National Academies Press: OpenBook

Investigating Safety Impacts of Energy Technologies on Airports and Aviation (2011)

Chapter: Chapter Two - Energy Technologies and Types of Impacts

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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
×
Page 10
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
×
Page 11
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
×
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
×
Page 13
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Suggested Citation:"Chapter Two - Energy Technologies and Types of Impacts." National Academies of Sciences, Engineering, and Medicine. 2011. Investigating Safety Impacts of Energy Technologies on Airports and Aviation. Washington, DC: The National Academies Press. doi: 10.17226/14590.
×
Page 14

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7This section of the report describes the energy technologies of interest and the types of impacts that they may produce. This chapter also summarizes the types of information avail- able for assessing existing impacts of energy technologies on airports and aviation, including reviewing the regulatory def- inition of airspace that is used to evaluate potential impacts. ENERGY TECHNOLOGIES The energy technologies that are analyzed in this report are solar power [both photovoltaic (PV) and concentrating solar power (CSP)], wind turbine generators (WTGs), and traditional power plants. The report also considers issues associated with the new electric transmission infrastructure necessary for delivering the electricity from these new facilities to high energy consumption load centers. Solar Photovoltaics and Concentrating Solar Power A solar PV system is made up of various components that collect the sun’s radiated energy, convert it to electricity, and transmit the electricity in a usable form. The main component is the solar panel, which is typically comprised of 40 individ- ual solar cells made from silicon that convert sunlight into electricity (see Figure 1). The panels are held in place by a frame that is either fastened to an existing structure or placed atop a stand that is mounted on the ground. Panels are covered by a thin layer of protective glass and the panel is attached to a substrate of thermally conductive cement that traps waste heat produced by the panel and prevents it from overheating. Several panels connected together in series are identified as a “string” and often operate as a single generating unit. Multi- ple strings assembled into one solar facility are referred to as an “array.” Other types of PV technologies include thin film and multi-junction versions. Solar PV systems may consist of just a few panels providing electricity to a single building or cover tens to hundreds of acres and transmit electricity to the power grid. Utility-scale solar plants are connected to the electricity grid by networks of transmission towers and high- voltage electrical lines (NREL 2010a). CSP systems use reflective mirrors in large arrays to focus the sun’s energy on a fixed point producing intense heat, which is then converted to electricity. The most common means for producing electricity in these systems is to heat water and produce steam, which drives a turbine, usually for the pur- pose of supplying commercial power to the grid. Three CSP designs are parabolic troughs, power towers, and dish engines (NREL 2010a). Parabolic troughs continually track the sun and concen- trate the sun’s heat onto receiver tubes filled with a heat trans- fer fluid (see Figure 2). The fluid is heated up to 750°F then pumped to heat exchangers that transfer the heat to boil water and run a conventional steam turbine producing electricity. Parabolic troughs have been producing 350 MW of utility- scale electricity at a site in the Mojave Desert for more than 15 years (NREL 2009). Whereas parabolic troughs focus sunlight to receivers located on each individual unit, power towers focus all the facility’s sunlight to a single receiver (see Figure 3). The power tower facility is comprised of individual heliostats (mirrors) that track with the sun. Each heliostat reflects sunlight onto the central receiver at the top of a tower. As with the para- bolic trough, a heating fluid transfers heat to create steam to drive a turbine and produce electricity. A 10 MW power tower pilot project is operating in Barstow, California (DOE 2008). A dish engine, also referred to as a dish stirling (Figure 4), is a stand-alone parabolic reflector that concentrates light onto a receiver positioned at the reflector’s focal point. The col- lected heat is utilized by an engine located at the focal point. They typically use two axes tracking to maximize potential solar radiation as its position in the sky changes (NREL 2010a). There are no commercial scale dish engine facilities in oper- ation. However, there is a 150 kW demonstration project at DOE’s Sandia National Laboratories (NREL 2011). As with traditional fossil and biofuel-fired power plants, CSP facilities boil water and drive a steam turbine. There- fore, they are equipped with either an evaporative wet or dry cooling system. Wind Turbine Generators WTGs convert air blowing across the earth’s surface into electricity. The WTG’s rotor is comprised of the rotor hub and typically three blades (see Figure 5). Behind the rotor is attached a box called the nacelle, which encloses the turbine CHAPTER TWO ENERGY TECHNOLOGIES AND TYPES OF IMPACTS

8FIGURE 1 Solar PV on roof [courtesy: Harris Miller Miller & Hanson Inc. (courtesy: HMMH)]. FIGURE 3 Power Tower at Sandia National Laboratories (courtesy: Dr. Clifford Ho, U.S. DOE, Sandia National Laboratories). FIGURE 2 Parabolic solar collector (courtesy: HMMH). FIGURE 5 Wind turbine schematic (courtesy: HMMH). and other equipment necessary for generating electricity. The nacelle sits on top of a tower. The WTG is secured to the ground using concrete and/or bolt anchors depending on the composition of the substrate. WTGs may be sited as single units providing local power or in expansive wind farms comprised of hundreds of units that contribute electricity to the electrical grid. Utility-scale wind turbines constructed on land can be as high as 500 ft above ground level to the blade tip height. Large wind farms are connected to the grid through traditional electric transmission infrastructure comprised of transmission towers and high-voltage lines (NREL 2010b). Utility-scale wind turbines are operating in 37 states, with Texas, Iowa, and California the top three states in generating capacity (AWEA 2011). Traditional Power Plants Traditional power plants utilize conventional fossil fuels and biofuels to make steam and drive a turbine to produce elec- FIGURE 4 Dish stirling at Sandia National Laboratories (courtesy: Dr. Clifford Ho, U.S. DOE, Sandia National Laboratories).

9tricity (see Figure 6). Because the fuel they run on is always available (unlike renewable sources), these plants provide base load electricity to the grid. Older plants operate with coal and oil, whereas newer plants typically utilize natural gas or bio- fuels, which comply with modern environmental regulations. Some smaller capacity plants, known as peakers, are being developed that can start up quickly during periods of peak energy consumption. Peakers typically fire up during the sum- mer months when air conditioners are operating or in the win- ter during periods of extreme cold when heaters are operating. Peaker plants are less efficient than base load plants and typi- cally have higher exhaust velocities and temperatures because they lack a heat recovery steam generator. This type of gener- ator extracts heat in the flue gas producing cooler exhaust tem- peratures and lower exit velocities. Because peaker plants can be designed with shorter stacks, they may not trigger an air- space review. In addition, the shorter stack produces a greater dispersion of the plume lower to the ground. When located near an airport, these high temperatures and exhaust velocities can create turbulence for aircraft passing through the plume. Traditional power plants require a cooling system to cool the exhaust steam for reuse. Cooling towers release heat pro- duced in the steam generation process and transfer it back to the environment, either to the water or air. There are two types of cooling towers: evaporative wet cooling and dry cooling. The mechanics of the systems vary; however, the end process is the same, to remove heat and cool water for reuse. They can use either evaporation to remove the excess heat and cool the liquid (wet cooled) or rely on air to cool the liquid to the ambient temperature (i.e., air cooled). Evaporative wet cool- ing systems release moisture into the air to transfer heat. Air- cooled condensers transfer heat to the ambient air not unlike an automobile radiator. The air-cooled condenser maximizes surface area for transfer of the heated steam exhaust to the sur- rounding air and fans blow the heated air skyward. Because water is denser than air its heat carrying capacity is greater, making wet cooling a more efficient heat transfer mechanism. However, owing to concerns about water scarcity, new power plants are often required to assess the feasibility of dry cooling. Electrical Transmission Infrastructure Transmission lines consist of towers and high-voltage lines necessary for carrying power produced at energy-generation facilities across distances to areas where the electricity is con- sumed (see Figure 7). Typically, new transmission lines are built to deliver electricity to locations where the lines can be integrated into the existing regional and local electrical network. The height of the towers can vary; however, taller towers generally mean that they are fewer in number, which tends to be more economical. Tower height and distance fol- low industry-published design guidelines (ASCE 1997; IEC 2003). Conventional towers are approximately 150 ft high. Because many new energy-generation technologies are located in remote areas, transmission lines are an important compo- nent of the energy project. ASSESSING IMPACTS This section describes information available for assessing impact. First, the definition of navigable airspace is provided to establish the geographic area where impacts can be pro- duced. Second, the forum for reviewing potential impacts (i.e., the regulatory process) is summarized to provide an under- standing of what processes are requiring the impact studies. Third, the community that is impacted by proposed energy projects is described. And fourth, the types of information that have been generated directly and indirectly as the result of regulatory reviews are summarized providing a snapshot of the current knowledge base. Defining Airspace One of the FAA prime objectives authorized by statute is to ensure the safety of air navigation and the efficient utilization of navigable airspace by aircraft (FAA 2008a). Under Title FIGURE 6 Power plant (courtesy: U.S. EPA website). FIGURE 7 Transmission lines at sunset (courtesy: HMMH).

49 of the United States Code, Section 40103(a)(1), “the United States Government has exclusive sovereignty over airspace of the United States.” The National Airspace System is a limited resource. New structures and activities that infringe on air- space are continuously proposed. It is the FAA’s responsi- bility to evaluate the significance of each proposal. When conflicts arise concerning a structure being studied, the FAA may advocate the need for conserving the airspace for aircraft; preserving the integrity of the National Airspace System; and protecting air navigation facilities from encroachments such as physical penetrations, electromagnetic interference, and visual impairments that would preclude normal operation. ACRP recently funded a principal reference for understand- ing airspace review (LeighFisher 2010). 14 CFR Part 77 provides the following regulatory guidance for FAA’s authority relative to airspace protection: (1) establishes standards for determining obstructions to navigable airspace (2) sets forth the requirements for notice of certain pro- posed construction or alteration (3) provides for aeronautical studies of obstructions to air navigation to determine their effect on the safe and efficient use of airspace (4) provides for public hearings on the hazardous effect of proposed construction or alteration on air navigation. Furthermore, “[t]he standards established in determining obstructions to air navigation are used by the Administrator to impose requirements for public notice of the construction or alteration of any structure where notice will promote air safety. Notices are used to provide the basis for determina- tions of possible hazardous effect of the proposed construc- tion or alteration on air navigation.” Airspace, as defined by federal regulation, begins at a height of 200 ft above ground level and extends upward. In closer proximity to airports and military installations, where aircraft approach and descend, the height of airspace is less than 200 ft. The FAA regulations refer to the invisible bound- aries that demarcate airspace as imaginary surfaces. These imaginary surfaces extend out from the runway in a manner that reflects where aircraft are likely to fly while also accom- modating unforeseen aircraft maneuvers. The height above the ground of the imaginary surface is lowest near the runway and increases at distance from the runway. State and local author- ities have attempted to regulate areas below 200 ft as airspace as a result of localized concerns about the impact of shorter structures on aviation. The FAA is responsible for conducting obstruction evalu- ations to determine potential impacts on airspace. Specifically, the evaluation may consider the effects on public use and mil- itary airports and aeronautical facilities; visual flight rule and instrument flight rule aeronautical departures, arrivals, and en route operations, procedures, and minimum flight altitudes; 10 physical, electromagnetic, and line-of-sight interference on navigation, communications, radar, and control system facil- ities; and airport traffic and service capacity (FAA 2008a). The FAA has established clear thresholds for defining airspace and created a notification process for requiring project proponents to notify the FAA of projects that may impact airspace. The definition of airspace is described in the section Physical Penetration of Airspace in this chapter. The process for evaluating potential hazards is described in Order JO 7400.2G, Procedures for Handling Airspace Mat- ters (FAA 2008a). For off-airport projects, proponents file a Form 7460 with the FAA Office of Obstruction Evaluation/ Airport Airspace Analysis (OE/AAA). The OE/AAA is a par- ticular office under FAA’s Air Traffic Organization whose responsibility it is to coordinate the FAA’s review of poten- tial hazards to air navigation. Regulatory Review Processes The energy technologies discussed in this report typically trigger federal, state, regional, and local permitting processes before being constructed. Under conventional project permit- ting, applications are filed, hearings are convened, presenta- tions are made, public input provided, and permit decisions rendered based on existing laws and regulations. Through this process, impact analyses are generated. In some cases, independent government studies may be initiated where the permitting process has not adequately resolved the issue. The primary regulatory processes associated with energy tech- nologies and impacts on aviation are described here. OE/AAA The FAA’s OE/AAA Division undertakes aeronautical studies to assess the potential impacts of a project on air navigation. It distributes the notice to representatives of the various FAA lines of business, including airports, technical operations, services, frequency management, flight standards, flight pro- cedures office, and military representatives. Each division has the responsibility of providing comments on the potential impacts of a proposal on its area of authority and expertise. As an example, air traffic personnel is responsible for identi- fying whether the structure impinges on airspace; assessing effect on existing and proposed aeronautic operations, traffic control procedures, and traffic patterns; providing comment on mitigation opportunities including marking and lighting; identifying when negotiations with sponsors are necessary; determining when circulation is necessary and coordinating that process; collecting all comments; and issuing the deter- mination. Technical operations staff identifies electromag- netic and/or physical effects including the effect of sunlight and reflections on air navigation and communication facilities. Upon completing the aeronautical study and obtaining input from the various divisions and organizations involved

11 in the review, the OE/AAA issues a hazard determination on the proposed structure or activity. If the project will not impact aviation, the OE/AAA will issue a Determination of No Hazard. If an impact is identified, the OE/AAA will issue a Determination of Presumed Hazard, the reason for the hazard, and changes that could be made to avoid the hazard. Unless the applicant agrees to the changes in writing, the Notice of Presumed Hazard will be reissued as a Determi- nation of Hazard as the FAA’s final determination on the matter. The determination, however, is not a permit enforce- able by law but is instead part of a notification process to identify potential hazards to aviation, require marking and lighting of potential hazards to minimize potential risk to avi- ation, and update aeronautical charts and flight procedures for pilots to avoid the hazard. In reality, however, a hazard determination is sufficient enough to deter project financing and underwriting owing to the potential liability associated with the determination. As an example, most utility-scale wind turbines are greater than 200 ft in height and are subject to airspace review by the OE/AAA. The receipt of a hazard determination from the FAA for a proposed wind turbine is considered by project developers to be a fatal flaw, thereby negating the project. National Environmental Policy Act Projects conducted by federal agencies, hosted on federal lands, financed with federal funds, or requiring a federal per- mit are subject to review under the National Environmental Policy Act (NEPA). Under NEPA, the lead federal agency responsible for the federal action facilitates a broad public review of the project that includes a variety of environmen- tal analyses such as potential impacts on transportation sys- tems. Applicants file reports and analyses that form the basis of a decision (known as an Environmental Impact Statement or EIS) by the lead agency regarding the project’s compli- ance with NEPA. Because the NEPA review is broad, it typ- ically catches all the possible environmental issues that a project might affect. EISs are rich with analyses of potential impacts of projects on airports and aviation. As noted earlier, the FAA Hazard Determination is not a permit and therefore is not considered a federal action for the purposes of NEPA. It alone cannot trigger a NEPA review. As a result, projects with potential aviation impacts will not be subject to a NEPA review unless there is another issue that triggers NEPA. Furthermore, project developers may not consider prepar- ing a Form 7460 for an airspace review until the latter stages of the regulatory process unless their project is located close to an airport and aviation issues are raised in the broader per- mitting context. This has been a common occurrence that has put the FAA in the challenging position of issuing a hazard determination for a project that has otherwise substantially pro- gressed and achieved regulatory approvals (Globa, personal communication, 2010). This is much in contrast to projects sub- ject to NEPA review that provide a forum for early comment from all agencies including the FAA. Recognizing the importance of the NEPA review for avi- ation impact issues, the Department of Defense (DoD) and Bureau of Land Management (BLM) have executed a mem- orandum of agreement (MOA) to evaluate and resolve con- flicts associated with projects proposed on BLM land. This is of consequence because the BLM has been issuing leases for energy projects on federal lands. Although the BLM is already obligated under NEPA to solicit input from other federal agencies, the MOA provides the aviation community and the military with an early notification process. Therefore, when the BLM initiates a process to lease land to an energy development company, the DoD is one of the parties notified about the project and can provide comment on facilities and activities and potential adverse impacts. Although the FAA is not party to the MOA, the BLM is obligated to notify the FAA under NEPA. In April and May of 2010 a military planning group com- prised of representatives from the Army, Navy, and Air Force, commented to the BLM that six wind farm projects in the Mojave Desert near Barstow, California, could negatively impact military activities in the area. The DoD reported that the projects will constrain flight operations, interfere with radar, and increase the chance of collisions. Those comments prompted one of the developers who had proposed three of the six projects to withdraw its applications for approval. State and Regional Regulatory Review State and regional regulatory authorities may facilitate broad environmental reviews of projects similar to those completed under NEPA. These reviews authorized under state legisla- tion (sometimes referred to as “little NEPAs”) are coordi- nated by state environmental agencies and/or state energy commissions. Some state and regional regulatory reviews require that FAA notification be secured as part of a land use permit. This was the case with the Shepherd Flats Wind Farm in the Columbia River Region of Washington State. Some friction between the different levels of government that are considering the potential impacts of energy projects on aviation has been reported. Local authorities see local issues and are concerned that state and federal authorities do not rec- ognize them. Meanwhile, decisions by state energy authorities may override local laws, regulations, ordinances, and standards owing to the overall public good in developing energy proj- ects (CEC 2010a). Projects proposed on federal land may be exempt from local and county land use regulations further leav- ing the local voice unheard (Riverside County 2010). Finally, the FAA has made it clear that airspace cannot be disparately defined and regulated across the country, making Part 77 the basis for all airspace regulation decisions (Whitlow 2009).

The Impacted Community Regulations have been developed to protect a resource (defined in chapter two as airspace) and to protect a user group of the airspace (i.e., pilots and the customers they serve). It is logical to ask about the community that is impacted by energy projects and what types of users exist. The affected community starts with the commercial aviation industry that operates from large and medium-sized airports across the country. Airlines provide a passenger transportation service for business and leisure that enhances businesses from each departure and arrival destination. Aircraft also transport commodities, particularly perishables and express packages that require short delivery times. Smaller general aviation (GA) airports across the country provide essential transportation between remote areas that are otherwise difficult to access by other means. GA airports are also home base for a large community of aviation enthusiasts who fly their own planes for recreational purposes. In addition, many GA airports operate flight training schools for teaching new pilots, while also supporting local airplane services from essential business activities such as crop dusting to entertain- ment activities such as sky diving and gliding. Finally, heliports are used by helicopters serving a variety of functions from medical flights to remote land surveying to metropolitan traffic reporting. Each project that is proposed that impinges on and degrades airspace has the potential to affect one or more of these user groups. The Current Knowledge Base Because many of the energy technologies assessed in this report are being deployed primarily by private developers at a larger scale in new geographic areas and at a more rapid pace, much of the existing information on potential impacts is found in federal and state environmental permit applica- tions submitted as part of regulatory approvals. Applicants file EISs for projects subject to NEPA, which describe a variety of potential project impacts. As these reviews are distributed for broad public comment, interest groups and organizations across the social spectrum submit written comments about how the proposed project may cause negative impacts, prompting the administering agency (under NEPA it is the lead federal agency) to require the applicant to study the impact and report the findings. In some cases, federal authorities have recognized a poten- tially systemic problem associated with a certain technology and has commissioned an independent analysis to define the potential impacts and assess the level of impact and potential ameliorating circumstances. An example of this described later was when the U.S. Air Force expressed concern about the impacts of large wind farms on the ability of the Air Force to train pilots, thereby affecting “military readiness.” 12 In other cases, the DOE has collaborated with other fed- eral agencies to conduct studies to assess potential impacts of new energy technology. One example of this collaboration is the research being undertaken by the Sandia National Labo- ratories to assess the effects of glare from CSP projects. To supplement the various permitting documents and gov- ernment reports, experts in the field of assessing emerging energy technologies and their potential impacts on airports and aviation were interviewed for this report, and their con- tributions are discussed throughout. As a result of a large volume of new energy proposals, a significant amount of analysis has been conducted on the types of impacts identified in this study. Some of these are summa- rized in the following sections. To assess impacts, these analy- ses could be compared with regulatory performance standards. However, in most cases, a clear threshold of impact has not been promulgated. TYPES OF IMPACTS The types of impacts identified during the preparation of this report included: (1) physical penetration of airspace, (2) communications systems interference, (3) visual impacts from glare, (4) wind turbine turbulence, (5) thermal plume turbulence, and (6) visual impacts of vapor plumes. Physical Penetration of Airspace Some objects exceed heights that penetrate aviation imaginary surfaces and thereby impact airspace. Any object that is 200 ft above ground level is determined to penetrate into airspace. Objects that are less than 200 ft in height but within 20,000 ft of an airport runway longer than 3,200 ft (or 10,000 ft for a run- way less than 3,200 ft) may still penetrate airspace depending on relative distance to the airport. In addition, some structures less than 200 ft above ground level, such as meteorological test towers, have been identified by local authorities as being a potential hazard. Airports are required to maintain vegetation, site new airport development, and manage any temporary construc- tion activity to ensure that airspace around runways is clear of objects. Any proposed structure off-airport that is 200 ft in height and/or within 20,000 ft from an airport runway has the potential to penetrate airspace. Applicants conduct a Section 14 CFR 77 (Objects Affecting Navigable Airspace) analysis to determine which structures are subject to airspace review. Such projects are required to notify the FAA by filing Form 7460, Notice of Proposed Construction or Alteration. Typical structures that impede 200 ft include large skyscrap- ers, communication towers, and wind turbines (see Figure 8). Solar power towers and power plant exhaust stacks may also exceed 200 ft in height or may penetrate airspace with smaller structures if located closer to an airport.

13 Communication Systems Interference Communication systems interference includes negative im- pacts on radar, navigational aids (NAVAIDS), and infrared instruments. Although Global Positioning Systems that com- municate with satellites and limit the need for traditional surveillance radar are being employed more widely and are expected to be the fundamental component of future navi- gational systems, the integrity of traditional radar facilities remains central to the current operational environment. Radar interference occurs when objects are placed too close to a radar sail (or antenna) and reflect or block the transmission of signals between the radar antenna and the receiver (either a plane or a remote location). Although it is possible for interfer- ence to be caused by other communication signals, more com- monly it is caused by a physical structure placed between the transmitter and receiver. NAVAIDS can be impacted similarly to radar, but they include passive systems with no transmit- ting signals. Impacts on infrared communications can occur because the solar collectors and receivers can retain and emit heat, and the heat they release can be picked up by infrared communications in aircraft causing an unexpected signal. Communications interference can result from any of the energy technologies discussed in this report. Potential impacts increase with larger structure size (and cross section) and shorter distance to radar facilities. Large wind farms have gen- erated the most problems and as a result have been studied the most. Transmission lines can also cause interference resulting from electrical signals irradiating from the lines. Impacts from other technologies are primarily from the structure’s mass and physical location blocking radar signals. Studies conducted during project siting may identify the location of radar trans- mission and receiving facilities and other NAVAIDS and determine locations that would not be suitable for structures based on their potential to either block, reflect, or disrupt radar signals. Off-airport solar projects are unlikely to cause radar inter- ference compared with those proposed on-airport unless located close to airport property and within the vicinity of radar equipment and transmission pathways. However, when located near a radar installation, CSP projects can reflect radar transmissions because of their metallic components. Visual Impacts of Glare Glare occurs when sunlight causes a temporary visual impair- ment to an observer. Glare can be produced when looking directly at the sun, such as when driving in its direction after sunrise or sunset, or at any time of day when sunlight is returned to the observer from a reflective surface. Surfaces that pro- duce glare include mirrors, metal roofs, still waters, and glass. Smooth polished surfaces, such as glass, can cause a specu- lar reflection that is more direct and intense (see Figure 9). Reflections from rough surfaces become diffuse and result in less of an impact. Solar PV, although designed to be absorp- tive of sunlight, can produce glare in certain instances because of its glass surface. CSP projects that use mirrors have a greater propensity to produce glare. The concern here is that, depending on the location of the solar project, glare could cause a momentary visual impairment to air traffic controllers or pilots. Wind Turbine Turbulence Turbulence occurs when air flow becomes chaotic and irreg- ular. Although turbulence is typically caused by changing FIGURE 8 Physical penetration of airspace schematic (courtesy: HMMH).

weather patterns or by dramatic topographic variations, turbu- lence can also be caused by man-made activities. The potential effects of turbulence are of greatest concern when there is a sudden and unforeseen turbulence on a small aircraft caused by some great force. Turbulence associated with wind turbines is less an issue of predictability, as the turbulence potential can be visualized by the presence of the wind turbines and whether or not they are spinning. The issue is more about understanding the dis- tance that rotor-induced turbulence may occur from a wind turbine and what the degree of turbulence might be compared with other sources of existing natural and man-made turbu- lence. What is a safe distance for aircraft to travel downwind of a wind turbine? Thermal Plume Turbulence Thermal plume turbulence is caused by the release of hot air from a power plant equipped with a dry cooling system. The 14 thermal plume rises causing upward moving turbulence. An aircraft might pass well above the structure of an air-cooled condenser and become subject to the invisible turbulence without warning. Visual Impacts of a Vapor Plume Vapor plumes produce a vapor cloud that can result in localized visual impairment. Plumes are produced by large-scale emis- sions of heated water vapor typically from an evaporative wet cooling system associated with a power plant. Wet cooling towers reject heat into the atmosphere by releasing water vapor. The air leaving the tower is saturated with moisture and warmer than ambient air producing a wet exhaust plume. The saturated exhaust plume may or may not be visible. During cool morn- ings in the fall or spring when the ambient air is moist cooling towers can add more water to the air, thereby saturating the air and adding water droplets resulting in fog. If the ambient tem- peratures are below freezing, the resulting water droplets could cause icing on nearby roadways and bridges surfaces. FIGURE 9 Specular and diffuse reflection schematic (courtesy: HMMH).

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 Investigating Safety Impacts of Energy Technologies on Airports and Aviation
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TRB’s Airport Cooperative Research Program (ACRP) Synthesis 28: Investigating Safety Impacts of Energy Technologies on Airports and Aviation explores physical, visual, and communications systems interference impacts from energy technologies on airports and aviation safety.

The energy technologies that are the focus of this report include the following:

• solar photovoltaic panels and farms,

• concentrating solar power plants,

• wind turbine generators and farms, and

• traditional power plants.

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