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15 CHAPTER THREE SOLAR ENERGY AND POTENTIAL IMPACTS This section describes the existing body of information on frequency from Blythe is 60 hertz (Hz). Frequencies employed the potential impacts of solar energy technologies on airports at the Air Force Base in Palmdale are 108135 MHz for very and aviation. The technologies described are solar PV and high frequency (VHF) and 225400 MHz for ultra high fre- CSP. Potential impacts associated with solar energy facilities quency (UHF) (CEC 2010b,c). include physical penetration of airspace, communication sys- tems interference, visual impacts from glare, turbulence from Potential physical obstructions are correlated with the thermal plumes, and visual impacts from vapor plumes. Note size of the structure and its proximity to a radar facility. that potential impacts vary significantly between PV and CSP. 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 PHYSICAL PENETRATION OF AIRSPACE Bakersfield (BFL) (see Figure 10) were required to meet set- backs from transmitters of 500 ft (A. Kekakeuwela, Oakland Solar energy facilities, including PV and CSP, can penetrate Port Authority, personal communication, 2010) and 250 ft airspace. However, because PV utilizes low profile equipment, (J. Gotcher, Airport Manager, Meadows Field, personal com- it is less likely to affect airspace unless it is located very close munication, 2010), respectively. to an airport runway. CSP, particularly those designed with power towers, can reach into airspace. Some reflections can be mitigated with RAM (radar absorb- Steam boilers are located high up on power towers. ing material) coatings but these can be cost-prohibitive. One Increased height allows for more mirrors to focus their reflected project located just outside the fence at the Phoenix Airport sun energy on the boiler. For the proposed Ivanpah Solar Elec- (PHX) was reviewed by the FAA and conditions were placed tric Generating System in southeastern California, the design on the airspace review approval to address potential concerns includes three power towers, each rising to 459 ft above with radar interference (J. Decastro, FAA Western-Pacific ground level (Bright Source Energy 2010). Region, personal communication, 2010). In many cases, com- munication and coordination with the proper FAA officials In addition, concentrating solar power projects that heat can mitigate the issues and concerns regarding solar power steam to drive a turbine require cooling systems to cool water installations in and around airports. CSP projects with large for reuse. Those that employ air-cooled condensers may also structures can also obstruct or reflect radar signals. penetrate airspace. Four air-cooled condensers proposed as part of the Blythe Solar Power Project will each rise to 120 ft GLARE VISUAL IMPACT above ground level. The potential impacts of reflectivity are glint and glare (referred COMMUNICATIONS SYSTEMS INTERFERENCE to henceforth just as glare) (glint is a momentary flash of bright light, whereas glare is a continuous source of bright light), Communications systems interference can be produced by which can cause a brief visual impairment (also known as after- either an electrical interference or as a physical obstacle image or temporary flash blindness) (FAA 2008a) (FAA Order between the communicator and receiver. However, electrical 7400.2f defines flash blindness as "Generally, a temporary interference has not been a concern during airspace reviews visual interference effect that persists after the source of illumi- (J. Decastro, FAA Western-Pacific Region, personal commu- nation has ceased"). The potential impact of glare can be mea- nication, 2010). In its approval of Palmdale, the California sured using the magnitude of reflection (referred to as retinal Energy Commission (CEC) did not identify electromagnetic irradiance) and the subtended angle of the reflection (derived interference concerns for the operating frequencies proposed from the size of the reflected area and its distance from the sen- (CEC 2010b: Solar Millennium 2010). CSPs at both Palmdale sitive receptor). [See Ho et al. (2009) for more information on and Blythe have submitted information to the CEC on electro- how to calculate reflectivity from solar power projects.] magnetic frequencies that will be emitted by electrical equip- ment associated with their projects. Both projects are located The reflectivity of a surface is influenced by two primary close to aviation facilities (Blythe is within one mile). The base factors: the color of the surface and its physical composition.

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