Bifacial Solar Panels
Updated: Apr 27
What Is A Bifacial Solar Panel Module?
Solar panels contain photovoltaic cells that convert sunlight into electricity. Traditional solar panel modules have a transparent top side that has an arrangement of solar cells that produce the electricity and a bottom side that is mostly made of an opaque polymer backsheet to which a junction box is attached. They can be thus said to be 'monofacial'. As is directly implied in the name, a bifacial solar panel is a solar module that is constructed in such a way to expose both the front and backside of the solar cells to sunlight so as to produce electricity from both sides of the panel.
Bifacial modules have been around since the 1960’s, however it was with the recent development of the Passivated Emitter Rear Cell technology that has significantly increased their efficiencies and expanded their potentials, that they recently became the disruptive trend in the solar module market. Since 2018, many manufacturers have been issuing new PERC bifacial cells or announcing that they would be increasing their bifacial module manufacturing capacities.
FUNFACT: The International Space Station Uses An Array of Bifacial Solar Panels.
How Does Bifacial Solar Panels Work?
In bifacial panels the top solar cells perform as in traditional monofacial panels: they directly capture sun rays and convert them into electricity. The upgrade is that bifacial modules come with a transparent backside that are able to generate electricity from the sun shining directly on them and also from the sunlight reflected on the opposite side or underneath the panel or off the ground.
While the original light is called incident light, this reflected light is called albedo light. They come from diffused light from clouds, buildings or other objects from which light rays can bounce off and hit the backside of the bifacial modules. When bifacial modules are installed on highly reflective surfaces, some bifacial module manufacturers say that their bifacial panels can give up to a 30% increase in production just from the extra power generated from the backside.
Results and studies have shown that bifacial modules can produce additional power between 10-20% over monofacial panels. If conditions are optimized and single axis trackers adopted, the additional power can be as reach up to 30-40%.
What Are the Considerations for Installing Bifacial Panels?
Monofacial solar panel systems are often installed on racks or flushed against rooftops. (Read our article on considerations for mounting a solar panel here.) Bifacial panels will not fulfil their production potential if they are installed directly on rooftops because the rear side would be blocked from receiving any incident light that would be reflected back to the rear side of the bifacial panel. They are thus least useful for rooftop installations. But they produce more electricity when they are installed at varying degrees of tilt or angle off the roof or ground. The more the tilt, the more their rears can receive reflected light off the surface and the more their production. This explains why bifacial modules perform better on flat commercial rooftops and ground-mounted arrays, because there is more room for tilt and bouncing reflected or albedo light to the rear of the modules.
Also, bifacial panels work well when installed on surfaces that have high albedos. For instance, metal roofs are often great reflectors of light.
The mounting system itself can affect the performance of the bifacial modules. Racking systems with support rails usually covered by a monofacial module’s backsheet will shade back rows of bifacial cells. Junction boxes on bifacial panels are constructed to be smaller or separated into multiple units positioned along the panel’s edge to prevent shading. (Read about shading here.) Mounting and racking systems specially designed for bifacial installations are to mitigate the shading of the backside of the panels.
Bifacial modules can also be installed vertically unlike monofacial panels which must necessarily tilted or angled. As a general rule, solar panels are most efficient when they are perpendicular to the sun’s rays. The reason being that sunlight falls at an angle to the earth's surface. Monofacial solar modules have to be tilted to degrees ranging from 28–30 degrees to optimize efficiency. Also, solar panels are titled for the rains to be able to flow off them and in the process help to wash off any accumulated dirt. That they can be installed vertically means that bifacial panels will most likely reach a double peak production each day.