Lifetime Extension of Wind Turbines

Wind energy continues to be one of the most important resources for renewable energy. New sites are being built at a tremendous speed to decarbonize and electrify the future. Over the past 30 years an enormous fleet of turbines has been built. Currently (2022) there is a cumulative European capacity of 255GW. This exceeds the European Nuclear capacity (151GW), the Solar capacity (159GW) and is equal to the European Hydro capacity (255GW).

This immense fleet of wind turbines has been built over the past 30 years. Some aging turbines have been replaced others have been improved or are still operational. However it is clear that a tremendous amount of maintenance and inspections has to be done to service this fleet.

The usual design lifetime of a wind turbine is 20 years, so what happens when maintenance costs increase and/or innovation brings more efficient turbines? This is where repowering and lifetime extension come into play.

Both go hand-hand until a certain point. In the case of repowering the entire turbine or parts can be replaced (like more efficient blades), however this is limited by the scope of the environmental permit. Replacing granted sites with larger and higher turbine models leads to resistance from the public in regard to expected noise, shade and horizon pollution. Also replacement does not favor the CO₂ footprint of the wind energy sector. So when repowering is not feasible, this is where lifetime extension comes into play.

Through testing, inspection, monitoring and maintenance a directed approach is designed to prolong the lifetime of the turbine and its parts. Most critical parts are the gearbox, generator, hub, blades and structure (tower, bedplate, foundation, etc.).

What damages can be expected?

• Gearbox – fatigue and wear
• Generator – bearing failure, magnet wedge loss, contamination
• Hub – bolt failure
• Blade – fracture, edge crack/corrosion, stuck, pitch failure, lightning damage
• Tower/Bedplate/Structure – fatigue and cracking

Identifying damages

In order to assess the state of the critical parts Kiwa applies various Non-Destructive Testing technologies (NDT).

• Bolts/Anchors: UT, LR-UT, PA-UT
• Bearings/Teeth: MPI, debris/microscopy
• Bedplates and other structural component: MT, ET, microscopy
• Blade: cracks with DRT or PA-UT, thermography, LPS testing, visual

Once the damages have been quantified a maintenance and monitoring program can be determined. This would normally include the application of strain gauges, vibration sensors, periodic inspection and non-destructive testing.

Together with our engineers we team up with your maintenance crew to get the most out of your turbine for the agreed period.

What does Kiwa offer?

Wind turbines have a typical design life of 20 years, affected by fatigue and other damage mechanisms. We help identify and address lifetime management issues in due time. Kiwa has a team of experts with deep knowledge within life management and lifetime extension, and they have during decades developed experience from several energy systems and industries.

We have experts within the different disciplines needed for the evaluation and assessment of lifetime. We integrate our disciplines with the goal to provide the owner a complete decision basis for an informed decision on future steps, such as continued operation, renovation or repowering.