Shop for solar panels today and you'll see three terms again and again: monofacial, bifacial and dual-glass (also called double-glass or glass-glass). They describe two different things. Monofacial vs bifacial is about which side of the panel makes power. Dual-glass is about what the back of the panel is made of. This guide explains each one, how they compare, and which makes sense for your roof, ground mount, RV or cabin.
Monofacial panels: power from the front only
A monofacial panel collects sunlight on its front face only. The solar cells sit under a sheet of tempered glass. The back is sealed with an opaque polymer backsheet, usually white or black. Any light that reaches the back of the panel is wasted.
For decades, this was the standard design, and it's still a great choice in many situations:
- Flush-mounted rooftops. When a panel sits a few inches above shingles, almost no light reaches its back, so a bifacial rear side would add very little.
- Looks. All-black monofacial panels with a black backsheet give a clean, uniform look on visible roofs.
- Weight. A polymer backsheet is lighter than a second sheet of glass, which helps on older roofs and in DIY installs.
Bifacial panels: power from both sides
A bifacial panel uses cells that can absorb light on both faces. The back of the panel is transparent, either a clear backsheet or a sheet of glass. The front still captures direct sunlight, and the rear captures light reflected off the ground, snow, gravel or a white roof.
Two numbers decide how much extra energy the rear side adds:
- Bifaciality is how strong the rear side is compared with the front under the same light. Modern N-type TOPCon panels usually land between 70% and 85%. For example, the JA Solar JAM54D41 LB series lists 80% ±10%, and some TOPCon models list up to 85%.
- Albedo is how much light the surface under the panel reflects. Grass and dark soil reflect little. Light gravel, concrete and white roofing reflect more. Fresh snow reflects the most.
Bifaciality is not a guaranteed production increase. Real-world gain depends on mounting height, tilt, row spacing, shading and the ground surface. Field results show what is possible in a snowy climate. A Sandia National Laboratories study in Vermont measured 10.7% to 13.4% more energy from bifacial strings than from matching monofacial strings on solar trackers. Winter snow cover drove the biggest gains.
Where bifacial pays off: ground mounts, pole mounts, carports, pergolas, flat roofs with tilted racking, and any array raised well above a light-colored or snowy surface. In northern states with months of snow cover, bifacial ground mounts are especially worthwhile. Bright desert gravel and light concrete in the Southwest also reflect plenty of light.
Where it adds little: panels mounted flush to a dark shingle roof. A bifacial panel still works fine there, and it performs at least as well as a monofacial panel on its front side. Just don't count on much bonus energy.
Dual-glass bifacial panels: glass on the front and the back
A bifacial panel needs a transparent back, and manufacturers build it in one of two ways:
- Transparent backsheet: tempered glass on the front, with a clear polymer sheet on the back.
- Dual-glass (glass-glass): glass on both the front and the back, with the cells sealed between the two sheets. Most of today's high-efficiency N-type bifacial panels use this design. Examples include the JA Solar JAM54D41 LB 455W and the Trina 710W/720W i-TOPCon dual-glass module.
Dual-glass construction brings several practical benefits:
- Better moisture protection. Glass blocks water vapor far better than a polymer sheet. That protects the cells from corrosion and slow degradation in humid, wet or coastal conditions.
- A stronger, more balanced build. The cells sit in the middle of a symmetrical glass "sandwich," which reduces stress on the cells and the risk of micro-cracks under snow and wind loads.
- Longer power warranties. Many dual-glass panels carry a 30-year linear power warranty. JA Solar's JAM54D41 series, for example, guarantees 87.4% of rated power at year 30, after 1% first-year and 0.4% yearly degradation. Many backsheet panels carry 25 years.
- Better fire behavior. Glass doesn't burn, so a glass back adds no fuel the way a plastic backsheet can.
The trade-offs:
- Weight. Glass on both sides adds a few kilograms per panel. The two sheets are usually thinner (for example 1.6 mm front and 1.6 mm back), which keeps 54-cell residential sizes around 22–24 kg (49–53 lb).
- Careful handling and mounting. Thin glass edges can chip if dropped or clamped incorrectly. Always use the clamping zones and mounting methods in the manufacturer's installation manual.
Not every dual-glass panel is bifacial. A few glass-glass panels use opaque cells or a tinted rear for looks. When in doubt, check the datasheet for a bifaciality rating.
Side-by-side comparison
| Feature | Monofacial (backsheet) | Bifacial with transparent backsheet | Dual-glass bifacial |
|---|---|---|---|
| Generates power from | Front only | Front + rear | Front + rear |
| Back of panel | Opaque polymer backsheet | Clear polymer backsheet | Glass |
| Extra energy from the rear | None | Depends on mounting height and ground reflectivity | Depends on mounting height and ground reflectivity |
| Moisture resistance | Good | Good | Excellent |
| Weight | Lightest | Light | Heaviest |
| Typical power warranty | 25 years | 25–30 years | Often 30 years |
| Best for | Flush-mounted rooftops, all-black looks | Raised or tilted arrays where weight matters | Ground mounts, carports, snowy sites, long-term value |
Typical values. Always check the datasheet and warranty terms for the specific model.
Design tips for bifacial panels
- Raise the array. More space between the panel and the ground lets more reflected light reach the back. Ground mounts at about 3 ft (1 m) or higher work well.
- Brighten the ground. Light gravel or white roof membranes reflect far more than grass or dark asphalt.
- Size your inverter for bifacial gain. The rear side adds current. Check your inverter or charge controller's maximum input current per MPPT, and check string voltage at your coldest expected temperature. Inverters with high current per MPPT, like the Growatt SPH 18000TL-HU-US (40 A per MPPT), handle large bifacial panels with room to spare.
- Keep racking clear of the rear. Rails and cross-members behind the cells cast shadows on the bifacial side. Use racking designed for bifacial panels where possible.
The bottom line
- Choose monofacial for a simple, flush-mounted rooftop where looks and weight matter most.
- Choose bifacial wherever light can reach the back of the panel: ground mounts, carports, tilted flat-roof arrays and snowy sites.
- Choose dual-glass bifacial for the toughest build and the longest power warranty, especially in snow, high wind, coastal or humid climates.
Browse our solar panels or solar panel pallets, or contact the ROCKSOLAR team and we'll help you pick the right panel for your site.
Sources
- Burnham, Riley, Walker & Pearce, bifacial vs monofacial field study on solar trackers in Vermont, Sandia National Laboratories, osti.gov/servlets/purl/1640786
- JinkoSolar, "Transparent backsheet vs dual glass: advantages and disadvantages," PV Tech
- JA Solar JAM54D41 LB series datasheet