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Experiments were performed with a large laboratory-scale high solidity cross-flow turbine to investigate Reynolds number effects on performance and wake characteristics and to establish scale thresholds for physical and numerical modeling of individual devices and arrays. It was demonstrated that the performance of the cross-flow turbine becomes essentially R e -independent at a Reynolds number based on the rotor diameter R eD ≈ 106 or an approximate average Reynolds number based on the blade chord length R ec ≈ 2 × 105 . A simple model that calculates the peak torque coefficient from static foil data and cross-flow turbine kinematics was shown to be a reasonable predictor for Reynolds number dependence of an actual cross-flow turbine operating under dynamic conditions. Mean velocity and turbulence measurements in the near-wake showed subtle differences over the range of R e investigated. However, when transport terms for the streamwise momentum and mean kinetic energy were calculated, a similar R e threshold was revealed. These results imply that physical model studies of cross-flow turbines should achieve R eD ∼ 106 to properly approximate both the performance and wake dynamics of full-scale devices and arrays.

At a global level, hydrokinetic power has been considered as a renewable energy source, and it has become an attractive alternative for the rural electrification of non-interconnected areas with the presence of water resources. Aspects such as the low rural electrification rate, the increase in energy demand, the decrease in fossil reserves and the climate change, are some of the factors that have driven the use of this technology for the electricity production. The aim of this work is to give a review of the hydrokinetic energy potential of water resources, the requirements and impacts of the implementation of hydrokinetic technology in different countries, and the current development in the Colombian case. At present, it can be observed that the implementation of this technology in different regions of the world, especially in Colombia, has several challenges and barriers, including gaps in knowledge, information and data, such as well as limitations of water resources and infrastructure, finally, impacting on a low adoption of this technology. On the other hand, publications on studies of implementation and potential of hydrokinetic technology have been increasing over time, indicating that this topic has been gaining interest despite the challenges.

The hydrokinetic energy of river current, as one of the essential and widespread renewable energies, is difficult to be harvested in low flow velocity and shallow water areas. In this work, a three-dimensional (3D) fully-enclosed triboelectric nanogenerator (FETENG) with bionic fish-like structure for harvesting hydrokinetic energy is reported, which is comprised of the triboelectric power-generation unit, bionic fish-like structure and connection unit. Through the bionic structure, the FE-TENG realizes zero head power generation in shallow water with low flow velocity. What’s more, the effect of external excitations and bionic structures on the electrical performance are systematically studied in this work. The FE-TENG can generate peak power density of 7 and 0.36 W/m 3 respectively under the simulated swing state with frequency of 1.25 Hz and simulated river current with flow velocity of 0.81 m/s. In practical applications, due to the 3D fully-enclosed design, the FE-TENG immersed in water for 35 days demonstrates excellent immersion durability with undiminished electrical performance. Therefore, the work proposes an efficient method realizing zero head power generation, and provides a good candidate for long-term service in the river current.

Flow-induced oscillations (FIO) are energy-rich hydrodynamic phenomena that can be exploited to harvest renewable energy from ocean and river currents. The hydrodynamics of tandem cylinders have recently gained attention in the literature, and this study investigates a hybrid energy harvesting system based on tandem cylinder configurations. The upstream–downstream wake interference is modeled through coupled van der Pol and wake oscillators, with particular emphasis on accurately capturing both vortex-induced vibration and galloping mechanisms. Three configurations, including piezoelectric (PZT-H), electromagnetic (EMT-H), and a new proposed hybrid piezoelectric–electromagnetic coupled with tandem cylinders (HEPT-H), are analyzed under varying spacing ratios and reduced velocities. Findings highlight that galloping is the dominant instability driving large-amplitude responses, and its proper modeling is critical for predicting and maximizing harvested energy. The proposed HEPT-H system takes advantage of this mechanism, nearly doubling the harvested power and improving efficiency by about 20% compared with single-harvester systems. A multi-criteria decision-making method (TOPSIS) was employed to rank the harvesters under different cylinder spacing configurations according to their relative closeness to the ideal solution. The HEPT-H system with a center-to-center cylinder spacing of four diameters indicated the best performance, achieving a maximum output of 0.071 W and a peak efficiency of 69.78%. This research emphasizes the significant potential of HEPT-H systems in FIO and demonstrates that tandem configurations outperform isolated cylinders, underscoring their effectiveness for advancing sustainable hydrokinetic energy applications.

This study investigates the techno-economic feasibility of an off-grid integrated solar/wind/hydrokinetic plant to co-generate electricity and hydrogen for a remote micro-community. In addition to the techno-economic viability assessment of the proposed system via HOMER (hybrid optimization of multiple energy resources), a sensitivity analysis is conducted to ascertain the impact of ±10% fluctuations in wind speed, solar radiation, temperature, and water velocity on annual electric production, unmet electricity load, LCOE (levelized cost of electricity), and NPC (net present cost). For this, a far-off village with 15 households is selected as the case study. The results reveal that the NPC, LCOE, and LCOH (levelized cost of hydrogen) of the system are equal to$333,074, 0.1155 $ /kWh, and 4.59 $/kg, respectively. Technical analysis indicates that the PV system with the rated capacity of 40 kW accounts for 43.7% of total electricity generation. This portion for the wind turbine and the hydrokinetic turbine with nominal capacities of 10 kW and 20 kW equates to 23.6% and 32.6%, respectively. Finally, the results of sensitivity assessment show that among the four variables only a +10% fluctuation in water velocity causes a 20% decline in NPC and LCOE.

A hydrokinetic turbine with a vertical axis is specifically designed to harvest the kinetic energy from moving water. In this study, three vertical axis water turbines, namely Gorlov, Darrieus, and Savonius turbines, were compared for their efficiency via numerical modeling for steady-state conditions via the ANSYS 2022 R2 Fluent model. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) was implemented with an SST k-ω turbulence model. The dynamic mesh technique, which allows modeling according to changes in angular velocity at each time step, was used to simulate flow around the turbines for six different velocities (from 0.5 to 3 m/s). The efficiency of the turbines was compared and the results were analyzed. The pressure, velocity, and turbulence kinetic energy distributions around the rotor were measured at different rotational angles and results indicated a wider operating range for the Darrieus and Gorlov turbines compared to the Savonius turbine. The highest power coefficient of 0.293 was achieved in the model featuring a Darrieus turbine, corresponding to a TSR value of 1.34, compared to 0.208 for the Gorlov and 0.257 for the Savonius turbine, at TSR values of 1.3 and 1.06, respectively. Numerical modeling results pointed to a significantly higher self-starting capacity for the Savonius turbine compared to the others.

In the effort to mitigate climate change, the Marine Hydrokinetic (MHK) energy from ocean currents emerges as an important renewable source due to its large potential, although it remains underexploited. In the Southwestern Tropical Atlantic, surface potentials linked to the North Brazil Current (NBC) are known, but the subsurface North Brazil Undercurrent (NBUC) remained unquantified. This study addressed this gap by applying a two-step approach using more than 20 years of high-resolution (1/12°) climatological and daily reanalysis data to estimate current power density (CPD) throughout the water column along the Brazilian shelf (4° N–12° S), with focus on energetic hotspots where maximum CPD exceeds 1000 W m−2. The climatological analysis revealed 12 persistent hotspots (H1–H12). Daily analyses show highly energetic but seasonally variable surface hotspots north of 4° S linked to the NBC (H4–H12; >885 W·m−2) and weaker but more stable subsurface hotspots south of 4° S associated with the NBUC at depths of 130–266 m (H1–H3; 831–808 W·m−2). These patterns are likely influenced by flow–topography interactions along the continental margin. Overall, subsurface resources exhibit greater reliability than surface counterparts, highlighting the importance of incorporating subsurface dynamics in future MHK assessments and development along the Brazilian margin.

In this paper, a stochastic techno-economic optimization framework is proposed for three different hybrid energy systems that encompass photovoltaic (PV), wind turbine (WT), and hydrokinetic (HKT) energy sources, battery storage, combined heat and power generation, and thermal energy storage (Case I: PV–BA–CHP–TES, Case II: WT–BA–CHP–TES, and Case III: HKT–BA–CHP–TES), with the inclusion of electric and thermal storage using the 2m + 1 point estimate method (2m + 1 PEM) utilizing real data obtained from the city of Espoo, Finland. The objective function is defined as planning cost minimization. A new meta-heuristic optimization algorithm named improved fire hawk optimization (IFHO) based on the golden sine strategy is applied to find the optimal decision variables. The framework aims to determine the best configuration of the hybrid system, focusing on achieving the optimal size for resources and storage units to ensure efficient electricity and heat supply simultaneously with the lowest planning cost in different cases. Also, the impacts of the stochastic model incorporating the generation and load uncertainties using the 2m + 1 PEM are evaluated for different case results compared with the deterministic model without uncertainty. The results demonstrated that Case III obtained the best system configuration with the lowest planning cost in deterministic and stochastic models and. This case is capable of simply meeting the electrical and thermal load with the contribution of the energy resources, as well as the CHP and TESs. Also, the IFHO superiority is proved compared with the conventional FHO, and particle swarm optimization (PSO) achieves the lowest planning cost in all cases. Moreover, incorporating the stochastic optimization model, the planning costs of cases I–III are increased by 4.28%, 3.75%, and 3.57%, respectively, compared with the deterministic model. Therefore, the stochastic model is a reliable model due to its incorporating the existence of uncertainties in comparison with the deterministic model, which is based on uncertain data.

Renewable energy resources and energy efficiency measures are effective means of curtailing CO2 emissions. Solar and wind technologies have been mostly developed to meet the energy demand of off-grid remote areas or locations without grid connections. However, it is well-known that the power generation of these resources is affected by daily fluctuations and seasonal variability. One way to mitigate such an effect is to incorporate hydrokinetic resources into the energy system, which has not been well investigated yet. Therefore, this study examines the prospects of designing a hybrid system that integrates hydrokinetic energy to electrify an off-grid area. Hydrokinetic energy generation depends on water flow velocity (WFV). We estimate WFV by a model-based approach with geographical and weather data as inputs. Together with the models of the other components (wind turbine, PV panel, battery, and diesel generator) in the micro-grid, an optimization problem is formulated with the total net present cost and the cost of energy as performance criteria. A genetic algorithm (GA) is used to solve this problem for determining an optimal system configuration. Applying our approach to a small community in Nigeria, our findings show that the flow velocity of a nearby river ranges between 0.017 and 5.12 m/s, with a mean velocity of 0.71 m/s. The resulting optimal micro-grid consists of 320 kW of PV, 120 units of 6.91 kWh batteries, 2 (27 kW) hydrokinetic turbines, an 120 kW converter, zero wind turbines, and a 100 kW diesel generator. As a result, the total energy generated will be 471,743 kWh/year, of which 12% emanates from hydrokinetic energy. The total net present cost, the cost of energy, and the capital cost are USD 1,103,668, 0.2841 USD/kWh, and USD 573,320, respectively.

A cubic-spring restoring function with high-deformation stiffening is introduced to passively improve the harnessed marine hydrokinetic power by using flow-induced oscillations/vibrations (FIO/V) of a cylinder. In these FIO/V experiments, a smooth, rigid, single-cylinder on elastic end-supports is tested at Reynolds numbers ranging from 24,000 < Re < 120,000. The parameters of the tested current energy converter (CEC) are cubic stiffness and linear damping. Using the second generation of digital virtual spring-damping (Vck) controller developed by the Marine Renewable Energy Laboratory (MRELab), the cubic modeling of the oscillator stiffness is tested. Experimental results show the influence of the parameter variation on the amplitude, frequency, energy conversion, energy efficiency, and power of the converter. All experiments are conducted in the low turbulence-free surface water (LTFSW) channel of the MRELab of the University of Michigan. The main conclusions are: (1) The nonlinearity in the cubic oscillator is an effective way to extend the vortex-induced vibration (VIV) upper branch, which results in higher harnessing power and efficiency compared to the linear stiffness cylinder converter. (2) Compared to the linear converter, the overall power increase is substantial. The nonlinear power optimum, occurring at the end of the VIV upper branch, is 63% higher than its linear counterpart. (3) The cubic stiffness converter with low harnessing damping achieves consistently good performance in all the VIV regions because of the hardening restoring force, especially at higher flow velocity.