There is very little experience in operating offshore floating wind farms. Only a few floating offshore wind farms have been installed and have an operational track record. The Opex costs for the systems are high due to the lack of experience.
During the lifetime operations of the floating wind system there will be a requirement to replace a number of major nacelle components, such as the blades, gearbox, generator and electrical components.
As the structure is floating, replacement of any components, on a standard tower, will be very weather dependant. The relative motion between the crane hook on the support vessel and the component on the floating structure will be critical to the operation. These operations will have to take place in flat calm conditions to avoid any risk of damage.
This is not a commercially acceptable situation as any downtime on the system will result in a loss of generating income. The system could be out of service for a number of months in the winter in the event of a critical component failure.
The systems should be designed from the beginning to minimise the Opex costs. The Reliability, Availability and Maintainability (RAM) of the system should be assessed and then the components and operating procedures designed to minimise the costs involved and maximise the generation capacity.
Existing floating wind systems require a high lift crane vessel to remove the heavy generator/gearbox from the nacelle at the top of the tower.
With a weight of 500Te, this lifting operation would involve a very expensive heavy lift vessel.
The vessel motions between nacelle and crane hook would make this a very weather dependant operation.
With the Spintral system, as the generator is located below the main deck in the machinery room then it can be easily be handled on and off a support vessel.
The generator would be disconnected from the gearbox and then lifted on a handling system.
This could typically be an overhead gantry system that would lift the generator and then transfer it through the aft access door to suspend it above the support vessel.
The generator would then be lowered onto the support vessel and shipped onshore for repair.
Installing a replacement generator would be the reverse of the procedure.
The operation would not be very weather dependent as it would take place in the lee of the centre float in relatively calm seas.
The gantry system could incorporate active controlled winches to manage the lowering/lifting operation to minimise impact risk.
Installing and removing blades normally require the use of a specialised high reach crane vessel.
For floating wind applications, this operation is very weather sensitive due to the relative motion between the crane vessel and the floating structure.
The Spintral system provides a handling winch on the main deck. The wire is routed through the tower centre to enable the blades to be lowered down into the horizontal position on the floating structure or support vessel deck. The blades can be removed using a standard vessel and crane.
A gantry can be provided on the nacelle to enable other heavy components to be handled using the winch.