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Extending the Lifecycle of Wind Turbines with BladeSave

A good quality, modern wind turbine will generally last for 20 years, although this can be extended to 25 years or longer depending on environmental factors and the correct maintenance procedures being followed. However, the maintenance costs will increase as the structure ages.

Wind turbines are unlikely to last much longer than this because of the extreme loads they are subjected to throughout their lives. This is partly due to the structure of the turbines themselves, since the turbine blades and the tower are only fixed at one end of the structure and therefore face the full force of the wind. Of course, as the wind speed increases, so do the loads that turbines are subjected to. This can reach levels almost 100 times greater than the design loads at rated wind speed, which is why many turbines are designed to shut down to protect themselves at higher wind speeds.

Factors That Determine the Lifespan of a Wind Turbine and What Damages Wind Turbine Blades?

One of the primary factors that determine the lifespan of a wind turbine are the environmental operating conditions faced by the wind industry. These conditions are site specific and include average wind speeds, turbulence intensities and (for offshore wind farm operators) the cyclic loading of foundations, jacket structures, and monopiles caused by waves.

In addition to these environmental factors, there are the usual concerns for any structure based around fatigue failure from use over the lifespan of the asset. These include a variety of different parts and components, from wind turbine blades to wiring and hydraulic systems.

Wind turbine blades need a special mention, as they are particularly prone to damage. As a moving component, the rotor blades are subject to higher levels of loading and fatigue, and can also suffer damage from birds or other objects striking them as well as the impact of high wind speeds or lightning strikes.

Can their Lifetime be Extended?

The lifecycle of a turbine can be extended through careful monitoring and maintenance. This requires the condition of the asset to be assessed and compared with the expended lifespan of the turbine, based upon the expected loads and fatigue as well as environmental factors for the wind energy site.

These assessments will determine whether continued operation is possible and when any components may need replacing to extend the life of the overall structure. This is known as a lifetime extension assessment and includes both theoretical and practical analysis, such as on-site inspections and the evaluation of design load data.

A status report will detail the maintenance requirements, from which an accurate estimate of the cost of wind turbine lifetime extension can be generated. This allows operators to determine the continued operational costs and risk of failure against the cost of replacement or even decommissioning. The report can also be used to apply for insurance policy extensions and is also often required by service providers at the end of a turbine’s design life.

How Often Do Wind Turbines Require Maintenance to keep them in Operation for Longer?

As mentioned above, the actual amount of maintenance required to keep a wind power asset in operation will vary depending upon factors including specific operating conditions and the materials used. However, wind turbines generally require preventative maintenance check-ups two or three times per year. The need for these check-ups may need to increase as the turbine ages and also requires more maintenance to keep it in operation.

What are the Challenges to Maintaining Offshore Wind Turbines?

Offshore power generation assets face their own set of particular challenges to maintain. The challenges faced by onshore assets are often exacerbated by the offshore operating conditions while also adding their own specific problems. These challenges include corrosion, erosion and biofouling alongside the usual materials, fatigue and wind-based factors.

As the reliance on offshore renewable energy sources grows, it will become increasingly important to address these challenges to maintain operational availability.

What Techniques are used to Monitor, Inspect and Maintain?

Analytical Assessment

In order to maintain safe operation, it is important to establish the structural stability of wind turbines. Safety devices, braking systems and turbine control systems all require testing in order to verify the structural stability but there is also a need to compare the design conditions loads to the actual loads the turbine has been exposed to. This loading information can be obtained from computer simulations representing design conditions after type testing alongside environmental operating conditions.

The environmental operating conditions include site-specific wind conditions, such as average wind speeds, turbulence, and any extreme weather events. These are monitored over the previous 20 years in order to calculate estimated loads during operation. Wind farms may require each turbine to have its own set of data. This data is then assessed alongside technical documentation for the turbine. This technical documentation includes that relating to turbine construction, commissioning, operating permits, operating and yield data and wiring and hydraulic diagrams. In addition, repair, inspection and maintenance reports are also assessed. A technical report is also required to document the rotor blade condition on an annual basis.

It is the responsibility of wind farm operators to provide the relevant documents and arrange assessments on time. In some instances, it is possible to obtain replacement documentation from a manufacturer, however, if the manufacturer is no longer available it is possible to use experience to compare a turbine with others.

These analytical calculations are used to create a statement citing any immediate actions that are required for continued operation, along with those that will need to be scheduled for a later date, such as the replacement of parts or a full inspection.

All of these simulations need to be backed up by on-site inspections. This has traditionally been undertaken in-person by an inspector, but is increasingly being done remotely using robots and technologies such as the BladeSave system.

Physical Monitoring

The condition of a wind turbine is assessed through an on-site inspection that is informed by the analytical assessment. This allows for specific weaknesses, defects or potential problems to be checked. Physical monitoring also looks for unusual wear or damage to components and equipment. Load-bearing and safety critical components require particular attention, with some types of wind turbine having their own design flaws or production issues that could lead to premature defects. 

Physical checks are performed on the turbine blades, the supporting structure and the foundation to look for signs of corrosion and cracking or to audibly listen for suspicious or unusual noises from the gear and bearing assemblies.

Significant damage can lead to the immediate shutdown of an asset, often incurring costly downtimes ahead of maintenance or repair. However, these checks tend to locate minor damage caused by corrosion, fatigue or weathering, allowing the defect to be fixed before it gets any worse.

Different parts require different levels of monitoring and maintenance, with turbine blades and cables requiring higher levels of inspection and care.

Physical monitoring also refers to monitoring the surrounding environment, and how this may influence the turbulence and wind speeds used in the analytical assessment.

How Much Does it Cost to Maintain a Wind Turbine (Onshore and Offshore) per Year?

The cost of operation and maintenance (also known as O&M costs) make up a sizeable proportion of the total annual costs of a wind turbine. These costs vary depending upon the age of the asset, but average out at around 20-25% of the total levelised cost per kWh produced over the lifetime of the turbine. For a new turbine, these costs may be only 10-15%, but can increase to 20-35% towards the end of the turbine’s lifecycle. Manufacturers are working on new designs to help reduce these costs by creating turbines that require fewer service visits and, consequently, less downtime.

Operation and maintenance costs cover the following expenses: insurance, regular maintenance, repair, replacement parts and administration.

Some of the actual costs associated with these expenses can be estimated, such as insurance and maintenance, since it is possible to obtain standard contracts covering much of a turbine’s lifecycle. However, costs for repair and replacement parts are more difficult to ascertain as they can be influenced by the age and condition of the turbine, frequently increasing as the asset ages. In addition, as very few turbines have reached the end of their life expectancy, there is little data on these costs later on the lifecycle, while many older turbines are smaller than those currently on the market.


Wind farm operators are faced with business decisions as their assets age – whether to continue operation, repower or to decommission. These decisions are affected by the physical condition compared to the theoretical lifetime of the turbines. On-site inspections and monitoring tools help evaluate these factors to ensure wind farms operate safely within their design lifetime. This lifetime can be extended or shortened, depending on damage caused by environmental factors and fatigue.

Certain components, such as the blades, require extra monitoring and maintenance and technologies, such as BladeSave, can simplify this process for the operator, allowing for the continual remote monitoring of wind turbine blade life.

If a wind farm is operated within the parameters of the design lifetime and conditions and maintenance is carried out regularly, they can operate beyond the design life. In many cases, the wind conditions at a site create lower loads than anticipated, meaning that turbine structures are free from significant damage. In these instances, repairs are minor and relatively inexpensive while a lifetime extension assessment could determine that a turbine can continue to operate beyond the original design life.

Wind Turbine Monitoring and Management at TWI

TWI has a wealth of experience with wind turbines, including addressing the particular challenges of offshore assets, such as the NDT inspection of offshore jacket foundations. We have also been part of the BladeSave consortium to develop a condition monitoring system for wind turbine blades and worked on the phased array ultrasonic testing of blade roots.

We provide independent expertise and advice related to materials, fabrication and inspection to offer solutions to the wind power industry and you can find out more about our services in this area here.

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Wind Turbine Blade Condition Monitoring with BladeSave

The joint efforts of the BladeSave Consortium, formed by Renewable Advice LtdTWIEmergya Wind Technologies B.V.Halliburton and ASSIST Software have resulted in what proves to be a successful project. Using a combination of the partners’ expertise in structural health monitoring (SHM), fibre optic sensing technology, and management software incorporating risk-based blade data analysis, the BladeSave system represents an innovative solution for the wind energy industry.

Wind energy is one of the fastest growing sectors in the world’s energy markets. However, wind turbine blades are susceptible to fatigue failure and adverse environmental effects. Once a fatigue crack has initiated, it will propagate, if it is not detected and mended in due time. This could be avoided by employing a condition monitoring system meant to constantly asses blade status. This way, blade flaws can be detected at an early stage and dealt with immediately, preventing, therefore, potential costly blade replacements.

The BladeSave system features an innovative design, which offers multi-sensing capabilities including acoustic emission (AE), vibrations and strain, achieved with Fibre Bragg Grating (FBG) sensors. This all-optic design brings the benefits of system’s immunity to static electricity, EMI noise and lightning. BladeSave also combines a blade management software (windmanager) linking the data from inspection and maintenance to the SHM data, providing, thus, a comprehensive solution for wind turbine blade monitoring, repair and management.

The solution offered by BladeSave has been thoroughly tested and the results of the 3- month try-outs in a wind turbine from project partner EWT have been more than satisfying. During the testing period, the system has obtained long-term operational profiles described by processed SHM data including AE, vibration and strain. The BladeSave system has been tested for ice accretion on blade surfaces with simulated mass. The results showed evident detection capabilities.

The final stage of this project, consisting in the ultimate test for a wind turbine blade, entailing destructive testing, will be conducted at TWI. For this testing, controlled cyclic loading will be applied repetitively to gradually simulate blade crack initiation and propagation. In order ensure the accuracy of the results and the efficiency of the BladeSave system, it will be installed to monitor the process, in tandem with a commercial system. BladeSave is expected to successfully demonstrate its capabilities to detect cracks in early stages and bolster upkeep dynamic.

The BladeSave project has received funding from the European Union’s Horizon 2020 programme under grant agreement No 760353.

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How Can Vibration Help with Structural Health Monitoring

Vibration is a physical phenomenon exists in operational rotating machineries and structures, even when they are in good condition. There are numerous sources of vibration, such as rotating shafts, meshing gear-teeth, rolling bearing elements, rotating electric field, fluid flows, combustion events, structural resonance and angular rotations. Because of its ubiquity, vibration is highly applicable for investigating the operational conditions and status of rotating machinery and structures.

Vibration can be measured through various types of sensors. Based on different types of vibrations, there are sensors designed to measure displacement, velocity and acceleration, with different measuring technologies, such as piezoelectric (PZT) sensors, fibre optic (FO) sensors, microelectromechanical sensors (MEMS), proximity probes, laser Doppler vibrometer and many others. Specially, FO sensors are drawing more attentions as they are passive and provide excellent noise immunity in harsh environment. In BladeSave system, the vibration is captured using this type of sensors.

To analyse vibration signals, one can extract information from both their time series as well as frequency spectrum using Fourier Transform. Vibration signals are usually up to 20 kHz, except for certain vibration resonances that can reach beyond that. In practice, the sampling rate should be carefully chosen, to make sure that the bandwidth containing frequencies of interest are captured. Additionally, the recording length for one measurement should be at least several periods of the lowest speed of the structural vibrating mode.

Ice detection of wind turbine blades is a typical usage of vibration for structure health monitoring. Under normal condition, the blade vibrates in certain modes and a fixed structural natural frequency. However, if the mass of the blade is changed due to ice-accretion, the natural frequency will shift with regard to the added extraneous mass. Below is an example where simulated mass was added on a wind turbine blade, and vibration signals were captured to validate the change of blade vibration pattern.

Figure 1 – Blade with simulated weight
Figure 2 – The frequency shift with added mass on the blade

As shown above, the blade’s natural vibration frequency shifted to lower range with added mass. All in all, vibration analysis is widely applied in condition monitoring and structural health monitoring, as it has advantages such as real-time reaction to the change of health conditions, supports remote condition monitoring, well-established processing and signal analysis methods/algorithms for predictive maintenance and supported by various sensors commercially available for different operational conditions. However, it lacks the ability to conduct fault localisation and it’s difficult to monitoring crack propagation on the structure. That’s where Acoustic Emission (AE), a high frequency elastic wave beyond audible frequency range can be useful. BladeSave is a complete FO system that combines the strengths of AE, vibration and strain, offering full monitoring of the wind turbine blade health. 

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Webinar on the Offshore Wind Energy Challenges

TWI Senior Project Leader, Ben Robinson, recently held a compelling webinar entitled ‘Materials Challenges in Offshore Wind’.

The speaker presented detailed information on the design and operation of offshore wind turbines, insisting on the challenges related to corrosion, fatigue, lightning strikes, erosion and biofouling.

Ben Robinson provided an interesting presentation, backed by relevant images and graphics, making the content accessible and easy to understand.

You can access the full webinar and dive into the captivating world of wind energy here:

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Why Acoustic Emission Structural Health Monitoring is the Future

Renewable Advice Ltd has been working in the field of blade inspection and repair since 2008. We have seen, first hand, the scale of damages and destruction that can result from the lack of regular inspection and subsequent maintenance of wind turbine blades. 

The challenge is normally one of budgets. A blade maintenance budget is capped and covers both inspection and repair. Therefore, most owners want to maximise the amount of budget available for blade repair as this has the greatest impact on blade and turbine performance. 

With conventional blade monitoring, strain gauges are employed to measure strains and therefore loads in the blade. This information is utilised to regulate blade pitch control to reduce loads. These systems will only detect a deviation in strain from a crack once the crack is sufficiently large. ‘Sufficiently large’ is a major structural repair or if not detected in time, catastrophic failure of the blade. 

Blade Save’s unique ability to ‘listen’ to the noises within the structure of the blade means that it can detect high frequency sounds that are generated when a crack forms and propagates. This results in early detection of a defect, meaning that the repair is smaller and turbine downtime is minimised. Smaller repairs simply mean that the maintenance budget goes a lot further.

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BLADESAVE System Installation on Real Wind Turbine

The installation of the BLADESAVE System took place at EWT wind turbine in the Netherlands.

Strain patches, accelerometers and AE sensors were installed in various location inside the blades. AE sensors were installed in LE, TE and blade shell locations. There were 6 AE sensors and 4 Strain sensors in each blade and one blade had additional 3 accelerometers. All AE sensors within blade were made as one array. The furthest away point for the installation of AE sensors was 8m; of accelerometers was 10m. Blade shell sensors were installed on the pressure side.

SmartSonic instrument and BladeSave laptop were installed in the specially made cabinets in the hub, SmartScan was installed in the pre-existing cabinet. The entire system was tested and right now is in production sending LIVE data.

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Inside of a Wind Turbine

Besides inspection and testing, right through to structural repair, serial defect resolution and long term blade service packages, BLADESAVE System will provide a complete monitoring system of the blade that can optimize the efficiency of wind turbines and provide performance peace of mind.

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