Quick definition
A standard, monofacial panel only has active solar cells facing one direction. A bifacial panel has cells on both sides, usually behind a transparent or semi-transparent back sheet, so it can also capture light that bounces off the ground, a roof surface, or nearby snow.
The extra output depends almost entirely on what's underneath and behind the panel, which is why the same bifacial panel can perform very differently on two different installations.
At a glance: bifacial gain is typically modest, roughly 2 to 5%, on a standard roof mount, and can run notably higher on raised or ground-mounted arrays over reflective surfaces.
Why it matters
Bifacial technology only pays off when the installation gives the panel's back side something worth capturing. A panel mounted flush against a dark asphalt shingle roof, with almost no gap and almost no reflectivity underneath, isn't going to see much benefit from its back-side cells. The same panel on an raised racking system over white gravel, or on a ground mount with light-colored soil beneath it, can see a real, measurable output gain; a widely cited Purdue-NREL modeling study, validated against NREL's own field data, puts that gain anywhere from under 10% at natural ground reflectivity up to around 30% once the surface is reflective and the panel is raised.
This is why bifacial panels show up far more often in utility-scale and commercial ground-mount projects than on residential rooftops, an application NREL's own bifacial research group actively models and validates against real test fields. Commercial installers have more control over what's underneath the array, and the extra output, even a modest percentage, adds up meaningfully at scale. A homeowner considering bifacial panels for a standard roof mount should weigh the real output gain for their specific setup against the added cost, rather than assuming the same gain quoted for ground-mount installations.
Climate matters too. Locations with regular snow cover can see a genuine winter production boost from bifacial panels mounted with enough clearance, since fresh snow is highly reflective and bounces a lot of light back up onto the panel's rear cells.
Where you'll see this
The output comparison: bifacial vs standard tool estimates the real-world output difference for your specific mounting setup, rather than relying on generic marketing numbers.
If you already have a system size in mind, the bifacial panel output addon calculator estimates how much extra energy switching to bifacial panels could add.
This term comes up most in ground-mount and raised racking proposals, a decision the ground mount vs roof mount space calculator can help frame, in commercial and utility-scale project quotes, and any time a panel spec sheet lists a bifaciality factor alongside its standard wattage rating.
Related terms
Frequently asked
It depends heavily on the mounting surface. Over a light-colored roof or gravel, the gain is often modest, in the low single digits. Over snow, white roofing membrane, or reflective ground cover, gains can run notably higher, since the back side is picking up meaningfully more reflected light.
Often not by much. A standard roof-mount installation, tight against the roof surface, gives the back side little room to capture reflected light. Bifacial panels show their biggest advantage on raised racking or ground mounts, where there's real airflow and reflection underneath.
Yes, typically. The price premium has narrowed as bifacial manufacturing has scaled up, but it's still a real cost difference to weigh against the expected output gain for your specific mounting situation.
Snow can help, somewhat counterintuitively. Fresh snow on the ground beneath an raised bifacial array reflects a lot of light onto the panel's back side, which can meaningfully boost winter output even while snow cover elsewhere reduces overall solar production.