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Energy harnessing from hydrokinetic systems has been explored over several centuries. With advancements in the technology in last decade, and the intermittent nature of other technologies for energy harvesting, interest in harnessing energy from water-based hydrokinetic systems has amplified. This paper reviews and studies the state-of-the-art of these systems in sea- and river-based applications. The history of development, working principles, different turbines classifications, and research prospects and opportunities are reviewed and discussed. We also conduct a survey of currently available commercial technologies. Elements of the design that need to be enhanced are presented in detail, along with further research prospects in areas related to the technology.

Split-belt treadmill walking, in which the two belts move at different speeds, reveals a mechanism through which energy can be extracted from the environment. When a person walks with positive step length asymmetry on a split-belt treadmill, the treadmill can perform net positive work on the person. Here we use a split-belt rimless wheel model to explore how people could take advantage of the treadmill. We show that a split-belt rimless wheel can passively walk steadily by capturing energy from the treadmill to overcome collision losses, whereas it loses energy on each step with no way to recover the losses when walking on tied belts. Our simulated split-belt rimless wheel can walk steadily for a variety of leg angle and belt speed combinations, tolerating both speed disturbances and ground height variability. The wheel can even capture enough energy to walk uphill. We also built a physical split-belt rimless wheel robot and demonstrated that it can walk continuously without additional energy input. In comparing the wheel solutions to human split-belt gait, we found that humans do not maximize positive work performed by the treadmill. Other aspects of walking, such as costs associated with swing, balance, and free vertical moments, likely limit people's ability to benefit from the treadmill. This study uses a simple walking model to characterize the mechanics and energetics of split-belt walking, demonstrating that energy capture through intermittent contact with two belts is possible and providing a simple model framework for understanding human adaptation during split-belt walking. [ABSTRACT FROM AUTHOR]

Power generation is becoming an increasing problem in South Africa. South Africa produces approximately 90% of its electricity from coal-fired power stations and only 5% from hydroelectric power stations and pumped storage. Durban has a very steep topography, which results in high pressure in certain parts of the water distribution network (WDN). Leakage is costly and contributes to a large extent to non-revenue water (NRW) in the network. Pressure reducing valves (PRVs) are used in WDNs to control the pressure in the pipework to reduce leakage. This excess pressure can be used to generate electricity by a pump acting as a turbine (PAT). The electricity generated is a function of the flow rate and the pressure reduction through the PAT. The hydraulic modelling software EPANET 2.2 is used for the analysis of the Cornubia Integrated Human Settlement Development Phase 2A WDN in Durban. EPANET is used to determine the strategic placement of PATs in the WDN and their setting and configuration to extract the most energy and reduce pressure in the system. A configuration of five PATs of different sizes extracts a total power output of 166.31 kW and reduces leakage in the WDN by 45.59 kL per month, which is an 18.16% reduction in leakage. [ABSTRACT FROM AUTHOR]

Power generation is becoming an increasing problem in South Africa. South Africa produces approximately 90% of its electricity from coal-fired power stations and only 5% from hydroelectric power stations and pumped storage. Durban has a very steep topography, which results in high pressure in certain parts of the water distribution network (WDN). Leakage is costly and contributes to a large extent to non-revenue water (NRW) in the network. Pressure reducing valves (PRVs) are used in WDNs to control the pressure in the pipework to reduce leakage. This excess pressure can be used to generate electricity by a pump acting as a turbine (PAT). The electricity generated is a function of the flow rate and the pressure reduction through the PAT. The hydraulic modelling software EPANET 2.2 is used for the analysis of the Cornubia Integrated Human Settlement Development Phase 2A WDN in Durban. EPANET is used to determine the strategic placement of PATs in the WDN and their setting and configuration to extract the most energy and reduce pressure in the system. A configuration of five PATs of different sizes extracts a total power output of 166.31 kW and reduces leakage in the WDN by 45.59 kL per month, which is an 18.16% reduction in leakage.

The organic matter was absent prior to planetesimal formation (4.6 Gyr) but at present abundant in planetary environments. The aim of this study was to combine information about the organic inventory of the Earth, which is accompanied by the evolution of life. A variety of available free energy sources, including geochemical energy, sunlight, oxygen and fire have supported life evolution. In the meantime these energy sources have mediated the diversity and complexity of living organisms and resulted in a concomitant increase in the diversity and complexity of organic matter, including microbial-, plant-, fire-, and human derived organics. The change of the diversity and complexity of organic matter (microbial-, plant-, fire- and human-derived organics) have in-return significantly influenced Earth's carbon cycle, planetary climate and ecosystems. Overall, energy harnessing and conservation of life entwined and expanded the evolutional histories of life and organic molecules on the planet. Considering the key role of organics on the stability of the oxygen level of the atmosphere, temperature, the tectonic rise of continents, and global habitability, the changing characters of organics over geologic time had an important shaping influence on Earth's geochemical cycles. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators are shown a recent development in the energy field in various applications powering sensors to biomedical applications. The research development of tribogenerators is trending in the renewable energy area as it can harness waste mechanical energy due to the friction. Studies have shown various mathematical modeling done on the triboelectric principle based on Gauss electric field principle. Triboelectricity generation due to contact electrification depends on various factors that include the surface charge density, materials, the geometrical features of the tribo pairs, the mode of operation in terms of velocity etc. The significance of nanomaterials in the generation of triboelectricity is a research area where polymers have shown good results. In this study, a detailed computational and numerical simulation is done on selected pairs of triboelectric material combination chosen from the triboelectric series. Computational simulation is performed using Comsol Multiphysics to evaluate the output performance in terms of Voc and Qsc. Numerical simulation is performed using MatLab to evaluate the output performance current, power, voltage with respect to time for selected input parameters. The numerical performance of the device is validated by the experiments. The numerical method adopted will be a useful tool for determining the output characteristics of any triboelectric pairs. [ABSTRACT FROM AUTHOR]

Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed.

The natural ocean/river currents energy can be harvested using Flow Induced Motion (FIM) phenomena. The effect of damping-ratio and mass-ratio on Flow Induced Motion energy harnessing of a square cylinder are numerically investigated for Reynolds number 15500 < Re < 232000 (0.2 m/s < flow velocity <3.0 m/s). Four typical regions can be observed in the Flow Induced Motion responses, including Vortex Induced Vibration (VIV) Initial Branch, Vortex Induced Vibration Upper Branch, Vortex Induced Vibration-Galloping Transition and Galloping. Results indicate that as the velocity increases, the number of vortices shed per cycle increases, and the harnessed power increases without upper limit. The energy conversion efficiency increases up to the highest value until the Vortex Induced Vibration upper branch. Then, it starts decreasing and tends to a relatively small value in the galloping region. Increasing mass-ratio will shorten the velocity range of Vortex Induced Vibration. High damping-ratio has a negative impact on oscillation amplitude, but provides a boost for energy harnessing. In all tests, the power (143 W) is considerable at damping-ratio = 0.6. As the damping-ratio reaches up to 0.8 (nearing critical damping), galloping will no longer occur. [ABSTRACT FROM AUTHOR]

[Display omitted] Phase change materials (PCM) are largely assessed on their ability towards energy storage and their enthalpy efficiency of discharging the stored energy. Nevertheless, their applications are limited by the low thermal conductivity behaviour, despite their tunable transition temperature abilities. The present work demonstrates a novel concept to develop and explore PCM composite by embedding two unique zinc oxide tetrapod classes to engineer the heat transfer mechanism for potential utilization in thermal energy storage. Tetrapods embedded phase change material (TPCM) composite displayed up to 94% enhancement in thermal conductivity without compromising melting enthalpy. TPCM composite with high thermal conductivity, high heat capacity, broad photo-absorptivity, improved stability in isothermal conditions, and long thermal cycles offer attractive solutions for effective thermal energy storage, efficient solar energy harnessing, and thermal management. With demonstrated abilities, the developed TPCM composite material could play a significant role in the progress of renewable energy needs in future. [ABSTRACT FROM AUTHOR]

Energy harnessing for the purpose of powering low power electronic devices has received much attention in the last few years. By harnessing ambient energy from the environment it will eliminate the need for batteries and supplying the portable electronic devices such as cell phones, laptops and MP3 players with infinite amount of energy. The ambient energy that can be harnessed to generate electricity comes from a wide range of sources but vibration energy shows a promising amount of power generation. This paper present the integration of instrumentation for conversion of mechanical vibration into electricity using piezoelectric vibration-to-electricity converter, quantification of the amount of power that can be generated and identification of electronic devices that can fully utilize this power. The research is conducted on the laboratory experiment on vibrating mechanical equipment such as turbine and centrifugal pump. The experimental result shows that for the turbine, as the speed of the turbine increases from 1150 rpm to 1450 rpm, the average power produced increases from 1.63 μW to 2.02 μW. Also, for the centrifugal pump, as the speed increases from 1700 rpm to 1900 rpm, the average power produced increases from 3.02 μW to 3.06 μW. The experimental results also revealed that within 30 minutes, 1.84 μW of energy could be harnessed from the vibration of the turbine at speed of 1450 rpm while 3.06 μW of energy could be harnessed from the vibration of the centrifugal pump at speed of 1900 rpm. This power output is sufficient for low-powered wireless sensor networks in silent mode which can be used in variety of applications as indicated in the previous literature. [ABSTRACT FROM AUTHOR]

Abstract: Maximization of the harvested energy from piezoelectric bimorphs has been the objective of many researchers in the past few years. Most of the previous work focused on bimorphs covered with a single pair of electrodes, leading to a great loss of generated power due to charge cancellation from areas with opposite strains. In this paper, we assume the bimorph is covered with multiple pairs of electrodes to overcome the problem of charge cancellation. We focus on circular bimorphs subject to base excitation at different frequencies. We also assume that the capacitances attached to the electrodes are controllable and can be optimized to maximize the power output at a given excitation frequency. Moreover, we change the topology of the bimorph by making its thickness vary with the radius of the bimorph. Numerical examples show that the harnessed power can be maximized by increasing the capacitance of anti-nodal elements while decreasing that of nodal elements. Also, decreasing the thickness of piezoelectric layers at anti-nodal elements allows more straining and hence the generation of more power. It is shown that the compatibility of the topology of the piezoelectric bimorph with the shape of the second axisymmetric mode yields more power compared with its compatibility with the first mode. [Copyright &y& Elsevier]

Vortex-induced oscillations offer a potential means to harness hydrokinetic energy even at low current speeds. In this study, we consider a novel converter where a cylinder undergoes angular oscillations with respect to a pivot point, in contrast to most previous configurations, where the cylinder undergoes flow-induced oscillations transversely to the incident free stream. We formulate a theoretical model to deal with the coupling of the hydrodynamics and the structural dynamics, and we numerically solve the resulting nonlinear equation of cylinder motion in order to assess the performance of the energy converter. The hydrodynamical model utilizes a novel approach where the fluid forces acting on the oscillating cylinder are split into components acting along and normal to the instantaneous relative velocity between the moving cylinder and the free stream. Contour plots illustrate the effects of the main design parameters (in dimensionless form) on the angular response of the cylinder and the energy efficiency of the converter. Peak efficiencies of approximately 20% can be attained by optimal selection of the main design parameters. Guidelines on the sizing of actual converters are discussed. [ABSTRACT FROM AUTHOR]

A stringent battery-less sensor concept stipulating the entire operation of sensing and result indication to be driven solely by the sensing element without any additional power source has been proposed and implemented with a completely self-powered accelerometer as an example. The operation involves energy harnessing of the vibration into electrical charge with a piezoelectric cantilever, accumulating the charge and then releasing it into an indicator device via an ultra-sharp switch. Deemed as an unprecedented accelerometer feature, the acceleration information at a single frequency is quantitatively indicated by the period of the pulsed light or sound from the self-powered indicator device, which is directly perceivable and comprehensible to the user. This letter realizes an energy autonomous sensor system as highly desired by the end users. [ABSTRACT FROM PUBLISHER]