Reliability and cost analyses of electricity collection systems of a marine current farm—A Taiwanese case study

The exploration of ocean energy for electric power production offers a sustainable option to enhance the use of renewable energy. In this article, the reliability and cost analyses results of electricity collection systems proposed for a marine current farm are presented. A methodology based on the probability density function of site current speed is developed to determine the speed specifications of marine current turbine. Reliability analyses are conducted by taking electricity collection structure, equipment failure rate and probability distribution of turbine power output into account. Non-delivered energy cost in conjunction with the investment cost, power loss, operations and maintenance costs are included in the cost analyses. Ocean current speed data measured at the Taiwan coastline situated in the Kuroshio stream path are used to calculate the life-cycle costs of the studied energy collection systems. Simulation results show that marine turbine parameters can be effectively specified, and a sectionalized radial collection structure provides an efficient scheme for harnessing ocean energy.     

垂直轴潮流能水轮机研究与利用现状

随着化石能源不断枯竭和环保要求的不断提高,世界各国对潮流能的开发利用愈加重视,垂直轴水轮机是潮流发电装置主要结构形式之一,本中介绍了垂直轴水轮机国内外利用现状和研究方法的进展情况,并指出垂直轴水轮机开发利用所需要解决和突破的技术难点和问题,为垂直轴水轮机开发利用指明了研究重点。     

海况条件对海上风力发电机组载荷的影响

文章针对海况条件对海上风力发电机组载荷的影响,以某5 MW海上机组为例,介绍海浪、海流和潮汐在载荷计算过程中采用的理论方法和支撑结构建模方法,对支撑结构和海浪能量分别进行模态分析和频谱分析,同时根据GL2005标准对极限载荷和疲劳载荷分不同情况分析,结果表明海况条件对海上机组的塔筒底部影响较大,对机组其他关键零部件影响很小,为大型海上机组关键零部件选取提供依据。     

Development of two-way diffuser for fluid energy conversion system

An experimental study was carried out to develop a new type of two-way diffuser suitable for a fluid flow energy conversion system. It is known that the power available from the fluid flow is proportional to the cube of the free stream velocity of the flow. Therefore, in order to take higher power output from the fluid flow, it is very important to construct a suitable system to increase the flow velocity. For a wind turbine, it has been reported that the speed of wind passing through it is dramatically increased by the use of a diffuser with a brim around the turbine. In this study, a new type of two-way diffuser suitable for a flow periodically changing its direction, such as a tidal current, was developed, applying the system to accelerate the wind speed for the wind turbine. The effects of the brim height and the outside body shape on the diffuser performance were experimentally investigated by measurement of the pressure and the velocity distributions along the center axis of the diffuser and around the diffuser. The present study is the first one to clarify the effect of these on diffuser performance.     

Performance analysis of a HAT tidal current turbine and wake flow characteristics

Having very strong current on the west coast with up to 10 m tidal range, there are many suitable sites for the application of tidal current power (TCP) in Korea. The turbine, which initially converts the tidal energy, is an important component because it affects the efficiency of the entire system. To design a turbine that can extract the maximum power on the site, the depth and duration of current velocity with respect to direction should be considered. To extract a significant quantity of power, a tidal current farm with a multi-arrangement is necessary in the ocean. The interactions between devices contribute significantly to the total power capacity. Thus, the study of wake propagation is necessary to understand the evolution of the wake behind a turbine. This paper introduces configuration design of horizontal axis tidal current turbine based on the blade element theory, and evaluating its performance with CFD. The maximum efficiency of the designed turbine was calculated as 40% at a tip speed ratio (TSR) of 5. The target capacity of 300 kW was generated at the design velocity, and the performance was stable over a wide range of rotating speeds. To investigate the wakes behind the turbine, unsteady simulation was carried out. The wake velocity distribution was obtained, and velocity deficit was calculated. A large and rapid recovery was observed from 2D to 8D downstream, followed by a much slower recovery beyond. The velocity was recovered up to 86% at 18D downstream.     

大型风力发电场选址与风力发电机优化匹配

从风能利用和风电成本两个角度出发,推导出风电场选址与风力机优化选型的目标函数,提出将风力机容量系数作为风电场选址与风力机选型的判据,同时给出了基于风速分布特性的风力机容量系数计算方法。通过我国云南省的13个实际风速观测点和国内外25种风力机代表机型的计算,给出了这些观测点的开发顺序及优化配置的风力机机型,并简要分析了影响风力机容量系数的主要因素。实践表明,这种方法物理意义明确,计算快捷方便,节省设计时间和设计工作量。     

太阳能烟囱与垂直轴风机耦合发电可行性分析

通过分析太阳能烟囱热气流发电和垂直轴风力机发电的技术及特点,提出了太阳能热气流烟囱与垂直轴风力机耦合发电的方法。对风力机—太阳能热气流烟囱互补发电系统的可行性进行了分析。互补发电的功率输出持续、稳定,具有大规模并网的良好条件,是实现太阳能与风能综合利用的有效途径。     

The concept of a smart wind turbine system

A smart wind turbine concept with variable length blades and an innovative hybrid mechanical-electrical power conversion system was analyzed. The variable length blade concept uses the idea of extending the turbine blades when wind speeds fall below rated level, hence increasing the swept area, and thus maintaining a relatively high power output. It is shown for a typical site, that the annual energy output of such a wind turbine that could double its blade length, could be twice that of a corresponding turbine with fixed length blades. From a cost analysis, it is shown that the concept would be feasible if the cost of the rotor could be kept less than 4.3 times the cost of a standard rotor with fixed length blades. Given the variable length blade turbine system exhibits a more-or-less linear maximum power curve, as opposed to a non-linear curve for the standard turbine, an innovative hybrid mechanical-electrical power conversion system was proposed and tested proving the feasibility of the concept.     

A novel small scale efficient wind turbine for power generation

A ‘proof of concept’ study of a novel wind turbine that overcomes some of the deficiencies and combines the advantages of the conventional horizontal and vertical axis wind turbines is presented in this paper. The study conducted using computational fluid dynamics and wind tunnel tests clearly demonstrate that such a proposition is feasible and a low cost, low noise, safe and easy to operate but enhanced performance wind turbine for small scale power generation in low wind speed is viable.     

Fluid‐structure interaction of a morphing symmetrical wind turbine blade subjected to variable load

A brief summary of the main challenges of rotor design in wind energy conversion (WEC) systems, most notably the horizontal axis wind turbine (HAWT), are presented. One of the limiting factors in HAWT design is choosing the rated capacity to maximize power output and turbine longevity. One such strategy to accomplish this goal is to widen the operational range of the WEC system by using pitch or torque control, which can be costly and subject to mechanical failure. We present a morphing airfoil concept, which passively controls airfoil pitch through elastic deformation. As a justification of the concept, a two‐dimensional fluid‐structure interaction routine is used to simulate the aeroelastic response of a symmetric NACA 0012 blade subjected to variable loading. The results suggest that the morphing blade can be designed to offer superior average lift to drag ratios over a specified range of attack angles by up to 4.2%, and possibly even higher. This infers that the morphing blade design can increase the power production of WEC systems while conceivably reducing cost because the passive deformation of the morphing turbine does not require active control systems that come at an added upfront and maintenance cost. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental verifications of numerical predictions for the hydrodynamic performance of horizontal axis marine current turbines

The conversion of the kinetic energy presented by ocean or marine currents offers an exciting proposition as it can provide regular and predictable energy resource. The majority of the proposed designs for converting this type of kinetic energy are based on the concept of the horizontal axis turbines, which has common characteristics to those being used in wind energy. Although a lot can be learnt and transferred from wind turbine technology, there are significant differences. These include the effects of the free surface and the occurrence of cavitation. Consequently, any developed numerical methods need to be verified. This study reports on the development and verification of simulation tools based on blade element momentum theory—a commercial code (GH-Tidal Bladed) and an academic in-house code (SERG-Tidal). Validation is derived from experimental measurements conducted on a model 800 mm diameter turbine in a cavitation tunnel and a towing tank. The experimental data includes measurements of shaft power and thrust generated by the turbine for a series of blade pitch settings and speeds. The results derived from the two codes are compared. These indicate that the two developed codes demonstrate similar trends in the results and provide a satisfactory representation of the experimental turbine performance. Such results give the necessary confidence in the developed codes resulting in appropriate tools that can to be utilised by developers of marine current turbines.     

A Metric Space with LCOE Isolines for Research Guidance in wind and hydrokinetic energy systems

This paper introduces a new Metric Space to guide the design of advanced wind energy systems and hydrokinetic energy converters such as tidal, ocean current and riverine turbines. The Metric Space can analyse farms that combine different or identical turbines and stand‐alone turbines. The first metric (M1) of the space considers the efficiency of the turbines in the farm, which is also proportional to the specific power per swept area at a given wind/water velocity (W/m²). The second metric (M2) describes the specific rotor area per unit of mass of the turbines (m²/kg). Both metrics depend on the primary design characteristics of the turbines, such as swept area, system size and mass, materials and efficiency, and are independent at first from external characteristics, such as atmospheric and ocean site conditions, cost of materials and economic factors. Combining both metrics, and for a given set of external characteristics, the resulting Metric Space M2/M1 displays the Levelized Cost of Energy (LCOE) standards as isolines. This graphical representation provides a quick understanding of the cost and state of the technology. It also offers a practical guidance to choose the research tasks and strategy to design advanced wind and hydrokinetic energy systems. The paper applies the new Metric Space to several case studies, including large and small onshore wind turbines, floating and bottom‐fixed offshore wind turbines, downwind rotors, multi‐rotor and hybrid systems, airborne wind energy systems, wind farms and tidal energy converters.     

Influence of blade deformation and yawed inflow on performance of a horizontal axis tidal stream turbine

For a better design of tidal stream turbines operated in off-design conditions, analyses considering the effects of blade deformation and yawed inflow conditions are necessary. The flow load causes deformation of the blade, and the deformation affects the turbine performance in return. Also, a yawed inflow influences the performance of the turbine. As a validation study, a computational fluid dynamics (CFD) simulation was carried out to predict the performance of a horizontal axis tidal stream turbine (HATST) with rigid blades. The numerical uncertainty for the turbine performance with blade deformation and a yawed inflow was evaluated using the concept of the grid convergence index (GCI). A fluid–structure interaction (FSI) analysis was carried out to estimate the performance of a turbine with flexible composite blades, with the results then compared to those of an analysis with rigid blades. The influence of yawed inflow conditions on the turbine performance was investigated and found to be important in relation to power predictions in the design stages.     

Exceeding the Betz limit with tidal turbines

The Betz limit sets a theoretical upper limit for the power production by turbines expressed as a maximum power coefficient of 16/27. While power production by wind turbines falls short of the Betz limit, tidal turbines in a channel can theoretically have a power coefficient several times larger than 16/27. However, power extraction by turbines in large tidal farms also reduces the flow along the channel, limiting their maximum output. Despite this flow reduction, turbines in tidal farms can produce enough power to meet a stricter definition of what it means to exceed the Betz limit, one where the maximum power output of a turbine at the reduced flow exceeds the maximum output from a single Betz turbine operating in the unreduced flow. While having a power coefficient >16/27 is easily achieved by turbines in a channel, generating enough power to meet this stricter definition of exceedance is much more difficult. Whether turbines meet this stricter definition depends on their number, how they are arranged and tuned, and the dynamical balance of the channel. Arranging a tidal turbine farm so that the turbines within it exceed the stricter Betz limit would give tidal turbine farms an economic advantage over similarly sized wind farms. However, exceeding the stricter limit comes at a cost of both higher structural loads on the tidal turbines and the need to produce power from weaker flows. Farms in a channel loosely based on the Pentland Firth are used to discuss exceedance and structural loads.     

Analysis of a small horizontal axis wind turbine performance

A small‐scale horizontal axis wind turbine capable of producing 100 W of rated power has been designed and tested using a low‐speed wind tunnel. Power output from the wind turbine was calculated through measurements of the electrical current from a 12 V DC generator. Annual energy extraction from this wind turbine shows that a number of potential applications are possible especially in the remote areas where extension of power grid is not feasible. Copyright © 2001 John Wiley & Sons, Ltd.     

Ocean thermal energy conversion: a general introduction

The ocean thermal energy conversion (OTEC) concept is discussed with emphasis on the closed Rankine cycle using ammonia as a working fluid. The main features of OTEC, such as low efficiency high flow rates, and high capital cost are put in perspective in terms of energy cost at the bus bar. Sensitivity analyses of net output power to key design variables and to performance uncertainty are performed. It is concluded that even with a large error in estimating performance conditions, the plant produces net output power. This indicates the robust nature of current designs. Finally, cost figures of major system components are given and electricity cost based on a hypothetical capital cost is computed.     

聚风导流型立轴风力机设计及气动性能分析

针对传统的立轴风力机风能利用率低的问题,应用正交优化法和流场数值模拟技术对聚风导流型立轴风力机的结构设计参数进行了优化设计。在同尺度下与传统立轴风力机进行了对比分析。结果表明,聚风导流型立轴风力机叶轮的输出功率、风能利用率及自启动特性均得到了显著提高。     

驱动热泵的垂直轴风力机风轮气动特性数值分析

根据风能热泵系统的工作环境及匹配特性,针对给定供热面积的系统各参数选取方法以及垂直轴风力机风轮设计进行了探讨,在此基础上初步完成了额定功率为300 W的风轮设计,并利用二维数值模拟方法对不同叶尖速比下的性能曲线进行计算,分析得到了额定风速9.00 m/s时,驱动压缩机的最佳风轮转速为350~375r/min。结果表明,300 W垂直轴风力机的输出特性可满足风能热泵机组的工作要求,该数值分析结果可为风能供热技术的应用示范提供理论支撑。     

Sensitivity of southern California wind energy to turbine characteristics

Using output from a high‐resolution meteorological simulation, we evaluate the sensitivity of southern California wind energy generation to variations in key characteristics of current wind turbines. These characteristics include hub height, rotor diameter and rated power, and depend on turbine make and model. They shape the turbine's power curve and thus have large implications for the energy generation capacity of wind farms. For each characteristic, we find complex and substantial geographical variations in the sensitivity of energy generation. However, the sensitivity associated with each characteristic can be predicted by a single corresponding climate statistic, greatly simplifying understanding of the relationship between climate and turbine optimization for energy production. In the case of the sensitivity to rotor diameter, the change in energy output per unit change in rotor diameter at any location is directly proportional to the weighted average wind speed between the cut‐in speed and the rated speed. The sensitivity to rated power variations is likewise captured by the percent of the wind speed distribution between the turbines rated and cut‐out speeds. Finally, the sensitivity to hub height is proportional to lower atmospheric wind shear. Using a wind turbine component cost model, we also evaluate energy output increase per dollar investment in each turbine characteristic. We find that rotor diameter increases typically provide a much larger wind energy boost per dollar invested, although there are some zones where investment in the other two characteristics is competitive. Our study underscores the need for joint analysis of regional climate, turbine engineering and economic modeling to optimize wind energy production. Copyright © 2012 John Wiley & Sons, Ltd.     

Small wind power generation using automotive alternator

The objective of this paper is to evaluate the feasibility of using claw pole automotive alternator as a generator for small wind turbine and to compare its energy yield and generated electricity cost with commercially available systems. The comparison is based on the energy yield per swept area and cost per energy produced in a low wind speed climate. Concepts such as the selection of suitable turbine parameters and gear ratio were used to achieve good matching of the turbine characteristics with measured alternator performance in order to improve the energy yield from the alternator in battery charging application. The energy yield from the alternator integrated to a 3.9 m diameter turbine is comparable with many commercially available turbines. The generated electricity cost of a commercially available turbine can be reduced by more than a factor of 2 by replacing its generator with our proposed alternator. The alternator-based turbine system is therefore a low cost solution aimed at making wind energy available to areas where the current cost of wind technology makes it prohibitive.