Technical terms on glare, PV reflection and sun position in the meaning in which PV-GlareCheck uses them. Terms for which guidelines give numerical values name the source. Missing terms can be reported to info@pv-glarecheck.com.
A
Absolute glare
Glare in which the luminance of the source exceeds the adaptive capacity of the eye; it triggers protective reactions such as closing the eyelids or looking away. The guidelines give different thresholds: about 10⁵ cd/m² (LAI-Hinweise, Annex 2, No. 2.1, p. 21), about 10⁴ cd/m² (OVE Guideline R 11-3:2016, Sect. 4.1, p. 8) and more than 30,000 to 100,000 cd/m² when looking directly (FBA Eckpunktepapier, Sect. 3, p. 5). In the app, such a threshold can be taken into account via the luminance threshold.
Azimuth
Horizontal angle in degrees, measured clockwise from north: 0° = north, 90° = east, 180° = south, 270° = west. It describes the orientation of a PV area, the direction of the sun, the viewing direction of a field of view and the position of a glare source as seen from the observation point.
B
Backtracking
Back-rotation strategy of single-axis trackers: at low sun, the modules rotate to a flatter angle so that neighbouring rows do not shade each other. The back-rotation depends on the ratio of module width to row pitch (GCR) and follows the method of Anderson & Mikofski (2020) in pvlib. During backtracking, the rest angle applies as the minimum angle. Whether backtracking is active is set per tracker; without this entry the simulation does not start (Ch. 7.3).
Batch analysis
Simulation of several variants of a project state in one run (Pro). Per PV area, azimuth, tilt, module type and dual orientation can be varied; up to 20 variants are possible. Each variant becomes a read-only Version of its own and uses one simulation token (Ch. 13).
Beam spread
Opening angle by which reflected sunlight is scattered around the ideal mirror direction. It is a property of the module type, depends on the angle of incidence and is described as an elliptical reflection lobe with major and minor axis. Smooth glass bundles tightly (short, intense reflection), structured or anti-reflective surfaces scatter more widely (longer, weaker reflection).
Best-fit plane
Plane fitted through the corner elevations of a ground-mounted area by least squares; with three corners, it is the plane through these points. It is the alternative to the elevation grid in step 1 of the terrain menu: the area then lies on this plane, the cross tilt is the same everywhere, and zones (step 3) are not available (Ch. 7.5).
Bottom edge (UK)
Height of the lower edge of the module surface, with the same reference as the top edge. The top edge must lie above the bottom edge.
C
Core glare
Term used in glare reports for glare according to the simplified model of the LAI guidance: sun as a point source, modules as ideal mirrors without beam spread (Annex 2, No. 4, p. 24); German "Kernblendung". The reference values of 30 min per day and 30 h per year refer to this glare duration. In PV-GlareCheck it is calculated with the module type "Perfect mirror", with point-shaped observation points and the sun as a disc of 0.53°; each glare phase is therefore about one minute longer at its start and end than with a point-shaped sun (Ch. V.3). With a realistic module type, scattered reflection is added and the glare duration is longer (Ch. VI.1). The core of an intensity zone is not meant.
Cross tilt
Tilt of the modules along the table axis, i.e. across the orientation, e.g. due to a slope falling away sideways. It changes the effective azimuth and effective tilt and thus the direction of reflection. For ground-mounted areas, it is set uniformly in step 2 of the terrain menu and differentiated in step 3 ("Zones") if needed; for trackers, it acts as the axis tilt (Ch. 7.6).
D
Demo project
Free project that every account can create once. It uses no project token, includes 2 simulation tokens and calculates in full; report, PDF and image downloads carry the watermark "DEMO", the Excel export the note "DEMO". Buying simulation tokens turns it into a regular project (Ch. 3).
Diffuse reflection
Scattered reflection in many directions outside the mirror angle, with low luminance. PV-GlareCheck does not calculate it separately; scattering around the mirror direction is represented by the reflection lobe.
DNI (direct normal irradiance)
Direct solar radiation on a surface perpendicular to the sun, in W/m². PV-GlareCheck uses the clear-sky irradiance according to the Ineichen model for every time step; together with the reflection profile, it determines the luminance of the reflection.
Dual orientation (east-west)
Mounting in which the modules of one area face two opposite directions, e.g. east and west ("Dual Orientation"). One azimuth is entered; the second lies 180° opposite. For the quantity limits of the plan, the area counts once.
E
Effective azimuth / effective tilt
Actual orientation and tilt of the module surface when a cross tilt is present. They then differ from the entered azimuth and tilt and determine the direction of reflection.
Elevation / Sun elevation
Elevation angle above the horizon in degrees: 0° = horizon, 90° = zenith. For the sun, the apparent value including atmospheric refraction applies. Elevation also describes the position of glare sources in the 3D perspective. The filter "Min. sun elevation" (default off, 3°) does not count time steps with a lower sun as glare duration.
Elevation data
Terrain heights above sea level from which the ground level (GL) is derived. They come from a source chain in the "Elevation data" menu that is queried from top to bottom: terrain models in the project, official point query for Germany, Austria and Switzerland, Google Elevation API. Every value carries its source (E, A or G). Elevation data must be checked regardless of the source (Ch. 6).
Elevation grid
Support points of a ground-mounted area at regular spacing plus points along the edges, step 1 of the terrain menu. The grid spacing follows the source: 25 m with a terrain model in the project, 50 m with the official point query or Google elevations. The simulation spans the surface through corner and support points. The elevation grid samples the terrain, the terrain model describes it (Ch. 7.5).
Excluded area
Sub-area marked in the editor within a PV area that carries no modules, e.g. a skylight, a chimney or a path. Before the calculation, the area is cut out of all PV areas it overlaps and produces no reflections. Facades are not clipped (Ch. 7.7).
F
Far-field shading (horizon line)
Shading of a PV area by mountains and distant terrain. For each PV area, a horizon line can be retrieved from PVGIS (European Commission, JRC; terrain model with a grid of about 90 m, 48 directions in 7.5° steps) at the centre of the area. If the sun is below this line, the area counts as shaded. Far-field shading only acts between sun and PV area; it does not block sight lines to observation points and contains no buildings or vegetation (Ch. 10.2).
Field of view / FOV
Viewing region of an observation point: viewing direction (azimuth), horizontal opening angle on both sides ("H±"), vertical angles downwards and upwards ("V-Ground", "V-Sky") and tilt of the gaze axis. A rectangle of azimuth and elevation range is checked, not a cone; the tilt only shifts the elevation range (Ch. V.6). It only takes effect when activated per point; without a field of view, an all-round view applies. Reflections outside are filtered by the geometry filter "Outside field of view". Reference: the FBA Eckpunktepapier assumes a relevant field of view of ± 30° around the main viewing direction (Sect. 3, p. 5), OVE R 11-3 a cone of about 30° around the main viewing direction (Sect. 4.2, p. 9). The LAI-Hinweise do not regulate a field of view.
G
Gaze axis
Central axis of a field of view: viewing direction as azimuth and optionally a vertical tilt ("Viewing-axis tilt", default 0° = horizontal). The min. gaze axis distance and the exception "Distance to gaze axis" in the filters "Illuminance" and "Vertical glare source" refer to it. Guidelines speak of the main viewing direction; the FBA Eckpunktepapier names ± 10° as the central and ± 30° as the relevant visual range (Sect. 3, p. 5).
Glare
Disturbing or vision-impairing effect of a bright light source in the visual field. It is assessed by brightness (luminance, illuminance), position in the visual field and duration. PV-GlareCheck calculates reflections and their characteristics; the assessment as glare in the sense of a guideline is described in Part VI (Ch. VI.1 to Ch. VI.4).
Glare duration / Glare minutes
Duration during which at least one reflection that passes all active filters is visible at the observation point; reported per day and as an annual total. At a resolution of one minute, each such time step corresponds to one glare minute. Since the calculation assumes a clear sky every day, the glare duration is the astronomically maximum possible one. Guideline values: at most 30 min per day or 30 h per year (LAI-Hinweise, Annex 2, No. 4, p. 24; OVE R 11-3:2016, Sect. 7.1, p. 13); for residential zones at most 30 min on any number of days, 60 min on at most 60 days, 120 min on at most 20 days and 60 h per year (EnergieSchweiz/Swissolar guide, June 2023, Annex 1, pp. 40–41). In the report: "Total glare duration per year", "Max. daily glare", "Affected days" and "Days >30 / >60 / >120 min glare".
Ground level (GL)
Height of the natural terrain surface at a point in metres above sea level (m a.s.l.); German abbreviation GOK. It is retrieved from the elevation data or entered manually for corner points, support points, obstacle points and observation points. Many height values, e.g. the observer height, refer to the GL.
Ground-mount
Ground-based PV system on open land, in the editor the PV system type "Ground Mount". Only ground-mounted areas have the terrain menu (elevation grid, cross tilt, zones) and can be tracked (Tracker).
Group
Collection of observation points, e.g. all points along a road or at a building. Groups are labelled G1, G2 …; in the report, the points of a group are filtered and evaluated together.
H
Heatmap
Chart "Glare times (day × time)" in the report, per observation point. The horizontal axis shows the days of the year, the vertical axis the time of day in standard time. Red marks moments with glare, grey marks moments excluded by a filter. The intensity is shown in a separate chart with the same axes.
I
Illuminance
Luminous flux per area at the observer's eye, in lux (lx). It grows with the brightness and apparent size of the glare source. PV-GlareCheck calculates it per direction as the product of luminance and solid angle and sums it within a time step over all visible glare sources. The filter "Illuminance" (default off, 50 lx) does not count time steps below the threshold as glare duration.
Intensity
Collective term for the brightness quantities of a reflection: luminance (cd/m²) and illuminance (lx). The intensity-coded charts and the reflection map can show either of the two quantities.
Intensity zone (core, ring)
Concentric region of a reflection lobe with its own luminance and axes. A module type can have up to three zones: "Core" (required), "1st ring" and "2nd ring"; the reflection offset is shared by all zones. For a given direction, the innermost zone that contains it applies.
L
Luminance
Brightness of a surface from a particular direction in candela per square metre (cd/m²), independent of the size of the surface. PV-GlareCheck calculates it per reflection from the reflection profile of the module type (referenced to 100,000 lx), the direct irradiance (DNI), the angle of incidence and the luminous efficacy of sunlight as a function of sun elevation (after Littlefair). In the report: "Peak luminance".
Luminance threshold
Threshold of the filter "Luminance": time steps whose luminance is below the value do not count as glare duration. Default on with 30,000 cd/m², changeable per group. Reference: reflections up to 30,000 cd/m² are regarded as not significantly impairing in the FBA Eckpunktepapier (Sect. 3, p. 6); EASA CS-ADR-DSN gives at most 20,000 cd/m² for solar panels (GM1 ADR-DSN.M.615 (k)(2), p. 162); the Swissolar guide names more than 50,000 cd/m² as the previous recommendation, which is under review (Annex 1, p. 38). The LAI-Hinweise and OVE R 11-3 do not set a luminance threshold for the glare duration.
M
Min. gaze axis distance
Smallest angle between the gaze axis and a glare source over all glare events of an observation point, only with a defined field of view. Reported three-fold: absolute (spatial angle), horizontal (pure azimuth offset) and vertical (pure elevation offset); the three values are independent minima and may stem from different moments. In the filtered view, they refer to the events that pass all filters except the field-of-view filter.
Module profile
Data set of a module type that describes the reflection behaviour: per intensity zone, the reflection profile and the major and minor axis of the reflection lobe in 10° steps of the angle of incidence from 0° to 90°, plus the shared reflection offset. Values between the sampling angles are interpolated linearly (Ch. 8).
Module type
Named set of reflection properties (module profile) assigned to every PV area. System module types are predefined and cannot be changed; custom module types can be created via "Manage Module Types" and are saved with the project version (Ch. 8).
O
Observation point (OP)
Location for which the glare impact is calculated, e.g. a window, a point on a road or on a flight path; German "Betrachtungspunkt" (BP). Every point has a position, ground level (GL), observer height above GL and optionally a field of view. It always belongs to a group; the label "G1-3" stands for the third point of group 1 (Ch. 9).
Obstacle
Object in the near range entered in the editor that can interrupt light between sun and PV area (shading) and between PV area and observation point (blocking), e.g. a building, a row of trees, an embankment. New obstacles always have a height above ground; topography obstacles from older projects continue to be calculated (Ch. 10.1, Ch. 10.5). Terrain between PV area and observation point is captured by terrain occlusion.
P
Plan
Free or PV-GlareCheck Pro. Both calculate with the same method and the same time resolution; Pro extends the quantities per simulation run (50 instead of 3 PV areas, 100 instead of 30 observation points, 100 instead of 10 obstacles) and the storage (25 instead of 2 GB) and unlocks individual functions. Projects and simulations are paid for with tokens in both plans (Ch. 3).
Pre-analysis
Preliminary display in the editor of the compass directions in which the PV areas reflect, for a selected moment or the whole year, according to the model of the selected module type. It uses no token, takes into account neither obstacles nor excluded areas nor elevation differences and produces no report; it serves to place observation points (Ch. 11).
Project
Unit of work for one PV site with project area, versions, simulations and reports. A project is created with a project token and receives 30 simulation tokens (Ch. 4).
Project area
Circle with a 3 km radius around a centre that is set when the project is set up. All PV areas must lie within it; observation points, obstacles and excluded areas may lie outside. The project area cannot be changed after confirmation (Ch. 5).
Project token
Account credit for creating a project. Every new project uses one project token, also with PV-GlareCheck Pro; the demo project is the exception (Ch. 3).
Protected room
Room for which guidelines assess glare (German "schutzwürdiger Raum"): living rooms and bedrooms, classrooms, offices, practices and workrooms. Terraces and balconies are treated equally during the day (6 a.m. to 10 p.m.) (LAI-Hinweise, Annex 2, No. 3, p. 23); OVE R 11-3 additionally names garden pavilions and sunbathing areas (Sect. 6.1, p. 11). In the app, such a place is represented as an observation point, e.g. at window height (Ch. VI.1).
PV area
Area of a PV system drawn or imported in the editor, with PV system type, orientation, heights and module type. The calculation distributes calculation points over the area; excluded areas are cut out (Ch. 7).
PV system type
Kind of PV area, chosen when creating it: "Roof Parallel" (modules parallel to the roof surface), "Roof Mounted" (tilted modules on a flat roof), "Facade" (vertical modules on a facade, fence or freestanding, entered as a line) and "Ground Mount" (ground-based system, fixed or tracked). The type determines the input fields and the height reference of top edge and bottom edge (Ch. 7.2).
R
Reflection event / glare event
Time step in which sunlight is reflected from a PV area to the observation point, with moment, sun position, direction of the glare source, angle of incidence and intensity. The report condenses the events of a year into key figures and charts.
Reflection lobe
Spatial region into which a PV module reflects sunlight: a lobe around a direction close to the ideal mirror direction, shifted towards flatter angles by the reflection offset. It is circular or elliptical with a major axis (in the plane of incidence) and a minor axis (perpendicular to it) and can be divided into up to three intensity zones. Its width is the beam spread.
Reflection map
Top-down map in the report per observation point ("Reflection map (top-down)"). It shows from which directions reflections of the PV areas are visible at the observation point, for the whole year or a selected moment. The 3D perspective shows the same glare sources from the observer's point of view.
Reflection offset (δ)
Angle by which the centre of the reflection lobe is shifted from the ideal mirror direction towards flatter angles of reflection. It is stored per module type as a function of the angle of incidence and is particularly pronounced for strongly low-glare, e.g. satin-finished glass.
Reflection profile
Characteristic curve of a module type: luminance of the reflection as a function of the sun's angle of incidence, referenced to an illuminance of 100,000 lx; values between the sampling angles are interpolated linearly.
Report
Interactive evaluation of a simulation in the browser with cover page, chapters on project, PV areas, obstacles and observation points, results per group and appendix. Filters, base maps and cover page details are saved with the report; PDF, image downloads and (Pro) the Excel export are produced from it (Ch. 14).
Rest angle / Stow angle
Minimum magnitude of the tracking angle during Backtracking ("Rest Angle"); required with backtracking switched on, initial value 5°: at the edges of the day, the modules remain at this angle instead of lying completely flat.
S
Simulation
Annual calculation of a Version: for every observation point and every minute of a year (calculation year 2025, 365 days) with the sun above the horizon, it is checked whether reflections reach the point and how bright they are. A simulation uses one simulation token; after successful completion, the server creates a read-only version (Ch. 12, Ch. V).
Simulation token
Credit of a project for simulations; not transferable to other projects. A simulation or a variant of a batch analysis uses one token; in case of an error, it is refunded (Ch. 3).
Specular reflection
Reflection according to the law "angle of incidence equals angle of reflection". It concentrates sunlight into a narrow solid angle and can produce very high luminances at the observation point. Real modules deviate from it by beam spread and reflection offset.
Standard time
Local time of the selected time zone without daylight saving time. All times in simulation and report are standard time; clock changes are not taken into account. If daylight saving time applies at the site, the legal clock time is one hour later during those months.
Sun overlap
Position of a reflection close to the sun as seen from the observation point: if the angle between sun and reflection is small, the reflection is outshone by direct sunlight. The filter "Sun overlap" (default off, 10°) does not count such time steps as glare duration; the additional condition "+ low sun ≤" (default 5°) restricts this to low sun positions. Reference: only constellations with a difference angle of at least 10° (LAI-Hinweise, Annex 2, No. 4, p. 24) or more than 10° (OVE R 11-3, Sect. 9, p. 14) are to be counted; Swissolar names more than 20° (Annex 1, p. 38); the FBA Eckpunktepapier only accepts the overlap by the sun as an argument at sun elevations up to 5° (Sect. 3, p. 6).
Support point
Point inside or on the edge of a ground-mounted area at which the ground level (GL) is retrieved from the elevation data. Support points are created as an elevation grid and, together with the corner points, span the triangle mesh that the module surface follows; they are not placed individually.
T
Terrain model (terrain model in the project)
Raster file with terrain heights stored with the project: uploaded by the user ("Add your own terrain model") or loaded as an official section ("Load official terrain model"). It provides heights across the whole area and is required for the terrain view, cross tilt zones and terrain occlusion. Values from it carry the marker "E"; the report lists name, description and date (Ch. 6).
Terrain occlusion
Effect of the terrain from the terrain model in the project on both paths. Between PV area and observation point it blocks reflections: at the start of the simulation a near horizon is calculated for every observation point; a reflection counts as occluded if nearer terrain reaches its elevation angle, and it is filtered like obstacle blocking. Towards the sun it shades the PV areas: horizons at sampling points above each area show when the terrain hides the sun; these cells count as shaded. The calculation uses the terrain that is available; where it is missing, the report says so. The switch "Terrain occlusion" in the menu of the same name is on by default as soon as a terrain model is activated. Buildings and vegetation are not included. Distant mountains outside the model are captured by far-field shading.
Tilt
Angle between the module plane and the horizontal in degrees: 0° = horizontal, 90° = vertical. For roof-parallel systems, it equals the roof pitch. With "Facade", a new area starts at 90°; for inclined modules the value can be set in the object card.
Time step
Smallest time unit of the calculation: one minute. All minutes of a year in which the sun is above the horizon are calculated. Reference: the FBA Eckpunktepapier requires a resolution of at least 5 minutes (Sect. 4, pp. 6–7).
Time zone
Fixed offset of local time from UTC, selectable in the "Project Settings" from UTC−12 to UTC+14, including the zones with half and three-quarter hours (e.g. UTC+5:30). When the project area is set, it is determined for its centre, or estimated from the longitude as a fallback; the suggestion must be checked (Ch. 5). All times are treated as standard time. Examples: Germany, Austria, Switzerland UTC+1; United Kingdom, Ireland, Portugal UTC+0; Greece, Finland UTC+2.
Top edge (OK)
Height of the upper edge of the module surface. For ground-mounted areas, facades and roof-parallel systems above ground level (GL), for roof-mounted systems above the roof surface; for trackers referenced to the tilt at the full angle range. Together with the bottom edge, it determines the vertical position of the area.
Topography
Shape of the terrain in the surroundings. In PV-GlareCheck, on the one hand a deprecated type of obstacle that can no longer be created, whose top edge is the line through the GL values of its points and which is closed downwards (Ch. 10.5); on the other hand the terrain from elevation data and terrain models that determines the position and height of all objects.
Tracker (tracked system)
Ground-mounted area whose modules follow the sun on a single axis (Pro). Parameters: "Axis Orientation", "Module Angle Range" (initial value ±60°), "Axis Tilt" (set as cross tilt in the terrain menu), "Backtracking" (initial value on), "Ground Coverage Ratio (GCR)" (initial value 0.5) and "Rest Angle" (initial value 5°). The simulation calculates the tracking angle per time step (Ch. 7.3).
Tracking angle / Tracker tilt
Rotation angle of the modules of a Tracker about the axis at a given moment. The simulation calculates it for every time step from the sun position and the tracking parameters; the same calculation provides the column "Tracker tilt (°)" in the Excel export and the twelve monthly curves in the editor, which are only for checking.
V
Version
Saved state of a project with all objects and settings. A project can have any number of versions. After a successful simulation, the server saves the state at the start as a read-only version ("… · Sim-Backup" with date and time) to which the results are attached. Work continues in the editable version; "Duplicate" creates an editable copy of any version (Ch. 4).
Version comparison
Side-by-side comparison of 2 to 5 versions of the same batch run in the report ("Compare versions") (Pro); a worst-case combination can be created from the selection (Ch. 13).
Vertical extent (glare source)
Apparent height of a glare source as seen from the observation point, as angle β. The filter "Vertical glare source" (default off, 0.3°) does not count time steps with an extent at most equal to the value as glare duration; the exception "Distance to gaze axis" (default off, 10° horizontal when switched on, axis selectable) keeps sources close to the gaze axis in the count. Reference: a vertical size up to 0.30° outside the central visual range of ± 10° is regarded as not significant in the FBA Eckpunktepapier (Sect. 3, p. 6).
W
Worst-case combination
Merging of 2 to 5 versions of the same batch run into one result (Pro): a time step counts as glare if it causes glare in at least one variant; per time step, the highest intensity and the smallest distance to the gaze axis apply. The combination becomes a read-only version of its own and uses no token (Ch. 13).