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