Small-scale Hydropower Systems Research Articles

Design and optimization of a siphon turbine using the response surface methodology

A comprehensive examination of siphon turbine design and optimization using the response surface methodology (RSM) is presented in this study. The goal was to improve the turbine efficiency by analyzing the impact of two key factors: the number of blades (n) and the ratio between the hub diameter (d) and the outer diameter of the rotor (D), (d/D). The application of RSM facilitated the creation of a response surface, unveiling the optimal combination of factors for maximizing efficiency. The novelty of this article lies in utilizing the response surface methodology to refine the design of existing turbines, resulting in a more streamlined and effective design process tailored to the specific requirements of the installation. The findings indicated that rounding the number of blades to 5 and maintaining a constant d/D ratio of 0.35 yielded the highest efficiency (41.4%). Experimental validation was carried out and the accuracy of the optimized design was demonstrated, paving the way for practical applications in renewable energy solutions. Therefore, the effectiveness of RSM in optimizing siphon turbine designs is supported since valuable insights are provided for enhancing the energy efficiency in small-scale hydropower systems. The investigation contributes to the development of sustainable and clean energy technologies, showcasing the potential of siphon turbines in harnessing low-head water sources for power generation.

Incorporating Landscape Dynamics in Small-Scale Hydropower Site Location Using a GIS and Spatial Analysis Tool: The Case of Bohol, Central Philippines

Hydropower depends on the elevation head and water flow of a river. However, other factors must be considered, such as the risk associated with surface processes and environmental factors. The study aims to analyze a landscape’s dynamics and locate potential sites for small-scale hydropower systems (<10 MW) using a geographic information system, the curve number method, and the TopoToolbox with a digital elevation model and available spatial datasets. Across Bohol Island in the central Philippines, the study found 94 potential sites with hydraulic heads ranging from 20–62.4 m, river discharges between 0.02 to 9.71 m3/s, and a total hydropower capacity of 13.595 MW. The river profile analysis classified the sites to five levels of risk to geo-hazards, with three-fourths of the sites being at ‘high’ to ‘very high’ risk levels while more than 50% of the total power can be generated in ‘low’ risk areas. Land-use and population constraints reduced the sites to 25 and the hydropower capacity by 60%. Although limited to the table assessment phase of hydropower development, the study showed the potential of small-scale hydropower systems in the study area, their spatial distribution, and the risk associated with each site. The study results provided data-limited resource managers’ and energy planners’ insights in targeting potential locations and minimizing field investigation costs and time.

Progress for On-Grid Renewable Energy Systems: Identification of Sustainability Factors for Small-Scale Hydropower in Rwanda

In Rwanda, most small-scale hydropower systems are connected to the national grid to supply additional generation capacity. The Rwandan rivers are characterized by low flow-rates and a majority of plants are below 5 MW generation capacity. The purpose of this study is to provide a scientific overview of positive and negative factors affecting the sustainability of small-scale hydropower plants in Rwanda. Based on interviews, field observation, and secondary data for 17 plants, we found that the factors contributing to small-scale hydropower plant sustainability are; favorable regulations and policies supporting sale of electricity to the national grid, sufficient annual rainfall, and suitable topography for run-of-river hydropower plants construction. However, a decrease in river discharge during the dry season affects electricity production while the rainy season is characterized by high levels of sediment and soil erosion. This shortens turbine lifetime, causes unplanned outages, and increases maintenance costs. Further, there is a need to increase local expertise to reduce maintenance cost. Our analysis identifies environmental factors related to the amount and quality of water as the main current problem and potential future threat to the sustainability of small-scale hydropower. The findings are relevant for energy developers, scholars, and policy-makers in Rwanda and East Africa.

Design optimization of a small-scale hydropower harvesting device

This paper presents a semi-analytical model that facilitates the optimum design of small-scale hydropower systems, so that maximum possible energy can be harvested under low head and streamflow conditions in run-of-the-stream settings. The hydropower harvesting model developed and tested at the University of Connecticut (Malla et al., Renewable Energy 36(5):1568–1577, 2011) comprises a rotating cylinder attached to a piston producing reciprocating motion when placed in moving water. Taking this model as the base, the semi-analytical model employs genetic algorithm–based optimization and develops optimal dimensions for the system, with the objective to minimize the time period while at the same time maximizing the stroke of the piston. The semi-analytical model is tested in steps: first with single-objective optimization for the time period and the stroke of the piston separately and then using multi-objective optimization to produce a set of Pareto optimal solutions. As many energy harvesting approaches are based on the reciprocating motion of the mechanical/structural system, which is greatly affected by the geometric dimensions of the system, optimization of the system geometry becomes crucial for energy harvesting. Compared to the hydropower harvesting model tested before (Malla et al., Renewable Energy 36(5):1568–1577, 2011), the semi-analytical model is able to reduce the arms’ dimensions while obtaining a much higher stroke of piston for much lower time period. The model has some limitations but is able to produce optimization results comparable to laboratory experimental data and applicable to actual flow data from Shetucket River in Willimantic, CT, USA.

Powering institutions for development—Organizational strategies for decentralized electricity provision

The study addresses the question of how to achieve and sustain well-functioning local service delivery in institutionally difficult contexts, characterised by low levels of generalised trust, widespread corruption and poor institutions. We study a relatively successful case of decentralized electrification in Tanzania, and the process whereby an international NGO establishes a small-scale hydropower system with a local utility to own and operate it. Building on institutional theory, we investigate how to build trust in an organization, through a strategy of credible commitment; and how free-riding problems can be handled in a local development project. The qualitative study includes 119 semistructured interviews with project staff, villagers, and local and district government, observations and document analysis. The results indicate the importance of a positive ‘history of play’, sustained over time, and keeping distance from corrupt institutions, in order to build trust. Strict enforcement of rules was decisive for handling free riding behaviours, and impartiality in enforcement for perceptions of legitimacy and trustworthiness. Deviations undermined relations of trust. The results add nuance to more generic theoretical propositions and provide insights on un/intended consequences of institutional strategies. These are relevant for creating and sustaining local service organizations for electricity access and other public goods.

A new nozzle design methodology for high efficiency crossflow hydro turbines

Small-scale hydropower systems are mainly used in remote locations for generating electricity where reasonable hydropower resources are available. Many small-scale systems employ crossflow turbines due to their simplicity in design and manufacture, low cost, sturdy construction and longer life-span. However, compared to most advanced and efficient designs, such as Pelton and Francis turbines, they suffer from a lower maximum efficiency. In a crossflow turbine, the nozzle increases the velocity of the flow and directs it at a suitable angle to the runner whose axis is tangential to the flow. The runner extracts the angular momentum of the flow. Therefore, the runner entry flow is critical for the turbine efficiency. However, it is not yet known clearly how the entry flow affects the runner performance and how the best nozzle can be designed. This study presents a new nozzle design method so that high efficiency crossflow turbines can be designed. An analytical model is formulated to convert the head into kinetic energy at the entry and obtain a suitable flow angle. Three-dimensional Reynolds-Averaged Navier-Stokes simulations were conducted on a 7kW turbine with a measured maximum efficiency of 69% and a 0.53kW turbine with a maximum efficiency of 88%. The predictive capability of the computational model was assessed by comparing the computational and experimental results for the power over a range of operating conditions on both turbines. By redesigning only the nozzle of the 7kW turbine by the new method, the maximum efficiency increased from 69% to 87%. Thus the nozzle design has a significant influence on turbine performance, and we conclude that the conversion of head into kinetic energy and matching of the nozzle flow with the runner design are fundamental in turbine design.

Sustainable and economical small-scale and low-head hydropower generation: A promising alternative potential solution for energy generation at local and regional scale

Accounting for more than 16% of the world’s net electricity production, hydropower is one of the most commonly used renewable sources of energy. Small-scale hydropower (SSH) systems are becoming increasingly successful options for hydropower generation, particularly in small localities and remote areas. Regardless of its low capacity, small-scale hydropower produces cheap, clean, and reliable electricity. The objective of this study is to provide a sustainable and economical solution for the increasing demand of electricity through small-scale hydropower generation in Pakistan. River flow and low head potential were investigated at twenty sites along the Upper Swat Canal and Swat River for hydropower generation. The sites were selected based on large differential head, velocity, ease of access, close proximity to dense population, and structural support. Hydropower capacity was calculated for each site based on the collected flow and hydraulic data. The cost per kWh of energy generated has been estimated by dividing the average annual recurring cost with annual generation over the lifetime of the project. Cost analysis indicated that purchasing one unit at 0.04 US$ is suitable for both the consumer and the government. Results revealed that each site is qualified to provide stable energy to more than 1500 houses based on the maximum consumption per home. The cost of the proposed power system was identified as the incentive factor in this study. In addition to the minimal variation in the seasonal production, the studied sites produced as much as 21% of the total Swat River production. The proposed spatial power distribution scenarios have contributed a potentially flexible alternative and cost-effective solution to the proposed SSH system.

The Hydropower Potential Assessment Tool (HPAT): Evaluation of run-of-river resource potential for any global land area and application to Falls Creek, Oregon, USA

Small-scale hydropower systems are popular both in the United States and much of the developing world due to the emphasis on renewable energy and the general cost-competitiveness of hydroelectric power generation. We present a novel modeling package, referred to as the Hydropower Potential Assessment Tool (HPAT), to assess historic and projected future small-scale run-of-river hydropower resource potential at a single location or distributed over a study region. HPAT implements a fully-distributed streamflow model, which is coupled to a digital elevation model to assess hydropower resource potential. To demonstrate HPAT, we implement the models for a privately-owned run-of-river facility on Falls Creek outside of Sweet Home, Oregon, USA. We use an ensemble of Global Climate Models (GCMs) for two future climate scenarios to project a plausible range of future changes at this site. For the Falls Creek facility, HPAT projects that the timing of peak streamflow will shift from spring to winter and that mean annual hydropower potential will likely decrease slightly from average 1980–2010 historic conditions through the end of the 21st century. All inputs to HPAT are globally available, except for streamflow observations necessary for calibration.

Cavitation Inception in Crossflow Hydro Turbines

Cavitation is a common flow phenomena in most hydraulic turbines and has the potential to cause vibration, blade surface damage and performance loss. Despite the fact that crossflow turbines have been used in small-scale hydropower systems for a long time, cavitation has not been studied in these turbines. In this paper, we present the findings of a computational study on cavitation inception in crossflow turbines. Cavitation inception was assessed using three-dimensional (3D) Reynolds-Averaged Navier–Stokes (RANS) computations. A homogeneous, free-surface two-phase flow model was used. Pressure distributions on the blades were examined for different flow rates, heads and impeller speeds to assess cavitation inception. The results showed that cavitation occurs in the second stage of the turbine and was observed on the suction side near the inner edge of the blades. For the particular turbine studied, cavitation always occurred at shaft speeds greater than that, giving the maximum efficiency for each combination of flow rate and head. The implication is that the useful operating range of crossflow turbines is up to and including the maximum efficiency point.