Likelihood of wind energy assisted hydrogen production in three selected stations of Fiji Islands

ABSTRACT

Majority of the people have been paid attention towards renewable and clean sources of energy like wind. Due to the uncertainties related to wind turbines, issues of energy storage are noteworthy. One of the aptest methods of energy storage is the production of hydrogen from the wind. The main aim of this paper is to investigate the potential of wind energy assisted hydrogen production in three selected stations of Fiji Islands using various wind turbines. From the analysis of results and discussion, Vestas V110-2.0 provides acceptable capacity factors among all inspected wind turbines with the highest value of 77.06% for the station at Labasa. Additionally, the highest energy production was from the Vestas V110-2.0 wind turbine with an annual production of 13,501,620?kWh. The conversion system used in this study resulted in a linear relationship between generated wind energy and the amount of hydrogen produced. Therefore, the highest amount of yearly hydrogen production (240.19 ton-H) is related to the largest examined wind turbine, installed in the station at Labasa.     

Using buildings to harvest wind energy

Research and development by Altechnica into the applied use of wind energy suggests the novel and innovative solution of employing buildings as primary wind collectors. Buildings can be designed with the means of extracting wind energy advantageously. The roof design of a building can direct and accelerate the wind flow to turbines along the ridge. Dr Derek Taylor of Altechnica introduces the idea of a wind energy system for (new and existing) buildings that can augment solar power, work for a range of building typologies and settings, generate electricity for the building and contribute into the larger electric grid.     

Wind turbine power curve estimation based on cluster center fuzzy logic modeling

Wind energy applications and turbine installation at different scales have been increased for last decade. Technically wind turbine capacity has been improved at high levels. However, electricity could not be generated at all stages of wind speed and so there are some limits related to cut-in and cut-out data. One of the main problems in wind engineering is to estimate output data of wind turbines depends on wind speed and system values. Wind speed problematic values, that are less than cut-in and greater than cut-out, take the most important role for estimating wind power curve models. All wind turbines have different cut-in and cut-out limits and generating of electricity could be achieved in a certain interval that could be called as affective interval. Fuzzy logic that is a new and novel verbal logical approach has many applications in the field of engineering. Cluster center fuzzy logic modeling is also a new and the effective method in this scientific area. In this paper, the first power curve of a wind turbine is modeled by least square methodology. After that depending on the fuzzy logic approach a new application is realized. It is seen that, this curve type could be well represented and modeled by the clustering center fuzzy logic modeling than classical least square methodology. It is estimated that four or five cluster centers are enough for representing wind turbine power curve by running proposed method.     

Urban energy generation: Influence of micro-wind turbine output on electricity consumption in buildings

Small scale wind turbines installed within the built environment is classified as microgeneration technology. Such turbines may soon become a commercial reality in the UK as a result of both advancements in technology and new financial incentives provided by the government. In addition, microgeneration technologies, especially those with appreciable resource, have the potential to reduce built environment related CO₂ emissions coupled with reductions in consumers’ electricity costs. In many cases payback on capital investment is within the lifetime of the device. Micro-wind turbines installed in certain areas in the UK will fit within such criteria. The work presented here addresses modelling of such installations around the UK and presents a methodology to assess the suitability and the economic viability of micro-wind turbines for domestic dwellings. A modelling tool “μ-Wind” has been developed specifically for studying both energy yields and the payback periods for micro-wind turbines. μ-Wind predicts wind turbine performance prior to installation according to specific power curves either defined by turbine manufacturers or the user. Numerical consideration of wind speed data at specific UK sites was used to estimate energy yields and the results are projected to real electricity demand data from monitored dwellings in the UK. The results show that it is possible to predict with a good degree of accuracy the expected financial payback period for a typical domestic dwelling. Furthermore, the paper postulates that micro-wind technology could have the potential to make a significant impact upon domestic electricity generation when located at the windiest sites in the UK. The likelihood of a proliferation of these turbines in the urban or suburban environment is low but at coastal or inland high elevation sites the technology appears to have a promising future.     

Micro wind turbines in the UK domestic sector

The micro-scale wind turbine industry is expanding in the UK with institutional support and UK legislation encouraging the development of numerous companies with a profusion of design options. The application of micro wind turbines in urban environment is encouraged in the UK via a grant scheme which provides a proportion of the initial capital costs. This development is predicated on the assumption that micro wind turbines have the potential to reduce built environment CO₂ emissions. Current methods of estimating the wind speed are reported to over predict by approximately 2.0 m/s. The energy yields of a range of typical micro wind turbines (in the 0.4–2.5 kW size range) were estimated here using two wind speed datasets sited within 1 km of each other recorded with a temporal precision of 10 min. The annual energy yield of a 1.5 kW turbine was found to be 277 kWh and 2541 kWh for the two sites analysed indicating the problem with the current method of yield estimation. Between 33 and 55% of the electricity generated would be exported dependant on the dwelling's electrical demand. For the high yield site, the simple economic payback of this turbine was found to be 26.8 years i.e. beyond the likely life time of the turbine with CO₂ savings of 1093 kg CO₂. The research suggests that this technology does represent a possible route for reducing CO₂ emissions but this is unlikely to be realised unless an adequate method is found for more accurately predicting energy yield at a specific site.     

Comparison of the dynamic responses of monopiles and gravity base foundations for offshore wind turbines in sand using centrifuge modelling

Monopiles and gravity base foundations (GBF) are two of the most commonly used foundations for offshore wind turbines. As resonance can cause damage and even failure of wind turbines, understanding the difference between the dynamic responses of monopiles and GBFs under free vibration is important. However there is little experimental data regarding their natural frequency, especially from model tests carried out at correct stress levels. This paper presents the results of novel monopile and GBF tests using a centrifuge to directly determine the natural frequency (f_n) of the foundation-soil system. The natural frequencies of wind turbine monopiles and GBFs in centrifuge models were measured during harmonic loading using a piezo-actuator, with the results confirming that soil-structure interaction must be considered to obtain the system’s natural frequency as this frequency reduces substantially from fixed-base values. These results will contribute in preventing resonance induced damage in wind-turbines.     

Using buildings to harvest wind energy

Research and development by Altechnica into the applied use of wind energy suggests the novel and innovative solution of employing buildings as primary wind collectors. Buildings can be designed with the means of extracting wind energy advantageously. The roof design of a building can direct and accelerate the wind flow to turbines along the ridge. Dr Derek Taylor of Altechnica introduces the idea of a wind energy system for (new and existing) buildings that can augment solar power, work for a range of building typologies and settings, generate electricity for the building and contribute into the larger electric grid.     

Buckling of cylindrical open-topped steel tanks under wind load

Vertical cylindrical welded steel tanks are typical thin-walled structures which are very susceptible to buckling under wind load. This paper investigates the buckling behavior of open-topped steel tanks under wind load by finite element simulation. The analyses cover six common practical tanks with volumes of 2×10³ m³ to 100×10³ m³ and height-to-diameter ratios H/D<1. The linear elastic bifurcation analyses are first carried out to examine the general buckling behavior of tanks under wind load, together with comparison to that of tanks under uniform pressure and windward positive pressure (only loaded by positive wind pressure in the windward region). The results show that for larger tanks in practical engineering, the stability carrying capacity of wind load is relatively lower. It is also indicated that the buckling behavior of tanks under wind load is governed by the windward positive pressure while wind pressure in other region of tank essentially has no influence on the buckling performance. The geometrically nonlinear analyses are then conducted to investigate the more realistic buckling behavior of tanks under wind load. It is found that the buckling behaviors of perfect tanks and imperfect tanks are much different. The weld induced imperfection only has little influence on the wind buckling behavior while the classical buckling mode imperfection has significant influence, leading to a considerable reduction of wind buckling resistance. The influences of thickness reduction of cylindrical wall, liquid stored in the tank and wind girder on the buckling behavior are also examined. It shows that the thickness reduction of cylindrical wall considerably reduces the wind buckling resistance while sufficient liquid stored in the tank and wind girder significantly increase the wind buckling resistance.     

风力发电机组塔架的结构形式及其风载、地震作用综述

风力发电机组的塔架属于高耸结构,承受风荷载和地震作用,可采用钢筒、钢格构、钢筋混凝土筒和钢一混凝土组合筒等多种结构形式。本文简要分析了各种结构形式的优缺点及研究现状,认为随着风力发电机组越来越大型化,钢塔筒面临运输和施工吊装困难。而其它形式的塔架,如钢格构、钢筋混凝土筒和钢一混凝土组合筒塔架,具有易运输、易施工的优点,已获得一定应用,并可能进一步推广。目前,对钢塔筒的研究较多,而对其它形式的塔架研究较少;并且由于叶片数据缺乏,风力发电机组承受的风、地震作用的计算不很准确;此外,研究者分析的风力发电机组数量有限,所得结论不一定具有普遍性。     

Assessment of electricity generation by wind power in nine costal sites in Malaysia

In this article, the wind power potential in Malaysia is examined. Hourly wind speed data for nine sites in Malaysia are used to optimally design wind power systems for remote housing electrification. These nine sites are Bintulu, Kota Kinabalu, Kuala Terengganu, Kuching, Kudat, Mersing, Sandakan, Tawau and Pulau Langkawi. The designed wind power systems are supposed to supply hourly load demand 6.13?kWh/day, 0.52?kW peak with 1% loss of load probability. The unit cost of the energy produced by each system is calculated and compared to the unit cost of the energy produced by a standalone photovoltaic (PV) power systems and a diesel generator power systems. The results show that the average unit cost of the energy produced by a wind power system in Malaysia is 1.6–7.29?USD/kWh while it is 0.35–0.5?USD/kWh and 0.27–0.30?USD/kWh for PV power system and diesel generator power system, respectively. Based on this, the use of wind power systems as standalone systems is not recommended for the selected sites.     

Regime-switching modelling of the fluctuations of offshore wind generation

The magnitude of power fluctuations at large offshore wind farms has a significant impact on the control and management strategies of their power output. If focusing on the minute scale, it looks like different regimes yield different behaviours of the wind power output. The use of statistical regime-switching models is thus investigated. Regime-switching approaches relying on observable (i.e. based on recent wind power production) or non-observable (i.e. a hidden Markov chain) regime sequences are considered. The former approach is based on either self-exciting threshold autoregressive (SETAR) or smooth transition autoregressive (STAR) models, while Markov-switching autoregressive (MSAR) models comprise the kernel of the latter one. The particularities of these models are presented, as well as methods for the estimation of their parameters. The competing approaches are evaluated on a one-step ahead forecasting exercise with time-series of power production averaged at a 1, 5, and 10-min rate, at the Horns Rev and Nysted offshore wind farms in Denmark. For the former wind farm, the one-step ahead root mean square error (RMSE) is contained between 0.8% and 5% of installed capacity, while it goes from 0.6% to 3.9% of installed capacity for the case of Nysted. It is shown that the regime-switching approach based on MSAR models significantly outperforms those based on observable regime sequences. The reduction in one-step ahead RMSE ranges from 19% to 32% depending on the wind farm and time resolution considered. The presented results clearly demonstrate that the magnitude of fluctuations of offshore wind power cannot be considered as simply influenced by the generation level only.     

A laboratory experiment of shear-induced natural ventilation

When the wind direction is parallel to the opening façade, the wind shear near the building opening generates turbulence and entrains air across the opening. This kind of shear-induced ventilation cannot be predicted by the orifice equation because the time-averaged pressure difference across the opening is close to zero. This study uses wind tunnel experiments and the tracer gas decay method to investigate the ventilation rate of shear-induced ventilation. The influences of opening area A, external wind speed U and wind direction on the ventilation rates Q, of single-sided and two-sided openings are systemically examined. The experimental results indicate that the dimensionless ventilation rate, Q^* = Q/UA, of shear-induced ventilation is independent of the wind speed and opening area, and the value of Q^* of two-sided openings is larger than that of a single-sided opening. In addition, a cosine law was used to predict the ventilation rate of building with two-sided openings under various wind directions, and the results are compared with the prediction of the multizone ventilation model COMIS.     

Roof-top wind turbines for microgeneration in urban houses in New Zealand

Microgeneration using roof-top wind turbines is at present not common in New Zealand. It is, however, being trialled by the electricity network company, Vector, in a range of urban locations. Limitations of size mean roof-top wind turbines may not satisfy the total energy requirement of New Zealand houses. Ensuring structural stability and complying with stringent noise standards in New Zealand are further issues. In addition, roof-top turbines may be inefficient in terms of net energy and carbon emissions, performance indicators that are fundamental for the adoption of this technology. This paper considers the feasibility of using roof-top wind turbines in urban houses in New Zealand and, using life cycle assessment, evaluates the net energy and carbon emissions associated with their use. The results indicate that the electricity-generating potential of centralised wind farms in New Zealand using large turbines is 11.3-7 times the generating potential of roof-top turbines mounted on urban houses. In spite of this the roof-top turbines that are currently being trialled, could have the potential to reduce the energy and carbon intensity of New Zealand electricity by 81% and 26%, respectively.     

Simulation of honeycomb-screen combinations for turbulence management in a subsonic wind tunnel

Honeycomb and screens, mainly used for turbulence reduction, are the key elements of a subsonic wind tunnel. In this paper, design aspects of these elements are addressed for an open-circuit wind tunnel, installed at Indian Institute of Technology Guwahati (IITG), India. The effectiveness of honeycomb and honeycomb-screen combinations, in reducing swirl and turbulence level in the test section, is studied by simulating the flowfield using commercial computational fluid dynamics (CFD) package ANSYS-CFX. RNG k−ε turbulence model, with scalable wall functions, is used for modeling turbulence. Results of these simulations for turbulence management, using honeycombs of different lengths, cell shapes and screens of different open area ratios, are found to be in good agreement with experimental and theoretical results available in open literature. These simulations have confirmed the methodology to be adopted for design of wind tunnel subsections. Thus validated design parameters have been used for fabricating the honeycomb and screens for the IITG wind tunnel.     

The vibration modes of a wind turbine support structure

Lightweight wind turbines offer a considerable reduction in capital and operating costs for electricity generation from the wind. Environmental impact of installation works can be reduced. Lightweight machines are likely to be structurally flexible. It is essential for the designer to study their dynamic characteristics in order to reduce:

1. The magnitude of the stresses in the structure particularly in components loaded cyclically;

2. The electrical noise and power fluctuation experienced by electricity consumers;

3. The acoustic noise emitted.

Using Rayleigh analysis, the vibration frequencies of a mathematical model of the wind turbine support tower can be estimated. Additional structural components can easily be added and components can be modelled more accurately as the process is refined.

Available experimental measurements compare favourably with corresponding predictions.     

A phenomenological model for the dynamic response of wind turbines to turbulent wind

To predict the average power output of a wind turbine, a response model is proposed which takes into account: (i) the delayed response to the longitudinal wind speed fluctuations; (ii) a response function of the turbine with arbitrary frequency dependence; (iii) wind fields of arbitrary turbulence intensity. In the limit of low turbulence intensity, the dynamical ansatz as proposed in 1992 by Rosen and Sheinman is reproduced. It is shown, how the response function of the turbine can be obtained from simulation experiments of a specific wind turbine. For two idealized situations the dynamic effect of fluctuating wind is estimated at turbulence intensities 0?I_u?0.5. At the special mean wind speed , the turbine response function is determined from simulation data published by Sheinman and Rosen in 1992 and 1994.     

母线槽在风电行业的应用

根据风电行业工程实践经验．介绍我国风电发展情况．分析母线槽干线系统在风电行业使用的技术优势．重点讨论母线槽在风电行业的现场测量、安装流程及注意事项。     

Comparative analysis of three numerical methods for estimating the onshore wind power in a coastal area

Although there are many studies concerning the estimation of wind potential in different locations of Iran, an adequate evaluation of wind power for onshore locations of this country has not been investigated yet. The purpose of this research is to evaluate the potential of onshore wind in the south of Iran along the Gulf of Oman by comparing three Weibull numerical methods. In the first step, it became clear that the maximum likelihood method (MLM) compared to other methods represented the actual wind data with the lowest error rate and therefore it was selected as an accurate statistical distribution to model the wind speed of the investigated location. Using the MLM, the estimation of wind speed characteristics as well as the techno-economic evaluation of different wind turbines has been investigated. It was concluded that both technically and economically the studied area does not have sufficient wind power for the development of large-scale or grid-connected wind turbines. However, it may have enough power for non-grid-connected mechanical applications, such as wind generators for water pumping. Therefore, in the last part of this paper, an investigation of water pumping potential of the studied site by using adequate and modern wind turbines with lower start-up wind speed was recommended for future studies. Furthermore, it was suggested that the current methodology used in this research could be employed and extended in future studies to evaluate the wind potential of all onshore locations of Iran including onshore locations along the Persian Gulf and Caspian Sea.     

Parametric analysis of wind siting efficiency

The effect of wind climatic characteristics on the efficiency of the WECS is examined by means of the Weibull general model and a simple model of power curve. Two efficiency parameters—the plant utilization factor (F_u) and the site effectiveness (ε)—are considered as functions of three parameters: the Weibull shape parameter (k), a dimensionless mean wind speed (α), and the design ratio between rated and cut-in speed (φ). It is shown that only for intermediate values of α and φ the plant utilization factor can be considered independent of k, being otherwise either improved or penalized in no negligible measure by it, depending on the values of α and φ. The effect of increasing k on the site effectiveness is always beneficial. The effect of increasing α is beneficial for the plant utilization factor but largely penalizing for the effectiveness. However, no maximization is possible for neither of the efficiency parameters.It is shown that the correct use of F_u and ε for comparison is significant only for a given WECS, while the WECS data have to be used when comparing different or modified wind machines. The data of 35 commercial WECS are examined to show that the common assumption of constant rated or maximum efficiency is not acceptable.