Most of the solar panels you see are monofacial solar panels. Sunlight hits the top face of the panel and it generates electricity.
But those aren’t the only kind of solar panel that is out there. There’s another type - bifacial PV panels. With bifacial panels, there’s an extra part of the panel that produces electricity - the back face. Bifacial panels 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. Diffused light from clouds, buildings, or other objects can also hit the back and generate electricity.
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If you’re familiar with how solar panels work, you’ll know that the silicon cells capture photons from sunlight and convert them to energy. These cells are held together in a frame, sandwiched between a protective glass coating that keeps the cells safe but lets sunlight through, and a protective, opaque back sheet.
When it comes to bifacial solar modules, however, the opaque back sheet is switched for a clear back sheet. This allows photons from reflected and diffused light to hit the back of the panel and generate power.
In order to optimize the amount of energy produced by the backside of the panel, shading caused by obstructions like the panels’ racking system needs to be minimized. In a traditional ground mount system, horizontal and vertical support bars are used to support the solar panels.
However, because this traditional racking takes up valuable electricity-producing real estate on the backs of bifacial panels, these systems oftentimes have different mounting systems. The support rails across the back are thinner and there are fewer vertical support poles.
Bifacial panels can be a great way to pack a big punch with less room. If you’re limited on space, opting for bifacial panels can help your system produce more electricity with fewer panels. However, bifacial panels aren’t for everyone. There are a few factors that increase how much your bifacial system will produce.
The more vertical the bifacial panels are tilted, the more light will reach the backside, and the more energy they can produce. Because of this, bifacial panels often perform the best as ground mounts or as raised mounts on flat roofs, making them a good option for many commercial and utility-scale systems.
Bifacial panels installed on tilted roofs are often not ideal, because the panels are flush against the roof, leaving little to no room for light to get to the rear side. As many homes have sloped roofs, bifacial solar panels are not commonly used on residential solar systems. However, if you are looking to install a ground mount system, solar carport, or solar pergola, bifacial panels may make sense for you.
Surface Reflectivity or Albedo
Another important factor when it comes to the success of bifacial panels is the reflectivity or albedo of the surface below the panels. Albedo is how much light is reflected by a surface. An example of something with a high albedo is snow, whereas black asphalt would have a lower albedo.
Bifacial panels love surfaces that have high albedos because they’ll take all that reflected sunlight and turn it into energy. Metal roofs are often great reflectors of light, as are cool roofs. Cool roofs can have an albedo of 0.65, or 65% light reflecting back. While cool roofs limit the heat island effect and keep buildings cooler, they also are great for bifacial solar panels.
If you’re considering a ground mount, grass and soil often have a lower albedo than cool roofs, but still offer some reflectivity. One of the most reflective naturally occurring materials is snow. If you live in an area that gets a lot of snow, bifacial panels will keep on producing even if the front of your system stays covered. While solar panels are designed to shed accumulated snow, you will lose out on production while they’re covered. However, with bifacial panels, sunlight reflected off the snow on the ground means your panels will keep on generating electricity from the backside as the snow above melts.
The main advantage of bifacial panels is the additional production. While most properly-designed bifacial solar systems should produce more electricity than a monofacial system, don’t expect production to double. Because the backside is using reflected energy, it will inevitably produce less than the front side that’s receiving direct sunlight.
Because there are so many factors, like installation angle and surface albedo, it’s hard to give a solid estimate on how much extra electricity bifacial panels will generate. Most sources say you could see an increase in production between 5% and 30%.
Bifacial solar panels do cost more than traditional monofacial panels. According to a 2019 study by NREL, the price difference between monofacial and bifacial panels ranges from $0.01 to $0.05 per watt for large projects, typically utility-scale. Smaller commercial or residential systems will be closer to $0.20 per watt.
But can bifacial panels make up for their extra cost with extra production? If you’re trying to offset your home or business’s electricity, you’ll need fewer solar panels if you go with bifacial and install them in a way that maximizes their efficiency. Your solar installer will be able to help guide you through the decision based on the characteristics of your property and your goals for the project.
In 2012, the Seattle Mariners installed a 32.76 kW solar system at their Major League Baseball stadium as part of the first 1 megawatt (MW) of bifacial solar installed in the world. Since then, over 100 MW of bifacial solar panels have been installed as of May 2019.
While monofacial panels still make up the majority of solar systems installed today, that’s expected to steadily shift as bifacial panel technology becomes more available. You may find it difficult to find a plethora of installers that install bifacial panels this year, all signs are pointing to that changing as they gain more popularity.