Calculating the power of wind turbines with the blade element momentum theory

Abstract

Purpose - Conversion of a FORTRAN program of the Blade Element Momentum Theory (BEMT) into an Excel program and to show how Excel (with the Solver) can be used to optimize the geometry of the blade geometry (pitch angle, taper ratio, number of blades). --- Methodology - Literature review, work with fundamental wind energy equations, spread sheet programming. --- Findings - Various free tools are available to calculate the aerodynamic power output of wind turbines. However, a spread sheet opens up all methods and equations and offers easy access to check and change the code and to adapt to a given problem. Cone and axis angle are usually parameters to be freely chosen, because classical Horizontal Axis Wind Turbine (HAWT) have 90° cone angle and 0° axis angle. Beyond the fundamental CP-lambda curves also the curve power versus wind speed is of importance including stall behavior of the plant. --- Research Limitations - Although the aerodynamic coefficients are from 2D measurements they can be used successfully in a quasi 3D setting. Realistic results require the lift coefficient to be known well beyond the stall angle of attack. --- Practical Implications - The BEMT is made available via a spread sheet including optimization.