The use of wind turbines and the problem of icing

Abstract

The world’s energy demand is increasing. Wind energy plays an important role in meeting this demand. Investments in wind energy have been increasing in recent years. It can be said that the source of wind energy will be unlimited since there will be wind as long as there is sun. Most governments meet a large energy need by generating electricity from wind. At the end of 2019, the total amount of electricity generated from wind was 650 GW. Wind energy capacity is increasing with offshore wind pairs. Offshore wind turbines are a new field and research studies are ongoing. Wind turbines have the capacity to be installed anywhere in the world, and each government will have its own energy source. There is a problem of icing in wind power plants installed in cold climates. With this problem, efficiency in wind turbines decreases. Many methods have been found and developed in studies on icing problems. In this article, wind turbines were investigated, states’ perspectives on wind energy, developments and investments in wind energy, and the problem of icing were examined. Many articles in the literature have been reviewed and a solution to the icing problem of wind turbine blades has been sought.

Keywords

Wind energy wind turbine wind turbine blade deicing ultrasonic deicing renewable energy

Introduction

As a result of the sun’s warming the earth, pressure differences occur in the atmosphere. The region where the cold air mass is located creates the high pressure areas, and the regions where the hot air mass is formed constitute the low pressure areas. Wind is formed as air moves from a high pressure area to a low pressure area. It causes natural phenomena such as wind, hurricane, tornado, and tsunami. This power of wind was used to obtain energy. Wind energy has been used in electricity generation and has shown that it is clean and renewable energy (Chehouri et al., 2015). Wind turbines are needed to generate electricity from wind. Wind turbines convert the kinetic energy of the wind into mechanical energy (Wind Energy, 2020). It is possible to generate electricity with wind energy by using low carbon sources (Rand and Hoen, 2017). Wind energy is a type of energy that was used as a windmill by farmers centuries ago and has evolved into modern wind turbines today. In fact, wind is an important energy source for every period and this importance has increased even more today. Because the importance of wind energy has increased with the depletion of fossil fuel reserves, increasing energy demands, clean energy agreements of the states, and the increase of confidence in renewable energy. Energy produced by renewable energy sources accounted for one third of the total energy in 2018 (Murdock et al., 2019). Another advantage of renewable energy sources is that there is no fuel cost. In the natural gas power plant, the fuel cost constitutes approximately 40% of the total cost (Blanco, 2009). Among the renewable energy sources, wind energy is a rapidly developing energy source that grows with promising clean energy and infrastructure works (Grujicic et al., 2010). One of the biggest advantages of wind energy is its low carbon dioxide emission. Evans et al. (2009) in their study, they stated that wind energy emits less greenhouse gases than hydroelectric, photovoltaic, and geothermal energy. Wind energy is the most used energy after hydroelectric energy and constitutes 25% of renewable energy (Murdock et al., 2019). Denmark built the world’s first multi-megawatt wind turbine in 1978 (Nissen and Christensen, 2009). Leading companies in wind turbine production are given in Figure 1 (Murdock et al., 2019).

Figure 1.

Wind turbine producers in the World 2018 (Murdock et al., 2019).

Investments in wind energy are at the top of China, the USA, and Germany. USA plans to meet 20% of its energy demand with wind energy by 2030 (Lindenberg et al., 2008). The EU met about 14% of its electricity needs with wind energy in 2018 (Ministerio de Industria Energia y Mineria, 2020). In the report of the World Wind Energy Association, it is stated that the total capacity of wind turbines increased by 10.1% in 2019 and reached 650.8 GW (WWEA, 2020). The data of the World Wind Energy Association are shown in Figure 2.

Figure 2.

Total installed capacity of wind turbines in the world (WWEA, 2020).

Wind energy use is increasing regularly every year. China became the first country to increase its total installed wind turbine capacity to more than 200 GW (WWEA, 2020). The top ten countries in the world in wind energy use are as follows: China, USA, Germany, India, Spain, England, France, Brazil, Canada, Italy, and their energy capacities are given in Table 1 (Wind Energy, 2020).

Table 1.

Countries by wind energy capacity (Wind Energy, 2020).

Country	Total installed capacity (GW)	Country	Total installed capacity (GW)
China	221	USA	96.4
Germany	59,3	India	35
Spain	23	United Kingdom	20.7
France	15,3	Brazil	14.5
Canada	12,8	Italy	10.1

Wind farms are now a system that can be installed both on land(onshore) and at sea(offshore). Wind farms established on land have been used for electricity generation for many years (Bilgili et al., 2011). Wind farms established in the sea have been increasing in recent years. In general, the advantages of offshore wind farms are: higher power generation capacity and higher energy source than onshore wind farms because they are more stable and have higher wind speeds (Bergström et al., 2014; Thomsen et al., 2006). The disadvantage is that offshore wind farms are far from the shore, considering the maintenance and operating costs, its availability is less than that of onshore wind pairs (Zhixin et al., 2009). Offshore wind farms are costly, but their electricity generating performance is also better. In Figure 3, the investments of the EU on wind farms are given (European Wind Energy Association, 2009).

Figure 3.

Wind energy Investments from 2000 to 2030 (Billion Euro) in the EU (European Wind Energy Association, 2009).

As can be seen in Figure 3, investments in offshore wind turbines are gradually increasing.

Figure 4 shows the annual increase in total installed offshore wind energy capacities between 2008 and 2018 in Europe, Asia, and North America (Murdock et al., 2019).

Figure 4.

Offshore wind energy capacity (GW) in Europe, Asia, and North America (Murdock et al., 2019).

As investments in offshore wind turbines increase, the energy capacity generated from offshore wind turbines also increases.

In Table 2, compares setup cost, operating speed, energy production, operating cost, common usage rate of onshore, and offshore wind farms (Elibüyük and Üçgül, 2014).

Table 2.

Comparison of onshore and offshore wind farms.

	Onshore	Offshore
Setup cost	Low	High
Operating speed	Low	High
Energy production	Low	High
Operating cost	Low	High
Common usage rate	High	Low

Offshore wind energy is a new field of study and is open to development and it has an ever-increasing energy capacity over the years. Many studies have been conducted on this energy, the problems have been investigated and it is expected that its disadvantages will be minimized in the coming years (Adelaja et al., 2012; Bilgili et al., 2011; Costoya et al., 2020; Enevoldsen and Valentine, 2016; Johnston et al., 2020; Wei et al., 2021; Zhixin et al., 2009).

ICE problems of wind turbines in cold climates

Wind turbines can be installed anywhere in the world. Wind energy and air density are lower in warm climates than in cold climates (Lamraoui et al., 2014). Therefore, the number of wind turbines installed in cold climates is more than the number of wind turbines installed in hot climates due to the greater wind potential and high air density (Battisti et al., 2005). However, in cold climates, some problems arise such as icing of the turbine blades. In fact, wind power generation is more efficient in cold climates depending on wind speed and air density. Icing is a big problem as it reduces the efficiency of a wind turbine. Annual production losses of wind turbines can be up to 50% depending on the frequency and duration of icing (Fakorede et al., 2016). As a result of icing, major problems arise such as rotor vibration, increased noise level, risk of ice spillage and, most importantly, low aerodynamic performance of the turbine blade (Battisti, 2015). With the accumulation of ice, the weight and vibration of the turbine increases, the life of the turbines decreases and the noise intensity increases (Shu et al., 2018). Studies and experiments have been carried out to analyze the power loss due to turbine icing and ice accumulation on the turbine blades increases the resistance coefficient and decreases the lift coefficient, causing a decrease in power generation (Barber et al., 2010; Duncan et al., 2008; Homala et al., 2010; Horák et al., 2008; Mortensen, 2008; Virk et al., 2010).

According to the research conducted by Durstewistz, the problems caused by icing are given in Table 3 and stated that 2% of the turbine failure reasons are icing problems (Virk et al., 2010). According to the results of the research, wind farms became inoperable when there was an icing problem (Durstewitz, 2003).

Table 3.

The effect of the icing problem on the wind turbines (Durstewitz, 2003).

Reported impact or failure	Frequency (%)
Plant stoppage	89
Reduced power output	13
Vibration	5
Noise	2
Overspeed	1
Overload	1
Other results	5

The annual loss of production resulting from icing of wind turbines is given in Table 4 (Ronsten et al., 2012).

Table 4.

Annual loss of production due to icing of wind turbines (Ronsten et al., 2012).

Meteorological icing (annual %)	Instrumental icing (annual %)	Production loss (annual %)
0–0.5	<1.5	0–0.5
05–3	1–9	0.5–5
3–5	6–15	3–12
5–10	10–30	10–25
>10	>20	>20

It is seen that production loss increases with the increase in icing rate. Therefore, production losses will be minimized if necessary precautions are taken against the icing problem.

Ice problem solving techniques in wind turbines have improved in recent years (Pedersen and Yin, 2014). These techniques can be divided into two categories: the first method is to remove or prevent ice before it forms, the other method to remove ice after ice has formed (Parent and Ilinca, 2011). Special coating, black paint, and special chemicals are used to protect the wind turbine blades from icing. If we look at the special coating method first, it is low cost but not effective in preventing ice when used alone (Kimura et al., 2003; Seifert, 2003). Black dye is effective in places where there is less icing; if icing increases and becomes more frequent, it becomes insufficient (Laakso and Peltola, 2005; Weis and Maissan, 2003). Chemicals are also insufficient alone, cannot stay on the wing for a long time (Tammelin et al., 2000). There are also flexible blades and active stepping methods to protect wind turbine blades from icing. Flexible wings are the method that loosens the ice and allows it to spill (Dalili et al., 2000). With the active step method, the iced blade is turned toward the sun, it can be used when there is not much icing, but it has been reported that it damages wind turbines (Laakso and Peltola, 2005).

Other methods that may solve the icing problem are: heating resistance, hot air and radiator, flexible pneumatic boots, and electro impulsive/propulsion methods (Battisti et al., 2006; Botura and Fisher, 2003; Dalili et al., 2000; Peltola et al., 2003; Pinard and Meissan, 2003). With the heating resistance method, a water layer will be formed by heating the bottom of the ice layer and then this layer is the system that will allow ice to pour out with centrifugal force. Thermal efficiency is high but still at prototype level (Battisti et al., 2005, 2006; Laakso and Peltola, 2005). Hot air and radiator methods are similar to heating resistors. Here, the rotor blade is heated with special pipes, a water layer is formed and it tries to get rid of the ice with centrifugal force (Battisti et al., 2006; Parent and Ilinca, 2011; Seifert, 2003). It is used more in temperate climates, it is not preferred in cold climates because it consumes too much power. The flexible pneumatic boat is located on the wing surface uninflated. When there is icing, the boots are inflated to break the ice, but it disrupts the aerodynamic structure of the wing (Peltola et al., 2003). Electro-impulsive/impulsive method is a method that tries to de-icing by electromagnetically induced vibration pulses and has not yet been tested (Dalili et al., 2009; Mayer, 2007; Mayer et al., 2007).

Other anti-icing methods for wind turbine blades are: microwave, air layer, and thermal methods (Dalili et al., 2009; Mayer, 2007; Mayer et al., 2007; Parent and Ilinca, 2011). Microwave and air layer methods are not used much today (Dalili et al., 2009). Thermal de-icing method is an effective method, but are more energy amount consumed (Mayer, 2007). There are three different types of this method. These are direct current deicing method, short circuit current deicing method, over current deicing method (Heyun et al., 2001; Liu et al., 2012; Wang, 2010). Its use in this method is limited. The short circuit current deice technique aims to short circuit the high voltage line and melt the ice with the heat released. This method also has excessive electricity consumption (Li et al., 2006). Single phase short circuit, two phase short circuit and three phase short circuit techniques constitute the short circuit current defrost method. Generally, the three-phase short circuit method is used more (Li et al., 2006). In the direct current ice melting method, heat is generated by using direct current through the high voltage line, this heat is used to melt the ice (Liu et al., 2012). This method needs a large power supply.

It can also be defrosted mechanically. It is aimed to spill the ice by applying external force to the icing area (Gu et al., 2009). The ultrasonic deicing technique is low-cost, simple, energy-saving, and increasingly used (Ramanathan et al., 2000). The ultrasonic deicing method is to apply the effect of heating, cavitation, especially vibration, to the areas where the adhesive shear strength of the ice substrate interface is weak (Daniliuk et al., 2020). In this method, a specific piezoelectric material should be preferred for the ultrasonic transducer. PMN-PT (lead magnesium niobate), PZT (lead zirconate titanate), and LiNbO₃ (lithium niobate) are examples of these materials. Since PMN-PT and PZT converters contain harmful substances such as lead oxide, LiNbO₃ should be used instead. LiNbO₃ and PMN-PT have higher performance than PZT piezoelectric transducer (Tian et al., 2007). PZT piezoelectric transducer is widely used today. Daniliuk et al. (2020) made a detailed research on ultrasonic deicing technique, compared LiNbO₃, PMN-PT, PZT transducers. According to the experimental results, it was concluded that the performance of all three converters was good, but the design of the LiNbO₃ converter is better, the amount of power consumption is low, and it contains materials that do not harm the environment (Daniliuk et al., 2020). The ultrasonic method is suitable for wind turbine blades made of composite material because composite materials absorb the resulting stress and fluctuation movement (Wang et al., 2018). The developing ultrasonic method is one of the most researched methods today.

Conclusion

Environmental problems caused by fossil fuels affect the whole world. Therefore, the use of fossil fuels should be terminated as soon as possible and clean energy resources should be used and found instead. Countries invest in renewable energy resources in order to minimize their energy costs and to become self-sufficient in energy. Wind energy is a renewable energy source and an energy type that has increased in importance in recent years. It has the capacity to be installed anywhere in the world, regardless of offshore or onshore, hot climate regions, or cold climate regions. Therefore, researches and studies are carried out to get more energy from the wind. The problems of established wind couples are investigated and resolved, and investigations are carried out to increase the energy generation efficiency of existing wind turbine farms. In the coming years, one fourth of the electricity generation will be met by wind energy in the first place, and this ratio will increase in the following years. The current problem with wind turbines installed in cold climates is icing. Aerodynamic structure deteriorates as a result of icing of wind turbine blades. The problem of icing reduces both the energy efficiency and the service life of the wind turbine blades. If the icing increases, the wind turbines will stop, there will be a great loss of power. On the other hand, energy efficiency increases as the air density is high in cold climate regions. But the icing problem causes performance loss for the wind turbine. Maintenance and repair done to solve the icing problem brings additional costs.

In recent years, various researches have been conducted on this problem and solutions have been sought. The coating method is easy to maintain, economical but alone cannot solve the icing problem, it should be combined with other systems (Kimura et al., 2003; Seifert, 2003). Chemicals have a short protection time, low cost, and requires constant maintenance (Tammelin et al., 2000). Flexible pneumatic deicing method is also not preferred because it disrupts the aerodynamic structure of the turbine blades (Parent and Ilinca, 2011). Thermal methods are mostly found on the leading edges of the wings. It is good at preventing icing, but this method is not good at defrosting. It is better to use it with other methods. Thermal methods perform better than other methods but have more energy consumption than ultrasonic deicing (Mayer, 2007). As a result, most of the methods alone were insufficient, could not have an effect on the wings with high icing, and results were obtained only in areas with little icing.

The articles (Daniliuk et al., 2020; Ramanathan et al., 2000; Tian et al., 2007; Wang et al., 2018) on ultrasonic deicing were reviewed and the following conclusions were reached. The ultrasonic deicing method is a capacity that can eliminate the icing problem and can be a solution to the icing problem when used alone. The experiments of the ultrasonic deicing method and the results obtained from numerical simulations have proven that they can solve the icing problem. If this method is used, the power consumption of wind turbines decreases, energy efficiency increases and it is a low-cost method that does not harm the environment. If the ultrasonic deicing method is used continuously, there will be no icing problem in the wind turbine blades (Daniliuk et al., 2020; Ramanathan et al., 2000; Tian et al., 2007; Wang et al., 2018). Ultrasonic deicing method should be widely used in wind turbine blades. It is possible that new ultrasonic transducer piezoelectric materials will be found and developed for the future.

Footnotes

Appendix

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Cevahir Tarhan

Mehmet Ali Çil

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