The offshore wind farm that is being considered is located around 35km north of the island of Heligoland and 35km west of North Frisian island, Germany. The distance of the wind farm from the mainland is about 40km. The offshore wind farm consists of 80 wind turbines with an installed capacity of 3.6 MW each, capable of producing 288 MW in total. The turbines have a rotor diameter of 120m and are situated in waters between 20 and 25 m deep. They are resting on monopile steel foundations of length 15m and support structures of 21 to 26m length.
The wind farm generates 288MW of power for the functioning of the Railway Power Supply System, the Vertical Lift Bridge, and operates in conjunction with the Nuclear Power Plant and supplies the energy required during the maintenance interventions of the same.

Geometry:
The subsystem comprising of the support structure and the foundation of the offshore wind turbine was chosen for the life cycle analysis. The design configuration with a monopile support structure and the foundation were found to be the best-performing design configuration both in terms of reduced emissions and energy consumption. Moreover, taking into account the site parameters, wind turbines with monopile support structure cum foundation is best suited for installation at water depths of up to 25m.

Fig1. Offshore wind turbine with monopile foundation cum support structure.

Table 1. Dimensions of monopile foundation cum support structure

	Length (m)	Diameter (m)	Thickness (m)
Support structure monopile	40	7	0.04
Steel pile foundation	35	7	0.04

Material Properties

• Young’s modulus- 210 GPa
• Density- 8,500 kg/m3

Maintenance Intervention:
The designed average life span of an offshore wind turbine is expected to be 20 years during which the wind turbine typically performs well before it reaches a critical condition and deteriorates after that stage. On reaching the critical condition the offshore wind turbine needs a major replacement. However, it has been observed that the lifetime of wind farms could increase to 25 – 30 years with proper maintenance strategies.

Intervention	Amount of years occurrence	Frequency per lifetime	Duration[days]
Regular Preventive Maintenance	1	19	1.5
Repairs in foundation and support structure	5	4	7
Wind Turbine Replacement	20	1	60