Jon G. McGowan

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.

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.

Optimizing the Layout of Offshore Wind Energy Systems

Already a European reality, offshore wind energy technology is poised, in the near future, to significantly contribute to the United States energy supply as well. A complex problem in which many trade-offs are involved is offshore wind farm layout. For example, just as electrical costs and losses increase with turbine spacing, so does energy production. Installation costs, transmission, foundation, operations and maintenance, and energy production all increase with distance from shore. A thorough understanding of the physics behind the trade-offs determines the dominating factors, which can help lower energy costs from these farms through optimal layout. Results of a study investigating these trade-offs and developing a wind farm layout optimization method during offshore wind energy system design micrositing phase are presented. A method for offshore wind farm energy cost analysis and an offshore wind farm layout optimization tool development summary are presented. An example of optimization tool use for offshore wind far design in Hull, Massachusetts, and an initial optimization tool validation are also given.

A COMBINED PROBABILISTIC TIME-SERIES MODEL FOR WIND DIESEL SYSTEMS SIMULATION

Abstract This article describes a new simulation model for wind/diesel systems. It involves a combined time series and statistical approach to estimate the fuel use of diesel generators. In addition to provision for modeling non-identical diesels, the model allows the inclusion of multiple, non-identical wind turbines whose output may or may not be correlated. Three diesel dispatching strategies are provided. One assumes no storage, and when storage is employed, either a peak shaving or cycle charge control option can be used. The storage module uses a flexible battery model specially designed for time series simulation codes. A key assumption for the main analytical model is that, within each time step, the load and wind power are assumed to be normally distributed. The mean net load is the mean load less the mean wind power and its variance is found from the variance of the load and the wind power. A loss of load probability is used to find the maximum and minimum anticipated values of the net load. In addition to summarizing the overall analytical model, this article presents the results of a number of simulations demonstrating the performance prediction (diesel fuel usage) capabilities of the model. For one of these cases (a no storage system), the results show excellent correlation between the model and actual data. Other cases summarized show that the use of the model greatly facilitates the integration of storage into the control scheme, and gives the fuel saving potential for several different wind/diesel system configurations.

Utilizing Reanalysis and Synthesis Datasets in Wind Resource Characterization for Large-Scale Wind Integration

As wind plants become a more substantial portion of the generation resource, the ability of and manner in which this new fleet of generation supports meeting the power system load in a given area must be quantified in order to ensure security of supply. This paper describes the manner in which a reanalysis dataset—the National Aeronautics and Space Administration (NASA) Modern Era Retrospective-Analysis for Research and Applications (MERRA) dataset—was utilized in conjunction with the National Renewable Energy Laboratory (NREL) Eastern Wind Integration Dataset in order to perform an estimation of the interannual variability in wind power production as related to the capacity value of the investigated potential wind plants. Also described in the paper is a comparison of the MERRA data with publicly available wind data collected by the University of Massachusetts Wind Energy Center (UMass WEC).

A Techno-Economic Analysis of a Proposed 1.5 MW Wind Turbine with a Hydrostatic Drive Train

This paper presents a techno-economic feasibility study for a proposed 1.5 MW wind turbine utilizing a continuously variable ratio hydrostatic drive train between the rotor and the generator. The estimated cost of energy is compared to that of a conventional wind turbine of equivalent rated power. The annual energy production is estimated for the hydrostatic turbine using an assumed wind speed distribution and a turbine power curve resulting from a steady state performance model of the turbine. The initial capital cost of the turbine is estimated using cost models developed for various components unique to the hydrostatic turbine as well as economic parameters and models developed by the National Renewable Energy Lab (NREL) in the WindPACT advanced wind turbine drive train study. The resulting cost of energy, along with various performance characteristics of interest, are presented and compared to those of the WindPACT baseline turbine intended to represent a conventional utility scale wind turbine.

Wind/Hybrid Power System Applications for New England Islands

This paper summarizes a feasibility study of potential wind-hybrid power systems for the islands of New England. The work included the compilation of an inventory of New England coastal islands, a categorization of the islands according to energy related criteria, and an overview of their present electricity supply. It also includes a proposal of wind-hybrid power systems for two selected islands, and an estimation of their technical performance and economic merits.

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.

Wind diesel system simulation : a screening level model

This paper describes a screening level simulation model for wind/diesel systems. It is intended for use to give a quick overview of the possible appropriateness of a wind/diesel system and indicate whether more detailed analysis would be of use. The model was developed for use on personal computers and to trade complexity for ease of operation. The wind/diesel system modeled may include: 1) Wind regime, 2) One or more wind turbines, 3) System electrical load 4) One or more diesel generators, 5) Dump load, 6) Short term storage, and 7) System controller. The model does not consider storage explicitly, but does distinguish between the no storage and minimal storage (power smoothing) systems. This work is based on the more detailed simulation models previously developed at the University of Massachusetts, but uses probabilistic methods rather than time series data inputs. As such it requires only mean and standard deviation of wind speed and load for each month or season. The model functions by assuming that...

Useful Computer Codes for Wind Energy Engineering Applications

At the University of Massachusetts a number of wind engineering computer codes (the “UMass Mini-Codes”) have been developed during the past for educational, research, and design purposes. The purpose of this paper is to present an overview of these codes. A summary description of each of these codes (categorized by groups: data analysis, data synthesis, rotor aerodynamics, electrical, dynamics, and turbine/system performance) is given which contains the overall methods employed, underlying algorithms, and appropriate references. It is expected that these codes will be used for educational purposes, or for general use by the wind energy engineering community.