Wind Energy Systems

Optimising Design and Construction for Safe and Reliable Operation

John Dalsgaard Sørensen, Jens N Sørensen

• Publisher: Woodhead Publishing
• Year: 2010
• ISBN:
  9780857090638
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Large-scale wind power generation is one of the fastest developing sources of renewable energy and already makes a substantial contribution to power grids in many countries worldwide. With technology maturing, the challenge is now to increase penetration, and optimise the design, construction and performance of wind energy systems. Fundamental issues of safety and reliability are paramount in this drive to increase capacity and efficiency.Wind energy systems: Optimising design and construction for safe and reliable operation provides a comprehensive review of the latest developments in the design, construction and operation of large-scale wind energy systems, including in offshore and other problematic environments.Part one provides detailed coverage of wind resource assessment and siting methods relevant to wind turbine and wind farm planning, as well as aeroelastics, aerodynamics, and fatigue loading that affect the safety and reliability of wind energy systems. This coverage is extended in part two, where the design and development of individual components is considered in depth, from wind turbine rotors to drive train and control systems, and on to tower design and construction. Part three explores operation and maintenance issues, such as reliability and maintainability strategies and condition monitoring systems, before discussing performance assessment and optimisation routes for wind energy systems in low wind speed environments and cold climates. Part four reviews offshore wind energy systems development, from the impact of environmental loads such as wind, waves and ice, to site specific construction and integrated wind farm planning, and of course the critical issues and strategies for offshore operation and maintenance.With its distinguished editors and international teams of contributors, Wind energy systems is a standard reference for wind power engineers, technicians and manufacturers, as well as researchers and academics involved in this expanding field.

• Reviews the latest developments in the design, construction and operation of large-scale wind energy systems
• Offers detailed coverage of wind resource assessment and siting methods relevant to wind turbine and wind farm planning
• Explores operation and maintenance issues, such as reliability and maintainability strategies and condition monitoring systems

Part I

Fundamental wind energy resources, design, safety and reliability

1

Meteorology and wind resource assessment for wind farm development

R.J. Barthelmie and S.C. Pryor, Indiana University, USA

Abstract:

Assessing wind resources (wind speeds, directional distribution, turbulence intensity, etc.) for wind energy projects demands a level of detail and accuracy regarding the spatial and temporal variations of the wind and turbulence climate, which is beyond that required for other purposes. Hence a wide range of measurements and models have been developed and are employed to provide assessments for initial site identification, quantifying the long-term wind resource based on short-term measurements, extrapolating the vertical wind speed profile, calculating the potential power output from each turbine and for wind farm layout to optimize power output. Here we give an overview of the state of the art in wind resource assessment and look to the near-future in terms of developments in modeling and measurement techniques.

Key words

wind resource

measurements

modeling

wakes

climate

1.1 Introduction

The process of identifying promising sites for wind energy development depends not only on the magnitude of the wind energy resource,¹ but also on other factors such as the proximity to the electrical grid. Environmental impact assessments and/or planning restraints often result in wind turbines within wind farms or even whole wind farms being modified, moved or even rejected during the planning phase. Nevertheless, herein we shall exclusively focus on the meteorological parameters that dictate the wind resource and review the mechanisms by which a robust wind resource assessment can be made. We will further discuss the meteorological factors that dictate the actual power production at a site and briefly articulate the methods used to make power production forecasts.

1.2 Assessment of the wind climate

The wind climate of a particular location is a function of processes at numerous temporal and spatial scales,² and the variability of wind and turbulence on scales from decades to seconds impacts the overall economics/desirability of a site from a wind energy perspective. In order to characterize site specific wind energy resources for wind energy development, a number of steps are usually undertaken that are shown schematically in Fig. 1.1 and are described in the following sections.

1.1 Steps towards developing site climatology.

1.2.1 National assessments

A regional-scale wind climate assessment can be made using a variety of data sources and methods that are not necessarily of sufficient accuracy to constitute a ‘bankable’ wind resource, but will likely identify areas worthy of further investigation. The precise wind speed and energy density climate necessary to make a development economic varies according to, among other things, the type of support mechanism in place and whether extension of the electrical grid to the site is necessary and will be installed by the transmission operator or whether this has to be part of the wind energy development. This means that the wind climate is frequently articulated in terms of wind speed classes so that users can make their own judgments about whether the available wind resources designate the area or site as worth pursuing.

Wind climate assessments have been made for some countries/regions by governmental or other agencies (e.g. national meteorological services or departments of energy) using a variety of approaches and data sources, including:

1. Analysis of reanalysis products.^3–5 Reanalysis projects draw data from a range of sources, which are quality controlled and assimilated with a consistent data simulation system (models). These reanalysis products are thus a hybrid of the observations that are assimilated and ‘background’ information used to provide complete representations of the atmosphere that are derived from a short-range forecast initiated from the most recent previous analysis. The reanalysis products thus comprise four-dimensional, homogenized and systematic datasets. The reanalysis systems were not designed principally for wind climates, and comparisons with independent observations of wind speeds exhibit substantial discrepancies.⁶ Nevertheless, they have the advantage of being physically consistent and continuous in time and space, but the disadvantage is that global reanalysis datasets are available only on fairly coarse time and space (horizontal and vertical) scales. However, recently regional reanalyses with relatively high temporal and spatial resolution have been undertaken (e.g. the North American Regional Reanalysis is available at a resolution of ~ 32 × 32 km for 1979–2006).⁷

2. Pressure gradient data.^8,9 An estimate of the geostrophic wind speed (i.e. the wind speed that would be attained in the absence of frictional effects and curvature of isobars) may be derived from mean-sea-level pressure data. The technique has proved particularly useful in the context of reconstructing longtime series in order to examine climate variability,¹⁰ but naturally does not reflect the actual wind climate at a specific location. Pressure gradients have also been used to estimate extreme wind speeds.¹¹

3. Near-surface meteorological or other wind speed measurements from national weather observing networks.^12,13 Observational records of near-surface wind speeds are subject to data inhomogeneities associated with the introduction of new measurement technologies or protocols (e.g. deployment of the Automated Surface Observing System in the USA during the 1990s) or site relocations/modification of site characteristics, hence care has to be taken in interpreting these data.⁶

4. Mesoscale modeling. Numerical and analytical¹⁴ models have been applied to map the wind climate and wind energy resource at a range of spatial resolutions for regional, national and continental domains, e.g. Ref. 15 and Ref. 16. These...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Energy
• Part I: Fundamental wind energy resources, design, safety and reliability
• Part II: Wind energy system materials, design and component development
• Part III: Wind energy system operation and maintenance, performance assessment and optimisation
• Part IV: Offshore wind energy system design, construction, operation and maintenance
• Index