In the early days of the wind power industry, a drive train was typically of modular design and consisted of an assembly of individual components from various suppliers, each with a proven industrial track record in applications outside wind. That approach was more or less enforced on the wind turbine pioneers. The wind power industry was nowhere near large enough to command special treatment from suppliers of off-the-shelf parts. Wind turbine designers had to take what was available in the form of gearboxes, generators and couplings.
During the 1990s the demand level of the wind industry became significant and the suppliers of those key major components that had their origins in other industries, notably the gearbox and generator, began to take more notice of the special requirements of the wind industry. This was both on account of technical challenges from the variability of wind loading and market growth.
The modular drive train is still in use today, but is often more specialised than in the past. Special main rotor bearings integrated with the gearbox and integrated castings for the gearbox and generator are examples of the greater overall integration of the drive train seen in some current designs, such as the Vestas 3 MW -- and in this example not without problems (Windpower Monthly, June 2008). More radically different drive trains have been evolving in recent years (main story).