Glare from PV systems on roads

In road traffic, the focus is not on the duration of a reflection but on whether it appears in a driver's field of view, how close to the viewing direction and how bright. For points along the carriageway, PV-GlareCheck calculates when reflections lie within the field of view, at what angle to the line of sight and with what luminance.

Guidelines

Germany – position paper of the Federal Highway Authority (FBA). The position paper “Photovoltaik – Blendwirkungen und Blendgutachten” (as of November 2025) applies to glare reports and expert statements on PV systems along federal trunk roads. It considers reflections within the relevant field of view of ±30° around the main viewing direction. Among the criteria under which a reflection can be classified as not significant, the paper names a luminance of up to 30,000 cd/m². It requires a full-year analysis with a resolution of at least 5 min, module-typical reflection with beam spread, eye heights of 1.0 m (car) and at least 2.7 m (truck), and consideration of cross slopes. In addition, the FBA lists the required documents (as of January 2025).

For state, district and municipal roads, the sources evaluated contain no requirements of their own.

Austria. OVE R 11-3 has been formally withdrawn and is unofficially often still applied for orientation; it names a cone of about 30° to the main viewing direction. RVS 05.06.11 covers information and advertising signs and provides transferable reference values.

The classification of a reflection against these criteria remains with the responsible expert and the competent authority.

What PV-GlareCheck calculates

• every minute of the year, under clear sky,
• observation points along the carriageway per direction of travel, with a field of view in the direction of travel and a freely selectable eye height,
• distance of the reflection from the line of sight, horizontal and vertical,
• luminance, illuminance at the eye and the vertical extent of the glare source,
• duration and time periods of reflections per point,
• cross slope of the PV area from the terrain, single-axis tracking with backtracking,
• occlusion by recorded noise barriers, embankments and structures and by the terrain.

The criteria of the position paper can be set as filters per group; the report shows their effect without a new simulation.

Workflow

1. Enter the system and the road on the map; points along a line per direction of travel and vehicle type.
2. Use the pre-analysis to narrow down the sections within the possible reflection area.
3. Run the annual simulation with a module type with a measured reflection profile.
4. Set the filters in the report; export the 3D perspective, glare times and metrics per point as a PDF.

Limits

The simulation is a model-based screening and does not replace an expert report. Each observation point is stationary; the time a passing driver sees a reflection is not shown directly. Sun visor and vehicle geometry are not modelled.

Next: Settings, filter combinations and a calculated example are described in the manual, chapter VI.2 Road traffic.