Anthony L. Rogers

Uncertainty Analysis in MCP-Based Wind Resource Assessment and Energy Production Estimation

This paper presents a mathematical framework to properly account for uncertainty in wind resource assessment and wind energy production estimation. A meteorological tower based wind measurement campaign is considered exclusively, in which measure-correlate-predict is used to estimate the long-term wind resource. The evaluation of a wind resource and the subsequent estimation of the annual energy production (AEP) is a highly uncertain process. Uncertainty arises at all points in the process, from measuring the wind speed to the uncertainty in a power curve. A proper assessment of uncertainty is critical for judging the feasibility and risk of a potential wind energy development. The approach in this paper provides a framework for an accurate and objective accounting of uncertainty and, therefore, better decision making when assessing a potential wind energy site. It does not investigate the values of individual uncertainty sources. Three major aspects of site assessment uncertainty are presented here. First, a method is presented for combining uncertainty that arises in assessing the wind resource. Second, methods for handling uncertainty sources in wind turbine power output and energy losses are presented. Third, a new method for estimating the overall AEP uncertainty when using a Weibull distribution is presented. While it is commonly assumed that the uncertainty in the wind resource should be scaled by a factor between 2 and 3 to yield the uncertainty in the AEP, this work demonstrates that this assumption is an oversimplification and also presents a closed form solution for the sensitivity factors of the Weibull parameters.

An Investigation of Wind-Shear Models and Experimental Data Trends for Different Terrains

The importance of characterizing the wind-shear at a given site for a utility-scale wind turbine cannot be overemphasized. Such characterization is needed for an accurate prediction of its power output. Thus, the objective of this work based on the use of several US tall tower wind data sets was to determine the accuracies of different wind-shear enumeration methods, especially when used at sites having hills and/or forests. In addition, average wind-shear variations with respect seasonal and annual effects and data length are presented for various long data sets, recorded to between 1995 and 2005. Wind direction and atmospheric stability were not a factor in the analysis. At some of the sites the greatest average wind-shear was found during the summer. For the site with the most complex terrain, the average annual all-direction wind-shear varied by up to 7% between different years; this was partly due to year-to-year variations of the direction distribution. There was found to be no significant difference between the performance of the log and power laws; using either may give inaccurate predictions of hub-height mean wind speeds.

An offshore wind resource assessment study for New England

This paper gives a summary of ongoing work on the assessment of the wind energy resource off the coast of southern New England in the United States. This project was carried out to determine the potential for the near-term development of offshore wind energy projects in that region. The work summarized here consists of four aspects: (1) a review of existing offshore wind data, (2) the measurement of new data at an offshore site, (3) correlation and prediction of long-term data at a new offshore site by reference to a longer-term island site and (4) assessment of the overall coastal resource through the use of the MesoMap software.

Uncertainty Analysis in Wind Resource Assessment and Wind Energy Production Estimation

This paper presents a mathematical approach to properly account for uncertainty in wind resource assessment and wind energy production estimation. The evaluation of a wind resource and the subsequent estimation of the annual energy production (AEP) is a highly uncertain process. Uncertainty arises at all points in the process, from measuring the wind speed to the uncertainty in a power curve. A proper assessment of uncertainty is critical for judging the feasibility and risk of a potential wind energy development. Many current methods for assessing uncertainty either oversimplify the process or make faulty assumptions, leading to erroneous estimates of uncertainty. The approach in this paper yields a more accurate and objective accounting of uncertainty, and therefore better decision making when assessing a potential wind energy site. Three major aspects of site assessment uncertainty are presented here. First, a method is presented for combining uncertainty that arises in assessing the wind resource. Second, uncertainty in wind turbine power output and energy production is characterized. Third, a method for estimating the overall AEP uncertainty when using a Weibull distribution is presented. While it is commonly assumed that the uncertainty in the wind resource should be scaled by a factor between two and three to yield the uncertainty in the AEP, this work demonstrates that this assumption is an oversimplification, and also presents a closed form solution for the sensitivity factors of the Weibull parameters.

An investigation of variable speed operation of diesel generators in hybrid energy systems

This paper provides a preliminary assessment of the performance and economic potential of a hybrid energy system (wind/diesel) power system which includes a variable speed diesel generator. Recent development in power electronics would be utilized to allow asynchronous operation of the diesel generator, while simultaneously delivering constant frequency electric power to the local electrical grid. In addition to the variable speed diesel, the system can include wind and/or solar electric sources. A hybrid energy system model recently developed at the University of Massachusetts is used to simulate this system configuration and other more conventional wind/diesel hybrid energy systems. Experimental data from a series of variable speed diesel generator tests were used to generate a series of fuel consumption curves used in the analytical model. In addition to performance (fuel savings) comparisons for fixed and variable speed systems, economic cost of energy calculations for the various system designs are presented. It is shown that the proposed system could offer both performance and economic advantages.

A year 2000 summary of offshore wind development in the United States

Abstract This paper presents an overview of the status of offshore wind energy development in the United States. It includes an overview of the research conducted at the University of Massachusetts in the early 1970s on large floating offshore systems and designs for offshore systems sited in the Great Lakes. It also presents a summary of the present US work on offshore energy, including the most recent work in New England as well as national and regional efforts to define the potential offshore wind energy resource. Also included is a review of the regulatory and permitting issues that must be addressed for offshore wind energy systems development. The paper concludes with a summary of current commercial and developmental activities in the US.

Design requirements for medium-sized wind turbines for remote and hybrid power systems

This paper provides an overview of the design requirements for medium-sized wind turbines intended for use in a remote hybrid power system. The recommendations are based on first-hand experience acquired at the University of Massachusetts through the installation, operation, and upgrade of a 250-kW turbine on a mountain top with difficult access in Western Massachusetts. Experience with the operation of this turbine and the design of its control system, together with a long history in the design and analysis of hybrid power systems, has made it possible to extend the work in Western Massachusetts to remote or hybrid power systems in general. The University test site has many attributes of more remote sites and the overall wind turbine installation is typical of one that could power a hybrid wind system. For example, access to the site is limited due to steep terrain, snow, and environmental restrictions. Also, the power lines feeding the turbine exhibit voltage sags and phase imbalance, especially during start-up. This paper is based on the experience gained from the operation of this wind turbine and assesses the requirements for the design and operation of medium to large wind turbines in remote locations. The work summarizes lessons learned relative to: (1) sensors, communication, and control capabilities; (2) grid connection issues; and (3) weather-related problems. The final section of the paper focuses on design requirements to ensure successful installation and the completion of maintenance and repairs at remote sites.

Addressing Ground Clutter Corruption of SODAR Measurements

Echoes from ground clutter around a SODAR may result in a low bias in the wind speed measured by a SODAR. Typically, some, but not all, of the data collected by a SODAR at a site with ground clutter may be corrupted in this manner. In this study, methods to identify acceptable data points in already-collected data are explored, as well as the use of those remaining data points for the estimation of wind speeds. The paper also explores two approaches to filtering that can remove the effects of ground clutter from the raw data, before averaging. One filters out individual wind speed measurements based on signal amplitude. The other approach attempts to filter the raw acoustic data, using wavelets, to eliminate the effect of ground clutter before any further data processing. The filtering of data based on signal amplitude works well, but may result in few data samples with which to determine 10-minute averages. The wavelet approach did not successfully filter out the effects of ground clutter.

Wind Turbine Siting in an Urban Environment: A Successful Case Study at Hull, Massacchusetts

The installation of a Vestas 660 kW wind turbine at Windmill Point in Hull, Massachusetts represents a high point in the long history of wind energy activity at this location. The site is in a highly populated coastal area, within 8 miles of Boston (city hall) and within 5 miles of Logan Airport. This paper documents the history of this project, from its early precursors in the 1800s, through the installation of a 40 kW Enertech machine in the 1980s to the installation of the new turbine. The issues that were addressed and the factors that led to successful realization of the project are discussed here. In addition, a summary of the first years performance of the wind turbine is given. The paper also presents an overview of possible future wind generation projects that are under discussion in the town.

Status of offshore wind energy in the United States

This paper provides an overview of the status of offshore wind energy development in the United States. The paper covers the period from the early 1970s until the present time.