James F. Manwell

Lead acid battery storage model for hybrid energy systems

This paper describes a new battery model developed for use in time series performance models of hybrid energy systems. The model is intended to overcome some of the difficulties associated with currently used methods. It is based on the approach of chemical kinetics. This model, which can be used for charging and discharging, is specifically concerned with the apparent change in capacity as a function of charge and discharge rates. It assumes that the charge can be stored in two ways, either as immediately available or as chemically bound. As described in this paper, it requires the determination of as few as three constants. Examples of the deviation of the battery model constants and comparisons of the new model with those used previously are given. Based on the success of the new model, it has been incorporated into the latest versions of the University of Massachusettss wind/diesel simulation codes.

Condition monitoring and prognosis of utility scale wind turbines

Abstract The state of the art in condition monitoring in wind turbines, and related technologies currently applied in practice and under development for aerospace applications, are reviewed. Condition monitoring systems estimate the current condition of a machine from sensor measurements, whereas prognosis systems give a probabilistic forecast of the future condition of the machine under the projected usage conditions. Current condition monitoring practice in wind turbine rotors involves tracking rotor imbalance, aerodynamic asymmetry, surface roughness and overall performance and offline and online measurements of stress and strain. Related technologies for monitoring of load history and fatigue crack growth in aircraft structures are evaluated for their applicability to wind turbine blades. Similarly, condition monitoring practice in wind turbines is compared with monitoring and prognosis in helicopter gearboxes. The state of the art in condition monitoring of electronic controls, power electronics and towers is also evaluated and compared with the state of the art in aerospace. Based on these comparisons, technology needs and future challenges for the development of condition monitoring and prognosis for large wind machines, both onshore and offshore, are summarised.

Algorithms for Offshore Wind Farm Layout Optimization

Offshore wind energy is positioned to facilitate substantial growth in wind energy production, but further reductions in the cost of energy will strengthen its ability to compete directly with other energy generating technologies. One simple solution is the optimal use of current technologies. To this end, this study investigates the use of optimization algorithms for offshore wind farm micrositing. First, a discussion is given of five different types of optimization algorithms: gradient search, heuristic, pattern search, simulated annealing, and evolutionary algorithms. The relevance of each algorithm to wind turbine micrositing is then evaluated by considering two separate objectives: minimization of the levelized production cost and maximization of the energy production. The genetic and greedy heuristic algorithms are further evaluated through the use of design simulations. Finally, these algorithms are employed to optimize the layout of a potential, real-world offshore wind farm near Hull, Massachusetts.

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.

HYBRID WIND/PV/DIESEL SYSTEM EXPERIENCES

The past ten years have seen significant developments in the design, analysis and installation of hybrid (wind/PV/diesel) power systems. This paper presents a summary of recent progress on this subject in the United States with emphasis on the analytical and experimental work carried out at the University of Massachusetts. Topics discussed here include: 1) System configuration and hardware, 2) Modeling and design tools, and 3) Recent applications.

Hybrid wind/PV/diesel hybrid power systems modeling and South American applications

This paper presents an applications case study and comparison of performance results between two computational models for simulating the performance of hybrid power systems. The first model, HYBRID2, was developed at the University of Massachusetts under National Renewable Energy Laboratory (NREL) sponsorship. The second model, SOMES, was developed at Utrecht University in the Netherlands. Both models have been designed to predict the technical and economical (life cycle cost) performance of hybrid power plants that typically might be comprised of renewable energy sources, a battery bank, and a diesel generator. A South American (Brazil) based hybrid power system used to power a remote telecommunications system was used for the applications case study. A final system configuration be used as a basis for model prediction comparison was established as a result of HYBRID2 parametric evaluation. Both codes yielded similar performance results, and this work points out that the predicted performance discrepancies are due basically to different subcomponent models and differences in control strategy. The generalized nature of this work is intended to be of interest to engineers involved with the design and analysis of hybrid power systems.

A Comparison of Alternative Approaches for the Synthetic Generation of a Wind Speed Time Series

These approaches include: the use of independent values from a specific probability distribution, the use of an algorithm based on the statistical behavior of a one-step Markov chain, the use of an algorithm based on the behavior of a transition probability matrix that describes the next wind speed value statistically as a function of the current wind speed value and the previous wind speed value, the use of Box-Jenkins models, the use of the Shinozuka algorithm, and the use of an embedded Markov chain. The statistical properties of interest are the probability distribution of wind speed values, the autocorrelation function of the wind speed values and the spectral density of the wind speed values

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.

Offshore Wind Farm Layout Optimization (OWFLO) Project: Preliminary Results

Optimizing the layout of an offshore wind farm presents a significa nt engineering challenge. Most of the optimization literature to date has focused on land -based wind farms, rather than on offshore farms. Typically, energy production is the metric by which a candidate layout is evaluated. The Offshore Wind Farm Layout Optimization (OWFLO) project instead uses the levelized production cost as the metric in order to account for the significant roles factors such as support structure cost and operation and maintenance (O&M) play in the design of an offshore wind farm. The objective of the project is to pinpoint the major economic hurdles present for offshore wind farm developers by creating an analysis tool that unites offshore turbine micrositing criteria with efficient optimization algorithms. This tool will then be use d to evaluate the effects of factors such as distance from shore and water depth on the economic feasibility of offshore wind energy. The project combines an energy production model —taking into account wake effects, electrical line losses, and turbine avai lability —with offshore wind farm component cost models. The components modeled include the rotor -nacelle assembly, support structure, electrical interconnection, as well as O&M, installation, and decommissioning costs. The models account for the key cost drivers, which include turbine size and rating, water depth, distance from shore, soil type, and wind and wave conditions. When integrated within an appropriate optimization routine, these component models work together to better reflect the real -world c onditions and constraints unique to individual offshore sites. The OWFLO project considers several optimization algorithms —including heuristic and genetic methods —to minimize the cost of energy while maximizing the energy production of the wind farm. Par ticular attention has been paid to the results of recent European studies, including the ENDOW and DOWEC projects. This paper summarizes the initial results from this project. A comparison of model results and data from the Middelgrunden offshore wind far m is presented. The overall energy and cost of energy estimations compare well with the real data, but further improvements to the models are planned. A summary of the on -going and future phases of the project is also presented.

Recent renewable energy driven desalination system research and development in North America

Abstract This paper summarizes the current status of renewable energy driven water desalination projects built or designed in North America. It considers both solar and wind energy as the energy sources. It discusses results of experimental projects and assessments that have been made of them. It also includes a discussion of advances in development of components that have been used in such systems. The following processes are considered: simple distillation, multistage flash distillation, freeze separation, vapor compression, electrodialysis, and reverse osmosis (RO). As indicated, the paper specifically addresses projects of North American origin. Among the most successful renewable energy driven plants to date have been those that use RO. Reverse osmosis is, in fact, the most commonly used method of conventionally powered desalination in the United States. For example, approximately 100 RO systems are known to be operating in Florida. For that reason a particular effort has been directed at describing those developments in RO technology in North America that can be applied in renewable energy driven applications. Similarly, advances in wind energy system design make wind turbines more readily usable for powering RO systems reliably and cost effectively than they could do so in the past. The paper discusses these advances in the context of desalination, and suggestions are made for future development which could further enhance wind energys potential for use in desalination.