with respect to flow rate conditions. Nevertheless, such efficiency commonly ranges between 70% and 85%, which is lower than that of other water turbines like Turgo, Pelton, or Francis turbine. The objective of this work is to determine the maximum theoretical efficiency of an MBT and its associated geometrical parameters by implementing Particle Swarm Optimization. The results show a higher effectiveness of the mathematical formulation compared with other cases from literature and show the performance of the optimization method proposed in this study in terms of solution and processing time. Finally, a maximum MBT efficiency of 93.3% was achieved

Experimental assessment of the impact of number of stages on vertical axis multi-stage centrifugal PATs

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.

Performance Study of Twisted Darrieus Hydrokinetic Turbine With Novel Blade Design

Abstract Twisted Darrieus water turbine is receiving growing attention for small-scale hydropower generation. Accordingly, the need for raised water energy conversion incentivizes researchers to focus on the blade shape optimization of twisted Darrieus turbine. In view of this, experimental analysis has been performed to appraise the efficiency of a spiral Darrieus water rotor in the present work. To better the performance parameters of the studied water rotor with twisted blades, three novel blade shapes, namely U-shaped blade, V-shaped blade, and W-shaped blade, have been numerically tested using a computational fluid dynamics three-dimensional numerical model. The maximum power coefficient of the Darrieus rotor reaches 0.17 at a 0.63 tip-speed ratio using twisted blades. Using V-shaped blades, the maximum power coefficient has risen to 0.185. The current study could be practically applied to provide more effective employment of twisted Darrieus turbines and to improve the generated power from flowing water such as river streams, tidal currents, or other man-made water canals.

Studies on application of vertical axis hydro turbine for sustainable power generation in irrigation channels with different bed slopes

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.

Numerical assessment of the vulnerability to impact erosion of a pump as turbine in a water supply system

Abstract Nowadays, the installation of pumps as turbines (PATs) in water supply systems (WSSs) is considered attractive because it is able to effectively combine the pressure regulation with the small-scale hydropower generation. One critical aspect concerns the behaviour of the PAT in the presence of solid particles in the flow which impinge against the inner surface of the device, producing a loss of material termed impact erosion. In this paper, the numerical assessment of PAT erosion is performed, by referring, as a case study, to an existing pressure control station in Southern Italy. The variable operative strategy (VOS) was applied to derive the frequency distribution of flow rates over the PAT operation, under the hypothesis of performing the hydraulic regulation of the hydropower plant. The commercial computational fluid dynamics (CFD) code Ansys Fluent was employed for simulating the liquid–solid flow inside the PAT and then coupled with an in-house code to estimate the erosion. The vulnerability of the PAT to wear was analysed by varying its flow rate, aiming at characterizing the decay of PAT components at a constant rotational speed. Finally, a detailed characterization of the PAT response to the particle impingement at its best efficiency point (BEP) was developed and discussed.

Computational parametric analysis of the design of cross-flow turbines under constraints

Abstract The cross-flow turbine is an attractive technology for small-scale hydropower generation thanks to its low capital cost and relatively high efficiency even under partial discharge operating conditions. It has been proposed that this kind of turbine can be manufactured from standard steel pipe sections given its simple geometry, an alternative that would further decrease the turbine’s capital cost compared to highly engineered cross-flow designs. This article explores the trade-offs encountered during the design of cross-flow turbines under the constrains imposed by the discrete set of dimensions available for commercial steel pipes. First, the computational model is presented, analyzed in terms of its convergence behavior, and validated with experimental data. Then, a parametric analysis is performed to understand the relative importance of the design variables and their optimum value in regard to the turbine efficiency. Based on the design guidelines derived from the parametric analysis, an example cross-flow turbine design is presented and thoroughly characterized, demonstrating that it is possible to engineer a cross-flow turbine of competitive efficiency out of commercial steel pipes. These guidelines may encourage the use of cross-flow turbines as an appropriate technology for off-grid regions.

Performance study of a Helical Savonius hydrokinetic turbine with a new deflector system design

The use of renewable energy sources has becoming a necessity to generate electricity. Helical Savonius rotors have been preferred for small-scale hydropower generation. Numerous studies were carried out to improve the performance of the Helical Savonius rotor which has not been fully explored. In this paper, an experimental study was carried out to evaluate the performance of a Helical Savonius water rotor in an irrigation channel. In order to enhance the performance of the studied water rotor, a new deflector system design was proposed. Different configurations of the proposed deflector system were tested numerically using the commercial software ANSYS FLUENT 17.0. Without a deflector system, the maximum power coefficient is found to be equal to 0.125 at tip-speed ratio of 0.7. Using the optimal configuration of the new deflector system, the maximum power coefficient reaches 0.14. The utilization of this new design system is predicted to contribute towards a more efficient use of flows in rivers and channels for electricity production in rural areas.

Characteristics and internal flow of a low specific speed pump used as a turbine

PAT (Pump as Turbine) has gradually been a popular solution for the small-scale hydropower generation. Because of the rich assortment and the low initial investment. However, PAT is designed as a pump but not a turbine. Therefore, a lot of research was conducted about the performance prediction and the loss distribution of pump and turbine mode. In this paper, we focused on the internal flow and loss mechanisms of the best efficient point of both modes. The characteristic and internal flow were investigated by experimental and computational approaches. The reasons of efficiency reduction in turbine mode and loss mechanisms were clarified by the computational results. The separation flow region occurs on the suction side or pressure side in non-BEP, and the swirling flow counter-rotates the PAT occurring at the outlet in BEP might be the reasons of the efficiency reduction. Moreover, because of the camber line shape of PAT, the separation flow occurs near the inlet could not reattach soon which induces the loss region. Furthermore, the secondary flow near the blade surface and the flow from the pressure side to suction side interfere with each other which induced the loss region.

Measurement of fill level and effects of overflow in power-generating Archimedes screws

ABSTRACTArchimedes screw generators are an increasingly popular form of small-scale hydropower generation. The power output of an Archimedes screw depends on water fill level within the rotating screw, which is difficult to directly observe. Fill level in a very small screw with a transparent plastic trough has been successfully measured photographically, but this is not practical in larger screws. An alternative, non-optical method was developed using a static pressure sensor in the screw trough to measure fill height during screw operation, which is a new capability. Non-dimensional fill height was measured with an uncertainty of ± 0.072. This method was then used to experimentally investigate overflow in operating screws as a function of fill height. Existing overflow models are based on fill height, screw geometry and inclination angle assuming static water conditions. Results of these experiments showed that overflow in laboratory-scale screws is also dependent on rotational speed.

Economic effects and greenhouse gas emissions of small-scale hydropower projects in Japan: evidence from a 47-prefecture interregional input–output analysis

This study investigates the economic effects (output, value added and employment) and greenhouse gas (GHG) emissions of small-scale hydropower [comprising construction and operation/maintenance (O&M) stages] using a 47-prefecture interregional input–output analysis. We evaluated both backward and income linkage effects using the Miyazawa model, and consequently demonstrated that: (1) with respect to output and employment, the backward linkage effects of the O&M stage are smaller than the construction stage, while the opposite is true for the income linkage effects. This may be mainly attributed to high value-added ratios of the O&M sectors, and implies relatively lower inputs and labor are required for running hydropower facilities than for constructing them. (2) Income linkage effects with respect to all the parameters are dispersed over several prefectures due partly to the income redistribution effect. (3) Analyses of life-cycle GHG emissions in physical terms reveal that the smaller the hydropower plant, the larger the GHG emissions per unit electricity production. This may be because more machinery must be used per unit electricity production at smaller plants, causing more emissions from both construction and maintenance works. (4) Assuming small-scale hydropower generation is conducted across 1602 sites in place of the general (including fossil fuel) power sector, Japan’s national GHG emissions are expected to be moderated by 0.145%, of which 55% is due to the technological effect and the remaining portion is through the electricity-saving effect from higher prices for small-scale hydropower.

Internal flow and loss mechanisms of specific speed 160 m-kW shroudless hydro turbine

High efficiency and low-cost hydro turbines are becoming more popular for medium and small-scale hydropower generation in underdeveloped locations. Because of this, a shroudless hydro turbine of medium specific speed 160 [m-kW] was developed based on a low specific speed 80 [m-kW] design concept previously studied in the author’s laboratory. We are aiming to develop an optimal design method and further improve performances of the medium- specific speed 160 [m-kW] shroudless hydro turbine. The most important factors are the internal flow and the loss mechanism of each flow path component. In this study, the internal flow and loss mechanisms were investigated and clarified by experimental and computational approaches. The main loss mechanisms in the double circular cascade is the high swirling strength vortices extending from the guide vane inlet to the outlet near the end wall of guide vanes. Furthermore, it has been found that the interference of the secondary flow and leakage flow, and the tip leakage vortex are the predominant loss mechanisms of the shroudless runner.