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This paper investigates the impact of combining CO2 capture and storage with alternative systems for biomass-based combined heat and power production (CHP) in Kraft pulp and paper mills. We compare heat, power, and CO2 balances of systems with alternative configurations of the CHP and CO2-capture systems. Because the captured CO2 comes from renewable biomass, the studied systems yield negative CO2 emissions. It is shown that pulp mills and integrated pulp and paper mills have the potential to become net exporters of biomass-based electricity while at the same time removing CO2 from the atmosphere on a net basis. The study shows that that the overall best CO2 abatement is achieved when CO2 capture is carried out within a biomass integrated gasifier with combined cycle where the syngas undergoes a CO-shift reaction. This configuration combines efficient energy conversion with a high CO2 capture efficiency. Furthermore, cost curves are constructed, which show how the cost of CO2 capture and storage in pulp and paper mills depends on system configuration and the CO2 transportation distance.

Empty fruit bunches (EFB) of oil-palm are one of the most recent renewable energy resources. The objective of this study is to find the most economically-feasible pathway among three energy conversions from 400 t/d wet EFB, which are bioethanol and jet fuel by bioconversion, combined heat and power via gasification, and hydrocarbons through fast pyrolysis and biooil upgrading. A hierarchical four-level economic potential approach (4-level EP) was employed to perform the preliminary techno-economic analysis (TEA) for the three pathways. The 4-level EP includes the input/output structure, the flowsheet structure, the heat integration (HI), and the economic feasibility. The economic potential of the three plants was compared at each level, and the most promising process among them was identified at Level 4, where economic criteria including return on investment (ROI), payback period (PBP), and internal rate of return (IRR) were evaluated. It was found that the biooil hydrocarbon plant is most economical due to the highest economic potential, ROI, and IRR. The heat consumption was reduced considerably by HI in the bioethanol and jet fuel plant. The sensitivity analysis informed that the plant size, the product yield, and the total capital investment highly influenced ROI and PBP in all three processes.

The operation stability demands for low and uniform wall temperature in the parabolic trough collector which acts as an energy conversion component in concentrating thermal conversion technology. In order to reduce the local high temperature with moderate pump power consumption, this paper proposed longitudinal swirls impinging cooling method. Three types of novel inclined curved-twisted baffles (A1, A2, and A3) were devised to realize this method. With selecting the absorber tube as research model, this paper numerically compared the impinging cooling characteristics, wall temperature uniformity performance, and efficiency performance by inserting the three types of baffles. The A1 and A2 types each generated a pair of longitudinal swirls while the A3 type generated two pairs of longitudinal swirls. The impinging cooling always appeared near the front edge of inclined baffles. The A1 type was the best in wall temperature uniformity and efficiencies among three baffles. Furthermore, as the inlet temperature increased from 400 K to 600 K at a mass flow rate of 1.13 kg/s in the A1 type tube, the average wall temperature difference between bottom half tube and top half tube was decreased by 55.1%. Meanwhile, the average overall efficiency and exergy efficiency were increased by 0.52% and 0.22%, respectively.

This paper studies the multidisciplinary nature of two body wave energy converters by a parametric study based on the Taguchi method which helps to understand the effect of different dependent parameters on the wave energy conversion performance. Seven different parameters are analyzed and their effect on the maximum captured power, resonance frequency and bandwidth is studied. An interesting comparison between a cylindrical submerged body and a spherical one was made in terms of the system's viscous damping and hydrodynamics. The best system parameter combinations based on the maximum output power, best resonant frequency and frequency bandwidth were identified from the outcomes of the Taguchi method and optimized to capture the maximum power to operate in the specific (Australian) sea regions where the waves' frequencies are relatively low. This paper should provide a guideline for designers to tune their parameters based on the desired performance and sea state.

After the strategic concept of global energy Internet constructed, it has produced a strong response in the world. In recent years, countries around the world are actively promoting energy transformation and have developed clean energy development goals and plans. This paper constructs a comprehensive evaluation index system for the level of clean energy development by considering policies and regulations, energy supply, environmental impact, energy consumption, technology, economy and so on. At the same time, China, Germany, the United States and other countries are selected as evaluation objects. On the basis of searching, processing and analyzing a large number of data, firstly, the research uses the principal component analysis method to carry out the correlation cluster analysis of the index and then uses the rough set method to assign the weight of the extracted principal components. Finally, the weight of each index in the index system is calculated. The results of the comprehensive evaluation of each country are compared and analyzed, which shows that the weight determination method based on rough set theory and principal component analysis is more reasonable and objective. At the end of the paper, some suggestions are proposed to promote the development of clean energy.

Due to that the conventional backward-curved blades centrifugal impellers do not effectively match the turbine’s running, the performance of the pump-as-turbine (PAT) was usually not ideal. Therefore, to improve significantly the performance of PAT, one kind of special impeller with forward-curved blades was designed for the turbine’s working condition, and the method for determining blade inlet angle that played important role in the energy conversion was also studied deeply in this paper. Moreover, four forward-curved blades impellers with different blade inlet angles were numerically investigated by using a verified computational fluid dynamics (CFD) technique, and relevant external characteristic experiments were also conducted to benchmark the numerical calculation. Based on the results, the flow rate of numerical best efficiency point (BEP) is very close to that of theoretical BEP, and the flow rate of BEP increases with extending the blade inlet angles. Additionally, the energy loss within the impeller reaches the minimum if suitable blade inlet angle is selected, so the value of blade inlet angle is recommended in a reasonable range in special impeller used in turbine mode of PAT. Furthermore, compared with the original backward-curved blades impeller, the maximum efficiency of the forward-curved blades impeller increases from 59.98% to 67.91%, and the flow-efficiency curve is more flat, which reflects that the forward-curved blades impeller in the PAT has obvious superiority. This paper is very instructive to the design of the special impeller using in the PAT.

International audience; In this paper, technical and economical studies conducted on the SEAREV Wave Energy Converter (WEC) are presented. This technology was first proposed in 2002 with the aim of addressing critical challenges in wave energy conversion. It consists of a closed floating hull in which a heavy pendulum oscillates. The controlled relative motion of the pendulum is used to produce electricity. The SEAREV WEC was developed over twelve years. Through the development process, three main generations of the technology were defined and studied in detail. They are presented in the paper, showing how each new generation brought significant improvements over the previous generation with respect to production and costs. In 2013, an economical model for wave energy farms was developed to assess the viability and competitiveness of the SEAREV technology. Although results show that the SEAREV technology is a sound technical solution, the cost of energy projection is still too high to allow direct access to mass electricity market in European countries in the short term. Finally, in light of the lessons learned from the SEAREV WEC development, the need for innovative technologies with higher technology performance level (TPL) or alternative markets is discussed in the context of wave energy.

A solar photovoltaic (PV) energy conversion system requires power converters for maximum power extraction and grid integration. At present, typical converter configurations used in a solar PV system include central, string and micro-converter based PV systems. In order to develop efficient and reliable photovoltaic energy conversion technologies, this paper compares the energy extraction characteristics of a PV system for different converter schemes. The paper particularly focuses on how energy extraction characteristics of a PV array are affected by uneven shading and how different bypass diode arrangements improve and affect PV system energy extraction characteristics under different converter configurations. A detailed comparison study is conducted for central, string and micro-converter based PV systems. It is found that compared to micro-converter based PV systems, the central converter PV systems with large-scale distributed bypass diode connections could be an economic solution to enhance PV system efficiency, reliability and performance, in particular for utility-scale PV generators.

This paper presents a numerical study of the savonius type direct drive turbine incorporated in the rear bottom of typical chamber geometry of an oscillating water column chamber (OWC) for wave energy conversion. The paper deals with a numerical modelling devoted to investigate the effect of wave on the performance and internal flow of the savonius turbine in the components of an oscillating water column (OWC) system used for the wave energy capture. In the present paper, the flow behaviour is modelled by using the commercial code ANSYS CFX. The numerical flow models have been elaborated and simulated independently with different inlet geometries of a water chamber. Constant periodic wave flow calculations were performed to investigate the flow distribution at the turbines inlet section, as well as the properties of the savonius type turbine. The flow is assumed to be two-dimensional (2D), viscous, turbulent and unsteady. The commercial CFD code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme. Turbulence is modelled with the k–e model. Simulation result shows that the water velocity, differential pressure, and the best efficiency vary considerably depending on the savonius rotor angle. The obtained results also indicate that the developed models are well suitable to analyze the water flows both in the chamber and around the savonius rotor.

Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric power conversion of the vast ocean wave energy. The suggested linear electric energy converter is adapted to the natural wave motion using straightforward technology. Extensive simulations of the wave energy concept are presented, along with results from the experimental setup of a multisided permanent magnet linear generator. The prototype is designed through systematic electromagnetic field calculations. The experimental results are used for the verification of measurements in the design process of future full-scale direct wave energy converters. The present paper, describes the energy conversion concept from a system perspective, and also discusses the economical and some environmental considerations for the project.

Historically, energy constraints have limited the spatial range, endurance and capabilities of ocean observation systems. Recently developed wave energy conversion technologies have the potential to help overcome these limitations by providing co-located and persistent power generation for ocean observations, enabling new opportunities for ocean research. In this paper, we develop the first techno-economic model for wave-powered ocean observation systems and use the model to study system characteristics and cost drivers. Our model utilizes time-domain simulation and optimization to identify cost-optimal system characteristics and to estimate capital and operational costs. Using our model, we evaluate the use of wave energy to power a 200 W ocean observation system deployed for five years at five unique geographic locations. We found that, depending on the geographic location, cost-optimal wave energy powered systems require an ≈ 0.5–3 kW wave energy converter and an ≈ 15-50 kWh battery. The corresponding range of power system costs over the deployment duration is between $110,800 and $673,200. We build on these results by performing a sensitivity analysis of key model parameters and identifying the potential economic impact of future technology advancements. Overall, our results indicate that characteristics of the geographic location, power system durability, and electrical power demand are key drivers of power system economics for ocean observing.

Worldwide increasing energy demands promote development of environment-friendly energy sources. As consequences, ocean wave is exploited as an ideal energy source to mitigate greenhouse gas emissions. In this paper, a hydraulic energy-storage wave energy conversion system is constructed, and a mathematical model of main components is built for analysis. Control strategies of generator-side and grid-side are defined for the system, where a Vienna rectifier is applied to converter of generator-side. A two-level space vector plane simplified modulation method for Vienna rectifier is designed for the three-level system and a modulation algorithm is detailed, which has lower complexity compared with traditional three-level space vector pulse width modulation (SVPWM) algorithm. An improved adjusting factor method is proposed to solve the potential imbalance of neutral point caused by uneven charging to the upper and lower capacitors in the three-level structure, which optimizes sector division and inhibits the neutral-point potential offset and fluctuation effectively. Using Matlab/Simulink, the intermittent and continuous power conversion modes of the system under different wave conditions are simulated. The results indicate stable operation of the system, feasible topology scheme, modulation algorithm and control strategy, and effective suppression of AC-side harmonics.

Two-body point absorbers are useful for wave energy conversion in high energetic and high wave period sea locations. Analysis and simulation show that the two-body point absorbers have high efficiencies which makes them a potential candidate to promote wave energy harvesting technology towards commercialization and implementation. The submerged body of the two-body point absorbers has a large effect on their performance, hence the question arises: which geometric shape of the submerged body will lead to the best performance of the two-body wave energy harvesters? This paper presents a comprehensive study that analyses the different shapes of the submerged bodies based on the numerical wave tank simulated viscous drag coefficient and hydrodynamic property parameters of the oscillating device. A set of transient and three-dimensional computational fluid dynamic simulations of a numerical wave tank were carried out in Ansys Fluent to determine the viscous drag coefficients of the different submerged body shapes. And then the boundary element hydrodynamic simulation and linear dynamic frequency-domain modeling have been applied to identify the optimized PTO damping. Finally, non-linear time-domain modeling has been applied with the identified viscous damping drag coefficient and PTO damping coefficients to predict and compare the power output performance of different large-scale devices with different shapes of submerged bodies. It is found that each submerged body shape is suitable for a different range of wave frequencies, as one must establish a balance between the hydrodynamic properties and the viscous drag of the submerged body based on the sea location. It is also found that the typical viscous drag coefficient values used in the past studies underestimate the drag coefficient, and the linearized model widely adopted in frequency domain models is non-accurate for the devices with large viscous drag forces.

This paper presents the work carried out to predict the behavior of a 0.6 m impulse turbine with fixed guide vanes with 0.6 hub to tip (H/T) ratio under real sea conditions.This enhances the earlier work done by authors on the subject by including the effects of damping applied by the turbine. Real wave data for different wave sites were used as the input data. A typical oscillating water column (OWC) geometry has been used for this simulation. Standard numerical techniques were employed to solve the non-linear behavior of the sea waves. Considering the quasi-steady assumption, uni-directional steady flow experimental data were used to simulate the turbine characteristics under irregular unsteady flow conditions. The test rotor used for this simulation consisted of 30 blades with elliptical profile with a set of symmetric, fixed guide vanes on both up-stream and down-stream sections of the rotor, with 26 vanes each. The results show that the performance of this type of turbine depends on the level of damping applied by the turbine and the prevailing wave site conditions. The objective of this paper is to predict the effects of applied damping on the behavior of impulse turbine under irregular, unsteady conditions for wave power conversion using numerical simulation.

This paper briefly reviews the need for renewable power generation and describes a medium-power Autonomous Renewable Energy Conversion System (ARECS), integrating conversion of wind and solar energy sources. The objectives of the paper are to extract maximum power from the proposed wind energy conversion scheme and to transfer this power and the power derived by the photovoltaic system in a high efficiency way to a local isolated load. The wind energy conversion operates at variable shaft speed yielding an improved annual energy production over constant speed systems. An induction generator (IG) has been used because of its reduced cost, robustness, absence of separate DC source for excitation, easier dismounting and maintenance. The maximum energy transfer of the wind energy is assured by a simple and reliable control strategy adjusting the stator frequency of the IG so that the power drawn is equal to the peak power production of the wind turbine at any wind speed. The presented control strategy also provides an optimal efficiency operation of the IG by applying a quadratic dependence between the IG terminal voltage and frequency V∼f 2 . For improving the total system efficiency, high efficiency converters have been designed and implemented. The modular principle of the proposed DC/DC conversion provides the possibility for modifying the system structure depending on different conditions. The configuration of the presented ARECS and the implementation of the proposed control algorithm for optimal power transfer are fully discussed. The stability and dynamic performance as well as the different operation modes of the proposed control and the operation of the converters are illustrated and verified on an experimental prototype. © 1999 Elsevier Science Ltd. All rights reserved.

The horizontal axis turbine is one of the most promising energy extractors for tidal stream energy utilization. However, there is no widely accepted model for describing the wake structure of a tidal stream turbine. Besides, the flow velocity variation in wakes is accompanied by energy transformation and has hardly been investigated to date. In this paper, a brief review of existing laboratory tidal stream turbine experiments is first presented, followed by a discussion about the controlling variables that includes cross-comparisons between different results from physical laboratory tests. Theoretical derivation and experimental data analysis are conducted to enable a better understanding of the energy transformation and wake development processes, and tidal stream energy extraction. It has been found that part of the flow kinetic energy has been converted into potential energy before reaching the rotor, commonly used power coefficients are not equivalent when quantifying energy extraction, and it is possible to reconstruct turbine wakes using 3 independent data-based parameters.

A key aspect of CAES is the optimal configuration of the thermodynamic cycle. In this paper, the situation of cooperation between the current conventional power plants and wind farms is analyzed, and then, based on thermodynamic models, the process of storing thermal and electrical energy in the CAES system coupled with a heat storage and recovery is developed. Therefore, three levels can be distinguished, namely: the global level of energy production; the central level of energy conversion and storage; and the local level of heat storage. Two different types of a CAES, with and without an Underground Heat Exchanger (UHE), were analyzed. The round-trip efficiency of CAES with a UHE approaches 52.26%. The article also analyses transient phenomena of charging and discharge the heat storage with UHE. The heat transfer rate and temperature received from the underground thermal energy storage was estimated. For this purpose, preliminary thermal-FSI approach was coupled with zero-dimensional model of CAES. The newly proposed CAES with a UHE, never studied before, can be used for applications requiring a high round-trip efficiency.

Electricity powered vehicles/Electric vehicles using renewable energy are becoming more and more popular, since they have become an effective way to solve energy shortage, and environmental pollution. Battery electric vehicles with zero emission characteristics are being developed on a large scale. With the scale of electric vehicles, electric vehicles with controllable load and vehicle-to-grid functions can optimize the use of renewable energy in the grid. This puts forward the higher request to the battery performance. The energy density of the batteries and renewable energy conversion efficiency have greatly also affected the application of electric vehicles. This paper presents an overview of the research for improving lithium-ion battery energy storage density, safety, and renewable energy conversion efficiency. It is discussed that is the application of the integration technology, new power semiconductors and multi-speed transmissions in improving the electromechanical energy conversion efficiency, and the issues and challenges of increasing battery energy density. In order to improve the safety, it is analyzed how to improve the estimation accuracy and temperature control performance of the battery management system. As the demand for fast charging and renewable energy of electric vehicles increases, the latest developments and technical challenges of on-board rapid charging technology are introduced.

A Collective Control is developed in this paper for arrays of Wave Energy Converters (WECs). The proposed controller applies a Proportional-Derivative feedback control law for each WEC with the optimized controller gains. A surrogate model, composed of only mechanical elements, is adopted to replace the hydrodynamic model during the optimization process. An indirect exterior penalty function approach is implemented to handle the constraints on the displacement and control. The weight of the penalty function is updated in subsequent iterations in the Sequential Unconstrained Minimization Technique. A numerical simulation is first conducted for identification of the surrogate model parameters. With the control gains optimized based on the surrogate model, the energy conversion is compared for three models: the surrogate model, a model that uses a boundary element tool to compute the hydrodynamic forces, and a simulation using AQWA. The results show a good agreement of the energy conversion among the models. Finally, the performance of the surrogate model is analyzed. It is shown that the proposed controller maximizes the energy conversion of the entire WEC array while satisfying the constraints. Moreover, the surrogate model can replace the hydrodynamic model to predict the system behavior with adequate accuracy and more efficiency.

This paper provides a feasibility study on a low cost system called Hydrokinetic Wells turbine for surface wave energy conversion without using plenum chambers. The elimination of the plenum chamber and its complicated valve systems can reduce the expenses of wave energy conversion up to 23%.The feasibility process were done for high and low frequency conditions. For the low frequency waves, we offer the 300 rpm angular velocity as an optimum selection for further studies. For the high frequency condition a reliable analytical approach based on validated methods was developed. The analytical results indicate that a wells turbine with 60 cm diameter could produce up to 1600 Watts power in high frequency waves. The efficiency and power coefficient values in high frequency condition are less in compared with low frequency situation, nevertheless the vast usage of the small scale and elimination of the plenum chambers can reduce the total cost of the conversion. The abundant availability of high frequency surface waves is a motivation for developing Hydrokinetic Wells turbine farms to harvest a great source of clean energy with lower cost levels.

The aim of this paper is to experimentally and numerically study a coupled-pitching hydrofoil under the fully activated mode. In the experimental study, the operating zones for the energy-releasing state and the energy-capturing state were identified. The phase relationship between the hydrodynamic torque and the angular velocity, which is determined by the combination of the primary and secondary pitching amplitudes, plays a key role in the switch of the energy releasing/capturing states. The primary pitching motion dominates the energy conversion of the hydrofoil under the fully-activated mode. The peak values of the averaged power coefficient and energy converting efficiency are achieved at 1.17 and 0.40, respectively. The numerical study found that the effective angle of attack determines the generation of the leading-edge and trailing-edge vortexes, and in turn affects the pressure distribution of the hydrofoil surface and torque generation. Compared to the traditional heaving-pitching mode, the coupled-pitching mode is horizontally affected by the negative torque because of the restriction of the primary pitching system, resulting in a lower energy capturing efficiency.

Vortex-Induced Vibration (VIV) is a kind of high-energy phenomena and can be used to harvest energy from ocean/river currents. In this paper, a spring-mounted circular cylinder in VIV was numerically investigated with 2-dimensional simulations to examine the effects of submergence depth on the energy conversion. The flow speed changes from 0.2 m/s to 1.3 m/s (1.61 × 104 9.7 × 104), the oscillation amplitude of the cylinder decreases to zero. In this case, the oscillation response doesn’t belong to VIV.

Alternating lift technology (ALT) harnesses hydrokinetic energy from currents and tides and is different from conventional steady lift technologies (turbines). ALT is still under development with an important research issue being the mitigation of wake effect on downstream cylinders in Flow Induced Oscillations (FIO) of multi-cylinder Current Energy Converters (CEC). Rather than adjust the configuration/parameters of the converter, a more direct and effective way is to actively adjust the harnessed power. In this paper, a hydrokinetic energy converter using FIO of two cylinders in tandem in one-degree-of-freedom oscillators, with nonlinear adaptive damping and linear spring stiffness, is tested experimentally. FIO include Vortex Induced Vibrations (VIV), galloping, and their coexistence. Introducing adaptive damping into the tandem cylinders overcomes the shielding effect, which previous research on two tandem cylinders has shown to reduce power output by the downstream cylinder. Shielding along with fixed damping result either in ceasing motion due to excessive damping, or in low harnessed energy due to insufficient damping. In this experimental study, damping-to-velocity rate, linear spring-stiffness, cylinder spacing, and flow-velocity are the parameters with Reynolds number 30,000 ≤ Re ≤ 120,000. Comparison to linear-oscillators in FIO shows that this nonlinear converter, with velocity-proportional damping coefficient, is more effective over the entire FIO range but especially in galloping, where both flow and cylinder speeds are higher. Experimental results for energy harvesting, efficiency and instantaneous energy of the converter are presented and discussed supported by amplitude and frequency response data. The results show that the nonlinear, adaptive, velocity-proportional damping coefficient is an effective way to increase the overall harnessed power and the power of downstream cylinder. The harnessed power in the VIV to galloping transition increases by up to 94%. The most significant improvement is in the galloping region, where the increase in harnessed power and efficiency is around 33%.

CECO is a wave energy converter (WEC) of the oscillating body type equipped with an inclined PTO system and being developed at the Faculty of Engineering of the University of Porto. In the last years, several research studies have been performed to assess and to improve the performance of this WEC, using both physical model tests and numerical simulations. The main objective of this paper is reviewing the most significant findings of past research works, so as to provide a detailed overview about the present status of knowledge, but also presenting recent outcomes on the development of CECO and the next research steps. It discusses the influence of the PTO slope angle and damping on the efficiency of CECO harvesting wave energy and describes its energy conversion stages. Furthermore, the intra-annual variability of the wave resource (i.e., on a monthly basis) is considered in the analysis of the influence of the PTO inclination and local water depth at the deployment site on CECO captured energy and captured energy efficiency, along the North Atlantic coast of the Iberian Peninsula. The results have shown significant differences between the summer and winter months and also highlighted the fact that the initial geometry of this WEC is more suitable for the less energetic wave climates, characteristic of the southern locations of the case study area and of shallow waters. The conclusions obtained supported the design of an enhanced version of CECO, prepared for the more energetic stretches of the study area, which presents a hydrodynamic efficiency of more than twice the original one, for the target wave conditions.

Presence of dust and/or condensate film affects the transmissivity of solar radiation through the transparent canopy/cover of solar collectors. This paper presents experimental investigation results of water vapor film condensate on the upper and lower surfaces of the canopy and how it affects solar chimney performance. The experimental measurements were carried out utilizing the solar chimney model, which has a collector of 7.0 m diameter and chimney of 6.5 m height above the collector. After 10 days of measurements and observation, radiation transmittance was considerably reduced from 7:30 a.m. until 10:30 a.m. due to the presence of condensate. Consequently, collector and solar chimney performance were influenced. A 9%–10% variation in solar radiation transmittance was found between dry and wet canopy. The condensate film required 2.0–3.0 h to evaporate. During the evaporation time (7:30 a.m. to 10:30 a.m.), the increase in the collector air temperature under wet canopy was 3.0 °C–5.0 °C less compared with that under dry canopy. Solar radiation from the sun until 10:30 a.m. was absorbed by the condensate film to evaporate. A delay was observed in the energy conversion processes from solar to thermal to kinetic, thereby delaying power generation. The presence of water condensate film reduced the hydrothermal performance of the solar chimney by two ways: by reducing the transmittance of solar radiation and by absorbing solar radiation from the water vapor particles to evaporate. An auxiliary heat source that supplies heat before sunrise is necessary to evaporate the condensate film and allow the solar chimney to operate early.

The use of solar-powered Stirling engines to convert thermal energy into electricity is a promising and renewable technological solution that can contribute to reducing dependence on fossil fuels for electricity generation. Unfortunately, the lack of experimental performance data and operating parameters for this type of technology limits its detailed characterization, difficult its modeling and design and consequently its utilization. This paper aims to validate the mathematical model of the Dish/Stirling system previously published by Mendoza et al. (2017) with the TRINUM system, installed at the Federal University of Itajuba-Brazil. For nominal conditions, the Dish/Stirling system generates an electric power of 1.00 kW at a solar irradiation of 725 W/m2 with a system overall efficiency of 17.6%. The results show that for solar irradiance values between 520 and 950 W/m2 the experimental tests and the results of the mathematical modeling do not present considerable differences, obtaining an electric power of 1089 kWe and an efficiency of 17.98%, which represents deviations in the range of 2%–12%.

In this paper, a two-step mathematical model is developed to simulate the solar-thermal energy conversion and consequent change in the properties of working fluid in an unconventional solar thermal water pump with flat plate collector. The available thermal energy to the working fluid for the incident solar radiation is calculated in the first step of the model. A single component boiling model is used in the second step to calculate the working fluid's boil-off rate and therefore number of moles of working fluid in each phase (liquid and vapour phases) at an instant. As the accurate thermodynamic property estimation is essential, Peng-Robinson equation of state is used for this purpose. An experimental set-up of an unconventional solar thermal water pump with pentane as working fluid is used to validate the model. The experimentally obtained temperature and pressure of working fluid in the relevant tanks under no-pumping but the energy conversion during solar day are compared with the model predictions. A close agreement between the experimental and simulated values are seen. The reasons for the deviations of experiment and model predicted values are elucidated. The relevance of the developed two step model for evaluating the performance of the pump is presented.

To achieve optimal power in a wave energy conversion (WEC) system it is necessary to understand the device hydrodynamics. To maximize conversion efficiency the goal is to tune the WEC performance into resonance. The main challenge then to be overcome is the degree to which non-linearity in WEC hydrodynamics should be represented. Although many studies use linear models to describe WEC hydrodynamics, this paper aims to show that the non-linear viscosity should be carefully involved. To achieve this an investigation into the hydrodynamics of a designed 1/50 scale point absorber wave energy converter (PAWEC) in heave motion only is implemented to indicate the non-linear viscosity effect. A non-linear state-space model (NSSM) considering a quadratic viscous term is used to simulate PAWEC behaviors. The non-linear model is compared with the linear counterpart, and validated by computational fluid dynamics (CFD) and experimental data. A conclusion is drawn that the non-linear PAWEC hydrodynamics (including amplitude and phase responses, conversion efficiency) close to resonance or at high wave heights can only be described realistically when the non-linear viscosity is correctly taken into account. Inaccuracies in its representation lead to significant errors in the tuning procedure which over-predict the dynamic responses and weaken the control system performance.

Icing is a strong limitation for the performance of wind turbines in cold climates and the prediction of the performance loss due to ice accretion is essential for designing effective ice mitigation measures. This paper presents a numerical approach capable of simulating the ice accretion transient phenomenon and its effects on wind turbine performance. This approach is applied to the NREL 5 MW reference wind turbine to predict (i) its performance during and after an icing event lasting for 8 h and (ii) the potential improvement in energy harnessing due to different operational strategies. The results show that by decreasing the turbine rotational speed and accepting a slight energy conversion decrease during the icing event, the performance can improve up to 6% when full operation is restored compared to the baseline operational strategy. Whereas, sustaining the rotational speed during the icing event can generate a 3% of performance loss afterwards compared to the same baseline. The developed workflow can be used for optimising performance of wind turbines by accounting for environmental conditions, the duration of the icing event, and performance after the icing event itself, thus constituting a valuable tool to maximise profitability of wind turbines in cold climates.

Flow Induced Motions (FIMs) of rigid circular cylinders, and particularly VIV (Vortex Induced Vibrations) and galloping, are induced by alternating lift. The VIVACE (VIV for Aquatic Clean Energy) Converter uses single or multiple cylinders, in tandem, on elastic end-supports, in synergistic FIM, to convert MHK energy to electricity. Selectively distributed surface roughness is applied to enhance FIM and increase efficiency. In this paper, two cylinders are used in tandem with center-to-center spacing of 1.57, 2.0 and 2.57 diameters, harnessing damping ratio 0.00

Currently, two maximum power point tracking (MPPT) units are used in hybrid photovoltaic (PV)/fuel cell (FC) systems, one for the PV subsystem and the other one for the FC stack, which significantly complicates the system implementation, and increases cost. This paper addresses this problem by presenting a novel fast and highly accurate unified MPPT technique for extracting maximum output power from hybrid PV/FC energy conversion systems. It is the only unified MPPT technique reported in the literature that uses a single algorithm to concurrently track the maximum power points (MPPs) of both PV module and FC stack used in a hybrid PV/FC system. A hybrid PV/FC energy conversion system has been built to evaluate the performance of the method. It is experimentally verified that the proposed MPPT method performs a very fast and highly accurate MPPT process, so that, the MPPT efficiency in the PV and FC subsystems is more than 99.60% and 99.41%, respectively, along with a very short convergence time of at most 12 ms and 33 s, respectively. Comparison between the MPPT method presented in this work and the state-of-the-art MPPT methods has been also performed that explicitly demonstrates the method has the highest MPPT efficiencies (99.60%, and 99.41%) along with the shortest convergence time (12 ms) compared to the state-of-the-art MPPT methods, while it concurrently performs two tasks (tracking two MPPs) but others perform only one task (tracking one MPP).

This paper presents a novel process for high efficiency production of hydrogen and desalination of brine water based on the concept of solar spectrum splitting. The advantage of this system is concurrent production of hydrogen and distilled water using a sustainable process at large scale. The harvested energy from the separated solar spectral bands is used to supply the required energy for high temperature steam electrolysis and a double-stage flash distillation system. The integrated solar system is designed to reduce the energy conversion deficiencies, considerably. In order to investigate the performance of this system, a process simulation code is developed. An exergy analysis is conducted and the economic feasibility of the plant is evaluated. The sensitivity of the integrated cycle performance on solar insolation, electrolyzer temperature, and pressure is analyzed, and the results indicate that utilization of concentrator cells, with a multi-band gap mirror can increase the productivity of the cycle, drastically. It is observed that hydrogen and distilled water production rate can be increased by more than 1.6 times, when the harvested solar power increases from 28 MW to 55 MW. It is concluded that the maximum energy and exergy efficiencies of the integrated solar cycle is about 45%.

In this paper, a comprehensive numerical model was developed by coupling Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) for simulating the energy conversion process in the linear Fresnel reflector (LFR) with a Trapezoidal Cavity Receiver (TCR). Based on the model, firstly, the optical performance of a typical LFR was studied, followed by analyzing its heat transfer characteristics and thermal performance at various conditions. Then, the effects of key parameters were investigated. Finally, a LFR prototype was simulated to illustrate the application of the model. The results indicate that the solar fluxes on the absorber tubes exhibit non-uniform characteristics which would result in the non-uniform temperatures. The annual optical efficiency of 60.1%–44.7% from the equator to N50° and the collector efficiency of 48.3%–72.0% for the superheating section at normal incidence can be achieved, respectively. Moreover, the heat transfer characteristic study reveals that the radiation loss from the tubes is the dominant mode and contributes around 81%–87% at typical conditions. Parameter studies indicate that the energy absorbed by the glass which influences the heat loss obviously should be considered in the heat loss study of TCR. And the heat loss from the tubes increases rapidly with the coating emissivity, so the coating with low emissivity should be recommended for the TCR. In addition, the application in the realistic LFR indicates that the present model is an exercisable and useful tool for the LFR.

The use of Concentrated Solar Power technology for energy generation relies on the heating of fluids to high temperatures. One of the limitations of this technology is the low working efficiency of current solar receivers which hinders its application and utilization as a renewable clean energy source. This paper presents a novel concept to improve concentrated solar receiver efficiency through the recirculation of solid particles laden flow within the receiver. The recirculating characteristic of the fluid and solid particle mixture is expected to generate higher output fluid temperature than conventional solar receivers. This is expected to lead to significant improvements in the working performance of the concentrated solar receiver. The numerical study investigates this concept, using a commercial CFD package, employing the discrete particle model (DPM), a RNG k- e flow model and a discrete ordinate (DO) radiation model. It is found that the use of recirculating solid particles improves the energy absorption within the receiver and with it the thermal efficiency of the proposed solar receiver reaches to around 70%. Moreover, comparing this with a conventional solar receiver, this new concept exhibits a more uniform temperature distribution inside the cavity, which is mainly due to the recirculating flow characteristic and the well-controlled mixing of air and particles. The advantages of this novel concept of the solar receiver present its potential benefits in further applications in the process of energy conversion providing on enhanced heat transfer medium.

Compressed air energy storage (CAES) system is an “electricity to electricity” device. To reveal the energy conversion process and understand the energy loss principle are critical to improve the energy conversion efficiency. In this paper, the charge/discharge process analysis of an axial turbine based CAES with constant volume is executed in constant turbine inlet pressure mode and variable turbine inlet pressure mode. Firstly, the energy efficiency analysis of a whole round trip cycle of CAES system under design condition is carried out. The second law efficiencies of the operation mode 1 and the operation mode 2 are 44.56% and 45.16%, respectively. It also can be found that the throttling loss in operation mode 1 can be offset by the benefits of higher isentropic efficiency of turbines. Then, the off-design analysis of these two operation modes is implemented by considering the different power levels and speed levels. The mass flow rates of working fluids across the expansion train both increase with the increased load rate or the decreased speed. The load rate or speed both have the positive effect on the exergy efficiency and the energy generated per unit volume of storage, but have the negative effect on the heat rate.

Energy conversion technologies, especially for power generation and refrigeration, driven by the low temperature heat source are gathering the momentum recently. This paper presents a novel cogeneration cycle combining power and refrigeration with energy storage function. MnCl2–CaCl2–NH3 is selected as the working pair. Phase change materials of “50 wt% NaNO3 + 50 wt% KNO3” and “65 mol% capric acid + 35 mol% lauric acid” are chosen for heat and cold storage, respectively. Heat and mass transfer property of composite adsorbents are investigated, and isentropic efficiency of scroll expander is tested by compressed air. Based on experimental results, a cogeneration system with power of 300 W maximum and cooling power of 2 kW is designed and analyzed. Analysis shows that total energy efficiency of cogeneration system increases from 0.316 to 0.376 and energy efficiency decreases from 0.402 to 0.391 when evaporation temperature increases from −10 to 20 °C. Cold releasing process is able to last 91 min with cold storage function.

In this paper we derive the dynamical model of a four-cylinder double-acting wobble-yoke Stirling engine. In addition to the classical thermodynamics methods that dominate the literature of Stirling mechanisms, we present a control systems viewpoint to analyze the dynamic properties of the engine. We show that the Stirling engine can be viewed as a closed-loop system, in which the pressure variations in the cylinders behave as the feedback control law. (C) 2014 Elsevier Ltd. All rights reserved.

Oscillating water column based wave energy extracting system has a low efficiency due to the poor performance of its principal power extracting component, the bidirectional turbine. In the present work, flow over a bidirectional impulse turbine was simulated using CFD technique and optimized using multiple surrogates approach. The surrogates being problem dependent may produce unreliable results, if a wrong surrogate is selected. Hence, multiple surrogates such as response surface approximation, radial basis function, Kriging and weighted average surrogates were incorporated in this problem. Same design points were used to generate multiple optima via multiple surrogates to enhance the robustness of the optimization process. Numbers of guide vanes and rotor blades were chosen as the design variables, and the objective was to maximize the blade efficiency. Reynolds-averaged Navier–Stokes equations were solved for analyzing the flow physics. The computed results were used to train the surrogates and find the optimal points via hybrid genetic algorithm. The surrogates were further applied to find the optimal flow parameters by changing flow velocity and turbine speed. The relative efficiency enhancement through our present approach was about 16%. Detailed methodologies, analysis of the results and surrogate applicability have been presented in this paper.

The use of photovoltaic (PV) systems has been showing a significant growth trend but for a more effective development of this technology it is essential to have higher energy conversion performances. Producers of PV often declare an higher efficiency respect to real conditions and this deviation is mainly due to the difference between nominal and real temperature conditions of the PV. To improve the solar cell energy conversion efficiency many authors have proposed a methodology to keep lower the temperature of a PV system: a modified PV system built with a normal PV panel coupled with a Phase Change Material (PCM) heat storage device. In this paper is described a thermal model analysis of the PV–PCM system based on a theoretical study using finite difference approach. The authors developed an algorithm based on an explicit finite difference formulation of energy balance of the PV–PCM system. To this aim, a forward difference at time t and a first-order central difference for the space derivative at position x was used. Two sets of recursive equations were developed for two types of spatial domains: a boundary domain and an internal domain .The reliability of the developed model is tested by a comparison with data coming from a test facility. Results of this experience confirm the performed numerical simulations and show that the proposed model is valid and can be used to determine the thermal behaviour of a solar cell coupled with a PCM heat storage device.

This paper presents an advanced design methodology for electric power generation from the vast ocean wave energy. A novel single-buoy heaving device called wave energy converter (WEC) based on hydrostatic transmission (HST), or can be shortened as HSTWEC, is proposed to convert mechanical energy generated by ocean waves into electric energy. Modeling and simulations with both regular and irregular waves were then carried out to investigate working performances of the designed HSTWEC. The results showed that more than 78% of wave energy can be absorbed. In addition, an adaptive controller was designed to improve the performance of the suggested device. Effectiveness of the overall HSTWEC control system was finally proved by simulations.

This paper reports on the development of a two-dimensional, fully nonlinear Computational Fluid Dynamics (CFD) model to analyse the efficiency of fixed Oscillating Water Column (OWC) Wave Energy Conversion (WEC) devices with linear power take off systems. The model was validated against previous experimental, analytical and numerical results of others. In particular, the simulation results show excellent agreement with the analytical results obtained by Sarmento and Falcao [1] for linear waves in a 2D channel and with previous experiments by others on the interaction between nonlinear waves and a fixed barge. Results are presented for linear waves on the influence of the seaward wall draft and thickness of the OWC device on the resonant frequency and the capture efficiency of the OWC. The key outcome of the present work is that for fully nonlinear waves a substantial decrease in the hydrodynamic capture efficiency of the OWC device was observed with increasing wave height, which represents a significant departure from the linear wave case. The optimal pneumatic damping coefficient for the OWC was also found to be dependent on the wave height. By analysing the magnitude of the first and higher order components of the incident nonlinear waves and the response of the OWC it was found that the first order capture efficiency decreases with increasing wave height, which in turn implies that the OWC hydrodynamic system is fully nonlinear and that the behaviour of an OWC in a nonlinear wave train cannot be accurately represented by the superposition of the linear response to a number of component linear waves. These results have significant implications for the design and operation of practical OWC systems.

This paper investigates wave energy conversion in open water where the goal is to utilize the wave-field focusing effect of a stationary disc submerged a short depth beneath the water surface. Dynamic interaction of the disc with additional coupled, submerged inertias is used to minimize its oscillation. The method used to enable and extend this favorable dynamic coupling is discussed here. An oscillating water column in a submerged duct attached under a small circular opening in the disc and driven by the wave-field over the disc is used for wave energy conversion. Non-real-time reactive control of the water column response to enhance energy absorption is examined. Added mass, radiation damping, and exciting force values for the submerged disc are computed, and the focusing effect of a submerged stationary disc is confirmed with numerical calculations of surface elevation over the disc. Calculations of hydrodynamic performance suggest that energy absorption from the oscillating water column is significantly greater under control holding the disc stationary, and can be improved further by applying reactive loads tuned to the optimal susceptance and conductance associated with the oscillating water column. Although the control forces involved in holding the disc stationary may be large at lower wave numbers, the maximum deflection amplitudes of the compensation system are found to be within reasonable limits.

The paper presents the results of pyrolysis process applied as pre-treatment sequence for grape marc within energy conversion chain. Experimental campaign for proximate, ultimate and calorimetric characterization of the product was conducted. The product equivalent chemical formula was established – C 4 H 7 O 3 . The atmospheric pressure pyrolysis with external heat source at temperatures between 350 °C–600 °C was studied with respect to process parameters influence on end-products formation, distribution and physical–chemical properties. Based on experiments the product activation energy of 111.5 kJ/mol was determined. The process parameters influence on end-products energy content, pyrolysis energy consumption and global energy efficiency was established. The research focused on maximum net energy content delivered in pyrolysis products as high quality fuel for energy conversion processes. The study revealed that pyrolysis gas alone can ensure the process self-sustenance for the applied temperature range. The optimum treatment temperature with respect to global energy balance was found at 550 °C.

This paper presents an investigation of a hybrid DC/AC integration paradigm to establish microgrids (MGs) by using a conventional three-phase local power delivery system. This approach adds an additional DC power line to the local power distribution system in order to collect energy generated by distributed domestic renewable sources. The local renewable distributed generation (DG) works in conjunction with the conventional grid utility to reduce the power draw from the grid. Researchers designed an energy conversion station to mix energy from the local DGs with energy from the grid utility. This approach, therefore, uses a continuous energy mixing strategy for DC integration of local generation and grid energy to supply energy to MG consumers via the conventional three-phase power distribution system. Thus, local distributed renewable generators do not have to contend with AC integration problems, such as AC stability and line synchronization. This approach can facilitate the transformation of conventional local power distribution systems into reliable MGs in an affordable way for stakeholders and it is a step towards construction of future smart grids.

In this paper, a switched modulated power filter-green plug (SPF-GP) scheme for wave energy conversion (WEC) systems is presented. In order to reduce the interfacing power quality problems and improve the energy utilization of WEC systems, design and realization of a novel SPF-GP and effective control strategies are studied. To illustrate the effectiveness of the proposed techniques, a simulation model is developed in Matlab/Simulink/Simpower Software Environment. Besides, experimental prototype models of the proposed SPF-GP system and error driven controllers have been setup to verify the digital simulation model by comparing the results, which validate the effectiveness of the proposed interfacing device and the control algorithms. Both the simulation and the experiments were done for several cases and results of the same operating conditions from both platforms were compared for model validation as well as system performances. It has been shown that the proposed FACTS power filter compensator and control strategy developed by the third author are very effective on eliminating stochastic wave effects on load side voltage and load variations on source side by reducing voltage sags and swells.

This paper presents the geometry optimization of a floating oscillating water column (OWC). The device consists of a floater pierced by a small thickness tube open at the bottom to the sea water and at the top to the OWC chamber. The dimensions of the floater and tube are optimized in order to maximize the wave energy extraction under certain geometric constraints. The formulation considers linear water wave theory. A boundary element method code is used to calculate the hydrodynamic coefficients. The floater and the water column are assumed to oscillate only in heave. The top of the water column is modeled as a piston. The compressibility effect of the air inside the chamber is accounted for. A Wells turbine with a linear characteristic curve is considered as a power take-off system. The system is modeled in the frequency domain, assuming two degrees of freedom. The power extraction from real sea waves is simulated through a stochastic model, using an energy spectrum and the wave climate conditions off the western coast of Portugal. The dimensions of the floating OWC are optimized using two distinct optimization algorithms. Results have shown that the diameter of the floater, the submerged length and the air chamber height have a large impact on the annual average power extraction.

This paper treats the design and control of two hybrid source using supercapacitors, fuel cell, with and without batteries on the DC link. A fuel cell, as a slowest dynamic source in these systems (because of its auxiliaries) acts to supply the permanent energy. The supercapacitors, as a high dynamic and high power density device, compensate the intrinsic limitations in embedded sources and shave transient power peaks. The batteries module, as a high energy density device, operates for supplying energy if limitations of the power and energy sources occur. The load is a single phase DC machine connected directly in the DC bus. Our interest is focused on the comparison of the two structures and on the principles of control of this two hybrid power sources. Some results are presented and discussed.

Creating better understanding between environmental quality and energy use, this paper collects 150 household energy use data sets, using questionnaires, from households in Lanzhou, China. Converted to kilograms of coal standardized energy equivalent, urban energy usage is calculated at a yearly rate of 490.37 kgce/a per capita and 1598.61 kgce/a per household. Types of emissions are also specified. Coal is the dominant energy source, and maximum environmental benefit is shown to be gained from substituting natural gas and solar energy for coal, and specific measures for substitution are identified.

This paper presents a sensorless control for a variable speed wind turbine (WT) operating at partial load in order to eliminate the direct measurement of the wind speed. In this proposal, the estimated aerodynamic torque is used to determine the optimal reference of the speed control for maximum energy conversion. The maximization of the efficiency on energy conversion and the minimization of detrimental dynamical loads are control trade-offs considered in the design of an optimal discrete-time feedback LQG/LTR controller for the Wind Energy Conversion System (WECS), which is based on the optimization of a quadratic cost function. The performance of the proposed control when the WT is submitted to a gust or step variation on wind speed is evaluated from computational simulations. It is also presented some proposals for sensorless control of the electrical generator.

This paper presents an overview of the SeaBeavI project which began in the fall of 2006 and culminated in the ocean testing of a 10 kW direct-drive wave energy conversion system in the fall of 2007. The SeaBeavI project was an interdisciplinary effort bringing together researchers from electrical, mechanical, and ocean engineering. A systems design approach was used to develop the taut-moored dual-body wave energy converter concept with the detailed design focused on production and ease of maintenance.