Bifacial solar panels generate electricity from both faces, using direct sunlight up front and reflected light on the rear for higher yield.
For the full breakdown, see our best Bifacial Solar Panels guide.
Two active faces are becoming the standard at utility-scale solar farms, and the reason is simple: a bifacial solar panel collects light on both sides, not just the face aimed at the sky. The front behaves like any conventional panel, absorbing direct beam sunlight. The rear does what a standard module can’t — it harvests reflected and diffuse light bouncing off the ground and nearby surfaces.
That second harvest is the whole point of the design, and also why bifacial is not a simple “double your power” upgrade. Extra output depends on where and how the panel is mounted, not on the panel alone.
How Bifacial Solar Panels Work
Bifacial panels produce power from two light paths at the same time. The front face converts direct sunlight; the rear face converts reflected sunlight and diffuse sky light reaching the back of the module. NREL models the total as front-side irradiance plus rear-side irradiance scaled by a bifaciality factor.
The bifaciality factor is the ratio of rear-side power to front-side power measured under the same test light, so 0.80 means the rear produces 80 percent as much as the front when both receive equal light. What the rear actually receives depends on two site realities: ground reflectivity, known as albedo, and the open space behind the module. Rear shading, dark ground, or tight racking starve the second face.
How Much Extra Power Do Bifacial Panels Actually Produce?
There is no fixed number, and NREL says so directly: gain is site-specific, and the same module may add almost nothing in one location while adding close to 9 percent in another. The best predictor is the cell’s bifaciality factor. NREL’s bifacial photovoltaic research records typical values around 0.65–0.80 for p-type bifacial PERC, 0.75–0.90 for n-PERT, and 0.85–0.95 for silicon heterojunction (Si-HJT) modules.
One NREL validation context cites modeled annual gains of roughly 6 percent for PERC and 9 percent for Si-HJT — useful planning figures, not guarantees. NREL stresses that gain and bifaciality values are model- and measurement-dependent and should not be copied between projects without validation.
The site factors below decide how much the rear face actually contributes.
| Factor | Effect On Rear-Side Output |
|---|---|
| Ground albedo | Light surfaces, snow, and pale gravel boost reflected light; dark soil and grass cut it |
| Mounting height | More clearance behind the module lets more reflected light reach the rear face |
| Row spacing and tilt | Wider row spacing and steeper tilt limit self-shading from nearby rows |
| Single-axis tracking | Trackers keep the rear face open to sky and ground light through the day |