Guidance and information on using ForgeSolar analysis tools
These help pages include documentation and guidance on the ForgeSolar tools. This includes detailed descriptions of the editor, analysis methodology and results. ForgeSolar was built with the Solar Glare Hazard Analysis Tool technology (SGHAT), licensed from Sandia National Laboratories. Portions of the Help content is taken from the SGHAT User's and Technical Manuals.
With growing numbers of solar energy installations throughout the United States, glare from photovoltaic (PV) arrays has received increased attention as a real hazard for pilots, air-traffic control personnel, motorists, and others. The ForgeSolar suite of tools provide a quantified assessment of:
- when and where glare will occur throughout the year for a prescribed solar installation
- potential effects on the human eye at locations where glare occurs, and
- annual energy production from the PV system so that alternative designs can be compared to maximize energy production while mitigating the impacts of glare
ForgeSolar employs an interactive Google map where the user can quickly locate a site, draw an outline of the proposed PV array(s), and specify observer locations or paths. Latitude, longitude, and elevation are automatically queried from Google, providing necessary information for sun position and vector calculations. Additional information regarding the orientation and tilt of the PV panels, reflectance, environment, and ocular factors are entered by the user.
If glare is found, the tool calculates the retinal irradiance and subtended angle (size/distance) of the glare source to predict potential ocular hazards ranging from temporary after-image to retinal burn. The results are presented in a simple, easy-to-interpret plot that specifies when glare will occur throughout the year, with color codes indicating the potential ocular hazard. The tool can also predict relative energy production while evaluating alternative designs, layouts, and locations to identify configurations that maximize energy production while mitigating the impacts of glare.
ForgeSolar currently includes two tools for glare analysis, which are both accessed via the editor:
- GlareGauge - annual glare hazard analysis of PV arrays and receptors
- GlaReduce - optimization analysis of a single PV array over a range of module configurations (tilts and orientations)
For questions or feedback on Help content, please contact us.
Background and theory regarding solar glare and regulatory policies
About Glint & Glare
Glint is typically defined as a momentary flash of bright light, often caused by a reflection off a moving source. A typical example of glint is a momentary solar reflection from a moving car. Glare is defined as a continuous source of bright light. Glare is generally associated with stationary objects, which, due to the slow relative movement of the sun, reflect sunlight for a longer duration.
The difference between glint and glare is duration. Industry-standard glare analysis tools evaluate the occurrence of glare on a minute-by-minute basis; accordingly, they generally refer to solar hazards as 'glare'.The ocular impact of solar glare is quantified into three categories (Ho, 2011):
- Green - low potential to cause after-image (flash blindness)
- Yellow - potential to cause temporary after-image
- Red - potential to cause retinal burn (permanent eye damage)
These categories assume a typical blink response in the observer. Note that retinal burn is typically not possible for PV glare since PV modules do not focus reflected sunlight.
The ocular impact of glare is visualized with the Glare Hazard Plot. This chart displays the ocular impact as a function of glare subtended source angle and retinal irradiance. Each minute of glare is displayed on the chart as a small circle in its respective hazard zone. For convenience, a reference point is provided which illustrates the hazard from viewing the sun without filtering, i.e. staring at the sun. Each plot includes predicted glare for one PV array and one receptor.
Reflections from PV panels may impair observers. Studies have found that 7 W/m2 is enough to cause an after-image lasting 4 to 12 seconds (Ho, 2009). This represents a reflection of only 1-2% of typical solar irradiance (incoming sunlight) for a given location, which typically ranges between 800-1000 W/m2.
A key factor of reflectance is the position of PV modules relative to the sun. A panel that absorbs 90% of direct sunlight may reflect up to 60% when not directly facing the sun. This situation is common for low-tilt panels during sunset and sunrise (Yellowhair, 2015). The oft-repeated claim that PV panels reflect less than 5% of sunlight only holds true when the panels directly face the sun. For fixed-mount panels, this claim only applies during a few minutes of the day, at most.
Module Reflectance Profiles
Sandia National Laboratories developed five generic PV module material reflectance profiles by analyzing over twenty PV module samples. These profiles are available in ForgeSolar and allow for customizing the material properties of the PV array during analysis.
The figure to the right illustrates the reflectance of each material profile as a function of incidence angle, where an angle of 0° implies the panels are directly facing the sun. For example, a high glancing angle near 90° for panels with 0° tilt (lying flat) occurs daily at sunrise and sunset.
Anti-reflective coatings (ARC) and surface texturing can reduce panel reflectivity, but this reduction is typically less than 8% (Yellowhair, 2015). In addition, greater surface texturing can increase the size of the subtended source angle (i.e. glare spot).
Guidance on conducting glare analyses and optimizations
In ForgeSolar, sites and glare analyses are organized as follows:
Site Configuration - represents a group of one or more PV arrays (or Vertical Surfaces), each with a single module orientation and tilt, and relevant receptors. A comprehensive assessment may comprise more than one Site Config in order to evaluate various orientation and tilt options. A Site Config is the "atomic" unit of glare analyses, and is typically created in the Map Editor.
Glare Analysis - annual analysis of a Site Config to determine expected glare from PV arrays toward receptors.
Project - container which holds one or more related Site Configs in a specified timezone. A Project is akin to a folder containing all the Site Configs of a proposed PV installation.
Example: a proposed installation of PV arrays on two rooftops near San Francisco International Airport (SFO) could be organized as follows:
- One Project with timezone offset of -8
- One Site Config with both PV arrays and SFO receptors (flight paths, ATCT)
- More Site Configs, cloned from the original, to evaluate alternative PV module tilts and orientations
- Each Site Config would include glare analysis results after submission via the Editor
The ForgeSolar tools can also be used to conduct a module optimization analysis with the GlaReduce Optimization Tool. The Optimization analysis evaluates a single PV array over a range of tilts and orientations to aid in identifying the optimal module configuration. To conduct a PV array optimization, select GlaReduce Optimization from the Tools menu.
Related Site Configurations and Optimizations are contained within a single Project. Use Projects to organize any number of Site Configurations and results corresponding to a real-world project. The quantity of glare analyses and optimizations available for a Project is determined by the Project Tier.
- Project name
- Unique name to distinguish a particular project. For example, "LAX parking rooftop PV" or "Main street solar farm"
- 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
- 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.
- 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.
|System size (approx.)||< 1 MW||Any size|
|PV area||< 8 acres (32,370 m2)||Any size|
|# PV footprints||10||20|
|# Vertical surfaces||10||20|
|# Flight paths||10||20|
|# Observation points||20||40|
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 such as the FAA 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.
- Sun angle (mrad)
- The average subtended angle of the sun as viewed from earth is ~9.3 mrad or 0.5°.
- 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.
- 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.
- Observation point method
- Version of glare analysis method to employ when assessing discrete Observation Point receptors. The V2 method was released in mid-2019 and included enhancements to drastically increase the consistency of OP analysis results.
- Flight path method
- Version of glare analysis method to employ when evaluating 2-mile Flight Paths. Currently only V1 is available.
- Route method
- Version of glare analysis method to employ when evaluating Routes. Currently only V1 is available. V2 is in active development.
- Create PV glare data file(s)?
- The glare analysis will also output an XLS file containing data on times of glare for each receptor
- 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).
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:
- Analysis results header
- Glare Analysis Summary tab
- PV Array Results tab
- Vertical Surface Results tab
The various properties and component parameters should be verified before utilizing glare analysis results, to ensure their accuracy.
Result Header Section
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.)
Glare Analysis Summary Tab
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.
PV Array Results Tab
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, at the request of the FAA.
Annual Glare Occurrence Plot
The annual glare occurrence plot displays the approximate times of year and times of day for which glare is expected for the specified receptor. The x-axis denotes the times of year, while the y-axis indicates times of day. Occurrences are color-coded by predicted ocular impact.
Daily Glare Duration Plot
The daily glare duration plot sums expected minutes of glare on a daily basis to provide an approximation of the total number of minutes glare will be evident each day, on an annual basis.
Glare Hazard Plot
The glare hazard plot presents the expected ocular impact of each minute of predicted glare. The x-axis represents the subtended source angle, i.e. the angle subtended by the visible glare spot. The y-axis represents the retinal irradiance impacting the observer.
The three hazard zones, described by the colors green, yellow, and red, are derived from literature and indicate the expected impact (see About Glint & Glare section.
The reference point (yellow with blue outline) indicates the hazard due to viewing the unfiltered sun.
Plot of Path location and Time of Glare
PV Footprint Glare-Spot Heatmap Plot
Plot of Path Positions Receiving Glare
Result Data Files
Annual PV glare analyses can provide an XLS file containing data on times of glare for each receptor. To enable this, check the Data File option under the Site Config settings in the Editor.
The data file includes a worksheet for each receptor expecting glare. Each worksheet contains the following data columns for times when glare is expected:
- 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)
- 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).
Components & Receptors
Information on creating and editing PV arrays, flight paths, routes and observation points
PV Array Component
Photovoltaic systems are represented by a contiguous planar polygon footprint and a set of customizable parameters. Each footprint comprises three or more vertices, defined by a latitude, longitude, elevation and height. Each distinct PV installation should be modeled with it's own PV array footprint in the editor. 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 Array Footprint
PV arrays are simulated spatially with a contiguous planar convex polygon. This polygonal footprint comprises three or more vertices which are defined by a latitude, longitude, elevation and height. The footprint should encompass all planned PV modules in a given area. Non-contiguous PV systems, or those with substantial concavities, should be modeled with multiple PV array footprints.
ForgeSolar will modify the vertex elevations if they do not initially reside on a single planar surface. For example, if a user attempts to model a non-planar footprint, such as multiple sides of a hill, the system would smooth the footprint and effectively flatten the hill. (In this example, a more accurate approach would be to model each hillside as a separate PV array.)
Note that ForgeSolar will convert the footprint polygon into a convex polygon during analysis by filling in any concavities. For example, a 'C'-shaped footprint would be modified into a half-circle. This adjustment is currently required by the glare-check algorithm during analysis.
Large PV array sites with many concavities should typically be modeled with multiple PV array footprints, instead of one large PV footprint. This can yield more accurate results which do not over-predict glare by over-estimating the size of the PV array after the required gap-filling.
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.
PV Array Parameters
General PV array parameters are described below. Module configuration, tracking and vertex parameters are described in subsequent sections.
- Descriptive alphanumeric name of this PV array
- Optional textual description of array
- Axis tracking
- Whether PV array modules are fixed-mount or utilize single- or dual-axis tracking
- 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.
- 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|
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.
Tracking System Parameters
Single-axis module tracking systems are described by a unique set of parameters. These angular inputs model the tracking axis, rotation range and backtracking behavior. Dual-axis module tracking systems are assumed to track the sun at all times.
- 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°.
- Orientation of tracking axis (°)
- Azimuthal angle of axis over which panels rotate. Angle represents the facing of the axis and system. For example. typical tracking system in northern hemisphere has tracking axis oriented north-south with an orientation of 180°, allowing panels to rotate east-west with potential south-facing tilt. Typical tracking system in southern hemisphere runs south-north with axis orientation of 0°, yielding east-west rotation with potential north-facing tilt.
- Offset angle of module (°)
- Additional tilt angle of PV module elevated above tracking axis/torque tube. Offset angle is measured from the torque tube.
- Maximum tracking angle (°)
- Maximum angle of rotation of tracking system in one direction. 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. Used to model backtracking. Panels will revert to the position described by this rotation angle at all times when the sun is outside the rotation range. Setting this equal to the maximum tracking angle implies the panels do not backtrack.
- 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.
2-Mile Flight Path Receptor
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.
Follow these steps to create FPs in the map editor:
- Activate the FP drawing mode by clicking the FP button above the map.
- In the map, click once on the runway threshold location to set the FP threshold point. A marker will be placed and a line will extend from the marker to the mouse cursor.
- Click a second time in the direction of the flight path, away from the runway, to set the FP direction. The system will automatically create the 2-mile point in the specified direction.
- Modify the FP glide slope, direction, or elevation values in the FP data section to the right of the map.
- 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, and is acceptable to FAA. (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.
Observation Point Receptor
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.
Follow these steps to create an Observation Point in the map editor:
- Activate the OP drawing mode by clicking the OP button above the map.
- Click once on the desired map location to place an OP at that location.
- Modify location coordinates, including height above ground, in OP data section to right of map. For example, a height of ~5-6 ft. to simulate a stationary observer at ground level.
- To simulate an ATCT, ensure the Is ATCT? checkbox is checked.
- Geodetic coordinate defined by WGS-84 datum in decimal degrees with range of -90° to 90°
- Geodetic coordinate defined by WGS-84 datum in decimal degrees with range of -180° to 180°
- 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 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 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:
- Activate the Route drawing mode by clicking the Route button above the map.
- Click once on a location in the map to begin drawing a route
- Click once to add a vertex to the route. Repeat as many times as is necessary; routes can include many line segments
- Double-click on final position to end the Route
- 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.
- 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).
Assumptions & Limitations
Summary of assumptions and abstractions required by the SGHAT/ForgeSolar analysis methodology
- Times associated with glare are denoted in Standard time. For Daylight Savings, add one hour.
- Result data files and plots are now retained for two years after analysis completion. Files should be downloaded and saved if additional persistence is required.
- 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.
- 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.
- 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.
- 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.)
- 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.
- The algorithm does not 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.
- 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.
- 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.
- 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.
- 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.
- Glare locations displayed on receptor plots are approximate. Actual glare-spot locations may differ.
- Glare vector plots are simplified representations of analysis data. Actual glare emanations and results may differ.
- The PV array tracking model assumes the modules move instantly when tracking the sun, and when reverting to the rest position.
Additional resources and research on solar glare
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)
Federal Aviation Administration (2013). Interim Policy, FAA Review of Solar Energy System Projects on Federally Obligated Airports. Federal Register: 63276-63279 (link)
Rogers, J. A., et al. (2015). Evaluation of Glare as a Hazard for General Aviation Pilots on Final Approach, Federal Aviation Administration ( link )
Ho, C. K. and Sims, C. A., 2013, Solar Glare Hazard Analysis Tool (SGHAT) User's Manual v. 3.0. (Download)
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)
Overview presentation of the Solar Glare Hazard Analysis Tool (SGHAT) (Download)
Ho, C. K., April 2013, Relieving a Glaring Problem, Solar Today Magazine (Download)
Barrett, S., June 2013, Glare Factor: Solar Installations And Airports, Solar Industry, Volume 6, Number 5. (link)
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)
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)
Ho, C. K., 2011, Summary of Impact Analyses of Renewable Energy Technologies on Aviation and Airports, Presentation to Federal Aviation Administration, Feb. 16. (Download)
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)
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)
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)
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. (Presentation)
Sliney, D.H. and B.C. Freasier, 1973, Evaluation of Optical Radiation Hazards, Applied Optics, 12(1), p. 1-24.
Miscellaneous links and information
Summary of updates and changes
Analysis results may change between releases as updates and enhancements are developed. Results should be saved and downloaded upon analysis completion.
The 2021A "V2" Release contains substantial updates to accounts, projects, and analysis methodologies. See the 2021A Update page for more information.
- Revamp projects with tiering and per-project tool limits.
- Implement enhanced "Version 2" point and path analysis methodologies.
- Implement new Data Access Subscription plan for maintaining view access to existing projects.
- Add tabular display of temporal (distinct) glare data filtered by month and hour.
- Add new heatmap visualization for approximating section(s) of path receiving glare.
- Restore original column ordering in analysis XLS data file and add panel glancing angle column
- Enhance error handling and display
- Increase analysis timeout duration
Improved analysis handling
- Server upgrades! Server capacity, including analysis processing, has been doubled.
- you can now activate email notifications for long-running analyses.
- Email notifications are automatically activated when an analysis takes longer than the timeout limit.
- Analyses can now be quickly canceled from the progress dialog.
Data File Export Update
Analysis data files are now in XLS format and contain all results for a specified PV array - no more having to compile one CSV per receptor! 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. Site settings now include option to select the method to use (inactive for now).
- 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.
- 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
- 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.
Added aviation-pertinent PDF summarizing glare analysis results for typical aviation requirements
- 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
ForgeSolar includes GlareGauge, the leading solar glare analysis tool used globally every day. ForgeSolar is based on the Solar Glare Hazard Analysis Tool ("SGHAT") licensed from Sandia National Laboratories. Our tools meet the FAA standards for glare analysis.