G NER Y SE E CU O R T I A T Y N NATO ENERGY SECURITY

C E CENTRE OF EXCELLENCE E C N T N R E E LL OF EXCE ENERGY HIGHLIGHTS

ENERGY HIGHLIGHTS 1 Content

7 Introduction

11 Chapter 1 – Energy Systems and Technologies

25 Chapter 2 – Radar Systems and Wind Farms

36 Chapter 3 – Wind Farms Interference Mitigation

46 Chapter 4 – Environmental and societal impacts of wind energy

58 Chapter 5 – Wind Farms and Noise

67 Chapter 6 – and

74 Chapter 7 – Case Studies

84 Conclusions

86 A Way Forward

87 Bibliography

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2 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 3 Role of windfarms for national grids – challenges, risks, and chances for energy security

by Ms Marju Kõrts

ACKNOWLEDGEMENTS EXECUTIVE SUMMARY AND KEY have arisen in other countries wher wind power RECOMMENDATIONS The author would like to acknowledge the work and insights of the people who contributed to this is expanding. study either via the conducted interviews or their fellowship at the NATO Energy Security Center of apid growth of wind energy worldwide Excellence in summer and autumn 2020. I would like to especially thank the following people: has led to the increased installation of There is no fundamental physical constraint that wind farms that are more efficient, pow- prohibits the accurate detection of aircraft and Jan Schlüter erful, and have taller wind turbines. As weather patterns around wind farms. On the Max Planck Institute, (Chapter 1) Rwind development continues to grow and expand other hand, the aging radar infrastructure signifi- to new areas of the country, so does the possibil- cantly increases the challenge of distinguishing Johann Seebass ity that some turbines would be located within signatures from airplanes or weather. Max Planck Institute, Germany (Chapter 1) the line of sight of radar systems. This could have On one hand, wind turbines are getting bigger potential effect on national flight safety, weather and more powerful to harvest more energy, on Dujon Goncalves – Collins forecasting, and national defence radar opera- the other hand there will be more challenges for Vattenfall Wind Power, (UK Case Study) tions. Wind turbines can cause radar interference the defence radars to cope with this situation. whereby the blades appear as „clutter“ on radar Thus, the probability for wind development to screens and can be mistaken for aircraft. Plans present conflicts with radar missions related to to set ambitious targets have air traffic control, weather forecasting, national been impacted by the objections of the Minis- security and defence is also likely to increase, as tries of Defence that wind turbines interfere with is the potential severity of those conflicts. Cer- military radars. In a number of cases the military tainly, the positioning of aviation infrastructures has claimed that the wind farms are an encroach- such as airports and helipads, and wind infra- ment on military radar facilities, and have stalled structures such as wind farms and turbines, will construction on the wind farm. Similar problems continue to be a challenge. Therefore, a justified

by Ms Marju Kõrts Ms Marju Kõrts is an Estonian career diplomat who has hold several positions at the Estonian Ministry of Foreign Affairs. She graduated with her Masters degree in political science at Tartu University in Estonia. With the current function as the Estonian Subject Matter Expert at the Research and Lessons Learned Division of the NATO Energy Security Center of Excellence in she focusses on the new energy technologies. At present she is conducting a research study: “Offshore Wind Farms – Challenges, risks and opportunities for building more resilient national energy system. E-mail: [email protected]

4 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 5 question can be posed whether wind farms can terference are required. Although a great deal is ties, there is still quite a lot of resistance to the 2. The evaluation system should include a cost co-exist with radar installations? now understood about the potential effects of wind developments due to the environmental benefit analysis of mitigation strategies. Once wind turbines on many types of radar as well as and societal reasons. The local residents often the potential for different mitigation measures Progress forward requires the development of their impacts on the missions those radars sup- claim about the noise or light pollution. Noise are understood, there is no hurdle for estab- mitigation measures, and quantitative evaluation port, nevertheless new issues are likely to arise. emissions may be heard, felt, or sensed. Some of lishing regulations that are simple to under- tools and metrics to determine when a wind farm One class of mitigation solutions is the augmen- them are in the audible range, the others are in stand and simple to implement, with a single poses a sufficient threat to a radar installation for tation or „infill“ radars. Where a potential siting the low frequency range and those may be heard. government entity taking responsibility for corrective action to be taken. Mitigation measures conflict manifests itself, an impacted legacy ra- There are mainly two sources of noise in a wind overseeing the process. may include modification to wind farms (such as dar’s performance loss may be restored by plac- turbine: aerodynamic that is generated by the methods to reduce radar cross-section; and telem- ing one of these infill radars, with advanced clut- motion of air around the blades, and mechanical INTRODUCTION etry from wind farms to radar), as well as modifi- ter suppression techniques, closer to wind farms caused by the motion of the mechanical and elec- By the end of this year European countries are cations to radar (such as improvements in process- to restore the lost surveillance coverage. Anoth- trical components. Light pollution occurs in the due to deliver on their 2020 renewable energy ing; radar design modifications; radar replacement; er approach is to improve the inter- form of strobing (also known as „shadowflicker- targets and will start implementing their 2030 and the use of gap fillers in radar coverage). ference mitigation capabilities of existing radars ing“) or from aircraft warning lights mounted on National Energy & Climate Plans (NECPs) to- through signal processing, software upgrades and the towers. Improving warning lights to lit up the wards the 32% renewable energy goal. The de- Establishing the optimal mitigation strategy minor hardware modifications, which are likely wind turbine only when there is an actual aircraft pletion of conventional energy sources and the for a specific case requires in-depth analysis of to result in lower-cost solutions to wide-scale to warn in its vicinity is not a new idea, and indi- rising greenhouse gas emissions are fueling the the particular site. However the most common deployment of short-range infill radar systems. vidual tests to achieve this has been successfully adoption of renewable energy sources across technological solutions currently employed also New design and operational methods for future carried out in the past. Due to the large number the world. Wind is one of the most abundant include blanking where radar returns within the wind turbines deployed in close proximity to vi- of wind farms, Germany is especially interested and efficient sources of power generation. Coun- wind farm boundary are not shown on the radar tal radar assets could reduce radar impacts either in this issue and is at present implementing new tries such as , , Germany, and the screen. This eliminates the issue of wind turbines independently or in conjunction with mitigation regulations to enforce an on-demand warning United Kingdom produce more than 10% of their showing up as targets on a radar screen, but it measures applied at the impacted radar systems. light system as requirement for wind farms. power from wind energy. also means that an aircraft overflying the wind farm will not be displayed. In the United King- Beyond radar-absorbing materials, there are ad- All in all, wind energy developments can also be Several studies, e.g “Wind Energy in Europe: Out- dom for example, the industry together with the ditional at-the-turbine solutions, e.g. reduced seen as an opportunity and not as a problem as look to 2022” prepared by WindEurope reinforce aviation sector has also looked at changing the radar impact lightning protection systems, ma- the experience of shows. Namely, with the idea that wind energy will play a key role in turbine design, but that is not always possible or terials, and structures are especially important the use of new generation mine-sweepers that the necessary energy transition to meet the chal- it has not always given the desired results. for over-the-horizon radar systems. New opera- also rely on drone technology, the offshore wind lenges of climate change and produce clean en- tional methods in which data from individual tur- farms matrix can be used for the logistical sup- ergy. The study “Utility of the Future”1 by Mas- Collaboration is the key as the wind industry rec- bines are combined with data in real time could port of this network (e.g. recharging the drones’ sachusetts Institute of Technology points out ognizes the need for technical solutions so that also be explored as a potential mitigation meth- batteries). the key factors that can be seen in the electricity the presence of turbines does not have any im- od for current or newly deployed wind farms. sector in the future: decarbonisation, combating pact on radars. In some countries (e.g. UK, USA) Once the potential for different mitigation mea- climate change, new technologies, digitization, the dialogue has been ongoing for years. Gov- Besides radar interference, obstruction and safe- sures are understood, there is no hurdle for es- and the advancement of renewable energy. ernment and the aviation authorities recognize ty can be considered as additional concerns for tablishing regulations that are technically based the crucial need to develop renewable energy to the Ministries of Defence that are related to wind and simple to understand and implement. According to the estimates of the WindEurope’s tackle climate change, and the wind industry rec- turbines. A single wind turbine or wind farms study mentioned above, the installed capacity ognizes the need for technical solutions so that which has the potential to endanger aviation in Based upon the factors discussed above, some will grow an average by 17.4 GW per year be- the presence of turbines does not have any im- navigable airspace or has the potential to inter- recommendations can be given how to foster tween 2018 and 2022, due to the development pact on aviation radar (both civilian and military). fere with the operation of navigation, should be the development of wind energy and ensure that of wind farm projects both onshore and offshore. With appropriate planning, coupled with fund- lighted. The number of light levels recommended the national defence needs are not compromised. Germany, Spain and the United Kingdom will ing the deployment of appropriate mitigation depends on the height of the structure. The ob- continue to being the countries with the largest solutions, the impact of wind turbines on radar stacle lights should be installed on the 1. It would be recommendable that the Govern- fleet of wind turbines in Europe. systems may be minimized or eliminated for the to provide an unobstructed view for aircraft ap- ment move beyond a policy of unilaterally near, mid,- and long-term. proaching from any direction. blocking wind farms on the basis of any ob- Growth is expected to slow in Germany and will servable impact on existing radars, and move accelerate in Spain and . In terms of to- To preserve critical radar missions as well as to The so-called radar objections mentioned above to a collaborative and mutually agreed, tech- tal installed capacity, wind power is the leading accommodate future wind development, new are not the only impediment to the development nically based rule system for determining the renewable energy technology after hydropower, technologies to mitigate wind turbine radar in- of wind energy. In many countries and communi- severity of the interference.

1 MIT Energy Initiative “Utility of the Future”, 2016, Massachusetts, USA 6 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 7 with more than half a terawatt installed glob- can cause a number of problems on air traf- the atmosphere, electromagnetic waves are gen- productive and greener. This would entail chang- ally as of the end of 2018. Global installed wind- fic radar displays such as clutter (also known as erally bent or refracted downward (e.g diffraction es inter alia in energy production, transport, for- generation capacity onshore and offshore has in- interference), reduced sensitivity and overload- effects) that reduces the “dead zone” but causes estry and agriculture. This also means that the creased by a factor of almost 75 in the last past ing of processing functions. Wind turbines have fault in the distance and height measuring simul- role of renewable energy solutions in the energy two decades, jumping from 7.5 gigawatts (GW) significant electromagnetic reflectivity, as large taneously. Several studies have also underlined portfolio, including production of electricity from in 1997 to some 564 GW by 2018, according to structures and blade cause large and numerous the possibility that wind turbine structures, if wind energy will increase in the future (Estonian the International Renewable Energy Agency’s Doppler returns due to their motion relative to positioned with certain geometries and distances NECP 2030)8. For a number of years, the Esto- (IRENA) latest data2. the affected radars4. relative to ATC radars, might cause those radars nian Ministry of Defence has denied permits for to fail to detect desired targets with adverse im- onshore wind projects on the grounds of national The Doppler Effect5, specifically the shift in fre- plications for safety-of-life and national security. defence needs. Especially problematic for the quency of the reflected signal that occurs when Various studies have been carried out to deter- military are wind farms located close to the state an object is moving, was first discovered by mine minimum safe distance between a wind border or those wind farms located close to the Christian Doppler, an Austrian physicist and farm and radar system but without success. Due air defence radar. The same tendencies can be mathematician who carried out experiments to numerous different constructions, and indi- seen in the neighboring countries, for example, with both moving sources and moving observers. vidual site circumstances, it is not possible to de- Sweden recently denied permit for the Blekinge Doppler shift applies to all propagating waves termine a universally accurate minimum distance offshore wind farm, located 17 km off the south- and is particularly useful for radars. This Doppler where interactions between a turbine and a radar ern coast of Sweden. This area was of strategic shift results from the fact that the frequency of a would occur. It is however, possible to determine importance for the Swedish defence forces as signal received by an observer will depend upon a minimum distance where effects from wind they needed it for practicing military maneuvers. whether the source of that signal is stationary, turbines would not be anticipated. moving forward, or moving away from the ob- Thus, erecting a wind farm involves many consid- Figure 1. Wind Power Global Capacity and Annual server. For radar applications, the “source” of the The impact of wind farms, particularly on ground erations including consultation with various civil Additions, 2009-2019 signal is the radar wave reflected by the target. If based aviation radars such as those operated for or military aviation stakeholders. Radar beam the target is moving away from the radar, the fre- air defence and military and civil air traffic con- blocking is the most serious effect that wind quency of the reflected signal will be lower than trol purposes are likely to become particularly turbines have on radar. Beam blockage occurs Europe could install 90 GW of new wind energy the originally transmitted frequency. acute as the governments of the EU Member when radar beams are partially or totally blocked capacity over the next five years, if governments States strive to meet the requirements for en- by nearby obstacles. On land, beam blockage is adopt clear and ambitious NECPs, resolve their As the size and number of wind turbines increase, ergy generation under the renewables targets usually caused by terrain and buildings, including current issues around wind farm permitting and their operation can affect the military readiness by 2030. The assessment of Member States’ wind turbines if they are located close enough to continue investing in grid infrastructure. This of the surveillance radar installations near wind National Energy and Climate Plans shows that the radar. As a result, the radar is unable to “see” would give Europe 277 GW of installed wind farms and the proper functioning of other civilian Member-States are accelerating their energy and behind the turbine because it blocks the pulses capacity by 2023 (WindEurope 2019)3. By 2023 systems such as Air Traffic Control (ATC) Radar climate transition. It indicates that the share of of energy. Beyond the wind farms, the signal is Germany will remain the country with the largest and Weather Radar, especially when the wind renewable energy in the EU could reach 33.7% by attenuated9 to varying degrees which in case of wind fleet (72 GW), followed by Spain (32 GW) farms are within the radar line-of-sight (LoS). 2030, going beyond the current target of at least weather radars leads to underestimation of pre- and the United Kingdom (29 GW). These three The electromagnetic waves follow the rules of 32% (European Commission, 2020)7. cipitation measurements and a loss of sensitivity countries will account for just half of Europe’s optics in higher frequencies (>100 MHz). All ra- of Doppler measurements. To limit these effects cumulative installed wind capacity by 2023. The dar unit systems almost without exception work The co-existence of wind farms and military ra- it is recommended to maintain the blockage ratio decline in costs for renewable technology and in this frequency domain. Therefore, the wave dars is a topical issue in Estonia. The Estonian of radar beams below 10%, which corresponds to other key technologies, such as batteries and fronts also propagate to quasi-optical rules. The long-term objective is transition to a low carbon a maximum underestimation of 20 to 30% of the electrolyzers, will impact the entire energy sector earth’s curvature may prevent the radar seeing emission economy, which would mean purpose- measurement of rainfall intensity located at 100 going forward. a target within the maximum range (distance) ful reorganization of the economy and energy kilometers. given by the radar range equation6. This results system to make them more resource efficient, There are also challenges that come with the in a “dead zone” for every radar system in which benefits of wind energy generation. Wind farms certain targets cannot be detected. However, in 6 If the echo signal is having the power less than the power of the minimum detectable signal, then radar cannot detect the target since it is beyond the maximum limit of the radar’s range. The range of the target is said to be maximum range when the received echo signal is having the power equal 2 IRENA, 2019, Renewable Capacity Statistics 2019, International Renewable Energy Agency (IRENA), Abu Dhabi to that of the detectable signal. 7 3 “Wind Energy in Europe: Outlook to 2023”, WindEurope, October 2019 The European Commission. “State of the Union: Commission raises climate ambition and proposes 55% cut in emissions by 2030”, press release, 17 September 2020, , Belgium. 4 Radar is a system for detecting the presence or position or movement of objects by transmitting radio waves, which are reflected back to a receiver. 8 Estonian National Energy and Climate Plan (NECP 2030), 2018. 5 A Doppler radar is a specialized radar that uses the Doppler Effect to produce velocity data about objects at a distance. It does this by bouncing a mi- 9 crowave signal off a desired target and analyzing how the object’s motion has altered the frequency of the returned signal. This variation gives direct and Attenuation is the scattering and absorption of energy as it passes through a medium. Gases and water vapor in the atmosphere absorb some of the highly accurate measurements of the radial-component of a target’s velocity relative to the radar. Doppler radars are used in aviation sounding satellites. radio waves energy. The higher the frequency, the greater the absorption of energy.

8 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 9 Electromagnetic radiation is a form of energy ex- as a renewable energy source and the desire to and security. The research objectives are to an- on specific energy policy options and measures to hibiting wave like behavior as it travels through maintain the performance of existing radar sys- swer the following questions: (1) how significant foster wind . Conclusions of the space. A wave is a disturbance that propa- tems. are the wind turbine related radar and military this study can be found at the end of the report. gates through space and time, usually with the site concerns that have been raised by the mili- transference of energy from one point to another Even though both radars and wind turbines have tary; (2) how viable are the proposed solutions CHAPTER 1 – WIND ENERGY SYSTEMS AND without permanent displacement of particles of been in use for many decades it is only in the last to these concerns? (3) What is required (e.g. gov- TECHNOLOGIES the medium (Malik, 2013)10. In the atmosphere, few years that the interference problem has re- ernance and resources) to implement the most Wind power capacity has increased dramatically the wave propagates with a speed slower than ceived substantial attention. The reason for this viable solution so that wind farms can co-exist in the recent years – and accompanying that, the the speed of light. The wave’s speed, direction of is simple; in recent years wind turbines have in- with the radar installations? turbines have become more efficient and more propagation, and amplitude are dependent upon creased in number and in size at the same time affordable for power producers. Wind energy gen- several atmospheric variables including tem- radar systems have become increasingly sensitive. The research methodology of this study uses a eration is power generation that converts wind perature, moisture, and pressure (Ford, 1995)11. synthesis of literature analysis and industry in- energy into electric energy. The wind generating The atmospheric refractivity gives rise to bend- In recent years, important research projects have terviews. In the study, there is a separate chap- set absorbs wind energy with a specially designed ing of radio waves. The diffraction of the radar been carried out, in order to characterize the sig- ter where the energy policies and wind energy blade and converts wind energy to mechani- waves will reduce the intensity of the propagat- nals scattered by the wind turbines and to de- developments are viewed in depth. The inter- cal energy, which further drives the generator ing wave directly behind the turbines as well as termine the impact these reflected signals may views with selected representatives from the rotating and realizes conversion of wind energy the reflected signal from a target. This two-way cause on the detection capability of the radars. field of radar, the wind industry, and governmen- to electric energy. A typical modern turbine will reduction in signal strength will increase the dif- Additionally, a significant effort has also been put tal agencies were conducted either via phone or start to generate electricity when wind speeds ficulty in detecting and tracking targets flying in into developing various mitigation techniques, other online devices. In order to give a broader reach six to nine miles per hour (mph), known low altitude in the immediate vicinity of the wind some of them based on the wind turbine designs, energy policy perspective, both on- and offshore as the cut-in speed. Another common feature of turbines. This effect will be most pronounced for but the others in signal processing in the receiver wind energy were covered in particular countries, wind energy production is called . targets with a small Radar Cross Section12. The or in the development of specific techniques for although the study in itself focuses on onshore This measures the amount of electricity a wind surface area of simple geometric bodies depends filtering the interfering signals. wind energy. The phone or online interviews were turbine produces in a given period of time (typi- on the shape of the body and the wavelength, or semi-structured with a transcript of the interview cally a year) relative to its maximum potential. rather on the ratio of the structural dimensions A number of technologies are being pursued to being scribed throughout, and responses and of the object to the wavelength. In practice, some assist in mitigating the impact of wind turbine on conversational leads were later reviewed with Although wind energy is a clean and renewable energy is absorbed and the reflected energy is both aviation and marine radars. These include the person interviewed. Only non-classified in- source of electric power, many challenges must not distributed equally in all directions. There- additional post-processing of radar returns, the formation was sought, and included subsequent be addressed. Wind turbines are complex ma- fore, the Radar Cross-Section is quite difficult to use of gap filler radars to improve coverage, phys- detailed questioning. chines, with large flexible structures working un- estimate. This means that some targets at the ra- ical obscuration to remove radar-wind farm line der turbulent and unpredictable conditions, and dar’s screen are inherently the most challenging of sight, antenna tilting or modification to ensure The study “Role of wind farms for national grids – are connected to a constantly varying electrical in all circumstances, and this added burden will that wind farms are not illuminated by eleva- challenges, risks, and for energy security” consists grid with changing voltages, frequency, and pow- result in a noticeable reduction in probability of tion side lobes, and the lay-out of wind turbines of 7 chapters and its structure is the following. er flow. Wind turbines have to adapt to those detection for them. within a farm to reduce coherent summation of Chapter 1 is dedicated to wind formation and dif- variations, so their efficiency and reliability de- returns for radars at fixed locations. The applica- ferent types of wind turbines. Chapter 2 provides pend heavily on the control strategy applied. As As a result, all these aspects can lead to raising tion of so-called “stealth” technology13 has the a detailed overview of the radar concepts and wind energy penetration in the grid increases, ad- the so-called “radar objections” from air traffic potential to reduce both aviation and marine ra- systems with a special focus on wind turbines’ ditional challenges are being revealed: response control and military authorities, asking for exam- dars interference. electromagnetic footprint. Chapter 3 addresses in grid disturbances, active power control and ple, to downsize or relocate planned wind farms. potential mitigation approaches that can be used frequency regulation, restoration of grid services This hinders wind energy development, at a time The aim of this study is to get further insight into to reduce the negative impacts wind turbines after power outages, and wind prediction, for ex- where there is significant push to expand the en- the radar- and military related concerns raised have on air defence. Chapter 4 deals with envi- ample. ergy production from renewable sources. Conse- around wind turbines, and to discuss alternative ronmental and societal aspects of wind energy. quently, there is a conflict of interest between options that may be introduced to mitigate the Chapter 5 in turn focuses on the noise pollu- The present chapter focuses on wind formation, the desire to encourage wind farm development impact of utility-scale wind turbines on defence tion and provides an overview of some reduction also covering the design and construction of technologies. The focus on Chapter 6 is on dif- wind turbines A separate section is dedicated to 10 H. Malik. “Electromagnetic Waves and Their Application to Charged Particle Acceleration”, Intech, 2013 ferent energy storage technologies that can be 11 the new emerging technologies (e.g. smart grids) B. Ford. “Atmospheric refraction: how electromagnetic waves bending in the atmosphere and why it matters”, U.S Naval Postgraduate School., used for storing wind energy. Chapter 7 includes Monterey, California, 2005 that are going to play a more important role in several case studies (Belgium, , Switzer- 12 Radar cross-section is a measure of how detectable an object is by radar. Therefore it is called electromagnetic signature of the object. It is a specific the future energy systems. parameter of a reflective object that depends on many factors, and which has units of m². land, , and the United Kingdom) focusing 13 It is also termed as low observable technology that is a sub-discipline of military tactics, passive and active electronic countermeasures, which cov- ers a range of methods used to make personnel, aircrafts, ships, submarines, satellites, and ground vehicles less visible.

10 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 11 1.1. FORMATION OF WIND forces acting on an object. From this natural law the centrifugal force. Thus, the body of the Earth Due to the fact that the wind is located near the of motion it can be seen that the acceleration of is deformed by the tidal forces and tidal abdomen coast, the differences in air pressure caused by Wind is atmospheric phenomenon due to the an object is directly proportional to the net force are formed as can be seen in Figure 1. The Earth’s temperature differences are to be explained us- heating of the sun. The sun radiates on the Earth pushing or pulling that body and inversely pro- own rotation relative to the sun and moon leads ing the example of the sea-land breeze in Figure a power of 1.74 x 10¹⁷ Watts and about 2% of it portional to the mass of the body. to periodic change and hence makes the Earth’s 3. To form a body, it is necessary to heat energy, is converted into wind energy. The Earth releases body elastic (Feynman et al., 2001)14 which in the case of the Earth comes from the the heat received from the Sun, but this is hardly Gravitational force, pressure and gradient force Sun. The higher and quicker warming of the land homogeneous. In those areas where less heat is are the most important forces responsible for compared to the sea, which has a higher heat released, the pressure of atmospheric gases in- such a change in the state of motion. Gravita- Figure 2: Effects of the gravitational pull of the Moon capacity, causes the air above it to expand (2). creases, while in those areas where more heat is tional force is the force that describes the mutual on the atmosphere and water cover of the Earth. This expansion causes the density of the air to released, the air becomes hot and the gas pressure attraction of masses. For example, objects fall to change, resulting in a pressure difference. There- is reduced. As a consequence, high pressure areas the ground, because it ensures that all masses are fore, a compensating flow from the land side fol- and low-pressure areas are formed, which are drawn towards the center of the earth. Pressure lows, as the higher pressure moves to the lower also influenced by the Earth’s rotation. When dif- is the force that indicates the force acting on sur- one (3). The higher the pressure difference, the ferent masses of air get in contact, the area with a face. In this particular case, it is an opposing force greater the initial flow. Above the sea, this results higher pressure tends to transfer air towards the to the gravitational force, because the pressure in overpressure and above the land in a lack of air area with lower pressure. It is the same as when on the particle near-earth is higher than the one particles, so that in addition to the upper move- we let a balloon deflate. The high pressure inside far away from the earth, so the force towards the ments towards the sea, there is a lower move- the balloon tends to transfer air outside, where air masses above must be higher, since the num- ment away from the sea (4). This in turn, creates the pressure is lower, originating a small airflow. ber of particles pressing down decreases with in- a cycle that moves the cold air near the ground to Therefore wind is a more or less rapid air transfer creasing height. Since the two forces mentioned the land, warms it up there, so that it begins to between different pressure areas. The higher is are directed against each other, they equilibrate rise and moves back to the sea (5). At night, there the pressure difference, the faster is the displace- each other, typically without any vertical move- Source: Feynman et al., 2001 is a reverse cycle, as the air cools down more ment and the stronger is the wind. ment. The gradient force is therefore of impor- quickly on land than over the sea, whereby less tance for the formation of wind. In the event of differences can be found during the day and there On weather maps, pressure is indicated by draw- a difference in air pressure in an environment, As a result, there are slight changes, especially in is less wind (6). Thus, the temperature near the ing isolines of pressure, called isobars, at regular this force ensures a compensating current along the tropics, since the Earth’s atmosphere moves coast should have a significant influence on the 4 millibar intervals (e.g., 996 mb, 1000 mb, 1004 the pressure gradient. This compensation always at a frequency of two oscillations per day. An- presence of wind in coastal regions. mb, etc.). If the isobars are closely spaced, it can takes place from higher to lower pressure, with other important reason for pressure differences be expected that the pressure gradient force to the compensating force. lies in the temperature dependence. Due to an be great, and wind speed to be high. In areas increase in temperature, the air molecules are Figure 4: Example of land and sea wind where the isobars are spaced widely apart, the Thus, wind is created until the difference in air able to move faster and thus cause the force per pressure gradient is low and light normally pressure has dissolved. The air pressure decreases area to rise, as can be seen in Figure 3. exist. High speed winds develop in areas where with increasing altitude. Similarly, the gravita- isobars are closer. tional force is also responsible for a change in air pressure, as the mutual attraction of earth and Figure 3. Relation between temperature and densi- Wind is the result of a limited number of acceler- moon changes periodically. As a result, air parti- ty of air. As the temperature increases, the volume ating and decelerating forces, and that the action of a body increases, i.e. the density decreases, as it cles rise/sink as they are more strongly attracted/ of these forces is controlled by specific funda- is defined as mass per unit volume. repelled by the Moon. The emergence of the tides mental natural laws. Sir Isaac Newton formulat- can again be attributed to attraction force. The ed these laws as several laws of motion. The first gravitational pull of the Moon acts on the Earth, law suggests that an object that is stationary will applying force not only on the tides of the sea, remain stationary, and an object in motion will but also on the body of the Earth and the atmo- stay in motion as long as no opposing force is put sphere. By movement of the Moon and Earth on the object. This law also suggests that once in around a common central position, the mutual motion an object’s path should be straight. New- forces of attraction balance each other out. This tons’ second law of motion suggests that the means that the water and air on the side facing force put on an object equals its mass multiplied away from the Moon are less strongly attracted, by the acceleration produced. The term force in Source: Feynman et al., 2001 because the Moon’s gravitational pull is weaker this law refers to the total or net effect of all the than in the Earth’s interior, where it equilibrates 14 R. P. Feynman; R.B. Leighton (2001). “Feynman vorlesungen über physik band i: Mechanik, strahlung, wärme”. Oldeburg Wissenschaftsverlag GmbH

12 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 13 1.2. WIND POWER GENERATION AND Figure 5. A layout of a wind farm All of the above, and other previous work, have While these techniques can improve the energy WIND FARMS focused on wind farms consisting of horizontal- produced by horizontal-axis wind turbine (HAWT) axis wind turbines (Chamorro and Porte-Agel arrays, vertical-axis wind turbines (VAWTs) have The commonly used wind power generation sys- 2010; Lu and Porte-Agel 2011)18. However, re- been shown to facilitate additional strategies for tems include the direct-driven wind power gener- cently Dabiri19 (2011) has suggested the possi- performance. They can also include blades, or be ating set and the double-fed wind power generat- bility of an order of magnitude increase power bladeless. The top-heavy nature of conventional ing set; the direct-driven wind power generating for wind farms when vertical-axis wind turbines wind turbines requires high-quality components set is connected to the grid through a full power (VAWTs) are used. Due to their axis of rotation, to avoid structural damage. On the other hand, converter, while the double-fed wind power gen- VAWT wakes and the flow in a VAWT farm are with the recent innovation of bladeless wind tur- erating set is connected to the grid through a distinctly different from their HAWT counter- bines, the risk of structural damage to the sys- double-fed converter. parts. tem can be reduced significantly. Bladeless wind turbines do not include rotating blades and are There are three main types of wind energy: Professor John Dabiri and his team used fish- designed in such a way that they stand erect and schooling pattern to inspire wind farm design for oscillate in response to the vortices. Bladeless • Utility-scale wind: Wind turbines that range in Source: Adapted from Paul Breeze article “Wind optimal energy harvesting. Rather than following wind turbines contain only a few moving parts. size from 100 kilowatts to several megawatts, Power”, in Power Generation Technologies, 2019. the conventional horizontal-axis approach and They not only help in eliminating noise, but also where the electricity is delivered to the power spacing turbines far apart, they placed vertical- do not pose a threat to birds. On the other hand, grid and distributed to the end user by electric axis turbines in close proximity. Dabiri and his bladeless wind turbines at a nascent stage, are utilities or power system operators. In a wind farm, turbines should be far enough team found that if neighboring turbines are stag- less efficient in the conversion of captured wind • Distributed or “small” wind: Single small wind apart to allow wind speeds to recover, through gered and rotate in opposite directions, the al- power into electrical energy, thus limiting their turbines below 100 kilowatts that are used to lateral or vertical momentum entrainment, after teration of wind speed and direction by adjacent implementation on a large scale (Evwind, 2019)22. directly power a home, farm or small business deceleration by the upwind generator (Cortina turbines can actually be beneficial for collective and are not connected to the grid. et al, 2016)15. Spacing the turbines also reduces performance of the wind farm. Dabiri (2011)20 1.3. WIND TURBINES the fatigue load generated by turbulence from and his collaborators (Kinzel et al., 2012)21 per- • Offshore wind: Wind turbines that are erected A wind turbine is a machine that converts kinetic the upstream turbines and thus increases turbine formed experiments on various counter-rotating in large bodies of water, usually on the conti- energy from the wind into electricity. The blades lifetime (Chamorro and Porte-Agel, 2009)16. The configurations of 9 meter tall vertical-axis wind nental shelf. Offshore wind turbines are larger of a wind turbine turn between 13 and 20 revolu- large majority of existing farms use horizontal- turbines and demonstrated that, unlike the typi- than land-based (onshore) turbines that can tions per minute, depending on their technology, axis wind turbines (HAWTs); the behavior of cal performance reduction of horizontal-axis wind generate more power. at a constant or variable velocity, where the ve- horizontal-axis turbines in large wind farms, and turbines with close spacing, there is an increase in locity of the rotor varies in relation to the velocity the required spacing between, have been exten- VAWT performance when adjacent turbines are A wind farm is a collection of wind turbines that of the wind in order to reach a greater efficiency. sively studied. Calaf et al (2010)17 investigated arranged to interact synergistically. However, operate as a single . Depending the vertical transport momentum and kinetic en- high experimental costs and time requirement upon its size, a wind farm will normally have a Nowadays, modern wind turbines are reliable, ergy in a fully-developed HAWT-array boundary prevent the extension of these field investiga- dedicated substation into which power from all quiet, cost-effective and commercially competi- layer (defined as the internal boundary layer de- tions to large farm scales or the assessment of the wind turbines is fed and from which it is car- tive as the wind turbine technologies are proven veloping above a wind farm). They showed that, a large number of configurations. The previous ried to the nearest access point to the grid sys- and mature. At present, technical challenges are for large wind farms, regeneration of the kinetic findings thus only pertain to limited number of tem. Currently, increasingly larger wind farms are generally associated with ever-growing wind energy is mainly from downward vertical fluxes turbines where the mean kinetic energy is pri- being deployed, and the continued spread and turbine size, power transmission, energy stor- across the plane delineating the top of the farm, marily replenished by stream-wise advection and expansion of these farms poses a challenge since age, energy efficiency, system stability and fault unlike farms with a limited number of wind-tur- cross-stream turbulent transport, rather than by the required land area will increase. A major goal tolerance. The power converter malfunction will bine rows where the stream-wise advection of vertical transport as in large farms. of current energy research is thus to increase the cease the operation of wind turbine and gener- kinetic energy dominates. wind-farm power density, i.e. how much energy can be produced per unit land area used.

18 L. Chamorro; F. Porte-Agel (2009), “A wind-tunnel investigation of wind turbine wakes: boundary-layer turbulence effects. Boundary-Layer Mete- orol 136:515-533. https://doi.org/10.1007/s10546-009-9380-8 15 G.Cortina, M. Calaf, and R.B.Cal (2016). “Distribution of mean kinetic energy around an isolated wind turbine and a characteristic wind turbine of a 19 very large wind farm”. In Phys Rev Fluids 1:74402, https://doi.org/10.1103/PhysRevFluids.1.074402 J. O. Dabiri (2011). “Potential order-of magnitude enhancement of wind power density via counter-rotating vertical-axis wind turbine arrays”, In Renewable Sustainable Energy. 16 L. Chamorro; F. Porte-Agel (2009), “A wind-tunnel investigation of wind turbine wakes: boundary-layer turbulence effects. Boundary-Layer Mete- 20 orol 136:515-533. https://doi.org/10.1007/s10546-009-9380-8 Ibid, 2011 21 17 G.Cortina, M. Calaf, and R.B.Cal (2016). “Distribution of mean kinetic energy around an isolated wind turbine and a characteristic wind turbine of a M. Kinzel; Q. Mulligan and J.O. Dabiri. “Energy exchange in an array of vertical-axis wind turbines”. In Journal of Turbulence, vol. 13, No.38, 2012, very large wind farm”. In Phys Rev Fluids 1:74402, https://doi.org/10.1103/PhysRevFluids.1.074402 pp. 1-13. Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, CA, USA 22 “Bladeless Wind Turbines – Less Efficient in the Conversion of Captured Wind Power Into Electrical Energy”, Evwind press release, 31 May, 2019

14 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 15 ate disturbance to the grid. Recently, it has been of 4 to 7 meters. It contains an opening on the allow a maximum production of electricity. The ings, the isolation of gear and generator shafts widely accepted in wind industry that the power ground to allow access to variety of equipment. height at the tip of the blade varies between 90 from mechanical bending loads, the integrity and converter should be robust, and have good capa- The rotor is located upwards where the wind is and 150 meters for the largest wind turbines. The load paths. Although, it may be easier to service bility of fault tolerance. strongest, and which allows for a lengthy blade. blades of a wind turbine turn at an average speed separate wind turbine components such as gear- The pivoting nacelle is located at the peak of the of 10 to 20 rotations per minute. The rotor blades boxes, bearings and generators, the industry is Wind turbines first emerged more than a century tower, it houses the generator that transforms extract kinetic energy from the moving air mass- increasingly in favor of system design of the inte- ago. Following the invention of the electric gen- the mechanical wind energy into electric energy. es according to the buoyancy principle as seen in grated drive train components. erator in the 1830s, engineers started attempt- The nacelle is made by a ladder and/or a lift is Figure 5. Here the upper side of the wing is larger ing to harness wind energy to produce electric- located inside the tower. than the lower side, due to the different distance 1.3. TYPES OF WIND TURBINES ity. Wind power generation took place in the the air must move at a higher speed at the upper Wind turbines can be categorized by the orien- United Kingdom and the United States in 1887 Wind turbines come with different topologies, side than at the lower side. tation of their axis of rotation into two groups: and 1888, but modern wind power is considered architectures and design features. The schematic horizontal axis wind turbines (HAWTs) and verti- to have been first developed in Denmark, where of a wind turbine generation system is shown in In order to convert the kinetic energy into elec- cal axis wind turbines (VAWTs). The latter typi- horizontal-axis wind turbines were built in 1891 Figure 6. trical energy at a rotor speed of 30 to 50 rota- cally have fewer moving parts and a generator lo- and a 22.8 meter wind turbine began operation tions per minute (rpm), a speed of approximately cated at ground level which could ultimately lead in 1897. 1500 rpm is required for most four-pole genera- to higher availability and lower maintenance tors in the network specification (50 Hz). Usu- cost (Eriksson, 2008)23. Furthermore, it has been Tall, tubular steel towers support a hub with ally, the gearbox forms a part of the drive train, shown that the concept is more suitable for up- three attached blades and a “nacelle”, which which divides the drive shaft into a slow and a scaling than the HAWT concept. And of special houses the shaft, gearbox, generator, and con- fast generator shaft. The gearbox is located in the interest for this work, VAWTs has potentially trols. Wind measurements are collected, which nacelle of the wind turbine. The friction of the lower noise emissions. direct the turbine to rotate and face the stron- gearwheels results in low energy losses, which gest wind, and the angle or “pitch” of its blades is manifest themselves through heat radiation and 1.3.1. HORIZONTAL AXIS WIND TURBINES optimized to capture energy. Modern wind tur- acoustic noises. bines are large structures, many reach more than Horizontal axis wind turbines (HAWTs) are the 150 meters above the ground. Clusters of densely One of key components in the wind turbine is its most common wind machine design is use today. spaced with wind turbines, so called wind farms, drive train, which links aerodynamic rotor and It may produce less than 100 kW for basic appli- are being built both on- and offshore. Wind farms electrical output terminals. Optimization of a cations and residential use, or as much as 6 MW. vary in size from a small number of turbines to wind turbine generators cannot be realized with- The HAWT is a wind turbine in which the main several hundred wind turbines covering an exten- Source: Futuren Group (2020). out considering mechanical, structural, hydrau- rotor shaft is pointed in the direction of the wind sive area. lic and magnetic performance of the drive train. to extract power. The principal components of a Generally, drive train technologies can be broken basic HAWT are shown in Figure 8. HAWTs utilize The smallest turbines are used for applications Wind turbines include critical mechanical com- down into four types according to their structure: aerodynamic blades (i.e. airfoils) fitted to a rotor, such as battery charging for auxiliary power for ponents such as turbine blades and rotors, drive which can be positioned either upwind or down- boats or caravans or to power traffic warning train and generators. In general, wind turbines • Conventional: gearbox and high speed genera- wind. HAWTs are typically either two- or three- signs. Larger turbines can be used for making are intended for relatively inaccessible sites plac- tor with few pole pairs; bladed and operate at high blade tip speeds. contributions to a domestic power supply while Machines with upwind rotors require a yaw, or ing some constraints on the designs in a number • Direct drive: any drive train without a gearbox selling unused power back to the utility supplier tail vane, to help them orient into the wind while of ways. and low speed generator with many pole pairs; via the electrical grid. Arrays of large turbines, downwind rotors have blades that are coned al- known as wind farms, are becoming an increas- The part of the wind turbine that converts the en- • Hybrid: any drive train with a gearbox and the lowing turbine to orient on its own. One draw- ingly important source of intermittent renewable ergy contained in the wind into a mechanical ro- generator speed between the two types men- back identified with downwind rotors, however, energy and are used by many countries as part of tary motion is the rotor. It consists of one or more tioned above; is that they have been known to “walk” around a strategy to reduce reliance on fossil fuels. when trying to line up with winds during low rotor blades of composite material from 25 to 60 • Multiple generators: any drive train with more speed energy production (Gipe, 2009)24. meters in length and it is connected by the rotor than one generator. An onshore wind turbine is made up of three hub. The number of rotor blades is related to the main parts as seen in Figure 4: the tower, the Modern HAWTs use the aerodynamic lift force rotor speed in order to achieve the best possible Drive train topologies may raise the issues such rotor, and the pivoting nacelle. The tower is to turn each rotor blade, in a manner similar to wind speed reduction. For this reason, modern as the integration of the rotor and gearbox/bear- most often metallic and cone shaped, it is usu- plants have from one to three rotor blades. The ally white and meets aeronautical requirements. rotor pivots 360 degrees to face the wind and to 23 It is 40 to 110 meters tall, with a base diameter S. Erikkson (2008). “Direct driven generators for vertical axis wind turbines”, Doctoral dissertation, ACTA UNIVERSITATIS UPSALIENSIS, Uppsala 24 P. Gipe (2009). “Wind energy basics: a guide to home and community scale wind energy systems”, Chelsea Green Publishing.

16 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 17 the way an airplane flies. The lift force generally Downwind machines have been built, despite the when HAWTs are arrayed in a wind farm, down- 1.3.2. VERTICAL AXIS WIND TURBINES works as follows. When exposed to winds, air problem of turbulence (mast wake), because they stream turbines perform less efficiently than in Stanford University researchers created a cutting flows around both the upper and lower portions do not need an additional mechanism for keep- isolation due to the incoming turbulent wake cre- edge lab model of vertical wind turbine (VAWT) of a blade. As a result of the blade’s curvature, ing them in line with the wind, as well as in high ated by upstream turbines. Studies have shown arrangements that will help with design and however, air passes over the top of the blade winds the blades can be allowed to bend which that a HAWT spacing on the order of 20 turbine implementation in the future. VAWT is a wind more quickly (owing to a longer fetch length) reduces their swept area and thus their wind re- rotor diameters, D, is needed to provide space turbine design where the generator is vertically than the lower portion, producing a low-pressure sistance. Since cyclical (that is repetitive) turbu- for the flow to re-energize sufficiently for down- oriented in the tower, rather than sitting horizon- area on the topside. The pressure difference cre- lence may lead to fatigue failures, most HAWTs stream turbines to achieve performance levels tally on top. Vertical Axis Wind Turbine (VAWT) ated between the top and bottom sides of the are of upwind design. similar to those demonstrated in isolation. De- are a type of wind turbine used to convert kinetic blade produces a force in the direction of the top spite this, modern HAWT farms typically space energy from moving air into electrical power by blade. turbines approximately 3-5 D in the cross-wind means of lift producing blades. They differ to Figure 8. Basic parts of a HAWT direction and 6-10 D in the stream-wise direc- the conventional Horizontal Axis Wind Turbines Horizontal-axis wind turbines (HAWTs) have the tion26. (HAWT) by having the main shaft transversely main rotor shaft and electrical generator at the aligned with the wind direction. Vertical Axis top of a tower, and must be pointed into the A variety of solutions have recently been proposed Wind Turbines are seen as a viable solution to wind. Small turbines are pointed by a simple wind to effectively manage the tradeoff between tur- urban and peri-urban power generation require- vane, while large turbines generally use a wind bine efficiency and wind farm footprint. Instead ments leading into 2020. sensor coupled with a servo motor. Most have of optimizing for individual turbine efficiency, a gearbox, which turns the slow rotation of the optimization can focus on the total power pro- This type of wind turbines could be either ar- blades into a quicker rotation that is more suit- duction of turbine arrays. More recently, a row- ranged in groups or interspersed within horizon- able to drive an electrical generator. offset arrangement was demonstrated to allow tal-axis wind turbines (HAWT) arrays. A VAWT for a greater wake recovery due to the increased has an overall cylindrical shape, with the blades Since a tower produces turbulence behind, the stream-wise spacing within the array. Moreover, aligned parallel to, and rotating around, the turbine is usually positioned upwind of its sup- by decreasing the power output of upstream tur- pole on which the rotor is mounted. These “egg- porting tower as seen in Figure 7. Turbine blades bines, the performance of downstream turbines beater” VAWTs tend to be much smaller than are made stiff to prevent the blades from being and the power output of the array as a whole can the “propeller” HAWTs, typically about 10 times pushed into the tower by high winds. Addition- be increased27. Source: Electrical Academy 2020 shorter in height, and output about 0.1 percent ally, the blades are placed at a considerable dis- as much power per turbine. tance in front of the tower and are sometimes Even though the HAWT has by far been the most tilted forward into the wind a small amount. successful concept with the large and economi- The main design principle of horizontal axis wind While a single VAWT is not as energy-producing cally feasible turbines of today the VAWT con- turbine is almost exclusively a propeller design. as an individual HAWT, the wind flow synergies cept has some advantages that are explained One of the advantages of this propeller type is created in a closely-spaced array of VAWTs can Figure 7. Configuration of HAWTs more detail in the next section of this chapter. that by adjusting the rotor blades around their potentially generate up to 10 times more power A variety of solutions have recently been proposed longitudinal axis, the rotor speed and the power per unit of land area than an array of widely- to effectively manage the tradeoff between tur- output of the wind turbine can be controlled. The spaced HAWTs. bine efficiency and wind farm footprint. Instead adjustment of the rotor blades is the most ef- of optimizing for individual turbine efficiency, fective means of protection against over-speed, There are two different ways of converting wind optimization can focus on the total power pro- especially in case of extreme wind speeds. With energy into mechanical energy for the vertical duction of turbine arrays. More recently, a row- an optimal design of the rotor blade shape, maxi- axis converters. Here, either the thrust or the suc- offset arrangement was demonstrated to allow mum utilization of the principle of aerodynamic tion of the wind is used to generate a rotary mo- for a greater wake recovery due to the increased lift can be achieved. Systems of such a propeller tion, hence a closer look at the two most impor- stream-wise spacing within the array. Moreover, design, as shown in Figure 8, consist of the follow- tant representatives of this design will be taken. by decreasing the power output of upstream tur- ing components: foundation, nacelle and rotor. bines, the performance of downstream turbines The Savonius wind turbine is a type of vertical- and the power output of the array as a whole can An industry and academic focus on large, utility- axis wind turbine invented by the Finnish engi- be increased28. scale horizontal-axis wind turbines (HAWT) has neer Sigurd Savonius in the 1920s. It consists of led to the development of HAWTs capable of ef- Source: Modified from Boulouiha & Denai (2017) in ficiencies near the theoretical Betz limit of maxi- 25 According to Betz’ law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind. The factor 16/27 is known as Betz’ co-efficient. Practical utility-scale wind turbines achieve at peak 75-80% of the Betz limit. “Clean Energy for Sustainable Development. 25 mum wind energy extraction, 59.3% . However, 26 Brownstein et al (2016), Performance enhancement of downstream vertical-axis wind turbines, Journal of Renewable Energy, 8 27 Ibid 28 Ibid 18 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 19 two to three “scoops” that employ a drag action Figure 10. Functioning of a Savonius wind ro- A can spin at many times 1.4. WIND TURBINE GENERATORS to convert wind energy into torque to drive a tor. Here the wind is first pressed into one of the the speed of the wind hitting (i.e. the tip speed One of limiting factors in wind turbines lies in turbine. When looked at from above in cross- counter-rotating, curved, overlapping shells and ration is greater than 1). Hence a Darrieus wind their generator technology. A generator converts section, a two scoop Savonius turbine looks like then deflected into the second shell, so that a drive turbine generates less torque than a Savonius the mechanical rotary motion of the drive train an S-shape. Due to the curvature of the scoops, movement is created. but it rotates much faster. This makes Darrieus into electrical energy. This is done by alternating the turbine encounters less drag when moving wind turbines much better suited to electricity current generators, which achieve efficiencies of against the wind than with it, and this causes the generation rather than water pumping and simi- 90 to 98% depending on the load range. There is turbine to spin in any direction of wind regardless lar activities. The centrifugal forces generated by no consensus among academics and the industry of facing. Aerodynamically it is the simplest wind a Darrieus turbine are very large and act on the on the best wind turbine generator technology. turbine to design and build which reduces its turbine blades which therefore have to be very Traditionally, there are three main types of wind cost drastically compared to the aerofoil blade strong – however the forces on the bearings and turbine generators (WTGs) which can be consid- designs of the other VAWTs and HAWTs. generator are usually lower than the case with a ered for the various wind turbine systems, these Savonius. being direct current (DC), alternating current Figure 9. Savonius wind turbine After the First World War, G.J.M. Darrieus, a (AC) synchronous and AC asynchronous genera- A disadvantage of the Darrieus turbine is that it French aeronautical engineer, invented a VAWT tors. In principle, each can be run at fixed or vari- is not a self-starting wind turbine. Therefore a by adopting airfoil profile for the blades. He pat- able speed. Due to the fluctuating nature of wind small powered motor is required to start off the ented the design in France in 1925 and in the power, it is advantageous to operate the WTG at rotation, and then when it has enough speed the USA in 1931 and put the working principle as a variable speed which reduces the physical stress wind passing across the aerofoils starts to gener- biomimicry of birds’ wings which enabled to give on the turbine blades and drive train, and which ate torque and the rotor is driven around by the the blades a stream line section analogous to improves system aerodynamic efficiency and wind. Two small Savonius rotors are mounted on that of the wings of birds. It offered the minimum torque transient behavior. resistance to forward movement. As well it was the shaft of the Darrieus turbine to start rota- tion. As a result it slows down the Darrieus tur- capable of converting it into mechanical energy The advantages of asynchronous generators are bine when it gets going however these two small the maximum available amount of energy of the its robustness and low maintenance costs. Fur- rotors make the whole device a lot simpler and fluid by means of the useful component of the thermore, they can ensure simple synchroniza- 30 easier to maintain. Variants of the Darrieus wind The air is trapped in the concave part and pushes traverse thrust which this section underwent . tion with the mains, which they load with reac- turbine are the giromill and cycloturbine. the turbine. The flow that hits the convex part The patent covered two major configurations: tive current. Asynchronous generators can be does produce a drag that is lower than the one on curved and straight blades. coupled to the grid smoother as compared to the concave part. It is the differential of the drag Figure 11. Darrieus wind turbine. their synchronous counterparts, but they have a force that causes this turbine to rotate. This low- Most wind turbines designed for the production lower efficiency. However, for the synchronous ers the efficiency of the turbine as some of the of electricity have consisted of two or three blad- generators with a higher efficiency, power invert- wind’s power is used pushing the convex part and ed propeller rotating around a horizontal axis. ers are required to be connected to the grid. is hence “wasted”. More blades can be added to These blades tend to be expensive, high technol- the S shape design, and the same principle causes ogy items, and the turbines has to be oriented AC Synchronous Generator Technologies it to spin as shown in figure 9. into the wind, another expensive task for the larger machines. These problems have led many Since the early time of developing wind turbines, considerable efforts have been made to utilize According to Wilson et al29, “a Savonius rotor re- researchers in search of simpler and less expen- three-phase synchronous machines. AC synchro- quires 30 times more surface for the same pow- sive machines. One that has seen considerable nous WTGs can take constant or DC excitations er as a conventional rotor blade wind-turbine. development is the Darrieus wind turbine. from either permanent magnets or electromag- Therefore, it is only useful and economical for nets and thus termed PM synchronous genera- small power requirements”. This makes Savonius Unlike the Savonius wind turbine, which accumu- tors (PMSGs) and electrically excited synchro- ideal for small applications with low wind speeds. lates the energy for rotation, the Darrieus is a lift- nous generators (EESGs), respectively. When the Savonius are hence desirable for their reliability, type VAWT. Rather than collecting the wind in rotor is driven by the wind turbine, a three-phase as they are able to work at several magnitudes of cups dragging the turbine around, a Darrieus uses power is generated in the stator windings which wind speed. lift forces generated by the wind hitting aerofoils to create rotation. are connected to the grid through transformers and power converters. For fixed speed synchro- nous generators, the rotor speed must be kept at 29 R. Wilson; P. Lissaman. “Applied Aerodynamics of Wind Power Machine”, National Science Foundation, 1974 exactly the synchronous speed. Otherwise syn- 30 W. Tiju; T. Marnoto; S. Mat; M. Ruslan; K. Sopian. “Darrieus vertical axis wind turbine for power generation I: Assessment of Darrieus VAWT configu- rations”, In Renewable Energy, volume 75 (2015), pp. 50-67 Source: Wordpress 2017. chronisation will be lost.

20 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 21 Synchronous generators are a proven machine tor develops its own magnetic poles, which in turn by the load rather than by adjusting the turbine. aging. With drones, photo can be taken remotely technology since their performance for power become dragged by the electromagnetic force Electric utilities do have some load management and autonomously without the need for a pilot, generation has been studied and widely accept- from the rotating magnetic field in the stator. capability, but most of their load is not control- cloud computing can then stitch these images to- ed for a long time. In theory, the reactive power lable by the utilities. The utilities therefore adjust gether, before finally passing them over to an AI characteristics of synchronous generators, ran- These induction generators fall into two types: the prime mover input (by a valve in a stream (artificial intelligence) system that is programmed dom wind speed fluctuations and periodic distur- fixed speed induction generators (FSIGs) with line, for example) to follow the variation in load. to identify any problems with the blade i.e. – bances caused by tower-shading effects and nat- squirrel cage rotors, and doubly-fed induction That is, supply follows demand. In the case of cracks, for example. The highly digitalized process ural resonances of components would be passed generators (DFIGs) with wound rotors. wind turbines, the turbine input power in is just means maintenance issues can be identified at an onto the grid. the power in the wind and it is not subject to con- early stage, enabling technicians to be deployed trol. Turbine speed still needs to be controlled for before the problem becomes serious enough to Figure 13. Doubly-fed induction generator optimum performance, and this can be accom- warrant shutting down the turbine. Figure 12. Structure of a Synchronous Generator. plished by an electrical load with the proper char- With stator (in black color), rotor (in green and acteristics, as can be seen. Digitalization is not only restricted to the tech- red), and slip rings (in orange) nology of the wind turbine itself, it expand across It can be expected that the use of asynchronous the industry with ideas such as an intelligent electricity to continue, and perhaps even to grow, “smart grid” developing. In essence, the smart for a number of reasons. The use of wind power at grid is a digital technology that enables commu- remote communication sites for charging batter- nication between the utility provider and the cus- ies can be expected to increase as less expensive, tomer. The smart grid can be conceptualized as more reliable wind turbines are developed. Space an extensive cyber-physical system that supports heating and domestic hot water heating are nat- and facilitates significantly enhanced control- ural applications where propane or oil are now lability and responsiveness of highly distributed being used. Another large potential for market resources within electric power systems. Smart would be the many thousands of villages around grids consist of series of computers, automated Source: Adapted from CPEL Energy (2020) the world which are not interconnected with any process and new technologies working together AC Asynchronous Generators large utility grid. Economics may preclude the to create a responsive grid. For example, if there Whilst conventional power generation utilizes possibility of such a grid, so each village may be is an emergency such as a blackout, the smart synchronous machines, modern wind power sys- When supplied with three-phase AC power to forced to have its own electric system. grid technologies can detect this and isolate the tems use induction machines extensively in wind the stator, a rotating magnetic field is estab- problem, containing it before it grows to become turbine applications. One reason for choosing lished across the airgap. If the rotor rotates at One final reason for having asynchronous capa- a large-scale blackout. this type of generator is that it is very reliable a speed different to synchronous speed, a slip is bility on wind turbines would be the possibility of and tends to be comparatively inexpensive. The created and the rotor circuit is energized. Gener- its being needed if electrical grid should fall apart. The uncertainty and intermittency of wind and generator also has some mechanical properties ally speaking, induction machines are simple, reli- solar generation are major complications that which are useful for wind turbines, like the gen- able, inexpensive and well developed. They have 1.5. FUTURE TRENDS IN WIND TURBINES must be addressed before the full potential of erator slip and a certain overload capacity. high degree of damping and are capable of ab- TECHNOLOGIES these renewables can be reached. Smart grid sorbing rotor speed fluctuations and drive train concepts – an evolution of electricity networks As the technology matures, advancements are on transients (i.e fault tolerant). However, induction towards greater reliance on communications, The key component of the asynchronous gen- the horizon that will extend wind project lifespan machines draw reactive power from the grid and computation, and control – promises a solution. erator is the cage rotor that makes the asynchro- whilst simultaneously lowering the operational thus some form of reactive power compensa- The term gained prominence through the U.S nous generator different from its synchronous costs. Some of the main areas of innovation are: tion is needed such as the use of capacitators Energy Independence and Security Act (EISA) of counterpart. The rotor consists of a number of (1) longer and lighter rotor blades – with some or power converters. For fixed-speed induction 2007, the European Technology Platform for the copper or aluminium bars which are connected reaching 95 meters long; (2) blades with curved generators, the stator is connected to the grid via Electricity Networks of the Future, and similar electrically by aluminium end rings. When the tips that are designed to take maximum advan- a transformer and the rotor is connected to the initiatives across numerous other countries. The current is connected, the machine will start turn- tage of all wind speeds; (3) more reliable gear- wind turbine through a gearbox. The rotor speed current grid structure reflects carefully consid- ing like a motor at a speed which is slightly below boxes; and (4) digitalization of processes. the synchronous speed of the rotating magnetic is considered to be fixed (in fact, varying within a ered trade-offs between cost and reliability. The narrow range). responsiveness achievable through smart grid field from the stator. There is a magnetic field Turbines at present, are not very digital. But as concepts will, however, play a vital role in achiev- which moves relative to the rotor. This induces a technology, in general, evolves to become more The asynchronous system has one rather inter- ing large-scale integration of new forms of gen- very strong current in the rotor bars which offer sophisticated. Use of drones is also another esting mode of operation that electric utilities eration and demand. Renewable generation will very little resistance to the current, since they are technological advance the wind industry is lever- short circuited by the end rings. Therefore the ro- do not have. The turbine speed can be controlled make an increasingly important contribution to

22 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 23 electric energy production into the future. Inte- aged when further operated. In this way, actions The characteristic features of wind energy as age, and classify targets while suppressing strong gration of these highly variable, widely distrib- can be taken in advance to increase the efficiency its volatility and unpredictability can cause dif- unwanted interference such as echoes from the uted resources will call for new approaches to of the grid and its parts. This can be applied on ferent problems. On one hand, to keep the pro- environment (known as clutter) and countermea- power system operation and control. Likewise, the power grid of a country as well as micro-grids vided power at a steady level the power feed in sures (jamming). Radar jamming and deception is new types of loads, such as plug-in electric ve- of for example single buildings (Ricalde et al., of other sources has to be adjusted or the wind a form of electronic countermeasures that inten- hicles and their associated vehicle-to-grid po- 2011)31. power generation itself has to be controlled in tionally sends out radio frequency signals to in- tential, will offer challenges and opportunities. some way. Therefore making predictions on the terfere with the operation of radar by saturating Establishing a cyberinfrastructure that provides Different systems can be integrated into the wind power feed in is essential to solve the issue. its receiver with noise or false information. ubiquitous sensing and actuation capabilities will smart grid to provide a more efficient and more The most common models for forecasting wind be vital to achieving the responsiveness needed stable network. This also includes the data trans- are time series models and machine learning ap- for future grid operations. Sensing and actuation mission of sensors on wind turbines to get the proaches. Thus, wind power can be predicted on Figure 14. Basic principle of a radar will be pointless, though, without appropriate actual generation information as well as data short and medium time intervals from minutes controls. The premise of the smart grid is a huge related to maintenance issues. As renewable en- to a few days. Based on these forecasts, adjust- industry-level change that will take a decade to ergy by its nature is fluctuating, a precise obser- ments can be made to ensure a stable grid. On implement, but it will bring great rewards such vation is necessary to prevent blackouts. Further, the other hand, fluctuations on very short time as, the ability to predict demand and coordinate the smart grids can be used for optimization of intervals like a couple of seconds cannot be ac- storage at multiple levels. It could be used to tell the grid to make adjustments in case, the power counted for in the same way. Instead, other ap- the turbines in a wind farm when to run; depen- demand increases or decreases. Basis for this is proaches have to be taken. One of them is to dent on what the current demand for energy is, the fast communication between all parts of the evaluate the effects of this short term fluctua- meaning energy usage becomes much more ef- grid (Li et al., 2010)32. tion via simulation and take adjustments in the ficient and cost-effective. grid to prevent blackouts (Zhang et al., 2019)35. However, smart grids do not only feature high A smart power grid can be characterized by four level observation and fast communication they CHAPTER 2. RADAR SYSTEMS AND WIND Radar originally was developed to meet the needs different features: collecting (real-time) informa- also yield a high amount of data, which can be FARMS of the military services, and it continues to have tion, its transfer and aggregation, evaluation and used to predict events even before they occur. A radar is an electromagnetic system for detec- critical applications for national defence purposes. analysis as well as making adjustments. At first, Since more than two decades researchers try to tion, location and recognition of target objects, For instance, radars are used to detect aircraft, a smart power grid enables to gather information find the most efficient way to predict the wind which operates by transmitting electromagnetic missiles, artillery and mortar projectiles, ships, at the different parts of the grid. As an example, generation in different scenarios. This can be signals, receiving echoes from target objects land vehicles, and satellites. In addition, radar a sensor at a turbine measures the current power done by traditional time series models or other within its coverage volume, and extracting loca- controls and guides weapons; allows one class of generation and indicates when it has to be main- probabilistic approaches. Currently artificial in- tion and other information from these echo sig- target to be distinguished from another; aids in tained. Other potential use can be gathering in- telligence (AI) algorithms are the most common- nals. Detection involves directing a beam of ra- the navigation of aircraft and ships; and assists formation about the power demand of a city or ly used method for wind generation predictions. dio-frequency waves over a region to be searched. in reconnaissance and damage assessment. Mili- the current wind speed or level of sunshine at a These algorithms take advantage of a complex When the beam strikes a reflecting object, some tary radar systems can be divided into three main specific location. This information is transferred system which is weighting different factors of in- of the beam’s energy is reflected. A very small classes based on platform: land-based, shipborne, and aggregated at a central point, for example a fluence and is optimized by powerful computers part of this reflected energy is returned to the and airborne. Within these broad classes, there are data center where the data is further processed to provide the best prediction results (Di Piazza et radar system. several other categories based mainly on the op- and can be finally observed by a human or com- al., 2016)33. They can also be used for other fore- erational use of the radar system. There is also a puter who evaluates and analyses the data by casts, for example the power demand of private Using the coordinate systems, radar systems trend to develop multimode radar systems. using different methods, for example a machine households. This part of the power demand is an- provide early detection of surface or air objects, learning algorithm which categorizes the mainte- other factor of volatility which can be reduced by giving extremely accurate information on dis- In 1904 the German engineer, Christian Hüls- nance level of a wind turbine. Based on the anal- predictions besides solar and wind power (Raza tance, direction, height, and speed of the objects. meyer obtained a patent for a device capable of ysis, adjustments can be made, for example the et al., 2017)34. Radar measurement of range (or distance) is detecting ships. This device was demonstrated shut-down of the turbine as it is seriously dam- made possible because of the properties of ra- to the German navy, but failed to arouse interest diated electromagnetic energy. Modern radars, probably due in part to its very limited range. In 31 L. J. Ricalde; E. Ordoñez; M. Gamez and E.N. Sanchez. “Design of a smart grid management system with renewable energy generation”. In 2011 IEEE Symposium on Computational Intelligence Applications In Smart Grid (CIASG), Paris, 2011, pp. 1-4., www.doi.org/10.1109/LIASG.2011.5953346 however, are sophisticated transducer/computer 1922, Guglielmo Marconi drew attention to the 32 F. Li; F. Wu and J. Zhong. “Communications Requirements for Risk-Limiting Dispatch in Smart Grid”. 2011 IEEE International Conference on Com- systems that not only detect targets and deter- work of Hertz and repeated Hertz experiments munications Workshops, Capetown, South – Africa, 2010, pp. 1-5 mine target range, but also track, identify, im- and eventually proposed in principle what is now 33 A. Di Pizza; C. Di Piazza and G. Vitale. “Solar and wind forecasting by NARX neural networks”. In 2016 Renewable Energy and Environmental Sustain- ability, volume 1, Issue 39. https://doi.org/10.1051/rees/2016047 34 M. Raza; M. Nadarajah; D. Hung; Z. Baharudin. “An intelligent hybrid short-term load forecasting model for smart power grids”. In 2017 Sustainable 35 X. Zhang; C. Ma; M. Timme (2019). “Dynamic Vulnerability in Oscillatory Networks and power Grids” ort-term load forecasting model for smart Cities and Society, 31, pp.264-275 power grids”. In 2017 Sustainable Cities and Society, 31, pp.264-275

24 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 25 known as marine radar. It was a pulsed radar, Once a movement occurs in the detection field, the spectrum that can be defined and categorized by natures for the purpose of classification. There radiating differentiated video pulses, generated microwaves come back to the sensor with a differ- the respective electromagnetic wavelengths. are two sources for the distance measurement: by a spark gap. Hülsmeyer’s ideas were based on ent frequency and this results in a detection. a coarse but unambiguous information by mea- the experiments by Heinrich Hertz in 1888, when Electromagnetic waves can be grouped accord- surement of the wave travelling time and a fine he detected the polarization dependent reflec- The phenomenon of electromagnetic radiation ing to the direction of disturbance in them and but ambiguous information by phase measure- tion of electromagnetic waves. Radar systems is caused by the mutually reinforcing interaction according to the range of their frequency. This ment. The accuracy is in the order of meters have evolved tremendously since their early days of charged electrical and magnetic fields operat- means that there are two things going on: the down to decimeters for the first kind and in the when their functions were limited to target de- ing perpendicular to each other and that travel disturbance that defines a wave, and the prop- order of fractions of the wavelength (millime- tection and target range determination. through space at the speed of light. Each pulse agation of wave. In this context the waves are ters) for the second. By using the phase modu- emanating from the interplay of the electrical grouped into the following 2 categories: 36 lations over time (Doppler frequency) the radar The radar technology, also known as microwave and magnetic fields’ results in a force that creates can measure also the radial velocity with a high technology is based on the Doppler Effect: the radar a wave of energy. Electromagnetic wavelength • Longitudinal waves – a wave is called longi- accuracy (Ender, J, 2005)37. sensor continuously emits microwaves with a cer- refers to the measured distance between the tudinal when the disturbances in the wave are tain frequency in a defined area. These microwaves crest and trough of each adjacent wave gener- parallel to the direction of propagation of the There are two different basic concepts of radar: are reflected back to the sensor by all of the objects ated by the electromagnetic disturbance. Radio wave. For example, sound waves are longitu- the first aims at the detection and localization present in its environment. If the objects in this area waves, television broadcasts, X-rays, visible and dinal waves because the change of pressure of targets; here the resolution cell size (range, do not move, the microwaves come back to the invisible light, and microwave radiation are each occurs parallel to the direction of wave propa- direction, Doppler) is greater or equal to the ex- sensor with the same frequency as the initial one. discrete components of the electromagnetic gation. tensions generated by the object. Target classi- fication can be achieved via the signal strength • Transverse waves- a wave is called a trans- (radar cross section, RCS), Doppler modulations Figure 15. Radar frequencies and Radar Bands verse wave when the disturbances in the wave by moving parts of the object, polarization38, and are perpendicular (at right angles) to the direc- the dynamics of motion. The second concept is Band Designation Frequency Range Usage tion of propagation of waves. that of radar imaging. The aim is to generate a High frequency (HF) 3-30 MHz OTH surveillance36 quasi- optical image (SAR, ISAR)39. In this case The intensity of electromagnetic radiation is a the resolution cells have to be much smaller than Very high frequency (VHF) 30-300 MHz Very-long-range surveillance function of the frequency of the waves generated the objects extension. Information about the in each second. Specific frequencies are identified target can be extracted from the two- or three- Ultra high frequency (UHF) 300 MHZ – 1 GHz Very-long-range surveillance by the number of cycles generated each second. dimensional images or even one-dimensional im- Long-range surveillance The spectrum of electromagnetic waves has fre- L 1-2 GHz ages (range profile, micro-Doppler). En route traffic control quencies up to 10²⁴ Hz. This very large range is subdivided into different subranges due to dif- Moderate-range surveillance Radar systems in its simplest form can be seen ferent physical properties. There are different S 2-4 GHz Terminal traffic control in Figure 16. Radar is a sensor system utilizing working frequencies ranging from S-band (2.0- Long-range weather electromagnetic radiation in the radio frequency 4.0 GHz) to X-band (8.0-12.0 GHz) in the case of (RF) special region, spanning from approximately Long-range tracking weather and marine radars, and L-band (1.0-2.0 C 4-8 GHz 3 MHz to around 100 GHz. An elementary form Airborne weather detection GHz) as seen in Figure 15. of radar consists of a transmitting antenna emit- Short-range tracking ting electromagnetic radiation generated by an Missile guidance 2.1. THE RADAR CONCEPT X 8-12 GHz oscillator of some sort, a receiving antenna, and Mapping, marine radar A radar system measures the distance and di- an energy-detecting device, or receiver. Airborne intercept rection to the object, its velocity and some sig- High-resolution mapping Ku (“under” K-band) 12-18 GHz Satellite altimetry

Little use (water vapor) 36 K 18-27 GHz Over-the-horizon radars (OTH), sometimes called beyond the horizon (BTH), is a type of a radar systems with the ability to detect targets at very 24.65-24.75 GHz long ranges, typically hundreds to thousands of kilometers, beyond the radar horizon, which is the distance limit for ordinary radar. 37 Ender, J. “Introduction to Radar, Part I: Scriptum of a lecture at the Ruhr-Universität Bochum, Frauenhofer Institute for High Frequency Physics and Very-high resolution mapping Ka (“above” K-band) 27-40 GHz Radar Techniques. Airport surveillance 38 In all electromagnetic radiation, the electric field is perpendicular to the direction of propagation, and the electric field direction is the polarization of the wave. Radars use horizontal, vertical, linear, and circular polarization to detect different types of reflections. Millimeter 40-100+GHz Experimental 39 SAR – Synthetic Aperture Radar is a form of radar that is used to create two-dimensional images or three-dimensional reconstructions of objects, such as landscapes. SAR uses the motion of the radar antenna over a target region to provide finer spatial resolution than conventional beam-scanning radars. Inverse synthetic aperture radar (ISAR) is a radar technique imaging to generate two-dimensional high resolution image of a target. It is analo- rd Source: Adapted from Skolnik, M. “Radar Handbook”, 3 ed. NY: McGraw-Hill, 2008. gous to conventional SAR, except that ISAR technology uses the movement of the target, rather than the emitter to create a synthetic aperture.

26 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 27 Figure 16. Basic elements of a radar system • Technology, in imaging and non-imagine ra- relatively short burst of pulses, and after each Figure 18. Diagram of a typical 3-D radar, a mix of dars: Primary, Secondary, Continuous Wave, pulse, the receiver is turned on to receive the vertical electronic beam steering and mechanically Frequency Modulated, Frequency Modulated echo. According to the primary missions, radars horizontal movement of a pencil-beam. Interrupted Continuous Wave, Pulse, Bi-static, can be classified into search radars and tracking and Side-looking Airborne; radars. Search radars continuously scan a volume of space without dwelling at any location. Their • Design used in radars: Air Defence, Fly Surveil- primary missions are detecting targets and deter- lance, and Ground penetrating; mining a target’s range and direction. • Data monitoring used: Weather radars, Noise radar, etc. 2.2.1. PRIMARY SURVEILLANCE RADARS Air defence radars typically operate in what is Each of the radar systems described is designed termed a “Primary Surveillance” mode. When to detect a specific kind of target, and therefore, operated in that manner they are referred to as Source: Federation of American Scientists (FAS, 2020) they feature different working regimes and fre- “Primary Surveillance Radar” (PSR). This type of quency bands, operation ranges, etc. Weather ra- radar will send out radio frequency waves (radar Source: Christian Wolf (2003) dars aim at detecting meteorological phenomena energy) focused by the antenna to provide an “il- The electronic principle on which radar operates like clouds, rain, or storms, while air traffic radars luminated” volumetric region of coverage. Radar is very similar to the principle of sound-wave re- (ATCs) aim at detecting aircrafts, and maritime The main disadvantage of Primary Surveillance coverage describes the space controlled by a ra- flection. Radio-frequency energy is transmitted radars at ships and boats. Radar (PSR) is the necessity of a large power radi- dar or a network of radars. to and reflected from the reflecting object. A por- ated as to ensure the returning from the target. tion of the transmitted signal is intercepted by a Radar systems can also be classified into many This is especially needed if long range is desired. Primary Surveillance Radar is generally rotated reflecting object (target) and is reradiated in all types based on specific radar characteristics, such Another disadvantage refers to the small amount about a vertical axis to extend the volume of directions. It is the energy reradiated in the back as system configuration (mono-static, bi-static of energy returned at receiver, which may be coverage. The angle of rotation may be as little direction that is of prime interest to the radar. or multi-static), desired application, waveform easily disrupted by changes of targets, attitude as a few degrees to observe a small sector or up The receiving antenna collects the returned en- used (continuous wave and pulse radars) and fre- of the turbine blades, signal attenuation due to to 360 degrees to cover the entire airspace sur- ergy and delivers it to a receiver, where it is pro- quency bands (Skolnik, 2008)40. The monostatic heavy rain, etc. This may cause that the displayed rounding the radar. Alternatively, the antenna cessed to detect the presence of the target and radar has a common antenna used for both trans- target to “fade”. may oscillate back and forth over a small angle to extract its location and relative velocity. The mitting and receiving, while the bistatic radar has to cover only a sector of airspace. Systems of this distance to the target is determined by measur- transmitting and receiving antennas separated by The information provided by 3-D radar has long type able to rotate a full 360 degrees can often ing the time taken for the radar signal to travel a considerable distance. According to the wave- been required, particularly for air defence and be observed in use around airports. to the target and back. The direction, or angular forms transmitted, radars can be classified into interception. Interceptions must be told the al- position, of the target may be determined from continuous wave (CW) radars or pulsed radars. titude to climb to before making an intercept. Radars of this type are often referred to as 2-D the direction of arrival of the reflected wave A CW radar’s transmitter operates continuously Before the advent of single unit 3-D radars, this radars since they are able to determine the posi- front. The usual method of measuring the direc- as seen in Figure 17. A pulsed radar transmits a was achieved with separate search radars (giving tion of an aircraft in terms of range and bearing tion of arrival is with narrow antenna beams. If range and azimuth) and separate height finding angle (angular position of the aircraft with re- relative motion exists between target and radar, radars that could examine a target to determine spect to north) but are unable to determine the the shift in the carrier frequency of the reflected altitude. This type of radars had little search ca- height at which the airplane is above the surface wave (Doppler Effect) is a measure of the target’s Figure 17. Radars classification pability, so they were directed to a particular azi- of the earth. In contrast, most radars designed relative (radial) velocity and may be used to dis- muth first found by the primary search radar. tinguish moving targets from stationary objects. to inherently determine aircraft range, bearing, and altitude employ multiple beams. Radars able There are 2 different types of multi-beam 3-D ra- to determine all three aircraft parameters are 2.2. TYPES OF RADARS dars, the first employs several “stacked” transmit typically referred to as being three-dimensional units to produce overlapping illumination lobes. Radar systems have been designed for a variety (3-D) radars as seen in Figure 18. In addition to Similar to the 2-D radar, the entire antenna would of applications and missions. These systems in- range, the more common two-dimensional radar be rotated about a vertical axis to sweep the illu- clude radars for air defence, air traffic control, provides only azimuth for direction, whereas 3-D minated area over the volume of airspace to be missile warning, weather, etc. Generally, they radar also provides elevation. Applications in- covered. The second type of 3-D radar is known may be classified depending on: Source: Radar Tutorial (2020) clude weather monitoring, air defence, and sur- as a phased-array radar as seen in Figure 18. In veillance. a phased-array radar, hundreds of thousands of 40 M. Skolnik. “Radar Handbook”, 3rd ed. NY: McGraw-Hill, 2008.

28 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 29 small transmitters and receivers make up the face 2.3. RADAR FUNCTIONS ognized air picture (RAP) with the aim of preserv- time, the resultant waves is the complex sum, or of the antenna. Radar beam patterns are formed ing the integrity of airspace through air policing. superposition, of the waves. This complex sum Modern systems apply these major radar func- by precisely adjusting (shifting) the phase angle The RAP is produced by allocating track identities depends on the amplitudes and phases of waves. tions in an expanding range of applications, from of the signal sent to each transmit element. Em- to each radar return (or “plot” of interest). A ra- For example, two in-phase waves of the same the traditional military and civilian tracking of air- ploying a similar technique, the receive beam can dar plot can often fade from a radar display for frequency will produce a resultant wave with an craft and vehicles to two- and three-dimensional also be “electronically steered” over an area to a period of time due to a number of factors, but amplitude that is the sum of the two waves’ re- mapping, collision avoidance, Earth resources cover a specific volume of airspace. Mechanical the track identity will remain, indicating that the spective amplitudes (constructive interference), monitoring, and many others. steering can also be employed to increase the associated plot is actually still present (Upton & whilst two out-of-phase waves will produce a re- “field of regard” for a phased array radar. Thurman, 2001)41. sultant wave with an amplitude that is less than 2.3.1. AIR TRAFFIC CONTROL (ATC) the sum of the two amplitudes (destructive inter- 2.2.2. SECONDARY SURVEILLANCE RADAR Air Traffic Control Radar is the umbrella term for 2.3.3. WEATHER RADAR ference). all radar devices used to secure and monitor civil Secondary Surveillance Radar (SSR) is an “inter- Weather radar, also called weather surveillance and military air traffic. They are usually fixed -ra Two waves of equal amplitude that are out of active” radar in a sense that it requires the coop- radar and Doppler weather radar, is a type of dar systems that have a high degree of special- phase will produce a null result (i.e., no wave). eration of the target aircraft. The SSR systems radar used to locate precipitation, calculate its ization. Common applications of air traffic con- The importance of the concept of superposition are considered to be tracking systems. It oper- motion, and estimates its type (rain, snow, hail trol radars include: (1) en route radar systems; (2) is seen in many topics related to radar. Among ates by sending out a coded signal (interrogation) etc.) Modern weather radars are mostly pulse- Air Surveillance Radar (ASR) systems; (3) Preci- these are the formation of a defined beam pro- that is received by a transponder system on an Doppler radars, capable of detecting the motion sion Approach Radar (PAR) systems; (4) surface duced by an antenna, the total Radar Cross Sec- aircraft. The airplane’s transponder system trans- of rain droplets in addition to the intensity of the movement radars, and (4) special weather radars. tion (RCS) of a target as a result of the many scat- lates the interrogation and responds by transmit- precipitation. Both types of data can be analyzed Radar performs two functions for air traffic con- ters, and the effects of multipath. ting a coded signal back to the radar. This coded to determine the structure of storms and their trol: signal will contain information about the aircraft potential to cause severe weather. Wind turbines can cause electromagnetic inter- and other data such as its flight altitude. The fre- a) Airport surveillance radar allows air traffic con- ference via three principal mechanisms, namely quencies of the interrogation and response are Weather radars usually work with three main trollers to provide air traffic services to aircraft near field effects, diffraction and reflection/scat- different and both are different from the primary types of data. In the reflectivity mode, return in the vicinity of an airport. This service may tering. Near-field and far-field diffraction effects radar frequency so that this signals do not inter- echoes from targets are analyzed for their in- include vectoring aircraft to land, providing ra- were studied by the Danish physicist Christian fere with each other. The operating frequencies, tensities to establish the precipitation rate in dar service to departing aircraft, or providing Huygens and the French physicist Augustin-Jean signal strength, message format, and other key the scanned volume. In the Doppler mode, the service to aircraft either transiting through the Fresnel. Whenever a travelling wave encounters a parameters influencing the performance of tran- precipitation’s motion is calculated. Finally, in area or in the airfield circuit; line of objects, the objects will disrupt the propa- sponders are defined by published standards. the polarization mode, orthogonal polarization gation of the wave in that location. This phenom- pulses are used to evaluate drop shapes and dis- b) En route (or area) radar is used to provide ser- ena can be illustrated as propagation of spherical A major advantage of SSR is that the return from tinguish amongst different precipitation types, vices to traffic in transit. This includes com- waves from each of the objects. These waves will the aircraft transponder is much stronger than such as rain, snow, or hail. mercial airliners and military traffic. Area radar combine constructively and destructively on the the typical primary (skin) radar return and it is has a longer range than airport radar, particu- far side of the objects. In the zones of the dis- generally unaffected by clutter sources that can 2.4. ELECTROMAGNETIC INTERFERENCE larly at high altitudes. En route radars monitor rupted waves the reflection of the radar signal is affect the primary radar return. This is because AND ITS IMPACT ON RADARS the air traffic outside the special airfield areas. significantly different from areas where it has not the SSR system does not depend upon the “re- En route radar sets initially detect and de- Electromagnetic radiation is energy propagating been disturbed. These differences include varia- flection” of its interrogation message. Instead, termine the position, course and speed of air in the form of an advancing disturbance, or wave, tions in intensity and phase angle and are a func- it receives a different signal actually broadcast targets in a relatively area. En route radars are in the electrical and magnetic fields. As electro- tion of original frequency and the spacing of the by the aircraft. Thus, wave propagation losses in Primary Surveillance Radars that are coupled magnetic energy propagates through the atmo- objects causing disruption. Wind turbines cause each direction are minimized. This in turn allows to a Secondary Surveillance Radar. sphere, it is attenuated (i.e., undergoes a loss in three types of problems for Doppler radars: clut- much smaller antenna to be employed for SSR. overall energy) by absorption and scattering. In ter, blockage, and erroneous Doppler measure- 2.3.2. AIR DEFENCE the case of data path, these effects can range ments. A disadvantage of the SSR is that the aircraft from an increase in error rate to a total loss of must have a functioning transponder. Not all air- Air defence radar is used in two ways. On one the data. 2.4.1. BLOCKAGE OF THE RADAR’S BEAM craft are required to have transponders. Addition- hand, it performs a function similar to its Air Traf- The principle of superposition states that when ally, even for transponder-equipped airplanes, if fic Control (ATC) counterparts, being used by air This is the main anticipated effect on air defence two or more waves having the same frequency the transponder fails or is turned off, the SSR will defence controllers to provide control services to surveillance radar. Such radar works at high ra- are present at the same place and at the same not be able to track the airplane. Under these cir- military (usually air defence) traffic. It is however, dio frequencies and therefore depends on a clear cumstances, only a primary radar will be able to also used to monitor all air traffic activity within detect or track the aircraft. the country and it approaches to produce a rec- 41 L.O. Upton; L.A. Thurman (2001). “Radars for the Detection and Tracking of Cruise Missiles”. Massachusetts Institute of Technology (MIT), Lincoln Laboratory, MA, USA

30 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 31 “line of sight” to the target object for successful Figure 19. Blocking of the radar beam and “shadow For a weather radar, clutter refers to all non- phenomena. For any type of wave, one way to detection. It follows that any geographical fea- volume” (in red) generated behind each wind turbine. meteorological radar echoes. Typical examples define diffraction is the spreading of waves, i.e., ture or structure lying between the radar and the of clutter include echoes from terrain, build- no change in the average propagation direction, target will cause a shadowing or masking effect; ings, and clear-air targets (e.g insects, birds, at- while scattering is the deflection of waves with a military aircraft wishing to avoid detection read- mospheric turbulence). Clutter can further be clear change of propagation direction. However, ily exploits indeed this phenomenon. divided into two categories: static and dynamic. the terms “diffraction” and “scattering” are often Static clutter typically originates from terrain and used interchangeably, and hence a clear distinc- Objects in the path of an electromagnetic wave buildings, whereas dynamic clutter is caused by tion between the two is difficult to find (Berg & affect its propagation characteristics. This in- moving targets such as clear-air returns. Static Sorensen, 2018)43. They conclude that diffraction cludes actual blockage of wave propagation by clutter has zero or near-zero radial velocity and is the spreading of waves but demonstrates that large individual objects and interference in wave can be removed by built-in clutter filter whereas all diffraction patterns are the result of scattering. continuity due to diffraction of the beam by indi- dynamic clutter originates from targets having vidual or multiple objects. The effect caused by Source: Adapted from the article by de la Vega D., radial velocities larger than the clutter filter lim- Scattering is a term used in physics to describe a either of these is often termed to cause “shadow- Fernandez C., and Wu Y., et al “Software tool for its. Dynamic clutter can therefore not be sup- wide range of physical processes where moving ing” of the radar beam. the analysis of potential impact of wind farms on pressed by conventional clutter filters. particles or radiation of some form, such as light radio communication services” (2011). or sound, is forced to deviate a straight trajectory The presence of a single tall building within the Operating wind turbines generate both static and by localized non-uniformities (including particles radar field of view provides a typical example for dynamic clutter. Since the static clutter from the and radiation) in the medium through which they blockage. Since the tall building effectively blocks 2.4.2. WIND TURBINE CLUTTER wind turbines is suppressed by clutter filters the pass. Electromagnetic waves are one of the best all propagation of radar radio frequency wave, the Radar returns may be received from any radar- dynamic wind turbine clutter, mainly originat- known and most commonly encountered forms zone immediately behind the building will not be reflective surface. In certain geographical areas, ing from the rotating blades, has the largest im- of radiation that undergo scattering. Several dif- illuminated by the radar. If the building is close or under particular meteorological conditions, pact on weather radar measurements. Dynamic ferent aspects of electromagnetic scattering are to the radar there will be zones of complete and radar performance may be adversely affected wind turbine clutter is often difficult to separate distinct enough to have conventional names. For partial shadowing. This is illustrated in Figure 19. by unwanted returns, which may mask those of from precipitation echoes and may therefore in- example, Rayleigh scattering, named after the It shows an example of assessment of the volume interest. Such unwanted returns are known as correctly be interpreted by the weather radar as 19th century British physicist Lord Rayleigh, is the behind the wind turbines where the radar beam “clutter”. It is displayed to a controller as “in- precipitation. In addition, wind turbine clutter is predominantly elastic scattering of light or other is blocked, causing the misidentification of pre- terference” and is primarily a problem for air highly variable in time since the amplitude of the electromagnetic radiation by particles smaller cipitation phenomena in case of weather radars. defence and airport radar operators as it occurs scattered signal depends sensitively on the wind than the wavelength of the radiation. Scatter- more often at lower altitudes. turbine’s yaw- and tilt angle. ing occurs when the rotating wind turbine blades Blocking of the beam occurs when the radar reflect or refract radar waves in the atmosphere. is pointing in direction of the wind turbine and For military surveillance radar clutter can for ex- Several turbines in close proximity to each other These are then subsequently absorbed either by there is direct line of sight (e.g distance) between ample consist of precipitation echoes whereas and painting on radar could present particular the source radar system or another system and them. If the physical area of a wind turbine blocks for weather radar echoes from, e.g aircraft are difficulties for long-range air surveillance radar. A can then give false information to that system. It part of the radar beam, this obstruction, even unwanted. Echoes from wind turbines are con- rotating wind turbine is likely to appear on a radar may affect both primary and SSR radars. This ef- if partial, can lead to errors in the precipitation sidered clutter by most radars. Blockage occurs display intermittently. Multiple turbines, in prox- fect as yet not quantified but is certainly possible. monitoring. when obstacles such as buildings or terrain ob- imity to each other, will prevent several returns scure the radar line of sight. Measurements be- during every radar sweep, causing a “twinkling Diffraction phenomenon is the most pro- The Meteorological Office is also concerned with hind such obstacles become incomplete or non- effect”. As these will appear at slightly different nounced when the wavelength of the radiation the effect of shadowing on their sensors as the existing. Wind turbines located near a radar may points in space, the radar system may interpret is comparable to the linear dimensions of the weather radars look at a relatively narrow alti- block substantial part of the radar’s measure- them as being one or more moving objects and obstacle. When sound of various wavelengths or tude band that is a near to the earth’s surface as ment region. In addition, there is another con- a surveillance radar will then initiate a “track” frequencies is emitted from a loudspeaker, the possible. Due to the sensitivity of the radar, wind cern. Namely, if the turbine generates clutter on on the returns. This can confuse the system and loudspeaker itself acts as an obstacle and casts turbines, if they are poorly sited, have the poten- the radar screen, and the controller recognizes may eventually overload it with too many tracks. a shadow to its rear so that only the longer bass tial to significantly reduce weather radar perfor- it as such, he may choose to ignore it. However, notes are diffracted there. When a beam of light mance (Novak, 2009)42. such unwanted returns may obscure others that 2.4.3. “SCATTERING”, “REFRACTION” falls on the edge of an object, it will not continue genuinely represent aircraft, thereby creating a AND/OR FALSE RETURNS in a straight line, but will be slightly bent by the contact, causing a blur at the edge of the shadow potential hazard to flight safety. This may be of The concepts of diffraction and scattering are of the object; the amount of bending will be pro- particular concern in poor weather. considered fundamental in optics and other wave

42 A. Novak. “Wind Farms and Aviation”. In Aviation 2009, 13 (2): 56-59. 43 M. Berg; C. Sorensen. “A Review and reassessment of diffraction, scattering and shadows in electronics”, In Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 210, May 2018, pp. 225-239

32 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 33 portional to the wavelength. Due to diffraction, Figure 21. Fresnel zone One type of refractive condition can extend the omni-directionally broadcasted, and a signal of radio frequency shadow can occur causing dead normal detection range of radar and, if condi- variable amplitude that sweeps around a vertical coverage zones or receive degraded signals. tions intensify, produce false echoes or ghosting. axis 30 times a second. Doppler VOR systems are The latter can cause returning echoes to fool the based on VOR systems, but they use the Dop- radar equipment into displaying far away echoes pler shift of an electronically rotating antenna Figure 20. Diffraction as though they are much closer than they actu- to generate the variable signal, and therefore, ally are. to improve the accuracy. The variable signal is modulated such that it is in phase with the direc- With another type of refractive condition, anom- tional signal only when detected from the north alous propagation may produce a shadow zone in the aircrafts. From other directions, the phase (commonly referred to as a radar hole), some- difference between the two signals indicates the times allowing an aircraft or ship to approach receiver’s bearing from the beacon (Kayton et al., Source: Pager Power (2020) within visual range but to remain undetected by 1997)46. Source: WordPress (2020) radar. In this case, the radar equipment operated To determine if an obstruction of the Fres- properly. ILS (Instrument Landing System) is a collection nel zone will exist, the volume occupied by the of radio transmitting stations used to guide air- Because of the point-to-point nature of these turbine due to the blade rotation and the rotor To calculate this exclusion zone, the interference craft to a specific airport runway for landing, es- links, and the frequency range they use, unob- orientation must be considered, together with caused by a wind turbine should be assessed by pecially during times of reduced visibility. Typi- structed line of sight between both ends of the the terrain conditions. If there is no intersection means of the bistatic radar equation, where the cally, an ILS includes a localizer antenna centered links is intended. Diffraction effects occur in the between the exclusion zone and the volume oc- wind turbine is characterized in terms of its maxi- on the runway beyond the stop end to provide forward scattering zone of the wind turbines, cupied by the turbine, no impact due to the link mum RCS. In case the wind turbine causes inter- lateral guidance, a glide slope located beside the where the turbine obstructs the path between obstruction is expected. ference, it should be moved away from the link runway near the threshold to provide vertical transmitter and receiver, located at the two end path, in order to decrease the interference level. guidance, and marker beacons located at discrete points of the link. The criterion for avoiding dif- Changes in temperature, moisture, and pressure The proper location for the turbine to not disturb positions along the approach path to alert pilots fraction effects is based upon an exclusion vol- in the atmospheric column cause a change in at- the radio link can be assessed by applying the bi- of their progress along the glide-path and radia- ume around the radio path of a fixed link. In the mospheric density, which in turn causes varia- static radar equation in suitably small increments tion monitors47. specific case of a wind farm, an exclusion zone tions in the speed of the electromagnetic waves of the distance of the wind turbine to the radio equal to the second Fresnel zone is proposed in in both the vertical and horizontal. These changes path until the required value of C/I is obtained For the VOR receiver on-board the aircraft, de- (Bacon, 2002)44. in speed lead to changes in the propagation di- (Bacon, 2002). pending on the importance of the multipath, rection, or bending, of the waves. The bending some azimuth direction shift may occur. If the A Fresnel zone, named after physicist Jean Fres- of electromagnetic waves as they pass through 2.5. NAVIGATION AIDS total bearing error rises above 3 degrees, the 45 service will be no longer available. Doppler VOR nel, is one of a series of confocal prolate ellip- the atmosphere is an example of refraction. It Many aircrafts are fitted with a variety of navi- seems to be less susceptible to multipath inter- soidal regions of space between and around a is always such that the waves turn toward the gation aids, such as Automatic direction finder ference (Morlaas et al., 2008)48. For ILS systems, transmitter and a receiver as seen in Figure 21. medium in which they ravel more slowly, as they (ADF), inertial navigation, compasses, radar navi- flight calibration results may be worsened. Transmitted radio, sound, or light waves can pass from a faster speed medium into a slower gation VHF omnidirectional range (VOR), and follow slightly different paths before reaching a speed medium. Refraction causes waves to turn Global navigation satellite system (GNSS). receiver, especially if there are obstructions or back toward the slower speed medium as they The International Civil Aviation Organization (ICAO) defines safeguarded distances named as reflecting objects between the two. The waves pass from the slower into the faster medium. VOR (VHF omnidirectional radio) is a radio- Building Restricted Areas (BRAs) the shape of can arrive at slightly different times and will be navigation system which enables aircrafts to which and dimension are dependent upon indi- slightly out of phase due to the difference path Some amount of refraction is always present in determine their position and stay on course, to vidual facility types. These protected areas are lengths. Depending on the magnitude of the the atmosphere, however, when the structure of support both approach and departure procedures also applicable to the deployment of wind farms. phase shift, the waves can interfere construc- the atmosphere causes abnormal bending of the and navigation on route. VOR operational fre- In case of a wind farm infringing these limits, po- tively or destructively. The size of the calculat- energy waves, anomalous propagation occurs. quency band is between 108.0 and 117.95 MHz. tential issues concerning wind turbines should be ed Fresnel zone at any particular distance from It takes place when an unusual, other than nor- VOR transmitters, located on the ground, radiate dealt with on a case by case basis (ICAO, 2009)49. the transmitter and receiver can help to predict mal vertical distribution of temperature, mois- two VHF radio signals: a reference signal that is whether obstructions or discontinuities along the ture, and pressure exists within the atmosphere. The Civil Aviation Authority (CAA), a public and path will cause significant interference. Anomalous propagation occurs in many forms. 46 M. Kayton; W. Fried; J. Wiley. “Avionics navigation systems”, 1997. 47 Ibid, 1997 48 C. Morlaas; M. Fares; B. Souny. “Wind turbine effects on VOR system performance”. In IEEE Transport Aerospace Electronic Systems, 2008; 44 (4); 1464-76 44 D.F. Bacon. “Fixed-link wind turbine exclusion zone method”, OFCOM: 2002 49 International Aviation Organization. “European guidance material on managing building restricted areas”, ICAO EUR Doc 015: 2009. 45 The prolate spheroid is the approximate shape of the ball in several sports, such as in rugby football.

34 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 35 independent specialized aviation regulator and radio waves by a wind turbine and the effect of craft flying in good weather during the initial and Mitigations measures may include modifications provider of air traffic services in the United King- large blades rotating. Wind turbines can cause final stages of flight, or in the vicinity of the air- to wind farms (such as methods to reduce radar dom, suggests a similar criterion not based on large fades in the signal received by one of the port. On the other hand, wind turbines are most cross-section; and telemetry53 from wind farms BRAs, but on the following rule of thumb: a wind ends of the link, thus reducing the power of the problematic to primary surveillance radar (PSR), to radar). This list of mitigation techniques also farm whose blade tips at their maximum height received signal (obstruction), or generated inter- which is either used for air traffic control or air includes modifications to radar (such as improve- are below the visual horizon when viewed from a fering reflected signals that reduce the wanted- defence – Primary Surveillance Radars (PSR) that ments in processing radar design modifications; point located 25 m above an aeronautical radio to-unwanted protection (scattering)52. Other ef- detect non-cooperative, i.e. all, targets. As the radar replacement; and the use of gap fillers in station site may be acceptable (CCA, 1998)50. fects such as near-field effects are not probable capacity of each wind turbine is expected to grow radar coverage). For the purpose of this section, in the UHF (ultra-high frequency) band or higher in the future, the inevitable size increase will the word “mitigation” is specifically defined to According to ICAO, proposed wind farms should frequencies. Therefore, two main degradation result even higher Radar Cross-Section (RCS), include either an approach that completely pre- be assessed to a distance of 15 km from the VOR mechanisms may have an effect on a radio-link which means careful selection of proper sites to vents any negative impact from occurring or an facility, with special attention to any turbines and must be considered in the impact studies: install wind turbines, needs to be conducted. approach that sufficiently attenuates any nega- within the BRA delimited by the flowing criteria: diffraction effects and refraction or scattering. tive impacts so that there is no significant influ- any turbine infringing a 600 m distance or a 1 A number of recent trials in wind turbine clut- ence on the capability of an air defence. degree slope from the center of the antenna at To sum it up, definitely, there is no single “gold ter have demonstrated the adverse impact that ground level to a distance of 3 km, or a 52 m hori- bullet” solution to the wind turbine/radar service it has on the air defence capability. Analysis of In recent times, significant research has gone into zontal surface from a distance of 3 km to 15 km. problem that could be applied to all scenarios these trials has concluded that current mitiga- characterizing the signals scattered by the wind The consultation zone of 15 km is also proposed and make the problem disappear. In reality, it is tion methodologies are insufficient to meet the turbines and determining the impact of these re- by Radio Advisory Board of Canada and Canadian not simple. Each wind farm is unique in the lay- agreed aviation specification. In addition, many flected signals on the detection ability of these Wind Energy Association. out, type and number of turbines, the surround- of the mitigations applied to civilian radar sys- radars to detect and track aircraft flying in the ing terrain, the orientation and range with re- tems cannot be applied to Ministry of Defense’s vicinity of wind farms. Additionally, there has In practice, most cases of single wind turbine de- spect to the radar systems and the aircraft flight primary surveillance radar assets, in part due to been significant research underway into devel- velopments are acceptable at distances greater paths. Apart from the technical issues, of course the age and type of these assets. Further, Air oping various mitigation techniques in the radar than 5 km, and wind farms of less than 6 turbines there are also financial issues; the overall profit- Defence staff cannot rely on transponder data, receiver to suppress the windfarm returns while are acceptable at distances greater than 10 km ability of the site may take certain options more standard flight paths, and standard flying heights preserving aircraft target components. Some of from the facility. Wind turbine developments to attractive than others, for example. Each case, on potential enemy aircraft who may intend to these techniques are also based on the design a distance of 15 km from the facility should be therefore requires detailed analysis to determine remain hidden. and site installation of the wind turbines, but analyzed, and further assessment is required for the impact of the wind farm on the radar system the others include development of specific tech- any turbine within the BRA. In cases where there and the likely efficacy of potential mitigation op- The current state-of-the art mitigation solutions niques for filtering these interfering signals at are existing wind turbines within the 15 km zone, tions, and any agreed mitigation action is likely can be largely grouped into two areas; radar- various detection stages in the signal processing the evaluation of new proposals needs to con- to be the output of negotiations with a number based solutions (radar hardware upgrades or new chain of the radar receiver. sider the accumulative effect of all the turbines of stakeholders. installations) and material solutions (“stealth (ICAO, 2009)51. windfarms”). An example of the former would be Various companies have tried to fix the prob- CHAPTER 3 WINDFARMS INTERFERENCE the acquisition of new radar equipment capable lem, for example, there are at least 50 mitiga- 2.6. RADIO LINKS MITIGATION of distinguishing wind farms from aircraft. How- tion solutions that have matured at some point ever, the high upfront cost of this is not viable in the past 10 years. Many of these solutions A radio link is a telecommunication facility between Radar objections to wind turbines have been for all wind farm applications, particularly small are developed in order for the radar to become two fixed points located over terrain that aims at the source of the most intractable source of the wind farms or those in unique geographical lo- “Windfarm Compliant”, which will prevent block- two point data transmissions by means of radio safeguarding disputes for over a decade. Wind cations. Only with a complete suite of solutions ing wind energy development because of radars. waves, featuring specified characteristics of quality turbines can have a safeguarding impact due to available, will energy developers be able to miti- As an illustration, the radar manufacturer Thales and availability. Radio-links use different frequency their physical impact or their technological im- gate all objections to wind farm applications. In- has installed a STAR 2000 PSR in at In- bands between 800 MHz and 22 GHz, depending pact. On one hand, a wind turbine can be an aero- deed, many radar experts believe that the only verness, an airport which is surrounded by many on their data transmission capacity. Therefore, they drome obstacles, if it is within reasonably close solution to this emerging issue of wind turbine windfarms. are sometimes called microwave links. proximity to the aerodrome, e.g within 15 km, electromagnetic interference saturation is a com- and infringes the Obstacle Limitation Surfaces. It bination of radar and material-based strategies, For air surveillance radar, where airplanes are The performance of a fixed radio link might be defines the airspace surrounding an airport that necessitating innovation in both areas. separated from wind turbines by altitude, con- degraded due to obstruction or scattering of must be protected from obstacles to ensure air-

53 Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (tel- 50 United Kingdom Civil Aviation Authority. “CAP 670 ATS safety requirements”, 1998 ecommunication) for monitoring. Telemetry is used in complex systems such as missiles, spacecraft, oil rigs, and chemical plants since it allows the 51 International Aviation Organization. “European guidance material on managing building restricted areas”, ICAO EUR Doc 015: 2009. automatic monitoring, alerting and record-keeping necessary for efficient and safe operation. 52 B. Randhawa; R. Rudd. “RF measurement assessment of potential wind farm interference to fixed links and scanning telemetry devices”, Ofcom 54 Constant false alarm rate (CFAR) detection refers to a common form of adaptive algorithm used in radar systems to detect target returns against report 2008-0568: 2009. a background noise, clutter an interference.

36 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 37 current beam processing and enhanced Constant can select illuminators of opportunity, e.g. pres- Figure 22. Primary Surveillance Radar (PSR) recommended ranges. False Alarm Rate (CFAR) detection algorithm54 ent radar signals (e.g. PSR and SSR), digital ter- are planned for future system upgrades. The role restrial television broadcasts (DTTB), mobile Zone Zone 1 Zone 2 Zone 3 Zone 4 of the CFAR circuitry is to determine the power communications, global navigation satellite sys- threshold above which any return can be consid- tem, and so on. Looking at Multi-static Primary Further than 15 km ered to probably originate from a target. If this Surveillance Radar techniques and ongoing trials, 500 m – 15 km and in but within maxi- Further than 16 Description 0-500 m mum instrumented km or not in ra- threshold is too low, then more targets will be MSPSR might be tested as a potential low-cost radar line of sight detected at the expense of increased numbers of replacement for the aging primary surveillance range and in radar dar line of sight false alarms. Conversely, if the threshold is too radar system. Recently, there have been both line of sight high, then fewer targets will be detected, but the passive and active MSPSR trials in England, Ger- Assessment Safeguarding Detailed Assessment Simple Assessment No assessment number of false alarms will also be low. In most many and Japan. Requirements radar detectors, the threshold is set in order to This chapter will describe a number of potential achieve a required probability of false alarm. The mitigation approaches that could be employed Source: Adapted from EUROCONTROL Guidelines for Assessing the Potential Impact of Wind Turbines on methodology behind is radar Line of Sight (LoS) to reduce or eliminate the adverse impacts wind Surveillance Sensors”. Technical Report EUROCONTROL-GUID-130. avoidance, which may work for cooperative air- turbines can have on air defence and missile crafts, but could also lead to loss of track for low- warning radars. The Primary Surveillance Radars (PSR) safeguard- a weather radar, and wind farm developers are altitude non-cooperative targets. ing range where no wind turbine shall be built is recommended to submit plans of wind farms lo- 3.1.1. GUIDELINES PUBLISHED BY REGULA- derived from the ICAO recommendations pro- cated at a distance within 20 km from the radar Three development axis, depending on the type TORY BODIES vided in the ICAO EUR 015 document57 which is for the development of an impact study. The In- of situation to tackle can be identified: Some regulatory bodies have published guide- applicable for any obstacle. ternational Telecommunications Union (ITU) has lines to estimate and avoid the impact of wind also recognized the problem, but it has not yet • The upgrade of existing radars: software pro- farms on radar services. Most of them aim to PSR radar designs vary considerably and the de- stated any specific guidelines; only recommend- cessing can be improved, in particular by add- define rules-of-thumb and safeguarding zones sign choices made the PSR manufacturers influ- ed protection level for weather radars is stated, ing wind farm filters which allow to filter out that are easy to understand by a non-technical ence the susceptibility of their radars to wind as an interference over noise level of – 10dB60. the wind turbine spurious signals once they audience (from a radar perspective), such as wind turbines. The figure for the PSR recommended Although all these above-mentioned guidelines are classified as such, farm developers. limit between detailed and simple assessment provide safeguarding distances and rules-of- • Gap-filler radars: in the case of existing radars is therefore derived from the best practices col- thumb, they all propose the development of a for which such an upgrade is not envisaged or Regarding the Air Surveillance Radars (ASR), the lected from the ECAC58 member states and it case-by-case analysis, based on a detailed mod- yet for solving specific issues such as masking, Eurocontrol has published a document aimed at is also a figure recognized in the ICAO EUR 015 eling of the scenario. then gap-filler radar solutions (e.g. installed both providers of air navigation services and wind document. Therefore, these figures are applica- on the wind turbine itself) can be proposed. farms developers (Borely, 2014)56. This document ble to current , e.g 3-blades, 3.1.2. WIND FARM LAYOUT defines a number of zones and provides guide- 30-200 m height, and horizontal rotation axis. • Next generation radars: windfarm “clutter” Wind turbines are usually installed in so called lines within each of these zones. These range from For other types of turbines, it is recommended to will be considered as a requirement, and new wind farms consisting of a group of wind turbines “safeguarding zones”, within which no wind tur- undertake the detailed assessment as long as the architectures are already studied for propos- located at a site to generate electricity. Nowa- bines should be placed, through zones requiring wind turbine is in radar line of sight. ing the best solutions. Among these architec- days, the progress of technologies, such as power an impact assessment to be conducted, to zones tures, Multi-Static Primary Surveillance Radar electronics, wind speed forecasting, coordinated in which no impact is expected. The first step in Both the World Meteorological Organization (MSPSR)55 shows built-in good features for control, together with the increased experience the assessment is to determine if any part of a (WMO) and the Network of European Meteoro- mitigating windfarm effects. of wind farm construction and operation have logical Services have issued general guidelines for turbine is within line-of-sight of the radar. If this enabled the development of modern wind farms. is not the case, then it is stated that there will be the development of wind turbines near weather Recently, multi-static primary surveillance radar These are larger, smarter wind farms, which are no impact to the radar. The definition of these radars, based on safeguarding distances (WMO, (MSPSR) has attracted the attention of research- typically consisted of hundreds of utility-scale zones is reproduced in Figure 22. It should be not- 2010)59. According to these guidelines, no wind ers. MSPSR can cover the shadow areas of the (multi-MW sized) wind turbines and with a total ed that the radar line-of-sight depends on atmo- turbine should be deployed closer than 5 km to conventional primary surveillance radar (PSR) capacity of hundreds MW. For space and cost rea- spheric refraction, which at some locations may and can be used as an alternative variant. As the deviate from standard propagation conditions. MSPSR is classified into passive bistatic radar, it 57 International Civil Aviation Organization. ‘European Guidance Material on Managing Building Restricted Areas”. ICAO EUR DOC 015, 3rd Edition. 58 ECAC- European Civil Aviation Conference was founded in 1955 as an intergovernmental organisation that seeks to harmonise civil aviation policies 55 Such systems differ from typical modern active radar systems through consisting of multiple spatially diverse transmitter and receiver sites. Due to and practices amongst its members. Currently is composed of 44 Member-States, e.g. Estonia joined ECAC in 1995. this spatial diversity, these systems present challenges in managing their operation as well as in usefully combining the multiple sources of information 59 World Meteorological Organization (WMO). “Commission for Instruments and Methods of Observation”. Technical Report, WMO-No 1046, WMO, to give an output to the radar operator. Helsinki, , 2010 56 M. Borely. “EUROCONTROL Guidelines for Assessing the Potential Impact of Wind Turbines on Surveillance Sensors”. Technical Report EUROCON- 60 International Telecommunications Union (ITU-R). “Technical and Operational Aspects of Ground-Based Meteorological Radars. Recommendation TROL-GUID-130. Eurocontrol: Brussels, Belgium, 2014. ITU-R”. Technical Report M.1849; ITU; Geneva, Switzerland, 2009.

38 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 39 sons, the wind turbines should be as close as pos- A variety of mitigation approaches are available agation which means travel in a direct path from • Software which would allow aircraft radar sig- sible to each other, but not mutually influence to help minimize wind energy’s impact on radar, the source to the receiver. The rays of waves may natures to be injected into digital processors each other. To avoid mutual interference, the including the following siting practices: be diffracted, refracted, reflected or absorbed by on modern radars, allowing the “assessments” wind turbines need to be arranged in a layout ac- the atmosphere and obstructions with material of the ability of that radar to detect and track cording to the prevailing wind direction, in order • Designing the windfarm layout to minimize and generally cannot travel over the horizon or aircraft under real world conditions which to harvest the maximum energy. the impacted area of radar coverage or to al- behind obstacles. may otherwise hinder performance. low for maximum radar coverage within the Wind turbines can be adapted to meteorologi- project, such as by increasing the spacing be- The performance of a radar will not be affected by In most cases, siting and other mitigations have cal conditions due to their aerodynamic shape. tween turbines within the project; objects that do not appear within its line of sight solved conflicts and allowed wind projects to co- In order to take the site condition into account, unless exceptional circumstances exist. With re- exist effectively with radar missions. The best • Eliminating proposed turbines located in areas the potential location of a wind turbine must be spect to objects projecting upward from the sur- mitigation technique is to avoid locating wind that result in high radar interference impacts. examined in advance. For the selection of suit- face of the earth, such as wind turbines, radar line turbines in the radar line of sight (LoS). This able locations, numerical simulations are mostly of sight is determined by four factors when there strategy may be achieved by distance or terrain Wind turbine siting alone may not eliminate im- used which examine the meteorological and oro- is no intervening terrain. These factors are the masking. Mitigation of impacts, if turbines are pacts or reduce them to an acceptable level. In graphic conditions in advance. height of the focal point of the radar above the located in the LoS, can be achieved by reducing these cases, other mitigation techniques, includ- earth’s surface, the height of the wind turbine, the number of turbines in the LoS, the amount ing the deployment of new radar-related soft- Taking this into account, each wind farm is unique its distance from the radar, and how much the of blade penetration into the LoS, greater sepa- ware upgrades and/or hardware can also reduce in the layout, type and number of turbines, the atmosphere will refract the radar beam. ration from the radar, or through selective tur- potential wind energy impacts on radar opera- surrounding terrain, the orientation and range bine siting, e.g. to reduce the azimuthal extent of tions. Examples include: with respect to the radar systems and the aircraft The curvature of the earth influences the line the turbines with respect to the radar. However, path. Apart from the technical issues, of course of sight. As an estimating rule, radar engineers in some proposed locations, wind turbines will • Adding infill radars in or around the wind proj- there are also financial issues; the overall profit- often use a “4/3rds earth” approximation to ac- cause disruptive radar interference that cannot ect to maintain existing radar coverage; ability of the site may make certain options more count for the effect of atmospheric refraction be effectively mitigated. At such sites, wind de- attractive than others, for example. Each case, • Modifying the existing radar system soft- near the surface of the earth. When doing this, velopment would probably not proceed. therefore requires detailed analysis to determine ware’s constant false alarm rates, clutter they multiply the radius of the earth by the factor the impact of the wind farm on the radar system maps, or other filtering and/or preliminary 4/3 when performing the tangent line calculation 3.1.4. WIND TURBINE SUPPRESSION and the likely efficacy of potential mitigation op- tracking routines; to determine if an object is in a radar line of sight CONCEPTS tions, and any agreed mitigation action is likely (US Department of Defence report to the Con- • Upgrading the hardware or software of the af- The second potential mitigation area is the sup- to be the output of negotiations with a number gressional Defence Committees, 2006)61. fected radar to implement advanced filtering pression of wind turbine radar signatures. An of stakeholders. techniques that can remove interference from alternative approach, heretofore not technically Line-of-sight problems if potential interference turbines. feasible to great extent, is to reduce the radar The first step in the analysis is usually to esti- issues are identified during the formal review pro- cross-section of wind turbine to extent that they mate if the wind farm is in the line-of-sight of the cess, can be avoided by: The wind farm layout could potentially be modi- can be installed near existing radar installations. radar system, considering altimetry data, wind fied in some cases in order to reduce the impact The radar cross-section (RCS) is a figure of merit turbines dimensions and layout, which can be • Regulating wind turbines’ proximity to radar to the radar system. This clearly needs to be that can serve to estimate the effect of a wind used for initial site optimization. The next step systems based on their elevation and the cor- achieved without affecting the viability of the turbine on a system’s performance. Since the is to perform detailed modeling of the scenario, responding height of its tallest blade; wind farm. The effectiveness of such an option development of radar in the 1930s and 1940s, including technical specifications of the radar is dependent on terrain effects. A typical rule • “Terrain masking”, or placing turbines on the avoiding detection by reducing radar signature services and threshold values for evaluating the adopted is that if the wind turbine is not in the opposite side of elevated terrain in relation to has been an area of significant military interest. potential degradation of each service. As radars line-of-sight of the radar, it will not cause an im- the radar, thereby redirecting the line of sight The development and deployment of radar sig- are stochastic systems, it is not practical to pact on the radar. Alternatively, increasing the to avoid most of the turbines which would nature suppression technologies for military air- “turn-off” the effect of the wind farm but rather spacing between wind turbines in a farm in such a otherwise fall within the line of sight; craft naturally leads to the question of whether it is necessary to agree on threshold level, below way that they are individually resolvable will help or not a similar approach could be employed to which the interference is considered insignificant. • “Terrain relief”, which places the radar system with the detection of targets within the farm. suppress the radar signature of a wind turbine. The results of the analysis must provide numeri- on a high elevation such as a mountain/or hill- cal values regarding the clutter level generated by ock overlooking a valley that contained wind 3.1.3. LINE OF SIGHT MITIGATION Traditionally, there are three approaches to re- the turbines, as well as additional outcomes that turbines; TECHNIQUES ducing RCS: (1) shaping, (2) application of radar help to modify the wind farm layout for minimiz- ing the impact on the radar. Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave prop- 61 Department of Defence. “Report to the Congressional Defence Committees: The Effect of Farms On Military Readiness”, Office of the Director of Defence Research and Engineering, Washington D.C, 2006.

40 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 41 absorbing materials, and (3) cancellation tech- the RCS of the turbines, as it reduces the clut- These are large objects and their movement pro- The current leading technology in the “stealth niques. ter generated by the wind turbines (Matthews, duces a large, non-zero Doppler return that can windfarm” sector was deployed in Perpignan in 2007)64 is well established in military world, as affect the radar (Matthews et al, 2006)66. The 2016 in Southwest France70. It is known to be Shaping alters the geometry of a plane, missile, it has been studied extensively since the early aerodynamic shape and the elevation angle of an effective solution for weather radar, and suc- or other object to direct radio frequency energy days of radar. Stealth techniques are based, the blades mean that a time varying return is cessfully reduced the average wind turbine radar away from the radar. It can only reduce RCS over mainly, on modifying the object by shaping and seen by the radar with a “flash” of high RCS for cross-section by 90%. However, the solution a limited range of angles, which is often an ef- coating with radar signal absorbing materials, certain blade rotation angles. Stealth treatment suffered from several drawbacks that prevented fective solution when the target is illuminated by in order to reduce the power scattered towards for the blades is not trivial due to the blade struc- wider adoption within the wind industry, includ- a single radar, and the radar location relative to the radar antenna. Much of this research can be ture and composition (they are made of various ing single-band absorption, high upfront cost, the target is known (as is often the case for plane transferred into the civil domain and applied to material layers incorporated to make a light, narrow absorption bandwidth and insufficient flying over radar). Shaping applied to the tower wind turbines, although there are various con- strong structure, and typically include some absorption strength for large wind turbines. In and nacelle could be somewhat effective, but it straints. First, a wind turbine represents a very form of lightning protection, either a mesh or a order for stealth windfarms to become truly vi- would have to be done with knowledge of the large surface area, and therefore, the cost per rod), and because the blade shape is determined able for wind developers across the world, a so- transmitter and receiver directions. Although, it square meter of stealth treatment must remain by aerodynamic factors. As an example, a 40 m lution must provide multi-band absorption at could reduce the RCS in some desired monostat- low. Additionally, any significant increase in mass turbine blade may cause RCS flashes of around L&X-band and S&X-band (suitable for windfarm ic or bistatic directions, it would likely increase it of turbine components is prohibitive due to the 45 dBsm. Theoretically, stealth technologies impinging on both civilian and military airports), in the others. Shaping of wind turbine structures overall impact on the structure (for example, the may reduce these flashes by 15-20 dB, still two wide absorption peaks (up to 1 GHz bandwidth) to reduce RCS has been investigated in (Pinto et impact on the gearbox loading due to the impact orders of magnitude greater than a typical light and high strength absorption (up to 40dB reduc- al., 2000)62. Most RCS reduction techniques use a on blade mass). Stealth technologies can be ap- aircraft, but recent studies only show a reduction tion), all designed from the ground up to mini- combination of shaping and radar absorbing ma- plied to the main elements of the turbine (mast, of 10 dB (Rashid et al., 2010)67. The reason of this mize cost. terials (RAM). Only RAM was considered for this nacelle and blades) in a different way. divergence comes from the fact that the stealth effort because the wind turbine-blade geometry treatment is applied in a way that minimizes 3.2. MITIGATION TECHNIQUES has significant mechanical and aerodynamic con- The wind turbine tower is typically an electrically the changes of the existing blade design, which ASSOCIATED TO THE RADAR SERVICES straints that prevent significant shaping. large cylinder and provides a very directive, large leaves very little room for the stealth material to Mitigation options can also be applied to the ra- radar return. The directivity, however, results in a be incorporated. A blade design that considers dar services. The main options are adaptive clut- Thus, the most promising approach is the appli- large return only when the radar stares directly at the radar material application from the beginning ter filters, the installation of gap filler radars, cation of radar absorbing material (RAM) that the tower. In cases where this does not occur, the may well achieve better reductions in RCS. radar processing techniques, and the use of adap- seeks to reduce Radar Cross-Section (RCS) by tower can remain unchanged. If the large return tive scanning in the radar antennas. absorbing the incident radio-frequency energy from the tower is received by the radar, much With a particular emphasis on blade fabrica- and converting it to heat (McDonald et al., 2012). of the return will be significantly reduced to the tion, for example, Sandia National Laboratories A variety of approaches have been suggested for The material would have to be lightweight, thin, Doppler processing, which will attenuate the in the USA demonstrated the technical feasibil- both hardware and software modifications to ra- durable, inexpensive, and provide sufficient RCS returns from a stationary object. Nevertheless, ity of integrating radar-absorbing materials into dars that would reduce their sensitivity to wind reduction to make it economically viable. Most a radar system will not necessarily completely the standard construction methods currently farm generated clutter. These include use of finer commercial RAM materials give a specular RCS cancel a very large return from a stationary ob- used for manufacturing wind turbines (McDon- clutter cells, use of more and/or adaptive Dop- reduction in the range of 15 to 20 dB (e.g., Em- ject, and some of the tower return may be de- ald et al., 2012)68. The study identified multiple pler filters, use of special post-processor track file erson and Cuming Eccosorb FGM)63; however, it tected65. In such a case, shaping of the tower into pathways to apply radar-absorbing material to a maintenance routines to prevent track drops, use varies widely with frequency and angle incidence. a more conical shape may be an option to direct blade in a targeted way that could minimize the of enhanced adaptive-detection algorithms, and A RAM coating might make sense if the wind tur- the specular return away from the radar. Appli- added cost leading to an economically viable the use of special clutter suppression algorithms bine was at a fixed location from a facility, such cation of radar absorbing materials on the mast mitigation option for the wind industry. , developed for other applications. as an airport radar. However, the bistatic RCS is is also an option, but it can be expensive, due to one of the largest global wind turbine manufac- so large that the aerodynamic degradation of the the large surface area and potential for increased tureres, developed a „stealth blade“ based on a All these techniques are aimed to remove the blades and cost of adding RAM would not gener- service costs. similar concept (Vestas, 2014)69. clutter and ghost targets from the wind turbines. ally be merited. Most work in the literature on stealth treatments 66 J. Matthews; J. Lord; J. Pinto. “RCS Prediction for Stealthy Wind Turbines”. In Proceedings of the European Conference on Antennas and Propagation, Stealth coating, as a technique for reducing for turbines has concentrated on the blades. Nice, France, 6-10 November, 2006 67 L. Rashid; A. Brown. “Partial Treatment of Wind turbine Blades with Radar Absorbing Materials (RAM) for RCS Reduction”. In Proceedings of the 4th European Conference on Antennas and Propagation”, , Spain, 12-16 April 2010 62 J. Pinto; J. Matthew; G. Sarno. “Stealth technology for wind turbines”. In IET Radar Sonar Navigation, vol 4 (1), pp. 126-133, 2000 68 J. McDonald; B. Brock; W. Patitz; S. Allen; H. Loui; P. Clem; J. Paquette; W. Miller; D. Calkins. “Radar-Cross-Section Reduction of Wind Turbines (Part 63 Emerson and Cuming, October 2012, http://www.eccosorb.com/products-eccosorb-fgm 1) (Technical Report)”. SAND2012-0480. Sandia National Laboratories (SNL), Albuqerque, NM, USA (2012). 64 J. Matthews. “Stealth Solutions to Solve the Radar Wind Farm Interaction Problem”. In Proceedings of the 2007 Loughborough Antennas and Propa- 69 Vestas (2014). “Vestas proud to install 1st large-scale wind farm using stealth blade technology. Big technological step but other options also avail- gation Conference, Loughborough, UK, 2-3 April 2007; pp. 101-104 able”, Statement. 65 Ibid, 2003 70 In 2014, EDF Energies Nouvelles started the construction of the windfarm where it installed the new Vestas-built turbines at the “Ensemble Eolien Catalan”.

42 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 43 Echoes from wind turbines are a stochastic phe- Such filters ideally identify the wind turbine sig- A more advanced version of adapting the scan- the susceptibility of such radars to clutter gen- nomenon, and therefore, the goal of completely nature, remove the corrupt measurements, and ning strategy may be possible using phased ar- erated beneath them as well as the capability of removing this clutter and avoiding a reduction in interpolate over the non-corrupt data to recon- ray radars (Yosikawa et al., 2012)75. It has been the air defence system to accept the additional the probability of detection is unrealistic. None- struct the signal. The difficulty lies in identify- suggested that the beam shape of the phased input, need to be performed to determine if there theless, these mitigation techniques have provid- ing the wind turbine signature as it is time vary- array radar can be altered in such a way that a are merits in pursuing this concept further. ed significant advances in the detection capacity ing and highly complex. Furthermore, the wind null in the antenna radiation pattern is created in in presence of wind farms. turbine signature often resembles the actual the direction of the wind turbine. For such radars, The underlying idea for the gap-filling radar weather signal. Nonetheless, several adaptive fil- this technique could provide an elegant way to concept is exceptionally simple: if one radar 3.2.1. DATA PROCESSING IN AIR ter techniques for removing or educing effects of reduce wind turbine clutter, but at the expense cannot see an object due to obscuration cre- SURVEILLANCE RADARS wind turbine clutter have been suggested (Norin of a heavy computational cost. ated by a wind farm, a second radar can be used & Haase 2012)73. Such adaptive clutter filters can that provides overlapping coverage. In addition Various aspects related to the data processing also help to mitigate erroneous wind measure- 3.2.3. CONCEPTS FOR GAP FILLER to large conventional radars, small distributed in the reception chain of an air surveillance ra- ments. If clutter is removed from signal, the aver- MITIGATION APPROACHES radars (known as gap fillers) are used to detect dar (ASR) can be modified to reduce the effect age wind velocity as well as the spectrum width low-flying aircraft penetrating gaps in large ra- of wind farms. Each options were often applied When a wind farm has caused an unacceptable loss can easily be estimated. dar coverage. It is possible to employ more than in the post-detection stage (once the radar has of coverage, a supplementary gap filler radar could one radar to provide additional coverage where determined the presence of the turbine). They be installed, with appropriate data fusion. The gap Adaptive clutter filters use in-phase and quadra- the probability of detection of the original radar include inhibiting track initiation in the vicinity of filler, by allowing a second view of the wind farm ture phase (I/Q) measurements of the electric has been reduced by the introduction of a wind the wind farm or range-azimuth gating (Sergey et radar interference, makes it considerably easier to field as input. Since weather radars normally farm, and combine the radar plots in a plot fu- al., 2008)71. The main drawback of these options is process this interference out through data/or sen- do not transmit I/Q data, but only the products sion process. The additional data may come from that they will also inhibit the detection of wanted sor fusion (Aarholt &Jackson, 2010)76. based on it (reflectivity, radial velocity, etc.), the an existing radar system or through the deploy- targets around the wind farm, and a “blind area” is adaptive clutter filter should be implemented in ment of a new radar. Current market leaders in generated around the wind farm area. In the case a new radar is deployed, it may be the radar’s signal processor. The main challenge this regard in the UK for example are the Terma a relatively simple, low-cost radar, specifically of this mitigation technique is that it requires fast, Scanter 4002 and the Avellant Theia series. They Pre-detection options are those applied to raw designed to provide enhanced detection in such reliable, and computationally effective filters. are being or have been installed at East Midlands, data, before the presence of an object is deter- small regions. For example, holographic radars Chester Hawarden/Liverpool John Lennon, Edin- mined by the radar. They include the use of el- have been proposed to achieve “unambiguous To speed up filtering, only radar cells containing burgh and Newcastle airports77. evation beam information to discriminate higher differentiation between aircraft and turbines. wind turbines should ideally be processed. This altitude aircraft from lower altitude wind farms. Over-the-horizon radars and AWACS (airborne may be achieved by keeping maps of all wind tur- Sensor fusion brings the data from each of these This data information is included further along warning and control systems) are even more bines near a weather radar, or by using automatic sensor types (e.g multiple radars, LIDARs, and the processing chain. Additional techniques such promising. The latter consist of large radar and detection schemes (Hood et al., 2009)74. cameras) together, using software algorithms to as enhanced CFAR, moving target detector pro- computation, display, and control systems, provide the most comprehensive, and therefore cessing, high resolution clutter maps and plot/ housed in large aircraft. First introduced for naval 3.2.2. ADAPTIVE SCANNING accurate mode possible. This improves percep- track filters (Perry & Biss, 2007)72. defence, they have become potentially effective tion by taking advantage of partially overlapping For weather radars, which primarily scan the sky over land with new developments in clutter-re- fields. As multiple radars observe the environ- 3.2.1. ADAPTIVE CLUTTER FILTERS for precipitation, the influence of wind turbines jection circuitry. ment around a vehicle, more than one sensor can be mitigated by adapting the scan strategy of Adaptive clutter filters have been applied in will detect objects at the same time. Interpreted the radar antenna. Changing the radar scan strat- An alternate approach would be to use a “gap weather radars to remove clutter signals from through global 360 degrees perception software, egy to pass over areas with wind turbines could filler” radar positioned within the wind farm but wind turbines. Clutter suppression is essential to detections from those multiple sensors can be limit the amount of wind turbine clutter received sufficiently high above the arcs of rotation of the radar signal processing, but it still suffers from overlapped or fused, increasing the detection and, therefore, reduce the undesired signal in turbine blades so as not to be affected by the severe problems. The moving target indication probability and reliability of objects around the the data processing. The drawback is that data clutter they can create. Certain types of small (MTI) is a commonly used approach in clutter vehicle and yielding a more accurate and reliable obtained in the direction of the wind farm area tactical radars developed for other applications cancellation, and is very effective when radar de- representation of the environment. would be gathered from higher altitudes, which may be suitable candidates. Analysis, including tects moving targets in clutter interference envi- may shorten the effective range of the radar. ronment. 75 E. Yoshikawa; T. Ushio; Z. Kawasaki; S. Yoshida; T. Morimoto; F. Mizutani; M. Wada. “MMSE beam forming on fast-scanning phased array weather 71 L. Sergey; O. Hubbard; Z. Ding; H. Ghadaki; J. Wang; T. Pondsford. “Advanced Mitigating Techniques to Remove the Effect of Wind Turbines and Wind radar”. In IEEE Transport, Geoscience, Remote Sensors, 2012, volume 51; pp. 3077-3088. Farms on Primary Surveillance Radar”. In Proceedings of 2008 IEEE Radar Conference, Rome, , 26-30 May, 2008; pp. 1-6. 76 E. Aarholt; C. Jackson. “Windfarm Gapfiller concept solution”. In Radar Conference (EuRAD), 2010 European, 2010, pp. 236-239 72 J. Perry; A. Biss. “Wind Farm Clutter Mitigation in Air Surveillance Radar”. In Proceedings of the 2007 IEEE Radar Conference, Boston, MA, USA, 17-20 77 Terma announced in summer 2016 contracts with NATS to mitigate windfarms at 3 airports – and https://www.terma.com/press/news-2016/ April 2007; pp. 93-98. terma-provides-wind-turbine-mitigation-radar-for-nats 73 L. Norin; G. Haase. “Doppler Weather Radars and Wind Turbines”. In Doppler Radar Observations –Weather Radar, Wind Profiler, Ionospheric Radar, and Avellant announced on 22 September 2016 the competition of the safety case and the CAA operational approval for its Theia 16A radar at East and Other Advanced Applications: Bech, J.; Chau, J., Eds.; InTech: Rieka, , 2012 Midlands Airport in respect of the Spondon Reservoir Windfarm – http://www.aveillant.com/news/aveillant-radar-receives-caa-operational-approval- 74 K. Hood; S. Torres; R. Palmer. “Automatic detection of wind turbine clutter for weather radars. Journal of Atmospheric Oceanic Technologies, 2010, east-midlands-airport/ 27, pp. 1868-1880 44 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 45 Each sensor type, or “modality” has inherent between wind turbines and human responses is soon be over, at least in Germany. The introduc- with other features in the landscape, including strengths and weaknesses. Radars are very strong a complex one, and many factors play a role in tion of night markings for wind turbines is one of the other wind farms. Utility-scale wind farms at accurately determining distance and speed – the public debate. Wind turbines can change the the measures of German wind action plan with may cover large area, and the individual wind even in challenging weather conditions – but they landscape, generate noise and can cause shadow- the aim to reinvigorate the wind energy sector turbine generators are very large structures in- cannot see the color of a stoplight. Cameras do flicker. It is the effect of the sun shining through that declined last year (ReNews Biz, 2020)79. corporating visually conspicuous, reflective sur- well reading signs or classifying objects, such as the rotating blade of a wind turbine, casting a faces and obviously non-natural geometry that pedestrians or other vehicles. However, they moving shadow. The awareness of the consequences of a wind contrasts strongly with natural landscapes. Con- can easily be blinded by sun, snow or darkness. farm can lead to intense, and sometimes emo- cerns regarding the visual impacts of utility-scale Lidars can accurately detect objects, but they do To ensure the safety of air traffic, aviation au- tional discussions about the need for wind energy, windfarms have emerged as major factors in the not have the range or affordability of cameras or thorities require wind turbines over a certain the suitability of the area, the visual and aesthet- delay or cancellation of planned windfarms. radar. height (typically a tip height of 150 meters) to ic aspects and noise-related issues are not un- be fitted with obstacle lights. Although essential common. The most persistent criticism levelled Optimal siting to reduce potential visual impacts Coordinating two radars by software does present for air traffic flying at low altitudes, these lights at onshore wind farms is their aesthetic effect on requires an accurate understanding of the visual a number of challenges. First, a radar can locate cause significant residential annoyance, espe- the local landscape. The concept of “not-in-my- characteristics of the different types of energy the position of a target only within a finite level cially at night, reducing public support for wind backyard”, or NIMBY-ism, comes to mind when facilities, including their visibility under the dif- of accuracy determined by the size of the resolu- energy. As next generation wind turbines have stakeholders generally support a technology, but ferent lighting conditions that occur at proposed tion cell. The resolution cell for one radar unit will become increasingly higher over the years, the do not want it located near them. People often project locations. Lightning conditions at a given never align with those of the other due to the off- majority of newly planned windfarms will require feel a strong attachment to their local area and location vary by season, time of day, sun direc- set positioning. Thus, inherent uncertainties are obstacle lights. As a result, these plans encounter value its aesthetic qualities. Wind projects are tion and angle above the horizon, and atmo- created in actual position when returns from one more and more resistance from local communi- particularly challenging in this respect because spheric factors, including the presence or absence must be compared with returns from the other. ties. Especially in populated regions, this public they can be seen for much greater distances. of clouds and the level of haze, which varies by resistance forms a serious challenge for wind region and by time of a day. Second, it is unrealistic to expect that the radar farm developers and energy ambi- The assessment of suitability of a certain loca- beams from each unit will sweep the exact same tions (van der Zee, 2016)78. tion for the installation of a wind turbine requires One of the first published analyses of the impact area of interest at precisely the same moment. As the consideration of multiple impact issues: vi- of distance on turbine visibility was conducted such, relative target motion will always occur be- At the beginning of this year, the German sual aspects, environmental effects such as the for the environmental statement for the Pen- tween the observations made by each radar. The Bundesrat, a legislative body that represents Ger- impact on wildlife and birds, and shadow flicker rhyddlan and Llidartywaun facilities in Wales (Eu- coordination software would need to account for many’s 16 regions at the national level, has ap- from wind turbines to name a few. The present ropean Commission, 1995)80. These wind energy that as well. proved amendments to a general administrative chapter will touch upon visual impact, wind en- facilities (managed as one site) were installed in regulation that will stop lights continually flash- ergy and land use conflicts and impacts on birds the early 1990s. From a visual assessment under- If the “blocking area” is a wind farm, each radar ing on wind turbines to warn aircraft. To reduce and bats. As environmental aspects of renewable taken at 22 locations around the 103-turbine site, will also experience false returns due to the ro- light pollution and thereby energy consumption, energy are wider, they also require some mitiga- 20 km was determined as the limit of visibility. tation of the turbine blades and bleed through the German – AVV introduced Anfang 6 for BNK tion strategies to find a right balance between Owing to the size of this wind energy facility and from the clutter map. There are no data available (Bedarfgesteuerte Nachtkennzeichnung von Win- wind energy development and biodiversity. The its early development, this distance became a at present to determine if such false returns will denergieanlagen, also known as Aircraft Detec- impacts of noise pollution are dealt in the next general standard for measuring the visibility of be seen by both radars concurrently. If they are tion Lighting Systems or ADLS). It makes BNK chapter. turbines and determining their relative impact. not, then the coordination software also will face systems mandatory for existing and new wind the challenge of determining if the changes in farms, with the intention of ensuring the adop- 4.1. VISUAL IMPACT In 1996, Gareth Thomas, a planning officer in observed position are due only to positional un- tion of technologies that further reduce light Montgomeryshire, Wales, attempted to define The advent of utility-scale wind energy is hav- certainty and relative motion of the target or rep- pollution. BNK systems combine the obstruc- the potential visual impacts of wind turbine us- ing a profound impact on scenic resources. Wind resent track “seductions” caused by false returns tion lighting with a system that detects when ing descriptors, which could be assessed in the turbines are large structures and taken together seen by one radar but not the other. This further an aircraft at night is within a radius of 4 km and field and could be repeated with constant ob- with associated development, such as access increases the coordination challenge. an altitude of less than 600 meters of the wind servations. His analysis was based on observa- tracks and associated buildings have the poten- farm, and turning the lights on at that time. This tions of the Cemaes and Llandinam windfarms tial to create significant visual and landscape CHAPTER 4 - ENVIRONMENTAL AND specific regulation will apply for German onshore located in Wales. As a result of his initial evalu- impacts. These impacts will be influenced by the SOCIETAL IMPACTS OF WIND ENERGY turbines from 31 December 2022 and for Ger- ations, Thomas concluded that a distance of 15 distance from which the turbines will be viewed man offshore turbines from 31 December 2023. km was appropriate for evaluating the visibility Most people have a positive attitude towards and whether the turbines are seen in isolation or This means that the blinking of wind turbines will of the windfarm. Using the information from his alternative sources of energy. The association

79 78 H.T.H van der Zee (2016). “Obstacle lighting of onshore wind: Balancing aviation safety and environmental aspects”. The Netherlands Aerospace ReNews Biz. “Germany advances turbine light relief”, newsletter, 14 February, 2020 Center, Amsterdam, NL 80 European Commission (1995). ExternE. Externalities of Energy, Vol 6. Wind & Hydro

46 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 47 observations of the two windfarms, Thomas de- passes across the wind turbine tower (Coates As- is to move these projects away from land entirely. be those with high biodiversity values. Planning veloped a matrix that incorporated nine bands of sociates, 2007). Wind is particularly amenable to moving offshore and respective siting can avoid negative biodi- visual impacts ranging from “dominant” to “neg- where winds are generally stronger, and wind versity impacts. Development of land with lower ligible”. The matrix accounted for turbine heights 4.2. WIND ENERGY AND LAND USE speed and direction are more consistent, leading conservation value could lead to lower capac- of approximately 25-31 m and overall heights of to greater potential generation and greater effi- ity factors and, hence, increase the specific land Even though people like wind power in the ab- 86 41-45 m. stract, some object to large projects near their ciency . Although offshore wind eliminates land footprint, although this also provides opportu- homes, especially if they do not financially use, but it raises opposition among those con- nity for the co-location of different generation Subsequent evaluations of the visual impact of benefit from the project. The NIMBY (Not-in cerned with the impact on the environment and technologies to improve land use efficiency and windfarms often utilized standard guidelines, scenic views. Community involvement in project reduce permitting, leasing and transmission costs my-backyard) discussion seriously affects the 89 building from these early studies for reference, in transition process towards a decentralized en- planning and regulation for land use and zoning (Gross, 2020) . determining the largest distance at which wind ergy supply, as residents feel restricted in their can help to alleviate these concerns. turbine was visible. One such standard includes quality of life by renewable technology systems 4.3. IMPACT ON BIRDS a division of the landscape into three areas – a Zoning refers to placing turbines a predetermined installed nearby. Power plants and transmission For wind electricity, one of the most vociferous distant area (a radius of over 10 km), an inter- distance from a radar to avoid interference. The lines will be located in areas not accustomed to environmental concerns relates to the death of mediate area (a radius of 1 km), and an immedi- U.S Department of Defence report87 recommends industrial development, potentially creating op- birds, and other avian species that can fatally col- ate area (a radius of less than 1 km). Within the a distance of 30 nautical miles for turbines with position. Siting of wind farms is especially chal- lide with turbine towers, blades, and power lines, distant area, wind turbines would be visible, but blade tips that protrude over 90 meters above lenging as modern wind turbines are huge. an issue termed “avian mortality”. Many ecolo- the nearest objects generally would dominate the local terrain. Zoning is a common mitigation gists, biologists, ornithologists, and environ- perception. However, within an “empty” land- measure supported by policies pertaining to wind The land footprint of wind farms varies consider- mentalists at large have spoken out against wind scape, the wind turbines could become the visual turbine siting in many European countries. In ably, based on the wind conditions, topography power on the grounds that it presents too great focus of observers. In the intermediate area, wind Austria, wind farms greater than 10 km from an and other factors. Thus, wind power similar to so- a risk to avian wildlife. Studies have generated turbines would be extremely dominant because air defence radar will receive no objections. In the lar, has a comparatively small land footprint and that onshore and offshore wind turbines pres- of their size and the rotational movement of the Netherlands, only wind farms within 24 km from similarly low greenhouse gas intensity compared ent direct and indirect hazards to birds. Birds can blades (Jallouli and Moreau, 2009)81. a military radar require review. In Germany, pol- to fossil electricity. Direct land use measures the smash into a turbine blade when they are fixated icy enforces a protection zone of 10 km around area occupied by wind turbines and other infra- on perching or hunting and pass through its rotor Additional research has been conducted to deter- all Air Traffic Control (ATC) radars, with an area structures, excluding the land between infra- plane: they can strike support structures; they mine the influence of wind turbine blade move- of interest up to 18 km from ATC radars. These structure elements. This takes into account that can hit parts of towers; or they can collide with ment in conjunction with distance. In general, zoning policies address both military and civilian overall land use of wind farms does not prevent associated transmission and distribution lines. the human eye can detect movement at large concerns over radar shadowing (for Germany and this land from fulfilling other functions such as Some species, face additional risks from the rap- distances. The rotary and very regular movement the Netherlands), and electromagnetic interfer- agriculture for example. Within the wind farm id reduction in air pressure near turbine blades, of wind turbine blades is not a common type of ence and obstacles to low flying routes (in Aus- boundaries, approximately 90 percent of the which can cause internal hemorrhaging through “natural” movement, especially at the scale of tria). Zoning is also a mitigation measure used in land is not occupied by wind power equipment a process known as barotrauma (Baerwald et al., large windfarm. Instead, this type of movement UK Civil Aviation Authority policy as a means to so that land is available for grazing or cultivation. 2011)90. Indirectly, wind farms can positively and has been found to be highly noticeable, and manage shadowing and false plots on secondary Wind turbine nevertheless, can cause noise up to negatively physically alter natural habitats, the Coates Associates (2007)82 suggested that it may surveillance radar (Auld et al., 2014)88. 100 decibels, depending on the type of turbine, quantity and quality of prey and the availability enhance the visibility of wind farms within the power capacity, and wind speed (Kaza & Curtis, of nesting sites. It has been suggested that some landscape. Some studies of onshore wind farms, Wind development may also be in conflict with 2014)85. This can restrict land use, especially if species, such as migratory bats, raptors and sea- for instance, have suggested that motion can ex- biodiversity, since bats, birds and insects can be human settlements are nearby. birds, may be particularly impacted, which may tend the viewshed of wind turbines to beyond 8 affected. Analyses for California found that areas at least be partly linked to visual acuity (Green, km (Tsoutsos et al., 2007)83 and up to 17 km in with the highest quality wind resources tend to Technological and policy solutions can lessen the 2012)91. clear weather, or when conditions of strong con- land use impact of renewable power and the re- trast between the rotors and the sky are present sulting public opposition. A number of technolo- (University of Newcastle, 2002)84. At times, the 85 N. Kaza; M. Curtis. “The land use energy connection”. In Journal of Planning Literature, 29 (4): 1-16 gies may help lessen the land use impact and pub- 86 blades may not be visible, but a slight “pulse” “Offshore Wind Research and Development”, U.S Office of Energy Efficiency and Renewable Energy, https://www.energy.gov/eere/wind/offshore- lic opposition to renewable development. One wind-research-and-development in the intensity of light can be seen as the blade potential solution to overcome land use concerns 87 U.S. Department of Defence. “Report on Congressional Defence Committee: Effect of windmill farms on military readiness”. 2006, Washington D.C, USA 88 T.Auld; M.P. McHenry and J.Whale (2014). “Options to mitigate utility-scale wind turbine impacts on defence capability, air supremacy, and missile 81 J. Jallouli; G. Moreau. “An Immersive Path-Based Study of Wind Turbines’ Landscape: A French Case in Plouguin”. In Renewable Energy, Vol. 34; pp. detection”. In Renewable Energy, Issue 63, pp. 255-262 597-607 89 S. Gross. “Renewables, Land Use, and Local Opposition in the United States”, Brookings Institution (2020), Washington D.C, USA 82 Coates Associates, 2007. “Cumbria Wind Energy Supplementary Planning Document: Part 2. Landscape and Visual Considerations”. Prepared for 90 the Cumbria County Council. E. Baerwald; R. Barclay. “Patterns of Activity and Fatality of Migratory Bats at a Wind Energy Facility in Alberta, Canada”. In Journal of Wildlife Management, 2011, 75 (S), pp. 1103-1114 83 T. Tsoutsos; G. Zacharias; K. Stefanos; P. Elpida. “Aesthetic Impact from Wind Parks”, 2007 91 M. Green. “Through birds’ eye: insight into avian sensory ecology”. In Journal of Ornithology, 153, 2012; pp. 23-44 84 University Of Newcastle. “Visual Assessment of Windfarms Best practice”. Scottish Natural Heritage Commissioned Report F01AA303A

48 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 49 The collision of birds with wind turbines has been tality rates from most studies range from three lation. Most fatalities reported from turbines in bines could attract bats into their vicinity (Cryan noted since the 1970s though only in light of to six birds per MW per year93 for all species com- the United States, Canada, and Europe are of spe- et al., 2009)103. The main reason for this attrac- the recent wind energy expansion has the prob- bined, and no publicly available study has re- cies that evolved to roost primarily in trees dur- tion appears to be the presence of great numbers lem been seriously recognized. One of the major ported more than 15 bird fatalities per MW year ing much of the year (“tree bats”), some of which of prey insect close to the turbines, lured by the studies recording bird strikes from wind turbines (Strickland et al., 2011; Loss et al., 2013a)94. migrate long distances in spring and late summer turbine’s color and heat emission. quote collision rates per turbine from 0 to over to autumn. 60 collision fatalities per year, which equals 0 Some studies have suggested that bird fatalities While it is still unclear why bats frequent wind to 20 birds per MW per year. Many bird species increase with tower height (Barclay et al., 2007; It is estimated that hundreds of thousands die at turbine installations, recent research has shown feature in the collision records, including gulls, Baerwald and Barclay 2011)95. However, tower wind turbines each year in North America alone that bats appear to actively investigate turbine raptors, such as griffon vulture, golden eagle, red height was found not to affect levels of bat fatali- (US Geological Survey, 2019)98. Unfortunately, rotors. Some species may be assessing them as kite, kestrels, and red-tailed hawks, though it is ties at Canadian facilities (Zimmerling and Fran- it is not clear why this is happening. Several hy- potential roost sites104, however there is also suggested that limited information existent on cis, 2016)96, and studies on birds suggest that the potheses have been proposed to explain why bats some evidence of foraging behavior around tur- passerines collisions with wind turbines is prob- relationship between tower height and bird col- are killed by wind turbines (Kunz et al., 2007, bines. Bats tend to be concentrated in areas of ably due to a combination of fewer studies, lower lisions is more nuanced (Smallwood and Karas, Cryan and Barclay 2009, Rydell et al., 2010a)99. high insect density and are much more likely to detection rates, rapid scavenger removal. 2009)97. Taller turbines often have much larger These include accidental encounter, particularly begin hunting when large numbers of insects are rotor-swept areas, and it has been hypothesized by migrating or juvenile animals; deliberate for- congregating. Reports into bat-turbine interac- The characteristics of collision with operating that collision fatalities will increase due to the aging around the blades; and deliberate use of tall tions frequently state the importance of investi- turbines have been extensively studied in the greater overlap with flight heights of nocturnal- structures as display sites by bats in the breeding gation into the possibility of insect attraction to Western Europe. Collision risk is primarily influ- migrating songbirds. The vast majority (<80%) of season. Recent research has shown that migrat- turbines (e.g Johnson & Kunz, 2004; Ahlen, 2004; enced by the location of a wind farm. Indeed, avian nocturnal migrants typically fly above the ing bats preferentially visit tall structures in the Rodriquez et al., 2006)105, particularly since the farms located at certain landscape features, such height of the most common rotor-swept zone landscape, potentially explaining their high tur- recent loss of feeding habitats may be pressur- as coastlines, hill tops, or large rivers have been (<150 m). bine collision rates (Jameson and Willis, 2014)100. izing bats to feed in alternative areas. Turbine associated with higher rates of mortality as birds In addition, the use of thermal imaging has color may play an important part in insect at- are known to use these linear features for naviga- Important factors associated with elevated colli- shown tree-dwelling bats preferentially orientat- traction (Ahlen, 2004)106, although to date this tion, especially during migration. Weather con- sion risk identified to date at onshore wind farms ing towards turbines and approaching turbines has not been closely investigated. Turbines are ditions also affect collision risk: nights with low include topography, turbine location, design, and from the leeward side (Cryan et al., 2014)101. It mostly painted white (Johnson & Kunz, 2004)107 wind speed, relatively warm temperatures, and configuration, including spacing, and land use has been suggested that tree bats use streams of or shades thereof; the reasoning behind painting no precipitation are associated with the highest close to turbines. In particular there is a signifi- air flowing downwind from wind turbines while turbines in light colors appears to be connected collision risk. In North America, it has been ob- cant interaction between the prevaling wind and searching for roosts and insect pray, similar to with making turbines “visually unobtrusive”, served that large-scale weather phenomena, such topography for raptors. When siting a wind farm those produced around trees at night102. against the skyline, to make them “blend well as high pressure and low humidity, were more ac- all these factors need to be considered in light of into the landscape”, or to make them easier to curate in predicting collisions than local weather the local bird population and their flight behav- The reasons for bat presence in the vicinity of locate for meteorological purposes. conditions (Arnett et al., 2008)92. Fatalities occur ior and thereby minimize the impact of the wind wind turbines have also been investigated, with mainly during autumn migration, roughly from turbines. the initial hypothesis that collisions between bats The species with the highest collision numbers August to mid-September, and a smaller peak and turbines are random. Another hypothesis in Europe are Pipistrellus pipistrellus, Pipistrel- can also occur during spring migration in certain 4.4. IMPACTS ON BATS suggests that bats are at a greater risk of collision lus nathusii, and Nyctalus noctula. However, this parts of Europe. The exact timing of fatalities var- while expressing certain behaviors, such as flying finding is derived mainly from Central Europe. Bats are long-lived mammals with low reproduc- ies latitudinally, e.g in Southern Europe the pe- high while migrating or hunting migratory in- In total, there are eight species that account for tive potential and require high adult survivorship riod of higher collision risk is longer. sects. Finally, there is also a hypothesis that tur- 98% of all the dead bats found at wind turbines to maintain populations. The recent phenom- enon of widespread fatalities of bats at utility The most bird collisions are with the rotating 98 US Geological Survey. “Bat Fatalities at Wind Turbines – Investigating the Causes and Consequences”, U.S Department of the Interior, 2019; Washington D.C scale wind turbines represents a new hazard with 99 turbine blades, although collisions with turbine J. Rydell; L. Bach; M. Dubourg-Savage; M. Green M; L. Rodrigues; A. Hedenström (2010). “Mortality of bats at wind turbines links to nocturnal insect the potential to detrimentally affect entire popu- migration”. In European Journal of Wildlife Research, 56 (6), pp. 823-827 towers are also possible. For birds, adjusted fa- 100 J. Jameson; C. Willis. „Activity of tree bats at anthropogenic tall structures: implications for mortality of bats at wind turbines“. In Animal Behavior, Volume 97, November 2014, pp. 145-152 92 E.B. Arnett; M. Schirmacher; M.M. P. Huso; J. P. Hayes. “Effectiveness of changing wind turbine cut-in speed to reduce bat fatalities at wind facili- 101 P. Cryan; P. Gorresen; C. Hein; M. Schirmacher; R. Diehl; M. Huso; D. Hayman; P. Fricker; F. Bonaccorso; D. Johnson; K. Heist; D. Dalton. “Behavior ties”, Final Report submitted to the Bats and Wind Energy Cooperative, Austin, TX, USA: Bat Conservation International of bats at wind turbines”, PNAS, 2014Geological Survey 93 Fatality rates are typically reported on a per turbine basis or per nameplate capacity (MW). 102 Ibid, 2014 94 S. Loss; T. Will; P. Marra. “Estimates of bird collision mortality at wind facilities in the contiguous United States”. In Biological Conservation, Volume 103 P. Cryan; R. Barclay. “Causes of Bat Fatalities at Wind Turbines: Hypothesis and Predictions”. In Journal of Mammalogy, Volume 90, Issue 6, 15 168 (2013), pp. 201-209 December 2009, pp. 1330-1340 95 E. Baerwald; R. Barclay. “Patterns of Activity and Fatality of Migratory Bats at a Wind Energy Facility in Alberta, Canada”. In Journal of Wildlife 104 Ibid, 2009 Management, 2011, 75 (S), pp. 1103-1143 106 I. Ahlen. “Wind turbines and bats – a pilot study”. Final report, 11 December 2003, Swedish National Energy Administration 96 J.R. Zimmerling; C. M. Francis (2016). “Bat mortality due to wind turbines in Canada”. In Journal of Wildlife management, volume 80, pp. 1360-1369 107 T. Kunz; E. Arnett; W. Erickson; A. Hoar; G. Johnson; R. Larkin; M. Strickland; R. Thresher and M. Tuttle. “Ecological Impacts of Wind Energy Develop- 97 K. W. Smallwood and B. Karas (2009). “Avian and bat fatality rates at old generation and repowered wind turbines in California”. In Journal of Wild- ment on Bats: Questions Research needs, and Hypothesis”. In Frontiers in Ecology and the Environment, Volume 5, No 6 (August 2007), pp. 315-324

50 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 51 in northwestern Europe (Rydell et al, 2010)108, or under-pressure (damage to lungs) in proximity large trees. Further, the exploration of wind tur- and bats, but only a few proved to be efficient and these are defined as “high-risk species” be- to the rotating blades, thus adding to the risk of bines for roosting possibilities by bats (Kunz et (Gartmann et al., 2016)119. Possible mitigation cause they face a higher probability of colliding wind energy to bats. al.,2007)117, or their utilization as social and mat- options to reduce collisions between birds, bats with the turbines. In addition to the three afore- ing sites, have also been proposed to explain the and wind turbines in existing wind-power plants mentioned species, the high risk species include The hypothesis that barotrauma was an impor- presence of bats nearby turbines, but so far, they can be categorized as either turbine-based or Vespertilio murinus, Eptesicus nilsonii, Pipistrellus tant source of bat mortality at wind facilities was have still not seen examined in detail. It is impor- bird-based. Mitigation options on turbines en- pygmaeus, Nyctalys leisleri, and Eptesicus sero- quickly accepted, although the evidence was tant to keep in mind that the relative importance compass wind-power plant design, micro-siting tinus109. Other species or species groups such as largely circumstantial and there have been few of each factor attracting bats to wind turbines of turbines, repowering and operation. Such the Myotis spp. and Rhinolophus spp. are rarely efforts to evaluate this hypothesis empirically. fluctuates depending on the considered species, measures have small or only indirect effects on found dead at wind turbines. Species that are Rollins et al. (2012)114 observed that many of the the sex and age of the individuals, the time of bird mortality. The other approach is to directly the most prone to collisions are predominantly symptoms associated with barotrauma were also year, or the location of the wind turbines. affect bird behavior. The mitigation options af- aerial hawkers with wings and echolocation calls consistent with traumatic injury as well as post- fecting bird behavior encompass turbine design, adapted for movement in open space: they are mortem processes occurring before the carcasses It is possible that wind turbines interfere with deterrence/harassment and habitat alterations. the species that hunt on flying pray, usually far were discovered. Simulations conducted at the seasonal migration and mating patterns in some The latter may be either inside (decreasing the from the ground or any structures (Barclay et National Renewable Energy Laboratory (NREL; species of bats. More than three quarters of the attractiveness of the area), or outside the wind- al., 2017; Foo et al., 2017)110. In turn, the low-risk presentation at 2015 BWEC Science meeting) bats fatalities at wind turbines are from species power plant area (increasing the attractiveness species such as Myotis spp. and Rhinolosophus suggested that there is a very limited area along known as “tree bats”, which tend to migrate long of other areas). The objective of this section is to spp. hunt close to surfaces or directly in the vege- a rotating turbine blade that creates pressure distances and roost in trees. These bats migrate focus on the methods currently used in Europe tation, which decreases the time that they spend differentials sufficient to cause barotrauma, and and mate primarily during late summer and early on operating turbines that have shown to be ef- in the rotor sweep zone, and further reduces the that bats would have to be in such close proxim- autumn, which is also when the vast majority of fective. Some of the methods presented decrease probability of colliding with the turbines. Despite ity to the blade to experience barotrauma-caus- bat fatalities at wind turbines occur. It is also pos- the collision risk and therefore the fatality rate of the earlier belief that only migratory bats were ing pressure changes that the risk of collision was sible that bats mistake slow or stopped turbine the wind farm, others attempt to avoid destruc- affected by collisions (Arnett et al., 2008; Kunz et almost certain115. blades for trees. tion of important habitats and features for birds al., 2007)111, it was discovered that both resident and bats. and migratory species are prone to collisions with Barotrauma continues to be cited as an impor- The impacts of wind farms on bats vary in nature wind turbines throughout Europe (Rydell et al., tant source of mortality for bats in both the pop- and duration, and can occur at all stages from the 4.5.1. TURBINE-SPECIFIC MITIGATION 2015)112. ular and scientific literature (e.g., USFWS, 2016, construction to the dismantling phase. The first OPTIONS Barclay et al., 2017)116. Whether it is important impact to possibly take place is the loss of habitat The first and probably the most effective way Individuals are either killed by direct collision to resolve questions around the significance of and the following changes in bat fauna during the to avoid impacts is the choice of the wind farm (blunt-force trauma) with the moving blades or barotrauma depends on whether it leads to an construction phase of a wind farm. However, the site itself as there are multiple factors to consider by barotrauma (tissue damage provoked by rapid underestimation of bat fatalities, particularly in fatalities observed during the operating time of a just regarding bats and birds. General opinion is pressure change) when flying close to the blade some species, from bats flying out of the search farm are the most visible impact (Mascarenhas et that the most effective way to lessen impacts on (Baerwald et al., 2008)113. Bat scientists speculat- area before dying for example, or whether the al., 2018)118. Furthermore, among the newly in- birds and bats is to avoid building wind farms in ed that bats would experience sudden pressure risk of barotrauma leads to different strategies vestigated topics in this field is the avoidance of areas of high avian abundance, especially where changes as they passed through rotating turbine for mitigating bat fatalities. operating wind farms and their vicinity by bats, threatened species or those highly prone to col- blades. An implication of the barotrauma hy- which could severely affect species in Europe by lision at present. Therefore, guidance suggests pothesis was that bats might avoid collision, but Another reason might be that bats are drawn decreasing their habitats’ availability. that strategic planning should be based on de- still suffer debilitating injury or die from either to tall structures, which are easy to perceive tailed sensitivity mapping of bird populations, over-pressure (damage to tympanic membranes) in the landscape and which they confuse with 4.5. AVOIDANCE AND MITIGATION habitats and flight paths, to identify potentially STRATEGIES IN MINIMIZING WIND sensitive locations. 108 J. Rydell; L. Bach; M. Dubourg-Savage; M. Green; L. Rodrigues; A. Hedenström (2010). “Mortality of bats at wind turbines links to nocturnal insect FARMS IMPACT ON WILDLIFE migration”. In European Journal of Wildlife Research, 56 (6), pp. 823-827 109 Ibid, 2010 Many methods have been developed to avoid or General guidelines recommend avoiding areas 110 C. Foo; V. Bennett; A. Hale; J. Korstian; A. Schildt and D. Williams. “Increasing evidence of bats actively forage at wind turbines”. In Animal Behavior, to reduce the impacts of wind turbines on birds which are extensively used by the involved spe- Conservation Biology, 2017 111 T. Kunz; E. Arnett; W. Erickson; A. Hoar; G. Johnson; R. Larkin; M. Strickland; R. Thresher and M. Tuttle. “Ecological Impacts of Wind Energy Develop- ment on Bats: Questions Research needs, and Hypothesis”. In Frontiers in Ecology and the Environment, Volume 5, No 6 (August 2007), pp. 315-324 112 J. Rydell; A. Wickman. “Bat Activity at a in the Baltic Sea” Acta Chiroterologica 17 (2), pp. 359-364 117 T. Kunz; E. Arnett; W. Erickson; A. Hoar; G. Johnson; R. Larkin; M. Strickland; R. Thresher and M. Tuttle. “Ecological Impacts of Wind Energy Develop- 113 E. Baerwald; R. Barclay. “Patterns of Activity and Fatality of Migratory Bats at a Wind Energy Facility in Alberta, Canada”. In Journal of Wildlife Man- ment on Bats: Questions Research needs, and Hypothesis”. In Frontiers in Ecology and the Environment, Volume 5, No 6 (August 2007), pp. 315-324 agement, 2011, 75 (S), pp. 1103-114. 118 M. Mascarenhas; A.T. Marques; R. Ramalho; D. Santos; J. Bernardino; and C. Fonseca. “Biodiversity and Wind Farms in Portugal”. Springer, 2018 114 K. Rollins; D. Meyerholz; G. Johnson; A. Capparella; and S. Loew. “A Forensic Investigation into the Etiology of Bat Mortality at a Wind Farm: Baro- 119 V. Gartman; L. Bulling; M. Dahmen; G. Geissler and J. Köppel. “Mitigation Measures for Wildlife in Wind Energy Development, Consolidating the trauma or Traumatic Injury?” In Journal of Veterinary Pathology, Volume 49, Issue 2, 2012 State of Knowledge – Part 1: Planning and Siting, Construction”. In Journal of Environmental Assessment Policy and Management, Volume 18, Number 3 115 The NREL study has not been published in the peer-reviewed literature. (September 2016) 116 USFWS – U.S Fish &Wildlife Service

52 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 53 cies or which play an important role in their life each turbine, because of the aforementioned with increased risk for collisions. In wind-power er, this approach requires a real-time surveillance cycle, principles that can also be utilized for birds avoidance effect, while a longer distance would plants where turbines were placed at more haz- program, which requires significant resources to and other species. For bats, this means avoiding, result in the opposite. ardous locations to bird collisions, these were ei- detect birds at risk. for example, hedgerows, forest edges, and other ther removed or relocated. Micro-siting has been wooded linear features, as they are extremely Wind turbines have a relatively short life cycle proposed in agricultural areas, wetlands and In addition to human observers, there are emerg- used for commuting and foraging. Wetlands are (ca 30 years) and equipment remodeling must be along ridges with many soaring raptors. Remov- ing new independent-operating systems that de- also important sites for foraging. Summer and undertaken periodically. Repowering is consid- ing “problem” turbines will specifically reduce tect flying birds in real-time and take automated winter roosts can be in various location types, ered an opportunity to reduce fatalities for the mortality at that location, but may possibly lead actions, for example radar, cameras or other but caves, forests and old trees, ridges and cliffs species of greatest concern: (1) wind farm sites to a shift of the problem to other turbines. Relo- technologies. These systems may be particularly can be highlighted. Migration flyways are of- that have adverse effects on birds and bats could cation of “problem” turbines instead may create useful in remote areas, where logistic issues may ten located on the coast or in fluviatelle valleys be decommissioned and replaced by new ones increased collision risk elsewhere: and has there- constrain the implementation of surveillance along rivers. Another recommendation is to avoid that are constructed at less problematic sites or fore a lower expected efficacy. It has for example protocols based on human observers; or during natural reserves, national parks or any protected (2) wind turbines of particular concern could be been suggested that outer turbines and turbines night periods. These new systems are based on areas, as they are designed to protect important appropriately relocated. It is essential that moni- at the end of each row may experience higher video recording images such as DTbird® (May et sites for numerous endangered or vulnerable toring studies are carried out first, before under- risk of collision. Unless ‘problem” turbines were al., 2012)128, or radar technology such as Merlin species, including bats. These zones usually have taking such potentially positive steps. placed at specific hazardous locations, such as SCADA™ Mortality Risk mitigation System. For defined limits and specific regulations, often for- breeding sites, migration bottlenecks or topogra- example, an experimental design at Smøla wind bidding the construction of wind turbines inside Also, as technology has rapidly progressed in re- phy creating thermals, the collision risk may be farm in Norway showed that the DTbird® system their perimeter anyway (Drewitt &Langston, cent years, there is a trend to replace numerous expected to be reduced when such turbines are recognized between 76% and 96% of all bird 2006)120. Buffer zones around these sensitive ar- small wind turbines by smaller numbers of larger removed or relocated. The efficacy of micro-sit- flights in the vicinity of the wind turbine. Analyzing eas are recommended (Arnett & Baewald, 2013; ones. The main changes have been a shift toward ing options is likely very site-specific and should the characteristics of these technologies and Marx121, 2017). higher rotor planes and increased open airspace preferably be done prior to the construction of taking into account factors influencing the risk between the wind turbines. Despite taller towers the wind-power plant. of collision, cameras can be particularly useful Studying flight corridors is essential to under- having larger rotor swept zones, and therefore a in small wind farms. Radar systems appear to be stand their importance for migratory and com- higher collision risk area than an old single wall To date, wind turbine shutdown on demand more powerful tool for identifying large-scale muting bats, and to choose the position of wind wind turbine, there is increasing evidence that seems to be the most effective mitigation tech- movements like pronounced migration periods, turbines accordingly: keeping a distance from fewer but larger, more power-efficient wind tur- nique. It assumes that whenever a dangerous sit- particularly during night periods. the flyways and placing turbines parallel to them bine may have a lower collision rate per mega- uation occurs, e.g birds flying in a high collision (Drewitt &Langston, 2006122; Baerwald &Bar- watt (Barclay et al., 2007; Smallwood & Karas, risk area or within a safety perimeter, the wind Turbine operation may be restricted to certain clay123, 2011). A simple wind farm design, such 2009)126. However, repowering has been raising turbine presenting greatest risk stop spinning. times of the day, seasons or specific weather con- as turbine rows or clusters has been found to be major concern for bats, so a trade-off analysis This strategy may be applied in wind farms with ditions (Smallwood & Karas, 2009)129. This cur- effective in keeping the impact on habitats low. must be conducted. high levels of risk, and can operate year-round or tailment strategy is distinct from that described The adequate distance between each tower is be limited to a specific period. beforehand in that it is supported by collision risk difficult to assess on both tight and wide spac- A similar approach to avoiding sensitive areas models. This approach may imply a larger inop- ing have pros and cons: turbines closer to each can also be adopted for micrositing, i.e., the po- De Lucas et al. (2012)127 demonstrate that wind erable period and, consequently, greater losses in other can reduce the cumulative avoidance effect sitioning of turbines and other facilities – roads, turbine shutdown on demand halved Griffon terms of energy production. As a result, it has not of turbines (Gartmann, 2016)124 and footprint on power lines, and substations – within the wind vulture fatalities in Andalucia, Spain, with only a been well-received by wind energy companies. habitats (Drewitt & Langston, 2006)125, but also farm area. Micro-siting options (i.e. removing or marginal (0.07%) reduction in energy production. decreases the commuting possibility between relocating turbines) aim at identifying locations In this region, wind farm surveillance takes place Restrict turbine operation revealed to be very ef- year-round, with the main objective being to de- fective for bats. Arnett et al. (2010) showed that tect hazardous situations that might prompt tur- reducing turbine operation during periods of low 120 A. Drewitt; and R. Langston. “Assessing the Impacts of Wind Farms on Birds: impacts of Wind Farms on Birds”. Ibis 2006, 148, pp.29-42. bine shutdown, such as presence of endangered wind speeds reduced bat mortality from 44% 121 G. Marx. “Le Parc Eolien Français et Ses Impacts Sur l’avifaune – Étude Des Suivis de Mortalité Réalisés En France de 1997 à 2015; LPO, France: Rochefort, 2017; p.92 species flying in the wind farm or the appearance to 93% with marginal annual power loss (≤ 1% 122 A. Drewitt; and R. Langston. “Assessing the Impacts of Wind Farms on Birds: impacts of Wind Farms on Birds”. Ibis 2006, 148, pp.29-42. of carcasses that might attract vultures. Howev- of total annual output)130. For birds it might not 123 E. Baerwald; R. Barclay. “Patterns of Activity and Fatality of Migratory Bats at a Wind Energy Facility in Alberta, Canada. In Journal of Wildlife Man- agement, 2011, 75 (S), pp. 1103-1114. 127 124 V. Gartman; L. Bulling; M. Dahmen; G. Geissler and J. Köppel. “Mitigation Measures for Wildlife in Wind Energy Development, Consolidating the M. De Lucas; G. Jans; and M. Ferrer. “Birds and Wind Farms: Risk Assessment and Mitigation”, University of Madrid, 2007 State of Knowledge – Part 1: Planning and Siting, Construction”. In Journal of Environmental Assessment Policy and Management, Volume 18, Number 3 128 R. May; O. Hamre; R. Vang; T. Nygard. “Evaluation of the DTBird Video-system at the Smøla Wind-Power Plant. Detection Capabilities for Capturing (September 2016) Near-turbine Avian Behavior”. NINA Report 910, 2012 125 A. Drewitt; and R. Langston. “Assessing the Impacts of Wind Farms on Birds: impacts of Wind Farms on Birds”. Ibis 2006, 148, pp.29-42. 129 K. W. Smallwood and B. Karas (2009). “Avian and bat fatality rates at old generation and repowered wind turbines in California”. In Journal of Wild- 126 K. W. Smallwood and B. Karas (2009). “Avian and bat fatality rates at old generation and repowered wind turbines in California”. In Journal of life Management, Volume 73, pp. 1062-1071 Wildlife Management, Volume 73, pp. 1062-1071 130 E. B. Arnett; M. Schirmacher; M.M.P. Huso; J.P. Hayes. “Effectiveness of changing wind turbine cut-in speed to reduce bat fatalities at wind facilities”, A final report submitted to the Bats and Wind Energy Cooperative, Austin Texas, USA: Bat Conservation International;

54 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 55 be so easy to achieve such results. However, re- sensory cues (olfaction133, microwaves). In addi- reflectors will only be effective when they reflect flight behavior. Depending on the exact wave- stricting turbine operation could be implement- tion, habitat alterations either within or outside (sun) light and lose their efficacy between sunset length, luminance and exposure regime used this ed when particularly high risk factors overlap. For of the wind-power plant may affect the birds’ and sunrise, they were recommended in combi- activity will likely result in high levels of evasive example, wind turbine on migratory routes could behavior. Although great difference exist among nation with other methods of scaring. At day- responses. However, the implementation may be shut down on nights of poor weather condi- species, generally birds’ hearing is inferior to hu- time, when also most birds are active, they may be more challenging as such deterrence systems tions for nocturnal bird migration. mans while their visual acuity and temporal reso- create an ever-moving myriad of lights reflecting should be installed on all („problem“) turbines lution is higher. Consequently, most measures off the blades. Due to these changing reflections, and require trustworthy triggering of the deter- Temporary shutdown has been tested in periods are based on visual cues. the blades may become more visible and may ring stimulus. Using laser renders similar efficacy with high bird activity, or when birds moved too attract attention to them resulting in increased as for visual deterrence. The difference being that close to the turbines. Methods used to assess When turbine blades spin at high speeds, a mo- responsiveness in the birds. laser may be directed more accurately at an ap- when birds flew too close to turbines were either tion smear (or motion blur) effect occurs, making proaching bird (Clark, 2004)137. However, this through visual observations or avian radar. An wind turbines less conspicuous. This effect oc- Mitigation measures based on active visual cues accuracy may also be with its limitation as it as- effective use of this measure, however, depends curs both in the old small turbines that have high include minimal use of turbine lighting, adjust- sumes that it will be possible to pinpoint a flying on a good monitoring scheme to limit unneces- rotor speed and in the newer high turbines that ment of turbine lightning regimes, visual deter- bird. The visual nuisance of laser may however be sary shutdown and thereby loss of energy gen- despite having slower rotor speeds, achieve high rence or laser. Minimal use of turbine lightning less pronounced than for lights. Lasers also work eration. Especially when shutdown is restricted blade tip speeds. Motion smear effect happens has been proposed especially for bats and noc- best under low light levels. Something that has to specific events of near-collisions, the efficacy when an object is moving too fast for the brain turnal migrating birds. However, observations not been proposed is to utilise UV lasers that will likely improve as this will limit possible ha- to process the images and, as a consequence, the showed no difference in fatality rates between lit sweep upwards during night time encircling the bituation effects. Too large shutdown periods moving object appears blurred or even transpar- and unlit turbines (Johnson et al., 2003, 2004)135. rotor swept zone. UV lasers are invisible to the may cause birds to adjust to this new situation, ent to the observer. The effect is dependent on Even though nocturnal (migrating) birds may be human eye but may deter nocturnal birds from leading to reduced avoidance of the turbines. the velocity of the moving object and the dis- attracted to the (red) flashing or steady-burning entering the rotor swept zone. However, other studies indicated that birds may tance between the object and the observer. The safety lights (Hötker et al., 2006)136. Although primarily be affected by the actual turbine struc- retinal-image velocity of spinning blade increases the implementation costs - air safety implica- Deterrent devices that scare or frighten birds and tures (Smallwood, KS et al., 2007; Muñoz et al., as birds get closer to them, until it eventually sur- tions aside - should be limited, minimal use of make them move away from a specific area have 2011131). passes the physiological limit of the avian retina lighting may have limited impact for reducing been broadly used as tools for wildlife manage- to process temporally changing stimuli. collisions. Although nocturnal birds may be pre- ment. Auditory deterrents are considered the 4.5.2. BIRD-SPECIFIC MITIGATION OPTIONS vented being attracted to the turbine lights, they most effective, although their long-term use has As a consequence, the blades may appear trans- are also not alaerted their presence. been proven to be ineffective due to habituation Another option for mitigation of collisions is to parent and perhaps the rotor swept zone appears by birds to certain stimuli (Bishop et al, 2003; alert birds to the turbines or affecting bird behav- to be a safe place to fly (Hodos, 2003)134. The ex- Visual deterrence includes the use of strobing, Dooling, 2002)138. Biacoustic techniques are ior. Alerting birds to the turbine structure may situ experiments by Hodos indicated that paint- flashing, revolving lights causing a temporary thought to be the most effective because they encompass making the rotor blades more visible, ing one of the three blades black reduced motion blinding and thereby confusion effect. This mea- use the birds’ natural instinct to avoid danger. where reduction motions smear has been the smear most. Depending on whether decreased sure will be most effective at low lights levels, Preliminary data on the use of the acoustic deter- major incentive. Alternatively mitigation mea- visibility of rotor blade tips is the cause of col- and may therefore mainly help mitigate collisions rent LRAD (Long Range Acoustic Device) in wind sures have been proposed to dissuade birds from lisions, reducing motion smear may enhance the of nocturnal birds. Habituation may be reduced farms showed that 60% of Griffon vultures had coming too close to the turbines through sensory exposure potential. As for all measures based on through randomized selection of a least two strong reactions to the device, and its efficacy cues. The efficacy of such measures is dependent passive visual cues, UV-coating only works during strobe frequencies; however use of bright lights depended on the distance between the bird and on the birds’ perception and response to the sen- daytime. UV-coating on rotor blades to increase may cause visual nuisance for local residents. the device, the bird’s altitude and flock size. sory cues (i.e. stressors). It is therefore crucial to their visibility has been proposed and tested in Also, its efficacy will be enhanced greatly when take into account the sensory constraints placed the USA with unclear conclusions on its efficacy. the visual deterrents are emitted only in situa- Deterrents can also be activated by automated upon the species of focus (Green, 2012)132. Miti- Reflectors in the form of mirrors and aluminium/ tion when birds are in close vicinity of a turbine. real-time surveillance systems as an initial mitig- gation options include passive and active visual silvered objects – e.g holograms may also provide This requires a functional, e.g based on video or tion step and prior to blade curtailment (May et cues (e.g painting or lightning), audible deter- to be an effective way of scaring birds. However, avian radar, system to continuously monitor bird al., 2012; Smith et al, 2011)139. Systems such as rence/harassment, and to a lesser extent other

135 G. D. Johnson; M. K. Perlik; W.P. Erickson; and M. D. Strickland (2004). “Bat activity, composition, and collision mortality at a large wind plant in Minnesota”. In Wildlife Society Bulletin, 32 (4), pp. 332-342 131 A. Muñoz; M. Ferrer; M. de Lucas; E. Casado. “Raptor mortality in wind farms of southern Spain: mitigation measures on a major migration bottleneck 136 area”. Proceedings of the conference on wind energy and wildlife impacts, 2-5 May 2011, Trondheim, Norway: Norwegian Institute for Nature Research H. Hötker; K. Thomsen; H. Jeromin. “Impacts on biodiversity of exploitation of renewable energy sources: the example of birds and bats – facts, gaps in knowledge, demands for further research, and ornithological guidelines for the development of renewable energy exploitation”, p. 65, Berghausen, 132 M. Green. “Through birds’ eye: insights into avian sensory ecology”, Journal of Ornithology, 153, 2012; pp.23-48 Germany: Michael-Otto-Institut in NABU: 2006. 133 Olfaction, the sense of odor, is the detection of chemicals dissolved in air (or in water, by animals that live under water). 137 T. L. Clark. “An autonomous bird deterrent system. [Dissertation]. University of Southern Queensland; 2004. 134 W. Hodos (2003). “Minimization of Motion Smear: reducing Avian Collisions with Wind Turbines”. University of Maryland/National Renewable Energy 138 R. Dooling. “Avian hearing and the Avoidance of Wind Turbines”, National Renewable Energy Laboratory, Colorado, USA Laboratory NREL/SR-500-33249, Colorado, USA 139 R. May; O. Hamre; R. Vang; T. Nygard. “Evaluation of the DTBird Video-system at the Smøla Wind-Power Plant. Detection Capabilities for Capturing Near-turbine Avian Behavior”. NINA Report 910, 2012

56 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 57 DTBird®or Merlin ARS™incorporate this option source; 2) background noise levels; 3) the terrain vealed a pattern of stress symptoms due to wind bine type, going for blade add-on elements to in their possible configurations. Although the re- between the emitter and receptor; and 4) the na- turbine noise including sleep disturbance, irrita- reduce aerodynamic noise or applying noise cur- sults are preliminary, this type of methodology ture of the noise receptor. The effects of noise bility, negative mood and a lack of concentra- tailment modes. However, these strategies often may have an unpredictable effect on the flight on people can be classified into three general cat- tion (e.g. Bakker et al., 2012, Hübner and Löffler, impact the project cost, and pretty much of all of path of a bird, so caution is needed, if it is ap- egories (National Wind Coordinating Committee, 2013; Pohl et al., 2018)146. them would impact expected revenues, making it plied at a short distance from a wind turbine or 1998)143: all the more important to apply them carefully within a wind farm. Nevertherless, it may be used To understand what influences the perceived and correctly. as a potential measure to divert birds from flying 1) Subjective effects including annoyance, nui- annoyance and stress reactions due to wind tur- straight at a wind turbine. sance, dissatisfaction bine noise, several moderators must be consid- 5.1. WIND TURBINE NOISE SOURCES 2) Interference with activities such as speech, ered: the visibility of wind turbine by residences CHAPTER 5 - WIND TURBINE NOISE sleep, and learning seems to increase annoyance. These decrease, It is well established that the dominant noise Wind energy development is inevitably related however, when residents have a financial inter- mechanisms for modern, industrial scale wind 3) Physiological effects such as anxiety, or hear- to certain negative environmental impact, since est in the wind farm project (e.g Health Canada, turbines are aeroacoustic. Mechanical noise ing loss. 147 when operating, wind turbines generate acous- 2014) . Annoyance induced by the planning and sources in modern designs can be reduced to a tic noise that can be defined as any unwanted construction of wind farms appears related to point where their contribution to total noise lev- In almost all cases, the sound levels associated sound. Distinguishing noise from sound is to a wind turbine noise annoyance as well as reported els is nominally negligible relative to aeroacous- with wind turbines produce effects only in the large extent subjective but generally sound from stress symptoms. Several studies also indicate tic noise sources. Aeroacoustic noise is produced first two categories. Workers in industrial plants, wind turbines is considered as unwanted and that residents with negative attitudes towards by several mechanisms, each ultimately caused and those who work around aircraft can experi- therefore it is referred to as noise in this chapter. wind energy or their local wind farm are more by various forms of unsteady aerodynamic flow ence noise effects in the third category. likely to experience wind turbine noise annoy- about the blades (Wagner et al., 1996)150. Some Wind turbine noise emissions are generated by ance and vice versa (e.g Pawlaczyk-Luszczynska of these mechanisms are not relevant for modern World Health Organization (WHO) recommends 148149 blades, as the blade tip passes through the air et al., 2014; Pohl et al., 2012, 2018) . Re- industrial-scale turbines. Blade tip-vortex inter- when estimating wind turbine environmental im- at rather high speed (250 km/h). A lot of focus markably, the distance of residences from wind action noise is minimized by the design of blade pact to evaluate the noise impact as low, aver- has been given to the issue over the years and turbine has been inconsistently correlated to tip geometry. age and high frequencies. Low frequency sounds this noise has been reduced by clever design and wind turbine noise annoyance and stress impact and infrasound, excite individual human body blade add-ons140. When stricter noise limits are (increased annoyance with decreased distance). Aeroacoustic noise (i.e. the noise of turbine parts and worsen general human well-being144. enforced to legacy wind turbines already de- blades passing through the air) is a limiting factor It is known that the noise of 32 dB (A) for some ployed, actions need to be taken. One solution is The present chapter focuses on noise prob- on performance of wind turbines. Aerodynamic people is a strong irritant for their nervous sys- retrofitting wind turbine blades with additional lems as they are the most frequently discussed i.e. flow-induced noise from the rotor is generally tem, whereas the noise of 40 dB (A) and higher outer layer skins that change their aeroacous- stress impact on residents. A number of mitiga- considered to be the most dominant noise source for most people evokes strong discomfort (Tay- tic footprint. Although the technology has ad- tion strategies are available for wind farm proj- for a modern large wind turbine, provided that lor et al., 2016)145. vanced, wind turbines have got much quieter, but ect developers to reduce this effect, and in any mechanical noise is adequately treated. There are noise from wind turbines is still a public concern. case to comply with applicable noise regulations. three main aerodynamic noise sources for wind It is one of the major hindrances in the develop- The process of developing stress begins with the Noise is generally regulated in national legisla- turbines, turbulence inflow noise, trailing-edge ment of wind industry141142. perception of possible stressors (e.g. wind tur- tion which restrains potential locations when noise and separation noise. Blade tip noise can bine noise as an ambient stressor), followed by planning for wind power. The mitigation strate- also be a problem, but for modern wind turbines Noise levels can be measured, but similar to the evaluation of those stressors (e.g., they are gies range from keeping a certain distance from tip noise is not contributing to the overall noise other environmental concerns, the public’s per- annoying), then psychological and physical reac- dwellings, carefully selecting the adequate tur- as it can be controlled by tip shape design. ception of the noise impact of wind turbines is tions to it. However, to date, the predominant in part a subjective determination. The concerns wind turbine impact indicator relied upon has been annoyance, while symptoms of wind tur- 144 It describes sound waves with a frequency below the lower limit of audibility (generally 20 Hz). Hearing becomes less sensitive as frequency de- about noise depend on 1) the level of intensity, creases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. frequency distribution and patterns of the noise bine noise have been studied. These studies re- 145 J. Taylor; C. Eastwick; C. Lawrence; R. Wilson. “Noise levels and noise perception from small and micro wind turbines”. In Renewable Energy, volume 55, July 2013, pp. 120-127 140 Blade add-ons are used to improve blade performance, they increase power input and reduce noise. 146 G. Hübner., J. Pohl; B. Hoen; J. Firestone; J. Rand (2019). “Monitoring annoyance and stress effects of wind turbines on nearby residents: A compari- 141 M. Dröes; H. Koster. „Renewable Energy and Negative Externalities: The Effect of Wind Turbines on House Prices“. In Journal of Urban Economics, son of U.S and European samples”, Environment International 132 (2019) 105090 vol. 96, pp 121-141 (2016), www.doi.org/10.1016/j.jue.2016.09.001 147 Health Canada (2014). “Summary of Health Canada study on wind turbine noise and health impacts” 142 J. L. Davy; K. Burgenmeister; D. Hillman. “Wind turbine sound limits: Current status and recommendations based on mitigating noise annoyance”. 148 M. Pawlaczyk-Luszczynska; K. Zaborowski; A. Dudarewicz; M. Zamojska-Daniszewska; M. Waskowska. “Response to Noise Emitted by Wind Farms In Applied Acoustics, vol. 140, pp. 288-295 (2018); www.doi.org/10.1016/j.apacoust.2018.06.009; in People Living in Nearby Areas”. In International Journal of Environmental Research and Public Health, vol. 15, no. 8 (2018), www.doi.org/10.3390/ 143 National Wind Coordinating Committee. “Permitting of Wind Energy Facilities: A Handbook, “RESOLVE”. NWCC, Washington D.C, USA, 1998 ijerph15081575 149 144 It describes sound waves with a frequency below the lower limit of audibility (generally 20 Hz). Hearing becomes less sensitive as frequency M. Pawlaczyk-Luszczynska, M; Dudarewicz, A; Zaborowski K; Zamojska-Daniszewska, M. “Annoyance Related to Wind Turbine Noise”. In Acoustics, decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. Volume 39, No 1, pp. 89-102 (2014) 150 145 J. Taylor; C. Eastwick; C. Lawrence; R. Wilson. “Noise levels and noise perception from small and micro wind turbines”. In Renewable Energy, S. Wagner; R. Bareib; and G. Guidati (1996). “Wind Turbine Noise”. Springer, Berlin, Germany volume 55, July 2013, pp. 120-127

58 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 59 Figure 23. The main elements of a wind turbine blade ongoing for the past three decades. There are must be increased, or in some cases, outright re- Mainly associated with the interaction of turbu- two primary classes of noise sources on a wind fusal of installation, due to the negative impact lence with the blade surface, aerodynamic noise turbine. These include mechanical noise due to of this noise to humans. There are two ways in can be divided into three main types: low fre- vibrations in the drive train and gear noise, and which mechanical noise is transmitted: airborne quency noise, turbulent inflow noise and airfoil aeroacoustic noise due to unsteady aerodynamic or structural. Airborne noise is straightforward, as self-noise. Low frequency noise occurs due to the processes on the rotor. Mechanical noise, while it the sound is directly emitted to the surroundings. passage of the blades through the tower’s wake. can potentially be a large contributor to overall Structural noise is more complex as it can be trans- In turn, turbulent inflow noise is generated due wind turbine noise, is usually relatively straight- mitted along the structure of the turbine and then to the interaction of turbulence of the incoming forward to reduce using techniques to dampen or into the surroundings through different surfaces, flow with the turbines blades. Airfoil noise is the isolate mechanical vibrations in the nacelle, or by such as the casing, the nacelle cover, and the rotor total noise produced when an airfoil encounters employing sound absorbing material (Wagner et blades. The drive gearbox is a significant source of smooth non-turbulent inflow and the noise is al, 1996)153. noise in wind turbines. The mechanical noise is of produced as this turbulence passes over the trail- less importance in modern wind turbines because ing edge. It is further divided into various noise 5.1.1. MECHANICAL NOISE of improved sound insulation of the hub (van den mechanisms; the two most relevant mechanisms Berg, 2005, Oerlemans et al., 2007)154. are turbulent boundary layer-trailing edge noise Mechanical noise is generated from components Source: Sørensen et al., 2004 (or, “trailing edge noise”), and blade tip vortex. within the wind turbine, such as the generator, 5.1.2. AERODYNAMIC NOISE At the tip of the blade the air flows from three the hydraulic systems and the gearbox. Other Turbulent inflow noise is reported as an impor- different directions causing a tip vortex which elements such as fans, inlets/outlets and ducts The most remarkable noise source of wind pow- tant aeroacoustic wind turbine broadband noise generates sound, especially when the vortex is also contribute to mechanical noise. The type er plants is their rotor blades that cause mainly source, coexistent with the airfoil self-noise interacting with the trailing edge. of noise produced by these mechanical compo- aerodynamic noise. The broadband aerodynamic sources (e.g., airfoil trailing edge noise and the nents tends to be more tonal and narrowband in sound of rotor blades is composed of four ma- low-frequency noise). Trailing edge noise is pro- Turbulent boundary layer – trailing edge noise is nature, which is more irritating for humans than jor components caused by flow turbulence: the duced by the scattering of convected turbulent considered to be one of the major contributors broadband sound. There are four types of noise trailing edge sound (turbulence boundary layer sources by a sharp edge. The Aero/Hydro-acous- to airfoil self-noise. It is the main source of high that can be generated by wind turbine operation: – trailing edge interaction), blunt trailing edge tics Laboratory in the USA has studied conven- frequency noise, especially for medium and large tonal, broadband, low frequency, and impulsive. sound, the tip vortex sound and the inflow tur- tional methods of treating trailing edge noise wind turbines (Oerlemans et al., 2007)157. For Tonal noise is defined as noise at discrete fre- bulent sound. The trailing edge sound among focused on modifications to the trailing edge installed fans, trailing edge noise corresponds quencies. Low-frequency noise with frequencies them seems to be the most remarkable (van den geometry (e.g. serrations). Most recently, they to the minimum achievable noise level. Rotors in the range of 20 to 100 Hz is mostly associated Berg, 2006)155. The angle of attack plays an im- have developed a novel method of reducing trail- and propellers are subject to other noise sources. with downwind turbines (turbines with the ro- portant role in the action of a wind turbine and ing edge noise by treating the boundary layer in- Some of these are broadband, for example lead- tor on the downwind side of the tower). Impul- in broadband wind turbine noise generation. It stead151. ing edge noise due to upstream turbulence, tip sive noise is a category of acoustic noise that is an important parameter in most three-dimen- vortex-induced noise and stall noise158. Others includes unwanted, almost instantaneous (thus sional aerodynamic models of rotating wind tur- In order to reduce noise, most wind turbine de- are tonal, as in the case of steady loading in the impulse-like) sharp sounds, typically caused by bines (Maeda &Schepers, 2011)156. However, the signs limit their rotational speed because of noise reference frame of the rotor, periodic unsteady electromagnetic interference. High levels of such definition of the angle of attack is based on the constraints, which reduces aerodynamic efficien- loading produced by stationary distortions in the a noise (200+ decibels) may damage internal or- wind tunnel environment as the angle between cy. With quieter gearbox and generator designs, flow. gans, while 180 decibels are enough to damage the chord line and the wind velocity vector, aeroacoustic noise is now considered the domi- human ears. which has the same direction as the uniform flow nant noise source for wind turbine operation. In any airfoil subject to a flow, a boundary layer among the wind tunnel walls. When the angle of This type of noise is more difficult to mitigate, develops on its surface, starting from the stagna- While the total wind turbine sound pressure level attack increases from its optimal value, the tur- and it is the dominant noise source on modern tion point close to the leading edge. As certain only incurs a minor increase due to this noise, bulent boundary layer on the low pressure side of wind turbines (Oerlemans et al, 2007)152. angle of attack and Reynolds number conditions the penalty it places on wind turbines and the the blade grows in thickness, decreasing power are met, the boundary layer transitions from nearest buildings is much greater. Many coun- performance and increasing sound level. Operating conditions and maintenance of the laminar to turbulent at a certain chordwise po- tries have regulations which stipulate distances wind turbine also affect noise production. Ef- between wind turbines and the nearest buildings 154 forts to quantify wind turbine noise have been G. Van den Berg. “Criteria for a wind farm noise: Lmax and Lden”, In The Journal of the Acoustical Society of America, June 2008 155 G. Van den Berg (2006). “The Sounds of High Winds, the Effect of Atmospheric Stability on Wind Turbine Sound and Microphone Noise”. Gronin- gen: University of Groningen. 151 This research is inspired by the silent flight of certain species of owls that have a fine downy coating on their feathers that is used to attenuate the 156 T. Maeda; G. Schepers. “Wind turbine performance assessment and knowledge management for aerodynamic behavior modelling and design: IEA strength and reduce the spanwise correlation of turbulence in the wind boundary layer. experience”. In Wind Energy Systems, 2011 152 Oerlemans, S., Sijtsma, P., Mendez-Lopez, B. “Location and quantification of noise sources on a wind turbine”, In Journal of Sound and Vibration, 157 S. Oerlemans; P.Sijitsma; B. Mendez-Lopez (2007). “Location and quantification of noise sources on a wind turbine”. Report, National Aerospace 299, pp. 869-883, 2007 Laboratory, Amsterdam, the Netherlands 153 S. Wagner; R. Bareib; and G. Guidati (1996). “Wind Turbine Noise”. Springer, Berlin, Germany 158 This is noise due to a non-zero angle of attack of the wind turbine blade creating a boundary layer separation wake at the trailing edge. Very high angles of attack lead to large-scale separation (deep stall) at the trailing edge causing the airfoil to radiate low-frequency noise. At high angles the airfoil is acting similar to that of bluff body in the flow. 60 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 61 sition. At higher Reynolds numbers159 turbulent Highest broadband sound levels have been mea- higher wind speeds would provide more back- without affecting the power output. These strat- boundary layers develop over much of the airfoil sured in the upwind and downwind directions, and ground sound which in turn would mask the egies have been inspired from the owl’s feathers and the noise occurs at the turbulent eddies pass lowest ones in the crosswind directions. Accord- increasing wind turbine noise level. It has been and consist in the modification of the airfoil at over the trailing edge. Beneath this boundary ing to Hubbard et al (1991)164, levels measured shown, especially for modern, tall turbines – that the trailing edge. Strategies for reducing mechan- layer, the turbulence induces a fluctuating pres- at night time are generally lower, particularly this assumption is incorrect when the atmo- ical and aerodynamic noise will be discussed in sure field. Turbulent boundary layer trailing edge in the crosswind directions, and the lower night sphere is stable, which is a common situation in this section. noise is perceived as a swishing sound i.e. broad- time levels are believed to be associated with the temperate climate zone after sundown. The band. Its peak frequency is typically in the order less intense inflow turbulence. According to van reason for this is that a stable atmosphere the 5.2.1. MECHANICAL NOISE REDUCTION of 500 – 1500 Hz (Wagner et al., 1996)160. den Berg, the above is only valid for small wind wind at higher altitude is decoupled from the One source of mechanical noise is vibration in- turbines, tall wind turbines produce on average near-ground wind. Then, high hub height wind duced by rotating components. Vibration control The turbulent flows coming from different sides more sound in night time than in day time. This speeds can occur with simultaneous low near- is used to suppress or eliminate unwanted vibra- of the blade strike at the trailing edge generat- is due to the atmospheric conditions presented ground wind speeds and thus high turbine sound tions. Depending on the case, different laws can ing a turbulent flow wake (Di Napoli, 2007)161. above. In near field most of the noise is produced levels occur at low background sound levels. In be chosen in order to minimize unwanted vibra- The turbulence in the boundary layer generates when the blades are moving downwards. fact, tall wind turbines in relatively flat land can tion. Additionally, dampening or increasing the sound, particularly when it interacts with the produce (near) maximum sound power at any effective mass can be realized by the controller trailing edge. The increase in the turbulence over Besides, aerodynamic pulsations are developed near-ground wind speed except the very lowest. (Kelly, 2000)166. Inferentially, the absorber works the blade is the higher the larger the change in the due to rotating interaction of blades with con- As a result the masking potential of background as an active system. This includes the use of blade profile is. The turbulence can be increased struction elements of wind turbine tower. Noise sound is not very different from what it is for oth- sound isolating materials, insulation, and closing by the geometry of the trailing edge (blunt), the may be broadband and tonal whereas broadband er industrial sources. In complex terrain the situ- the holes in the nacelles which would decrease roughness (dirtiness, icing) of the blade surface, noise is characterized by a continuous distribu- ation is more complicated, though it may lead to the sound transmitted to the air. Aside from loss and turbulence and the flow speed of the oncom- tion of sound pressure with frequencies greater the same conclusion. of power and increased maintenance costs, faulty ing flow. In modern blade profiles the area of the than 100 Hz. It is often caused by the interaction gearboxes also increase noise levels in wind tur- blade narrows towards the blade tip in which of wind turbine blades with atmospheric tur- 5.2. WIND TURBINE NOISE REDUCTION bines. As a result, researchers are developing case most of the noise is not generated at the bulence, and also described as a characteristic TECHNOLOGIES fault diagnostic systems for gearboxes with ap- tip but in region situating in the blade 0.75 – 0.95 “swishing” or “whoosing” sound. Besides aero- Acoustic emissions of wind farms have a nega- plications to wind turbines. A system has been from the base of the blade. The source region dynamic and mechanical noise, there always ex- tive impact on social acceptance of wind energy developed to integrate singular value decompo- moves outwards with increasing frequency and ists the environmental background noise, which and can be a barrier for the future spread of this sition noise reduction, time-frequency analysis it is larger with rough blades. The roughness of is conditioned by wind flows of the plants, re- source of renewable energy. To comply with lo- and order analysis methods in order to identify the blade surface raises the radiated sound level lief incongruities and other obstacles, transport cal regulations governing community noise, wind weak faults objectively and effectively (Wang especially at low frequencies. The bluntness of means, birds, industry objects, etc. The back- turbines are often designed to curtail their opera- et al., 2011)167. More recently, efforts have been the trailing edge causes a clear maximum (nar- ground environment noise intensifies during the tion, degrading efficiency, reducing energy cap- taken to develop intelligent techniques for online row band) in the sound spectrum (Oerlemans & day, whereas at night, it sometimes diminishes ture, and effectively increasing the cost of wind condition monitoring in machinery systems such Lopez, 2005)162. due to lower side effect impact (evoked by trans- energy. Thus, development of high quality noise as wind turbines. port, factories, fauna, etc.) (Moeller &Pedersen, prediction tools and innovative noise reduction Turbulence can be defined as temporal and spa- 2011)165. technologies are key objectives for wind turbine 5.2.2. AERODYNAMIC NOISE REDUCTION tial changes in wind velocity and direction, re- manufacturers. sulting velocity components normal to the airfoil Noise limits for wind turbines are more usually There are a number of adaptive noise reduction causing in-flow turbulent sound. The maximum given for a range of wind speeds. The reason for approaches for aerodynamic noise, including Various experimental and numerical techniques of its spectrum is typically in the infrasound re- this is that wind turbines produce more sound at varying the speed of rotation of the blades. Since have been developed for noise mitigation by tak- gion (van den Berg, 2006)163. higher wind speeds and it was thought that the the increase in rotational speed will also lead to ing advantage of our understanding of the noise increased noise production, lowering the rota- mechanisms which provide the insight into the 159 tional speed will lead to decreased sound. How- The Reynolds number is a commonly used non-dimensional parameter in fluid mechanics, which describes the inertial forces to viscous forces. With aero-acoustic characteristics of wind turbines. increasing Reynolds number the boundary layer gets thinner, which results in a lower drag. Increasing the Reynolds number also has a destabilizing effect ever, the rotational speed decreases power out- Researchers are focused on reducing noise with- on the boundary layer flow, which results in the transition location moving towards the leading edge, leading to a turbulent boundary layer over a longer put, and therefore should only be implemented part of the airfoil surface. out affecting the power generated by the wind 160 within a certain range of wind velocities, since S. Wagner; R. Bareib; and G. Guidati (1996). “Wind Turbine Noise”. Springer, Berlin, Germany turbine. Lately companies have started looking 161 C. Di Napoli. “Tuulivoimaloiden melon syntytavat ja leviärninen”. Helsinki: Ympäristöministeriö, Suomen ympäristö 4, 2007 high winds also have the added benefit of mask- for different strategies in order to suppress noise 162 S. Oerlemans and B. Lopez. “Localization and quantification of noise sources on a wind turbine”. First International Meeting on Wind Turbine Noise, ing the sound of the wind turbine with the sound proceedings. Berlin, 2005 163 G. Van den Berg. “The Sounds of High Winds, the Effect of Atmospheric Stability on Wind Turbine Sound and Microphone Noise”. Groningen: Univer- sity of Groningen, 2006 166 S. Kelly. “Fundamentals of Mechanical Vibrations”, Second Edition, McGraw Hill, 2000 164 H. Hubbard & K. Shepherd. “Aeroacoustics of large wind turbines”. In Journal of Acoustic Society of America, 1991, Volume 89, No 6, pp. 2495-2508 167 F. Wang; L. Zhang; B. Zhang; Y. Zhang; L. He. “Development of wind turbine gearbox data analysis and fault diagnosis system”, Power and Energy 165 H. Moeller; C. Pedersen (2010). “Low frequency noise from large wind turbines”. In Journal of the Acoustics Society of America, Volume 129, Issue 3727 Conference (APPEEC), 2011, Asia-Pacific

62 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 63 of the wind itself. The pitch angle of the wind tur- Turbulent boundary layer - trailing edge noise is To overcome this problem of flow alignment with turbines, many passive noise modification solu- bine blades also have an important role in noise one of the dominant sources of airfoil self-noise serrations, the concept of trailing edge brushes tions, based on the modification of the trailing- production. An increase in pitch angle will lead to emitted by well-designed modern wind turbines. was introduced. Experimental investigations edge geometry with attachable add-ons, have a reduction in the angle of attack. As the angle of This source of noise limits both the installation of by Herr (2007)173 and Finez et al (2010)174 prove been proposed (Arce-Leon et al, 2016)177. Among attack increases, the size of the turbulent bound- new wind turbines and the operational regimes the advantage of trailing edge brushes over ser- others, sawtooth add-ons are widely used for ary layer on the suction side of the airfoil grows, of existing ones, thus reducing the power pro- rations in reducing airfoil noise. Porous trailing their simplicity of manufacturing and installa- thereby increasing noise production in the wind duction and increasing the overall cost of energy. edge works similar to trailing edge brushes for tion. More recently, Oerlemans (2016)178 pro- turbine. Therefore, if the pitch angle is reduced, Wind turbines, depending on their manufacturer, reducing sudden change in acoustic impedance posed a variation of the conventional sawtooth a thinner boundary layer results on the suction may come equipped with low-noise operational encountered at the abrupt edge by near blade geometry, named as combed-sawtooth serration, side, which is considered the strongest source modes, which basically is an application of this flow. Trailing edge brushes and porous trailing with solid filaments filling the empty spaces be- of noise production (Brooks et al., 1989)168. This method. The trade-off is a loss in energy produc- edges are potential technologies which can help tween the teeth. This design showed additional 2 also implies that, on the pressure side, the effect tion by a less efficient capturing of the wind’s gain extra trailing edge noise reduction. Studies dB noise reduction during in-field measurements is the opposite; therefore when using this meth- energy. Depending on the economic viability of by Geyer et al (2009)175 and Kinzie et al (2013)176 for the frequency range of practical interest. od for noise control, it is important to find the using these settings, which might be better than, show potential in this technology for noise re- appropriate pitch angle range for optimal noise for example, shutting down a wind farm during duction, however, conclusive full scale experi- The prediction of the scattered noise in the pres- control. As with the previous method, the major the night because of stricter noise regulations mental studies are required. ence of sawtooth serrations is not straightfor- drawback to this adaptive noise control method (common in countries like Germany), they may ward because of the complex three-dimensional is the corresponding reduction of power since the prove useful without becoming a loss to the op- Most of the noise with trailing edge as the source flow generated by the spanwise varying geom- angle of attack is decreased. Despite the loss in erator (Arce Leon, 2012)171. is generated from outbound portions of the blade etry (Arce-Leon et al., 2016179; Avallone & Ragni power, the main advantage if wind turbines with where the flow velocity is higher. Methods like 2016180). Several analytical and semi-analytical optimized operating conditions is that the acous- Noise reduction is an important development di- serrated trailing edges for trailing edge noise models were developed to obtain reliable pre- tically affected areas are much smaller, allow- rection for aircrafts and wind turbines. Owl wings reduction are already being used in some wind diction for different trailing-edge shapes. While ing more wind turbines to be built in a specified have three unique morphological characteristics turbines but more effective methods for noise predictions based upon analytical models require area, e.g., a wind farm (Romeo-Sanz & Matesanz, (leading edge serrations, trailing edge serrations control are needed. Lot of work has been done only details of the geometry, semi-analytical 2008)169. and velvet-like surfaces) that effectively suppress in identifying and mitigating inflow turbulence ones need additional information on the bound- aerodynamic noise in low Reynolds numbers. noise. Bio-mimicry has yielded leading edge ser- ary-layer characteristics and on the spatial and The main drawback to adaptive methods (an Among them, trailing-edge serrations are widely rations and slits for reduction of noise from this temporal distribution of the surface pressure overall reduction of power) is a hindrance to that considered the most effective noise-reduction source. Leading edge slits have been shown to fluctuations. method of noise control. By breaking down the method. Trailing edge serrations provide a way outperform serrations and provide very signifi- noise sources it can be seen that the maximum to reduce the angle between eddy path and edge cant noise reduction. Tip noise reduction can be Selection of an appropriate airfoil for perfor- noise contribution occurs within the trailing below 90 degrees, thus decreasing the scatter- achieved by optimizing tip shape for reduced vor- mance is key to energy production of a wind tur- edge. The region between about 75-95% span is ing of sound. Experimental observations on full tex strength and less interaction of vortex with bine. An airfoil is a structure designed to obtain exposed to the maximum flow velocities and it scale wind turbine of 94 meter diameter with tip edges. Computational aero-acoustics can reaction upon its surface from the air through has the highest aero-acoustic noise levels (Oer- serrations have reported reductions of 3.2 dB help in faster optimization blade shape to reduce which it moves or that pass such a structure. lemans et al., 2001)170. Furthermore experimen- (Oerlemans et al., 2009)172. However, since the noise by introducing less computationally expen- Van Treuren and Hays (2017)181 studied the four tal tests showed that most of the noise is gen- serrations cannot always be aligned to the flow sive numerical techniques. Most of these tech- wind turbine airfoils for their aerodynamics and erated when the blade is moving downwards in direction due to variable incoming flow velocity, nologies require further experimental validation. noise generation. Airfoils can be made quieter by a clockwise rotation. Therefore, the majority of they lead to increased sound level at higher fre- designing them in such a way that the boundary modification procedures are aimed at reducing quencies. With the goal of reducing turbulent boundary layer flow results in less noise compared to air- the noise in this area. layer- trailing edge noise of already existing wind foils that perform aerodynamically similar. Nev-

173 M. Herr. “Design criteria for low-noise trailing edges”. 13th AIAA/CEAS Aeroacoustics Conference, 2007 174 168 T. Brooks; D. Pope; M. Marcolini. “Airfoil Self-noise and Prediction”, NASA Reference Publication 1218, National Aeronautics and Space Administra- A. Finez; M. Jacob; E. Jondeau; and M. Roger. “Broadband noise reduction with trailing edge brushes. 16th AIAA/CEAS Aeroacoustics Conference, 2010 tion, 1989, USA 175 T. Geyer; E. Sarradj; and C. Fritzsche. “Measurement of the noise generation at the trailing edge of porous airfoils”. In Experiments in Fluid, 2009; 48 169 I. Romeo-Sanz; A. Matesanz. “Noise management on modern wind turbines”. In Wind Engineering, 2008, 32, pp. 27-44. (2), pp. 291-308 176 170 Oerlemans, S.; Schepers, J.; Guidati, G.; Wagner, S. “Experimental demonstration of wind turbine noise reduction through optimized airfoil shape K. Kinzie; R. Drobietz; B. Petitjean and S. Honhoff (2013). “Concepts for wind turbine sound mitigation”. AWEA Wind Power and trailing edge serrations”. Proceedings of the European Wind Energy Conference and Exhibition, 2001, , Denmark 177 C. Arce Leon; R. Merino-Martinez; D. Ragni; F. Avallone; M. Snellen. “Boundary layer characterization and acoustic measurements of flow-aligned 171 C. Arce Leon. (2012). “Study on the near-surface flow and acoustic emissions of trailing edge serrations (for the purpose of noise reduction of wind trailing edge serrations”. In Exp Fluids (2016), volume 57, Issue 182 turbine blades)”, Delft Technical University, the Netherlands 178 S. Oerlemans. “Reduction of Wind Turbine Noise using Blade Trailing Edge Devices”. 22nd AIAA/CEAS Aeroacoustics Conference, 30 May – 01 June, 172 S. Oerlemans; M. Fischer; T. Maeder and K. Kögler. „Reduction of wind turbine noise using optimized airfoils and trailing-edge serrations”. In AIAA 2016, Lyon, France 179 Journal 2009; 47 (6), pp. 1470-1481 F. Avallone F; van der Velden; D. Ragni. “Benefits of curved serrations on broadband trailing –edge noise reduction”. In Journal of Sound and Vibration, Volume 400, 21 July 2017, pp. 167-177 180 Ibid, 2017 181 K. Van Treuren. (2018). “Wind Turbine Noise: Regulations, Siting and Noise Reduction Technologies”. Proceedings of Montreal 2018 Global Power and Propulsion Forum 7th- 9th May, 2018, Canada 64 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 65 ertheless, the similarity of airfoils (for the pur- source was turbulent boundary layer-trailing done regarding noise from VAWTs include (Iida end up at the point of consumption. If storage ca- pose of stating that one in low-noise compared edge noise from the outer 25% of the blade. et al., 2004)187 and (Dumitrescu et al., 2010)188 pacity is located at a few large-scale facilities, en- to another) is a broad and open question that is The outcome of the SIROCCO project shows where numerical methods are used to simulate ergy must be delivered there first, which comes purpose driven. very encouraging results on noise reduction with aerodynamic noise from VAWTs and which for at a cost because the power grid is not 100% ef- serrated trailing-edge blades. Roughly 3.2 dB both studies indicates lower noise levels com- ficient. Then that energy must be delivered again By looking at a typical airfoil profile, such as the overall sound power level reduction is observed pared to HAWTs. This is further supported by to the point of consumption. On the other hand, cross section of a wing, several obvious charac- compared to the noise of baseline blades (Kama- results of (Dessoky et al., 2019)189, (Ghasemian with distributed storage it is only necessary to teristics of design can be seen. The major objec- ruzzamann et al., 2017)182. et al., 2015)190 and Möllerström et al., 2014)191. deliver energy once. Distributed energy storage tive in wind turbine airfoil design is to achieve In combination with a wind farm system pro- is currently dominated by hydroelectric dams, a high aerodynamic performance that ensures Alternatively, a slower rotating rotor could be posed by (Dabiri et al., 2011)192 or (Hazavet et al., both conventional as well as pumped. Grid en- wind turbine blade to operate with high-power manufactured that would capture the same 2018)193 VAWT may be used at least similar pow- ergy storage is a collection of methods used for performance. When it comes to societal accep- amount of energy from the wind, but this must er density as HAWT with less acoustic and visual energy storage on a large scale within an electri- tance, the noise aspect becomes very impor- be done at the design stage of the blades and annoyances. Further (Hui et al., 2018)194 find that cal power grid. tant in particular onshore turbines, such that turbine. With slower rotating blades, to capture the public acceptance of VAWT is mostly higher low-noise wind turbine design is an important the same amount of energy, the torque that than for HAWT. Energy storage systems provide a wide array of competitive parameter. Therefore, the over- they produce must be increased. The trade-off is technological approaches to managing power all objective behind the design work is to make therefore found in having to increase the safety CHAPTER 6 – ENERGY STORAGE supply in order to create a more resilient energy wind energy production more efficient, while at limits of the entire system, including blades, tow- TECHNOLOGIES AND WIND POWER infrastructure and bring cost savings to utilities the same time lowering noise emissions through er and, very critically, the drivetrain. This results and consumers. There are diverse approaches One of the distinctive characteristics of the elec- gaining fundamental insight into the airfoil noise in a very steep hike in the cost of the turbine, of- currently being deployed worldwide, in broad tricity power sector is that the amount of elec- generation mechanism. ten making it prohibitively expensive for the ex- they can be divided into five main categories as tricity that can be generated is relatively fixed pected return and benefit of having lower noise seen in Figure 24: over short periods of time, although demand for The use of serrated trailing edges for wind turbine emissions. electricity fluctuates throughout the day. Devel- noise reduction has now become a mature tech- • Batteries – a range of electrochemical storage oping technology to store electrical energy so nology, academic-research institutions and wind Extensive research has been presented regarding solutions, including advanced chemistry bat- it can be available to meet demand whenever turbine manufacturers demonstrating its effec- noise from wind turbines. For example, interest- teries, flow batteries, and capacitators; needed would represent a major breakthrough in tiveness in wind tunnel and turbine tests leading ing work can be found in (Bolin, 2009)183 where electricity distribution. In theory, energy storage • Thermal – capturing heat and cold to create to commercial products. Researchers from the noise, sound masking and propagation modelling is a viable solution: it can absorb peaks in out- energy on demand or offset energy needs; National Aerospace Laboratory (NLR), Energy has been studied, in (Pedersen, 2007)184 where put from variable sources, such as wind and so- Research Center of the Netherlands (ECN) and the human response to wind turbine noise has • Mechanical storage – other innovative tech- lar power, and provide energy for when there are Institute of Aerodynamics and Gas Dynamics been investigated and in (Baath, 2013)185 where nologies to harness kinetic or gravitational en- peaks in demand. In practice, however, energy (IAG) at University of Stuttgart tried to reduce a substantial investigation of wind turbine noise ergy to store electricity storage is held back by high costs of implemen- turbulent boundary layer – trailing edge noise by in forestry areas is performed. However, most tation. Also, many proposed energy storage solu- • Hydrogen – excess electricity generation can modifying the airfoil shape and/or implement- research has been aimed at the more common tions are still immature technologies. be converted into hydrogen via electrolysis ing serrated trailing edge, during the European HAWTs and little attention has been given to the and stored project SIROCCO. In this project, acoustic field alternative VAWTs which have shown potential Some technologies provide short-term energy measurements on a 94 m diameter, three-bladed for lower noise levels. VAWTs usually has lower • Pumped hydropower –creating large-scale storage, while others can endure for much longer. wind turbine has been conducted. One standard tip speed ratio than HAWTs and should therefore reservoirs of energy with water. Regardless of where energy is generated, it will blade, one blade with acoustically optimized air- produce less aerodynamic noise and furthermore

foil shape, and one standard blade with serrated the drive train of a VAWT can be placed at ground 187 A. Iida; A. Mizuno; K. Fukudome. “Numerical simulation of aerodynamic noise radiated from vertical axis wind turbines”. Proceedings of the 18th trailing-edge were fitted on a HAWT. Test results level which limits mechanical noise propagation International Congress on Acoustics; Kyoto, Japan, 2004 for the baseline blade showed that the dominant (Ericksson et al., 2008)186. Work that has been 188 H. Dumitrescu; V. Cardos; A. Dumitrache; F. Frunzulica. “Low frequency noise prediction of vertical axis wind turbines”. Proceedings of the Romanian Academy, 2010; 11 (1): 47-54 189 A. Dessoky; T. Lutz; G. Bangga; E. Kraemer. “Computational studies on Darrieus VAWT noise mechanisms employing s high order DDES Model”. In Renewable Energy, vol. 143, pp. 404-425 182 M. Kamaruzzaman; J. Hurault; K. Madsen. “Wind turbine Rotor Noise Prediction &Reduction for Low Noise Rotor Design”, 7th International Confer- 190 M. Ghasemian; A. Nejat. “Aeroacoustics prediction of a vertical axis wind turbine using large Eddy Simulation and acoustic analogy”. In Energy, vol. ence on Wind Turbine Noise, Rotterdam, 2 to 5th May, 2017 88, pp. 711-717 (2015) 183 K. Bolin. “Wind Turbine Noise and Natural Sounds: Masking, Propagation and Modeling”. PhD thesis: Royal Institute of Technology; 2009 191 E. Möllerström; S. Larsson; F. Ottermo; J. Hylander; L. Baath. “Noise Propagation from a Vertical Axis Wind Turbine”. Presented at the International 184 E. Pedersen. “Human response to wind turbine noise: Perception, annoyance and moderating factors”. PhD thesis: University of Gothenburg; 2007 Noise (2014) 185 L. Baath. “Noise spectra from wind turbines”. In Renewable Energy; 2013; volume 57, pp. 512-519 192 J. O. Dabiri. “Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays”. In 186 S. Ericksson; H. Bernhoff; M. Leijon. “Evaluation of different turbine concepts for wind power”. In Renewable and Sustainable Energy Reviews; 2008; Renewable Sustainable Energy 3, 043104 (2011); www.doi.org/10.1063/1.3608170 volume 12 (5); pp. 1419-34 193 S.H. Hezaveh; E.Bou-Zeld; J. O. Dabiri; M. Kinzel; G. Cortina; L. Martinelli. “Increasing the power production of Vertical-Axis Wind Turbine Farms using Synergistic Clustering”. In Boundary-Layer Meteorology, vol. 169, no 2, pp. 275-296 (2018) 194 I. Hui; B.E. Cain; J.O. Dabiri. “Public receptiveness of vertical axis wind turbines”. In Energy Policy, vol 112, pp. 258-271 (2018)

66 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 67 Figure 24: Types of energy storage technologies There is a rapid growth of stationary utility-scale ancillary services, flywheels do not seem to be Figure 25. Bear Swamp Pumped Storage in South Korea storage projects, mostly used as stand-alone in- suitable candidates for storing energy in large stallations. Wind power can be used in off-grid quantities and for a long time. On the other systems, also called stand-alone systems, not hand, though rarely used despite its low cost connected to an electric distribution system or and self-discharge rate, compressed air comple- grid. In these applications, small wind electric sys- ments pumped hydro (currently described as one tems can be used in combination with other com- of the most prevalent method of grid-scale en- ponents – including a small solar electric systems ergy storage (Bañares-Alcántara et al., 2015)198. – to create hybrid power systems. These include Indeed, apart from offering ancillary services re- batteries, flywheels, power-to-gas, thermal stor- quiring short-term electricity storage, both tech- age and compress air energy storage. Lithium-ion nologies can also serve for long-term large-scale batteries represent most of the electrochemical energy storage, as they can cater for periodic and storage projects. The recycling of such systems seasonal storage as well as emergency back-up. should be taken into consideration, as well as This is not surprising as, notwithstanding their their effective lifetime. In the EU, the segment of relatively low energy density, compressed air Source: Modified from Emerson (2020) operational electrochemical facilities is led by UK and pumped hydro can provide significant stor- and Germany (European Commission, 2020)195. age capacity (ibid, 2015). However, the downside Source: Modified from De Oude Bibliotheek Acad- However, the number of projects used in combi- is that neither of these storage technologies is hours, water is pumped from the lower reservoir emy (2017) nation with wind farms, the so-called co-located transportable. In this sense, even if they could to the upper reservoir. When required, the water wind and storage projects is increasing too. potentially solve the problem of decarbonizing flow is reversed and guided through turbines to on-land grids, pumped hydro and compressed air generate electricity. Pumped hydroelectric stor- The length of time the energy must be stored This chapter identifies the numerous different will not be able to deliver energy over distance. age (PHS) projects generally involve an upper and will also affect the technology choice. For very types of energy storage devices currently avail- That is why mechanical applications do not seem lower reservoir. Some projects use a river as the long-term storage of days or weeks, a mechani- able that can be used with wind energy. Finally, to be suitable for providing the ultimate solution lower reservoir; others have used massive lakes or cal storage system is the best, and pumped hydro a brief comparison of the various technologies is to the challenge of large-scale, long-term, and even a sea or ocean. Another interesting concept storage is the most effective method provided provided. transportable energy storage. being developed is to locate one or both reser- water loss is managed carefully. Batteries are voirs below ground (sub-surface). While a proj- also capable of holding their charge for extended 6.1. MECHANICAL ENERGY STORAGE 6.1.1. PUMPED-HYDRO ENERGY STORAGE ect utilizing sub-surface reservoirs has yet to be periods. Energy loss in other systems will make completed, these types of projects are attractive them less practical for long-term storage. For Mechanical energy storage technologies (such as The pumped- hydro energy storage (PHS) is the due to their perceived site availability and their daily cycling of energy, both pumped hydro stor- flywheel, compressed air, and pumped hydro), world’s largest battery technology, accounting potential for reduced environmental risks. age and compressed air energy storage are suit- while each performing quite different roles, have for over 94 per cent of installed energy storage able, while batteries can be used to store energy greater industrial applicability in a net-zero car- capacity, well ahead of lithium-ion and other The flexibility of pumped storage hydro-power for periods of hours. bon scenario, due to their lower installation costs types of batteries (International Hydro-energy that it provides though its storage and ancillary when compared to supercapacitors and super- Association, 2020)199. This technology is an ideal grid services is increasingly important in securing Much of the current growth in energy storage is conductors. Despite their high energy density complement to modern clean energy systems, as stable power supplies. PHS provides flexibility battery systems, helped by plunging battery pric- (80-200 Wh/l) and round-trip efficiency (0-95 pumped storage can accommodate for the inter- through system inertia, frequency control, volt- es. Battery technologies are becoming more ma- per cent)196, flywheels are approximately similar mittency and seasonality of variable renewables age regulation, storage and reserve power with ture with significant reduction in their costs. The to electrical types of energy storage in terms of such as wind and solar power. Hydro power is not rapid mode changes, and black-start capability. role of batteries in balancing power grids and sav- low capacity (about 0.0001GWh) and extreme- only a renewable and sustainable energy source, All of these are vital to support the ever-growing ing surplus energy represents a concrete means ly high daily energy loss (self-discharge of 5-15 but its flexibility and storage capacity also make proportion of variable renewable energy in grid of improving energy efficiency and integrating per cent/hour) (Fuchs et al., 2012)197. Therefore, it possible to improve grid stability and to sup- systems. more renewable energy sources into electricity although currently assisting with fast response port the deployment of other intermittent re- systems. newable energy sources such as wind and solar. Pumped storage excels at long discharge dura- tion and its high power capacity will be crucial in 195 European Commission. “Study on energy storage – Contribution to the security of the electricity supply in Europe”. Final report, March 2020, Brussels Pumped hydro storage uses two water reservoirs avoiding renewables curtailment, reducing trans- 196 Energy storage typically consumes electricity and saves it in some manner, then hands it back to the grid. The ratio of energy put in (MWh) to energy re- which are separated vertically as seen in Figure mission congestion, and reducing overall costs trieved from storage (in MWh) is the round efficiency (measured as a percentage). The higher the round trip efficiency, the less energy was lost due to storage. 25. In times of excess electricity, often off peak and emissions in the power sector. 197 G.Fuchs, B.Lunz, M. Leuthold, and D. U. Sauer (2012). “Technology overview on electricity storage: Overview on the potential and on the deployment perspectives of electricity storage technologies”. Aachen: ISEA 198 R. Alcántara et al., (2015). “Analysis of islanded ammonia-based energy storage systems”. Oxford, UK: University of Oxford. 199 According to their estimates pumped storage hydro-power projects now store up to 9, 000 gigawatt hours (GWh) of electricity globally.

68 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 69 Multiple studies have identified vast potential ity has been adopted to increase the storage ca- fissures as any ingress of water through cracks then gets stored and reapplied to the air during for pumped storage sites worldwide and there pacity of lower lakes at some PHS plants (Madle- will dissolve salt, which then crystallizes and cre- the expansion process. is growing research on possibilities for retrofit- ner & Specht, 2013)202 and allows full isolation ates air-tight seals. ting disused mines, underground caverns, non- of the lower reservoir mitigating the interaction 6.2. ELECTROCHEMICAL ENERGY STORAGE powered dams and conventional hydro plants. between the used water and the underground en- Compressed air storage (CAES) plants are large- Electrochemical energy storage is represented by Abandoned mines, caverns, and man-made stor- vironment. While the reuse of abandoned works ly equivalent to pumped-hydro power plants in four main types of batteries (redox-flow, lead- age reservoirs have all been proposed as poten- (deep mines or open pits) is cheaper, the impacts terms of applications. But, instead of pumping acid, lithium-ion, and high temperature). With tial project reservoir options, and there are ex- on groundwater can be a problem. Consequently, water from a tower to an upper pond during peri- electrification set to be one of the main pathways amples of several projects under initial phases the interaction between UPSH plants and lo- ods of excess power in a CAES plant, ambient air to decarbonisation of energy systems, batteries of development. The underground excavation or cal acquifers must be considered to determine or another gas is compressed and stored under as electricity storage devices will become one of material-handling costs, construction risks, and the main impacts of such a system. Acqifer is an pressure in an underground cavern or container. the key enablers of a low-carbon economy. Sta- time required for underground excavation and underground layer of water-bearing permeable When electricity is required, the pressurized air tionary devices that use chemical interactions construction could make the economics of such rock, rock fractures or unconsolidated materials is heated and expanded in an expansion turbine between materials to store electricity at a set a project difficult, so most developers are look- (gravel, sand, or slit). Any detailed studies on this driving a generator for power production. location for later use. Li-ion batteries predomi- ing to utilize existing subsurface structures or interaction have not been published before. nate in the stationary battery market, mainly be- minimize underground costs through the sale of There are two major problems associated with cause they have been around longer and have had excavated materials (ore, aggregate, etc.). 6.1.2. COMPRESSED AIR ENERGY STORAGE CAES. The first is that when air is compressed, it more time to mature as a technology. Lithium- heats up. Unfortunately the warmer the air, the Compressed air energy storage is the second big- ion technology has the highest round-trip effi- As a result of resurgence of interest in this tech- less will be the amount of air that can be stored. gest form of energy storage currently behind ciency and storage capacity among batteries and nology, with more than 100 projects in the pipe- The second problem is that on releasing the com- pumped storage. It involves converting electrical could dominate the energy storage future as its line, IHA estimates that pumped hydro storage pressed air, the pressure in the cavern is slowly energy into high-pressure compressed air that continuing decline in price, along with improved capacity is expected to increase by almost 50 reduced and this affects the amount of electricity can be released at a later time to drive a turbine performance, it will likely open new markets (Re- percent – to about 240 GW by 2030. produced in the turbine. The first problem can be generator to produce electricity. This means that newable Energy World, 2019)203. There are also dealt with in three ways: adiabatically, by storing it can work along with technologies such as wind arguments in favor of vanadium redox flow bat- Underground pumped storage electricity (UPSH) the heat and reusing it when the air is expanded turbines to provide and store electricity 24/7. teries, due to the fact that there is much vanadi- could be an alternative means of increasing the to produce power; isothermally, with the aid of There are a number of storage options, but the um in the earth’s crust than lithium, which makes energy storage capacity in flat areas where the heat exchangers; and diabatically, by dissipating best option is to store the compressed air in ex- this technology more scalable (Energy Post, absence of mountains does not allow for the con- the heat to the atmosphere. The second problem isting geographical formation such as disused salt 2019)204. The other two technologies (lead-acid struction of pumped hydro storage (PHS) plants can be dealt with by controlling the rate at which mines. Salt caverns are usually free of cracks and and high temperature), however, are not suitable (reservoirs must be located at different heights the air is discharged and thus creating a con- for large-scale use as their energy capacity is sev- requiring location in mountainous regions). stant supply of electricity. Another solution be- eral times smaller in comparison with lithium-ion UPSH plants consist of two reservoirs, with the ing researched by Seamus Garvey at Nottingham Figure 26. Compressed air energy storage and redox-flow (Fuchs et al., 2012)205. Although upper one located at the surface or possibly at University is to store the air in large energy bags lithium-ion and redox-flow are potential candi- shallow depth underground, while the lower deep in lakes or in the sea. In this way, the pres- dates for global utility-scale storage capacity, one is underground. These plants provide three sure of the air leaving the bags remains constant, none of these technologies has progressed suf- main benefits: (1) more sites can be considered being the hydrostatic pressure. ficiently to increase its energy storage capacity in comparison with PHS plants (Meyer, 2013)200, to a level comparable with that of fossil fuels, (2) landscape impacts are smaller than those of New technology is being developed by compa- in order to make the transportation of batteries PHS plants, and (3) the head difference between nies to try to increase the heat retained from over long distances economically feasible. Thus, reservoirs is usually higher than in PHS plants; the compression process. For example, SustainX electrochemical energy storage will have to be therefore, smaller reservoirs can generate the from the USA has working on a process to remove further advanced to address the long-term large- same amount of energy (Uddin & Asce, 2003)201. the heat by injecting water vapor into the com- scale energy storage dilemma. Underground reservoirs can be excavated or can pressed air. The water absorbs the heat which be constructed using abandoned cavities such as old deep mines or open pits. The former possibil- Source: U.S Department of Energy (2020) 203 Renewable Energy World (2019). Why lithium-ion technology is poised to dominate the energy storage future. [Online]. Available from: https:// ww.renewableenergyworld.com/2019/04/03/why-lithiumion-technology-is-poised-to-dominate-the-energy-storage-future/. (Accessed: 20 November 2020). 200 F. Meyer (2013). “Storing wind energy underground”, FIZ Karlsruhe – Leibniz Institute for Information Infrastructure, Eggenstein Leopoldshafen, 204 Energy Post (2019). Can Vanadium Flow Batteries beat Li-ion for utility scale storage? [Online]. Available from: https://energypost.eu/can-vana- Germany dium-flow-batteries-beat-li-ion-for-utility-scale-storage/ 201 N. Uddin; M. Asce. (2003), “Preliminary design of an underground reservoir for pumped storage”, Geotech Geological Engineering, vol 21: 331-355 (Accessed: 19 November 2020) 202 R. Madlener; J.M. Specht. (2013). “An exploratory economic analysis of underground pumped-storage hydro power plants in abandoned coal mines”, 205 G.Fuchs, B.Lunz, M. Leuthold, and D. U. Sauer (2012). “Technology overview on electricity storage: Overview on the potential and on the deploy- FCN working paper no. 2/2013, Institute for Future Energy Consumer Needs and Behavior, RWTH Aachen University, Aachen, Germany. ment perspectives of electricity storage technologies”. Aachen: ISEA

70 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 71 6.2.1. REDOX-FLOW AND OTHER BATTERIES tery is planned for energy storage in the South have roughly the same energy intensity and storage of liquid hydrogen in the space industry Australian town of Port Augusta, and China is costs (Fuchs et al., 2012)206. However, as “liquid and the large salt cavity storages in Texas, USA, Among the frontrunners for large-scale station- building the world’s largest vanadium flow bat- ammonia has over 50 per cent more volumetric and Teeside, UK, are notable examples (Crotogi- ary storage of wind and solar power are flow bat- tery, expected to come online in 2020. There are energy than liquid hydrogen; more than twice the no, 2016)209. teries, which consist of two tanks of liquids that two main downsides: the liquids can be costly, so volumetric energy of hydrogen gas at 700 bar”, feed into electrochemical cells. The main differ- there is a greater up-front cost for the batteries, it seems to be more economically advantageous Power-to-gas (P2G) is another technology option ence between flow and conventional batteries and flow batteries are not quite efficient as Li- (US Department of Energy, 2010)207. In addition, for long-term energy storage that uses renew- is that flow batteries store the electricity in the ion batteries. Similar to lithium batteries, there in comparison to hydrogen, ammonia is easier able or excess electricity to produce hydrogen liquid rather than in the electrodes. NASA stud- are multiple types of flow batteries with a variety and less dangerous to handle. Specifically, its va- (Power-to-Hydrogen) via water electrolysis. Hy- ied the use of redox-flow batteries (RFB) for the of chemistries. For example, researchers at RMIT por pressure is much lower (10 bar at 25 degrees drogen produced in this way can be used directly space program during the 1970s, and the concept University in Melbourne are developing a proton Celsius), which to a great extent simplifies the de- as a final energy carrier or converted to methane, of using chemical reduction and oxidation reac- battery that works by turning water into oxygen sign of storage tanks for transportation purposes synthesis gas, electricity, liquid fuels or chemi- tions for energy storage dates back even further. and hydrogen, then using the hydrogen to power (Rivard, Trudeau, and Zaghib, 2019)208. Therefore cals, for example. The reasons for using P2G are The flow-batteries are far more stable than Li- a fuel cell. Several other research teams are ex- (if it is generated through a carbon-free process), diverse. The main purpose is to store energy long ion, they have longer life-spans and the liquids ploring completely lithium-free ion batteries us- ammonia can be used for storing large amounts term by converting it to other easily storable en- are less flammable. ing materials such as graphite and potassium for of energy for a long time in a transportable form ergy carriers, and at the same time reducing the the electrodes. because of its specific physical features; this is es- load of the electricity grid by controlled operation In RFBs, two chemical components are dissolved sential for achieving a low-carbon future. (flexible demand). Furthermore, the production of in liquids within the system, and are separated by Zinc-hybrid technology is among the latest ad- renewable fuels for transportation, households, or a membrane. The membrane facilitates the ion vanced chemistries with early field results in 6.3.1. HYDROGEN ENERGY STORAGE industry, as well as for chemical production, can exchange and the electric current flows, while the grid-scale storage use. The first rechargeable be a main driver for Power-to-gas. liquids are kept separate in anolyte and catholyte Hydrogen energy storage is a process wherein the zinc-based batteries came in 1996 and were even- tanks. The chemical reduction and oxidation re- surplus of energy created by renewables during tually used to power small and mid-sized buses Neither electrolysis nor methanisation are yet actions that take place in these tanks store the low energy demand periods is used to power elec- in Singapore. The proliferation of electric vehicles close to cost competitive. These conversion pro- generated energy in liquid electrolyte solution trolysis, a process in which an electrical current and distributed energy resources have ramped cesses are especially difficult and costly to run in and are what the “redox” (reduction oxidation) is passed through a chemical solution in order up the demand for battery systems that are af- an intermittent mode. They have low “round trip name refers to it as seen in Figure 26. to separate hydrogen. Once hydrogen is created fordable to produce. Zinc-hybrid technology also efficiency” of storing and then re-generating elec- through electrolysis it can be used in stationary holds the promise of a purpose-built battery for tricity an estimated 34-44% for the hydrogen fuel cells, for power generation, to provide fuel grid-scale solutions that could leapfrog com- pathway and 30-38% for the methane pathway. Figure 26. Flow battery consists of two tanks of for fuel cell vehicles, injected into natural gas petitive technologies with regard to cost. Zinc is Research, development, and pilot deployment, electrolytes pumped against each other separated pipelines to reduce their carbon intensity, or even widely available and typically less expensive than and pilot deployment of these technologies is by a membrane. stored as a compressed gas, cryogenic liquid or the materials used to create lithium-ion or flow needed to drive down cost supported by carbon wide variety of loosely-bonded hydride com- batteries. Zinc-hybrid batteries are at an earlier pricing that adequately values the climate ben- pounds for later use. Hydrogen created through stage in the commercialization process, so their efits of power-to-gas (as well as “renewable gas” electrolysis is showing great promise as an eco- costs have further to fall than most other emerg- from sources like landfills and wastewater treat- nomic fuel choice, with data from the Interna- ing battery technology solutions. ment facilities). tional Energy Agency predicting that hydrogen generated from wind will be cheaper than natural 6.3. CHEMICAL ENERGY STORAGE In Europe many hydrogen energy storage proj- gas by 2030. ects have been created, such as the Energiepark Chemical energy storage is viewed as an impor- Mainz in Germany. The Energiepark uses excess tant candidate for a large-scale, long-duration, The storage of hydrogen in pure, molecular form wind energy to create hydrogen fuel, which is lat- and transportable form of energy storage as, can be achieved in the gas or liquid phase. These er used to generate electricity when wind power apart from sources such as natural gas, energy are the only types of hydrogen storage that are cannot match demand. can be stored in the form of hydrogen and am- currently employed on any significant scale. The monia. As natural gas does not fully align with environmental objectives in the absence of car- 206 G.Fuchs, B.Lunz, M. Leuthold, and D. U. Sauer (2012). “Technology overview on electricity storage: Overview on the potential and on the deploy- bon capture, utilization, and storage (CCUS), ment perspectives of electricity storage technologies”. Aachen: ISEA One type of flow battery, the vanadium flow the solution of the long-term large-scale energy 207 US Department of Energy (2010). Alternatives to electricity for transmission and annual-scale firming storage for diverse, stranded, renewable battery, is already available commercially. A storage dilemma seems to belong to either hy- energy resources: Hydrogen and Ammonia [Online]. Available from: https://www.osti.gov/etdeweb/servlets/purl/21396853 grid-scale 50 megawatt vanadium flow bat- drogen or ammonia. Hydrogen and ammonia 208 E. Rivard, M. Trudeau, and K. Zaghib (2019). “Hydrogen storage for mobility: A review”, MDPI, 12 (1973), pp. 1-22 209 F. Crotogino. “Larger scale hydrogen storage”. In: Storing energy. Elsevier; 2016, pp. 411-29

72 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 73 Orsted, Denmark’s largest energy company, is such wind development can cause potential in- mains an issue. Small hydro projects below 1 MW planning to use excess energy from its proposed terference for radar systems involved in air traf- capacity have now been banned by the ES 2050 This tool identifies areas that may be suitable North Sea wind farms to power electrolysis and fic control, weather forecasting, national defence from receiving public support, due to environ- for wind developments, designates authorities create renewable hydrogen energy. The proposed missions and the internal security. If potential mental impact. There are exceptions, but they are to be involved in the early planning stages, speci- wind farms would have a nameplate capacity of interference issues are identified during the for- limited to specific project circumstances. The po- fies procedures and helps to integrate the spatial 700 MW and be linked to the grid. During period mal review process, a variety of approaches are tential for wind power is limited by the country’s plans of the cantons. It also sets an unbinding of time where the wind farms oversupplied ener- available to help minimize wind energy’s impact mountainous topography. There are some excel- wind energy target for each canton with wind gy, this excess power would be used to generate on radar (e.g designing the wind farm layout to lent wind sites, but they are located in only a few power generation potential, with the cantonal hydrogen through electrolysis which would later minimize the impacted area of radar coverage or regions. In 2016, a total of 37 wind power plants department of energy should take into consider- be sold to large industrial customers. terrain masking). This chapter provides an over- at ten locations produced around 140 gigawatt ation in its cantonal energy plan. This tool, which view of the approaches used in Switzerland, Po- hours (GWh) of electricity (IEA, 2018)210. applies only to turbines 30 meters or higher, Hydrogen production based on wind power can land, UK, France and Belgium to overcome the shows high potential zones, and areas that would already be commercially viable today. Until interference issue. While the Swiss population is, in principle, sup- be protected. The document includes 3 maps: one know, it was generally assumed that this envi- portive of wind power, there is local opposition showing wind speed, one showing high potential ronmentally friendly power-to-gas technology 7.1. SWITZERLAND to their construction once sites have been identi- zones, and another showing restricted zones. In could not be implemented profitably. Econo- fied, with concerns for landscape, tourism, noise addition, the document specifies turbines should Switzerland has the lowest carbon intensity mists at the Technical University of Munich, the pollution and bird protection. Public opposition not be built within at least 300 m of homes. among IEA countries, owing to a carbon free elec- University of Mannheim and Stanford University is well organized and has successfully prevented tricity sector dominated by nuclear and hydro have now described, based on the market situa- several large wind projects from progressing. De- The Swiss Federal Office of Energy (SFOE) is re- power generation. However, following the 2017 tions in Germany and Texas, how flexible produc- lays with obtaining permissions or the need to sponsible for practical management of national decision of the Swiss people to gradually phase tion facilities could make this technology a key reduce the originally planned size of the instal- energy policy within Federal Department of the out nuclear power, Switzerland’s energy sector is component in the transition of the energy sys- lations have undermined the economic viability Environment, Transport, Energy and Communi- undergoing a considerable transition. tem. Today, most of hydrogen for industrial ap- of some projects, which have been abandoned by cations (DETEC). Cantons are consulted during plications is produced using fossil fuels, above all project promoters. federal energy policy and law-making processes. In 2017, the Swiss electorate approved a new en- with natural gas and coal. In an environmentally They have much leeway in adopting their own ergy law being part of an innovative strategy to friendly energy system, however hydrogen could No additional siting for new wind installations energy laws, policies and measures, within the be implemented by 2050. This new energy law play a different role. has been approved since 2012; expansion of ex- boundary set by federal legislation. This results also includes phasing out of nuclear energy. Hy- isting facilities has been pursued instead. Just in a diversity of cantonal policies and measures. droelectricity power, which provides just under CHAPTER 7 – CASE STUDIES three new wind installations have become op- Cantons play an important role in energy policy 60% of total electricity production, is the most erational since 2015. There is extensive project making and implementation, zoning and permit- Several European governments have developed important domestic source of renewable energy. at the advanced planning stage, but it has been ting for energy infrastructure. policies and procedures to address the siting of The Swiss “Energy Strategy 2050” (ES 2050) is a delayed due to institutional and approval issues. wind turbines in locations to reduce their impact strategic policy package for advancing the energy Switzerland has only constructed 34 wind tur- The SFOE has also established a dedicated one- on air defence and air traffic control radars. The transition of Switzerland towards a low-carbon bines over the last 20 years, which produce stop window for wind energy questions, to serve policies vary considerably, reflecting different economy. It consist of a comprehensive set of around 0.15% of the nation’s electricity, accord- permitting authorities and project developers. degrees of understanding that government poli- new and revised laws and ordinances, as well ing the experts at Swiss Federal Institute of Tech- cymakers have of the effects that wind turbines as policy measures that will be implemented in nology and UNIL, two universities located in Lau- 7.1.1 SWISS APPROACH have on radar, different radar systems employed phases. sanne. According to their estimates around 100 by that country, and different relationships be- The basic principle of the one-stop window high-potential locations could accommodate tween the military and industrial communities. The complete revision of the Energy Act of 1998, means that the Swiss Federal Office of Energy is 700 turbines. Together they could generate 7 This chapter gives a brief overview of the current which entered into force on 1 January 2018, the main focal point for the formal review pro- percent of Switzerland’s electricity. Wind power policies employed by each of several European jointly with related new and revised laws and or- cess in case of new wind farms planning process. is expected to increase to 1 760 GWh by 2035 governments in regulating/influencing the place- dinances, is central to the strategy. The ES 2050 They will carry out an evaluation procedure by and 4 300 GWh by 2050 (compared to 140 GWh ment of wind turbines in the vicinity of radar sys- has three pillars: (1) withdrawal from nuclear sending the application submitted by the project in 2016) under the ES 2050. This is to be reached tems. energy; (2) reduction of energy consumption and developer to all relevant authorities (e.g. Federal through the construction of 600-800 turbines. emissions per capita and (3) promotion of renew- Civil Aviation Authority, the Swiss Army, and the The Swiss Federal Office of Energy (SFOE) in- As wind development continues to grow and able energy sources and energy efficiency. representatives of a canton and municipalities in- troduced a new tool, the so-called “wind energy expand to new areas, the likelihood that some volved). concept”, in 2017. turbines will be located within the line of sight Hydropower and wind power are controversial of radar systems also increases. If not mitigated, topics in Switzerland, and public acceptance re- 210 “Energy Policies of IEA Countries: Switzerland 2018 Review”, IEA, Paris, 2018

74 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 75 The evaluation process is quite simple and the means integrating more renewable energy, in- create jobs and its environmental coherence, is a municipalities with onshore wind farms, give some delegated authorities have to fill in the form of cluding wind into the energy mix. pillar of the energy transition in France. sort of preference in tenders to onshore wind proj- 1-2 pages and provide their feedback to the proj- ects by local residents and ease repowering. ect under question. It is possible to approve the 7.2. FRANCE Despite this strongly developing market, the de- project, deny it or give a conditional approval. In ployment of the technology is often slowed down 7.2.1. THE FRENCH APPROACH France plans a massive expansion of renewables case, a concrete project proposal will get a nega- or even stopped. In general, the highest barriers in order to reduce its reliance on nuclear, ac- Government policy is supportive of renewable tive answer than the one-stop window actually in France are seen to be administrative and legis- cording the energy policy roadmap – known as energy with electricity market conditions fa- asks grounds for not approving the proposal. In lative ones. New wind energy projects in France “programmation pluriannuelle de l’energie (PPE)”. vorable towards onshore wind developments. many cases, there are certain restrictions to the have come to a standstill due to the government’s The country is currently moving away from nu- French onshore wind farms developments are project, but it is possible to implement it by us- indecision over who should be responsible for de- clear power, which previously delivered 75% of increasingly receiving radar objections as devel- ing certain additional mitigating solutions. For livering construction permits. In December 2017, the country’s energy needs, and will fill the gap opers seek to build projects closer to radar and example, it is possible to build lower or smaller the Conseil d’Etat, the highest administrative ju- by increasing its renewables share. Based on its also because safeguarding criteria are becom- than previously planned wind turbines. risdiction in France, annulled a decree giving the 2030 National Energy and Climate Plan (NECP) ing more stringent. Radar objections prevent regional perfect authority for issuing environmen- France will aim for 33% renewable energy in its wind farm developments with Météo France and The impact on aviation needs further examina- tal permits needed to build new wind farms. In energy mix in 2030. This means approximately Ministère des Armées being the most prominent tion. The potential impacts of aviation from wind addition, French wind farms have suffered from 40% renewables in the power sector – wind en- objectors in France. For military radar sites a new turbine developments can be assessed in 3 areas: the cumbersome appeals process caused by a mis- ergy could deliver half of it. It foresees onshore assessment process is being developed known those that have a direct impact, an indirect im- placed pessimism towards the technology both wind reaching around 35 GW in 2028, compared as Dempere (DEMonstrateur de Perturbation des pact, or a cumulative impact on aviation interests onshore and offshore. The country’s stringent per- to 15 GW today. Éoliennes sur les Radars Électromagnétiques) and operations. It is not just wind turbines that mitting process also means that while projects are project for assessing wind farm radar interfer- require planning consideration for their potential constantly delayed in the courts, developers’ are France has also confirmed plans to boost its ca- ence on French military radar. It is a process and effects on aviation. Aircraft may be re-routed in unable to alter the turbine choice. According to pacity base and become a “world leader” in float- software system that will predict the impact of order to avoid flying over an area of clutter and WindEurope data, projects in France could take up ing offshore wind under its multi-year energy wind turbine on radar. With the introduction of therefore maintain the controller’s understand- to seven years to be fully permitted as compared plan (PPE). The development of offshore wind Dempere the 30 km safeguarding limit for wind ing of the air situation. As well airplanes can fly to three or four years in Germany. and large wind turbine technology has been a pri- farm developments is being lifted which means higher in order to ensure flight security. ority in the recent years. France has a favorable that objections to developments more than 30 Permitting takes so long due to a typical French phe- situation for floating wind, local harbor facilities, km from French military radar are likely in future. The following siting practices can also be used to nomenon in which third parties can challenge wind and a local naval and offshore oil and gas industry minimize wind energy’s impact on radar: projects in the courts. According to OPTRES, this capable of addressing this market. In the past developers would not have pursued is because renewable energy policies are not fully sites with these objections - they would have • Designing the wind farm layout to minimize clear or consistent, and a large number of authori- Wind power is an increasingly significant source simply moved on to an alternative development. the impacted area of radar coverage or to al- ties are involved in granting the building permit. In of renewable electricity production in France, ac- However the number of developers and the de- low for maximum radar coverage within the 2018, the government of France announced a set of counting for nearly 28% of all installed renew- mand for good wind farm sites is decreasing. The project, such as increasing the spacing be- measures to simplify the wind project approval pro- able power capacity. However, hostility to wind number of objections to wind farm radar interfer- tween turbines within the project; cess and cut development times. These measures energy is “deeply rooted” in France, as much of ence in France is likely to increase substantially in • Terrain masking, or placing turbines on the are expected to halve the average time for complet- the population considers wind turbines to be the coming years if nothing is done. opposite side of elevated terrain in relation to ing and connecting a wind farm to the national grid. ugly and noisy. the radar so they will be blocked from view; This plan included 10 points, among which propos- For most radar types there are currently specific • Relocating proposed turbines or reducing their als to remove one level of jurisdiction in the appeal Overall, the government will speed development safeguarding distances beyond which wind tur- height so that they fall outside the radar line process, reduce the number of night-time lights on of the most competitive technologies, while tak- bine objections will not be made. These distances of sight; wind turbines, distribute a higher grid tax share to ing into account environmental issues, local fea- are shown below: • Eliminating proposed turbines located in areas sibility and conflicts of use. Among other things, that result in high radar interference impacts. the government will encourage the repowering of Radar Operator Radar Type Safeguarding Distance (km) existing sites, support citizen’s participation and, For proposed wind turbines less than the speci- Another mitigation strategy is to hire flight man- Directorate General of Civil Aviation (DGAC) Primary 30 in 2023, make it obligatory to recycle decommis- agers at the wind farms who are entitled to stop sioned turbines. It will continue to simplify the DGAC Secondary 16 the work of wind turbines in case there is a flight permitting process for onshore wind. The targets safety related danger. This can be organized in Météo France C Band 20 could have been more ambitious, but the govern- co-operation with the wind farms and the Swiss ment confirms that onshore wind energy, through Météo France S Band 30 army. Although it should be highlighted the army its competitiveness, its reliability, its capacity to Ministère des Armées Defence 30 has to support the Swiss energy policy which also

76 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 77 fied safeguarding distance technical and opera- get because some emissions can remain if they is a global leader in this sector. This lead will be The UK’s onshore wind capacity should increase tional assessments are undertaken to determine are offset by removal from the atmosphere and/ reinforced when the world’s largest offshore farm by almost threefold in the next 15 years to meet whether the proposed development will be ac- or by trading in carbon units. In addition, under Dogger Bank, starts up off Yorkshire’s coast in climate goals at low cost. This would require ceptable. For DGAC civil radar sites proposed the 2019 “Net Zero” legislation, the Committee 2023. The cost of new offshore wind has fallen the UK to grow its onshore wind capacity from wind farms inside the safeguarding distance a on Climate Change (HMG’s advisory body) has by 50% since 2015 and is now one of the lowest 13,000 MW now to 35,000 MW, or an average of subject to an operational assessment to deter- predicted a requirement at least 75 GW of elec- cost options for new power in the UK – cheaper more than 1,400 MW a year. mine whether the development should be al- tricity from offshore wind by 2050. It is expected than new gas and nuclear options. By 2030 wind lowed. that this will be achieved by a number of current and solar are expected to reach above 50%, more At the moment, the UK government is conduct- offshore windfarm developers and operators in- than any other country. ing a review of current energy infrastructure at The situation in France is similar with the UK ten stalling additional, larger, offshore windfarms sea as it sets the sights on expanding offshore years ago for the following reasons: (1) the gov- around UK. It is unlikely that these ambitious tar- That will set the course for onshore wind, solar, wind energy. The review will focus on improving ernment strongly supported onshore wind; (2) gets will be possible without a step-change in the and the two latest objects of prime minister’s the cabling and transmission infrastructure to re- there were a good market incentives for onshore technology of wind turbines; allowing develop- desire – hydrogen produced by surplus off-peak duce the costs and impacts of connecting of new wind development; (3) there was a very competi- ers to utilize new and more advanced manufac- wind energy; and carbon capture, where emis- wind farms to the onshore electric grid. It will tive market for wind farm sites; (4) the maximum turing techniques. sions are caught and pumped into underground also consider how hybrid projects could combine distance at which radar operators objected in- rocks. Like Japan and Germany, UK has increas- offshore wind turbine connections with intercon- creased following wind farm radar interference The Offshore Wind Sector Deal published in ingly looked to hydrogen as a way of lowering nections to neighboring markets – helping export research and flight trails from the Ministry of De- March 2019 set out an ambitious partnership emissions. The cleanest form of hydrogen – the more green energy abroad. fence; (5) there was a large increase objections to between government and industry to raise the so-called green hydrogen, which is usually gen- wind farms due to radar. productivity and competitiveness of UK compa- erated from water using clean electricity sources 7.3.2. UK’S APPROACH nies to ensure that country continues to play a like offshore wind – is still expensive to make. The UK Government is committed to the devel- The UK wind industry addressed this issue in a leading role as the global market grows in the de- opment of wind energy in the country through number of ways: cades to come211. The Offshore Wind Sector Deal The government secures funding for large-scale the use of offshore and onshore wind farms. confirmed the UK’s aim to achieve 30 GW of off- renewables through contract-for-difference Wind turbines can have significant effects on ra- Within government between Defence, Trans- shore wind by 2030, up from 8 GW today. The UK (CfD) auctions or agreements. CfDs fix a price 1. dar, which in turn is a major barrier of develop- port and Energy departments; Prime Minister, Boris Johnson, has recently set per unit of power that a developer will receive. ment. Aviation radar objections to wind farms in out new plans to “build back greener” by making Renewables such as offshore wind have been suc- 2. Within industry via Renewable UK (formerly the UK mainly arise from three distinct groups; the UK the world leader in clean energy – creat- cessful in these auctions, and prices have fallen BWEA) the MoD (for air defence and military traffic con- ing jobs, slashing carbon emissions and boosting dramatically. However onshore wind and solar, 3. Research and development of technical miti- trol); NATS En Route in respect of its regulated exports212. That should set out the UK govern- some of the cheapest technologies, were not gation solutions en route air traffic control service; and terminal ment plan to achieve its goals. Government’s able to compete for funding in the last two auc- civilian air navigation service providers, namely 4. On a case by case basis for each wind develop- commitment in the 10-point plan also means tions, due to Government manifesto commit- airports. This conflict illustrates the constraint ment facing an objection. that the target for capacity ments. on aviation’s ability to meet its commitment to by 2030 will be set from 30 gigawatts to 40 giga- Governments policies; international obligations 7.3. THE UNITED KINGDOM watts. These commitments are the first stage of Recently, the UK Government announced turn- and license conditions (Memorandum of Under- a 10-point plan for a “green industrial revolution” around on its land-standing ban on the onshore Renewable electricity, is now a significant part of standing, 2010)213. Department of Energy and Cli- from the government to accelerate the progress wind. It means that the government will reverse the UK’s electricity mix providing over a third of mate Change (DECC), Department of Transport towards net zero emissions by 2050. The 10-point its block on onshore projects, overturning the annual generation. This ambition to become the (DfT), Ministry of Defence (MoD), RenewableUK, plan released on 18 November 2020 is not a de- public veto policy in England and introduced by leader in the renewable energy sector is clearly Civil Aviation Authority (CAA) and National Air tailed blueprint, the Government’s commitment David Cameron in 2015. Previous Conservative seen in the UK energy and climate legislation. Traffic Services (NATS/NREL) signed a memo- will be seen in the energy “white paper” (a policy government policy on onshore wind develop- randum of understanding (MoU) in 2008 which document that precedes new legislation) due at ment had allowed for communities to vote down In June 2019 the UK Government laid the draft committed them to work together to identify the end of November 2020. projects based on their impact to the local area. “Climate Change Act 2008 (2050 Target Amend- mitigation solutions, and drive towards progress The government will remove a block against on- ment)” Order 2019 to amend the Climate on projects corralled under an “Aviation Plan”. Change Act 2008 by introducing a target for at The UK is the world leader in offshore wind, with shore wind projects by allowing schemes to com- more installed capacity than any other country. pete for subsidies alongside solar power devel- least a 100% reduction of greenhouse gas emis- Offshore windfarms, when in the line of sight of With a third of the world’s offshore wind instal- opments and floating offshore wind projects, in a sions (compared to 1990 levels) in the UK by radar, may have a detrimental effect on Minis- lations and the first floating wind farm, the UK new auction scheme. 2050. This is otherwise known as a net zero tar- try of Defense’s (MoD) primary surveillance ra-

211 “Industrial Strategy; Offshore Wind Sector Deal”, policy-paper, March 2019 213 Policy paper: “Wind turbines and aviation radar mitigation issues”, Memorandum of understanding, 2011 update 212 T. Raphael. “Welcome to Boris Johnson (Green) Revolution”. Bloomberg news, 19 November 2020 214 It is a zone where a radar ignores interference.

78 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 79 dar capability used to deliver a recognized air including civil and defence radar and low-flying dar mitigation system using Artificial Intelligence stallation of Northwester 2, the country’s largest picture for Air Defence. A number of trials have operations. However, there is not a “one-size- and Doppler filtering. offshore wind farm, Belgium – more specifically demonstrated the adverse impact that this has fits-all” solution, given the unique operational the northern region of Flanders – has achieved on the UK’s air defence capability. The Doppler environment of air infrastructure. Therefore, future mitigation solutions should 1,775 MW in installed capacity and outranks shift on ground radar returns mimics the signals exist for Air Defence Radar, which may be ap- Denmark as fourth – largest offshore wind energy of fast moving aircraft, curtailing the RAF’ (Royal It is also obvious that the existing mitigation plicable to new developments. There are tech- producer worldwide. In Europe, Belgium ranks Air Force) ability to detect incoming, low-flying, strategy has to be reviewed in the light of the nologies which have the potential to mitigate 3rd. With the Marine spatial planning 2020-2026, aircraft threats. Analysis of these trials has con- technological progress where wind turbines are impacts at Air Traffic control radar installations. there has been established the framework for cluded that current mitigation methodologies becoming bigger and more efficient. To mitigate However, the high cost of mitigating impacts of additional wind zone of 281 km² (at the frontier (including Non-Automatic Initiation Zones)214 the negative effects of wind turbines of the next (onshore) wind development on military radars with France), in addition to the wind zone of 225 may be insufficient to meet future and to be generation, additional methods are required, ei- may threaten to make some proposed (onshore) km² which already exists (at the border with the agreed aviation specifications. When properly ther technical, procedural or a combination of developments uneconomic. Netherlands). implemented interference is rejected whilst gen- those two. Mitigation measures can be set at uine targets (aircraft) are displayed. Non-Auto national, regional, cluster or project levels. The 7.4. BELGIUM When the government approved the reduced Initiation Zones (NAIZs) are sometimes used to UK MoD will elaborate a new mitigation strat- level of support for three last wind farms to be Renewable energy potential in Belgium is rela- mitigate the effects of wind turbines. For larger egy next year to tackle air defence mitigation. built by 2020, ministers decided to organize as tively low. The country is flat, densely popu- wind developments infill mitigation may be more There is a joint programme of work between from 2020 a competitive bidding procedure for lated and not particularly sunny, and large-scale suitable. Sometimes a mitigation scheme can stakeholders to support the development of this the realization of new renewable energy projects use of hydro, onshore wind and solar solutions combine radar blanking and Transponder Manda- new strategy. Starting in August 2019, the Task in the North Sea, such as it is also the case in the faces challenges in spatial planning and in pub- tory Zones by NATS and for Ministry of Defence Force’s programme of studies and works includes neighboring countries and in accordance with the lic support. Under current technologies, biomass (MoD) Air Traffic Control mitigation. In addition, the BEIS funded DASA Innovation Challenge, European state aid rules. and offshore wind have the most potential (IEA, some of the mitigations applied to civilian radar the sector funded MoD Air Defence Mitigation 2016)217. The first ocean (wave) energy facility systems may not be suitably applied to MoD (Air Feasibility Study, a MoD funded Next Genera- For that purpose, the Belgian Parliament has ad- (Mermaid, 20 to 61 megawatts) received a con- Defence) primary radar surveillance assets. The tion Mitigation Study led by Defence Science & opted a law on 4 April 2019 (ratified by the King cession in 2012 and started operation in 2019. detrimental effect of offshore windfarms may be Technology Laboratory, and MoD leading on op- on 12 May 2019) which establishes the general exacerbated by the increasing size, number, and erational analysis through the Defence Science principles of the commitments at competitive Belgium’s Government coalition has a strong fo- scale of future installations. & Technology Laboratory and strategy develop- bidding procedure. With this new legal frame- cus on climate and energy policies. Today Belgium ment works. The Aviation Taskforce is planning a work Belgium aims at achieving commitments at has 2.3 GW of onshore wind capacity and 1.6 GW Given these challenges, more than half of the set of Concept Demonstration activities to bet- European level and within the framework of the of offshore wind capacity. To accommodate for current offshore wind farm development pipeline ter understand the capabilities of mature mitiga- Paris Climate agreement. This legal framework a target of 55% or higher greenhouse gas reduc- are subject to objections from the aviation sec- tion solutions. Informed by these inputs, the aim should enable the federal government to realize tion, the coalition agreement foresees to expand tor (civilian and military); potentially preventing is to publish an initial Air Defence and Offshore the proposed 4 GW of offshore wind energy (in- onshore wind capacity in Flanders to 2.5 GW up the development of projects within radar line Wind Mitigation Strategy & Implementation clusive the already operational or planned wind from 1.3 GW today and in Wallonia to 4.600 GW of sight of many air defence radar installations. Plan in early 2021, with follow on studies and farms) in the inter-federal Energy Plan by 2030 at up from 1,500 GWh by 2030. It will also aim to With accelerated deployment of offshore wind work planned in 2021-22 to update the Strategy the latest. In addition, the new law also aims at double the country’s offshore wind capacity to 4 farms needed to meet the goals set out in leg- & Implementation Plan for future offshore wind realizing after 2029 the largest possible share of GW in the next decade by exploring the potential islation, there is a clear need to mitigate the im- deployment.215 additional offshore electricity production capac- for additional capacity in the North Sea. pact of wind turbines on radar and allow the wind ity from renewable energy sources at the lowest farm developments to go ahead. UK government and the wind industry have in- possible societal cost. In Belgium renewable energy is a regional mat- vested in the research and development which ter, with exceptions for offshore wind power, hy- UK so far has relied on good cooperation within enable to get cutting-edge innovation off the Electricity from renewable sources is promoted dropower and renewable energy sources used in the government and the stakeholders. The dia- ground. For example, Defence and Security Ac- mainly through a quota system based on the transport which are governed by national regula- logue between the aviation, defence and wind in- celerator (DASA) recently organized competition trade of certificates. The individual green cer- tions. Belgium will double the area of its North dustries have been ongoing for many years. Pro- that offered wide-range and complex ideas to tificate systems differ in many ways between Sea waters made available to offshore wind active and collaborative approach has resulted in tackle radar interference216. Thales, in collabo- regions. They vary according to the quota obli- farms after 2020 as part of its exit strategy from the identification of opportunities and solutions ration with the University of Birmingham and gation, the basis for granting green certificates, nuclear power. The country has 4 offshore wind which enable mitigation measures to be imple- SMEs, will develop surveillance to mitigate wind- technology specific support levels, calculation of farms that produce 871 megawatts of power and mented in a significant number of situations, farm “clutter”, whereas Saab is developing a ra- minimum price levels, duration of support and wants to increase that capacity to 2.2 gigawatts tradability. by 2020 and to 4 gigawatts by 2030. With the in- 215 https://cdn.ymaws.com/www.renewableuk.com/resource/resmgr/sector_deal_progress_update_.pdf 216 Defence and Security Accelerator (DASA). “Offshore Windfarms development boosted by 2 billion GBP research”. Press release, 28 October 2020. 217 International Energy Agency. “Energy Policies of IEA Countries: Belgium 2016 Review”, IEA, 2016, Paris, France

80 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 81 7.4.1. BELGIUM’S INTEGRATED APPROACH military, aeronautical, or traffic-related restric- which has severely hindered the development of of the distance rule act has been presented yet, tions) and lengthy permitting procedures. The land-based wind parks both in the Flemish and but according to the Polish Wind Energy Associa- Standing off the coast of Belgium are found federal administration has created a “one-stop Wallonia regions. Belgium has limited space for tion (PWEA), legislative work on it could be com- enough wind turbines to generate more than 5 shop” aimed at simplifying and speeding up the wind energy compared to many other countries. pleted by the end of the year. percent of the national energy demand, increas- license procedures. However, because of their relatively high avail- ing to 20 percent beyond 2020. Despite its rela- ability, offshore wind resources provide the most The development ministry is finalizing work on tively small coastal zones, Belgium is third in Eu- The Flemish government aims to speed up the potential, according to an IEA in-depth review in provisions that would allow for shorter distances rope behind the United Kingdom and Denmark in planning process and decrease the large number 2015. between new wind turbines and farm buildings wind energy production. Instead of solely com- of rejected permit requests. The goal is to inte- or protected areas, which under current distance plicated navigation, the cooperation with wind grate the environmental and building permit and For the development process to be successful, it rule need to be 10 times the tip height – which in industry could prove very useful (Lundquist, establish more collaboration between the differ- is necessary to have an integrated approach of practice means a distance of 1.5 to 2 km. 2019)218. The Belgium Navy that is responsible for ent levels and domains through the Wind Work- the wind farm project from the very beginning coastal security (critical to offshore wind farms) ing Group. The Flemish Government also aims of the process. It means that the way of work- So far the biggest role in increasing the share of has used three Cs: collaboration, coordination to focus on developing and facilitating zones in ing to identify potential sites is already part of renewable energy in the Polish electricity bal- and counter-together. In terms of collabora- the harbor areas and next to highways where a decision-making process, since all the stages ance was played by private energy companies tion, the same radar system should be used, the fewer people live, in order to limit the risk of of a wind farm life-cycle (development process, and companies-prosumers, who collectively built same data protocol between military and wind local opposition. They also see a larger role for construction, deployment, operation and dis- 81% of all renewable capacity installed between farms. Cooperation means working together on Wind Working Group in advising developers be- mantling) are taken into account when site pros- 2013 and 2019. The total capacity of halted proj- common issues, while counter-together means fore they actually request a permit for their proj- pecting so that their impacts can be reduced to ects in various stages of development in Poland developing measures to counter unidentified ob- ect and assisting the development of positively minimum levels. amount to 4.1 GW, including 3.4 GW in projects jects together. advised wind farms. To conquer “NIMBY” (not that have a signed connection agreement. Accord- in my backyard) feelings, the FEA advises earlier At the local and provincial level, there is a better ing to the estimates of PWEA, Poland has an on- Belgium’s Navy is a blue-water navy that is ca- involvement of the municipal council, financial application of more participatory planning which shore wind potential of some 22-24 GW, almost pable of distant open-ocean operations. The participation for residents and more “objective” allows discussion of different views, knowledge, four times the 6.2 GW currently in operation. new mine-sweeper ships will remain outside information to tackle misconceptions about wind values and interests of the various stakeholders. minefields and rely on a “toolbox” of off-board turbines. Next to the enormous potential for wind on land, remote and unmanned systems to enter the dan- 7.5. POLAND pressure from the EU to phase out coal (which ger zones while the ship remains at a safe dis- The simplification of the planning procedure is currently accounts for more than 70% of polish tance. As drone technology matures, the newer The development of renewable energy sources important step and improves the efficiency of electricity). And the hunger for green power by capabilities can replace the older systems. These in Poland, including wind power is the priorities wind power planning by decreasing the politi- large state-owned firms, mid-term voter strate- off-board systems can be controlled from the listed in the document “Polish Energy Policy un- cal distances between various policy levels, but gy aspect may also play a role for Poland’s warm- ships, or from containerized control stations that til 2040”. In addition to different tools for policy it does not necessarily increase the acceptability ing up to onshore wind. can be placed where needed ashore. These un- implementation, the document includes e.g., of projects. For example, the Flemish government manned underwater vehicles can carry sensors “hierarchy-based spatial planning ensuring the has not yet tackled the major current bottleneck The government led by the right-wing populist such as synthetic aperture sonars and side scan- implementation of energy policy priorities. This in planning: the wind “rush” on the sparse zones Law and Justice Party (PiS) had introduced the ning sonar, as well as neutralization charges to means that the spatial planning system should for wind power development. wind distance rule also to cater wind protesters destroy mines. The matrix of wind structures can involve the implementation of energy policy at in coal and rural constituencies that are impor- help create an underwater network to commu- all the government levels: national (country), re- Lengthy legal procedures also affect the sector. tant for its voter support. After winning elections nicate with the drones, and even recharge their gional (Voivodship) and local (municipal). Hence For example, cases where local communities ap- for municipalities, parliament and president in batteries. Therefore the co-existence of wind the regional and local authorities are expected to pealed against the construction of wind energy 2018, 2019 and 2020 respectively, the PiS does farms with military radars and other equipment actively implement the energy policy. In Poland, facilities have taken years to resolve. Such legal not need to face another important vote for can also be seen as an opportunity, not always as just as in Sweden and the United States, local cases could potentially be avoided by involving several years. Until then, renewables develop- a technical challenge to overcome. governments have a good deal of authority over the local communities more closely at the proj- ers hope the government – together with the spatial planning, and decisions on wind farm sit- ect planning stage and by offering them the op- wind industry – can convince rural constituencies Belgium is not an exception and similarly to some ing are taken at a local level. portunity to take part in investments through more of the beneficial aspects of wind farms, and other countries in Europe has certain problems or cooperatives. offer local regions substantial support to ease barriers that need to be overcome to boost the Poland’s government plans to “liberalize” a dam- possible job losses in coal in the wake of the ener- wind energy deployment to a greater scale. Such aging distance rule from 2016 that has brought The main issue affecting growth for wind is the gy transition. The government in 2018 and 2019 barriers include spatial planning limitations (i.e. new wind power developments on land to a near number of judicial appeals at the State Council, had carried out tenders that included a combined stand-still, shutting down the largest onshore 3.2 GW in onshore wind projects in an advanced 218 E.Lundquist. “Belgian Navy Sees Cooperation Opportunities for Wind Farm Industry”. Sea-power Magazine, 12 February 2019. wind energy market. No draft for an amendment

82 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 83 stage of development, which fetched record-low also outlined a new subsidy scheme. According to mitigate the negative effects of wind turbine on which either comes in the form of a built-on prices for winning bids. Another 1.2 GW of ad- the Polish Wind Energy Association (PWEA), off- radars. “windfarm filter” or are inherent to the radar de- vanced projects have valid building permits, and shore wind farms in the Baltic Sea with an overall sign. For example, no “windfarm tolerant” next could be auctioned off soon. capacity of 5.9 GW are set to “receive support The research found that genuine concerns have generation radar has yet been installed in the UK under a two-sided contract for difference be- been raised in many countries in Europe and and approved by its Civil Aviation Authority, but Poland’s expansion targets for offshore wind tur- tween the investor and the regulator”. Awarding elsewhere about the impact of wind turbines on work continues and some airports have expressed bines are ambitious. Poland does not have any support under this formula will be time-limited radar and military sites. The concerns are varied, an interest in such a holistic mitigation solution. offshore wind farms as yet, but by 2030 they aim until the end of June 2021. however the research clarifies that each con- Furthermore, some existing radars have advanced to have installed 3.8 GW offshore wind energy cern is theoretically plausible. Additional clut- processing capabilities which afford a degree of – with 10 GW of new capacity awarded CfD by CONCLUSIONS ter, shadow, and flight obstructions are the main “wind farm tolerance” in particular circumstanc- then. By 2050 they want a massive 28 GW, which concerns that the Ministries of Defence have es – for example, Raytheon S and L band radar Given the expected increase in the wind energy would make Poland the largest operator of off- raised, and a particular concern is the use of radar (as used by NERL219 at Lowther Hill and Great development, and the role of renewable electric- shore wind power in the Baltic Sea. New agree- clutter and shadow zones by unfriendly aircraft Dun Fell and, it is understood, Liverpool airport ity in the future, wind farms, both onshore and ments and the planned Offshore Wind Act could to move below the radar, enabling them to po- as well as at military bases in the Netherlands220. offshore, will play a vital part. This also means improve the conditions for developers, investors tentially conduct missions undetected. Air Traffic The conducted interviews highlighted the im- that wind farms are here to stay and they are ex- and lenders. Poland is ambitious where the de- Control Radar providers, thus take a conservative portance of co-operation between governmen- pected to increase in size and number in the years velopment of offshore wind farms is concerned. view on a wind farm deployment and they often tal agencies and wind developers, dedicated to come. Unfortunately, wind farms may affect Thanks to the legal framework the Polish govern- end up in conflict with wind farm developers. funding, a common research plan, and stream- the proper operation and reduce the detection ment seeks to create, Poland will become a very lining certification procedures as necessities for capability of the surrounding radars. If not miti- interesting growth market for key players in the The interference problems can be solved by us- implementing and expanding the range of ap- gated, such wind development could cause clut- offshore wind sector. ing operational & procedural mitigation tools proved mitigation solutions available to address ter and interference for radar systems involved in (e.g. procedurally safeguarding vital radars and the impact of wind farms on radar and military air traffic control, weather forecasting, internal The development of offshore wind is part of the areas or operationally amending activity routes operations. It is clear from the literature and security, and national defence missions. Polish National Energy and Climate Plan for 2021 and using mandatory transponder zones in wind the interviews that wind industry stakeholders -2030 and also enshrined in the Polish Energy farms areas). The other possibility is to use tech- seek “early engagement” from authorities with Wind turbines due to their physical characteris- Policy until 2040. Poland believes that offshore nical mitigation measures, e.g. maximizing cur- distinct requirements such as the Ministry of tics (more powerful and bigger) are contributing wind is one of the key technologies for achiev- rent radar capabilities (clutter mapping, sector Defence, the Ministry of Energy, the Ministry of evermore complex clutter interference to the ing the EU’s renewable energy target for 2030. blanking). A common approach to create a clut- the Interior, Aviation Authority/Agency to ensure ever noisier radio-frequency spectrum, therefore If Poland met its 28 GW target, it would be the ter map is to divide the observation area into wind turbine projects are not unduly delayed or they give rise to the bigger surveillance challenge. largest operator of offshore turbines in the Baltic predefined clutter cells and to count the number prevented, and that the defence capability is not This also means that the military have to adapt Sea. The Polish government’s focus on offshore of measurements appearing in the respective cell compromised. and evolve to operate in evermore “complex wind energy is very reasonable given the coun- on a given time interval. Clutter map computa- clutter interference”. To solve the problem, wind try’s commitment to increase its share of renew- tion is of great importance in order to reduce the Certain countries have adopted wind turbine in- turbines and surveillance systems must become able energy to 21% by 2030, from 10.9% in 2017. amount of false alarms by a tracking algorithm. terference mitigation strategies (e.g the USA) or more electromagnetically compatible – it is the The proposed solutions available to help resolve have concluded country level memorandum of ability of the devices and systems to operate In July, 2020, representatives of the Polish gov- wind turbine interference with radar and mili- understandings (e.g. U.K) to foster co-operation in their electromagnetic environment without ernment and members of the offshore wind en- tary concerns are numerous, with gap filler radar, between the agencies and the wind industry. Un- impairing their functions and without faults. In ergy sector agreed to take joint action to develop software upgrades, radar upgrades, and stealth der a Memorandum of Understanding signed in this context, the currently used approaches are the offshore energy market in Poland. The co- technology as favored solutions. Initial research 2014 and building off the successful Interagency not enough, and the existing siting processes operation is set out to develop, sign and imple- between government agencies and academia will Field Test & Evaluation radar mitigation testing as well as mitigation approaches need to be re- ment the so-called Polish Offshore Sector Deal. focus on the viability of adaptive clutter map- campaigns, in the USA, a consortium of federal viewed and enhanced. This enables to guarantee The declaration will be similar in character to the ping, in-fill radar, and concurrent beam radar to agencies composed of the U.S. Department of continued development of this important renew- British sector deal for offshore wind energy, but provide mitigation solutions. Defence, Department of Energy, the Federal Avi- able energy resource while maintaining vital de- it will take into account Polish reality and condi- ation Administration, and the National Oceanic fence readiness. All these factors can give rise to tions. Poland’s ambition is to become an offshore A number of radar manufacturers are developing and Atmospheric Administration established a number of conflicts between the wind energy leader on the Baltic Sea and a net exporter of what they term “next-generation” radar which the Wind Turbine Radar Interference Mitiga- and aviation sectors (both civilian and military). cheap and clean energy. includes an element of “wind farm tolerance’, tion Working Group to address these conflicts. Definitely, the co-existence of windfarms and

radar installations is challenging, but possible. 219 In July 2020, the Polish government published a NERL is the sole provider of civilian en-route air traffic control over the United Kingdom and is regulated by the Civil Aviation Authority (CAA) Therefore, the solutions have to be found how to which, for example determines the charges NERL can make. new draft of the so-called Offshore Wind Act that 220 “RenewableUK Members’ Briefing Note: Aviation Safeguarding and Radar Mitigation: Introductory Overview”. Issue 1, 13 October 2016, Amend- ment 1, 29 January 2019

84 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 85 Through collaborative activities and coordinated A WAY FORWARD Security of Excellence conducted in 2021. The fo- Wind Energy Cooperative, Austin Texas, USA: Bat investments, this Working Group seeks, by 2025, cus of the study ““The offshore wind farms – chal- Conservation International; The demand for sustainable offshore energy can to fully address wind turbine radar interference lenges, risks and opportunities for building more encourage companies to establish offshore wind 7. Baath, L. “Noise spectra from wind tur- as an impact to critical radar missions, ensure resilient national energy system” would be on the power plants. The introduction of offshore wind bines”. In Renewable Energy; 2013; volume 57, the long-term resilience of radar operations in main barriers in the deployment of offshore wind turbines helps to generate electricity, which as pp. 512-519 the presence of wind turbines, and remove radar farms; it would also map the potential solutions a result is expected to evolve the offshore wind interference as an impediment to future wind en- and best practices to ensure national security on 8. Baerwald, E; Barclay, R. “Patterns of Ac- power market. The mature offshore wind tech- ergy development. To address, the interference one hand, and making the energy transition pos- tivity and Fatality of Migratory Bats at a Wind nology makes it possible to install wind turbines issue at early stage, several other countries use sible on the other hand. Among other aspects, Energy Facility in Alberta, Canada. In Journal of on the seabed in large projects that take advan- one-stop shop approach while reviewing the new the study should give an overview on the current Wildlife Management, 2011, 75 (S), pp. 1103-1114. tage of strong and steady winds. Offshore wind windfarm applications. Whenever there is an im- technological trends starting from radars and ca- has rapidly become a mature technology in Eu- 9. Bakker, R., Pedersen, E., van den Berg, G., pact for civilian or military radars, the mitigation bles to turbines including power-to-X technology. rope, and a significant growth of capacity is also Stewart, R., Lok, W., Bouma, J. (2012), “Impact of options are sought. forecasted in Asia and in the USA. wind turbine sound on annoyance, self-reported BIBLIOGRAPHY sleep disturbance and psychological distress”, There are a number of other hurdles on the way Europe is expected to lead the global offshore 1. Alcántara, R. et al., (2015). “Analysis Science Total Environment, 425, pp. 42-51 towards large-scale wind energy deployment, for wind market with increasing number of invest- of islanded ammonia-based energy storage sys- example, there are different rules that have been 10. Barone, M. (2011). “SANDIA report: Sur- ments in offshore wind projects. Furthermore, tems”. Oxford, UK: University of Oxford. established at different times regarding paint vey of techniques for Reduction of Wind Turbine the region is likely to hold a major share in the markings on turbines and the position of lights 2. Angulo, I; de la Vega, D; Cascon, I; Cani- Blade trailing Edge Noise”, SANDIA National global market owing to favorable governmental on turbines, etc. However, there is no overall zo, J; Wu, Y; Guerra, D; Angueira, P. “Impact Anal- Laboratory, US Department of Energy, California initiatives. Other factors likely to drive the mar- trend on positioning and brightness adjustabil- ysis of wind farms on telecommunication servic- ket share are energy security initiatives and de- 11. Behr, O.; Brinkmann, R.; Hochradel, K.; ity (for example, brightening lights during search es”, In Renewable and Sustainable Energy Reviews, carbonisation reforms in Europe. Mages, J.; Korner-Nievergelt, F.; Niermann, L.; volume 32, April 2014, pp. 84-99. and rescue operations). This lack of EU regulation Reich, L.; Weber, N.; Nagy, M. “Mitigating Bat means there are major disparities in terms of how New challenges may emerge as the next range of 3. Arce Leon, C. (2012). “Study on the mortality with Turbine-Specific Curtailment Al- rules are interpreted and implemented, depend- offshore wind turbines are introduced that may near-surface flow and acoustic emissions of trail- gorithms: A Model Based Approach”. In Wind ing on the location. Wind industry, aviation regu- be floating in deeper waters and are likely to be ing edge serrations (for the purpose of noise re- Energy and Wildlife Interactions; Springer Inter- lators and the military should work together to- further offshore; for example, what to do with duction of wind turbine blades)”, Delft Technical national Publishing: Cham, 2017; pp. 135-160 wards a more simple and uniform categorization cable in floating offshore wind installations and University, the Netherlands. https://doi.org/10.1007/978-3-319-S1272-3_8. to overcome these issues. Another important ground conditions. issue is the lighting regime of the wind turbines Arce Leon, C; Merino-Martinez, R; Ragni, D; Aval- 12. Bolin, K. “Wind Turbine Noise and Natu- that different countries have used. Therefore, a lone, F; Snellen, M. “Boundary layer characteriza- ral Sounds: Masking, Propagation and Modeling”. Among the most promising innovations, floating proportional approach to this issue would be tion and acoustic measurements of flow-aligned PhD thesis: Royal Institute of Technology; 2009 offshore wind energy is the future solution for ex- desired like Germany does by using transpon- trailing edge serrations”. In Exp Fluids (2016), vol- panding the scope of offshore operations. In ad- 13. Borely, M. “EUROCONTROL Guidelines der based solutions that do not disturb the local ume 57, Issue 182. dition to traditional solutions, floating offshore for Assessing the Potential Impact of Wind Tur- community so much. The harmonization of simi- wind power will allow projects to be installed in 4. Auld, T; McHenry, M.P. and White, J. bines on Surveillance Sensors”, technical Report lar regulation at European Union level could be areas of great depth, further from the coast or in “Options to mitigate utility-scale wind turbines EUROCONTROL-GUID-130; Eurocontrol: Brus- useful. windy areas. on defence capability, air supremacy, and missile sels, Belgium, 2014 detection”. In Renewable Energy, 2014, issue 63, Some of the hurdles for successful co-existence 14. Boulouiha H.; Denai, M. “Grid Integra- With respect to storage and batteries, significant pp. 255-262 between wind farms and radars can be hopefully tion of Wind Energy Systems”. In Clean Energy progress has been made to drive costs down and solved by the adoption of the Estonian maritime 5. Avallone F; van der Velden. G; Ragni D. for Sustainable Development” (2017) enhance capacity. Various forms of storage will plan that is a thematic plan of the marine area “Benefits of curved serrations on broadband trail- be needed, from very short durations to long- 15. Breeze, P. “Wind Power Generation”. In for the whole Estonian maritime area. It also in- ing –edge noise reduction”. In Journal of Sound term durations. Storage will support market de- Power Generation Technologies (2019) cludes planning and assessment of the inland sea and Vibration, Volume 400, 21 July 2017, pp. 167- velopments and help to manage peaks and drops and exclusive economic zone. For wind energy 177 16. Brownstein, I, Kinzel, M, Dabiri, JO in volatile markets. (2016), “Performance enhancement of down- development, it will also give a clue for the wind 6. Arnett, EB; Schirmacher, M.; Huso MMP; energy developers where onshore windfarms can stream vertical-axis turbines”, Journal of Renew- As a follow-up to the present study, the challeng- Hayes, JP. “Effectiveness of changing wind tur- be planned (e.g. national defence restrictions). able Sustainable Energy es and potential for offshore wind power will be bine cut-in speed to reduce bat fatalities at wind covered in a separate study by the NATO Energy facilities”, Final report submitted to the Bats and 17. Brooks, T.; Pope, D.; Marcolini, M. “Air- foil Self-noise and Prediction”, NASA Reference

86 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 87 Publication 1218, National Aeronautics and Nexrad Now, 2008, 18, pp. 1-7 38. Energy Post (2019). Can Vanadium Flow ter”, Chapter 5, Technical University of Madrid Space Administration, 1989, USA Batteries beat Li-ion for utility scale storage? [On- and Spanish Meteorological Agency 28. Dabiri, J. (2011). “Potential order-of- line]. Available from: https://energypost.eu/can- 18. Chamorro, L., Porte-Agel, F. (2009), “A magnitude enhancement of wind farm power 50. Gaultier, S; Blomberg, A; Ijas, A; Vasko, vanadium-flow-batteries-beat-li-ion-for-utility- wind-tunnel investigation of wind turbine wakes: density via counter-rotating vertical-axis wind V; Vesterinen, E; Brommer, J; Lilley, and T. “Bats scale-storage/ boundary-layer turbulence effects. Bound- turbine arrays”, Renewable Sustainable Energy, and Wind Farms: The Role and importance of the ary-Layer Meteorol 136:515-533. https://doi. https://doi.org/10.1063/PT.3.2559 39. Ericksson S; Bernhoff H; Leijon M. “Eval- Baltic Sea Countries in the European Context of org/10.1007/s10546-009-9380-8 uation of different turbine concepts for wind Power Transition and Biodiversity Conservation”. 29. Dai, K., Bergot, A., Liang, C., Xiang, WN. power”. In Renewable and Sustainable Energy Re- In Environmental Science & Technology, 2020, 54, 19. Cho, JYN; Huang, S and Frankel, S Huang, Z. “Environmental issues associated with views; 2008; volume 12 (5); pp. 1419-34 pp. 10385-10398 (2012). “NextGen Surveillance and Weather Ra- wind energy – A review”, Renewable Energy, dar capability Siting Analysis (Project Report)’. 2015; 75, pp. 911-921 40. Estonian National Energy and Climate 51. Ghaseminan, M; Nejat, A. “Aeroacous- ATC-391. MIT Lincoln Laboratory, Lexington, MA Plan (NECP 2030), Ministry of Economic Affairs tics prediction of a vertical axis wind turbine us- 30. Davy, J.L; Burgenmeister, K; Hillman, D. (US), http://web.mit.edu/jync/www/abstracts/ and Communications, Tallinn, 2018. ing large Eddy Simulation and acoustic analogy”. “Wind turbine sound limits: Current status and Cho+etal-2012 In Energy, vol. 88, pp. 711-717 (2015) recommendations based on mitigating noise 41. European Commission (1995). ExternE. 20. Clark, TL. “An autonomous bird deter- annoyance”. In Applied Acoustics, vol. 140, pp. Externalities of Energy, Vol 6 Wind & Hydro 52. Gehring J; Kerlinger P.; Manville AM. rent system. [Dissertation]. University of South- 288-295 (2018); www.doi.org/10.1016/j.apa- “Communications towers, lights, and birds: suc- 42. European Commission. “State of the ern Queensland; 2004. coust.2018.06.009; cessful methods of reducing the frequency of Union: Commission raises climate ambition and avian collisions”. In Ecological Appliances 2009; 21. Coates Associates (2007). “Cumbria 31. Defence and Security Accelerator proposes 55% cut in emissions by 2030”, press 19: 505-514 Wind Energy Supplementary Planning Docu- (DASA). “Offshore Windfarms development release, 17 September 2020, Brussels, Belgium. ment: Part 2. Landscape and Visual Consider- boosted by 2 billion GBP research”. Press release, 53. Geyer T; Sarradj E; and Fritzsche C. 43. European Commission. “Study on en- ations”. Prepared for the Cumbria County Council 28 October 2020. “Measurement of the noise generation at the ergy storage – Contribution to the security of the trailing edge of porous airfoils”. Experiments in 22. Cortina, G, Calaf, M, and Cal, R.B (2016). 32. Deshmukh, S., Bhattacharya, S., Jain, electricity supply in Europe”. Final report, March Fluid, 2009; 48 (2), pp. 291-308 “Distribution of mean kinetic energy around an A., Paul, A, “Wind turbine noise and its mitiga- 2020, Brussels isolated wind turbine and a characteristic wind tion techniques: A review”, Energy Procedia 160 54. Gipe, P. “Wind energy basics: a guide 44. Finez A; Jacob M; Jondeau E; and Roger turbine of a very large wind farm”. In Phys Rev (2019), pp. 633-640, 2nd International Confer- to home and community scale wind energy sys- M. “Broadband noise reduction with trailing edge Fluids 1:74402, https://doi.org/10.1103/PhysRev- ence on Energy and Power, ICEP2018, 13-15 De- tems”, Chelsea Green Publishing, 2009 brushes. 16th AIAA/CEAS Aeroacoustics Confer- Fluids.1.074402 cember 2018, Sydney ence, 2010 55. Green M.” Portugal, SJ.” Murn, CP. “Vi- 23. Council of Canadian Academies (2015), 33. Dessoky. A; Lutz, T; Bangga. G; Kraemer, sual fields foraging and collision vulnerability in 45. Fioranelli, F., Patel, J., Horne, C., Palama, “Understanding the Evidence: Wind Turbine E. “Computational studies on Darrieus VAWT Gyps vultures”, 2012, 154, pp. 626-631 (https:// R., Griffiths, H., Danoon, L., Brown, A. (2018), Noise: The Expert Panel on Wind Turbine Noise noise mechanisms employing s high order DDES doi.org/10.1111/j.1474-919X.2012.01227.x) “Experimental measurements of radar signatures and Human Health”, Ottawa, Canada Model”. In Renewable Energy, vol. 143, pp. 404- of large wind turbine”, The Journal of Engineering, 56. Green, M. “Through birds’ eye: insights 425 24. Cortina, G., Galaf, M, Cal RB (2016), IET International Radar Conference into avian sensory ecology”, Journal of Ornithol- “Distribution of mean kinetic energy around an 34. Dooling, R. “Avian hearing and the ogy, 153, 2012; pp.23-44 46. Ford, B. “Atmospheric Refraction: How isolated wind turbine and a characteristic wind avoidance of Wind Turbines”. National Renew- Electromagnetic Waves Bend in the Atmosphere 57. Gross, S. “Renewables, Land Use, and turbine of a very large wind farms”, Phys Rev Flu- able Energy Laboratory, Colorado, USA and Why It Matters”? 2005 Local Opposition in the United States”. Brookings ids 1:74402, https://doi.org/10.1103/PhysRev- 35. Drake, P. “Overview of Raytheon wind Institution, 2020, Washington D.C, USA Fluids1.074402 47. Fritsche, U., Benders, G., Cowie, A., Dale, farm mitigation techniques and test results”, pre- V, Kline, K., Johnson, F., Langerveld, H., Sharma, 58. Harris, RE; Davis, RA. “Evaluation of the Crotogino, F. “Large scale hydrogen sto- sented at the CNC/ATM, Orlando, FL, 2011. 25. N., Watson, H. “Global Land Outlook working pa- efficacy of products and techniques for airport rage”. In Soring Energy, Elsevier, 2016, pp.411- 36. Dröes, M; Koster, H. „Renewable Energy per : Energy and Land Use”, IRENA, 2019 bird control”, King City, Ontario, Canada: LGL 429 and Negative Externalities: The Effect of Wind Limited; 1998 48. Fuchs, G, Lunz, B; Leuthold, M. and Sau- 26. Cryan, P., Gorresen, P., Hein, C., Schir- Turbines on House Prices“. In Journal of Urban er, D.U (2012). “Technology overview on electric- 59. Herr M. “Design criteria for low-noise macher, M., Diehl, R, Huso, M., Hayman, D., Economics, vol. 96, pp 121-141 (2016), www.doi. ity storage: Overview on the potential and on the trailing edges”. 13th AIAA/CEAS Aeroacoustics Fricker, P., Bonaccorso, F., Johnson, D., Heist, K., org/10.1016/j.jue.2016.09.001 deployment perspectives of electricity storage Conference, 2007 Dalton, D. (2014), “Behavior of bats at wind tur- 37. Dumitrescu H; Cardos V; Dumitrache A; technologies”. Aachen: ISEA bines” PNAS 60. Her Majesty’s Government. “Industrial Frunzulica F. “Low frequency noise prediction of 49. Gallardo-Hernando, B., Perez-Martinez., Strategy; Offshore Wind Sector Deal”, policy- Crum, T., Ciardi, E., Sandifer, J. “Wind vertical axis wind turbines”. Proceedings of the 27. Aguado-Encabo, F. (2010), “Wind Turbine Clut- paper, March 2019 farms; Coming soon to a WSR-88D near you”, Romanian Academy, 2010; 11 (1): 47-54

88 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 89 61. Hezaveh, S., Zeid, E., Dabiri, J., Kinzel, 70. International Energy Agency. “Energy 79. Kaza, N.; Curtis, M. “The land use energy European protected Species (bats) at Onshore M., Cortina, G, Martinelli, L. (2017) “Increasing Policies of IEA Countries: Switzerland 2018 Re- connection”. In Journal of Planning Literature, 29 Wind Turbine Sites to inform Risk Management”, the Power Production of Vertical-Axis Wind-Tur- view”, IEA, Paris, 2018 (4): 1-16 Final Report, University of Exeter bine Farms Using Synergetic Clustering”, Spring- 71. International Energy Agency. “Global 80. Kelly, S. “Fundamentals of Mechanical 91. Matthews, J.; Lord, J.; Pinto, J. “RCS Pre- er, Princeton University, USA Energy &CO₂ Status Report 2019: Emissions”, Vibrations”, Second Edition, McGraw Hill, 2000 diction for Stealthy Wind Turbines”. In Proceed- 62. Hodos, W (2003). “Minimization of IEA, Paris: 2019 ings of the European Conference on Antennas 81. Kern, L., Seebass, J., Schlüter, J. (2019), Motion Smear: Reducing Avian Collisions with and Propagation, Nice, France, 6-10 November, 72. Isom, B., Palmer, R., Secrest, G., Rho- “Das Potenzial von vertikalen Windenergiean- Wind Turbines”. University of Maryland/National 2006 ton, R., Saxion, L., Allmon, T., Reed, J., Crum, T., lagen im Kontext wachsender Flächendennut- Renewable Energy Laboratory, NREL/SR-500- Vogt, R. “Detailed observations of wind turbine zungskonflikte und Akzeptanzprobleme der 92. Matthews, J., Sarno, C., Herring, R. “In- 33249, Colorado, USA clutter with scanning weather radars”, In Journal Windenergie”, Energiewirtschaft (2019), https:// teraction of Wind Turbines with Radar Systems”. 63. H. Hubbard & K. Shepherd. “Aeroacous- of Atmospheric Ocean Technology, 2009, 26, pp. doi.org/10.1007/s12398-019-00264-7 In Proceedings of the 2008 Loughborough Anten- tics of large wind turbines”. In Journal of Acoustic 894-910 nas and Propagation Conference, Loughborough, 82. Kinzie K; Drobietz R; Petitjean B and Society of America, 1991, Volume 89, No 6, pp. UK, 17-18 March 2008, pp. 461-464 73. International Telecommunication Union Honhoff S (2013). “Concepts for wind turbine 2495-2508 (ITU-R). “Technical and Operational Aspects of sound mitigation”. AWEA Wind Power 93. May R.; Hamre O.; Vang R.; Nygard T. Hui, I; Cain, B.E; Dabiri, J.O. “Public re- ground-Based Meteorological Radars. Recommen- “Evaluation of the DTBird Video-system at the 64. 83. Lagrange, H.; Roussel, E.; Ughetto, AL.; ceptiveness of vertical axis wind turbines”. In En- dation ITU-R”; Technical Report M.1849; Interna- Smøla Wind-Power Plant. Detection Capabili- Melki, F.; Kerbiriou, C. “Chirotech – assessment ergy Policy, vol 112, pp. 258-271 (2018) tional Telecommunication Union, Geneva, Swit- ties for Capturing Near-turbine Avian Behavior”. of research programme 2006-2011, Vilnius, 2011, zerland, 2009 NINA Report 910, 2012 65. Hötker H.; Thomsen K.; Jeromin H. “Im- Jerez, 2012, Bourges 2012. pacts on biodiversity of exploitation of renew- 94. Meyer, F (2013). “Storing wind energy 84. Loss, S.” Will, T,” Marra P. “Estimates able energy sources: the example of birds and underground”, FIZ Karlsruhe – Leibniz Institute 74. Jakobsen, J., Anderson, B. (1993), “Aero- of bird collision mortality at wind facilities in the bats – facts, gaps in knowledge, demands for fur- for Information Infrastructure, Eggenstein Leop- dynamic Noise from Wind Turbine Generators: contiguous United States”. In Biological Conser- ther research, and ornithological guidelines for oldshafen, Germany Experiments with Modification of Full scale vation, Volume 168 (2013), pp. 201-209 the development of renewable energy exploi- Rotors”, Danish Acoustical Institute, EFP, No 95. Moeller, H., Pedersen, C. “Low-frequen- tation”. Michael-Otto Institut in NABU 2006; 85. Lundquist, E “Belgian Navy Sees Coop- 1364/89-5 JOUR-CT 90-0107, pp. 1-97, June cy noise from large wind turbines”, In Acoustic Berghausen, Germany eration Opportunities for Wind Farm Industry”. 1993 Society of America, 2011; 129 (6), pp. 3727-3744 Sea-power Magazine, 12 February 2019. 66. Hübner, G., Löffler, E. (2013), „Wirkun- 75. Jallouli J; Moreau G. “An Immersive 96. Muñoz, A.; Ferrer, M; de Lucas, M.; Casa- gen von Windkraftanlagen auf Anwohner in der 86. Lute, C., Wieserman, W. “ASR-11 Radar Path-Based Study of Wind Turbines’ Landscape: do, E. “Raptor mortality in wind farms of southern Schweiz: Einflussfaktoren und Empfelungen (Im- Performance Assessment over a Wind Turbine A French Case in Plouguin”. In Renewable Energy, Spain: mitigation measures on a major migration pact of wind turbines on residents in Switzerland: Farm”, In Proceedings of the 2011 IEEE Radar Vol 34, pp. 597-607 bottleneck area”, Proceedings of the conference Impact factors and recommendations). In Insti- Conference, Kansas, MO, USA, 23-27 May 2011, on wind energy and wildlife impacts, 2-5 May tut für Psychologie der Martin-Luther Universität, 76. Jameson J; Willis C. “Activity of tree bats pp. 226-230 2011, Trondheim, Norway: Norwegian Institute Halle, Wittenberg, Germany at anthropogenic tall structures: implications for 87. Malik, H. “Electromagnetic Waves and for Nature Research mortality of bats at wind turbines”. In Animal Be- 67. Hübner, G., Pohl, J., Hoen, B., Fires- Their Application to Charged Particle Accelera- havior, Volume 97, November 2014, pp. 145-152 97. Möllerström, E; Larsson, S; Ottermo, tone, J., Rand, J. (2019), “Monitoring annoyance tion”, article in Intech 2013 F; Hylander, Baath, L. “Noise Propagation from and stress effects of wind turbines on nearby 77. Kamaruzzaman, M.; Hurault, J.; Mad- 88. Marx, G. “Le Parc Eolien Français et Ses a Vertical Axis Wind Turbine”. Presented at the residents: A comparison of U.S and European sen, K. “Wind turbine Rotor Noise Prediction & Impacts Sur l’avifaune – Étude Des Suivis de Mor- International Noise (2014) samples”, Environment International 132 (2019) Reduction for Low Noise Rotor Design”, 7th Inter- talité Réalisés En France de 1997 à 2015; LPO, 105090 national Conference on Wind Turbine Noise, Rot- National Wind Coordinating Commit- France: Rochefort, 2017; p.92 98. terdam, 2 to 5th May, 2017 tee. “Permitting of Wind Energy Facilities: A Iida A; Mizuno A; Fukudome K. “Numeri- 68. 89. Mascarenhas, M., Marques, A., Ramalho, Handbook, “RESOLVE”. NWCC, Washington D.C, cal simulation of aerodynamic noise radiated 78. Karlson B.; LeBlanc B.; Minster D.; Es- R., Santos, D., Bernardino, J., Fonseca, C. “Bio- USA, 1998 from vertical axis wind turbines”. Proceedings till D.; Miller,B.; Busse F.; Keck C.; Sullivan J.; diversity and Wind Farms in Portugal – Current of the 18th International Congress on Acoustics; Brigada D.; Parker L.; Younger R.; Biddle J.; Biddle Nicholls, B; Racey, PA. “The aversive Knowledge and Insights for an Integrated Impact 99. Kyoto, Japan, 2004 J. “IFT &E Industry Report: Wind Turbine-Radar effect of electromagnetic radiation on foraging Assessment Process”, Springer berlin Heidelberg: Interference Test Summary (Technical Report)”. bats – a possible means of discouraging bats from International Energy Agency. “Energy New York, NY, 2018 69. SAND2014-19003. Sandia National Laboratories approaching wind turbines”, PLoS one 2009; 4: Policies of IEA Countries: Belgium 2016 Review”, (SNL), Albuquerque, NM (US). 90. Mathews, F., Richardson, S., Lintott, P., e6246. IEA, 2016, Paris, France Hosken, D. (2012) “Understanding the Risks to

90 ENERGY HIGHLIGHTS ENERGY HIGHLIGHTS 91 100. Norin, L., Haase, G. (2012). “Doppler nate-the-energy-storage-future/. Butchart, Newbold, T., Green, R., Tobias, J., 134. Van den Berg, F. “Criteria for a wind Weather Radars and Wind Turbines”, Swedish Foden, W., O’Brien, S., Pearce-Higgins., J. “Bird farm noise: Lmax and Lden”, In The Journal of the 112. Rivard, E., Trudeau, M. and Zaghib. K Meteorological and Hydrological Institute and bat species’ global vulnerability to collision Acoustical Society of America, June 2008 (2019). “Hydrogen storage for mobility: A re- mortality at wind farms revealed through a trait- 101. Oerlemans, S., Sijtsma, P., Mendez- view”, MDPI, 12 (1973), pp. 1-22 135. Van der Zee, H.T.H (2016). “Obstacle based assessment”, Royal Society, UK, 2017 Lopez, B. “Location and quantification of noise lightning of onshore wind: balancing aviation 113. Rodrigues, S. (2012). “Aeroacoustic Op- sources on a wind turbine”, In Journal of Sound Thiel, A., Schouten, M., de Jong, W. “A safety and environmental aspects”. The Nether- timization of Wind Turbine Blades”, Tecnico Lis- 124. and Vibration, 299, pp. 869-883, 2007 Radar and Wind Turbines: A Guide to Acceptance lands Aerospace Center, Amsterdam, NL boa Criteria”. In Proceedings of the 2010 IEEE Interna- 102. Oerlemans S; Fischer M; Maeder T and 136. Van Treuren, K. (2018). “Wind Turbine 114. Rodrigues, L.; Bach, L; Dubourg-Savage, tional Radar Conference, Arlington, VA, USA, 10- Kögler K. „Reduction of wind turbine noise using Noise: Regulations, Siting, Perceptions and Noise M.; Karapandza, B.; Kovac, D.; Kervyn, T.; Dekker, 14 May 2010, pp. 1355-1361 optimized airfoils and trailing-edge serrations”. In Reduction Technologies”, Proceedings of Mon- J.;Kepel, A.; Bach, P.; Collins, J.; Harbusch, C.; AIAA Journal 2009; 47 (6), pp. 1470-1481 Tsoutos T; Zacharias G; Stefanos K; Elpi- treal 2018 Global Power and Propulsion Forum 7th Park, K.; Micevski, b.; Minderman, J. “Guidelines 125. da P (2007). “Aesthetic Impact from Wind Parks” – 9th May, 2018 103. Palmer, R. “Impacts of wind turbine sit- for Consideration of Bats in Wind Farm Projects”, ing on radar clutter mitigation”, Conference Pa- Revision 2014; EUROBATS Publication Serie; 126. Tunnicliffe, A. “Aviation and wind farms: 137. Voight, C.; Roeleke, M.; Marggraf, L.; Pe- pers. 2013, USA UNEP/EUROBATS: Bonn, 2015; pp. 133. working together for a safer future”. Interview tersons, G.; Voight-Heucke, S. “Migratory Bats with the representatives of RenewableUK and Respond to Artificial Green Light with Positive 104. Pawlaczyk-Luszczynska, M; Dudarewicz, 115. Rogers, T., Omer, S. “The effect of tur- NATS, Airport Technology, 23 July 2020 Phototaxis”, PLoS One, 2017, 12 (S), e0177748 A; Zaborowski K; Zamojska-Daniszewska, M. bulence on noise emissions from a microscale “Annoyance Related to Wind Turbine Noise”. In horizontal axis wind turbine”, In Renewable En- 127. Uddin, N; Asce, M. (2003), “Preliminary 138. Voigt, c.; Rehnig, K.; Lindecke, O.; Pe- Acoustics, Volume 39, No 1, pp. 89-102 (2014) ergy 2012; 41, pp. 180-184 design of an underground reservoir for pumped tersons, G. “Migratory Bats Are Attracted by Red storage”. In Geotech Geological Engineering, Vol Light but Not by Warm-White Light: implica- 105. Pedersen, E. “Human response to wind 116. Romeo-Sanz, I.; Matesanz, A. “Noise 21: 331-355 tions for the Protection of Nocturnal Migrants”. turbine noise: Perception, annoyance and mod- management on modern wind turbines”. In Wind In Ecology Evolution, 2018, 8 (18), pp. 9353-9361 erating factors”. PhD thesis: University of Go- Engineering, 2008, 32, pp. 27-44. 128. United Nations Environmental Program. thenburg; 2007 “The Emissions Gap Report 2016: A UNEP syn- 139. Zimmerling, JR, Francis, CM (2016). 117. Rydell J; Bach L; Dubourg-Savage M; thesis report”, Nairobi: United Nations, Environ- “Bat mortality due to wind turbines in Canada”. 106. Poot H.; Ens BJ.; de Vries H; Donners Green M; Rodrigues L; Hedenström A. „Mortality ment Programme In Journal of Wildlife Management, volume 80, M.; Wernard MR.; Marquenie JM. “Green light for of bats at wind turbines links to nocturnal insect pp. 1360-1369 (https://dx.doi.org/10.1002/ nocturnally migrating birds”. In Ecological Sci- migration“. In European Journal of Wildlife Re- 129. University of Newcastle. “Visual Assess- jwmg.21128) ence 2008, vol 13, Issue 13, p. 47 search, 2010, 56 (6), pp. 823-827 ment of Windfarms Best Practice”. Scottish Nat- ural Heritage Commissioned Report F01AA303A, 140. Wagner, S., Bareiss, R., Guidati, G. 107. Raphael, T. “Welcome to Boris Johnson 118. Schepers, J. “SIROCCO: Silent rotors by UK (2012), “Wind turbine noise”. Berlin: Springer (Green) Revolution”. Bloomberg News, 19 No- acoustic optimization”. In Second International 2012 vember, 2020 Meeting on Wind Turbine Noise, Lyon, France, 130. US Department of Energy (2010). Al- 2007. ternatives to electricity for transmission and an- 141. Wang, W. (2013), “Detecting and Miti- 108. Rashid, L.; Brown, A. “Partial Treatment nual-scale firming storage for diverse, stranded, gating Wind Turbine Clutter for Airspace Radar of Wind turbine Blades with Radar Absorbing Ma- 119. Skolnik, M. “Radar Handbook”, 3rd ed. renewable energy resources: Hydrogen and am- Systems”, In The Scientific World Journal, Volume terials (RAM) for RCS Reduction”. In Proceedings NY: McGraw-Hill, 2008 monia [Online]. Available from: https://www. 2013, http://dx.doi.org/10.1155/2013/385182 of the 4th European Conference on Antennas and 120. Smallwood, K.W; Karas, B (2009). “Avi- osti.gov/etdeweb/servlets/purl/21396853 Propagation”, Barcelona, Spain, 12-16 April 2010 Wang, F.; Zhang, L.; Zhang, B.; Zhang, an and bat fatality rates at old generation and re- 142. 131. U.S Department of Energy. “Federal In- Y.; He, L. “Development of wind turbine gearbox 109. RenewableUK Members’ Briefing Note. powered wind turbines in California”. In Journal of teragency Wind Turbine Radar Interference Miti- data analysis and fault diagnosis system”, Power “Aviation Safeguarding and Radar Mitigation: Wildlife Management, Volume 73, pp. 1062-1071 gation Strategy’. JANUARY, 2016, Washington and Energy Conference (APPEEC), 2011, Asia-Pa- introductory Overview”. Issue 1, 13 October, 121. Sorensen, J., Mikkelsen, R., Okulov, V., D.C cific. amended 29 January 2019 Troldborg, N., Shen, WS. “The Aerodynamics of 132. US Geological Survey. “Bat Fatalities 143. Wind Energy in Europe: Outlook to 110. ReNews Biz. “Germany advances tur- Wind Turbines”, Department of Mechanical Engi- at Wind Turbines – Investigating the Causes and 2023”, WindEurope, October 2019, Brussels, bine light relief”. Newsletter, 14 February, 2020 neering, Technical University of Denmark Consequences”, U.S Department of the Interior, Belgium 111. Renewable Energy World (2019). Why 122. Taylor, J., Eastwick, C., Lawrence, C., 2019; Washington D.C, USA Zayas, L.; J.; Derby M.; Gilman P.; An- lithium-ion technology is poised to dominate Wilson, R. “Noise levels and noise perception 144. U.S Office of Energy Efficiency and anthan S.; Lantz E.; Cotrell J.; Beck F.; Tusing R the energy storage future. [Online], https:// from small and micro wind turbines”, In Renew- 133. Renewable Energy. “Offshore Wind Research (2015). “Enabling Wind Power Nationwide”. U.S ww.renewableenergyworld.com/2019/04/03/ able Energy, Vol 55, July 2013, pp. 120-127 and Development”. U.S Department of Energy, Department of Energy. why-lithiumion-technology-is-poised-to-domi- 123. Thaxter, C., Buchanan, G., Carr, J., Washington D.C

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