# Browsing by Subject "wind energy"

###### Results Per Page

###### Sort Options

Item Open Access An Empirically Based Stochastic Turbulence Simulator with Temporal Coherence for Wind Energy Applications(2016) Rinker, Jennifer MarieIn this dissertation, we develop a novel methodology for characterizing and simulating nonstationary, full-field, stochastic turbulent wind fields.

In this new method, nonstationarity is characterized and modeled via temporal coherence, which is quantified in the discrete frequency domain by probability distributions of the differences in phase between adjacent Fourier components.

The empirical distributions of the phase differences can also be extracted from measured data, and the resulting temporal coherence parameters can quantify the occurrence of nonstationarity in empirical wind data.

This dissertation (1) implements temporal coherence in a desktop turbulence simulator, (2) calibrates empirical temporal coherence models for four wind datasets, and (3) quantifies the increase in lifetime wind turbine loads caused by temporal coherence.

The four wind datasets were intentionally chosen from locations around the world so that they had significantly different ambient atmospheric conditions.

The prevalence of temporal coherence and its relationship to other standard wind parameters was modeled through empirical joint distributions (EJDs), which involved fitting marginal distributions and calculating correlations.

EJDs have the added benefit of being able to generate samples of wind parameters that reflect the characteristics of a particular site.

Lastly, to characterize the effect of temporal coherence on design loads, we created four models in the open-source wind turbine simulator FAST based on the \windpact turbines, fit response surfaces to them, and used the response surfaces to calculate lifetime turbine responses to wind fields simulated with and without temporal coherence.

The training data for the response surfaces was generated from exhaustive FAST simulations that were run on the high-performance computing (HPC) facilities at the National Renewable Energy Laboratory.

This process was repeated for wind field parameters drawn from the empirical distributions and for wind samples drawn using the recommended procedure in the wind turbine design standard \iec.

The effect of temporal coherence was calculated as a percent increase in the lifetime load over the base value with no temporal coherence.

Item Open Access Energy Storage in Deregulated Market Structures(2009-12-04T17:06:31Z) Morris, GaryWind energy is able to provide electricity with a minimal environmental footprint and is therefore anticipated to play a much larger role in future electricity generation. Although wind is able to provide electricity with limited environmental externalities, it produces the most electricity at night, when there is little demand, and produces the least electricity during the day, when demand is highest. One approach to address this countercyclical production is the implementation of energy storage. The ability to store electricity enables an operator to match electricity production to demand. The focus of this project is to understand the revenue generating capabilities of energy storage in deregulated market structures. A model was developed to analyze the possible revenue generation of utility scale energy storage. The two main categories of energy storage, short-term and long-term applications, as well as two deregulated markets, ERCOT and CAISO, were evaluated. The objective of the analysis was to determine the energy storage application and market structure generated the most value. The model integrated the price of electricity and ancillary services with wind production data to determine the revenue generation of each application and each market. The results indicate that annual revenue generation between the different energy storage applications and the different markets is very similar. Although the storage applications provided similar revenues, the rate of return for each application was very different. The short-term application offered much higher rates of returns due to significantly lower upfront capital costs. The short-term application rate of return consistently exceeded the hurdle rate while the long-term application did not. Therefore, short-term energy storage is the only recommended investment. Additionally, due to the operation parameters of the model set to maximize revenue, the production curve did not change to match demand.Item Open Access Phase Coherence in Wind Data and Simulation(2014) Rinker, Jennifer MarieNovel wind turbine designs are deemed acceptable through a simulation-based certification process that involves generating a synthetic wind record and using it as an input to a computer model of the turbine. Naturally, whether the simulation loads reflect the loads that the turbine would actually experience depends on the accuracy of the wind turbine model and, more importantly, on the accuracy of the method used to generate the synthetic wind record. The simulation methods that are commonly used for this purpose are spectral-based and produce Gaussian, stationary random fields. These methods prescribe a power spectral density (PSD) of the wind velocity, which fixes the magnitudes of the Fourier components, then assumes that the Fourier phase angles are independent and uniformly distributed. An inverse Fast Fourier Transform (IFFT) is then used to transform the wind velocity field to the time domain.

This thesis applies the concept of phase coherence---i.e., Fourier phase angles that are not independent---to the stochastic modeling and simulation of wind velocity fields. Using a large dataset available from the National Wind Technology Center (NWTC), a joint distribution is characterized for the mean wind speed U, turbulence σ

_{u}, Kaimal length scale L, and a metric for the degree of phase coherence in wind data, R. The correlations between these four parameters, the vertical height, and another phase coherence parameter are presented; only U, σ_{u}, and L have any significant degree of correlation. The joint distribution is used to generate synthetic wind records, which are then compared with measured data that have the same parameter values. For data with low to medium coherence values, the synthetic records have a similar qualitative appearance to the data. For high levels of phase coherence, the records simulated with the proposed model were qualitatively different from records with the same parameter values due to the variation of the phase difference spread in the spectral domain. Lastly, the importance of correctly modeling phase coherence is demonstrated by using the data and the synthetic records as inputs to a single-degree-of-freedom (SDOF) oscillator and comparing the peak response statistics and damage equivalent loads (DELs).Item Open Access The Effect of Utilities Regulation on the Economics of Wind Energy in North Carolina(2009-04-24T17:19:21Z) Vale, SusannahIn order for wind energy to be feasible in the sounds of North Carolina, it must be economical. The price paid for electricity produced by wind must be sufficiently high to translate into a reasonable rate of return for developers and investors. Countervailing tensions on regulators, utilities and the renewable energy generators function to depress the price of wind energy. Lawmakers have passed utility regulations in order to improve the economic situation of wind energy projects by either diminishing the initial capital needed, lowering the risk or ensuring a fair price. The two primary utility statutes affecting the economics of wind energy in North Carolina, the federal Public Utility Regulatory Policies Act of 1978 and North Carolina’s Renewable Portfolio Standard of 2007, have thus far been ineffectual. If the North Carolina legislature wants to develop wind energy in their state, it should amend NC REPS to add a wind energy percentage requirement to put it on equal footing with solar. Alternatively, adding externalities into the cost calculation would make wind one of the most economical of all the electricity options.