Mitigation Techniques for the Impact of Solar Panel

Installations on Low-Level Military Flight Paths

Developed by:

October 2014

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TABLE OF CONTENTS

I. INTRODUCTION ....................................................................................................................... 3

II. SOLAR POWER SYSTEMS ......................................................................................................... 3

Concentrated Solar Power Systems .................................................................................... 3

Solar Photovoltaic Systems ................................................................................................. 4

Solar Thermal Systems ........................................................................................................ 4

III. SOLAR PANEL SURFACES ......................................................................................................... 5

IV. SOLAR PANEL SITING ............................................................................................................... 5

Solar Glare Hazard Analysis Tool ........................................................................................ 5

V. SAMPLE ORDINANCES ............................................................................................................. 6

Proposed Ordinance Regulating the Operation and Maintenance of Solar Energy

Facilities in Wayne County, NC ........................................................................................... 6

Template Solar Energy Development Ordinance for North Carolina ................................. 7

Other Ordinances ................................................................................................................ 8

VI. REFERENCES .......................................................................................................................... 12

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I. INTRODUCTION

While the interest in solar power systems and their benefits has continued to grow, a common concern

surrounding these systems is their potential to reflect sunlight and how this reflected sunlight can

impact surrounding structures and activities, especially those related to aviation (Shea 2012). “…In

conjunction with the United States Department of Energy (DOE), the FAA has determined that glint [a

momentary flash of light] and glare [a more continuous source of bright light] from solar energy systems

could result in an ocular impact to pilots and/or air traffic control (ATC) facilities and compromise the

safety of the air transportation system,” (Department of Transportation (DOT) 2013, p63276). These

ocular impact concerns from the FAA can also be shared with the military aviation community especially

with how glint and glare can impact low-level military flight paths.

There are several factors that may influence glint and glare from solar power generating systems. These

factors include the type of solar power generating system used, the surface type of a solar panel, and

siting of solar panels. The following report draws upon several documents by the Federal Aviation

Administration (FAA), the American Planning Association (APA), the University of North Carolina at

Chapel Hill School of Government, etc. to discuss in detail factors that may influence glint and glare. The

report concludes with several tools and sample ordinances which may be used to further mitigate the

potential glint and glare from solar panel installations. The information in this report is intended to be a

reference for the counties and municipalities surrounding military aviation operations and flight paths

who are interested in regulating solar power systems.

II. SOLAR POWER SYSTEMS

The three most prevalent solar power systems are: 1) concentrated solar power systems, 2) solar

photovoltaic systems, and 3) solar thermal systems (APA 2014). According to FAA, some solar power

generating systems are more suitable for on or around airports than other solar power systems due to

reasons such as glare potential (FAA 2010). The following section will define each solar power system

and their suitability for on or around airports.

Concentrated Solar Power Systems

Concentrated solar power (CSP) systems use large reflective surfaces, such as lenses or mirrors, in

massive arrays to focus sunlight on a fixed point to produce intense heat. This heat is then converted to

energy. The most common types of CSP systems are the parabolic trough and solar power tower (FAA

2010). “CSP systems are generally only commercially viable on the large scale, typically for large

industrial facilities or as a wholesale electricity generator… CSP systems require a significant amount of

land” (APA 2014, p12-13).

According to the FAA, CSP systems are not compatible with airports due to concerns about these

systems’ high reflectivity, thermal plumes, radar interference, and airspace penetration.

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Concerns about these systems hazard to safe air navigation include (FAA 2010, p9):

1. Potential glint and glare caused by CSP systems, such as the parabolic trough and heliostats

[i.e., large, flat sun-tracking mirrors], that might cause temporary loss of vision to pilots on

arrival or departure, or to Air Traffic Control personnel in the control tower.

2. Electromagnetic interference with on- and off-airport radar systems that may pick up a false

signal from the metal components of the CSP systems’ mirrors.

3. Physical penetration of navigable airspace from solar power towers.

4. Thermal plumes emitted by solar power towers that produce unexpected upward moving air

columns into navigable air space.

Solar Photovoltaic Systems

Solar photovoltaic (PV) systems are comprised of individual solar cells that collect the sun’s radiated

energy, convert the energy into electricity, and transmit the electricity into a usable form. These solar

cells are typically assembled in a solar panel which can be attached to an existing structure, such as a

rooftop, or be placed on a stand that is mounted on the ground. Solar PV systems have been used by

homes, businesses, manufacturing facilities, etc. (APA 2014, FAA 2010).

According to the FAA, “In comparison with CSP systems, solar PV is more compatible with airport land

use because it… is designed to absorb light (rather than reflect it), minimizing potential impacts of

glare.” (FAA 2010, p8). Solar PV panels are designed to absorb as much light as possible in order increase

electricity production efficiency. Due to this design, all light that passes through the front surface of the

panel is trapped in the layers below. Therefore, the only surface where reflection is a concern is the

front surface. A majority of solar PV system panels have a front surface made of glass that is designed to

maximize light absorption and minimize light reflection. Panels are constructed of dark, light-absorbing

materials and covered with an anti-reflective coating in order to limit reflection (Shea 2012). “Today’s

panels reflect as little as 2% of the incoming sunlight depending on the angle of the sun and assuming

use of anti-reflective coatings.” (FAA 2010, p37).

Solar Thermal Systems

Solar thermal systems use the sun’s thermal energy to heat a fluid, such as water, to provide hot water

or space heating and cooling needs for residential, commercial, or industrial facilities. This fluid heats up

from the sun’s thermal energy as it passes through panels or tubes. These systems are usually mounted

on rooftops (APA 2014). The compatibility of solar thermal systems with surrounding aviation land use is

similar to that of solar PV systems since the design of these two systems is similar (FAA 2010). Solar PV

systems and solar thermal systems are also commonly treated the same under zoning regulations since

they are very similar in land use impacts (Lovelady 2014).

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III. SOLAR PANEL SURFACES

One factor that can impact glare is the texture of the surface of a solar PV panel. The texture of the

surface of a solar panel can impact whether reflected light is: 1) specular or 2) diffuse. Specular reflected

light is more concentrated and therefore reflects with greater intensity and causes glare. Smooth or

polished surfaces such as mirrors or smooth glass produce more specular reflections. Diffused reflected

light is scattered and therefore is a less concentrated light. Because this light is not reflected directly,

glare is not produced. Rough or textured surfaces with small types of indentions produce diffuse

reflections (FAA 2010, Ho 2013).

“It is possible to provide a front surface texture to solar [panel] glass which will convert the reflected

light from effectively entirely specular to entirely diffuse. In installations where glare is thought to be an

issue but not resolvable by appropriate siting of the solar array, the use of an appropriately textured

front surface can eliminate glare problems completely.” (Shea 2012, p4). Textured glass, as well as anti-

reflective coatings on solar panels, can reduce the near-normal specular reflectance of solar panels to

approximately 1-2% (Ho 2013).

IV. SOLAR PANEL SITING

The siting of a solar panel installation is another factor that can impact glare. “Proper siting of solar

energy installations, taking into account the size of the solar energy system, distance, orientation,

environmental conditions and key observation points, is perhaps the most effective way to mitigate the

negative impacts of glare.” (Ho 2013, p31). One tool which can assist in determining the proper siting of

a solar PV installation in order to avoid or minimize glare is the Solar Glare Hazard Analysis Tool.

Solar Glare Hazard Analysis Tool

The Solar Glare Hazard Analysis Tool (SGHAT) is a free and available to the public web-based tool which

determines when and where glare will occur throughout the year from a solar PV system. This tool also

assesses potential effects on the human eye at locations where glare occurs. The SGHAT tool uses an

interactive Google map where the user can locate a site, draw an outline of the proposed solar PV

system, and specify observer locations or final approach paths. The user also enters information

regarding the orientation and tilt of the solar PV panels, reflectance, environment and ocular factors.

Through the Google interface, the SGHAT tool automatically records the latitude, longitude and

elevation in order to determine information regarding sun positioning. Results of the tool are presented

in a plot that specifies when glare will occur through the year, with color codes indicating the potential

ocular hazard. (Ho 2013).

In October 2013, an interim FAA policy that requires the use of the SGHAT tool to demonstrate

compliance with the standards for measuring ocular impact for any proposed solar energy system (i.e.,

solar PV or solar hot water) located on a federally obligated airport. These FAA requirements could be

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considered as requirements listed in ordinances which regulate solar installations in the counties and

municipalities surrounding military aviation operations and flight paths. According to the interim FAA

policy, “All sponsors of federally-obligated airports who propose to install or to permit others to install

solar energy systems on the airport must attach the SGHAT report, outlining solar panel glare and ocular

impact, for each point of measurement” (DOT 2013, p63278). “The airport sponsor is required to

demonstrate that the proposed solar energy system meets the following standards (DOT 2013, p63277):

1. No potential for glint or glare in the existing or planned Airport Traffic Control Tower (ATCT) cab,

and

2. No potential for glare or “low potential for after-image”… along the final approach path for any

existing landing threshold or future landing thresholds (including any planned interim phases of

the landing thresholds) as shown on the current FAA-approved Airport Layout Plan (ALP). The

final approach path is defined as two (2) miles from fifty (50) feet above the landing threshold

using a standard three (3) degree glidepath.

Ocular impact must be analyzed over the entire calendar year in one (1) minute intervals from

when the sun rises above the horizon until the sun sets below the horizon.”

The SGHAT tool was developed by Sandia National Laboratories, a contractor for the U.S. DOE’s National

Nuclear Security Administration and supports numerous federal, state, and local government agencies,

companies, and organizations. The SGHAT tool is available at: https://share.sandia.gov/phlux.

V. SAMPLE ORDINANCES

Proposed Ordinance Regulating the Operation and Maintenance of Solar Energy Facilities in

Wayne County, NC

Due to the presence of Seymour Johnson Air Force Base in Wayne County, NC, this county’s proposed

solar energy ordinance could be a useful reference for the counties and municipalities surrounding

military aviation operations and flight paths who are interested in drafting their own solar energy

ordinance. Wayne County’s proposed ordinance considers the AFB as well as the Air Installation

Compatible Use Zones (AICUZ). Section Five. Location states (p3):

B. All solar energy facilities shall be considered a special use in all areas of the county covered by

the Seymour Johnson AFB Airspace Control Surfaces as defined in the 2011 Air Installation

Compatible Use Zone (AICUZ) report or subsequent reports. Approval as a special use must be

from the Wayne County Board of Adjustment.

C. All solar energy facilities located in areas covered by the 2011 AICUZ report or subsequent

reports must receive a recommendation from the Seymour Johnson AFB base commander or

designated official.

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Section Six. Supplemental Regulations states (p3-4):

F. The design and construction of solar energy facilities shall not produce light emissions, either

direct or indirect (reflective), that would interfere with pilot vision and/or traffic control

operations as stated in section 3.2.2 of the 2011 AICUZ report.

G. The design and construction of solar energy facilities shall not produce electrical emissions that

would interfere with aircraft communications systems or navigation equipment as stated in

Section 3.2.2 of the 2011 AICUZ report.

The proposed ordinance in its entirety can be downloaded at the Wayne County’s website:

http://www.waynegov.com/Page/330.

Template Solar Energy Development Ordinance for North Carolina

The “Template Solar Energy Development Ordinance for North Carolina” was developed by the North

Carolina Clean Energy Technology Center (NCCETC) and the North Carolina Energy Association. Version

1.0 of the ordinance was released in December of 2013 and was produced through a study of current

North Carolina solar ordinances and available state model ordinances, five public forums across the

state, and input from a stakeholder working group. This working group was composed of

representatives of many agencies, institutions, organizations and local government, including the FAA,

the North Carolina Governor’s Office - Military Affairs, and the North Carolina Department of

Environment and Natural Resources - Military Affairs and Strategic Planning.

Overall, the ordinance is designed to be used by county and municipal governments in regulating the

construction, installation, and operation of Solar Energy Systems (SES). The ordinance addresses some of

the most common considerations that arise in the permitting of SESs, including aviation notifications

and potential impacts to low altitude military flight paths. Section 7: Aviation Notification states (p9-10):

The requirements below apply only to Level 1, 2, & 3 [solar energy] systems over half (½) an acre in

size:

a. A map analysis showing a radius of five (5) nautical miles from the center of the SES with any

airport operations within this area highlighted shall be submitted with permit application.

b. For consideration of potential impacts to low altitude military flight paths, notification of

intent to construct the SES shall be sent to the NC Commanders Council1 at least 30 days

before the CUP/SUP [i.e., Conditional Use Permit/Special Use Permit] hearing for Level 3

SESs and at least 45 days before starting construction for applicable Level 1 & Level 2 SESs.

1 Mail: Commanding General; Attn: Community Plans and Liaison (NC Commanders Council); Marine Corps Installations East (MCIEAST); PSC Box 20005; Camp Lejeune, NC 28542 Email: Subject: NC Commanders' Council Notification of Solar Development Project in "Town or County Name" Address: Gray CIV Alexander K [alexander.gray@mcw.usmc.mil]

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Notification shall include location of SES (i.e. map, coordinates, address, or parcel ID),

technology (i.e. roof-mounted PV, ground-mounted fixed PV, tracked PV, solar thermal,

etc.), and the area of system (e.g. 5 acres). Proof of delivery of notification and date of

delivery shall be submitted with permit application.

c. The latest version of the Solar Glare Hazard Analysis Tool (SGHAT)2 shall be used per its

user’s manual to evaluate the solar glare aviation hazard. The full report for each flight path

and observation point, as well as the contact information for the zoning administrator, shall

be sent to the authority indicated below at least 30 days before the CUP/SUP hearing for

Level 3 SESs and at least 45 days before starting construction for Level 1 & Level 2 SESs.

Proof of delivery of notification and date of delivery shall be submitted with permit

application.

i. Airport operations at airport in the National Plan of Integrated Airport Systems

(NPIAS)3 within 5 nautical miles of the center of SES: provide required information

to the Federal Aviation Administration’s (FAA) Airport District Office (ADO) with

oversight of North Carolina4

ii. Airport operations at airport not in the NPIAS, including military airports, within 5

nautical miles of the center of SES: provide required information to the NC

Commanders Council for military airports and to the management of the airport for

non-military airports

Any applicable SES design changes (e.g. module tilt, module reflectivity, etc.) after initial submittal

shall be rerun in the SGHAT tool and the new full report shall be sent without undue delay to the

contact specified in 7.b.i and 7.b.ii above for accurate records of the as-built system.”

Appendix F: Airports of the ordinance further discusses the SGHAT and recommended steps required to

complete the above aviation notification requirement in the ordinance. The ordinance in its entirety can

be downloaded at the NCCETC’s website: http://nccleantech.ncsu.edu/technology/renewable-

energy/solar/template-ordinance-for-solar-energy-development-in-north-carolina/.

Other Ordinances

Many communities around the country have developed ordinance regulations specific to solar energy

systems. The following section will provide examples of language used in these ordinances that

specifically address glare. However, these ordinances do not specifically address aviation operations and

low-level military flight paths. These ordinances discuss other requirements for installing solar energy

systems, but the following section will focus only on glare.

One item to note is that these ordinances are fairly general in their requirements concerning glare.

These ordinances usually states that solar power systems must be designed and sited to avoid glare on

2 http://sandia.gov/glare 3 http://www.faa.gov/airports/planning_capacity/npias/reports/ 4 As of October 2013 this is the Memphis ADO

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adjacent properties or roadways, but do require a glare study or the use of specific glare mitigation

techniques.

Iron County, Utah. 2013. Iron County Code. Title 17. Zoning. Chapter 17.33. Solar Power Plants. Section

17.33.050. Provisions for Conditional Use Permit Review.

Following the provisions of Chapter 17.28, Iron County Code, additional or more thorough consideration

shall be given to the following as the County determines whether the project needs to be approved,

denied, or conditionally approved:

E. Visual Impacts, Appearance, and Scenic Viewsheds. Potential visual impacts may be caused by

components of the project such as mirrors, solar towers, cooling towers, steam plumes,

aboveground electrical lines, accessory structures, access roads, utility trenches and installations,

and alteration of vegetation. Those projects that are within a sensitive viewshed, utilize reflective

components (e.g., exposed mirrors), or that propose structures taller than thirty feet must provide a

viewshed analysis of the project, including visual simulations of the planned structures and analysis

of potential glare impacts. The number of visual simulations shall be sufficient to provide adequate

analysis of the visual impacts of the proposal, which shall be from no less than four vantage points

that together provide a view from all sides of the project. More visually sensitive proposals (e.g.,

solar power towers or exposed mirrors in sensitive viewsheds) may require analysis from

significantly more vantage points, such as different distances and sensitive locations. The planning

commission may also require a Zone of Theoretical Visibility/Zone of Visual Impact (ZVI) Analysis,

which is a three hundred sixty degree computer analysis to map the lands within a defined radius of

a location that would likely be able to see an object. Significant visual impacts that cannot be

adequately mitigated are grounds for denial.

F. Height Restrictions and FAA Hazard Review. Compliance with any applicable airport overlay zoning

requirements and the ability to comply with FAA regulations pertaining to hazards to air navigation

must be demonstrated.

Available at: https://library.municode.com/index.aspx?clientId=16163

Monroe County, Pennsylvania. Model Ordinance for On-Site Usage of Solar Energy Systems

Section 1. The Zoning Ordinance of [Municipality name] [Section/Article], Definitions, shall be amended

to include the following definitions:

Solar Glare: The effect produced by light reflecting from a solar panel with an intensity sufficient to

cause annoyance, discomfort, or loss in visual performance and visibility.

Section 3. The Zoning Ordinance of [Municipality name] [Section/Article], Accessory Regulations, shall be

amended by adding [Section/Article#] as follows:

1. The installation and construction of a solar energy system shall be subject to the following

development and design standards:

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K. Solar panels shall be placed such that concentrated solar radiation or glare shall not

be directed onto nearby properties or roadways.

L. Solar panels shall not be placed in the vicinity of any airport in a manner that would

interfere with airport flight patterns. Acknowledgements from the Federal Aviation

Administration may be necessary.

Available at:

http://www.co.monroe.pa.us/planning_records/lib/planning_records/planning/model_monroe_county

_on-site_usage_of_solar_energy_systems.pdf

Cumberland County, Pennsylvania. 2011. “Solar Energy Systems Model Ordinance.”

Section 2 – Definitions

GLARE: The effect produced by light reflecting from a solar panel with an intensity sufficient to

cause annoyance, discomfort, or loss in visual performance and visibility.

Section 3 – Accessory Solar Energy Systems (ASES)

A. Regulations Applicable to All Accessory Solar Energy Systems:

9. Glare

a. All ASES shall be placed such that concentrated solar radiation or glare does not

project onto nearby structures or roadways.

b. The applicant has the burden of providing that any glare produced does not have

significant adverse impact on neighboring or adjacent uses either through siting or

mitigation.

Available at: http://www.ccpa.net/DocumentCenter/Home/View/7947

Oregon Department of Energy. 2005. “A Model Ordinance for Energy Projects.”

II. Model Ordinance

##.05 Permitting Process for Energy Projects

##.05.01. Application

An applicant for a Conditional Use/Special Use permit must submit an application to the

[county/city] Planning Department on the form prescribed by the Department…. The applicant

must include the following:

(2) Maps showing the physical features and land uses of the project area, both before and

after construction of the proposed energy project. The applicant must include at least one

map printed on a standard 8 ½” x 11” page. The applicant must include maps or color

photographs that show:

(h) The location and distance to public or private airports or airstrips.

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##.07 Specific Standards for Energy Projects

##.07.02. Solar Energy Generation

(5) Misdirection of Solar Radiation: The proposed solar energy project has been designed and

would be operated to prevent the misdirection of concentrated solar radiation onto nearby

property, public roads or other areas accessible to the public.

(7) Airport proximity: The proposed solar energy project is not located adjacent to, or within, the

control zone of any airport.

Available at: http://www.oregon.gov/energy/Siting/docs/ModelEnergyOrdinance.pdf

City of Albany, New York. 2011. City Code. Chapter 375. Zoning. Article XIV. Specific Use Regulations.

Section 375-93. Solar energy equipment.

A. Definitions. As used in this section, the following terms shall have the meanings indicated:

Solar Collector. A solar photovoltaic cell, panel, or array, or solar hot air or water

collector device, which relies upon solar radiation as an energy source for the

generation of electricity or transfer of stored heat.

E. Ground-mounted solar collectors are permitted as accessory structures in all zoning districts,

subject to the following requirements:

(4) The solar collectors do not emit unreasonable glare and negatively impact adjacent

properties.

City of Calabasas, California. 2011. Municipal Code. Title 17. Land Use and Development. Article III.

Site Planning and Project Design Standards. Chapter 17.20. General Property Development and Use

Standards. Section 17.20.190. Solar Energy Development Standards.

“Any proposed active or passive heating and cooling features shall be incorporated into the design of a

structure as follows:

D. Exterior surfaces of the collectors and related equipment shall have a non-reflective finish and

shall be color-coordinated to harmonize with roof materials and other dominant colors of the

structure."

Available at: http://library.municode.com/index.aspx?clientId=16235&stateId=5&stateName=California.

Township of Dundee, Michigan. 2010. Ordinance No. 09-10-01: Solar Panel Zoning Ordinance

Amendment. Section 5.44. Solar Panels.

“Solar panels shall be allowed in all zoning districts either attached to permitted principal or accessory

buildings or as accessory structures subject to the following regulations:”

3. Glare. Solar panels shall be placed and arranged such that reflected solar radiation or glare

shall not be directed onto adjacent buildings, properties or roadways."

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Available at: www.dundeetownship.info/zoning_ordinance.asp

City of Kingston, California. “Landscaping and Site Design Guidelines for Large-Scale, Ground-Oriented

Solar Energy Facilities.”

3. Visual Appearance and Impact

a) No solar energy facility will produce glare that would constitute a nuisance to occupants of

neighboring properties, to persons traveling on public roads, or within known local flight routes

to the Kingston Municipal Airport. Glare resistance solar panels should be used wherever

possible.

Available at:

https://www.cityofkingston.ca/documents/10180/66535/Solar+Design+Guidelines/660a6028-784f-

4635-948b-c368d17bffd8

VI. REFERENCES

American Planning Association (APA). 2014. Planning for Solar Energy. Report Number 575. Available at

https://www.planning.org/store/product/?ProductCode=BOOK_P575.

Department of Transportation (DOT), Federal Aviation Administration. 23 October 2013. “Interim Policy,

FAA Review of Solar Energy System Projects on Federally Obligated Airports.” 78 Federal Register 205.

p63276-63279. Available at http://www.faa.gov/airports/environmental/.

Federal Aviation Administration (FAA), Office of Airports. 2010. Technical Guidance for Evaluating

Selected Solar Technologies on Airports. Washington, D.C.: Federal Aviation Administration. Available at

http://www.faa.gov/airports/environmental/.

Ho, Clifford K. 28 April 2013. Relieving a Glaring Problem. Solar Today. Available at

https://share.sandia.gov/phlux/static/references/glint-glare/Ho-SolarToday-April13_v2.pdf.

Lovelady, Adam. 2014. Planning and Zoning for Solar in North Carolina. The University of North Carolina

at Chapel Hill, School of Government. Available at http://www.sog.unc.edu/node/30896.

Shea, Stephen P. 2012. Evaluation of Glare Potential for Photovoltaic Installations. Available at

http://www.suniva.com/documents/Suniva%20Reflection%20and%20Glare%20Report%20-

%20Marketing%20-%20August%202012.pdf.