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

Chapter: Chapter Three - Solar Energy and Potential Impacts

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Suggested Citation:"Chapter Three - Solar Energy and Potential 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 Three - Solar Energy and Potential 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 Three - Solar Energy and Potential 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 Three - Solar Energy and Potential 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 Three - Solar Energy and Potential 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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15 This section describes the existing body of information on the potential impacts of solar energy technologies on airports and aviation. The technologies described are solar PV and CSP. Potential impacts associated with solar energy facilities include physical penetration of airspace, communication sys- tems interference, visual impacts from glare, turbulence from thermal plumes, and visual impacts from vapor plumes. Note that potential impacts vary significantly between PV and CSP. PHYSICAL PENETRATION OF AIRSPACE Solar energy facilities, including PV and CSP, can penetrate airspace. However, because PV utilizes low profile equipment, it is less likely to affect airspace unless it is located very close to an airport runway. CSP, particularly those designed with power towers, can reach into airspace. Steam boilers are located high up on power towers. Increased height allows for more mirrors to focus their reflected sun energy on the boiler. For the proposed Ivanpah Solar Elec- tric Generating System in southeastern California, the design includes three power towers, each rising to 459 ft above ground level (Bright Source Energy 2010). In addition, concentrating solar power projects that heat steam to drive a turbine require cooling systems to cool water for reuse. Those that employ air-cooled condensers may also penetrate airspace. Four air-cooled condensers proposed as part of the Blythe Solar Power Project will each rise to 120 ft above ground level. COMMUNICATIONS SYSTEMS INTERFERENCE Communications systems interference can be produced by either an electrical interference or as a physical obstacle between the communicator and receiver. However, electrical interference has not been a concern during airspace reviews (J. Decastro, FAA Western-Pacific Region, personal commu- nication, 2010). In its approval of Palmdale, the California Energy Commission (CEC) did not identify electromagnetic interference concerns for the operating frequencies proposed (CEC 2010b: Solar Millennium 2010). CSPs at both Palmdale and Blythe have submitted information to the CEC on electro- magnetic frequencies that will be emitted by electrical equip- ment associated with their projects. Both projects are located close to aviation facilities (Blythe is within one mile). The base frequency from Blythe is 60 hertz (Hz). Frequencies employed at the Air Force Base in Palmdale are 108–135 MHz for very high frequency (VHF) and 225–400 MHz for ultra high fre- quency (UHF) (CEC 2010b,c). Potential physical obstructions are correlated with the size of the structure and its proximity to a radar facility. For on-airport solar PV projects, systems have been required to be set back from major on-airport radar equipment as a protected buffer. The solar fields at Oakland (OAK) and Bakersfield (BFL) (see Figure 10) were required to meet set- backs from transmitters of 500 ft (A. Kekakeuwela, Oakland Port Authority, personal communication, 2010) and 250 ft (J. Gotcher, Airport Manager, Meadows Field, personal com- munication, 2010), respectively. Some reflections can be mitigated with RAM (radar absorb- ing material) coatings but these can be cost-prohibitive. One project located just outside the fence at the Phoenix Airport (PHX) was reviewed by the FAA and conditions were placed on the airspace review approval to address potential concerns with radar interference (J. Decastro, FAA Western-Pacific Region, personal communication, 2010). In many cases, com- munication and coordination with the proper FAA officials can mitigate the issues and concerns regarding solar power installations in and around airports. CSP projects with large structures can also obstruct or reflect radar signals. GLARE VISUAL IMPACT The potential impacts of reflectivity are glint and glare (referred to henceforth just as glare) (glint is a momentary flash of bright light, whereas glare is a continuous source of bright light), which can cause a brief visual impairment (also known as after- image or temporary flash blindness) (FAA 2008a) (FAA Order 7400.2f defines flash blindness as “Generally, a temporary visual interference effect that persists after the source of illumi- nation has ceased”). The potential impact of glare can be mea- sured using the magnitude of reflection (referred to as retinal irradiance) and the subtended angle of the reflection (derived from the size of the reflected area and its distance from the sen- sitive receptor). [See Ho et al. (2009) for more information on how to calculate reflectivity from solar power projects.] The reflectivity of a surface is influenced by two primary factors: the color of the surface and its physical composition. CHAPTER THREE SOLAR ENERGY AND POTENTIAL IMPACTS

Color is important because some colors absorb light and its energy, whereas others reflect it. Light colors are most reflec- tive (white being the most), whereas dark colors are least reflective. Figure 11 shows the percentage of sunlight that is reflected from a variety of common surfaces. The values pro- vided are primarily influenced by color and include two dif- ferent types of solar technologies: PV and CSP. The color of the surface and the percentage of sunlight it reflects is only one-half of the equation; the other factor is the physical characteristics of the material’s surface. Flat, smooth surfaces will reflect a more concentrated amount of sunlight back to the receiver, which is referred to as specular reflection. The more a surface is polished, the more it shines. Rough or uneven surfaces will reflect light in a diffuse or scattered man- ner and therefore will not be received by the viewer as brightly. Reflections from natural surfaces have always occurred and people’s perception of exposure impacts must accommo- date for the glare. New construction may need to consider the impacts of reflectivity from its surfaces. The most com- mon type of project where the impacts of reflectivity have been evaluated is building facades constructed of glass, metal, or other highly reflective materials. Some building rooftops are being designed with white roofs with a high albedo value to purposefully reflect light and heat, and thereby minimize local trapping of heat referred to as “heat island effect.” PV solar panels use silicon to convert sunlight to electric- ity and silicon is naturally reflective. As a result, all solar pan- els are designed with a layer of anti-reflective material that allows the sunlight to pass through to the silicon but minimizes reflection. This design results in the dark appearance of the solar panel. Recent generations of panels have included an anti-reflective material on the outer surface of the glass to fur- ther limit sunlight reflection. The area of the aluminum frame is very thin and therefore reflection from the aluminum is not a concern. Another recent design feature to limit reflection is to roughen the protective glass surface (C. Ho, Sandia 16 National Laboratories, 2011). A roughened surface will pre- vent specular reflection, which can produce a sharper and more concentrated ray of light, and instead produce a diffuse reflection. Current solar panels reflect as little as 2% of the incoming sunlight depending on the angle of the sun and assuming use of anti-reflective coatings (Evergreen Solar 2010). However, because the surface of the solar panels is very flat and uniform, it is capable of reflecting a focused ray of sunlight (see Figure 12). CSP systems are designed to maximize reflection and focus the reflected sunlight and associated heat on a design point (heat collecting element or HCE) to produce steam that gen- erates electricity. Approximately 90% of incoming sunlight is reflected from a CSP mirror. However, because the reflected sunlight is controlled and focused on the HCE, it generally does not reflect back to other sensitive receptors. A small frac- tion of the sunlight may not be absorbed by the HCE so the potential for that reflection can be assessed. Another source of reflection is the light that contacts the back of the HCE and never reaches the mirror. Parts of the metal frame can also FIGURE 10 Solar PV at Meadows Field, Bakersfield, California (courtesy: HMMH). FIGURE 11 Reflectivity scale graphic (courtesy: HMMH).

17 reflect sunlight. In central receiver (or power tower) applica- tions, the receiver can receive concentrated sunlight that is up to a thousand times the sun’s normal irradiance. Therefore, reflections from a central receiver, although approximately 90% absorptive, can still reflect a great deal of sunlight. There- fore, different analyses are necessary to understand the poten- tial for glare impacts for each of these systems. Models have been developed and analyses have been performed to deter- mine when glint or glare from different sources can cause retinal burn or temporary after-image as a function of retinal irradiance and subtended source angle (Ho et al. 2009). Anecdotal observance of glare emitted from operating parabolic-style CSP projects has been described. These flights occurred over the Victorville 2 Hybrid Solar Project. Obser- vations from staff from the CEC and the Southern California Logistics Airport stated that no intense “specular” glare was observed (AECOM 2010). Subsequently, Solar Millennium commissioned a systematic aircraft fly-by of the Kramer Junc- tion solar facility in the Mojave Desert, which uses parabolic trough solar technology similar to the proposed Blythe Proj- ect to provide an assessment of glint and glare impacts on pilots. The pilot and passenger concluded in separate state- ments that the Kramer Junction Project does not reflect glint or glare that could significantly impact pilots. Based on their observations and the orientation of the Blythe Airport (BLH) runways to the McCoy Mountains, they determined that the Blythe Project would operate in a similar fashion without significant impacts (CEC 2010b). Analysis by the CEC con- cluded that a potential for glint and glare could occur close to sunrise and sunset. The CEC specifically indicated four distinct runway procedures that might be affected by glint or glare. Its decision imposed specific mitigation that would help minimize but not eliminate the potential for glint and glare. Because the Riverside County Land Use Compatibility Plan specifically prohibits development that can result in glint and glare, the CEC’s decision was a formal override of the county regulation. FAA tower personnel and airport managers from several airports were interviewed for anecdotal information about reflectivity from operating solar PV farms at airports. Two notable sites are Meadows Field (BFL) in Bakersfield, Cali- fornia, which hosts an 800 kW solar facility, located approx- imately 250 ft from the runway taxiway, and Fresno Yosemite International Airport (FAT) in Fresno, California, where there is a 2 MW facility in the Runway Protection Zone near the end of one of the runways. The Meadows Field solar project has been in operation since January 2009, whereas Fresno’s project has been operational since June 2008. In both cases, the air traffic controllers stated that glare has not affected their operations and they had not received complaints from pilots about glare being a problem (R. T. Martin, FAA Air Traffic Control Tower Manager, personal communication, 2010 and K. Powell, FAA Air Traffic Control Tower Manager, personal communication, 2010). THERMAL PLUME TURBULENCE A thermal plume is produced by power plants that employ a dry cooling system often referred to as an air-cooled con- denser. For the purposes of this report this could include CSP and peaking power plants. Dry cooling employs fans below the air-cooled condensers that blow hot air up to enhance cooling. The rising hot air can produce air turbulence. The worst case scenario for thermal plume impacts are low wind and large temperature differential, which typically occurs at sunrise for projects proposed in the Southern California desert area between May and October. The most problematic scenario is when the plume contacts only one wing (D. Moss, AeroPacific Consulting, personal communication, 2010). The CEC uses a 4.3 m/s vertical velocity as a significance criterion for the potential for a thermal plume to produce tur- bulence that could impact passing aircraft (CEC 2010a). The predicted vertical plume velocity for the air-cooled condensers proposed for the Blythe Solar Power Project is 4.5 m/s at the upper face of the condenser. Flow above the 4.3 m/s thresh- old used by the CEC was constrained to a few tens of meters above the condenser surface. The results predicted vertical flow velocity to be less than 2 m/s at 250 m above the air- cooled condenser. Velocity flows potentially encountered by aircraft would be similar to those that could be felt under nat- ural occurrences (AECOM 2010). The analysis of potential impact concluded that because of low vertical velocity and minimal air traffic over the condensers based on flight pattern [none of the traffic pattern envelopes (which constitutes 80% of all traffic) intersect with the condensers] impacts will be minimal. The analysis indicated that some air traffic could pass over the condensers but, if following flight procedures, are unlikely to be close enough to the condensers to be affected (Solar Millennium 2010). The CEC findings for the Blythe Solar Power Project deter- mined that the project has the potential to adversely impact low-flying aircraft in low wind conditions. Further it concludes that aircraft on arrival at Blythe will be flying at altitudes low FIGURE 12 Example of glare at Sandia National Laboratories (courtesy: Dr. Clifford Ho, U.S. DOE, Sandia National Laboratories).

enough to be impacted particularly when making a particular maneuver to a specific runway. To minimize the risk of this impact, the CEC required a notification to pilots as a condi- tion of its decision. VAPOR PLUME VISUAL IMPACT Vapor plume is typically produced by power plants, includ- ing CSP and peaking power plants, which utilize an evapora- tive wet cooling system. Whereas dry cooling transfers heat to the air which rises above the system, evaporative wet cool- ing produces steam as heat dissipates through evaporation. The mechanics of the two heat transfer systems is similar but the impacts are very different primarily because a vapor plume can be seen whereas a thermal plume cannot. Visible impact from steam is not expected to occur from air-cooled con- densers because the heat is cooled by air convection and not water (Solar Millennium 2010). Wet cooling has been the preferred cooling system owing to enhanced cooling efficiency (compared with dry cooling) and decreased cost. In the past, wet cooling was accomplished with once through cooling, but the impacts of heated dis- charge to water bodies encouraged the development of evap- orative wet cooling. The majority of new fossil fuel plants employ evaporative wet cooling (NREL 2010a). It has been employed at hundreds of power plants across the country, particularly those built in more recent years. For CSP proj- ects that are challenged to compete with traditional sources of electricity on price, use of wet cooling has been the con- vention with all operating projects as of March 2010 (SEIA 2010). However, as a result of environmental concerns over the scarcity of water, particularly in desert areas where CSP projects are located, newer projects are being forced to exam- ine dry cooling (CEC 2010b). Steam released from power plants occurs near airports in Pennsylvania. Pilots fly through a vapor plume on approach to Runway 9 at Perkiomen Valley Airport, Pennsylvania (A. Tezla, Mead and Hunt, Inc., personal communication, 2011). The Limerick Nuclear Power Plant is also close to the Pottstown Municipal Airport (PTW). Steam rises from the cooling towers of the Three Mile Island Nuclear Plant into the approach path at Harrisburg International Airport (MDT). It is possible that aircraft are less affected by vapor plumes (than thermal plumes) because they are a recurring feature that can be seen allowing pilots to make adjustments as needed. MITIGATION OPTIONS The following mitigation options have been considered in min- imizing the impacts of concentrated solar power on aviation: • For parabolic trough plants, use nonreflective or diffuse materials or coatings (e.g., paint) for bellows shields located every few meters at joints between heat collect- ing elements. 18 • The units should be rotated from stow away position to ready position before sunrise to limit potential inadver- tent glare. • Parabolic designs should consider using end caps to reduce glare that “spills” from the ends of the trough. • Curtailment in facility operations can be prescribed dur- ing periods when glare is expected to impact low-flying aircraft. • Flight procedures can be restricted during certain periods of the day when glare may occur. • County zoning ordinances may be put into place to limit glare-producing structures in airport influence zones (El Dorado County, California 2009; Clallam County, Washington 2010). SOLAR ENERGY IMPACT EXAMPLES The following section describes examples of solar energy impact. Blythe Solar Power Plant The Blythe Solar Power Plant is a proposed 1,000 MW CSP facility to be located in California’s inland desert on land owned by the BLM. The project will utilize parabolic trough technology that reflects sun from each trough device to a receiver tube. The heat transfer fluid in the tube is raised to 750°F and then piped through heat exchanges used to cre- ate steam that drives a traditional steam turbine generator to produce electricity. The Blythe Project provides a current example of the regulatory evaluation for a CSP facility. In September 2010, the CEC issued its Decision on the Appli- cation for Certification for the Blythe Solar Power Project. In its review, the CEC assessed many of the potential impacts of CSPs identified in this report. The following is a list of conditions in the CEC’s decision to mitigate impacts: • Proponents have comments or notations inserted in the appropriate Aeronautical Charts, Airport/Facilities Direc- tories, and Notice to Airmen publication to identify poten- tial hazard from glare and thermal turbulence. • Mirrors are (1) brought out of stowage before sunrise and are aligned to catch the first rays of the morning sun, and (2) returned to stow position after sunset. • Mirror function is continuously monitored by operators and system controllers. • The system is designed to automatically turn a malfunc- tioning mirror east so there is no reflection from the sun as it moves west. • The owner develops procedures to move mirrors east to avoid glare. • Mirrors in the southern portion of Units 3 and 4 are not to be rotated off axis during daylight hours when the azimuth angle of the sun is east or north of east. • Specific procedures for documenting, investigating, eval- uating, and resolving (if feasible) public complaints about glare are to be developed.

19 Oakland International Solar PV Project In 2007, the Port of Oakland entered into a lease agreement with a private solar developer to construct a solar PV proj- ect on airport property. Because the project was proposed on airport property, the FAA was responsible for approving the lease and evaluating potential impacts of the project on aviation. The Port selected a lease site close to the runways because the land was otherwise not useable for most avia- tion activities. To prevent a physical impingement of air- space, the angle of the row of solar panels closest to the runway were pitched close to flat (see Figure 13). To avoid any potential interference with communication facilities, the solar panels were required to preserve a 500-ft setback from the aviation surveillance radar. Glare was determined not to be a hazard from this project, although similar pro- jects at other airports have required in the field studies using solar panels at proposed project locations to assess impacts on the control tower. Ivanpah Solar Electric Generating Facility The Ivanpah Solar Electric Generating Facility is a 370 MW CSP facility utilizing power tower technology proposed in the Ivanpah Valley of California on land owned and man- aged by the BLM three miles west of the Nevada border. The project will consist of three tower facilities, each with heliostat mirrors used to focus the sun’s energy to boil steam and drive a steam turbine. Power plant 1 is a 120 MW facility. Power plants 2 and 3 are each 125 MW. The power towers will be 459 ft tall. The facility will be cooled using air-cooled condensers that are approximately 115 ft tall (CEC 2010d). The CEC issued separate decisions on each of the three individual projects in September 2010. The CEC’s decisions incorporated the following conditions to avoid impacts on aviation. 1. Preparation of a Heliostat Positioning Plan that would avoid potential for human health and safety hazards from solar radiation exposure. • The plan should identify the heliostat movements and positions (including reasonably possible mal- functions) that could result in potential exposure of observers at various locations including in air- craft, motorists, pedestrians, and hikers in the Clark Mountains to reflected solar radiation from heliostats. The plan should describe how programmed heliostat operation would avoid potential for human health and safety hazards at locations of observers as attrib- utable to momentary solar radiation exposure greater than the maximum permissible exposure of 10 kw/m2 (for a period of 0.25 second or less). • Preparation of a monitoring plan that would: (1) obtain field measurements in response to legitimate com- plaints; (2) verify that the Heliostat Positioning Plan would avoid the potential for human health and safety hazards including temporary or permanent blindness at locations of observers; and (3) provide require- ments and procedures to document, investigate, and resolve legitimate complaints regarding glare. The monitoring plan should be coordinated with the FAA, U.S. Department of the Navy, California Depart- ment of Transportation, California Highway Patrol, and Clark County Department of Aviation in rela- tion to the proposed Southern Nevada Supplemen- tal Airport and be updated on an annual basis for the first 5 years, and at 2-year intervals thereafter for the life of the project. 2. Preparation of a Power Tower Luminescence Moni- toring Plan to provide procedures to conduct periodic monitoring and to document, investigate, and resolve complaints regarding distraction effects to aviation, vehicular, and pedestrian traffic associated with the power towers: • Evaluate the effects of the intensity of the luminance of light reflected from the power tower receivers 90 days after commencement of commercial oper- ations, and after 5 years, as well as after any signif- icant design or operational modification, or after a significant complaint. • Coordinate monitoring protocol and results with agency stakeholders. 3. Lighting of the power towers as required by FAA under Part 77 Review. 4. Notification of pilots in the area about potential haz- ards associated with thermal turbulence. Notification should indicate that a hazard could occur up to 1,350 ft above ground level. Request that the FAA prohibit flights over the facility at or below the 1,350 ft altitude. FIGURE 13 Solar PV at Oakland International Airport, California (courtesy: HMMH).

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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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