A hybrid statistical approach for performance optimization of micro-scale wind energy systems

This paper provides an overview of the recent developments on small wind turbines in terms of their distinguishing characteristics, experimental research and structural and operational development of small vertical axis wind turbines. Emphasizing their decentralized generation capability, cost savings, and sustainability, the first part discusses the characteristics of small wind turbines. Then the review paper goes through a synthesis process of experimental research work on small wind turbines to evaluate their performance, technological advancements evolved in line with actual world problems encountered. The paper also describes what was achieved by way of small vertical-axis wind turbine design, material problems, and aerodynamic theories that control their operation. Finally, the study provides a review of experimental research studies that were conducted on the performance of small vertical axis wind turbines. The study also shows the functioning methods of small vertical axis wind turbines examined by means of experimental research, which investigate their efficiency under different environmental circumstances and where they may be optimized. Emphasizing the interdependence between theory and practice, this paper examines answers wind turbine researchers have already looked at. A small part of international research data seeking to improve the efficiency and design of small wind turbines is collated here.

The category of small wind turbines is a rapidly growing market. The U. S., Europe (UK), and China are of particular interest and seeing the most growth. This paper examines the category of small wind starting with the variety of definitions found in the literature. Growth world-wide, with an emphasis on these major markets, is analyzed for trends and predicted development. The focus is on fixed pitch, small horizontal axis wind turbines, with a direct drive DC generator in the 1–10 kW class. To understand small wind turbines it is necessary to discuss design tools available for design. Included in this design discussion is the necessity for computational fluid dynamic models as well as experimentally testing both open rotors and wind tunnel models. In order for small wind turbines to continue to improve, better technologies are necessary. For design, wind turbines must be optimized for peak performance to include startup/cut-in speeds and other modifications. These wind turbines will rely on new and purposely designed airfoils; however, for low Reynolds number conditions actual airfoil data are needed as many of the computational tools do not accurately predict separation. Increasingly, noise is an issue, especially if these wind turbines will be sited in populated urban areas. An analysis of noise generation as well as design techniques for reducing noise is necessary for future designs. Important discussions on the technologies particular to small wind turbines should include the topics of aerodynamics and structures/materials. Future applications of small wind turbines seem bright. Small wind turbines are contributing to the concept of distributed generation and helping to reduce the carbon footprint. Urban environments are becoming more accepted for small wind turbines which lead to studies of flow fields in and around buildings. Of particular note are hybrid systems which combine wind with other energy generation systems such as solar, internal combustion engines, and diesel engines to name a few. These systems are advantageous for the homeowner, small business, cell phone towers, remote locations, and backup emergency power systems (to include lighting). Lastly, the concept of energy storage must be addressed in the context of small wind turbines, especially those turbines used in an isolated application. Permitting and government incentives are critical to the future success of these wind turbines.

Small wind turbines come in a variety of designs, and have similarities in principles and technology to small hydrokinetic turbines (SHKTs). SHKTs, in turn, can play an important role in hydropower. Small wind and hydrokinetic systems can even work together, for example, to power farms, communities, campuses, rural as well as remote rural areas, and island regions. This concise book, written by experts in the field, provides an in-depth overview of small turbines for wind and hydropower. Chapters cover resource assessment for wind and water, turbine technology, design of vertical and horizontal axis turbines, blade element analysis, vibration-based energy harvesting, very low head turbines, diffuser augmented wind turbines, and numerous case studies. Small Wind and Hydrokinetic Turbines is a valuable summary for researchers involved with small wind turbines and SHKT development and deployment, both in academia and industry, for research on powering remote areas, as well as for advanced students and manufacturers of turbines.

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.

As an alternative to fossil fuels, wind energy is a clean, environmentally friendly and renewable energy source. In the design of wind energy conversion systems, the wind speed of the region is one of the most important parameters and the economic applicability of wind power generation depends on the wind speed. In this study, the feasibility of small scale wind turbine is investigated for Elazig province in the east of Turkey. For this purpose, the average wind speeds on a monthly basis of Elazig province for ten years were taken into consideration. Wind speed measurements were done both for December, which the average wind speed was the lowest in 2018 and for March, which the average wind speed was the highest in 2018 and the results were evaluated. The power energy potential that can be generated of the three-bladed small type wind turbine designed according to these data has been determined. In addition, in order to observe the effect of turbine installation height on wind speed, wind speeds were calculated at different installation heights and the effect of these values on the power generation potential of the designed small type wind turbine was determined. As a result, it was observed that small type wind turbines can be used for generate electricity in low speed regions. In case of wind turbine installed at a height of 50 m, it is observed that it is possible to generate significant amounts of electrical energy with small wind turbines in Elazig and these turbines can be a technically applicable option for power generation.

Small wind turbines are investigated as a possible solution for using wind energy at small scales in urban and suburban areas. Most turbines are suffering from a low aerodynamic performance due to turbulent and complex wind situations in cities. Therefore, increasing aerodynamic performance and reducing noise is an important factor to design small wind turbines. In order to optimize such turbines with respect to noise and efficiency it is important to understand the physical mechanisms. Measuring acoustic in urban environment it is hardly possible to obtain reproducible results, which are necessary for a comprehensively and profoundly investigation. Therefore, experimental studies have to been performed in anechoic wind tunnels. Those tunnels are mostly limited in size, which makes it quite difficult to investigate full small wind turbine models. Hence a model scale has to be used in order to measure the power and acoustic performance. For comparing the model scale results with original turbines, the same flow conditions around the airfoils are necessary. Due to the smaller size of the model scale the relative velocities of the blades are less, which can result in a laminar boundary layer. In order to force transition from laminar to turbulent, boundary layer trips can be used. The focus of this study is to examine and quantify the effect of boundary layer tripping on the aeroacoustics in case of small vertical axis wind turbines.

This paper examines the category of small wind turbines. Numerous definitions are found in the literature. However, this paper's focus is on fixed pitch, small horizontal axis wind turbines, with a direct drive DC generator in the 1–10 kW class. Small wind turbine growth world-wide is analyzed for trends and predicted development. It is necessary to discuss design tools available for design, including computational fluid dynamic models and experimentally testing both open rotors and wind tunnel models. Wind turbines must be optimized for peak performance to include startup/cut-in speeds and other modifications. These wind turbines will rely on new and purposely designed airfoils; however, for low-Reynolds number conditions, computational tools do not accurately predict separation. An analysis of noise generation as well as design techniques for reducing noise is necessary for future designs. Discussions on the technologies particular to small wind turbines should include the topics of aerodynamics and structures/materials. Small wind turbines are contributing to the concept of distributed generation. Urban applications are leading to studies of flow fields in and around buildings. Interest in hybrid systems, which combine wind with other energy generation systems such as solar, internal combustion engines, and diesel engines, is growing. These systems are advantageous for the homeowner, small business, cell phone towers, remote locations, and backup emergency power systems (to include lighting). Finally, the concept of energy storage must be addressed in the context of small wind turbines, especially those turbines used in an isolated application.

Small wind turbines, which are increasingly being used near residential areas, sound louder than their larger counter parts due to their close proximity to dwellings. Previous noise measurements on small scale wind turbines were performed using single microphones which only provide an overall estimate of the total noise emitted from the wind turbine. For wind turbine manufacturers trying to address the issue of noise reduction through design, the knowledge of the dominant noise source location and source mechanisms is important. This information can be obtained using a microphone array and sophisticated beamforming algorithms. In this paper we use a compact microphone array to locate and quantify noise sources on a small (8 kW) Viryd 8000 wind turbine. The results from the microphone array show that we are able to successfully locate and separate both mechanical and aerodynamic noise on the wind turbine using advanced deconvolution algorithms such as TIDY, CLEAN based on Source Coherence (CLEAN-SC), and Deconvolution Approach for Mapping Acoustic Sources (DAMAS). For frequencies above 4000 Hz, aerodynamic noise appears to be the dominant noise source and for frequencies below 3000 Hz, mechanical noise from the nacelle appears to be the dominant noise source.

Small, stand-alone wind turbines are a possible solution to the energy requirements of remote areas in Pakistan. However except for the coastal areas, wind speeds available in various areas of Pakistan are low to medium, especially in the northern areas. It is possible to produce significant power from a small wind turbine at low wind speeds provided the turbine can be started. In this paper “BEM function” and “Aerodynamic function” are used based on the Blade element momentum theory. These Matlab functions calculate the wind turbine blade parameters and aerodynamic forces that will act on wind turbine blades. Pro/E models were then developed on the basis of these parameters. Pro/E models were imported into ADAMS to calculate the output torques. Our analysis shows that most of the starting torque comes from the hub section of the blade. Various changes were incorporated into ADAMS models near the hub region of the wind turbine blade which showed an increase in the staring torque due to an increase in the blade angles and chord lengths. The wind turbine designs for the selected locations of Pakistan were successfully optimized by improving their starting behavior.

A small horizontal axis wind turbine rotor was designed and tested with aerodynamically efficient, economical and easy to manufacture blades. Basic blade aerodynamic analysis was conducted using commercially available software. The blade span was constrained such that the complete wind turbine can be rooftop mountable with the envisioned wind turbine height of around 8 m. The blade was designed without any taper or twist to comply with the low cost and ease of manufacturing requirements. The aerodynamic analysis suggested laminar flow airfoils to be the most efficient airfoils for such use. Using NACA 63-418 airfoil, a rectangular blade geometry was selected with chord length of 0.27[m] and span of 1.52[m]. Glass reinforced plastic was used as the blade material for low cost and favorable strength to weight ratio with a skin thickness of 1[mm]. Because of the resultant velocity changes with respect to the blade span, while the blade is rotating, an optimal installed angle of attack was to be determined. The installed angle of attack was required to produce the highest possible rotation under usual wind speeds while start at relatively low speed. Tests were conducted at multiple wind speeds with blades mounted on free rotating shaft. The turbine was tested for three different installed angles and rotational speeds were recorded. The result showed increase in rotational speed with the increase in blade angle away from the free-stream velocity direction while the start-up speeds were found to be within close range of each other. At the optimal angle was found to be 22° from the plane of rotation. The results seem very promising for a low cost small wind turbine with no twist and taper in the blade. The tests established that non-twisted wind turbine blades, when used for rooftop small wind turbines, can generate useable electrical power for domestic consumption. It also established that, for small wind turbines, non-twisted, non-tapered blades provide an economical yet productive alternative to the existing complex wind turbine blades.

Although fossil fuel is the main energy supplier of the worldwide economy, due to its ad‐ verse effects on environment, the scientists look for alternative resources in power genera‐ tion. Electricity generation using renewable energy has been well recognized as environmentally friendly, socially beneficial, and economically competitive for many appli‐ cations. Wind turbines, photovoltaic systems, full cells and PATs are main resources for dis‐ tributed generation systems [1]. Compared with other renewable energy, wind power is more suitable for some applications with relatively low cost [2,3]. Wind turbine system (WTS) technology is still the most suitable renewable energy technology. While most large companies are focusing on large wind turbines of the utility scale, small wind turbines as distributed power generators have attracted a growing interest from the general public, small farms and remote communities [4]. In recent years, the level of interest in small-scale wind turbine generators has been increasing due to growing concerns over the impact of fossil-fuel based electricity generation [5]. According to the American Wind Energy Associa‐ tion (AWEA) annual wind industry report, the U.S. market for small wind turbines (<100kW) grew 78% in 2008 adding 17.3 MW of installed capacity. Over 10,000 small wind turbines were sold in the U.S. in 2008 [6]. UK based consultants Gerrad Hassan also predicts that small wind turbine sales have the potential to increase to well over US$750 million by 2005 [4]. Small-scale wind turbines are particularly advantageous for power generation at a household level [5]. A small-scale wind turbine consists of a generator, a power electronic converter, and a control system. Among different types of small-size wind turbine, perma‐ nent magnet (PM) generator is widely used because of its high reliability and simple struc‐ ture [1,2]. The power electronic converter topology used depends on the required output power and cost of the system. Control systems are used to control the rotational speed of

Small wind turbines often have to operate in slow and highly turbulent wind. Whereas the aerodynamic design of rotor blades for small wind turbines is mostly based on tools and methods developed for large wind turbines, these aerodynamic requirements distinguish small wind turbines from larger models significantly. Nonetheless, steady blade element momentum (BEM) theory is employed to calculate the rotor aerodynamics, since this theory delivers reasonable results within a fast calculation time. Usually, steady state simulations which require much less computational effort than unsteady simulations tend to be preferred during the iterative design process of new rotor blades. This paper explores the worthiness of using computationally taxing unsteady flow simulations for determining the optimum rotor blade shape. A differential evolution algorithm in combination with an unsteady blade element momentum model is applied to derive an optimised blade shape for a small horizontalaxis wind turbine under turbulent inflow conditions. The results of this paper present, compared to steady optimisation, the effect of turbulent inflow on the optimum aerodynamic rotor blade shape and the rotor performance of a small wind turbine.

Flow analysis of shrouded small wind turbine with a simple frustum diffuser with computational fluid dynamics simulations

Electricity generation using wind energy has been well recognized as environmentally friendly, socially beneficial, and economically competitive for many applications. Because of crucial fossil energy resources shortage and environmental issues the wind energy is very important resource for electricity production. Small wind turbines, photovoltaic systems, full cells and pump as turbines (PAT) in small scale are main resources for distributed generation systems. Meanwhile, for remote areas wind energy beside photovoltaic system can combine as a hybrid system to provide necessary electric power of users. This system should be designed in such a way that the load demand of remote areas be provided with maximum reliability. Usually Direct coupled axial flux permanent magnet synchronous generator (AFPMSG), self-excited induction generator with gear box and permanent magnet synchronous generator(PMSG) with gear box can be used to connect to small wind turbine. In the past few years, there have been many studies on small scale wind energy conversion systems. Authors of (Jia Yaoqin et al., 2002), (Nobutoshi Mutoh et al., 2006), (T.Tafticht et al., 2006), (Ch.Patsios et al., 2008) and (M.G.Molina et al., 2008) presented maximum power point tracking(MPPT) methods for small scale wind turbines. (Etienne Audierne et al., 2009), (M.G.Molina et al., 2008), (Boubekeur Boukhezzar et al., 2005), (Md.Arifujjaman et al., 2005) and (Jan T.Bialasiewicz, 2003) described small scale wind turbine furling system and modeled small scale wind turbines. In this chapter we reviewed the working principles, over speed, output power control and MPPT control methods of small scale wind energy conversion system.

A parametric study of the effect of leading edge spherical tubercle amplitudes on the aerodynamic performance of a 2D wind turbine airfoil at low Reynolds numbers using computational fluid dynamics