In brief
How strongly a PV module glares depends above all on its glass surface: not on how much light it reflects, but on how concentrated the reflection is. Anti-reflective coating is standard today, but it serves the energy yield and does not make a module low-glare. Strongly textured glass is usually not low-glare either; satinated glass and some films glare considerably less. The system modules of the app contain mostly generic values for these glass classes, "Phytonics Folie" manufacturer data; a specific product requires its own measurement data.
8.6.1 What matters
- Concentration, not reflectance. The luminance of a reflecting surface depends mainly on how directional the reflection is, not on how much is reflected (Bucher et al. 2021, p. 3). A matte white wall reflects a lot of light and does not glare; a glass that reflects little but in a concentrated way can glare strongly.
- Flat incidence is decisive. Reflection increases with the angle of incidence for all surfaces. In the measurements for EnergieSchweiz, all modules stay clearly below 30,000 cd/m² up to an angle of incidence of about 40° to 60°; above 50° to 60°, practically all exceed it (Toggweiler et al. 2024, p. 23). A value measured at 10° alone therefore says little.
- "Low-glare" is not a protected term. The report for EnergieSchweiz defines: a surface is low-glare if, from every relevant viewing angle, it appears no brighter than a material generally regarded as non-glaring, such as a white wall (Toggweiler et al. 2024, p. 11). Product names such as "anti-glare" or "low-glare" do not prove this; only measurements can.
- Low-reflective is not low-glare. Standard solar glass counts as low-reflective because it reflects less than 5 % of the light over a wide range of angles (Toggweiler et al. 2024, p. 12). That does not make it low-glare.
8.6.2 Glass types at a glance
| Surface | Glare behavior | Luminance | System module in the app |
|---|---|---|---|
| Standard solar glass with anti-reflective coating | Almost always used today. The anti-reflective coating is meant to optimize the yield, not to reduce glare (Toggweiler et al. 2024, p. 12); it can even increase glare (Bucher et al. 2021, p. 1). Beam spread around 5° to 10° (Toggweiler et al. 2024, p. 35). | typically 500,000 to 100,000,000 cd/m² (Toggweiler et al. 2024, p. 35); on site 2.5 to 6 million cd/m² (Bucher et al. 2026, p. 7) | "Standard Modul (Generic)" |
| Float glass (window glass, rare, mostly building integration) | mirror-like; point-shaped, short but very strong glare (Toggweiler et al. 2024, p. 36) | very high at all angles; no measured values | approximation: "Perfect mirror" |
| Strongly textured or structured glass | Usually not low-glare: "sometimes glares" (Bucher 2024, slide 12). The maximum can lie away from the mirror direction, and results differ strongly between products; a flexible module with a coarsely structured surface performed very well (Toggweiler et al. 2024, p. 23). This can only be demonstrated with measurement data of the product. | product-dependent | custom module type from measurement data |
| Coated special glass (e.g. Deflect) | very low at steep incidence; from about 50° angle of incidence, glare can occur (Toggweiler et al. 2024, p. 39) | on site 100,000 to 200,000 cd/m² (Bucher et al. 2026, p. 7) | custom module type from measurement data |
| Satinated glass (chemically etched) | "the least glaring behavior of all known glass surfaces" (Toggweiler et al. 2024, p. 37); reflects in a widely scattered way, partly away from the mirror direction, then at much lower brightness (p. 30) | on site around 7,000 cd/m²; replacing standard modules reduced luminance by a factor of about 1,000 (Bucher et al. 2021, pp. 4 and 7) | "Satiniertes Modul (Generic)" |
| Anti-glare films (applied afterwards, e.g. Phytonics, PV-Print) | Properties differ from film to film; durability critical, experience largely lacking (Toggweiler et al. 2024, p. 40). Films redirect the reflection towards flat angles instead of removing it; the flatter the view, the brighter (Bucher et al. 2026, p. 7). Power loss in lab tests 1.2 % on float glass, almost 5 % on textured solar glass (p. 8). | on site Phytonics just under 20,000, PV-Print 30,000 to 60,000 cd/m² (Bucher et al. 2026, p. 7) | "Phytonics Folie" or custom module type from measurement data |
| Sandblasted glass | looks similar to satinated glass, glass is mechanically weakened, warranty is lost; no measurements (Toggweiler et al. 2024, p. 38) | no measured values | – |
The luminances in the table come from different measurements (laboratory under defined illumination, field measurement in real sunlight) and are comparable only in order of magnitude.
8.6.3 System modules in the app
| System module | Values | Use |
|---|---|---|
| "Perfect mirror" | no curves; luminance of the sun, hit region of the solar disc | calculation according to LAI and OVE R 11-3 (Ch. VI.1) |
| "Standard Modul (Generic)" | generic; core derived from the figures of a standard module in the EnergieSchweiz report (Toggweiler et al. 2024, Annex 8, Table V, p. 66; measured values Table III, p. 65), ring and lobe axes from a BRDF measurement of standard double glass (SPF Rapperswil) | standard solar glass with anti-reflective coating |
| "Satiniertes Modul (Generic)" | generic | satinated glass |
| "Phytonics Folie" | manufacturer data | Phytonics film |
- Generic values are reference values for a glass class. They do not replace a data sheet or a measurement of the product used. The values stored in the admin area apply; the report documents the values used in each case.
- "Phytonics Folie": the values are taken from the manufacturer. No warranty is given for their correctness, completeness or currency; suitability and status are to be agreed with the manufacturer.
- Viewing the values: the "Manage Module Types" dialog shows the curves of every module type; the report lists the values used in the appendix "PV Module Types" (Ch. 8, Ch. 14).
- Older system modules such as "Standard Modul" or "Phytonics Anti-Glare Film" may still appear in existing projects.
8.6.4 Using your own measurement data
For a specific product, a custom module type is created from its measurement data (Ch. 8, section 8.1).
| Type of measurement | Example | Suitability for a module type |
|---|---|---|
| BRDF or goniophotometer measurement over many angles of incidence | laboratory (e.g. SPF Rapperswil, Fraunhofer ISE) | suitable: provides luminance, axes and position of the maximum for each angle of incidence |
| single value at one angle of incidence | test report with luminance at 10° | not sufficient; flat angles are missing |
| luminance coefficient per angle of incidence | test according to MA 39 Vienna | limited; axes and position of the maximum are missing |
| field measurement on site | luminance camera, luminance meter | for plausibility checks; conditions vary (Bucher et al. 2026, p. 11) |
What a test report must provide. For each angle of incidence (0° to 80°, preferably to 90°, in 10° steps): maximum luminance of the core and, if applicable, of a ring in cd/m², opening along and across the plane of incidence in degrees, and position of the maximum relative to the mirror direction (offset δ). Reference: 100,000 lx on the module surface, independent of the angle of incidence (Ch. 8, section 8.2).
Check the reference quantity. Test reports normalize differently. If a report refers the illuminance to a surface perpendicular to the light source instead of the module surface, divide the values by cos θ before adopting them.
Record the origin. Enter the test institute, report number, date and page in the "Note" of the module type; the note appears in the report. Data sheet and test report belong in the appendix of the glare report. If measurement data are missing, this is stated in the report and not replaced by another profile.
8.6.5 Points to note
- Compare luminance thresholds only at the observation points. The curves apply to 100,000 lx on the module. At the observation point, the luminance is usually much lower: at flat incidence the module receives less light, and the low sun is weaker (Ch. V.5). Reference values such as 30,000 cd/m² are compared with the calculated values in the report, not with the curve.
- Films shift glare. Because they redirect light towards flat angles (offset δ), new locations can be affected where a standard module does not glare, albeit at much lower luminance. Compare variants for all observation points (Ch. 13).
- Long-term behavior of films and coatings is barely documented; no module type represents soiling or aging (Ch. VII).
- Guidelines: LAI and OVE calculate with ideally mirroring modules ("Perfect mirror"); the FBA position paper requires module-typical reflections, i.e. a real module type (Ch. VI.1, Ch. VI.2).
8.6.6 Sources
- Toggweiler, P.; Bohren, A.; Bucher, C.; Rechsteiner, T. (2024): Stand der Technik zu blendarmen Oberflächen bei PV-Modulen. Report on behalf of EnergieSchweiz, Swiss Federal Office of Energy, October 2024.
- Bucher, C.; Wüthrich, P.; Danaci, Ş.; Wandel, J. (2021): Glare Hazard Analysis of Novel BIPV Module Technologies. ISES Solar World Congress 2021, Conference Proceedings.
- Bucher, C. (2024): Blendung an PV-Anlagen: Erfahrungen mit blendarmen Produkten. Presentation, Solar Update Swissolar, 19.11.2024.
- Bucher, C.; Halle, L.; Burri, M. (2026): Praxistest blendfreie Photovoltaik-Module. Final report, Bern University of Applied Sciences, 02.02.2026, version 3.0.
- Ruesch, F.; Battaglia, M.; Brunold, S. (2016): Methode zur Quantifizierung der Blendung durch Solaranlagen – Vergleich mit anderen Materialien der Gebäudehülle. 26th Symposium Thermische Solarenergie, Bad Staffelstein.
- Babin, M.; Thorsteinsson, S.; Jakobsen, M. L.; Spataru, S. V. (2022): Glare Potential Evaluation of Structured PV Glass Based on Gonioreflectometry. IEEE Journal of Photovoltaics 12(6), 1314–1318.