Worldwide, nearly 800 GW of wind power have been installed so far, including over 110 GW in the US alone. As the market quickly grows and wind power supplants higher-polluting energy sources, de-icing and ice-proofing strategies are becoming essential.

Texas extreme cold weather event in February 14-19, showed how vulnerable wind turbines are to ice. The largest segment of Texas diverse portfolio of power generation is natural gas with 51,667 MW, followed by wind turbines with 31,390MW – 28,83% of its power capacity. Wind and Natural Gas made the majority of the loss capacity during the Texas power outage as seen in Graph 1.

Graph 1. Generation Capacity out by Fuel Type. Sourced by ERCOT.

Wind generation is supposed to be at its most effective at winter, when high wind speeds and air density (which increases at low temperatures) maximize generation. So, keeping ice off those blades is essential. Even light icing can produce enough surface roughness on wind turbine blades to reduce their aerodynamic efficiency, reducing power generation, as Texas experienced in February.

But power loss isn’t the only problem from icing. The uneven way ice forms on blades can create imbalances, causing a turbine’s parts to wear out more quickly. It can also induce vibrations that cause the turbines to shut down. In the case of extreme icing, restarting turbines may not be possible for hours and potentially days. Besides, risks of ice throwing on operators must also be taken into account.

To solve this problem, wind turbine manufacturers started making cold climate adaptations to their wind turbines and even developing de-icing methods for these to remain structurally safe. At low temperatures, materials tend to become brittle (reduced ability to deform without damage) and less tough - micro-cracking can occur if the stress is sufficient and if this phenomenon is not taken properly into account.

Examples of low temperature adaptations include the use of low temperature oil and greases, different material choices than used for standard wind turbines, heated sensors, additional sealing of the nacelle, specific heated turbine components, among others.

A list of the companies that have made adaptations of their wind turbines for cold climates are shown in Table 1. The table also shows the ice detection (ID) method used, if they provide an ice operation mode and their ice protection system.

Table 1. Available turbine manufacturers with cold climate conditions.

Independent ice protection system providers

Retrofit ice protection systems are an important technology option for turbines that have been built in icing conditions, but lack factory installed ice protection systems.

As most of the strategies for keeping ice off wind turbines blades come from aviation, many companies that prevent icing formation on the aviation industry started offering solutions for the wind power industry as well. Among these: Villinger with their Laminar De-Ice (LDI) system, Spitzner Engineers with their Anti- and De-Ice Operating System (ADIOS) and Kelly Aerospace with Thermablade. All of them provide electro thermal heating elements and have the advantage of being a retrofit solution or factory installed.

Still, airplane wings and wind turbines are built differently and operate under very different conditions. Wind turbines are more prone to encounters with freezing rain and other low-altitude, high-water-content environments - there can be more water in the air at ground level, and much more at sea (offshore wind). Besides, polymer-based turbine blades are also more likely to get covered by dust and insect collisions, which can change the smoothness of the blade surface and slow water running off the blade, promoting ice formation. And there’s another problem: water from melting ice may simply run back and refreeze elsewhere.

Wicetec was one of the first companies specialized in retrofit anti-icing and de-icing solutions. The company also offers for its solution to be factory installed if desired. Wicetec also uses electro-thermal heating, a technology with long track record and that optimizes power consumption as it is close to the blade surface and can have spanwise heat control.

Borealis Wind’s anti-icing and de-icing system works by heating the interior of the blade with hot air, thus heating the exterior and shedding the ice. A blower, heater and duct system target heat to the tip of the blade for being the critical area. It is also a retrofit solution, being able to install the system without removing the blades and with no need for rope access, and no lost production overnight. A network of sensors installed throughout the turbine actively monitors system performance. The control system integrates with the turbine safety chain, and collects data from the SCADA system. On the other hand, as there is a long distance from heat source to blade tip, and heat has to travel through the blade material to reach the blade surface, this method has a lower energy efficiency than electro-thermal heating.

Another strategy is to use surface coatings that repel water or prevent ice from sticking. However, according to Hui Hu - an aerospace and mechanical engineer, Professor of Aerospace Engineering in Iowa State University - none of these coatings have been able to eliminate ice completely, especially in critical regions near the blades’ leading edges.

Ice Solution’s retrofit system combines a microwave-based heating technology with carbon nano particles in a heatable coating. Their solution consists of a transitor microwave unit that moves along the tower of the wind turbine sending microwaves to the rotor blades which are covered by a Carbon Nano-Tubes (CNT) heatable coating, removing the ice of the blades. This solution has the advantage of being installed without removing the blades and having low energy losses compared to electro-thermal or hot air heating as heat is generated only on the surface of the blade. As a disadvantage, it works primarily as a de-icing method.

Further solutions are being developed combining heating (for the main blade) plus water-resistant icephobic coatings (for the tips). Also, other research studies are progressing on hydrophobic polypyrrole coatings, high-power ultrasonic guided waves and low-frequency forced vibrations for de-icing and even light de-icing technologies.

Ice protection systems avoid mechanical removal systems as rope access/skylift manual de-icing or helicopter/drone de-icing using hot liquids. These solutions are reactive solutions with long-waiting time and preparations and which can cause potential damage to the blades or operators.

If you are interested in learning more about this topic, you can learn more of active anti-icing and de-icing technologies on this framework. You can also find a vendor landscape on ice sensors here.

What technology are you applying to control icing on wind turbines?

References

Hui Hu. The science behind frozen wind turbines – and how to keep them spinning through the winter [Online]. The Conversation. Published: 03/04/2021. Accessed: 04/14/2021. Link.

IEA Wind TCP Task 19. (2018). Available Technologies for Wind Energy in Cold Climates (2nd edition). IEA Wind. Link.