Solar Panel System GuideA bifacial solar panel produces power from both faces of the module. The front side works like any panel while the rear side collects light reflected off the ground or roof. This page sources its facts from EnergySage and the U.S. Department of Energy.
How a bifacial panel captures light on both sides
EnergySage explains that bifacial panels capture sunlight from both the front and back surfaces. Because the rear side adds a second collection surface, a bifacial module can generate more electricity than a comparably sized traditional panel.
The rear side depends on light that reflects off the surface below the array. The Department of Energy notes that a photovoltaic cell contains a semiconductor material that can absorb sunlight and convert it to electricity, and that same photovoltaic effect drives both faces of a bifacial module.
Where bifacial gains are large and where they are modest
EnergySage reports that bifacial panels are now standard in utility scale projects, where open racking and reflective ground let the rear side contribute meaningful extra output. On residential rooftop installations the rear side gains are usually modest.
The reason is the mounting. The Department of Energy notes that photovoltaic arrays must be mounted on a stable, durable structure, and that rack mounting is currently the most common method. A close mounted rooftop rack leaves little room for reflected light to reach the back of the module.