What are bifacial solar panels?

In the race to create ever more efficient solar panels, manufacturers are making panels that capture light on both sides.

Lumos GSX

When you’re trying to choose the right solar panel for your project, solar panel efficiency stands out as one of the key features. One of the newer ways that manufacturers are improving efficiency is with bifacial solar panels.

A conventional monofacial solar panel is opaque at the rear, but a bifacial panel allows sunlight to enter from both the front and back. This can result in anywhere from a 5% to 30% increase in electricity production, depending on the panel and how it’s installed.

The majority of solar installations use conventional monofacial panels, but there are some situations where bifacial modules could make sense.

How solar panels are constructed

Here’s a diagram of how a conventional panel is constructed:

Diagram of a solar panel
Diagram of a conventional solar panel with an opaque backsheet. Credit: International Renewable Energy Agency

The backsheet is the layer that sits behind the photovoltaic cells. It has no photovoltaic properties, so while it plays an important role in the construction of the panel, it doesn’t generate any electricity.

Because of this, you might wonder what effect the backsheet could have on the electrical output of the panel. There are two things the backsheet does in a conventional solar panel that affects efficiency.

First, the default choice for solar panels is a white backsheet. This is because the color white reflects more light, and this can increase the light hitting the front of the solar cells. The way this happens is that the light hits the backsheet, reflects up through the top glass layer, and is refracted internally within the glass in a process called internal reflection. That refracted light increases the output of the solar panel.

The other thing the backsheet does is affect the temperature of the solar cells. A cooler cell is more efficient, so keeping the temperature of the solar panel lower is a good thing. Just as a white t-shirt keeps you cooler on a sunny day than a black shirt, a white backsheet absorbs less heat and keeps the panel a little cooler, thereby increasing its electrical output.

Sometimes people choose a black backsheet for aesthetic reasons, because an all-black solar panel tends to look nicer against a roof with dark shingles. The tradeoff is a loss in efficiency, although it’s minor. For example, the REC N-PEAK panel can hit 19.8% efficiency, while the N-PEAK Black reaches 19.5%.

How a bifacial solar panel is constructed

A bifacial solar panel replaces the traditional opaque backsheet with a transparent layer, such as glass or a clear backsheet. That transparent layer allows cells on both sides of the panel to receive light.

Solar panels require wiring and a component called a junction box that is mounted at the rear. Normally the appearance of these components doesn’t matter, but because a bifacial panel receives light from the rear, some manufacturers have redesigned the wiring and junction box of their bifacial panels to minimize the shading that these components cause.

There are also frameless bifacial panels that are described further below.

How do bifacial solar panels work?

The higher efficiency of bifacial solar panels is due to the ability of the rear of the panel to collect light. The amount of light available at the rear of the panel varies greatly with the type of installation.

In a residential rooftop with standard racking that places the panel only a few inches away from the roof surface, there will be very little additional light to be gained from the backside of the panel.

But in a ground-mounted installation or a rooftop install that uses a racking system that tilts the solar panels, there may be enough light reflected from behind the panels to make the use of bifacial modules worth it.

You might be surprised that grass or even dirt can reflect enough light on a sunny day to make a difference.

How much more efficient is a bifacial solar panel?

The efficiency gain depends greatly on the installation, but bifacial panels on average may see a 6-9% improvement in output over a conventional monofacial panel.

This is according to a study by the National Renewable Energy Laboratory that measured the performance of an installation of bifacial panels on a ground-mounted rack.

Frameless bifacial solar panels

There’s a special type of bifacial panel known as frameless glass-on-glass. These panels do away with the traditional metal frame and have glass to the edge of the panel. Tempered glass provides the product with rigidity.

These panels are usually chosen for specialized architectural applications where solar panels feature prominently in the design.

Here’s an example of a parking canopy that prominently features frameless glass-on-glass bifacial solar panels:

Terawatt Roofing
Terawatt Roofing

Without the alumimum frame between each panel, it almost looks like the parking canopy is made of one giant solar panel.

These panels look great, but they’re definitely intended for specialized applications and aren’t meant as a substitute for more conventional bifacial panels.

Still, if you think you might want a statement design for a backyard pergola or carport, frameless glass-on-glass panels can look great. You can check out our article on solar canopies and carports for some more examples.

Which companies make bifacial solar panels?

Many of the popular solar manufacturers have one or more bifacial products in their lineup. I’ve made a list of some of them, but it is by no means complete.

  • Auxin Solar
  • Canadian Solar
  • Hanwah QCells
  • Heliene
  • JinkoSolar
  • Trina Solar
  • Lumos Solar

How much more expensive are bifacial solar panels?

According to the NREL study mentioned above, the cost premium for bifacial modules is small: about 5 to 6 cents per watt. This means that for a 300 watt module, you might pay an additional $18. That’s not a lot, and if you are using a tilted rack or ground mount, the cost premium may very well pay for itself with higher electricity output.

Are bifacial solar panels worth it?

There are two reasons why you might choose bifacial solar panels:

In particular, homeowners with a flat roof could benefit from bifacial panels as these installations will often use tilted racks. Some residential roofs also use TPO (thermoplastic polyolefin), which is a light colored material that would benefit bifacial panels.

If your home has a flat TPO roof, you should definitely ask your installer about bifacial panels.

And if you’re planning a solar gazebo or a regular ground-mounted installation, you’re likely to have a decent amount of reflected sunlight hitting the back of the panel. If that’s the case, you might see an increased output of 6-9% with bifacial solar panels, which could make it worth it.

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