Recent developments in wind turbine design

Abstract

A critical review of wind turbine performance shows that outputs have steadily increased with the increases in wind turbine size. This article examines the increases in wind turbine size that have taken place and discusses the design options that have been used. 40 years ago wind was a nascent technology, but a number of large megawatt size machines, mostly government funded, were being constructed or planned. However, incentives in California and Denmark encouraged the construction of small wind turbines in large numbers and these evolved from the kilowatt size to the megawatt size and the trend is towards ever-larger machines. Focusing on performance issues and rating philosophy, the article shows that recent moves towards lower power ratings per unit area of rotor (the specific rating) have masked substantial reductions in wind turbine costs and given a misleading impression of increases in productivity. The article concludes with a brief summary of the characteristics of the largest wind turbines currently available, and points to an increasing preference for variable speed designs and a continuing quest for larger machines.