Quick Facts
What a bifacial solar panel is
A bifacial solar panel has solar cells whose front and rear surfaces both absorb light. Construction uses transparent material on both faces of the laminate, typically tempered glass on both sides (glass-glass) or glass front with a transparent polymer backsheet. The cells themselves can be Mono PERC, TOPCon, or HJT, with TOPCon and HJT extracting more energy from the rear face.
In a conventional monofacial panel, the back of the cell is metallised and the back of the module is an opaque polymer sheet. Light reaching the back is wasted. In a bifacial design, the rear of the cell can absorb the light reflected off the ground or roof and generate additional current.
The extra energy is called bifacial gain. It scales with surface albedo, mounting height, tilt, and the inherent bifacial factor of the cell technology used.
How bifacial gain works in practice
Sunlight reaching the ground beneath a solar array reflects in many directions. Some of it travels upward toward the rear of the panels. The bifacial cells absorb this rear-side light and add to the front-side current.
Several physical factors determine how much rear-side energy is captured.
Surface albedo: The reflectivity of the surface below the array. Higher albedo means more reflected light reaches the back of the panel.
Mounting height: The taller the panels above the surface, the larger the area of ground that contributes reflected light to each panel. Standard ground-mount tables sit 0.8 to 1.5 metres above ground.
Tilt angle: A steeper tilt exposes more of the rear face to reflected ground light. Trade-off against front-side optimum.
Row spacing: Wider gaps between rows reduce self-shading on the rear of panels.
Cell bifacial factor: The intrinsic efficiency of the rear face compared with the front, which is technology-dependent.
A 100 kWp bifacial Mono PERC ground-mount plant in Rajasthan on sandy desert albedo typically achieves 15% to 22% bifacial gain. The same plant on grass would see 8% to 12%.
Bifacial factor by cell technology
| Cell Technology | Typical Bifacial Factor | Notes |
|---|---|---|
| Bifacial Mono PERC | 70% to 75% | Rear contact pattern blocks some light |
| Bifacial TOPCon | 80% to 85% | Cleaner rear structure than PERC |
| Bifacial HJT | 85% to 95% | Symmetric design favours bifacial |
| Bifacial poly | 65% to 70% | Largely obsolete in 2026 |
The bifacial factor is published on every premium bifacial module datasheet. Designers use it when computing expected annual energy.
Indian use cases
Ground-mount utility-scale plants are the largest adopters of bifacial in India. Projects across Rajasthan, Gujarat, Andhra Pradesh, and Karnataka now default to bifacial designs, often paired with single-axis trackers. The combination delivers CUF in the 25% to 28% range against 20% to 23% for monofacial fixed-tilt.
Commercial rooftops in India increasingly choose bifacial when the roof is a flat concrete surface with elevated module mounting. Concrete albedo of 25% to 35% gives 8% to 12% bifacial gain at modest installation premium.
Residential rooftops adopt bifacial less often because most homes have sloped roofs where bifacial gain is limited. Some premium residential installations on terrace or flat roofs see useful gain.
BIPV applications such as solar canopies, agrivoltaics, and floating solar use bifacial because the geometry often favours rear-side light absorption.
Construction differences from monofacial
Bifacial modules typically use glass-glass construction, with 2 mm or 2.5 mm tempered glass on both sides. The total weight is similar to monofacial polymer-backsheet panels because the glass is thinner.
Encapsulation uses POE (polyolefin elastomer) instead of EVA, because POE resists acetic acid that can form when EVA is exposed to humidity on both sides.
Frames are aluminium, similar to monofacial. Some frameless bifacial designs exist for specific BIPV uses.
Junction boxes are smaller, with three bypass diodes rated for the front-and-back module current.
Mounting structures need slight adjustments to allow rear-side ventilation. Self-shading from horizontal purlins must be minimised. Triangular or torque-tube mounting arrangements that leave the rear largely clear give the best bifacial gain.
Benefits of bifacial
Higher annual energy yield per kWp installed, particularly on high-albedo surfaces.
Better lifetime energy due to glass-glass construction, which degrades more slowly than polymer-backsheet panels.
More uniform output through the day. Rear-side energy peaks in morning and evening, smoothing the generation curve.
Longer warranty terms from manufacturers, reflecting the durability of glass-glass construction.
Lower long-term LCOE for utility projects despite a small CAPEX premium.
Limitations and trade-offs
Modest gain on low-albedo surfaces. Dark soil, asphalt, and grass deliver only 4% to 8% bifacial gain, sometimes not enough to justify the premium.
Sensitivity to mounting design. Poorly designed racks shade the rear face and erode bifacial gain.
Higher weight per square metre than polymer-backsheet panels, occasionally requiring structural review for rooftop installations.
Higher front-glass tempering quality required to handle the additional loads of a glass-glass laminate.
Slightly more complex string design, because the bifacial gain shows up as additional current the inverter must handle.
Common mistakes in specifying bifacial
Treating “bifacial” as a single specification without checking the bifacial factor. Two bifacial Mono PERC modules from different makers can deliver 5% different rear-side efficiency.
Underestimating the importance of albedo. A bifacial plant on dark soil delivers little extra over monofacial.
Mounting bifacial too close to the ground. Clearance below 0.5 metre kills most bifacial gain.
Mixing bifacial and monofacial in the same string. Different rear-side current produces mismatch losses.
Ignoring rear-side shading from horizontal racking members. Even minor shadows on the rear face reduce gain disproportionately.
Sizing inverters as if the rear-side gain does not exist. A 1.2x DC oversizing target for monofacial may need adjustment to 1.1x for bifacial in some configurations.
Best practices
For ground-mount projects, default to bifacial unless the site has very low albedo or budget constraints rule it out.
Pair bifacial with single-axis trackers for utility-scale plants. The combination stacks the gains.
Specify the bifacial factor in tenders, not just “bifacial” as a generic label.
Design mounting structures with minimum rear-side obstruction and adequate clearance.
For rooftop installations, evaluate the actual albedo of the roof surface (concrete, white coating, tile, metal) before committing to bifacial.
Standards and certifications
Bifacial modules in India must comply with IEC 61215, IEC 61730, and IEC TS 60904-1-2 (which defines bifacial measurement methods). ALMM listing is required for government subsidy. Bankability assessments often include accelerated UV testing on the rear face, because rear surfaces face less direct sun but more diffuse exposure.
Related glossary terms
- Mono PERC
- TOPCon Solar Panel
- HJT Solar Panel
- Half-cut Cell
- Tilt Angle
- Azimuth
- Performance Ratio
- Capacity Utilisation Factor
- ALMM
Key takeaways
A bifacial solar panel produces electricity from both its front and rear surfaces, adding 5% to 25% to annual energy yield depending on surface albedo, mounting height, and tilt. The technology is now standard in Indian ground-mount projects and increasingly common on commercial rooftops. TOPCon and HJT cell technologies deliver higher bifacial factors than Mono PERC, making them the natural choice for premium bifacial installations.