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.


When you’re trying to choose the right solar panel for your project, solar panel efficiency stands out as one of the key features.

You might be familiar with polycrystalline and monocrystalline silicon, and know that mono solar cells have higher efficiency, generating more electricity from the same amount of sunlight compared to poly cells. But you generally pay more money for that higher performance.

In the quest for ever-higher efficiency, manufacturers have developed bifacial solar cells. These are solar cells that that have photovoltaic cells that can absorb sunlight not just from the front, but the back as well. They achieve this by replacing the opaque backsheet that is standard in conventional solar panels with a transparent layer. Here’s a diagram of how a conventional panel is constructed:

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

The role of the backsheet in a solar panel

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 itself doesn’t generate any electricity.

Because of this, you might wonder what effect the backsheet could have on the electrical output of the panel. Along with the structural role it serves, there are two things the backsheet does in a conventional solar panel that affects efficiency.

First, the default choice for solar panels is to use 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 better 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

Instead of a backsheet, a bifacial solar panel replaces the traditional opaque backsheet with a transparent layer, usually glass. That transparent layer allows cells on both sides of the panel to receive light.

Because a bifacial panel may be sandwiched between two layers of glass, the alumimum frame is often left out as well. These so-called frameless glass-on-glass modules have a very different appearance from conventional solar panels. They’re often chosen not for efficiency, but for aesthetic reasons.

Example of bifacial glass-on-glass solar panels. Courtesy Lumos Solar
Example of bifacial glass-on-glass solar panels. Courtesy Lumos Solar

You can see more examples in my article on solar canopies (although not all of the panels pictured in that article are bifacial).

However, not all bifacial panels are frameless, and not all frameless panels are bifacial. Be sure to read the specifications of your panel to find out.

How do bifacial solar panels work?

The higher efficiency of bifacial solar panels is due to the ability of the backside of the solar panel to collect additional 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 the ground to make the use of bifacial cells worthwhile.

You might be surprised that grass or even dirt will reflect enough light on a sunny day to make a difference. Go outside when it’s sunny, and look at how bright the tree, grass, and ground is. This is what gives a bifacial panel an advantage.

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 in the field of bifacial panels on a ground-mounted rack.

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.

An explanation of the specs below:

  • Frame: aluminum frame or frameless
  • Silicon: polycrystalline or monocrystalline
  • Frontside power: maximum power from the front of the panel
  • Backside power gain: maximum gain due to light hitting back of panel
  • Theoretical max power: total power from front and back combined

Canadian Solar BiKu

This polycrystalline panel from Canadian Solar uses half-cut solar cells to achieve better efficiency in the shade. It’s a high power panel, especially when used in an installation where you can take full advantage of the claimed 30% backside power gain.

Product photo of Canadian Solar BiKu. Courtesy Canadian Solar.
Framealuminium
Siliconpolycrystalline
Frontside power350 to 365 watts (depending on model)
Backside power gainup to 30%
Theoretical max power475 watts
Warranty25 year power, 10 year product

This polycrystalline panel uses half-cut solar cells to achieve better efficiency in the shade.

Product details

JA Solar JAM60D09

The JAM60D09 uses monocrystalline silicon which helps it to achieve a high theoretical output of 400 watts when including a backside gain of 25%. It uses frameless glass-on-glass construction, and has a better than average warranty. This panel is available in both 60 and 72-cell models.

Product photo of JA Solar JAM60D09. Courtesy JA Solar.
Frameframeless
Siliconmonocrystalline
Frontside power305 to 325 watts (depending on model)
Backside power gainup to 25%
Theoretical max power400 watts
Warranty30 year power, 12 year product
Product details

Jinko Solar Swan Bifacial HC

The “HC“ in the product name indicates that the Swan Bifacial makes use of half-cut solar cells to improve efficiency in the shade. It is available with both opaque and transparent backsheets for those applications where aesthetics are critical. The use of a transparent backsheet results in a very small power loss of 5 watts. The Swan Bifacial is avaiable in both 60 and 72 cell models, and has a 30 year power warranty.

Product photo of Jinko Solar Swan Bifacial HC. Courtesy Jinko Solar.
Frameframeless
Siliconmonocrystalline
Frontside power310 to 335 watts (depending on model)
Backside power gainup to 25%
Theoretical max power413 watts
Warranty30 year power, 12 year product
Product details

LG NeON 2 BiFacial

The LG NeON 2 BiFacial is a 72 cell panel with an aluminium frame. Like other products in the LG NeON series, it has outstanding efficiency and one of the best warranties in the industry.

Product photo of LG NeON 2 BiFacial. Courtesy LG.
Framealuminium frame
Siliconmonocrystalline
Frontside power390 to 395 watts (depending on model)
Backside power gainup to 30%
Theoretical max power514 watts
Warranty25 year power, 25 year product
Product details

LONGi Hi-MO4

The LONGi Hi-MO4 is a monocrystalline panel that comes in 60 and 72 cell sizes. It uses half-cut solar cells for better performance in the shade.

Product photo of LONGi Hi-MO4. Courtesy LONGi.
Framealuminium frame
Siliconmonocrystalline
Frontside power345 to 365 watts (60 cell); 415 to 435 watts (72 cell)
Backside power gainup to 25%
Theoretical max power444 watts (60 cell); 531 watts (72 cell)
Warranty30 year power, 10 year product
Product details

Trina Solar Duomax Twin

The Duomax Twin is an attractive frameless bifacial panel from Trina Solar that comes in both 60 and 72 cell sizes. It has decent efficiency and comes with a good warranty.

Product photo of Trina Solar Duomax Twin. Courtesy Trina Solar.
Frameframeless
Siliconmonocrystalline
Frontside power315 to 340 watts (60 cell); 385 to 410 watts (72 cell)
Backside power gainup to 25%
Theoretical max power425 watts (60 cell); 513 watts (72 cell)
Warranty30 year power, 10 year product
Product details

How much more expensive are bifacial solar panels?

According to the same NREL study, 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.

However, there are other cost factors in a solar project. The racking equipment and installation practices differ for frameless glass-on-glass modules. This means that your solar installer might not have much experience with this type of module, which can slow down the work and increase labor costs.

In addition, frameless modules require more care during installation, because excessive force can cause the glass to crack. Finally, glass-on-glass panels weigh more, which means that two people may be required to lift a panel, whereas a conventional panel is usually light enough for one person to carry.

Because of these factors, a solar installation that uses bifacial modules might end up costing more than a 5 to 6 cent premium due higher labor expenses.

Are bifacial solar panels worth it?

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

For a solar gazebo, a regular ground-mounted installation, or a tilted roof racking system, 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.

Whether or not it makes sense for your particular project requires a careful analysis by a qualified solar installer. To find an experienced pre-screened contractor, use The Solar Nerd to get multiple solar quotes.

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Use our calculator to get a financial payback and solar performance estimate customized to your home, including federal, state, and local incentives.

When you’re ready to make the leap, fill out our form to get up to three estimates from qualified solar installers.

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