Bifacial solar panels explained

Bifacial panels look like ordinary modules with a twist: they generate electricity from both faces. The front does the usual work with direct sun; the rear picks up light reflected off the surface below. Whether that adds much depends heavily on how and where the panel is mounted. Here is the physics without the hype.

How rear-side generation works

A conventional (monofacial) panel has an opaque back sheet. A bifacial panel replaces it with glass or a transparent backing and uses cells that are light-sensitive on both sides. Any light that reaches the rear — mostly sunlight that bounced off the ground or roof — produces additional current.

The extra output is real but conditional. It requires two things: reflected light hitting the back, and enough space behind the panel for that light to reach the cells rather than being blocked.

Albedo: the surface below

Albedo is the reflectivity of the surface beneath the array, and it is the single biggest driver of rear-side gain.

This is why bifacial modules earn their keep on white commercial roofs, light ground mounts, and snowy sites, and do less on a dark shingle roof.

Mounting height and clearance

Reflected light has to travel from the ground back up to the panel's rear cells. The more the array is elevated and tilted, the more reflected light reaches the back and spreads evenly across it. A flush-mounted residential array sitting close to the roof leaves little gap, so much of the rear face sees shadow or blocked light. Tilted racks, ground mounts, and elevated structures capture noticeably more rear-side energy.

Bifaciality and design numbers

Manufacturers publish a bifaciality factor — the rear side's efficiency as a percentage of the front's. But the actual system gain depends on albedo, height, tilt, and how much of the rear is shaded by the racking and mounting hardware.

For design and permitting, two things matter. First, do not over-count rear gain: on a typical flush residential roof it may be modest, so size conservatively and verify with the datasheet. Second, remember that the electrical ratings you build the design around — module Voc, Isc, and rated power — still come from the datasheet, and rear-side irradiance can raise operating current beyond the front-only nameplate. That feeds directly into PV string sizing and conductor and OCPD choices.

Bifacial technology is one more module option alongside the choices in solar panel types explained. Whether it pays off depends on your roof's reflectivity and mounting. Confirm all ratings on the manufacturer datasheet, and have a licensed electrician or PE review the final design.

Educational reference, reviewed 2026-07. A design aid, not a substitute for a licensed electrician or PE. Confirm the enforced NEC edition and local amendments with your AHJ.