Inter array cables buried under the seabed connect the wind turbines to each other and to three export cables also buried under the seabed. At landfall the export cables continue as buried cables to the substation in Wallasey. This substation steps up the electricity from internal wind farm voltage (33kV) to 132kV so that it can be fed into the local distribution network operators’ grid, and further on to the national electricity grid.
Each wind turbine is designed to run for approximately 6000 hours each year over 20 years. By comparison, the design life time of a car engine is 20 times less, i.e. only one year if the car is set to run 4,000 to 6,000 hours.
The design of the wind turbines allows for minimum service, but each wind turbine will need a few annual service inspections. In connection with maintenance inspections, service technicians will access the wind turbines by boat. For this purpose an operation and maintenance facility has been located in Liverpool harbour. The operation and maintenance facility will be used as base for the routine monitoring, management and maintenance of the wind farm. The 25 turbines are identical and each wind turbine comprises of a three-bladed rotor of 107m diameter (52m blades and hub) positioned in the front of the nacelle, all mounted on a 66 m tower, which again is mounted on the monopole 17 m above mean sea level. The rotor is connected directly to the gear box in order to transfer the rotational energy to the generator, which transforms the wind energy into clean electricity.
The production from the wind turbines depends upon the actual wind speed. As wind speed increases the turbines' output will increase according to the power curve. The increase can be seen on the power curve for the WTG.
The wind turbines start to generate power at a wind speed of only 4m/s, and level out at 3,6MW at a wind speed of 12-14m/s. When the wind speed exceeds 12-14m/s, the turbine will automatically and gradually pitch the blades out of the wind so as to prevent overload. If the wind velocity exceeds 25m/s, the turbines will disengage for safety reasons.
At a wind speed of 9 m/s, which is the expected average wind speed on the site, a total volume of 80,928 m3 of air is passing through the rotor every second. This equates to almost 100 tonnes of air per second!