Optimization of a Darrieus vertical-axis wind turbine using blade element – momentum theory and evolutionary algorithm

Wind turbine design procedures usually involve the adoption of the blade element – momentum theory. Nevertheless, its use is limited by the lack of extended database regarding the aerodynamic coefficients for most used airfoils. In the present work, an extended database generation procedure for symmetric profiles is discussed and validated with the aim of adopting numerical optimization methods for vertical-axis wind turbine design.Evolutionary algorithms are thereby utilized to provide optimal configurations for different design objectives. The pure performance and the annual energy production are here considered in order to show the capabilities of the numerical code. A relevant increase in performance is achieved for all the obtained results, showing that the numerical optimization can be successfully adopted in vertical-axis wind turbine design procedures.     

Modeling aspects of a floating wind turbine for coupled wave–wind-induced dynamic analyses

This paper deals with the numerical modeling of a catenary moored spar-type wind turbine in the integrated coupled analyses. The current spar-type wind turbine is inspired by the Hywind concept. In this paper, different hydrodynamic models based on the Morison formula, Pressure integration method and Panel method considering the mean drift, first and second order forces are studied. A floating wind turbine in deep water depth supporting a 5-MW turbine system is considered. Simo-Riflex (DeepC), HAWC2 and FAST codes are used to carry out the coupled wave–wind-induced analyses. The results show that the damping and inertia forces of the mooring lines are important for the tension responses; especially, the damping of the mooring lines can help to damp-out the high-frequency elastic-deformations of the mooring system. However, the motion responses are not significantly affected by the mooring line damping-effects. The drift and second order forces do not significantly affect the motion and tension responses. However, the heave motion is more affected by the drift and second order forces. The results indicate that either the Morison formula considering the instantaneous position of the structure or first order hydrodynamic forces based on the Panel method and considering the quadratic viscous forces can provide accurate results for the slender spar-type wind turbines. Considering the second order forces is found to be 10–15 times more time consuming while the responses are not significantly affected for the present floating wind turbine. The coupled aero-hydro-servo-elastic code-to-code comparison of HAWC2 and FAST codes shows that the dynamic motion responses, structural responses at the tower–spar interface and at the blade root as well as the power production are in good agreement.     

Mode I quasi–static and fatigue delamination characterisation of polymer composites for wind turbine blade applications

Abstract

Ambitious electricity generation targets from renewable sources set by many governments have lead to the rapid growth of the wind energy industry over the last two decades. The need for larger wind turbine blades for increasing energy generation has considerably increased the demand and use of high performance composites in wind turbine applications, mainly in blades. A common type of failure in composite materials is delamination of adjacent layers, which can occur either due to manufacturing inconsistencies or due to in service loads. Understanding and characterising delamination is very important in order to implement damage tolerant design methodologies. The present research work focuses on the assessment of the delamination behaviour of composites for wind turbine applications. Several composite systems were tested and their fracture toughness and fatigue delamination propagation behaviour under mode I (peeling) loading conditions were evaluated. Quasi–static tests were performed and delamination initiation values were evaluated. Fatigue delamination growth rate curves (da/dN versus G _Imax) were also produced. The carbon/epoxy and glass/epoxy material systems tested were compared in terms of resin type, fibre type and interfacial characteristics.     

Numerical simulations of a coupled radiative–conductive heat transfer model using a modified Monte Carlo method

Radiative–conductive heat transfer in a medium bounded by two reflecting and radiating plane surfaces is considered. This process is described by a nonlinear system of two differential equations: an equation of the radiative heat transfer and an equation of the conductive heat exchange. The problem is characterized by anisotropic scattering of the medium and by specularly and diffusely reflecting boundaries. For the computation of solutions of this problem, two approaches based on iterative techniques are considered. First, a recursive algorithm based on some modification of the Monte Carlo method is proposed. Second, the diffusion approximation of the radiative transfer equation is utilized. Numerical comparisons of the approaches proposed are given in the case of isotropic scattering.     

Validation of a three-dimensional viscous–inviscid interactive solver for wind turbine rotors

MIRAS is a newly developed computational model that predicts the aerodynamic behavior of wind turbine blades and wakes subject to unsteady motions and viscous effects. The model is based on a three-dimensional panel method using a surface distribution of quadrilateral singularities with a Neumann no penetration condition. Viscous effects inside the boundary layer are taken into account through the coupling with the quasi-3D integral boundary layer solver Q³UIC. A free-wake model is employed to simulate the vorticity released by the blades in the wake. In this paper the new code is validated against measurements and/or CFD simulations for five wind turbine rotors, including three experimental model rotors [20–22], the 2.5 MW NM80 machine [23] and the NREL 5 MW virtual rotor [24]. Such a broad set of operational conditions and rotor sizes constitutes a very challenging validation matrix, with Reynolds numbers ranging from 5.0⋅10⁴ to 1.2⋅10⁷.     

Economical assessment of a wind–hydrogen energy system using WindHyGen software

This paper considers the problem of analyzing the economical feasibility of a wind–hydrogen energy storage and transformation system. Energy systems based on certain renewable sources as wind power, have the drawback of random input making them a non-reliable supplier of energy. Regulation of output energy requires the introduction of new equipment with the capacity to store it. We have chosen the hydrogen as an energy storage system due to its versatility. The advantage of these energy storage systems is that the energy can be used (sold) when the demand for energy rises, and needs (prices) therefore are higher. There are two disadvantages: (a) the cost of the new equipment and (b) energy loss due to inefficiencies in the transformation processes. In this research we develop a simulation model to aid in the economic assessment of this type of energy systems, which also integrates an optimization phase to simulate optimal management policies. Finally we analyze a wind–hydrogen farm in order to determine its economical viability compared to current wind farms.     

“Blind test” calculations of the performance and wake development for a model wind turbine

This is a summary of the results from the “Blind test” Workshop on wind turbine wake modeling organized jointly by Nowitech and Norcowe in Bergen, October, 2011. A number of researchers were invited to predict the performance and the wake development for a model wind turbine that has been developed by and extensively tested at the Department of Energy and Process Engineering, NTNU. In the end, contributions were received from eight different groups using a wide range of methods, from standard Blade Element Momentum (BEM) methods to advanced fully resolved Computational Fluid Dynamics (CFD) and Large Eddy Simulation (LES) models. The range of results submitted was large, but the overall trend is that the current methods predict the power generation as well as the thrust force reasonably well, at least near the design operating conditions. But there is considerable uncertainty in the prediction of the wake velocity defect and turbulent kinetic energy distribution in the wake.     

Piecewise affine modeling and control of a boiler–turbine unit

In this paper, a discrete-time piecewise affine (PWA) model has been proposed for a nonlinear model of boiler–turbine unit using plant operating points. PWA model is one of the main classes of hybrid systems being equivalent to some other hybrid modeling frameworks such as mixed logical dynamical (MLD) model. In order to control the system, a model predictive control (MPC) strategy in explicit form has been used which calculates the control law as an affine function of system states. In this method, the computation of MPC is moved off-line. The off-line control law is easier to implement reducing to a look-up table in comparison with the on-line approach. Finally, the explicit model predictive control performance has been compared with the linear controller obtained using H_∞ approach. The results are illustrated by simulations. They show that the explicit MPC method has suitably improved the system performance, especially the quantity of control efforts is smaller and without saturation compared with that of H_∞ control system.     

Design of a cost-effective on-grid hybrid wind–hydrogen based CHP system using a modified heuristic approach

An economic model and optimization procedure is developed in this paper for grid-connected hybrid wind–hydrogen combined heat and power systems for residential applications in northeastern Iran. The model considers various significant factors: energy production cost, electrical trade with local grid, electrical power generation from the wind/hydrogen energy system, thermal recovery from the fuel cell, and maintenance. Also, various tariffs for purchasing and selling electrical energy from the local grid are considered for the hybrid system operation. The optimization objective is to minimize the system total cost subject to relevant constraints for residential applications. To achieve this aim, an efficient optimization method is proposed based on particle swarm optimization. The proposed algorithm performance is compared with that for the imperialist competition algorithm. The results show that the hybrid system is the most cost-effective for the residential load, and the results of the proposed algorithm are more promising than those for the alternative algorithm.     

Exergoeconomic machine-learning method of integrating a thermochemical Cu–Cl cycle in a multigeneration combined cycle gas turbine for hydrogen production

Integrating new technologies into existing thermal energy systems enables multigenerational production of energy sources with high efficiency. The advantages of multigenerational energy production are reflected in the rapid responsiveness of the adaptation of energy source production to current market conditions. To further increase the useful efficiency of multigeneration energy sources production, we developed an exergoeconomic machine-learning model of the integration of the hydrogen thermochemical Cu–Cl cycle into an existing gas-steam power plant. The hydrogen produced will be stored in tanks and consumed when the market price is favourable. The results of the exergoeconomic machine-learning model show that the production and use of hydrogen, in combination with fuel cells, are expedient for the provision of tertiary services in the electricity system. In the event of a breakdown of the electricity system, hydrogen and fuel cells could be used to produce electricity for use by the thermal power plant. The advantages of own or independent production of electricity are primarily reflected in the start-up of a gas-steam power plant, as it is not possible to start a gas turbine without external electricity. The exergy analysis is also in favour of this, as the integration of the hydrogen thermochemical Cu–Cl cycle into the existing gas-steam power plant increases the exergy efficiency of the process.     

Combustion and emissions characteristics of a hybrid hydrogen–gasoline engine under various loads and lean conditions

The addition of hydrogen is an effective way for improving the gasoline engine performance at lean conditions. In this paper, an experiment aiming at studying the effect of hydrogen addition on combustion and emissions characteristics of a spark-ignited (SI) gasoline engine under various loads and lean conditions was carried out. An electronically controlled hydrogen port-injection system was added to the original engine while keeping the gasoline injection system unchanged. A hybrid electronic control unit was developed and applied to govern the spark timings, injection timings and durations of hydrogen and gasoline. The test was performed at a constant engine speed of 1400 rpm, which could represent the engine speed in the typical city-driving conditions with a heavy traffic. Two hydrogen volume fractions in the total intake of 0% and 3% were achieved through adjusting the hydrogen injection duration according to the air flow rate. At a specified hydrogen addition level, gasoline flow rate was decreased to ensure that the excess air ratios were kept at 1.2 and 1.4, respectively. For a given hydrogen blending fraction and excess air ratio, the engine load, which was represented by the intake manifolds absolute pressure (MAP), was increased by increasing the opening of the throttle valve. The spark timing for maximum brake torque (MBT) was adopted for all tests. The experimental results demonstrated that the engine brake mean effective pressure (Bmep) was increased after hydrogen addition only at low load conditions. However, at high engine loads, the hybrid hydrogen–gasoline engine (HHGE) produced smaller Bmep than the original engine. The engine brake thermal efficiency was distinctly raised with the increase of MAP for both the original engine and the HHGE. The coefficient of variation in indicated mean effective pressure (COVimep) for the HHGE was reduced with the increase of engine load. The addition of hydrogen was effective on improving gasoline engine operating instability at low load and lean conditions. HC and CO emissions were decreased and NOx emissions were increased with the increase of engine load. The influence of engine load on CO₂ emission was insignificant. All in all, the effect of hydrogen addition on improving engine combustion and emissions performance was more pronounced at low loads than at high loads.     

Optimal design and techno-economic analysis of a hybrid solar–wind power generation system

Solar energy and wind energy are the two most viable renewable energy resources in the world. Good compensation characters are usually found between solar energy and wind energy. This paper recommend an optimal design model for designing hybrid solar–wind systems employing battery banks for calculating the system optimum configurations and ensuring that the annualized cost of the systems is minimized while satisfying the custom required loss of power supply probability (LPSP). The five decision variables included in the optimization process are the PV module number, PV module slope angle, wind turbine number, wind turbine installation height and battery capacity. The proposed method has been applied to design a hybrid system to supply power for a telecommunication relay station along south-east coast of China. The research and project monitoring results of the hybrid project were reported, good complementary characteristics between the solar and wind energy were found, and the hybrid system turned out to be able to perform very well as expected throughout the year with the battery over-discharge situations seldom occurred.     

Performance prediction and evaluation of the scroll-type hydrogen pump for FCVs based on CFD–Taguchi method

To improve hydrogen utilisation and provide superior water management, the recirculation hydrogen pump is one of the key components in a fuel-cell vehicle (FCV). This work focused on the performance estimation of a scroll-type hydrogen pump for FCVs. A series of CFD simulation cases were designed using the Taguchi method and were carried out to determine the optimum conditions for volumetric efficiency, and the effects of four factors, including pressure ratio, rotating speed, axial clearance, and radial clearance. The contributions of these factors on volumetric efficiency and shaft power were quantified by the analysis of variance (ANOVA) method. The results show that axial clearance and rotating speed are the main influencing factors on volumetric efficiency, and their contribution ratios are 45.3% and 39.6%, respectively, in the operational range of the hydrogen pump for FCVs. Pressure ratio and rotating speed should be considered first to reduce shaft power, and their contribution ratios are 40.9% and 55.4%, respectively. At last, the performance maps of the scroll-type hydrogen pump were obtained to reveal the dynamic changes at various working conditions. It is found that volumetric efficiency and shaft power are more sensitive to the change in rotating speed when the pressure ratio deviates from the designed value. The results can be used as guidelines for component matching in the design and operation of PEM fuel cell systems.     

Study and design of a hybrid wind–diesel-compressed air energy storage system for remote areas

Remote areas around the world predominantly rely on diesel-powered generators for their electricity supply, a relatively expensive and inefficient technology that is responsible for the emission of 1.2 million tons of greenhouse gas (GHG) annually, only in Canada [1]. Wind–diesel hybrid systems (WDS) with various penetration rates have been experimented to reduce diesel consumption of the generators. After having experimented wind–diesel hybrid systems (WDS) that used various penetration rates, we turned our focus to that the re-engineering of existing diesel power plants can be achieved most efficiently, in terms of cost and diesel consumption, through the introduction of high penetration wind systems combined with compressed air energy storage (CAES). This article compares the available technical alternatives to supercharge the diesel that was used in this high penetration wind–diesel system with compressed air storage (WDCAS), in order to identify the one that optimizes its cost and performances. The technical characteristics and performances of the best candidate technology are subsequently assessed at different working regimes in order to evaluate the varying effects on the system. Finally, a specific WDCAS system with diesel engine downsizing is explored. This proposed design, that requires the repowering of existing facilities, leads to heightened diesel power output, increased engine lifetime and efficiency and to the reduction of fuel consumption and GHG emissions, in addition to savings on maintenance and replacement cost.     

Time–frequency analysis based on Vold-Kalman filter and higher order energy separation for fault diagnosis of wind turbine planetary gearbox under nonstationary conditions

Planetary gearbox fault diagnosis under nonstationary conditions is important for many engineering applications in general and for wind turbines in particular because of their time-varying operating conditions. This paper focuses on the identification of time-varying characteristic frequencies from complex nonstationary vibration signals for fault diagnosis of wind turbines under nonstationary conditions. We propose a time–frequency analysis method based on the Vold-Kalman filter and higher order energy separation (HOES) to extract fault symptoms. The Vold-Kalman filter is improved such that it is encoders/tachometers-free. It can decompose an arbitrarily complex signal into mono-components without resorting to speed inputs, thus satisfying the mono-component requirement by the HOES algorithm. The HOES is then used to accurately estimate the instantaneous frequency because of its high adaptability to local signal changes. The derived time–frequency distribution features fine resolution without cross-term interferences and thus facilitates extracting time-varying frequency components from highly complex and nonstationary signals. The method is illustrated and validated by analyzing simulated and experimental signals of a planetary gearbox in a wind turbine test rig under nonstationary running conditions. The results have shown that the method is effective in detecting both distributed (wear on every tooth) and localized (chipping on one tooth) gear faults.     

Fabrication and characterization of a YSZ/YDC composite electrolyte by a sol–gel coating method

The compatibility of a composite electrolyte composed of a yttria stabilized zirconia (YSZ) film and a yttria-doped ceria (YDC) substrate in a solid oxide fuel cell (SOFC) that can be operated under 800 °C was evaluated. The YSZ film coated on a YDC substrate was derived from a polymeric YSZ sol using a sol–gel spin coating method followed by heat-treatment at 1400 °C for 2 h. The SEM and XRD analysis indicated that there were no cracks, pinholes, or byproducts. The composite electrolyte comprising a YSZ film of 2 μm thickness and a YDC substrate of 1.6 mm thickness was used in a single cell performance test. A 0.5 V higher value of open circuit voltage (OCV) was found for the composite electrolyte single cell compared with an uncoated YDC single cell between 700 and 1050 °C and confirmed that the YSZ film was an electron blocking layer. The maximum power density of the composite electrolyte single cell at 800 °C, 122 mW/cm² at 285 mA/cm², is comparable with that of a YSZ single cell with the same thickness at 1000 °C, namely 144 mW/cm² at 330 mA/cm². The hypothetical oxygen partial pressure at the interface between the YSZ film and the YDC substrate for the composite electrolyte with the same thickness ratio at 800 °C is 5.58×10⁻¹⁸ atm which is two orders of magnitude higher than the equilibrium oxygen partial pressure of Ce₂O₃/CeO₂, 2.5×10⁻²⁰ atm, at the same temperature.     

Optimal design and operation of a photovoltaic–electrolyser system using particle swarm optimisation

In this study, hydrogen generation is maximised by optimising the size and the operating conditions of an electrolyser (EL) directly connected to a photovoltaic (PV) module at different irradiance. Due to the variations of maximum power points of the PV module during a year and the complexity of the system, a nonlinear approach is considered. A mathematical model has been developed to determine the performance of the PV/EL system. The optimisation methodology presented here is based on the particle swarm optimisation algorithm. By this method, for the given number of PV modules, the optimal sizeand operating condition of a PV/EL system areachieved. The approach can be applied for different sizes of PV systems, various ambient temperatures and different locations with various climaticconditions. The results show that for the given location and the PV system, the energy transfer efficiency of PV/EL system can reach up to 97.83%.     

Fabrication and testing of a H2–O2 fuel cell using MoxRuySez

We report the results obtained in the preparation and characterization of Mo_xRu_ySe_z electrocatalysts for oxygen reduction reaction and the design, construction and characterization of a H₂–O₂ fuel cell using Mo_xRu_ySe_z. The catalysts were characterized with respect to their electrocatalytic properties. The fuel cell was designed and built with Mo_xRu_ySe_z supported on carbon as cathode, Pt supported on carbon as anode, and H₂SO₄ as the electrolyte. The fuel cell was tested at room temperature and atmospheric pressure. The H₂–O₂ cell showed an efficiency in the order of 30%.     

Multi-criteria optimization of a district cogeneration plant integrating a solid oxide fuel cell–gas turbine combined cycle,heat pumps and chillers

A simultaneous optimization of the design and operation of a district heating, cooling and power generation plant supplying a small stock of residential buildings has been undertaken with regards to cost and CO₂ emissions. The simulation of the plant considers a superstructure including a solid oxide fuel cell–gas turbine combined cycle, a compression heat pump, a compression chiller and/or an absorption chiller and an additional gas boiler. The Pareto-frontier obtained as the global solution of the optimization problem delivers the minimal CO₂ emission rates, achievable with the technology considered for a given accepted investment, or respectively the minimal cost associated with a given emission abatement commitment.     

Performance analysis of a trigeneration system based on a micro gas turbine and an air-cooled,indirect fired,ammonia–water absorption chiller

The objective of this paper is to experimentally determine the efficiency and viability of the performance of an advanced trigeneration system that consists of a micro gas turbine in which the exhaust gases heat hot thermal oil to produce cooling with an air cooled absorption chiller and hot water for heating and DHW. The micro gas turbine with a net power of 28 kW produces around 60 kW of heat to drive an ammonia/water air-cooled absorption chiller with a rated capacity of 17 kW. The trigeneration system was tested in different operating conditions by varying the output power of the micro gas turbine, the ambient temperature for the absorption unit, the chilled water outlet temperature and the thermal oil inlet temperature. The modelling performance of the trigeneration system and the electrical modelling of the micro gas turbine are presented and compared with experimental results. Finally, the primary energy saving and the economic analysis show the advantages and drawbacks of this trigeneration configuration.