Recent Advances in Finite Differences and Applied & Computational Mathematics

Wind Turbines & Weather Radar: A Review of the Problem T.G. KOSTIS1,2, A. K. GOUDOSIS2, I. DAGKINIS3, Ch.K.VOLOS1, N.V. NIKITAKOS3 1

2

Faculty of Mathematics and Engineering Studies Department of Military Science Hellenic Army Academy Vari, GR-16673 GREECE

Hellenic Quality Assurance Agency for Higher Education Leof. Syggrou 44, Athens 11742, GREECE 3

Key-Words: - Pulse Doppler Weather Radar, Wind Turbine, Interference, Renewable Energy Issues.

1 Introduction Doppler Radars and Wind Turbines have an asymbiotic relationship. Both wish to exist in the same environment of space and time but when doing so wind turbines pose great problems to Doppler radars. And this is important because Doppler radars are found in weather stations and air traffic control systems. Analytically wind turbines induce modulations in the Doppler radar that constitute false targets. Or these modulations can even make aircraft appear and reappear on the radar screen thus confusing the radar operator about the validity of a target. This paper will be of use to an audience that wishes to understand the technical foundations about the antagonistic relationship between Doppler

ISBN: 978-1-61804-184-5

radars and wind turbines. It is divided in six parts with this being the introduction. The next part reveals the intricacies of Pulse Doppler radars. There we will describe the operation of a Doppler weather radar and particularly explain its visibility potentials. Then in part three we will give an introduction to the wind turbine as a renewable energy form. In the following part four we will explain why this visibility potential of the pulse Doppler radar can be interfered by the modulations produced by the wind turbines and pose such great problems to the Doppler radarâ&#x20AC;&#x2122;s operation. In part five we will summarize the state-of-the-art solutions to this problem. And the last part provides the conclusions of this effort.

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Recent Advances in Finite Differences and Applied & Computational Mathematics

accuracy of the Doppler resolution. But these two characteristics are competitive with each other and we have the radar uncertainty principle. The radar uncertainty principle may sound familiar with the uncertainty principle of quantum mechanics but it is not. In the quantum mechanics field the uncertainty principle is a mathematical inequality that restricts to a limit the precision with which the position x and momentum p of a particle can be known simultaneously and with certainty. In radar engineering field this principle has another notion that low Pulse Repetition Frequency (PRF) eliminates range ambiguities but has velocity ambiguities and high PRF avoids velocity ambiguities but presents ambiguities in range. Therefore the logical upcoming question would be whether medium PRF multiple waveforms in the form of a schedule could provide a golden rule, in other words procure acceptable ambiguities for useful operational use. Actually medium PRF radars are the cornerstone of pulse Doppler radars. They are found in all related civilian (air traffic control) and military (surveillance and tracking) applications.

ISBN: 978-1-61804-184-5

3 Renewable Energy Systems The search for economical, renewable and sustainable solutions for electricity production, due to climate changes from fossil fuel emissions, has been focusing on solar, wind, biomass energy and is extracting energy from ocean waves and related water movements. Hence, if economical and technical solutions exist, the area of renewable energy exploitation would have a vast impact on the electricity production in the world. Wind energy, as a renewable energy source, is the kinetic energy of air in motion. Winds are produced by the movement of air that is caused as the sun warms the Earth's surface. This movement happens because some places of the Earth accept direct sun rays, while others get indirect sun rays, so different temperatures are created in the atmosphere. These differences arise the warm air, which weighs less. Then cold air moves and fills in the space that warm air used to occupy. This movement of air is what makes the wind blow. The terms "wind energy" or "wind power" describe the process by which the wind is used to generate mechanical power or electricity. How wind turbines exploit the wind energy? The Wind turbines convert the kinetic energy of the wind into mechanical power. This mechanical power can be used for specific tasks (such as

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Recent Advances in Finite Differences and Applied & Computational Mathematics

easily classified and rejected. Air traffic control and military personnel monitoring Doppler radar screens at installations important for civilian transport and homeland security may mistake a wind turbine for an aircraft or report nonexistent weather conditions. Moreover, this interference (clutter) may also create blind spots to the Doppler radar so that real or a small aircraft will not be seen, or disappear and reappear with all the grave consequences of this case.

grinding grain or pumping water) or a generator can convert this mechanical power into electricity used at homes, or integrate it to the electrical grid. Wind turbines, working like aircraft propeller blades, are rotate from the moving air and power an electric generator that supplies an electric current. Modern wind turbines are divided into two basic groups: the horizontal-axis variety, and the verticalaxis design, like the eggbeater-style Darrieus model, named after its French inventor. Most large modern wind turbines are horizontal-axis turbines and their components at a glance include: ď&#x201A;ˇ ď&#x201A;ˇ ď&#x201A;ˇ

blade or rotor, which converts the energy of the wind to rotational shaft energy, a drive train, usually including a gearbox and a generator, a tower that supports the rotor and drive train,

and other equipment, including controls, electrical cables, ground support equipment, and interconnection equipment. Today to achieve the economies of scale, the wind turbines group together into a single wind power plant, known as a wind farm, and generate bulk electrical power. These wind turbine farms are installed on mountain peaks or they are founded offshore as on floating or bottom supported platforms where potential wind energy is exploited. Electricity from these wind turbines is fed into a utility grid and is distributed to customers, just as with conventional power plants. Wind turbines are available in a variety of sizes, and therefore have power ratings. The largest machine has blades that span more than the length of a football field, stands on 20 stores high building, and produces enough electricity to power 1,400 homes. A small home-sized wind machine has rotors between 3 and 7 meters in diameter and stands at a height of 9 meters and can supply the power to all home electrics or a small business need.

4 Problem Formulation

5 Problem Solution

Therefore many wind turbines are grouped together in power farms, are placed in high elevations and have considerably big blade dimensions in order to produce a low cost kilowatt per hour utility. Unfortunately this configuration produces increased radar clutter to Doppler radar systems. Both the moving blades and the towers they sit on create false readings with a random nature that cannot be

ISBN: 978-1-61804-184-5

First of all older radar transmitters and receivers cannot mitigate the wind turbine problem. Therefore only modern solid-state components with specially designed waveforms and complementary reception processing abilities have the potential to further reduce false targets injected by renewable source energy moving part generators [11].

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Recent Advances in Finite Differences and Applied & Computational Mathematics

Concurrent Beam Processing, Improved Constant False Alarm Rate (CFAR), Clutter Map per Doppler Filter Optimization and Enhanced Tracking techniques. Prospective solutions will tend to extend the capability to deal with the clutter problem, for example [7]: Polarimetrics (Dual Polarization), by looking at the same target with multiple polarizations can deduce a conclusion about its validity. Pulse-burst (High PRF), high prf schedules induce more energy on the target and therefore can get stronger responses about the velocity of the contact. Blind Spot / Gap-Filler maybe with advanced medium PRF schedules that adaptively eliminate pulse Doppler radar blind areas of range and/or velocity.

ISBN: 978-1-61804-184-5

6 Conclusion The benefits of wind energy are valuable. It is a renewable resource that can provide energy both to the main electricity grid and to remote areas. On the other hand there is at least one hazard that although less obvious is of great importance; the injection of interference or clutter into Doppler radar systems. Considering that Doppler radars are used in civilian and military applications this is a problem that needs to be mitigated. There are numerous efforts that try to solve this problem. The main line of approach is the use of technology and the research of advanced pulse Doppler radars that will try to eliminate this interference using an adaptive clutter map methodology. In conclusion an air turbine is a radar target that we need it to be as stealthy as possible. In conclusion there are legal, operational, environmental and political issues that arise when wind turbines and operational pulse Doppler radars collide.

References: [1] Massachusetts Institute of Technology Lincoln Laboratory, Wind Turbine Impact Mitigation for QVN ARSR-3 Radar, Executive Summary, June 21, 2010, http://www.acq.osd.mil/ie/download/green_ene rgy/exec_sum_windturbinestudy.pdf. [2] B.M. Isom et al, Detailed Observations of Wind Turbine Clutter with Scanning Weather Radar, J. of Atmospheric & Oceanic, http://journals.ametsoc.org/doi/pdf/10.1175/20 08JTECHA1136.1

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Recent Advances in Finite Differences and Applied & Computational Mathematics

[3] Air Traffic Control Wind Farm Interference Mitigation, Raytheon Company, http://www.raytheon.com/newsroom/technolog y_today/2012_i2/airtraffic.htm [4] M. Brenner, Wind Farms and Radar, The MITRE Corporation, 2008. [5] Radar Cross Section Reduction of Wind Turbines, http://prod.sandia.gov/techlib/accesscontrol.cgi/2012/120480.pdf [6] Losco, Felix A.; Collick, Thomas F, When Wind Turbines and Radar Mix: A Case Study: Air Force Law Review, December 22, 2012 |. [7] P. Drake, Overview of Raytheon Wind Farm Mitigation Techniques and Test Results, , In. CNS/ATM Conference, 15 June 2011, http://www.afceaboston.com/documents/events /cnsatm2011/Briefs/03-Wednesday/Wednesday -PM%20Track-3/01-Drake-Wind%20Farm%20 Presentation-Wednesday%20Track3.pdf. [8] M. Kaveh et al, Wind Turbine Radar Interference, http://environment.umn.edu/e3/archive/archive _2010/E3_Kaveh.pdf [9] [http://www.nytimes.com/2010/08/27/business/ energy-environment/27radar.html?_r=0]. [10] [http://www.scientificamerican.com/article.cfm ?id=wind-farm-radar-clutter]. [11] [http://www.acq.osd.mil/ie/download/green_en ergy/exec_sum_windturbinestudy.pdf] [12] [http://prod.sandia.gov/techlib/accesscontrol.cgi/2012/120480.pdf]. [13] [http://www.raytheon.com/newsroom/technolo gy_today/2012_i2/airtraffic.html].

ISBN: 978-1-61804-184-5

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Wind Turbines & Weather Radar: A Review of the Problem

Wind Turbines & Weather Radar: A Review of the Problem

Wind Turbines & Weather Radar: A Review of the Problem

Wind Turbines & Weather Radar: A Review of the Problem