Small Wind and Hydrokinetic Turbines
2: Murdoch University, Australia
3: University of Calgary, Canada
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.
Inspec keywords: aerodynamics; blades; wind turbines; computational fluid dynamics; power generation control; hydraulic turbines; elasticity; rotors; tidal power stations
Other keywords: hydraulic turbines; blades; power generation control; aerodynamics; tidal power stations; computational fluid dynamics; elasticity; rotors; wind turbines
Subjects: Conference proceedings; General topics in manufacturing and production engineering; General fluid dynamics theory, simulation and other computational methods; Tidal power stations and plants; Mechanical components; General electrical engineering topics; Power and plant engineering (mechanical engineering); Fluid mechanics and aerodynamics (mechanical engineering); Education and training; Elasticity (mechanical engineering); Wind power plants; Engineering mechanics; Applied fluid mechanics
- Book DOI: 10.1049/PBPO169E
- Chapter DOI: 10.1049/PBPO169E
- ISBN: 9781839530715
- e-ISBN: 9781839530722
- Page count: 479
- Format: PDF
-
Front Matter
- + Show details - Hide details
-
p.
(1)
-
1 Wind resource assessment for small wind turbines
- + Show details - Hide details
-
p.
1
–20
(20)
Wind resource assessment (WRA) is the process of estimating a wind turbine's future energy production and is a key factor in the successful installation, operation, and performance of a small wind turbine (SWT). The definition of SWTs varies from country to country. For example, the US Department of Energy and Japan's NipponKaiji Kyokai (ClassNK) define SWTs as having a power rating less than or equal to 100 kW and 20 kW, respectively. The International Electrotechnical Commission (IEC) SWT design standard IEC61400-2 considers parameters other than power rating and defines SWTs as having a rotor swept area smaller than or equal to 200 m2, generating electricity at a voltage below 1,000-V AC or 1,500-V DC for both on-grid and off-grid applications. The level of detail and analysis in WRA typically increases with turbine size and cost. On the upper end of the SWT range, a simplified WRA might be followed by a more detailed analysis and feasibility study that includes on-site data collection to reduce risk.
-
2 Resource assessment for hydrokinetic turbines
- + Show details - Hide details
-
p.
21
–37
(17)
The performance of a wind or hydrokinetic turbine (HKT) depends on its "power curve"-the output power versus wind or water speed-and the magnitude of the resource. This chapter considers the assessment of the resource for HKTs and raises some interesting issues of the interaction with the turbine power curve. HKTs are a comparably newenergy conversion technology, and there are fewresource assessment tools available especially in comparison to wind turbines. The main aimof this chapter is to discuss the techniques of resource estimation for rivers and human-made water structures such as irrigation canals. The chapter presents the main features of existing models used for HKT resource prediction through hydraulic stimulation and then hydrological models for validation. The main outcome of resource estimation is the water velocity which can be combined with an HKT power curve, or used to provide the power density (PD), the available power per square meter of turbine rotor area. The two chief difficulties of resource assessment are described: the first is that most hydrological data is provided as volume flow rates in m3s that can be related to the velocity only if the river cross-section is available, which is not the case in general. Second, the velocity varies with time and the time period used to determine the average velocity is crucial to the resource assessment.
-
3 Small hydrokinetic turbines
- + Show details - Hide details
-
p.
39
–69
(31)
Electrical energy can be produced from the kinetic energy of flowing water in tides, rivers and potentially ocean currents. Tidal energy can be harnessed either from the potential energy in tidal rise and fall, or from the kinetic energy in flowing water by means of hydrokinetic turbines (HKT). The energy in rivers can also be harnessed either from potential energy from the kinetic energy inflowing water (hydrokinetic energy). This chapter deals with small-scale HKT designed to extract energy from rivers, tides and possibly ocean currents with minimal drop in surface elevation.
-
4 Computational methods for vertical axis wind turbines
- + Show details - Hide details
-
p.
71
–107
(37)
There are two major types of vertical axis wind turbines (VAWTs): the Savonius rotor, which is based on the drag force and the Darrieus rotor, which is based on the lift force. The vertical axis turbine has the option to be modeled in two-dimensional (2D), which offer significant speed improvements and can give good approximations of the turbine forces, but cannot handle all interactions within the turbine and are less suitable for wake modeling. The Savonius rotor is commonly modeled with traditional computational fluid dynamics (CFD) software, as flow separation is crucial to its operation. While CFD models with resolved boundary layers also can be applied to the Darrieus, it is computationally demanding and simplified models, where the blades are modeled by external force models, are commonly applied. The most simplified model is the streamtube model, which uses a very simplified stationary model for the flow through the turbine. A more advanced approach is the actuator cylinder model, where the stationary flow is modeled through Euler's equation, giving a more realistic flow field. If time-dependent solutions are desired, there are the options to use either the actuator line model (ALM) or the vortex method, where the ALMs typically are implemented within traditional CFD solvers, while the vortex method often is implemented as a Lagrangian method that uses the vorticity as discretization parameter. The simplified models are primary useful for turbines with a high tip speed ratio, while the deep stall that can occur at a low tip speed ratio often requires traditional CFD solvers that resolve the boundary layers.
-
5 VAWT wind tunnel experiments
- + Show details - Hide details
-
p.
109
–134
(26)
Experimental testing is an essential part of the wind turbine design path, as it provides early information about aerodynamics, mechanics, performance, and turbine control. According to the size and the budget or the certification purposes, the testing environment can be either natural through field testing, or controlled in dedicated facilities called wind tunnels. The testing procedure provides time series of measured data at a given sampling rate that needs proper data post-processing for a rational use. Following the stochastic nature of wind, the data treatment always needs statistical tools and appropriate uncertainty analysis. The advantage of infield measurements is to perform full-scale tests, from which the real turbine behaviour can be simulated and evaluated. The site has to be certified according to Annex A of IEC 61400-12-1,2005. A few sites have the characteristics suited to host wind turbine test campaigns, and depending on the windiness of the location from 1 to 2 years can be necessary to complete the measurements. On the other hand, wind tunnel tests can only be performed on scaled prototypes, with some dimensional limitations compared to real size turbines. The controlled environment conditions allow repeatable tests and to separate some effects that in open field tests are often superimposed and difficult to disaggregate. In particular, the calibration and validation of numerical codes can be made through controlled experiments. From the point of view of the market-oriented wind turbine development, wind tunnel tests can represent the very early stage of a more wide experimental campaign, followed by infield tests.
-
6 The aerodynamics of water pumping windmills
- + Show details - Hide details
-
p.
135
–156
(22)
Most small wind and hydrokinetic turbines produce electricity but an important alternative is to pump water. In this chapter, we discuss water pumping windmills which are multibladed, low-speed machines directly coupled to a mechanical pump. Water pumpers come in many different forms, but their basic aerodynamics is still not well known. Although they are still built in many countries, water pumping windmills are particularly appropriate to the developing world, and we will discuss them in that context. The resource assessment, mechanical design of the pump and connection to the rotor, and performance matching are complex issues that we will not cover in this review of the aerodynamics.
-
7 Blade element analysis and design of horizontal-axis turbines
- + Show details - Hide details
-
p.
157
–191
(35)
Horizontal-axis wind turbines (HAWTs) harness energy from the wind and horizontal-axis hydrokinetic turbines (HKTs) use the same basic principles in rivers, and tidal or marine currents. The value of wind turbines is well established. HKTs do not require large flooded areas or civil structures and so reduce environmental impacts. This chapter focuses on the analysis and design of HAWTs and HKTs using blade element momentum theory (BEMT). The theory is extended to deal with the major differences between wind and water operation-the possibility of cavitation in the latter-through the criterion of the local minimum pressure coefficient that is usually expressed as a cavitation number. We demonstrate the accuracy of BEMT and how it can be modified to include the effect of a diffuser surrounding the rotor as this modification has significant attraction for small turbines. Recent mathematical formulations to design diffuser-augmented turbines (DATs) are presented, and we consider BEMT design for maximum power and multidimensional optimization (MDO) when other objectives such as low noise and blade mass are also to be met.
-
8 Vortex-induced vibration-based energy harvesting
- + Show details - Hide details
-
p.
193
–212
(20)
As the perceived need for sustainable development and renewable energy quickly rises, power extraction based on new techniques will usher in various new development opportunities. In the domain of VIV-based energy harvesting for wind and MRE researchers, further studies are required to develop technologies that can harness energy from multiple degrees of freedom excitations and use intelligent regulating elements (controls systems, artificial neural networks, and machine learning) to enhance efficiency and energy output from these devices. More field-scale deployment is required to boost investor confidence. Besides, coupling VIV-based systems with other energy harvesting technologies like wind turbines and photovoltaic devices will broaden the range of applications.
-
9 Field testing of a 5-kW horizontal-axis wind turbine
- + Show details - Hide details
-
p.
213
–235
(23)
Small wind turbines have been operating in a range of different forms for well over 300 years. Most of the earlier machines were drag-type machines with some still in use today; for example, the Southern Cross Windmill is still used to pump water across rural parts of Australia. The oil price shock of the 1970s saw 'large' horizontal-axis wind turbines (HAWTs) with an output power of 50-100 kW being developed and grid connected; today, these turbines are now considered moderately sized. On-going research and development have seen a steady increase in the size of these turbines and design power outputs with commiserate improvements in efficiency and reliability leading to a steady reduction in the levelized cost of producing power. Small wind turbines, turbines with a rated power output of less than 50 kW, unfortunately missed out on this early research and development funding due principally to the commercial interest in large machines. This chapter describes the work done to increase the knowledge of the performance of small high-efficiency HAWTs operating in turbulent wind flows. Findings show that the size of the tail fin has a strong influence on the yaw performance of the turbine. Gyroscopic loading from an operating yawing turbine can lead to potentially significant cyclical loading on blades and other components of the turbine. In turbulent flows, the starting performance of the turbine is important to help maximize energy capture. For a range of starting scenarios, the starting time of the turbine can be accurately modelled.
-
10 Aeroelastic modelling of a 5-kW horizontal axis wind turbine
- + Show details - Hide details
-
p.
237
–264
(28)
Aeroelastic modelling is regularly used in the design and analysis of large wind turbines but has seen comparatively little use in the development of small wind turbines. Fewer studies still have considered experimental validation of model performance with field measurements. This study details the development of an aeroelastic model of a 5-kW horizontal-axis Aerogenesis turbine within the freely available software FAST (fatigue, aerodynamics, structures, and turbulence). The model includes rotor aerodynamics, blade and tower structural freedom, free-yaw tail fin dynamics, and a self-excited induction generator (SEIG) incorporating maximum power point tracking (MPPT) variable speed control. This model was compared to measured operating data to assess aerodynamic and structural performance. Blade loadings and deflections were simulated within 8% and 10%, respectively, at design conditions in the azimuthal domain. Simulated tail fin motions and yaw behaviour were bounded by measured field data. The simulated control system model was found to operate within the bounds of measured field data. Areas for future model improvement are discussed in this chapter. The resulting aeroelastic model and methodologies presented here are expected to further the use of aeroelastic modelling in the small wind turbine field. Particular applications may include the verification of performance and design loads specified in IEC 61400.2-2013, the international standard for small wind turbines.
-
11 The very low head turbine—a new hydro approach
- + Show details - Hide details
-
p.
265
–293
(29)
The very low head (VLH) turbine is a relatively new application of long-standing hydroelectric power technology using recently available modern technological advances. These advances have enabled a fundamental design shift that substantially improved all efficiency, cost and performance in the low head hydro regime. This chapter describes the conception of the VLH turbine design, the basic technology design improvements and the key adaptations used to make it suitable for use in cold climate regions followed by a case study of the first plant installation in Canada. The VLH turbine uses a variable-speed, permanent magnet generator (PMG), which is rare in the hydro industry, as most hydro turbine units are fixed speed, synchronized or induction generator systems. For VLH applications where the up-stream water level to downstream water level is in the order of a 2-5-m drop, the economics of the plants are very difficult. This is due to the large volume of water required to generate only a few hundred kilowatts of power. To solve this, the VLH was conceived to be installed at existing water control facilities, either adjacent to or within, to minimize civil works, reduce environmental impact and shorten regulatory approvals. The VLH itself is designed to provide multiple functions, over and above producing hydropower, including a water control gate, flood passage, debris rack, fish passage, water level control weir and rural electrical grid support.
-
12 Development and experience with a vertical-axis hydrokinetic power generation system
- + Show details - Hide details
-
p.
295
–324
(30)
This chapter chronicles New Energy Corporation Inc.'s development and experience with its vertical-axis cross-flow hydrokinetic power generation system. New Energy has taken this concept from initial trials to full commercialization. The vertical-axis turbine is suited to a wide variety of applications, including rivers, canals, industrial outflows, and tidal streams. The turbines can be installed on a floating platform or fixed in position. A distinguishing feature, the vertical orientation, means that the generator and power conditioning equipment can be situated above the water permitting the use of conventional components. These systems can be configured as complete water-to-wire solutions for both remote stand-alone and microgrid applications, and centralized grid-connected power generation applications in single unit or array configurations. The systems are quiet, unobtrusive, produce zero emissions, and have a low impact on aquatic life. To date, system sizes of 5-25 kW have been developed with plans to increase to 250 kW. New Energy has conducted a long-term development program primarily focused on building and field testing its systems in a variety of operating conditions and application types. Initial turbine rotor designs and control concepts were tested in the outflow of a wastewater treatment plant and then on a purpose built self-propelled platform in open water. The test program then moved to a hydro plant supply channel, testing throughout the winter in subzero temperatures, to evaluate and refine system designs in preparation for first deployments. New Energy has deployed its systems in various locations around the world in a variety of applications. These range from an installation in a small stream high in the Himalayas to power a village, to powering a school in Myanmar, to producing grid power from a canal in India. The installations have presented some unique challenges, including transporting hardware to a location with a 3-day walk from the nearest road, finding a local partner in geographically remote locations to provide long-term service and support, and dealing with different cultures and political situations.
-
13 SWTs for arctic applications: powering autonomous rovers
- + Show details - Hide details
-
p.
325
–339
(15)
In arctic regions, small wind turbines (SWTs) fill an important niche for powering weather and research stations as well as telemetry in the dark winter months. This chapter revolves around another, rather unusual, use-case: using SWTs for powering autonomous rovers. Specifically, rovers are designed to roam the Greenland ice sheet, with the purpose of monitoring ice sheet conditions during the dark winter months, when PV is not an option. The chapter is based on a study assessing the feasibility of powering a rover with a micro wind turbine, considering weather and wind conditions of a specific location on the ice sheet. It includes a study of local conditions and derived functional requirements, a review of SWTs with arctic references compared against established selection criteria, and lastly, a short field test of a selected turbine on the ice sheet mounted at a very low hub height and the results thereof. While the study was preliminary, we demonstrate that harvesting wind energy at very low hub heights is possible on the Greenland ice sheet due to low turbulence: that maximum thrust must be considered for rover stability; and that one off-the-shelf SWT performs significantly below manufacturer specifications, in part attributed to cold temperature effects.
-
14 Commercialisation of a small diffuseraugmented wind turbine for microgrids
- + Show details - Hide details
-
p.
341
–358
(18)
Small-scale distributed wind generation faces challenges in being cost competitive due to recent advances in solar photovoltaic (PV) and battery storage technology. Reductions in levelised cost of energy (LCOE) can be achieved by improvements in aerodynamic efficiency, generator controller design, or reducing cost of manufacture. In this chapter, we present a case study detailing the commercialisation of a novel 200-W high-efficiency diffuser-augmented wind turbine (DAWT). We highlight the particular challenges to be overcome when designing the electrical control system for interface with microgrid architecture. Results include increased rotor efficiency, bespoke controller design, and the novel use of manufacturing processes. Findings and conclusions are of direct interest to small wind turbine designers as they seek to develop innovative methods of reducing LCOE.
-
15 A tide like no other: harnessing the power of the Bay of Fundy
- + Show details - Hide details
-
p.
359
–392
(34)
This chapter provides an overview of efforts to demonstrate tidal stream technologies at the Fundy Ocean Research Centre for Energy (FORCE) in Minas Passage, Bay of Fundy. The power extraction potential in the Minas Passage is estimated at nearly 8,000 megawatts, roughly equivalent to the power needs of 3 million homes. Established in 2009, FORCE was created to explore the potential for tidal stream energy to contribute to Canada's future clean energy supply. While still an emerging technology, tidal stream technology has the potential to provide a predictable source of renewable energy and thereby reduce GHG emissions from electricity generation and help respond to climate change. Over the past decade, supportive government policy, combined with investment in technology demonstration infrastructure and technical and environmental research, has spurred the participation of over 500 companies in Atlantic Canada. Challenges remain: the sector has not yet converged on a single design solution for energy capture or mooring, working with new technologies in marine environments is expensive, and more research is required to understand any potential environmental effects. Interest remains high, however, as 2021 witnessed the construction of two new technologies in Nova Scotia, in anticipation of later deployment at FORCE.
-
16 Sustainable materials for small blades
- + Show details - Hide details
-
p.
393
–446
(54)
Increasing the power of hydrokinetic turbines (HKTs) and wind turbines (WTs) using blades with more efficient geometries is important. However, there is another important aspect: the materials that can be used in these applications. The requirements may include, for example, a combination of low density, high mechanical strength, high modulus of elasticity, high capacity to absorb energy on impact and high chemical and environmental resistance. In achieving these goals, synthetic-fiber-reinforced composites have advantages, such as ease of mixing with matrices, adaptation to various manufacturing techniques, very high specific resistance and good fiber-matrix interface, due to chemically reacting with the matrix that increases the composite strength. Regardless of the manufacturing techniques, it is necessary to have the conformity of the manufactured to the design shape. Small blades, therefore, need high tolerances in the tip region where the chord is smallest. Furthermore, the synthetic fibers, when combined with thermoset resins, for example, are energy-intensive and expensive due to the heating needed to cure them and are also very difficult to recycle, which it makes the blades of any size the least recyclable component of a WT. This creates a great opportunity for developing new materials, new methodologies and effective processes to produce composites reinforced by sustainable materials. This chapter draws a parallel between conventional materials with manufacturing methods and the newest materials with alternative methodologies for manufacturing small HKT and WT blades, and how the properties of sustainable materials are suitable these types of applications. We describe a range of natural reinforcement materials from the Amazon region in Brazil and a possible foam core replacement from a Brazilian palm tree.
-
Back Matter
- + Show details - Hide details
-
p.
(1)