Performance optimization of wind turbine rotors for wind farm operation

Abstract

Due to fierce competition on the electricity market, many wind energy related research projects are currently aimed at cost reduction. In order to establish cost reduction, more and more wind turbines are being clustered in (offshore) wind farms. Major drawback of wind farms however, is the energy production loss due to aerodynamic wake interaction between wind turbines. Optimizing wind turbine rotor designs on wind farm scale instead of focussing on wind turbine level, can increase the energy production of a wind farm. In the current project, optimization problems have been investigated that manipulate wind turbine thrust and power curves. The thrust and power curves were manipulated by Matlab's optimization toolbox, using built-in optimization algorithms. The optimization algorithm aims to reduce wake losses, which results in the maximum annual energy production of a wind farm. ECN's wind farm-wake simulation tool “FarmFlow-fast” was used to calculate the annual energy production of a wind farm, for each evaluated set of optimization parameter values. The current project involved two main objectives. First, the FarmFlow-fast model was validated for optimization purposes. This was done by comparing simulation data with power measurement data from the Horns Rev and Lillgrund wind farms. Secondly, the potential of wind turbine performance curve optimization was investigated. This was done by investigating multiple scenarios, in which the increase in annual energy production of a wind farm was calculated as function of the wind turbine thrust and power curves. It is found that FarmFlow-fast is capable to be used for optimization purposes. The most suitable optimization algorithm, concerning time consumption and objective function value decrement, was the “pattern search” algorithm. Unique optimum performance curves were found, depending on the wind farm layout, accounted wind speed and direction ranges and the parametrization and optimization method. Although the potential increase in annual energy production was rather small, the thrust reduction on wind turbine rotors around rated wind speed might as well be an important outcome of the optimization runs. The thrust reduction can result in cheaper wind turbine designs, which might even be a more promising result in terms of cost of energy reduction than the increase in annual energy production. The results of this project contribute to choosing new design parameters for future wind turbine rotor designs, in order to minimize the costs of energy.