"Applying the 9.5MW turbines means 16 fewer machines, plus their associated substructure, cables and installation costs. The individual substructure and turbine Capex and Opex are essentially the same, but there is modest AEP penalty at project level," Andersen said.

"in 2009, when offshore wind project Capex was very high, the total Capex saving of deploying fewer higher-rated turbines would have been modest. But now that it is much lower overall, the relative share of installation is substantial, and so has a much larger positive impact on LCOE."

Lean production

In August 2013, Windpower Monthly reported from Lindø on the building of a V164 prototype. Assembly was taking place in a largely empty former shipyard hall, a makeshift facility with a rough concrete floor and temporary steel sheets supporting the massive prototype assembly structure. Today’s multiple extensively upgraded halls dedicated to V164 serial production mark a sharp contrast.

Early days… The company's production facilities have changed a lot since this V164 prototype was made in Lindø in 2013

All components and sub-assemblies arrive by road in the factory warehouse, where they are checked and registered. Some critical components, such as the huge dark-blue coated gearboxes, are fitted with accelerator sensing devices. These record all acceleration forces imposed on the product during transportation and handling, and from manufacturered product to the installation of complete nacelles in a wind project.

The vast assembly hall is subdivided into a left part part for large components and sub-assemblies, and overhead cranes for internal hoisting, with the right part reserved for nacelle completion.

A key characteristic is a lean production process, still in development, based on Japanese Kaizen principles first developed by Toyota, and which includes multiple temporary fixed "tack" positions for the nacelles until completion. An air-conditioned tent is dedicated to creating a controlled environment for main shaft assembly. Individual main shafts are put inside in vertical position for shrink-fitting the largest front-bearing inner ring, followed by hoisting-in and lowering the cast housing over the shaft. The next step is shrink-fitting the rear-bearing inner-ring plus mounting a locking ring. The assembly process is finalised by 24-hour flushing with special oil to remove any metallic particles and other impurities.

"We decided on an oil-lubricated main shaft with oil filtration for optimal lubrication performance and bearing life, and minimal bearing pre-load variations during operation," said Andersen. "Full main shaft units can be exchanged without having to remove the rotor, and other drivetrain main components can also be individually replaced."

V-164 nacelles are huge viewed from the outside, and spacious and service-friendly inside. An unusual design feature is the upside-down mounting of the yaw motors inside the tower’s top section. It enables easy service access from an intermediate service platform, and more space with fewer obstructions inside the nacelle.

Continuous adjustment

Proven in many generations of Vestas turbines since the V27-225kW model is the yaw brake system comprising opposing steel and Teflon rings, and multiple spring-loaded friction pressure points. The solution is designed to last 25 years and enables continuous rotor adjustment to wind direction changes.

A distinct design achievement is the compact "closed" hub for enhanced stiffness, which incorporates two approximately 700kg pitch actuators for each blade, individually removable with the aid of a telescopic inboard crane. The pitch bearings feature 4.6-metre bolt-circle diameter, which is large compared with "only" 4.2 metres for the 8.5-metre longer blades of the Adwen AD 8-180 turbine.

The V164 is equipped with load-based individual pitch control (IPC). "Blade root loads are continuously measured during each rotor revolution and used in the control of the turbine," explained Andersen.