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.
An advantage of a vertical mounting is that snow or dust blown over in weather events will not block the panels and reduce their production. Also, vertically mounted bifacials will take up lesser space than conventional modules. Ideal for application in agricultural farms, vertically mounted bifacial modules can be used integrated into fencing walls between fields and other structures. They can also serve as windbreaks.
Comparative Advantages
The efficiency of a solar panel is how well it performs its function of converting the net sunlight that falls on its on its surface into electrical energy. In any case, bifacial solar panels do not necessarily double the efficiency of a monofacial solar cell even though they contain as many as twice as many solar cell surfaces as monofacial cells.
A 2018 study by LONGi Solar showed that bifacials can increase efficiency by 11% compared to a conventional solar panel system. The bifacial solar cell efficiency increase can be as high as 27% with a solar tracking system that adjusts the orientation of the solar panel continuously toward the sun during its trajectory across the sky.
Most bifacials are made of glass without any aluminium frames. This makes the panels more resistant to chemical erosion. Conventional panels with aluminium frames are already considered to be very durable. Because there are no aluminium parts, bifacials do not need to be grounded. Find out the conditions for grounding or earthing/grounding a solar system here.
To achieve the same degree of solar power as a typical monofacial solar array, fewer bifacial solar panels are needed. As the bifacial solar panel price becomes competitive with monofacials, consumers searching for maximum efficiency with fewer panels, because of limited space, for instance, would do best by choosing bifacial solar panels.
Warranty Offerings by Manufacturers
Due to glass covers on both sides of bifacial solar panels, they are more durable than conventional solar panel modules. As a result, warranties, in some cases, are typically 5+ years longer, and can reach up to from 20–25 years.
What Are The Prospects of Bifacial Panels?
Results and studies have shown that bifacial modules can produce additional power between 10-20% over monofacial panels. If conditions are optimum and single axis trackers adopted, the additional power can reach up to 30-40%.
Large-scale off-grid installations have found bifacial panels a more efficient and productive option, it is however, expected to find larger applications in even residential installations. According to a 2019 report, by 2024, the size of the bifacial market is poised to increase tenfold. Read full report here.
Cost Considerations
Bifacial panel technology are still in the early stages of development, and just like any new technology, they are still very costly. The production from the rear side of the panel still does not necessary justify the spike in cost. However, in the near future, bifacials are expected to become more cost-effective.
Bifacial solar panels are heavier than traditional panels because of the additional glass panel.
Also, a special mounting system is needed for bifacials as they are not held in aluminium frames like traditional panels. This mounting system is expensive and has to be constructed separately adding to the already-high cost of purchasing the panels.
Because of their durable and long-lasting parts, most manufacturers offer a 30-year warranty on their bifacial modules.
In Conclusion
Brands like LG, LONGi, Lumos Solar, Prism Solar, Silfab, Sunpreme, Trina Solar and Yingli Solar all offer bifacial modules. It is expected that as more manufacturers begin production and the ones already offering bifacial modules expand their manufacturing capacities, bifacial modules will soon become a staple niche product that may disrupt the mainstream or possibly displace the traditional monofacial panels. It is therefore safe to say that bifacial modules, by the estimation of the market experts and analysts, may be the future of solar panels.
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