Whitepaper

Ice detection to optimise your wind turbine

Learn how you can increase the yield of your wind turbine using a precise ice detection

Ice formation on wind turbines has a relevant influence on operational management in the cold season. In addition to reduced yield due to changed aerodynamic properties, the safety of the system and its surroundings is a key issue.

In this whitepaper you will find out why precise ice detection is relevant, the different solutions for ice detection and how they differ and the benefits by using an ice detection system.

One thing is certain: Precise ice detection and temperature measurement means more yield for your wind turbine..

We show you exactly how you can achieve this with your wind turbine in our whitepaper. Therefore, we summarise the results of some relevant studies so that you can get a clear picture.

Simply download the free whitepaper (21 pages)

We will address the following questions in our whitepaper ice detection:

Wind energy has emerged as a pivotal player in the global transition towards sustainable power sources. As wind turbines stand tall and harness the power of the wind, they are not without their challenges. One significant challenge that engineers and operators grapple with is the impact of lightning strikes on these towering structures.

Lightning strikes bring a unique set of challenges for wind turbine operators. The intense heat generated during a strike can compromise the structural integrity of various components. From blades to towers, being vigilant about potential damage is crucial for ensuring the safety and longevity of the turbines.

Beyond the immediate effects of a lightning strike, operators need to be aware of a subtler adversary – blade erosion. The heat from lightning can cause erosion and pitting on the turbine blades, affecting their aerodynamic efficiency over time. Regular inspections become a frontline defense to spot and address this silent challenge.

The intricate electrical systems that power wind turbines are susceptible to the impact of lightning. High currents and voltages can damage critical components, leading to potential malfunctions. For operators, understanding the vulnerability of these systems is key to minimizing downtime and maintenance costs.

With the combination of lightning’s heat and turbine materials, operators must be attuned to the risk of fires. Establishing robust emergency response protocols is not just a safety measure for the turbine but also for the surrounding areas. Swift action can make a significant difference in minimizing damage and ensuring the safety of both equipment and personnel.

Operators know that downtime is the enemy of productivity. Lightning-induced damage means not just repairs but also a potential dip in energy production. Efficient planning and proactive maintenance strategies are vital for minimizing downtime and keeping the turbines operational.

What can be done to minimise the risks of lightning strikes on wind turbines? There are various possibilities – we present three strategies below: monitoring tools and early detection, investing in lightning protection systems and adapting environmental practices.

In the world of wind turbine operation, knowledge is power. Implementing effective monitoring and detection tools can provide operators with early insights into potential lightning strikes. Early detection allows for timely assessments and proactive interventions, helping to keep turbines operational and reducing the overall impact (i.e. Lightning detection system).

For operators, investing in reliable Lightning Protection Systems (LPS) is a strategic move. These systems, including lightning rods and grounding solutions, act as a shield against the impact of lightning strikes. Well-designed LPS not only protect the turbines but also contribute to overall operational reliability.

Wind turbine operators often find themselves in ecologically sensitive areas. Understanding the environmental implications of lightning strikes, especially the risk of fires, underscores the importance of responsible and sustainable practices. Balancing energy production with environmental considerations is a delicate but necessary task.

As wind turbine operators navigate the complexities of their role, understanding and addressing the challenges posed by lightning strikes is essential. By embracing proactive maintenance, investing in monitoring technologies, and implementing robust Lightning Protection Systems, operators can not only weather the storm but also ensure that the turbines they oversee continue to generate clean, sustainable energy for years to come.

There are two main solutions for rotor blade heating established by wind turbine manufacturers (OEMs) on the market:

• hot air heating inside the rotor blade
• electro-thermal heating elements laminated in the blade surface

With this method, a heater-fan unit creates an air flow in specific channels in the rotor blade. The hot air passes by the leading edge, warms up the shell material to the blade surface above 0 °C and allows to thaw the ice layer. The same device can also be used as a de-icing system.

• enables continuous operation
• prevents ice accumulation

This method uses electro-thermal heating elements, which are embedded inside the rotor blade or laminated in the blade surface layer. This technology not only allows continuous operation, but also effectively prevents ice accumulation.

The operating strategy of the rotor blade heating plays a key role in both systems. This should be taken into account to optimize efficiency, reduce heating costs and prevent overheating and damages due to overheating.

Different OEMs* have developed different approaches to rotor blade heating to meet specific requirements.

Enercon’s technology combines an ice detection system with hot air circulation inside the rotor blades for efficient de-icing. The duration of the de-icing process depends on the ambient temperature and wind speed. As soon as the process is complete, the turbine can be restarted with ice-free rotor blades. At sites with minimal icing risk, the system allows de-icing to be carried out while the turbine remains running.

Key design features**

• Energy consumption between 46kW and 225kW
• first prototype in 1996
• more than 3000 blade heating systems installed worldwide

The Nordex system consists of an ice sensor and electrothermal heating mats (underneath the blade surface) at the leading edge of each rotor blade. The sensors continuously monitor ambient conditions and report the status to the wind turbine’s operational management system.

If icing conditions appear, the system offers two different options:

• stopping the turbine to protect structural integrity or
• removing the accumulated ice via the Nordex Advanced Anti-Icing system (AAIS)

Siemens Gamesa relies on a blade heating system** with an ice detection system, blade heating elements (integrated into the blade surface at the OEM) and a system to control the de-icing strategy.

Siemens Wind Power De-icing Strategy

•  ice detected (through power curve deterioration, ice detection sensor or low toque ice detector)
• the turbine is stopped in static or idle mode (0-2 Rotor rpm)
• the nacelle yaws so the rotor is in “back-wind” or in “safe angel of rotor disc vs. nearby objects”
• De-icing is activated on all three blades
• After x min, the nacelle yaws back into the wind
• Once the turbine is producing again, de-icing is deactivated

Vestas offers various solutions for sites with cold climates. The Vestas Anti-Icing System™ combines several independent heating elements and levels, which – according to Vestas – enable anti-icing measures tailored to the respective icing event.

Key design features

• Individual powering of heating elements to secure equal power distribution where it is needed
• Compatible with Vestas Ice Control (optional feature of the Vestas SCADA system that orchestrates the standard yawing and pausing functionalities of the turbine with different ice mitigation actions)

In addition to manufacturer solutions, there are various providers who offer retrofittable solutions. You can find more details in our white paper on blade heating.

Source (if there is no link in the text):

**Charles Godreau (2022): Tackling Icing on Wind Turbines with Ice Protection Systems, Current State -of-the-Art and Future Research, NERGICA, IGW Wind Industry Stakeholder Meeting

*** Will heat be the winner in de-icing turbine blades? | Reuters Events | Renewables. (o. D.). Abgerufen am 20. Oktober 2022, von https://www.reutersevents.com/renewables/wind-energy-update/will-heat-be-winner-de-icing-turbine-blades & Siemens Gamesa. (o. D.). Onshore technological solutions. Abgerufen am 17. September 2022, von https://www.siemensgamesa.com/en-int/-/media/siemensgamesa/downloads/en/products-and-services/onshore/brochures/siemens-gamesa-onshore-tech-solutions-en.pdf

In winter, especially in northern regions or colder regions (so-called cool climate regions), wind turbines are exposed to snow, ice and frost. Icing can significantly impair the performance of wind turbines. Intelligent de-icing systems minimize downtimes and thus yield losses.

Anti-icing systems can be divided into two main categories: Anti-icing systems (anti-icing systems) and De-icing systems (de-icing systems). Anti-icing systems prevent ice from accumulating on the rotor blades, while de-icing systems remove an existing layer of ice from the rotor blade surface.

Anti-icing systems are those that protect the wind turbine from icing. Specifically, this means that anti-icing systems prevent the formation of ice on the rotor blade surface. These systems can be divided into active systems, such as electronic heating elements in the rotor blades or hot air heating, and passive systems, such as special coatings, black paint or chemicals.

In contrast to de-icing systems, wind turbines can remain in operation as ice formation on the rotor blade surface is prevented.

De-icing systems are de-icing systems that remove an existing layer of ice that has formed on the rotor blades. They can also be divided into active systems, such as electronic heating elements in the rotor blades or hot air heating, and passive systems. However, the system must be stopped either manually or automatically for de-icing. Once the rotor blades have been checked and classified as ice-free, the affected wind turbines can be put back into operation.

Whether an active ice protection system is used as an anti-icing or de-icing system depends largely on the heating control strategy used, which in turn depends on various operational constraints, such as the permission for turbines to rotate with ice on the blades, operating restrictions for wind turbines, etc.

Read more about different heating control strategies in our whitepaper – Blade heating.Whitepaper Blade Heating

Wind turbines are designed to operate for 20 to sometimes even 30 years. During this time, they should deliver the maximum energy yield reliably and with the highest possible technical availability.

However, icing can significantly impair the performance of wind turbines in many respects. These include

• Downtimes that interrupt operation,
• yield losses,
• damage to the turbine itself,
• jeopardizing the safety of the service team and other people due to ice fall and ice throw,
• shortened service life due to increased loads on individual components and
• high costs for repairs.

You can find more information on the risk factor of icing in our blog article Dangers and risks due to ice formation on wind turbines.

The need for blade heating depends on various factors, such as location, weather conditions and turbine size. A good indicator is the loss of revenue (i.e. how much of the annual energy yield is lost due to icing of the rotor blades and the associated downtimes).
As a rule of thumb, the following losses justify the integration of a blade heating system:

• 3-5% AEP losses – when building a new wind turbine
• >5% AEP losses – for retrofitting existing turbines (due to the higher cost of retrofitting blade heaters)

In order to optimize the performance of a wind turbine, it is crucial to detect icing at an early stage and react with appropriate measures. Continuous monitoring of the rotor blades, whether with or without automatic restart, can be a decisive factor here. Ensure that your system is protected against icing in good time.

As part of a project (Meteotest (2021), Comparison of four detection systems of rotor icing installed on the same turbine, VGB Research Foundation, Project 401), a comprehensive field test was conducted from 2016-2020 in Stor-Rotliden, Sweden. The aim was to install all four established blade-based ice detection systems (IDS) from Polytech (former fos4x), Wölfel, Weidmüller and eologix on the same Vestas V-90 and comparing them over many icing events (none of the four IDS controls the WT during the field test).

Efficient operation of wind turbines under icing conditions requires accurate detection of icing, both in terms of timing and severity. The four different IDS detect rotor icing from the inside or outside of the rotor blades:

• The IDS from Polytech (former fos4X), Wölfel and Weidmüller detect rotor icing based on changes in the frequency spectrum of the blade vibrations – these are also referred to vibration-based ice detection systems (VBS)
• The eologix system detects rotor icing based on the electrical impedance directly on the rotor blade surface

eologix – www.eologix.com

eologix offers (retrofittable) sensor systems for early and exact ice detection based on the electrical impedance directly on the rotor blade surface. The sensors are wireless, flexible, smart and energy-self-sufficient and installed directly on the surface of rotor blades.

Polytech (ehemals fos4x) – www.polytech.com

The system measures and learns the natural frequencies of the rotor blades under various operating conditions. As soon as ice masses form on the blades, the vibration behavior of the rotor blades changes. Measuring accuracy of less than 9 mm or less than 10 kg per blade.

Weidmüller – www.weidmueller.de

BLADEcontrol® measures the degree of icing directly on the rotor blades and is based on a simple physical principle: The ice accumulation changes the natural vibration behavior of the rotor blade due to its additional weight, which reduces the vibration frequency.

Wölfel – www.woelfel.de

IDD.Blade measures the vibration behavior with sensors inside the rotor blades. If the mass of a rotor blade changes due to ice accumulation, the vibration behavior also changes.

After four winter seasons a data set of approximately 5700 operating hours (simultaneous operation of all four systems) of the wind turbines was collected, with approximately 2500 hours of icing (only rime ice). Several cameras have been used as a reference. This unique dataset allows a detailed comparison of the four blade-based IDS.

The analysis of the icing events showed that there is a consistensy between all four IDS and the camera images in terms of the timing of the icing events. The number of icing events for the three vibration-based IDS is very similar. However, differences in the total duration of turbine stops could be observed due to different sensitivity of the systems. Concerning the eologix system, there were significantly fewer and shorter downtimes.

Example of an ice event (VGB research project 401; Abstract presented at Winterwind 2021) – (Source: Comparison of four blade-based ice detection systems installed on the same turbine, Paul Froidevaux, Meteotest AG, Winterwind 2021, April 20, 2021)

Regarding the eologix ice detection system the following points were summarized as results:

• eologix is ​​the first system to detect icing on the rotor blade,
• the eologix system requires the shortest downtimes (if the wind turbine stops according to the system certifications),
• the eologix system stopped the wind turbine 2.5 times shorter than the three VBS,
• eologix was the only system with 100% availability of ice detection during production hours.

It was further noted, unlike the eologix system, the three vibration-based systems could not detect icing at low wind speeds or in the case of standstill.