Bifacial solar panels generate electricity not only from direct sunlight that hits the front side, but also from reflected light that reaches the rear side. In this article, we will look at the rooftop conditions where this technology increases generation efficiency, and where there will be no significant difference.
In most typical scenarios, bifacial panels on a roof will not deliver additional generation because there is nowhere for light to be reflected onto the rear side of the panel:
- the roof is dark (black tiles, bitumen);
- the panels are installed almost flush with the roof (clearance less than 10 cm);
- there is shading from chimneys, parapets, or air conditioners.
In this case, the efficiency gain is only 0–5%—that is, the difference is practically negligible.
When bifacial panels on a roof improve efficiency
Flat roofs with a ballasted system
- Distance from the roof: 15–30 cm.
- Tilt angle: 10–15°.
- Surface: concrete or light-colored gravel.
- Generation gain: +5–12%, especially if light geotextile or film is placed under the panels.
Light-colored metal roofs
- Light-colored metal tiles or white corrugated sheet.
- High light reflectance (albedo 0.4–0.6).
- Even with a minimal gap you can get +3–6% additional generation.
Green roofs or light-colored gravel
- Reflect light better than black bitumen.
- Generation gain: +4–8%.
Bifacial panels are beneficial even without rear-side generation
If you have a roof that does not reflect light, bifacial panels still have important advantages:
- Glass–glass construction — better protection against moisture, ultraviolet, and temperature fluctuations.
- Durability — degradation ≤0.4%/year. This is significantly less than with conventional panels.
- Warranty — up to 30 years for power retention and 15–25 years for the product itself.