This video provides a walk-through of a demo PV glare analysis. Watch as we evaluate an imaginary photovoltaic installation for potential solar glare reflections. We'll set up the PV system in the editor and model nearby receptors, including an airport. We'll also conduct a glare optimization to assess alternative module tilts and orientations.

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• Mozilla Firefox
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Projects are an organizational means of grouping together the related Site Configurations, analysis results, and Optimizations for a single real-world project. The quantity of glare analyses and optimizations available for a Project is determined by the Project Tier.

PV arrays within a project may be located up to 3 miles (5 km) from the first analyzed set of PV arrays. This project boundary is visualized in the editor as a blue circle encompassing the active project area.

Project name

Unique name to distinguish a particular project. For example, "LAX parking rooftop PV phase 1" or "Main street solar farm"

Tier

The project tier determines the PV system size, footprint area, and quantity of components that can be evaluated in a single glare analysis.

• Basic - PV systems up to 1 MW (8 acres), or projects containing Vertical Surfaces
• Advanced - PV systems of any size
• V1 - projects created prior to the 2021A update

Project Tiering	Basic	Advanced
System size (approx.)	< 1 MW	Any size
PV area	< 8 acres (32,370 m2)	Any size
Glare analyses	20	30
Optimizations	5	5
# PV footprints	10	20
# Vertical surfaces	10	20
# Flight paths	10	20
# Routes	10	20
# Observation points	20	40

Client

Optional name of client which will be displayed with results

Approximate system size

PV system size range under analysis. Not applicable for Vertical Surface projects.

Description

Optional description for user convenience.

Timezone offset

Numerical +/- offset from UTC/GMT of the site location. For example, a site in New York, USA would utilize a timezone offset of -5. Options range from -12 to +14.

Distance units

Whether the distances, including heights and elevations, should be displayed in feet or meters.

A Site Configuration, or "site config", includes 1+ reflective surfaces and 1+ receptors. Use site configs to describe a particular configuration of PV array(s) and/or vertical surfaces. For example, a project may contain several site configs, each describing a different module tilt and orientation of the same set of PV array footprints.

Site configs can be cloned in the editor (Site Configuration -> Save As...) to quickly duplicate a set of components to, for example, evaluate an alternative module design without overwriting the original.

Site name

Alphanumeric name describing this site and configuration

Configuration description

Optional description of this particular site and configuration

Time interval (min)

The time step, or sampling interval, for the annual glare hazard analysis. The sun position will be determined at each time step throughout the year. Regulatory authorities typically require a time-step of 1 minute. Other values can be used to conduct faster analyses or "spot check" alternative configurations. The time interval must evenly divide 1440 (i.e. number of minutes in a day); suitable alternatives are 2, 4, 5, 10, 15, 20.

Minimum sun altitude (deg) new

Lower bound denoting the minimum altitude at which the sun is visible (year-round). Glare occurring when the sun is below this altitude will be ignored. For example, a PV location surrounded by large hills would have a higher Minimum sun altitude. Defaults to 0 °.

Peak DNI (W/m² or Wh/m²)

The maximum Direct Normal Irradiance at the given location at solar noon. DNI is the amount of solar radiation received in a collimated beam on a surface normal to the sun during a 60-minute period. On a clear sunny day at solar noon, a typical peak DNI is ~1,000 W/m². More accurate values for a specific site location may be available from other data sources. The data sets from the U.S. National Solar Radiation Database contain similar values for locations throughout the U.S.

If seeking an alternative DNI, verify the data type and format are valid

DNI varies?

If checked, the peak DNI will be scaled at each time step according to the changing position of the sun and reduced DNI in the mornings and evenings. If unchecked, the DNI at every step will be set to the Peak DNI.

Assess luminance new

Instructs the analysis to compute glare luminance data (cd/m²) for the PV system(s) and receptors. The results will included luminance charts, peak luminance data, and per-step luminance data in the result data file.

Assess luminance if you need to satisfy policies regarding comparison with luminance thresholds like 20,000 cd/m²

Create PV glare data file(s)?

The glare analysis will also output an XLS file containing data on times of glare for each receptor

Sun angle (mrad)

The average subtended angle of the sun as viewed from earth is ~9.3 mrad or 0.5°.

Use enhanced subtended source angle calculation?

Whether the analysis utilizes improved computation of subtended source angle regarding glare-spot size (2022C Update).

Ocular transmission coefficient

Coefficient accounting for radiation that is absorbed in the eye before reaching the retina. A value of 0.5 is typical (Ho, 2011; Sliney, 1973).

Pupil diameter (m)

Defines the diameter of the pupil of the observer receiving predicted glare. The size impacts the amount of light entering the eye and reaching the retina. Typical values range from 0.002 m for daylight- adjusted eyes to 0.008 m for nighttime vision (Ho, 2011; Sliney, 1973).

Eye focal length (m)

Distance between the nodal point (where rays intersect in the eye) and the retina. This value is used to determine the projected image size on the retina for a given subtended angle of the glare source. A typical eye focal length is 0.017 m (Ho, 2011; Sliney, 1973).

An XLSX data file containing site and component data can be exported from the Site Components & Results page after the site has been saved. This data file is distinct from the glare analysis data file, which contains analysis results. The Component data file can be used in the XLS Import feature to create a new copy of the site; for example, to quickly edit PV vertex coordinates and then import the modified version into the project.

For more information on the component parameters and descriptions, refer to the XLS Import Template.

The Site Component Data File also contains sample tracking data if PV systems utilizing single-axis tracking and newer backtracking strategies are modeled. This should be used to understand and verify the tracking behavior. Tracking data is provided for each SAT system in separate worksheets and includes data and plots for Jan. 1, Jun. 21, and Dec. 21. Tracking data includes:

Time: the time-step of sampled data, in 10-minute increments

Sun altitude (°): elevation of sun above horizon.

Sun azimuth (°): orientation of sun, measured clockwise, with true north at 0°.

PV normal vector (i,j,k): vector components of normal vector describing PV module configuration. Components are (east, north, up). e.g. flat panels lying on flat ground have a normal vector of (0, 0, 1).

PV rotation angle (°): panel rotation angle, including backtracking, measured +west with flat at 0°. (Note that the vector component is +east.)

PV true tracking angle(°): "ideal" panel rotation angle, ignoring backtracking.

Glare analysis results are displayed on the Site Configuration Components & Results page after an analysis is submitted in the Editor. Results are displayed in the following sections:

The various properties and component parameters should be verified before utilizing glare analysis results, to ensure their accuracy.

The Result page header displays various properties of the project and site configuration, and includes additional buttons to generate an aviation report, open the Editor, and export a component data file.

A non-interactive Google map displaying the components will also appear in the header section. (Note that this map may not be displayed for complex sites, due to map generation limitations.)

The Glare Analysis Summary tab, which is displayed when first loading the site config page, includes a table summarizing expected glare, as well as compact tabulations of components and their parameters. Use this tab to quickly review components and analysis results.

The PV Array Results tab contains detailed data and visualizations of expected glare. The results are organized by PV array and then by component. A summary of glare expectations is provided first, and includes clickable PV names for convenient navigation.

A table of distinct glare, tabulated by month, is displayed below the analysis summary table. It describes total non-overlapping glare expected from each PV array for all receptors (see figure).

PV array analysis results for which glare is predicted will include various plots describing the expected times, duration, and location of glare for each receptor, on an annual basis. These plots are described below.

Note that plots will not be displayed when no glare is predicted for a particular receptor of PV array. Furthermore, some plots are excluded from the aviation report.

An XLS data file describing the times and characteristics of glare can be generated for each PV array and Vertical Surface. To enable data file creation, check the Create glare data file? option under the Site Config settings in the Editor.

The data file includes a worksheet for each receptor expecting glare. Glare characteristics for each time-step are tabulated in each sheet. Included data is described below. Note that some times of glare included in the data file may be excluded from the analysis results due to filtering.

Corneal Irradiance (W/cm²)

Irradiance (flux per unit area) at plane in front of cornea, from glare emanation

DNI (W/m²)

Direct Normal Irradiance from sun at location. Derived from scaling Peak DNI according to time and sun position.

Ocular Hazard #

Numeric representation of predicted glare hazard: 0 (no glare), 1 (green glare), 2 (yellow glare)

Reflectivity

Fraction of light reflecting toward receptor. Reflectivity depends on material, module configuration, and sun position.

Retinal Irradiance (W/cm²)

Irradiance (flux per unit area) impacting retina, at back of eye. Defines y-axis of hazard plot. Note that retinal irradiance does not depend on distance to source.

Subtended Glare Angle (rad)

Angle subtended by glare spot on PV array from point-of-view of receptor (i.e. effective glare spot size when viewed by observer). Defines x-axis of log-log hazard plot.

Sun Azimuth (°)

East/north component of angular position of sun. Measured clockwise from true north at 0°. Azimuth of 180° indicates sun is due south.

Sun Altitude (°)

Vertical (elevation) component of angular position of sun at given time. 0° implies sun is at horizon (i.e. sunrise/sunset). 90° indicates sun is directly overhead.

Sun Position Vector (i, j, k)

Cartesian unit vector describing position of sun, extending from PV array. (i, j, k) components represent (east, north, up).

Reflected Sun Vector (i, j, k)

Cartesian unit vector describing reflected sunlight emanating outward from PV array. i.e. path of glare. Note that methodology simulates glare as polyhedral or conical emanation to account for beam spread; this vector defines the conical/polyhedral axis.

Sun/module incidence angle (°)

Angle between panel normal vector and sun position vector. Angle of 0° indicates panel is directly facing sun. Angle of 90° indicates sun and panel vectors are orthogonal to each other (e.g. panel on flat ground and sunrise/sunset).

Luminance (cd/m²)

Solar glare luminance for human viewer observing glare source. This value utilizes the subtended glare angle of the reflected beam, the reflectance as a function of angle of incidence of the sun, and a direct solar luminance of 1.57E+9 cd/m².

Printable PDF documents can be downloaded to preserve glare analysis results. Several report variations are available and are described below. These reports can be obtained from the Site Configuration Results page, via the "Reports" button.

Generic Analysis Report new
The generic analysis report includes all analysis results except the "distinct glare per month" data table. It includes data and plots for each reflective surface and receptor component. This report duplicates the contents of the glare analysis results page for local storage and can act as documentation of the site evaluation.

FAA 2021 Aviation Report new
The 2021 FAA report document is themed for the U.S. Federal Aviation Administration Final Policy regarding PV projects on federally-obligated airports, released in May 2021. This report includes an executive summary page which estimates the adherence of the site results according to this policy, which requires no glare for Air Traffic Control Towers.

FAA 2013 Aviation Report
The 2013 FAA document is themed for the U.S. Federal Aviation Administration Interim Policy regarding PV projects on federally-obligated airports, released in 2013. This report includes an executive summary page which estimates the adherence of the site results according to this policy, which requires no glare for Air Traffic Control Towers and no yellow glare for aircraft on a 2-mile straight approach path.

If these reports do not satisfy your documentation needs, contact us to submit feedback.

Photovoltaic systems are represented by a contiguous planar polygon footprint and a set of customizable parameters. Each distinct PV installation must be modeled with it's own PV array footprint in the editor. PV footprints comprise 3 to 80 vertices which are described by a latitude, longitude, elevation and height.

During analysis, sunlight is reflected over each PV array on a minute-by-minute basis according to the user-specified module tilt and orientation or axis tracking parameters if the system is not fixed-mount. The system then checks whether the resulting solar reflections intersect (impact) the receptors.

PV footprint vertex coordinates, including elevation, are independent of the orientation and tilt. The vertices establish the tilt of the PV-array plane and do not influence the tilt or orientation of the individual panels themselves. For example, panels mounted flush on a 30° pitched roof will have PV-array vertices with different elevations to accommodate the pitched roof and resulting tilted PV-array plane (e.g., two vertices at 15 feet and two vertices at 10 feet). However, the panels should still be prescribed with a tilt of 30° (if they are flush mounted against the 30° pitched roof) and the appropriate orientation. A tilt of 0° indicates that the panels are parallel with the earth’s surface and facing upward, regardless of the prescribed vertex elevations.

ForgeSolar does not rigorously represent the detailed geometry of a system; detailed features such as gaps between modules, variable height of the PV array, and support structures may impact actual glare results. The PV array is simulated as a footprint filled with infinitesimally small panels reflecting sunlight in the trajectory of the tilt and orientation.

General PV array parameters are described below. Module configuration, tracking and vertex parameters are described in subsequent sections.

Name

Descriptive alphanumeric name of this PV array

Description

Optional textual description of array

Axis tracking

Whether PV array modules are fixed-mount or utilize single- or dual-axis tracking. Tracking parameters are described in later sections.

Rated power (kW)

Used to calculate the approximate maximum annual energy produced (kWh) from the system in the prescribed configuration (assuming clear sunny days). This is useful for comparing alternative configurations to determine which one has the maximum energy production. ForgeSolar system output calculations are approximate and should not supercede more accurate calculations conducted elsewhere.

Module surface material

The type of material comprising the PV modules. The reflectivities of the material choices have been characterized to generate scaled values for each time step. Refer to the Module Reflectance Profiles section for additional information.

Reflectivity varies with incidence angle

If checked, the reflectivity of the modules at each time step will be calculated as a function of module surface material and incidence angle between the panel normal and sun position.

Reflectivity

Specify the solar reflectance of the PV module. Although near-normal specular reflectance of PV glass (e.g., with antireflective coating) can be as low as ~1-2%, the reflectance can increase as the incidence angle of the sunlight increases (glancing angles); for example, at sunrise and sunset for low-tilt panels. Based on evaluation of several different PV modules, an average reflectance of 10% is provided as a default value. Only used if reflectivity does not vary with incidence angle.

Slope error (mrad)

Specifies the amount of scatter that occurs from the PV module. Mirror-like surfaces that produce specular reflections will have a slope error closer to zero, while rough surfaces that produce more scattered (diffuse) reflections have higher slope errors. Based on observed glare from different PV modules, an RMS slope error of ~10 mrad (which produces a total reflected beam spread of 0.13 rad or 7°) appears to be a reasonable value. Not used if correlate slope error to module surface type is checked.

Correlate slope error with surface type

If checked, the slope error value will be set per the table below, based on the selected material.

PV Cover Type	Average RMS Slope Error (mrad)	Average Beam Spread (mrad)	Standard deviation of slope error	Standard deviation of beam error
Smooth glass without anti-reflection coating	6.55	87.9	4.43	53.3
Smooth glass with anti-reflection coating	8.43	110	2.58	30.9
Light textured glass without anti-reflection coating	9.70	126	2.78	33.3
Light textured glass with anti-reflection coating	9.16	119	3.17	38.0
Deeply textured	82.6	1000	N/A	N/A

Fixed-mount PV panels are described by a tilt and orientation. These parameters are referred to as the module configuration of the PV array.

Module orientation/azimuth (°)

The azimuthal facing or direction toward which the PV panels are positioned. Orientation is measured clockwise from true north. Panels which face north, which is typical in the southern hemisphere, have an orientation of 0°. Panels which face south, which is typical in the northern hemisphere, have an orientation of 180°. If a known orientation is based on magnetic north, the location-specific declination must be used to determine the orientation from true north.

Module tilt (°)

The elevation angle of the panels, measured up from flat ground. Panels lying flat on the ground (facing up) have a tilt of 0°. Tilt values between 0° and 40° are typical.

PV Arrays can comprise up to 80 vertices. Each vertex is described by the following parameters.

Latitude (°)

North-south measurement of location relative to the equator, with range of [-90° to 90°]. Latitude is measured in decimal degrees and assumes the WGS84 datum.

Longitude (°)

Measurement of east-west position relative to Prime Meridian, with range of [-180°, 180°]. Longitude is measured in decimal degrees and assumes the WGS84 datum.

Elevation/altitude (ft or m)

Elevation above mean sea level at specified location. ForgeSolar automatically queries the Google Elevation services for an approximate value.

Height above ground (ft or m)

User-specified height above ground of point. The height of a rooftop PV system should measure from the ground to the PV panel centroid above the roof. A ground-mount system would have a height measured to the PV panel centroid.

Total elevation (ft or m)

Sum of the elevation and height above ground. The system will automatically calculate the height or total elevation when the other is provided. During analysis, the total elevation determines the Cartesian Z value of the point. For more accuracy, the user should perform analyses using minimum and maximum values for the vertex heights, based on the PV panel dimensions, to bound the height of the plane containing the solar array. Doing so will expand the range of observed solar glare when compared to results using a single height value.

Vertices describing a level rooftop should share an identical total elevation.

ForgeSolar can simulate single- and dual-axis tracking PV systems. Single-axis trackers follow the sun in one dimension (east-west), whereas dual-axis trackers track the sun in both dimensions.

• To model single-axis tracking, set the tracking parameter to single.
• To model dual-axis tracking, set the tracking parameter to dual.

Corresponding inputs for PV tracking will appear in the editor after the tracking parameter is adjusted.

Single-axis trackers, or SAT systems, follow the rotation of the sun along the east-west axis throughout the day. SAT arrays are typically oriented with their axis of rotation aligned north-south. SAT systems may reduce glare for nearby receptors because they typically reduce the incidence angle between the modules and the sun, yielding smaller glancing angles and a higher vertical trajectory for glare reflections.

The rotation angles over which the modules track the sun daily is referred to as the range of rotation or window of rotation. The limits of this range are set by the maximum tracking angle, which is applied in both positive and negative directions. In other words, the SAT range of rotation equals twice the maximum tracking angle. For example, a PV system with a maximum tracking angle of 60° will track the sun daily through a full range of rotation of 120° (+/- 60° east to west) and will backtrack (if enabled) when the sun is outside this range or when too much shading occurs, depending on the backtracking strategy selected.

The backtracking PV parameter can be used to simulate various strategies that rotate the modules away from the sun to reduce shading. These strategies typically take effect when the sun's position lies outside the range of rotation defined by the maximum tracking angle of the PV panels, or when substantial shading occurs, depending on the strategy selected. The backtracking strategies simulated in ForgeSolar may deviate from real-world backtracking behavior due to system design, environmental conditions, and other factors. Tracking data and plots should always be reviewed to verify the expected panel tracking behavior (see note above).

The following backtracking strategies are available in ForgeSolar:

shade-slope: slope-aware method designed to accommodate PV modules placed on arbitrarily-oriented slopes and reduce shading. This option is selected by default for newly-created PV arrays. This strategy is derived from (Anderson, 2020).

shade: non-slope-aware temporal strategy that assumes panels are on flat ground. This option may lose accuracy for systems built on a slope (i.e. with vertical offsets between rows.) This strategy is derived from (Lorenzo, 2011).

interval: step-based method that discretely backtracks the PV modules over time.

instant: "legacy" implementation wherein PV modules immediately revert to the rest position, defined by the rest angle input, whenever the sun is outside the range of rotation. Note: this simplified strategy is available "as-is" as a legacy option to preserve the previous backtracking approach of SGHAT/ForgeSolar prior to the 2022A Update. Newer implementations of backtracking, such as shade-slope or shade, are recommended.

none: PV modules rotate to track the sun through the range of rotation determined by the (+/-) maximum tracking angle. The modules will not rotate beyond this limit and will not backtrack. This option effectively disables backtracking for single-axis tracking systems.

The following graphics illustrate the difference in rotation angle when backtracking is used. The PV system in the first graphic uses single-axis tracking without backtracking. The panel rotation angle matches the true tracking angle throughout the day.

The second graphic includes backtracking, whereby the panel rotation angle deviates from the true tracking angle when the sun position causes substantial shading between panels. Similar plots can be generated for a modeled SAT PV system from the Site Configuration page. For instructions on obtaining these plots, refer to the Component Data File section.

SAT PV Without Backtracking:

SAT PV With Backtracking:

SAT systems utilize one or more of the following PV parameters. The selected backtracking strategy determines which parameters are available.

Tilt of tracking axis (°)

Tilt above flat ground of axis over which panels rotate (e.g. torque tube). System on flat, level ground would have axis tilt of 0°. Tracking axis tilt is only used by instant and none backtracking strategies. Other backtracking strategies either compute the tilt from the slope (shade-slope) or assume the modules are on flat ground with no axis tilt.

Maximum tracking angle (°)

Maximum angle of rotation of tracking system in both east and west directions. For example, a typical system with a 120° range of rotation has a max tracking angle of 60° (east/west).

Resting angle (°)

Angle of rotation of panels when sun is outside tracking range and backtracking rotation has settled. In legacy "instant" backtracking, panels revert to the position described by this rotation angle at all times when the sun is outside the rotation range. In backtracking modes shade, shade-slope, and interval, the rest angle describes the most shallow possible angle of east/west rotation of panels during times of possible backtracking (i.e. early morning and late evening). For example, a system with backtracking strategy "shade" and rest angle of 5° will begin the day at 5° east, rotate toward the sun, then follow it's path until backtracking again activates in the evening. The panels will then backtrack toward a final rest position of 5° west. Depending on the backtracking and location, the panels may not always reach the rest angle position while the sun is up.

ForgeSolar simulates dual-axis tracking systems by setting the module normal vector according to the position of the sun at each daytime time-step. The trackers will follow the sun in both dimensions, from sunrise until sunset. ForgeSolar does not currently model backtracking with dual-axis tracking systems.

Non-PV vertical reflective surfaces, such as glass buildings and reflective billboards, can be modeled with the Vertical Surface ("VS") component. Each Vertical Surface is described by a path of two or more vertices and lower and upper edge heights which bound the portion of the surface that is reflective. Vertical Surfaces may include more than one planar face; for example, a four-sided glass building could be modeled with a single Vertical Surface component comprising four faces. Double-sided surfaces can also be simulated.

During analysis, incoming sunlight is simulated on a minute-by-minute basis to determine whether reflections from one or both sides of the VS impact receptors.

The Route receptor is a generic multi-line representation which can simulate observers traveling along continuous paths such as roads, railways, helicopter paths, and multi-segment flight tracks.

Routes can be created quickly in the Map Editor:

1. Activate the Route drawing mode by clicking the Route button above the map.
2. Click once on a location in the map to begin drawing a route
3. Click once to add a vertex to the route. Repeat as many times as is necessary; routes can include many line segments
4. Double-click on final position to end the Route
5. To add an additional vertex to the Route after it has already been completed, click and drag one of the "ghost" points within the polyline in the map.

General Route parameters are described below. In addition to these parameters, each Route comprises 2 to 30 vertices which describe its poly-linear representation.

Name

Descriptive alphanumeric label of receptor

Is route one-way?

If checked, the system will assume observers travel along the route in the direction it was drawn (i.e. order of increasing vertex #). Together with the view angle parameter, this will filter out glare appearing behind the path of travel. If unchecked (default), the system will assume observers travel in both directions.

View angle (°)

Defines the left and right field-of-view of observers traveling along the Route. A view angle of 180° implies the observer sees glare in all directions. A view angle of 50° (default) implies the observer has a field-of-view of 50° to their left and right, i.e. a total FOV of 100°. This default is based on FAA research which determined that the impact of glare that appears beyond 50° is mitigated (Rogers, 2015).

The Observation Point receptor ("OP") simulates an observer at a single, discrete location, defined by a latitude, longitude, elevation, and height above ground. In addition, it can be marked to represent an Air Traffic Control Tower ("ATCT") for aviation purposes.

Latitude

Geodetic coordinate defined by WGS-84 datum in decimal degrees with range of -90° to 90°

Longitude

Geodetic coordinate defined by WGS-84 datum in decimal degrees with range of -180° to 180°

Elevation

Location altitude above sea level. By default, elevation value is provided by Google Elevation service. If marker is moved manually, elevation will be re-queried.

Height

Height above ground of observer receptor. Examples: large height for ATCT or 5-6 ft. for person at ground level.

Is ATCT?

Check to mark OP as representing an Air Traffic Control Tower. System will review ATCT results for policy adherence when generating aviation PDF.

The 2-Mile Flight Path receptor ("FP") simulates an aircraft following a straight-line approach path toward a runway, by default, including a restricted field-of-view to filter unrealistic glare. In addition, it can be modified to represent a worst-case approach and takeoff path.

Name

Descriptive alphanumeric label of receptor

Direction (°)

Azimuthal angle of approach of aircraft which defines the straight path toward the runway. Measured clockwise from true north.

Glide slope (°)

Angle of descent of aircraft toward runway. Default value of 3°.

Threshold crossing height

Height above ground of aircraft when it crosses the runway threshold. (Typically 50 ft.).

Consider pilot field-of-view from cockpit

if enabled, the analysis will filter glare when it's approximate location is beyond the user-specified field-of-view ("FOV") parameters during approach.
If disabled, the analysis will apply the maximum FOV: an azimuthal view of 180° and downward view of 180°. (Previously, the V1 analysis methodology filtered glare beyond 50° azimuth and 30° vertical as "lime green" when the pilot FOV consideration was disabled.)

Max downward viewing angle (°)

The vertical FOV of the pilot, measured positive downward from the approach path vector. Acceptable values are 0° to 90°, where 90° implies no downward restriction. A default value of 30° assumes glare appearing beyond the corresponding FOV is mitigated. (The V1 methodology measured the downward angle from horizontal.)

Azimuthal viewing angle (°)

The left and right field-of-view of the pilot during approach. Acceptable values are 0° to 180°. A view angle of 180° implies the pilot can see glare emanating from behind the plane. A view angle of 50° (default) implies the pilot has a FOV of 50° to their left and right during approach, i.e. a total FOV of 100°. This default is based on FAA research which determined that the impact of glare appearing beyond 50° is mitigated (Rogers, 2015).

Point coordinates

The threshold and 2-mile point ground elevation parameters can be modified in the FP Advanced dialog. The 2-mile point height is calculated from the point elevations and threshold crossing height to ensure a smooth 2-mile descent path.

1. Times associated with glare are denoted in Standard time. For Daylight Savings, add one hour.
2. Result data files and plots are retained for two years after analysis completion. Files must be downloaded and saved if additional persistence is required.
3. The algorithm does not rigorously represent the detailed geometry of a system; detailed features such as gaps between modules, variable height of the PV array, and support structures may impact actual glare results. However, we have validated our models against several systems, including a PV array causing glare to the air-traffic control tower at Manchester-Boston Regional Airport and several sites in Albuquerque, and the tool accurately predicted the occurrence and intensity of glare at different times and days of the year.
4. Several V1 calculations utilize the PV array centroid, rather than the actual glare spot location, due to algorithm limitations. This may affect results for large PV footprints. Additional analyses of array sub-sections can provide additional information on expected glare. This primarily affects V1 analyses of path receptors.
5. Random number computations are utilized by various steps of the annual hazard analysis algorithm. Predicted minutes of glare can vary between runs as a result. This limitation primarily affects analyses of Observation Point receptors, including ATCTs. Note that the SGHAT/ForgeSolar methodology has always relied on an analytical, qualitative approach to accurately determine the overall hazard (i.e. green vs. yellow) of expected glare on an annual basis.
6. The subtended source angle (glare spot size) is constrained by the PV array footprint size. Partitioning large arrays into smaller sections will reduce the maximum potential subtended angle, potentially impacting results if actual glare spots are larger than the sub-array size. Additional analyses of the combined area of adjacent sub-arrays can provide more information on potential glare hazards. (See previous point on related limitations.)
7. The algorithm assumes that the PV array is aligned with a plane defined by the approximate total heights of the PV vertices. For increased accuracy, the user should perform runs using minimum and maximum values for the vertex heights to bound the height of the plane containing the solar array. Doing so will expand the range of observed solar glare when compared to results using a single height value.
8. The algorithm does not automatically consider obstacles (either man-made or natural) between the observation points and the prescribed solar installation that may obstruct observed glare, such as trees, hills, buildings, etc.
9. The variable direct normal irradiance (DNI) feature (if selected) scales the user-prescribed peak DNI using a typical clear-day irradiance profile. This profile has a lower DNI in the mornings and evenings and a maximum at solar noon. The scaling uses a clear-day irradiance profile based on a normalized time relative to sunrise, solar noon, and sunset, which are prescribed by a sun-position algorithm and the latitude and longitude obtained from Google maps. The actual DNI on any given day can be affected by cloud cover, atmospheric attenuation, and other environmental factors.
10. The ocular hazard predicted by the tool depends on a number of environmental, optical, and human factors, which can be uncertain. We provide input fields and typical ranges of values for these factors so that the user can vary these parameters to see if they have an impact on the results. The speed of SGHAT allows expedited sensitivity and parametric analyses.
11. The system output calculation is a DNI-based approximation that assumes clear, sunny skies year-round. It should not be used in place of more rigorous modeling methods.
12. Hazard zone boundaries shown in the Glare Hazard plot are an approximation and visual aid. Actual ocular impact outcomes encompass a continuous, not discrete, spectrum.
13. Glare locations displayed on receptor plots are approximate. Actual glare-spot locations may differ.

1. Ho, C. K., Ghanbari, C. M., and Diver, R. B., 2011, "Methodology to Assess Potential Glint and Glare Hazards From Concentrating Solar Power Plants: Analytical Models and Experimental Validation", ASME J. Sol. Energy Eng., 133. (Download)

2. Federal Aviation Administration (2021). Final Policy, Review of Solar Energy System Projects on Federally Obligated Airports. Document Number 2021-09862. (link)

3. Federal Aviation Administration (2013). Interim Policy, FAA Review of Solar Energy System Projects on Federally Obligated Airports. Federal Register: 63276-63279 (link)

4. Rogers, J. A., et al. (2015). "Evaluation of Glare as a Hazard for General Aviation Pilots on Final Approach", Federal Aviation Administration ( link)

5. Ho, C. K. and Sims, C. A., 2013, "Solar Glare Hazard Analysis Tool (SGHAT) User's Manual v. 3.0". (Download)

6. Ho, C. K., Sims, C. A., Yellowhair, J. E. and Bush, H. E., 2014, "Solar Glare Hazard Analysis Tool (SGHAT) Technical Reference Manual", SAND2014-18360 O, Sandia National Laboratories, Albuquerque, NM. (Download)

7. Overview presentation of the Solar Glare Hazard Analysis Tool (SGHAT) (Download)

8. Ho, C. K., April 2013, "Relieving a Glaring Problem", Solar Today Magazine (Download)

9. Barrett, S., June 2013, "Glare Factor: Solar Installations And Airports", Solar Industry, Volume 6, Number 5. (link)

10. Ho, C. K., 2012, "Glare Impacts from Solar Power Plants near Airports", in Proceedings of ACC/AAAE Airport Planning, Design and Construction Symposium, Denver, Colorado, Feb. 29 - Mar. 2. (Download)

11. Ho, C. K., 2011, "Observations and Assessments of Glare from Heliostats and Trough Collectors: Helicopter Flyover and Drive-By Sightings", in proceedings of SolarPACES 2011, Granada, Spain, Sept. 20-23. (Download)

12. Ho, C. K., 2011, "Summary of Impact Analyses of Renewable Energy Technologies on Aviation and Airports", Presentation to Federal Aviation Administration, Feb. 16. (Download)

13. Ho, C. K., Ghanbari, C. M., and Diver, R. B., 2010, "Methodology to Assess Potential Glint and Glare Hazards From Concentrating Solar Power Plants: Analytical Models and Experimental Validation", SAND2010-2581C, in proceedings of the 4th International Conference on Energy Sustainability, Phoenix, AZ, May 17-22. (Download)

14. Ho, C. K. and Khalsa, S. S., 2010, "Hazard Analysis and Web-Based Tool for Evaluating Glint and Glare from Solar Collector Systems", in proceedings of SolarPACES 2010, Perpignan, France, Sept. 21-24. (Paper) (Presentation)

15. Ho, C. K., Ghanbari, C. M., and Diver, R. B., 2009, "Hazard Analyses of Glint and Glare From Concentrating Solar Power Plants", SAND2009-4131C, in proceedings of SolarPACES 2009, Berlin, Germany, Sept. 15-18. (Download)

16. Yellowhair, J. and C.K. Ho. "Assessment of Photovoltaic Surface Texturing on Transmittance Effects and Glint/Glare Impacts". ASME 2015 9th International Conference on Energy Sustainability collocated with the ASME 2015 Power Conference, the ASME 2015 13th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2015 Nuclear Forum. 2015. American Society of Mechanical Engineers. (PDF)

17. Sliney, D.H. and B.C. Freasier, 1973, "Evaluation of Optical Radiation Hazards", Applied Optics, 12(1), p. 1-24.

18. Anderson, K. and M. Mikofski, 2020, "Slope-Aware Backtracking for Single-Axis Trackers." Golden, CO. National Renewable Energy Laboratory. NREL/TP-5K00-76626. https://www.nrel.gov/docs/fy20osti/76626.pdf

19. Lorenzo, E., L. Narvarte and J. Munoz, 2011, "Tracking and back-tracking." Madrid, Spain. Progress in Photovoltaics: Research and Applications 19: 747-753. https://doi.org/10.1002/pip.1085

Analysis results may change between releases as updates and enhancements are developed. Always save/download analysis results upon analysis completion.

• Vertical Surface glare analyses can now compute per-minute luminance values
• Vertical Surface glare analyses can now generate an analysis data file
• The Vertical Surface section of the site analysis results page has been updated
• The FAQ has been updated

• New billing portal for streamlined subscription and payment management
• Simplified process for adding company billing details including tax IDs
• Updated Terms of Use and Privacy Policy to reflect billing portal changes

• Improve Obstruction functionality regarding discontinuities

• Add-on purchase invoices can now be downloaded from the Invoices page
• Various analysis improvements to glare filtering and luminance data displays.
• The component toolbuttons are now accessible when the map is in full-screen mode.
• Map labels can now be toggled on and off in both map modes.

Data File Export Update

Analysis data files are now in XLS format and contain all results for a specified PV array. Data file creation is now off by default, and can be enabled in the editor via the site settings (Site Configuration -> Settings).

Methodology Update Prep

Various enhancements have been implemented to prepare for upcoming glare analysis methodology improvements.

Misc. Updates

• Improved error messages during XLS uploads
• Expanded Help page content, including data file descriptions
• Numerous behind-the-scenes backend and testing improvements

• Various updates to Help page
• Numerous improvements and updates to server, queuing, and backend functionality

• Add Help page
• Various backend and server improvements
• Update free demo features
• Update upcoming subscription notification functionality

• Add cookie consent banner
• Add Invoices page under Account to view past invoices

New Route Receptor

Glare analyses can now utilize a generic route receptor to model continuous, multi-segment paths. Use routes to model receptors for roads, rail lines, helicopter paths and other multiline features.

Other Changes

• Updated Terms of Service and Privacy Policy to clarify subscription terms and accommodate GDPR
• Rename the flight path receptor to "2-mile flight path" for clarity
• Miscellaneous bug fixes and improvements

• Update error handling during analyses
• Update pricing and Glare Review pages
• Misc. bug fixes

Various Vertical Surfaces Updates

• Polish display of VS results
• Allow export of VS data

Methodology Updates

• Various improvements to accuracy and reliability of OP backward ray-tracing "scatter-point" glare check algorithm
• Various improvements to accuracy of sun scatter factor in path glare check algorithm
• Improve accuracy of glare impact calculations based on glare spot location

ForgeSolar is dedicated to providing the latest technology in glare analysis. Point and path glare analysis methods have been updated to provide even greater accuracy. These changes represent advancements in the study of PV glare. Future analyses may yield different results than prior analyses. Note that prior results will not change unless the analysis is re-run.

Aviation PDF

Added aviation-pertinent PDF summarizing glare analysis results for typical aviation requirements

Other updates

• Export component data to XLSX
• Upload KML with PV arrays (Beta)
• Mark OPs as ATCT for tailored results

OP Glare Spot Plot

Added plot displaying approximate locations of predicted glare spot centers (reflections) on PV array

• Module slope error is now based on selected PV module material by default
• PV systems with single-axis tracking now default to a max rotation angle of 60 deg
• Flight paths now limit pilot view to reasonable values by default. (This is acceptable to FAA).
• Analysis results now include a stacked column chart displaying number of minutes of glare per day.

• Upgrade server capacity and queuing system
• Updates to GlaReduce Optimization tool

• Move to forgesolar.com domain
• Update FAQ
• Numerous bug fixes

• Add component data to results page

• Increase max number of concurrent glare analyses
• Add Help pages
• Due to their impact on disk usage, PV Optimization analyses no longer create .CSV data files