I worked on outdoor coal-fired boilers in really tough places (Wyoming, high desert of Arizona) and it is not easy keeping those plants running. It is a hundred times worse offshore.
This is a ten year old paper, so reliability has probably gotten better. But it was abysmal in 2012 and the climate in which these machines must operate has not gotten any better.
In fact, with all the Greenie Weenie knickers-twisting moaning about more frequent and much stronger storms, why would they even propose putting windmills in such inhospitable places where you cannot repair and maintain them? Their argument for much more frequent and violent storms tells you that this is lunacy.
Review of offshore wind turbine failures and fault prognostic methods
SECTION II.Failures of Offshore Wind Turbine
Electrical control, gearbox, yaw system, generator, hydraulic, grid and blades are rated (60% of the total failures) as the most common failure components of wind turbines (>1.5MW) in the study of Danish turbines [6] (Figure 2). Those challenges cause extra cost on emergency maintenance, component screening, physical designs and so forth.
A. Electrical Control Failures
Damages of generator windings, short-circuit and over voltage of electronics components, transformers and wiring damages are the common failures of electrical control. These failures are reported as the results of lightning, poor electrical installation, technical defects and resonances within resistor-capacitor (RC) circuits.
B. Yaw System Failures
Yaw control system controls the nacelle rotation to place the blades facing the desired angle. It was reported that the cracking of yaw drive shafts, fracture of gear teeth, pitting of the yaw bearing race and failure of the bearing mounting bolts are all categorized as Yaw System Failures [10]. Icing problem in extreme weather and high vibration level during overload are also claimed as the cause of the failures.
C. Gearbox Failures
Gearbox is usually found in the turbines nowadays. However, it was one of the most frequently damaged rotational components in turbine. The failures are usually wearing, backlash, and tooth breakage. They are claimed as the result of particle contaminations, frequent stoppage and starting and high loaded operation conditions.
Figure 4. Tooth breakage caused by frequent [wind turbine] stoppage and starting.
E. Hydraulic Failures
Hydraulic components are used in many high pressure connections located in pitch, yaw, braking system and gearbox lubrication system. The leakages of these components are called hydraulic failure. Since the offshore turbines are usually located in extreme environmental conditions, the failure may occur during high/low temperature, corrosion, vibration. The reasons behind are claimed as improper installation, poor system design, poor component quality and system abuse. The improper installation rated as 60% of the total failure causes.
F. Blade Failures
Blades are the main rotors of wind turbine and they transfer wind power into up-lifting force by fluid dynamic physical design. Usually, any blade damages, cracks, breakups and bends are said as blade failures. Causes of the blade failures include turbulent wind, out-of-control rotation, lightning and production defects. [4] reported that a broken blade had travelled as far as 1.3km from its tower. Many countries, hence, set up regulations to forbid their civilians to get close to wind farms such as US and Germany.