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Technical Guidance for Evaluating Selected Solar Technologies on Airports
| By Michigan Tech's Open Sustainability Technology Lab.
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- 1 Note to Readers
- 2 Search List
- 3 Report Topics and Discussions
- 3.1 What does FAA has to say about Solar Power with Airports
- 3.2 How is Solar Energy Impacting Airports
- 3.3 Solar Power Generating Systems (other than PV module) Considered in the Report
- 3.4 Airport Design Standards
- 3.5 Case Study with Take Away Points
- 4 Random Points
- 5 Citations
Note to Readers
Please leave any comments on the Discussion page (see tab above) including additional resources/papers/links etc. Papers can be added to relevant sections if done in chronological order with all citation information and short synopsis or abstract. Thank You.
- Technical Guidance for Evaluating Selected Solar Technologies on Airports Federal
Report Topics and Discussions
Though complete detailed study is present in the 'Search List' provided above, below mentioned data is either the interpretation of the subjects or directly taken from the report as it is
What does FAA has to say about Solar Power with Airports
Solar energy has been evolving as a mainstream form of renewable energy generation since the early 1990’s. Solar energy presents itself as an opportunity for airports and aviation industry to satisfy on-site power demand and to reduce energy costs. While solar energy is seen beneficiary in all matters but in aviation sector particularly, it does introduce some new and unknown issues. The biggest one is said to be the possibility of glare (or reflectivity) and frequency interference in communication systems. The earlier mentioned two and a few other challenges have made the FAA FAA review and lay down approval process of this technology.
For the airport environment, PV can be placed in locations that are not used for aviation activities and therefore have little value to the airport or for alternative developments.
How is Solar Energy Impacting Airports
Its because of the availability of ample space and huge demand of power by the airports themselves has led to the huge interest of the power sector towards airports! But before going ahead there are a number of new challenges specific to aviation industry-
There are 3 subjects of major concern here apart from airport sponsor’s Federal obligations regarding financial self-sustainability and retention of airport revenue, as well as national environmental policy-
Reflectivity & Glare
Often 1000W/m^2 is used in calculations as an estimate of the solar energy interacting with a panel when no other information is available. According to researchers at Sandia National Lab, flash blindness for a period of 4-12 seconds (i.e., time to recovery of vision) occurs when 7-11 W/m^2 (or 650-1,100 lumens/m^2) reaches the eye. 
One has to consider whether the reflected light is “specular” or “diffuse”. Specular reflection are more concentrated type of light reflections and occurs when the reflecting surface is smooth and polished. The exact percentage of light that is specularly reflected from PV panels is currently unknown. Outside of very unusual circumstances, flash blindness can only occur from specular reflections. 
FAA has no specific standards for airport solar facilities and potential glare, the type of glare analysis that is needed may vary. Depending on site specifics (e.g., existing land uses, location and size of the project) an acceptable evaluation could involve one or more of the following levels of assessment:
(1) A qualitative analysis of potential impact in consultation with the Control Tower, pilots, and airport officials
(2) A demonstration field test with solar panels at the proposed site in coordination with FAA Tower personnel
(3) A geometric analysis to determine days and times when an impact is predicted.
- Assessing Baseline Reflectivity Conditions - Glare from PV needs to be considered with existing glare sources at the airport like, buildings, tilted sheds, water bodies etc.
- Geometric Analysis - As the suns position changed continuously with time and seasons, it is necessary to check Solar PV panels reflective behavior and impacts with it.
- Tests in the Field - Performing actual tests on samples in field from time to time as actual data may vary from prediction.
So far there has been no case from the existing airports with solar pv modules of glare affecting the functioning of the airport system.
Physical penetration of airspace
Solar Power Generating Systems (other than PV module) Considered in the Report
Not all discussed necessarily power producers but are called, as they save the electricity used for the purpose they solve
- Systems use large reflective surfaces in massive arrays to focus the sun’s energy on a fixed point to produce intense heat
Advantage - Heated fluids can be used to store energy and delivery Power later
Disadvantage - The central receiver tower will certainly breach airspace and other issues like reflectivity (Major as it is based on reflection instead of absorption compared to solar PV, thermal plumes, radar interference.
Solar Thermal Hot Water
- As name suggests, they are water heating panels and don't produce electricity, a suitable method where electricity is used for heating and is in continuous demand
Advantage - No problems regarding reflectivity, thermal plumes, radar interference or even airspace breach
Disadvantage - Suitable for domestic use compared to airport system
Transpired Solar Collectors
- Systems use heat absorbing metal surfaces on the walls to focus the sun’s energy on air heating for ventilation
Advantage - No problems regarding reflectivity, thermal plumes, radar interference or even airspace breach
Disadvantage - These systems are especially effective in sunny climates with long heating seasons.
Airport Design Standards
It is important to understand that not all the vacant land in an airport system can be used for Solar power generation. Locations like mentioned below must be clearly understood-
- Building Restriction Line
- Object Free Area
- Taxiway Safety Area
- Obstacle Free Zone
- Runway Protection Zone (RPZ)
- Runway Safety Area (RSA)
- Taxiway Object Free Area
In determining a proposed solar projects compatibility with aeronautical activities, following should be considered-
- The project cannot be located in a Runway Object Free Area, Obstacle Free Zone, Runway Safety Area, Taxiway Object Free Area or a Taxiway Safety Area.
- The project cannot penetrate imaginary surfaces that define the lower limits of airspace including the clearway.
- The project must demonstrate that glare will not impact airspace safety.
- The project must use airport property that is not designated for aeronautical activities or request a formal land release or change in land use.
RPZ - As the name suggests is not usually available for any kind of construction but exceptional cases like 'Solar Project Siting at Fresno Yosemite International Airport' do exist, where after proper consideration some exceptions were made.
Case Study with Take Away Points
Denver International Airport
2 projects carried out, one with single axis tracking system and the other with fixed mounted- Fixed mounted turned out to be more profitable as it was more robust and less affected by wind/ dust/ wear & Tear thus, reducing maintenance cost and frequency!
Fresno Yosemite International Airport
This airport used RPZ area after finding out that, This area, due to its location relative to air traffic, was unusable for any land uses requiring regular presence by people. In addition, unmanned structures were constrained to only low profile ones that did not penetrate into the approach zone. For those reasons, the land had little value which made it a very suitable location for a solar project.
Metropolitan Oakland International Airport
A great example where three of the major concerns of an airport+Solar colaboration was solved.
- Panels were kept at a minimum distance of 500ft from the nearest Radar system.
- Panels were positioned keeping Air traffic control tower in mind and it was made sure the effective glare from the panels was not a concern at any time of the year.
- The panels were located approximately 400 feet from the runway avoiding any penetration of the imaginary surface of airspace.
The electricity conversion efficiency for today’s photovoltaic panels is between 6 and 20% of the total energy available. In comparison, the burning of fossil fuels is about 28% efficient. Also, as operating panels age and degrade, their efficiency goes down (on average about 0.5% each year).
- With stationary water bodies close to airports, can we have floating panels (Saves a lot of space, probably will solve problems related with glare, airspace etc, might need longer transmission and probably not owned by airport)
- RPZ-Runway protection zones are suitable unused areas to explore. In general, the FAA does not recommend that airports locate solar projects in the RPZ. However, the FAA will review specific airport proposals like the one presented by Fresno Yosemite International Airport on a case-by-case basis.
- Airspace Penetration???
- FAA says - The exact percentage of light that is specularly reflected from PV panels is currently unknown. However, because the panels are a flat, polished surface, it is a reasonable assumption that most of the light is reflected in a specular way and thus is fundamentally different from that reflected off a rougher surface.
Often 1000W/m2 is used in calculations as an estimate of the solar energy interacting with a panel when no other information is available. According to researchers at Sandia National Lab, flash blindness for a period of 4-12 seconds (i.e., time to recovery of vision) occurs when 7-11 W/m2 (or 650-1,100 lumens/m2) reaches the eye. Using the previously mentioned value for solar irradiance, this would mean roughly 20 W/m2 are reflected off of a typical PV panel. This is close to that of water
- To minimize unexpected glare, windows of air traffic control towers and airplane cockpits are coated with anti-reflective glazing and operators will wear polarized eye wear. Potential glare from solar panels should be viewed in this context. Any airport considering a solar PV project should first review existing sources of glare at the airport and the effectiveness of measures used to mitigate that glare.
- The exact percentage of light that is specularly reflected from PV panels is currently unknown.
- Because the intensity of the light reflected from the solar panel decreases with increasing distance, an appropriate question is how far do you need to be from a solar reflected surface to avoid flash blindness? It is known that this distance is directly proportional to the size of the array in question but still requires further research to answer completely. An aviation-specific dynamic model that could evaluate potential impacts on fixed (Control Tower) and moving (aircraft) sensitive receptors would be a beneficial tool.
 Federal Aviation Administration November 2010, Technical Guidance for Evaluating Selected Solar Technologies on Airports.  Ho, Clifford, Cheryl Ghanbari, and Richard Diver. 2009. Hazard Analysis of Glint and Glare From Concentrating Solar Power Plants. SolarPACES 2009, Berlin Germany. Sandia National Laboratories.  https://share.sandia.gov/phlux/static/references/glint-glare/2011_Glare_J.SolarEnergyEngr_Vol133.pdf